bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2022‒12‒18
sixty-one papers selected by
Viktor Korolchuk
Newcastle University

  1. EMBO J. 2022 Dec 14. e111372
      Mitophagy, the elimination of mitochondria via the autophagy-lysosome pathway, is essential for the maintenance of cellular homeostasis. The best characterised mitophagy pathway is mediated by stabilisation of the protein kinase PINK1 and recruitment of the ubiquitin ligase Parkin to damaged mitochondria. Ubiquitinated mitochondrial surface proteins are recognised by autophagy receptors including NDP52 which initiate the formation of an autophagic vesicle around the mitochondria. Damaged mitochondria also generate reactive oxygen species (ROS) which have been proposed to act as a signal for mitophagy, however the mechanism of ROS sensing is unknown. Here we found that oxidation of NDP52 is essential for the efficient PINK1/Parkin-dependent mitophagy. We identified redox-sensitive cysteine residues involved in disulphide bond formation and oligomerisation of NDP52 on damaged mitochondria. Oligomerisation of NDP52 facilitates the recruitment of autophagy machinery for rapid mitochondrial degradation. We propose that redox sensing by NDP52 allows mitophagy to function as a mechanism of oxidative stress response.
    Keywords:  NDP52; autophagy; mitophagy; p62; redox
  2. J Cell Sci. 2022 Dec 01. pii: jcs259748. [Epub ahead of print]135(23):
      Mitochondria are crucial organelles that play a central role in various cell signaling and metabolic pathways. A healthy mitochondrial population is maintained through a series of quality control pathways and requires a fine-tuned balance between mitochondrial biogenesis and degradation. Defective targeting of dysfunctional mitochondria to lysosomes through mitophagy has been linked to several diseases, but the underlying mechanisms and the relative importance of distinct mitophagy pathways in vivo are largely unknown. In this Cell Science at a Glance and the accompanying poster, we describe our current understanding of how parts of, or whole, mitochondria are recognized by the autophagic machinery and targeted to lysosomes for degradation. We also discuss how this might be regulated under different physiological conditions to maintain mitochondrial and cellular health.
    Keywords:  BNIP3; HIF1; Mitochondria; Mitophagy; NIX; PINK1; Parkin; SLR; Selective autophagy
  3. J Biol Chem. 2022 Dec 09. pii: S0021-9258(22)01231-5. [Epub ahead of print] 102788
      Mechanistic target of rapamycin (mTOR) is a protein kinase that integrates multiple inputs to regulate anabolic cellular processes. For example , mTOR complex I (mTORC1) has key functions in growth control, autophagy and metabolism. However, much less is known about the signaling components that act downstream of mTORC1 to regulate cellular morphogenesis. Here we show that the RNA-binding protein Unkempt, a key regulator of cellular morphogenesis, is a novel substrate of mTORC1. We show that Unkempt phosphorylation is regulated by nutrient levels and growth factors via mTORC1. To analyze Unkempt phosphorylation, we immunoprecipitated Unkempt from cells in the presence or absence of the mTORC1 inhibitor rapamycin and used mass spectrometry to identify mTORC1-dependent phosphorylated residues. This analysis showed that mTORC1-dependent phosphorylation is concentrated in a serine-rich intrinsically disordered region in the C-terminal half of Unkempt. We also found that Unkempt physically interacts with and is directly phosphorylated by mTORC1 through binding to the regulatory-associated protein of mTOR, Raptor. Furthermore, analysis in the developing brain of mice lacking TSC1 expression showed that phosphorylation of Unkempt is mTORC1-dependent in vivo. Finally, mutation analysis of key serine/threonine residues in the serine-rich region indicates that phosphorylation inhibits the ability of Unkempt to induce a bipolar morphology. Phosphorylation within this serine-rich region thus profoundly affects the ability of Unkempt to regulate cellular morphogenesis. Taken together, our findings reveal a novel molecular link between mTORC1 signaling and cellular morphogenesis.
    Keywords:  Raptor; Unkempt; cellular morphogenesis; intrinsically disordered region; mTOR; phosphorylation
  4. J Cell Physiol. 2022 Dec 11.
      Recent developments in lysosome biology have transformed our view of lysosomes from static garbage disposals that can also act as suicide bags to decidedly dynamic multirole adaptive operators of cellular homeostasis. Lysosome-governed signaling pathways, proteins, and transcription factors equilibrate the rate of catabolism and anabolism (autophagy to lysosomal biogenesis and metabolite pool maintenance) by sensing cellular metabolic status. Lysosomes also interact with other organelles by establishing contact sites through which they exchange cellular contents. Lysosomal function is critically assessed by lysosomal positioning and motility for cellular adaptation. In this setting, mechanistic target of rapamycin kinase (MTOR) is the chief architect of lysosomal signaling to control cellular homeostasis. Notably, lysosomes can orchestrate explicit cell death mechanisms, such as autophagic cell death and lysosomal membrane permeabilization-associated regulated necrotic cell death, to maintain cellular homeostasis. These lines of evidence emphasize that the lysosomes serve as a central signaling hub for cellular homeostasis.
    Keywords:  autophagy; lysosomal biogenesis; lysosomal membrane permeabilization; lysosome; mechanistic target of rapamycin kinase
  5. Front Physiol. 2022 ;13 1015500
      Adenosine monophosphate-activated protein kinase (AMPK) is a significant energy sensor in the maintenance of cellular energy homeostasis. Autophagy is a highly conserved catabolic process that involves an intracellular degradation system in which cytoplasmic components, such as protein aggregates, organelles, and other macromolecules, are directed to the lysosome through the self-degradative process to maintain cellular homeostasis. Given the triggered autophagy process in various situations including the nutrient deficit, AMPK is potentially linked with different stages of autophagy. Above all, AMPK increases ULK1 activity by directly phosphorylating Ser467, Ser555, Thr574, and Ser637 at least four sites, which increases the recruitment of autophagy-relevant proteins (ATG proteins) to the membrane domains which affects autophagy at the initiation stage. Secondly, AMPK inhibits VPS34 complexes that do not contain pro-autophagic factors and are thus involved in isolation membrane forming processes, by direct phosphorylation of VPS34 on Thr163 and Ser165. After phosphorylation, AMPK can govern autophagosome formation through recruiting downstream autophagy-related proteins to the autophagosome formation site. Finally, the AMPK-SIRT1 signaling pathway can be activated by upregulating the transcription of autophagy-related genes, thereby enhancing autophagosome-lysosome fusion. This review provides an introduction to the role of AMPK in different stages of autophagy.
    Keywords:  AMPK; autophagosome autophagosome; autophagy autophagy; lysosome; mTOR
  6. Nutrients. 2022 Nov 24. pii: 5000. [Epub ahead of print]14(23):
      Paeonia species are well-known ornamental plants that are used in traditional Chinese medicines. The seeds of these species are rich in stilbenes, which have wide-ranging health-promoting effects. In particular, resveratrol, which is a common stilbene, is widely known for its anticancer properties. Suffruticosol C, which is a trimer of resveratrol, is the most dominant stilbene found in peony seeds. However, it is not clear whether suffruticosol C has cancer regulating properties. Therefore, in the present study, we aimed to determine the effect of suffruticosol C against various cancer cell lines. Our findings showed that suffruticosol C induces autophagy and cell cycle arrest instead of cell apoptosis and ferroptosis. Mechanistically, suffruticosol C regulates autophagy and cell cycle via inhibiting the mechanistic target of rapamycin complex 1 (mTORC1) signaling. Thus, our findings imply that suffruticosol C regulates cancer cell viability by inducing autophagy and cell cycle arrest via the inhibition of mTORC1 signaling.
    Keywords:  anticancer therapy; autophagy; cell cycle arrest; mTORC1; suffruticosol C
  7. Cells. 2022 Nov 28. pii: 3813. [Epub ahead of print]11(23):
      Eukaryotes utilize different communication strategies to coordinate processes between different cellular compartments either indirectly, through vesicular transport, or directly, via membrane contact sites (MCSs). MCSs have been implicated in lipid metabolism, calcium signaling and the regulation of organelle biogenesis in various cell types. Several studies have shown that MCSs play a crucial role in the regulation of macroautophagy, an intracellular catabolic transport route that is characterized by the delivery of cargoes (proteins, protein complexes or aggregates, organelles and pathogens) to yeast and plant vacuoles or mammalian lysosomes, for their degradation and recycling into basic metabolites. Macroautophagy is characterized by the de novo formation of double-membrane vesicles called autophagosomes, and their biogenesis requires an enormous amount of lipids. MCSs appear to have a central role in this supply, as well as in the organization of the autophagy-related (ATG) machinery. In this review, we will summarize the evidence for the participation of specific MCSs in autophagosome formation, with a focus on the budding yeast and mammalian systems.
    Keywords:  MAMs; autophagosome; endoplasmic reticulum; lipid droplets; lipid transfer; mitochondria; phagophore; plasma membrane; vacuole
  8. Sci Rep. 2022 Dec 16. 12(1): 21725
      Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in developed countries, characterized by the death of retinal pigment epithelial (RPE) cells and photoreceptors. Previous studies report an accumulation of damaged and dysfunctional mitochondria in RPE of human donors with AMD. Understanding how damaged mitochondria accumulate in AMD is an important step in discovering disease mechanisms and identifying therapeutic targets. In this report, we assessed mitochondrial fission and fusion by quantifying proteins and measured mitochondrial autophagy (mitophagy) via protein analysis and advanced imaging techniques using mitochondrial targeted mKeima in primary human RPE from donors with or without AMD. We report disease-specific differences in mitochondrial proteins that regulate fission, fusion, and mitophagy that were present at baseline and with treatments to stimulate these pathways. Data suggest AMD RPE utilize receptor-mediated mitophagy as a compensatory mechanism for deficits in the ubiquitin-mediated mitophagy pathway. These changes in mitochondrial homeostasis could lead to the buildup of damaged and dysfunctional mitochondria observed in the RPE of AMD donors.
  9. Biochim Biophys Acta Mol Cell Res. 2022 Dec 12. pii: S0167-4889(22)00203-8. [Epub ahead of print] 119411
      Sirtuin 3 (Sirt3), a mitochondrial deacetylase, regulates mitochondrial redox homeostasis and autophagy and is involved in physiological and pathological processes such as aging, cellular metabolism, and tumorigenesis. We here investigate how Sirt3 regulates doxorubicin (DOX)-induced senescence in lung cancer A549 cells. Sirt3 greatly reduced DOX-induced upregulation of senescence marker proteins p53, p16, p21 and SA-β-Gal activity as well as ROS levels. Notably, Sirt3 reversed DOX-induced autophagic flux blockage, as shown by increased p62 degradation and LC3II/LC3I ratio. Importantly, the autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ) partially abolished the antioxidant stress and antiaging effects of Sirt3, while the autophagy activator rapamycin (Rap) potentiated these effects of Sirt3, demonstrating that autophagy mediates the anti-aging effects of Sirt3. Additionally, Sirt3 inhibited the DOX-induced activation of the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway, which in turn activated autophagy. The PI3K inhibitor LY294002 promoted the antioxidant stress and antiaging effects of Sirt3, while the AKT activator SC-79 reversed these effects of Sirt3. Taken together, Sirt3 counteracts DOX-induced senescence by improving autophagic flux.
    Keywords:  Autophagy; PI3K/AKT/mTOR pathway; Senescence; Sirtuin 3
  10. Cells. 2022 Dec 01. pii: 3883. [Epub ahead of print]11(23):
      The engagement of B cells with surface-tethered antigens triggers the formation of an immune synapse (IS), where the local secretion of lysosomes can facilitate antigen uptake. Lysosomes intersect with other intracellular processes, such as Toll-like Receptor (TLR) signaling and autophagy coordinating immune responses. However, the crosstalk between these processes and antigen presentation remains unclear. Here, we show that TLR stimulation induces autophagy in B cells and decreases their capacity to extract and present immobilized antigens. We reveal that TLR stimulation restricts lysosome repositioning to the IS by triggering autophagy-dependent degradation of GEF-H1, a Rho GTP exchange factor required for stable lysosome recruitment at the synaptic membrane. GEF-H1 degradation is not observed in B cells that lack αV integrins and are deficient in TLR-induced autophagy. Accordingly, these cells show efficient antigen extraction in the presence of TLR stimulation, confirming the role of TLR-induced autophagy in limiting antigen extraction. Overall, our results suggest that resources associated with autophagy regulate TLR and BCR-dependent functions, which can finetune antigen uptake by B cells. This work helps to understand the mechanisms by which B cells are activated by surface-tethered antigens in contexts of subjacent inflammation before antigen recognition, such as sepsis.
    Keywords:  B cell; CpG; LPS; TLR; antigen extraction; autophagy; αV integrin
  11. Autophagy. 2022 Dec 15. 1-2
      Ischemia may be the most common pathological occurrence to restrict nutrient availability and induce macroautophagy/autophagy. As a self-digestive process, autophagy helps sustain nutrient/energy and restrict damages in short-term scenarios, but it switches to a self-destructive process leading to cell death in long-term scenarios. Notably, ischemia has been used as one clinical application to treat cancer, particularly transarterial embolization (TAE) and chemoembolization (TACE) as the first-line treatments of intermediate-stage hepatocellular carcinoma (HCC, the predominant type of liver cancer). Partly due to the induced autophagy together with hypoxia-induced angiogenesis, TAE/TACE is not successful to treat HCC in many cases. Our recent work demonstrated that simultaneous treatments with sorafenib (a first-line therapeutic agent for advanced HCC) can sensitize HCC cells to cell death induced by glucose starvation via impairing mitophagy, a mitochondria-specific form of autophagy. Moreover, we identified SIAH1 as an important E3 ubiquitin ligase for mitophagic induction in HCC cells.
    Keywords:  HCC; canagliflozin; glucose restriction; mitophagy; sorafenib
  12. Molecules. 2022 Dec 02. pii: 8475. [Epub ahead of print]27(23):
      Interstitial lung disease associated with rheumatoid arthritis (RA-ILD) can lead to interstitial fibrosis and even lung failure as a complication of rheumatoid arthritis (RA), and there is currently no effective treatment and related basic research. Studies have found that resveratrol (Res) can improve the progression of RA by regulating autophagy, and increasing evidence supports the connection between autophagy and common interstitial lung disease (ILD). We explored changes in autophagy levels in fibrotic lungs in RA-ILD and found that the level of autophagy is enhanced in the early stage but inhibited in the late stage. However, resveratrol treatment improved the level of autophagy and reversed the inhibition of autophagy, and attenuated fibrosis. We created corresponding cell models that exhibited the same phenotypic changes as animal models; under the effect of resveratrol, the level of fibrosis changed accordingly, and the fusion process of lysosomes and autophagosomes in autophagy was liberated from the inhibition state. Resveratrol effects were reversed by the addition of the late autophagy inhibitor chloroquine. These results suggest that resveratrol attenuates pulmonary fibrosis, increases autophagic flux, and modulates the autophagy-lysosome pathway, and particularly it may work by improving the formation of autophagic lysosomes, which may be an effective treatment for induced RA-ILD.
    Keywords:  P62/SQSTM1; RA-ILD; autophagy; fibrosis; resveratrol
  13. Ageing Res Rev. 2022 Dec 09. pii: S1568-1637(22)00259-8. [Epub ahead of print]84 101817
      Mitochondria play key roles in bioenergetics, metabolism, and signaling; therefore, stable mitochondrial function is essential for cell survival, particularly in energy-intensive neuronal cells. In neurodegenerative diseases, damaged mitochondria accumulate in neurons causing associated bioenergetics deficiency, impaired cell signaling, defective cytoplasmic calcium buffering, and other pathological changes. Mitochondrial quality control is an important mechanism to ensure the maintenance of mitochondrial health, homeostasis, and mitophagy, the latter of which is a pathway that delivers defective mitochondria to the lysosome for degradation. Defective mitophagy is thought to be responsible for the accumulation of damaged mitochondria, which leads to cellular dysfunction and/or death in neurodegenerative diseases. PINK1/Parkin mainly regulates ubiquitin-dependent mitophagy, which is crucial for many aspects of mitochondrial physiology, particularly the initiation of autophagic mechanisms. Therefore, in the present review, we summarize the current knowledge of the conventional mitophagy pathway, focusing on the molecular mechanisms underlying mitophagy dysregulation in prion disease and other age-related neurodegenerative diseases, especially in relation to the PINK1/Parkin pathway. Moreover, we list the inducers of mitophagy that possess neuroprotective effects, in addition to their mechanisms related to the PINK1/Parkin pathway. These mechanisms may provide potential interventions centered on the regulation of mitophagy and offer therapeutic strategies for the treatment of neurodegenerative diseases.
    Keywords:  Mitochondria; Mitochondrial quality control; Mitophagy; Neurodegenerative diseases; PINK1/Parkin
  14. Cells. 2022 Nov 25. pii: 3773. [Epub ahead of print]11(23):
      Cancer cells adapt multiple mechanisms to counter intense stress on their way to growth. Tumor microenvironment stress leads to canonical and noncanonical endoplasmic stress (ER) responses, which mediate autophagy and are engaged during proteotoxic challenges to clear unfolded or misfolded proteins and damaged organelles to mitigate stress. In these conditions, autophagy functions as a cytoprotective mechanism in which malignant tumor cells reuse degraded materials to generate energy under adverse growing conditions. However, cellular protection by autophagy is thought to be complicated, contentious, and context-dependent; the stress response to autophagy is suggested to support tumorigenesis and drug resistance, which must be adequately addressed. This review describes significant findings that suggest accelerated autophagy in cancer, a novel obstacle for anticancer therapy, and discusses the UPR components that have been suggested to be untreatable. Thus, addressing the UPR or noncanonical ER stress components is the most effective approach to suppressing cytoprotective autophagy for better and more effective cancer treatment.
    Keywords:  ER stress; UPR; autophagy; cancer therapy; tumerogenesis
  15. Biochem Biophys Res Commun. 2022 Dec 02. pii: S0006-291X(22)01656-4. [Epub ahead of print]640 40-49
      BACKGROUND: Metastasis, a complex multi-stage process, is the primary cause of breast cancer-related death. Unfortunately, the molecular mechanisms underlying tumor metastasis have not been fully elucidated thus far. Long noncoding RNAs (lncRNAs) dictate the behaviours of tumor cells via multiple signaling pathways, resulting in tumor cell migration and invasion, as well as all stages of cancer progression. LncRNAs function as regulators in shaping cellular activities directly through influencing key genes involved in biological processes of the tumor, and representing promising novel targets in cancer diagnosis and therapy. We therefore sought to define the correlations between lncRNA expression and breast cancer metastasis, especially to investigate the functional pathway underlying lncRNA-mediated tumor invasion and metastasis process.RESULTS: In this study, we compared the lncRNA transcriptome profiles between primary breast cancer 4T1 cells and high metastatic 4T1-LG12 cells. We found that many differently expressed lncRNAs greatly correlated to the metastatic propensity of 4T1-LG12 cells, particularly lncRNA-45, a new lncRNA without functional annotations, which was found to be the most upregulated lncRNA transcribed by an internal region within the regulatory associated with protein of mechanistic target of rapamycin kinase (mTOR) complex 1 (Rptor) gene. LncRNA-45 was uncovered to be involved in the epithelial-to-mesenchymal transition process of breast cancer cells, as evidenced by the observation that lncRNA-45 knockdown significantly suppressed the invasive capability of parental 4T1-LG12 cells. Molecular mechanistic investigation showed that reduced activity of mTORC1-associated pathway led to a decrease of total ribosomal protein S6 kinase, polypeptide 1 (S6K1) content and enhancement of autophagy, consequently compromising the metastatic propensity in lncRNA-45 knockdown cells.
    CONCLUSIONS: Overall, our experiments uncovered that the newly identified lncRNA-45 played a regulatory role in breast cancer cell metastasis.
    Keywords:  Breast cancer; LncRNA; Tumor metastasis; mTOR pathway
  16. Int J Mol Sci. 2022 Nov 30. pii: 14997. [Epub ahead of print]23(23):
      Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder. It is characterized by the accumulation of α-Synuclein aggregates and the degeneration of dopaminergic neurons in substantia nigra in the midbrain. Although the exact mechanisms of neuronal degeneration in PD remain largely elusive, various pathogenic factors, such as α-Synuclein cytotoxicity, mitochondrial dysfunction, oxidative stress, and pro-inflammatory factors, may significantly impair normal neuronal function and promote apoptosis. In this context, neuroinflammation and autophagy have emerged as crucial processes in PD that contribute to neuronal loss and disease development. They are regulated in a complex interconnected manner involving most of the known PD-associated genes. This review summarizes evidence of the implication of neuroinflammation and autophagy in PD and delineates the role of inflammatory factors and autophagy-related proteins in this complex condition. It also illustrates the particular significance of plasma and serum immune markers in PD and their potential to provide a personalized approach to diagnosis and treatment.
    Keywords:  Parkinson’s disease (PD); autophagy; neurodegeneration; neuroinflammation
  17. Int J Mol Sci. 2022 Dec 01. pii: 15109. [Epub ahead of print]23(23):
      Autophagy is essential for the maintenance of hepatic homeostasis, and autophagic malfunction has been linked to the pathogenesis of substantial liver diseases. As a popular source of drug discovery, natural products have been used for centuries to effectively prevent the progression of various liver diseases. Emerging evidence has suggested that autophagy regulation is a critical mechanism underlying the therapeutic effects of these natural products. In this review, relevant studies are retrieved from scientific databases published between 2011 and 2022, and a novel scoring system was established to critically evaluate the completeness and scientific significance of the reviewed literature. We observed that numerous natural products were suggested to regulate autophagic flux. Depending on the therapeutic or pathogenic role autophagy plays in different liver diseases, autophagy-regulative natural products exhibit different therapeutic effects. According to our novel scoring system, in a considerable amount of the involved studies, convincing and reasonable evidence to elucidate the regulatory effects and underlying mechanisms of natural-product-mediated autophagy regulation was missing and needed further illustration. We highlight that autophagy-regulative natural products are valuable drug candidates with promising prospects for the treatment of liver diseases and deserve more attention in the future.
    Keywords:  autophagy; liver diseases; natural products; pharmacodynamics; scoring system
  18. Sci Rep. 2022 Dec 12. 12(1): 21483
      Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent immuno-metabolic disease that can progress to hepatic cirrhosis and cancer. NAFLD pathogenesis is extremely complex and is characterized by oxidative stress, impaired mitochondrial function and lipid metabolism, and cellular inflammation. Thus, in-depth research on its underlying mechanisms and subsequent investigation into a potential drug target that has overarching effects on these features will help in the discovery of effective treatments for NAFLD. Our study examines the role of endogenous paraoxonase-2 (PON2), a membrane protein with reported antioxidant activity, in an in vitro cell model of NAFLD. We found that the hepatic loss of PON2 activity aggravated steatosis and oxidative stress under lipotoxic conditions, and our transcriptome analysis revealed that the loss of PON2 disrupts the activation of numerous functional pathways closely related to NAFLD pathogenesis, including mitochondrial respiratory capacity, lipid metabolism, and hepatic fibrosis and inflammation. We found that PON2 promoted the activation of the autophagy pathway, specifically the mitophagy cargo sequestration, which could potentially aid PON2 in alleviating oxidative stress, mitochondrial dysfunction, lipid accumulation, and inflammation. These results provide a mechanistic foundation for the prospect of PON2 as a drug target, leading to the development of novel therapeutics for NAFLD.
  19. Cells. 2022 Nov 30. pii: 3863. [Epub ahead of print]11(23):
      Targeting cancer metabolism has become one of the strategies for a rational anti-tumor therapy. However, cellular plasticity, driven by a major regulator of cellular growth and metabolism, mTORC1, often leads toward treatment resistance. Sestrin2, a stress-inducible protein, has been described as an mTORC1 inhibitor upon various types of stress signals. Immune assays and online measurements of cellular bioenergetics were employed to investigate the nature of Sestrin2 regulation, and finally, by silencing the SESN2 gene, to identify the role of induced Sestrin2 upon a single amino acid deprivation in cancer cells of various origins. Our data suggest that a complex interplay of either oxidative, energetic, nutritional stress, or in combination, play a role in Sestrin2 regulation upon single amino acid deprivation. Therefore, cellular metabolic background and sequential metabolic response dictate Sestrin2 expression in the absence of an amino acid. While deprivations of essential amino acids uniformly induce Sestrin2 levels, non-essential amino acids regulate Sestrin2 differently, drawing a characteristic Sestrin2 expression fingerprint, which could serve as a first indication of the underlying cellular vulnerability. Finally, we show that canonical GCN2-ATF4-mediated Sestrin2 induction leads to mTORC1 inhibition only in amino acid auxotroph cells, where the amino acid cannot be replenished by metabolic reprogramming.
    Keywords:  Sestrin2; amino acid deprivation; mTORC1; metabolic adaptation; nutritional stress
  20. Nat Commun. 2022 Dec 17. 13(1): 7792
      Dysregulation of mTOR complex 1 (mTORC1) activity drives neuromuscular junction (NMJ) structural instability during aging; however, downstream targets mediating this effect have not been elucidated. Here, we investigate the roles of two mTORC1 phosphorylation targets for mRNA translation, ribosome protein S6 kinase 1 (S6K1) and eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1), in regulating NMJ structural instability induced by aging and sustained mTORC1 activation. While myofiber-specific deletion of S6k1 has no effect on NMJ structural integrity, 4EBP1 activation in murine muscle induces drastic morphological remodeling of the NMJ with enhancement of synaptic transmission. Mechanistically, structural modification of the NMJ is attributed to increased satellite cell activation and enhanced post-synaptic acetylcholine receptor (AChR) turnover upon 4EBP1 activation. Considering that loss of post-synaptic myonuclei and reduced NMJ turnover are features of aging, targeting 4EBP1 activation could induce NMJ renewal by expanding the pool of post-synaptic myonuclei as an alternative intervention to mitigate sarcopenia.
  21. Acta Histochem. 2022 Dec 09. pii: S0065-1281(22)00145-3. [Epub ahead of print]125(1): 151986
      Lon protease 1(Lonp1) is an ATP-dependent protease located in the mitochondrial matrix and plays a crucial role in preserving normal mitochondrial function. Lonp1 overexpression is associated with tumorigenesis in various cancer types, including cervical cancer. In the present study, we show that the Lonp1 content is elevated in cervical cancer tissues compared to cervical paracancerous tissues. Conversely, Lonp1 knockdown suppresses cervical cancer cell proliferation, migration and invasion but promotes apoptosis. Mechanistically, Lonp1 knockdown decreases area of mitochondrial networks and induces mitochondrial depolarization. Furthermore, Lonp1 inhibition reduces the level of LC3-II/I, PINK1 and Parkin, but promotes the level of p62. Collectively, our study suggests that the anti-cancer effect caused by Lonp1 downregulation likely contributes to mitochondrial remodeling and suppression of autophagy and mitophagy.
    Keywords:  Autophagy; Lonp1; Mitochondria
  22. Plants (Basel). 2022 Nov 26. pii: 3247. [Epub ahead of print]11(23):
      Autophagy is a conserved cellular mechanism involved in the degradation and subsequent recycling of cytoplasmic components. It is also described as a catabolic process implicated in the specific degradation of proteins in response to several stimuli. In eukaryotes, the endoplasmic reticulum accumulates an excess of proteins in response to environmental changes, and is the major cellular organelle at the crossroads of stress responses. Return to proteostasis involves the activation of the Unfolded Protein Response (UPR) and eventually autophagy as a feedback mechanism to relieve protein overaccumulation. Recent publications have focused on the relevance of autophagy in two central processes of seed biology: (i) seed storage protein accumulation upon seed maturation and (ii) reserve mobilization during seed imbibition. Although ER-protein accumulation and the subsequent activation of autophagy resemble the Seed Storage Protein (SSP) deposition during seed maturation, the molecular connection between seed development, autophagy, and seed response to abiotic stresses is still an underexplored field. This mini-review presents current advances in autophagy in seeds, highlighting its participation in the normal course of seed development from embryogenesis to germination. Finally, the function of autophagy in response to the seed environment is also considered, as is its involvement in controlling seed dormancy and germination.
    Keywords:  autophagy; endoplasmic reticulum; environment; plants; seed germination; seed maturation; selective autophagy
  23. Nutrients. 2022 Dec 05. pii: 5171. [Epub ahead of print]14(23):
      Dietary polyphenols can be utilized to treat obesity and chronic disorders linked to it. Dietary polyphenols can inhibit pre-adipocyte proliferation, adipocyte differentiation, and triglyceride accumulation; meanwhile, polyphenols can also stimulate lipolysis and fatty acid β-oxidation, but the molecular mechanisms of anti-obesity are still unclear. The mechanistic target of rapamycin (mTOR) is a protein kinase that regulates cell growth, survival, metabolism, and immunity. mTOR signaling is also thought to play a key role in the development of metabolic diseases such as obesity. Recent studies showed that dietary polyphenols could target mTOR to reduce obesity. In this review, we systematically summarized the research progress of polyphenols in preventing obesity through the mTOR signaling pathway. Mechanistically, polyphenols can target multiple signaling pathways and gut microbiota to regulate the mTOR signaling pathway to exert anti-obesity effects. The main mechanisms include: modulating lipid metabolism, adipogenesis, inflammation, etc. Dietary polyphenols exerting an anti-obesity effect by targeting mTOR signaling will broaden our understanding of the anti-obesity mechanisms of polyphenols and provide valuable insights for researchers in this novel field.
    Keywords:  dietary polyphenols; mTOR; obesity; signal pathway
  24. Sci Adv. 2022 Dec 14. 8(50): eadd1436
      How the highly curved phagophore membrane is stabilized during autophagy initiation is a major open question in autophagosome biogenesis. Here, we use in vitro reconstitution on membrane nanotubes and molecular dynamics simulations to investigate how core autophagy proteins in the LC3 (Microtubule-associated proteins 1A/1B light chain 3) lipidation cascade interact with curved membranes, providing insight into their possible roles in regulating membrane shape during autophagosome biogenesis. ATG12(Autophagy-related 12)-ATG5-ATG16L1 was up to 100-fold enriched on highly curved nanotubes relative to flat membranes. At high surface density, ATG12-ATG5-ATG16L1 binding increased the curvature of the nanotubes. While WIPI2 (WD repeat domain phosphoinositide-interacting protein 2) binding directs membrane recruitment, the amphipathic helix α2 of ATG16L1 is responsible for curvature sensitivity. Molecular dynamics simulations revealed that helix α2 of ATG16L1 inserts shallowly into the membrane, explaining its curvature-sensitive binding to the membrane. These observations show how the binding of the ATG12-ATG5-ATG16L1 complex to the early phagophore rim could stabilize membrane curvature and facilitate autophagosome growth.
  25. Int J Mol Sci. 2022 Nov 23. pii: 14565. [Epub ahead of print]23(23):
      RNA-binding proteins (RBPs) and RNAs can form dynamic, liquid droplet-like cytoplasmic condensates, known as stress granules (SGs), in response to a variety of cellular stresses. This process is driven by liquid-liquid phase separation, mediated by multivalent interactions between RBPs and RNAs. The formation of SGs allows a temporary suspension of certain cellular activities such as translation of unnecessary proteins. Meanwhile, non-translating mRNAs may also be sequestered and stalled. Upon stress removal, SGs are disassembled to resume the suspended biological processes and restore the normal cell functions. Prolonged stress and disease-causal mutations in SG-associated RBPs can cause the formation of aberrant SGs and/or impair SG disassembly, consequently raising the risk of pathological protein aggregation. The machinery maintaining protein homeostasis (proteostasis) includes molecular chaperones and co-chaperones, the ubiquitin-proteasome system, autophagy, and other components, and participates in the regulation of SG metabolism. Recently, proteostasis has been identified as a major regulator of SG turnover. Here, we summarize new findings on the specific functions of the proteostasis machinery in regulating SG disassembly and clearance, discuss the pathological and clinical implications of SG turnover in neurodegenerative disorders, and point to the unresolved issues that warrant future exploration.
    Keywords:  G3BP; UPS; VCP; autophagy; chaperones; stress granule; ubiquitin
  26. Subcell Biochem. 2023 ;101 351-387
      Protein homeostasis relies on a balance between protein folding and protein degradation. Molecular chaperones like Hsp70 and Hsp90 fulfill well-defined roles in protein folding and conformational stability via ATP-dependent reaction cycles. These folding cycles are controlled by associations with a cohort of non-client protein co-chaperones, such as Hop, p23, and Aha1. Pro-folding co-chaperones facilitate the transit of the client protein through the chaperone-mediated folding process. However, chaperones are also involved in proteasomal and lysosomal degradation of client proteins. Like folding complexes, the ability of chaperones to mediate protein degradation is regulated by co-chaperones, such as the C-terminal Hsp70-binding protein (CHIP/STUB1). CHIP binds to Hsp70 and Hsp90 chaperones through its tetratricopeptide repeat (TPR) domain and functions as an E3 ubiquitin ligase using a modified RING finger domain (U-box). This unique combination of domains effectively allows CHIP to network chaperone complexes to the ubiquitin-proteasome and autophagosome-lysosome systems. This chapter reviews the current understanding of CHIP as a co-chaperone that switches Hsp70/Hsp90 chaperone complexes from protein folding to protein degradation.
    Keywords:  Autophagy; CHIP; Co-chaperones; Lysosome; Proteasome; STUB1; Ubiquitin
  27. Front Cell Dev Biol. 2022 ;10 1087214
    Keywords:  Endosomes; cholesterol; disease models; lipid droplets; lysosomal storage diseases; lysosome-related organelles; lysosomes; membrane contact sites
  28. Int J Mol Sci. 2022 Dec 03. pii: 15273. [Epub ahead of print]23(23):
      Autophagy, an evolutionarily conserved cell reprogramming mechanism, exists in all eukaryotic organisms. It is a fundamental and vital degradation/recycling pathway that removes undesirable components, such as cytoplasmic organelles, misfolded proteins, viruses, and intracellular bacteria, to provide energy and essential materials for organisms. The success of male reproduction depends on healthy testes, which are mainly composed of seminiferous tubules and mesenchyme. Seminiferous tubules are composed of Sertoli cells (SCs) and various germ cells, and the main functional part of mesenchyme are Leydig cells (LCs). In recent years, a large amount of evidence has confirmed that autophagy is active in many cellular events associated with the testes. Autophagy is not only important for testicular spermatogenesis, but is also an essential regulatory mechanism for the ectoplasmic specialization (ES) integrity of SCs, as well as for the normal function of the blood-testes barrier (BTB). At the same time, it is active in LCs and is crucial for steroid production and for maintaining testosterone levels. In this review, we expanded upon the narration regarding the composition of the testes; summarized the regulation and molecular mechanism of autophagy in SCs, germ cells, and LCs; and concluded the roles of autophagy in the process of spermatogenesis and testicular endocrinology. Through integrating the latest summaries and advances, we discuss how the role of autophagy is a double-edged sword in the testes and may provide insight for future studies and explorations on autophagy in male reproduction.
    Keywords:  autophagy; reproduction; spermatogenesis; testes
  29. Front Genet. 2022 ;13 997461
      Tuberous Sclerosis (TS) is a rare genetic disorder manifesting with multiple benign tumors impacting the function of vital organs. In TS patients, dominant negative mutations in TSC1 or TSC2 increase mTORC1 activity. Increased mTORC1 activity drives tumor formation, but also severely impacts central nervous system function, resulting in infantile seizures, intractable epilepsy, and TS-associated neuropsychiatric disorders, including autism, attention deficits, intellectual disability, and mood disorders. More recently, TS has also been linked with frontotemporal dementia. In addition to TS, accumulating evidence implicates increased mTORC1 activity in the pathology of other neurodevelopmental and neurodegenerative disorders. Thus, TS provides a unique disease model to address whether developmental neural circuit abnormalities promote age-related neurodegeneration, while also providing insight into the therapeutic potential of mTORC1 inhibitors for both developing and degenerating neural circuits. In the following review, we explore the ability of both mouse and human brain organoid models to capture TS pathology, elucidate disease mechanisms, and shed light on how neurodevelopmental alterations may later contribute to age-related neurodegeneration.
    Keywords:  GABA; mTORC; neurodegeneration; neurodevelopment; synapse; tau; tuberous sclerosis
  30. Open Biol. 2022 Dec;12(12): 220319
      Dietary interventions that restrict protein intake have repeatedly been shown to offer beneficial health outcomes to the consumer. Benefits such as increased stress tolerance can be observed when individual amino acids are restricted, thus mimicking dietary protein restriction. Here, we sought to further understand the relationship between dietary amino acids and stress tolerance using Drosophila melanogaster. Using a chemically defined medium for Drosophila, we found that transiently restricting adult flies of a single essential amino acid generally protects against a lethal dose of the naturally occurring insecticide, nicotine. This protection varied with the identity of the focal amino acid and depended on the duration and intensity of its restriction. To understand the molecular basis of these effects, we modified the signalling of two cellular sensors of amino acids, GCN2 and mTORC1, in combination with amino acid restriction. We found that GCN2 was necessary for diets to protect against nicotine, whereas the suppression of mTORC1 was sufficient to induce nicotine resistance. This finding implies that amino acid restriction acts via amino acid signalling to cross-protect against seemingly unrelated stressors. Altogether, our study offers new insights into the physiological responses to restriction of individual amino acids that confer stress tolerance.
    Keywords:  Drosophila melanogaster; GCN2; amino acid; dietary preconditioning; mTORC1; stress tolerance
  31. Toxicol Sci. 2022 Dec 15. pii: kfac130. [Epub ahead of print]
      Manganese (Mn), is an essential trace element that participates in various physiological and pathological processes. However, epidemiological observations indicate that overexposure to Mn is strongly associated with neurodegenerative disorders and has been recognized as a potential risk factor of neuronal apoptosis. Many mechanisms are involved in the pathogenesis of Mn-induced neuronal apoptosis, such as reactive oxygen species generation, neuroinflammation reactions, protein accumulation, endoplasmic reticulum stress (ER stress) and autophagy, all of which collectively accelerate the process of nerve cell damage. As sophisticated cellular processes for maintaining intracellular homeostasis, ER-mediated unfolded protein response (UPR) and autophagy both play bilateral roles including cell protection and cell injury under pathophysiological conditions, which might interact with each other. Although emerging evidence suggests that ER stress is involved in regulating the compensatory activation of autophagy to promote cell survival, the inherent relationship between ER stress and autophagy on Mn-induced neurotoxicity remains obscure. Here, our review focuses on discussing the existing mechanisms and connections between ER stress, autophagy and apoptosis, which provide a new perspective on Mn-induced neuronal apoptosis, and the pathogenesis of neurodegenerative diseases.
    Keywords:  Apoptosis; Autophagy; Endoplasmic reticulum stress; Manganese
  32. Int J Mol Sci. 2022 Dec 01. pii: 15138. [Epub ahead of print]23(23):
      4-O-methylascochlorin (MAC) is a 4-fourth carbon-substituted derivative of ascochlorin, a compound extracted from a phytopathogenic fungus Ascochyta viciae. MAC induces apoptosis and autophagy in various cancer cells, but the effects of MAC on apoptosis and autophagy in cervical cancer cells, as well as how the interaction between apoptosis and autophagy mediates the cellular anticancer effects are not known. Here, we investigated that MAC induced apoptotic cell death of cervical cancer cells without regulating the cell cycle and promoted autophagy by inhibiting the phosphorylation of serine-threonine kinase B (Akt), mammalian target of rapamycin (mTOR), and 70-kDa ribosomal protein S6 kinase (p70S6K). Additional investigations suggested that Bcl-2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP-3), but not Hypoxia-inducible factor 1 alpha (HIF-1α), is a key regulator of MAC-induced apoptosis and autophagy. BNIP-3 siRNA suppressed MAC-induced increases in cleaved- poly (ADP-ribose) polymerase (PARP) and LC3II expression. The pan-caspase inhibitor Z-VAD-FMK suppressed MAC-induced cell death and enhanced MAC-induced autophagy. The autophagy inhibitor chloroquine (CQ) enhanced MAC-mediated cell death by increasing BNIP-3 expression. These results indicate that MAC induces apoptosis to promote cell death and stimulates autophagy to promote cell survival by increasing BNIP-3 expression. This study also showed that co-treatment of cells with MAC and CQ further enhanced the death of cervical cancer cells.
    Keywords:  4-O-methylascochlorin; BNIP-3; HIF-1α; anticancer activity; apoptosis; autophagy
  33. J Neurosci. 2022 Dec 16. pii: JN-RM-1354-22. [Epub ahead of print]
      Hyperactivation of PI3K/PTEN-mTOR signaling during neural development is associated with focal cortical dysplasia (FCD), autism, and epilepsy. mTOR can signal through two major hubs, mTORC1 and mTORC2, both of which are hyperactive following PTEN loss of function (LOF). Here, we tested the hypothesis that genetic inactivation of the mTORC2 complex via deletion of Rictor is sufficient to rescue morphological and electrophysiological abnormalities in the dentate gyrus caused by PTEN loss, as well as generalized seizures. An established, early postnatal mouse model of PTEN loss in male and female mice showed spontaneous seizures that were not prevented by mTORC2 inactivation. This lack of rescue occurred despite the normalization or amelioration of many morphological and electrophysiological phenotypes. However, increased excitatory connectivity proximal to dentate gyrus granule neuron somas was not normalized by mTORC2 inactivation. Further studies demonstrated that, although mTORC2 inactivation largely rescued the dendritic arbor overgrowth caused by PTEN LOF, it increased synaptic strength and caused additional impairments of presynaptic function. These results suggest that a constrained increase in excitatory connectivity and co-occurring synaptic dysfunction is sufficient to generate seizures downstream of PTEN LOF, even in the absence of characteristic changes in morphological properties.SIGNIFICANCE STATEMENT:Homozygous deletion of the Pten gene in neuronal subpopulations in the mouse serves as a valuable model of epilepsy caused by mTOR hyperactivation. To better understand the physiological mechanisms downstream of Pten loss that cause epilepsy, as well as the therapeutic potential of targeted gene therapies, we tested whether genetic inactivation of the mTORC2 complex could improve the cellular, synaptic, and in vivo effects of Pten loss in the dentate gyrus. We found that mTORC2 inhibition improved or rescued all morphological effects of Pten loss in the dentate gyrus, but synaptic changes and seizures persisted. These data suggest that synaptic dysfunction can drive epilepsy caused by hyperactivation of PI3K/PTEN-mTOR, and that future therapies should focus on this mechanistic link.
  34. Redox Biol. 2022 Dec 05. pii: S2213-2317(22)00342-1. [Epub ahead of print]59 102570
      BACKGROUND AND AIMS: Caloric excess and sedentary lifestyles have led to an epidemic of obesity, metabolic syndrome, and non-alcoholic fatty liver disease (NAFLD). The objective of this study was to investigate the mechanisms underlying high fat diet (HFD)-induced NAFLD, and to explore NRF2 activation as a strategy to alleviate NAFLD.APPROACH AND RESULTS: Herein, we demonstrated that high fat diet (HFD) induced lipid peroxidation and ferroptosis, both of which could be alleviated by NRF2 upregulation. Mechanistically, HFD suppressed autophagosome biogenesis through AMPK- and AKT-mediated mTOR activation and decreased ATG7, resulting in KEAP1 stabilization and decreased NRF2 levels in mouse liver. Furthermore, ATG7 is required for HFD-induced NRF2 downregulation, as ATG7 deletion in Cre-inducible ATG7 knockout mice decreased NRF2 levels and enhanced ferroptosis, which was not further exacerbated by HFD. This finding was recapitulated in mouse hepatocytes, which showed a similar phenotype upon treatment with saturated fatty acids (SFAs) but not monounsaturated fatty acids (MUFAs). Finally, NRF2 activation blocked fatty acid (FA)-mediated NRF2 downregulation, lipid peroxidation, and ferroptosis. Importantly, the HFD-induced alterations were also observed in human fatty liver tissue samples.
    CONCLUSIONS: HFD-mediated autophagy inhibition, NRF2 suppression, and ferroptosis promotion are important molecular mechanisms of obesity-driven metabolic diseases. NRF2 activation counteracts HFD-mediated NRF2 suppression and ferroptotic cell death. In addition, SFA vs. MUFA regulation of NRF2 may underlie their harmful vs. beneficial effects. Our study reveals NRF2 as a key player in the development and progression of fatty liver disease and that NRF2 activation could serve as a potential therapeutic strategy.
    Keywords:  AKT; AMPK; ATG7; Autophagy; Fatty acids; Ferroptosis; High fat diet; KEAP1; Liver steatosis; NAFLD; NRF2; mTOR
  35. Front Oncol. 2022 ;12 1049436
      Pancreatic cancer is currently the seventh leading cause of cancer-related deaths worldwide, with the estimated death toll approaching half a million annually. Pancreatic ductal adenocarcinoma (PDAC) is the most common (>90% of cases) and most aggressive form of pancreatic cancer, with extremely poor prognosis and very low survival rates. PDAC is initiated by genetic alterations, usually in the oncogene KRAS and tumor suppressors CDKN2A, TP53 and SMAD4, which in turn affect a number of downstream signaling pathways that regulate important cellular processes. One of the processes critically altered is autophagy, the mechanism by which cells clear away and recycle impaired or dysfunctional organelles, protein aggregates and other unwanted components, in order to achieve homeostasis. Autophagy plays conflicting roles in PDAC and has been shown to act both as a positive effector, promoting the survival of pancreatic tumor-initiating cells, and as a negative effector, increasing cytotoxicity in uncontrollably expanding cells. Recent findings have highlighted the importance of cancer stem cells in PDAC initiation, progression and metastasis. Pancreatic cancer stem cells (PaCSCs) comprise a small subpopulation of the pancreatic tumor, characterized by cellular plasticity and the ability to self-renew, and autophagy has been recognised as a key process in PaCSC maintenance and function, simultaneously suggesting new strategies to achieve their selective elimination. In this review we evaluate recent literature that links autophagy with PaCSCs and PDAC, focusing our discussion on the therapeutic implications of pharmacologically targeting autophagy in PaCSCs, as a means to treat PDAC.
    Keywords:  Cancer Stem Cell (CSC); PDAC - pancreatic ductal adenocarcinoma; autophagy; hydroxychloroquine; pancreas; pancreatic cancer; pancreatic cancer stem cells
  36. Anal Chem. 2022 Dec 14.
      Autophagy and apoptosis play a central role in maintaining homeostasis in mammals. Therefore, discriminative visualization of the two cellular processes is an important and challenging task. However, fluorescent probes enabling ratiometric visualization of both autophagy and apoptosis with different sets of fluorescence signals have not been developed yet. In this work, we constructed a versatile single fluorescent probe (NKLR) based on the aggregation/monomer principle for the ratiometric and discriminative visualization of autophagy and apoptosis. NKLR can simultaneously perform two-color imaging of RNA (deep red channel) and lysosomes (yellow channel) in aggregation and monomer states, respectively. During autophagy, NKLR migrated from cytoplasmic RNA and nuclear RNA to lysosomes, showing enhanced yellow emission and sharply decreased deep red fluorescence. Moreover, this migration process was reversible upon the recovery of autophagy. Comparatively, during apoptosis, NKLR immigrated from lysosomes to RNA, and the yellow emission decreased and even disappeared, while the fluorescence of the deep red channel slightly increased. Overall, autophagy and apoptosis could be discriminatively visualized via the fluorescence intensity ratios of the two channels. Meanwhile, the cells in three different states (healthy, autophagic, apoptotic) could be distinguished by three point-to-point fluorescence images via the localization and emission color of NKLR. Therefore, the probe NKLR can serve as a desirable molecular tool to reveal the in-depth relation between autophagy and apoptosis and facilitate the study on the two cellular processes.
  37. Arch Biochem Biophys. 2022 Dec 10. pii: S0003-9861(22)00373-3. [Epub ahead of print] 109487
      Arsenic is abundant in the environment and takes the form of trivalent and pentavalent arsenic compounds. Arsenite has been reported to both promote and suppress erythropoietin (EPO) production and autophagy induction. EPO production is involved in hematopoiesis, and autophagy induction is involved in cytoprotection, both of which are thought to be cellular responses to arsenic stress. While there are reports that show the effects of EPO on autophagy induction, the relationship between EPO production and autophagy induction is unclear. Therefore, this study analyzed the effect of the pentavalent inorganic arsenic salt arsenate on EPO production in vitro and in vivo and EPO-induced autophagy in HepG2 cells. Exposure of HepG2 cells to low-concentration arsenate was observed to increase EPO production and induced autophagy. Moreover, a ROS scavenger suppressed the arsenate-induced increase in autophagy and EPO mRNA levels. Both EPO production and autophagy induction contributed to protection from arsenate-induced cytotoxic stress. HepG2 cells expressed the EPO receptor and production of EPO by HepG2 cells acted in an autoregulatory manner to suppress autophagy induction. In vivo administration of low-concentration arsenate to rats increased EPO mRNA levels in the liver and kidney. These results suggested that low-concentration arsenate promotes EPO production and autophagy induction in HepG2 cells, and the resultant EPO production contributes to cytoprotection of cultured cells via EPO receptor activation.
    Keywords:  Arsenate; Autophagy; Erythropoietin; Reactive oxygen species
  38. Front Neurosci. 2022 ;16 1040182
      Cerebral ischemia is one of the leading causes of death and disability worldwide. Although revascularization via reperfusion combined with advanced anticoagulant therapy is currently a gold standard treatment for patients, the reperfusion itself also results in a serious dysfunction termed cerebral ischemia-reperfusion (I/R) injury. Silent information regulator 1 (sirtuin 1, SIRT1), is a classic NAD+-dependent deacetylase, which has been proposed as an important mediator in the alleviation of cerebral ischemia through modulating multiple physiological processes, including apoptosis, inflammation, DNA repair, oxidative stress, and autophagy. Recent growing evidence suggests that SIRT1-mediated autophagy plays a key role in the pathophysiological process of cerebral I/R injury. SIRT1 could both activate and inhibit the autophagy process by mediating different autophagy pathways, such as the SIRT1-FOXOs pathway, SIRT1-AMPK pathway, and SIRT1-p53 pathway. However, the autophagic roles of SIRT1 in cerebral I/R injury have not been systematically summarized. Here, in this review, we will first introduce the molecular mechanisms and effects of SIRT1 in cerebral ischemia and I/R injury. Next, we will discuss the involvement of autophagy in the pathogenesis of cerebral I/R injury. Finally, we will summarize the latest advances in the interaction between SIRT1 and autophagy in cerebral I/R injury. A good understanding of these relationships would serve to consolidate a framework of mechanisms underlying SIRT1's neuroprotective effects and provides evidence for the development of drugs targeting SIRT1.
    Keywords:  SIRT1; autophagy; autophagy signaling pathway; cerebral ischemia-reperfusion; neuroprotection
  39. Aging Cell. 2022 Dec 12. e13751
      Autophagy defects accelerate aging, while stimulation of autophagy decelerates aging. Acyl-coenzyme A binding protein (ACBP), which is encoded by a diazepam-binding inhibitor (DBI), acts as an extracellular feedback regulator of autophagy. As shown here, knockout of the gene coding for the yeast orthologue of ACBP/DBI (ACB1) improves chronological aging, and this effect is reversed by knockout of essential autophagy genes (ATG5, ATG7) but less so by knockout of an essential mitophagy gene (ATG32). In humans, ACBP/DBI levels independently correlate with body mass index (BMI) as well as with chronological age. In still-healthy individuals, we find that high ACBP/DBI levels correlate with future cardiovascular events (such as heart surgery, myocardial infarction, and stroke), an association that is independent of BMI and chronological age, suggesting that ACBP/DBI is indeed a biomarker of "biological" aging. Concurringly, ACBP/DBI plasma concentrations correlate with established cardiovascular risk factors (fasting glucose levels, systolic blood pressure, total free cholesterol, triglycerides), but are inversely correlated with atheroprotective high-density lipoprotein (HDL). In mice, neutralization of ACBP/DBI through a monoclonal antibody attenuates anthracycline-induced cardiotoxicity, which is a model of accelerated heart aging. In conclusion, plasma elevation of ACBP/DBI constitutes a novel biomarker of chronological aging and facets of biological aging with a prognostic value in cardiovascular disease.
    Keywords:  aging; autophagy; cancer; cardiovascular diseases; diazepam-binding protein; metabolism
  40. JCI Insight. 2022 11 22. pii: e159136. [Epub ahead of print]7(22):
      A hallmark of HIV-1 infection is chronic inflammation, even in patients treated with antiretroviral therapy (ART). Chronic inflammation drives HIV-1 pathogenesis, leading to loss of CD4+ T cells and exhaustion of antiviral immunity. Therefore, strategies to safely reduce systematic inflammation are needed to halt disease progression and restore defective immune responses. Autophagy is a cellular mechanism for disposal of damaged organelles and elimination of intracellular pathogens. Autophagy is pivotal for energy homeostasis and plays critical roles in regulating immunity. However, how it regulates inflammation and antiviral T cell responses during HIV infection is unclear. Here, we demonstrate that autophagy is directly linked to IFN-I signaling, which is a key driver of immune activation and T cell exhaustion during chronic HIV infection. Impairment of autophagy leads to spontaneous IFN-I signaling, and autophagy induction reduces IFN-I signaling in monocytic cells. Importantly, in HIV-1-infected humanized mice, autophagy inducer rapamycin treatment significantly reduced persistent IFN-I-mediated inflammation and improved antiviral T cell responses. Cotreatment of rapamycin with ART led to significantly reduced viral rebound after ART withdrawal. Taken together, our data suggest that therapeutically targeting autophagy is a promising approach to treat persistent inflammation and improve immune control of HIV replication.
    Keywords:  AIDS/HIV; Cellular immune response; Inflammation; Innate immunity
  41. Science. 2022 Dec 16. 378(6625): 1201-1207
      Cell death induced by tumor necrosis factor (TNF) can be beneficial during infection by helping to mount proper immune responses. However, TNF-induced death can also drive a variety of inflammatory pathologies. Protectives brakes, or cell-death checkpoints, normally repress TNF cytotoxicity to protect the organism from its potential detrimental consequences. Thus, although TNF can kill, this only occurs when one of the checkpoints is inactivated. Here, we describe a checkpoint that prevents apoptosis through the detoxification of the cytotoxic complex IIa that forms upon TNF sensing. We found that autophagy-related 9A (ATG9A) and 200kD FAK family kinase-interacting protein (FIP200) promote the degradation of this complex through a light chain 3 (LC3)-independent lysosomal targeting pathway. This detoxification mechanism was found to counteract TNF receptor 1 (TNFR1)-mediated embryonic lethality and inflammatory skin disease in mouse models.
  42. Cancers (Basel). 2022 Nov 26. pii: 5839. [Epub ahead of print]14(23):
      Macroautophagy (autophagy) has been a highly conserved process throughout evolution and allows cells to degrade aggregated/misfolded proteins, dysfunctional or superfluous organelles and damaged macromolecules, in order to recycle them for biosynthetic and/or energetic purposes to preserve cellular homeostasis and health. Changes in autophagy are indeed correlated with several pathological disorders such as neurodegenerative and cardiovascular diseases, infections, cancer and inflammatory diseases. Conversely, autophagy controls both apoptosis and the unfolded protein response (UPR) in the cells. Therefore, any changes in the autophagy pathway will affect both the UPR and apoptosis. Recent evidence has shown that several natural products can modulate (induce or inhibit) the autophagy pathway. Natural products may target different regulatory components of the autophagy pathway, including specific kinases or phosphatases. In this review, we evaluated ~100 natural compounds and plant species and their impact on different types of cancers via the autophagy pathway. We also discuss the impact of these compounds on the UPR and apoptosis via the autophagy pathway. A multitude of preclinical findings have shown the function of botanicals in regulating cell autophagy and its potential impact on cancer therapy; however, the number of related clinical trials to date remains low. In this regard, further pre-clinical and clinical studies are warranted to better clarify the utility of natural compounds and their modulatory effects on autophagy, as fine-tuning of autophagy could be translated into therapeutic applications for several cancers.
    Keywords:  apoptosis; autophagy; autophagy-related diseases; cancer; natural compound; unfolded protein response
  43. Cell Cycle. 2022 Dec 12. 1-12
      Autophagy is essential for the maintenance of intracellular homeostasis, implicated in various biological processes. Forkhead box protein O1 (FOXO1) is regarded as a key mediator regulating skeletal development. Recent studies indicate that FOXO1 has a multifaceted role in autophagy regulation and dysregulation. Here, we aimed to elucidate the role of FOXO1-autophagy axis in osteogenesis. Osteoblast conditional Foxo1-knockout mice (Foxo1OB-/-, KO) and FOXO1 lentivirus overexpression (Len-FoxO1) model were constructed in vivo. Primary osteoblasts were isolated from KO and their wild-type (WT) littermates. And we also applied overexpression lentivirus to investigate the effects of FOXO1 in vitro. Using Micro-CT, fluorescence labeling detection, real-time qPCR and western blot analyses, we found that bone formation was promoted in Len-FOXO1 mice, which was impaired in KO group. Similarly, FOXO1 overexpression enhanced proliferation, migration and differentiation of osteoblasts, while FOXO1 ablation resulted in poor biological functions of osteoblasts. Through the investigation of autophagic process using mRFP-GFP-LC3 fluorescence labeling and co-immunoprecipitation, we observed that overexpression of FOXO1 initiated autophagy induction, with enhanced FOXO1 interaction with autophagy-related protein 7 (ATG7). On the contrary, FOXO1 knockout in osteoblasts impeded FOXO1-ATG7 conjugation, leading to impaired autophagic activity. Furthermore, inhibition of autophagy by chloroquine (CQ) could reverse favorable influences in bone formation induced by FOXO1 overexpression. Our findings confirmed that FOXO1 was an important regulator of bone formation and autophagy might be part of the underlying mechanisms, offering a significant avenue for the potential strategy in the treatment of bone-related disorders.
    Keywords:  Forkhead box protein O1 (FOXO1); autophagy; bone formation; osteogenesis
  44. Food Funct. 2022 Dec 16.
      Aging is an inevitable biological process and is accompanied by a gradual decline of physiological functions, such as the incidence of age-related diseases. Aging becomes a major burden and challenge for society to prevent or delay the occurrence and development of these age-related diseases. AMPK is a key regulator of intracellular energy and participates in the adaptation of calorie restriction. It is also an important mediator of nutritionally sensitive pathways that regulate the biological effects of nutrient active ingredients. AMPK can limit proliferation and activate autophagy. Recent studies have shown that nutritional intervention can delay aging and lessen age-related diseases in many animal and even human models. Polyphenols function as a natural antidote and are important anti-inflammatory and antioxidant agents in human diets. Polyphenols can prevent age-related diseases because they regulate complex networks of cellular processes such as oxidative damage, inflammation, cellular aging, and autophagy, and have also attracted wide attention as a potential beneficial substance for longevity. In this review, we systemically summarized the progress of targeting AMPK signaling by dietary polyphenols in aging prevention. Polyphenols can reduce oxidative stress and inflammatory response, and maintain the steady state of energy. Polyphenols can also modulate sirtuins/NAD+, nutrient-sensing, proteostasis, mitochondrial function, autophagy and senescence via targeting AMPK signaling. Therefore, targeting the AMPK signaling pathway by dietary polyphenols may be a novel anti-aging strategy.
  45. Exp Gerontol. 2022 Dec 12. pii: S0531-5565(22)00355-2. [Epub ahead of print] 112046
      Aging has been suggested to be associated with changes in oxidative capacity, autophagy, and mitophagy in the liver, but a simultaneous evaluation of these key cellular processes is lacking. Moreover, skeletal muscle Transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator(PGC)-1α has been reported to mediate inter-organ signaling through myokines with regulatory effects in the liver, but the potential role of muscle PGC-1α on hepatic changes with age remains to be resolved. The aim of the present study was therefore to investigate 1) the effect of aging on mitochondrial autophagy and mitophagy capacity in mouse liver and 2) whether muscle PGC-1α is required for maintaining autophagy and mitophagy capacity in the liver during aging. The liver was obtained from young (Young) and aged (Aged) inducible muscle-specific PGC-1α knockout (iMKO) and floxed littermate control mice. Aging increased liver p62, Parkin and Protein-interacting protein(BNIP)3 protein with no effect of muscle specific PGC-1α knockout, while liver Microtubule-associated protein 1A/1B-light chain 3(LC3) II/I was unchanged with age, but tended to be lower in iMKO mice than in controls. Markers of liver mitochondrial oxidative capacity and oxidative stress were unchanged with age and iMKO. However, Parkin protein levels in isolated liver mitochondria were 2-fold higher in Aged iMKO mice than in Aged controls. In conclusion, aging had no effect on oxidative capacity and redox stress in the liver. However, aging was associated with increased levels of autophagy and mitophagy markers. Moreover, muscle PGC-1α appears to regulate hepatic mitochondrial translocation of Parkin in aged mice, suggesting that the metabolic capacity of skeletal muscle can modulate mitophagy regulation of the liver during aging.
    Keywords:  Aging; Autophagy; Liver; Metabolism; PGC-1a; Parkin
  46. Cells. 2022 Nov 30. pii: 3861. [Epub ahead of print]11(23):
      KCC2 mediates extrusion of K+ and Cl- and assuresthe developmental "switch" in GABA function during neuronal maturation. However, the molecular mechanisms underlying KCC2 regulation are not fully elucidated. We investigated the impact of transforming growth factor beta 2 (TGF-β2) on KCC2 during neuronal maturation using quantitative RT-PCR, immunoblotting, immunofluorescence and chromatin immunoprecipitation in primary mouse hippocampal neurons and brain tissue from Tgf-β2-deficient mice. Inhibition of TGF-β/activin signaling downregulates Kcc2 transcript in immature neurons. In the forebrain of Tgf-β2-/- mice, expression of Kcc2, transcription factor Ap2β and KCC2 protein is downregulated. AP2β binds to Kcc2 promoter, a binding absent in Tgf-β2-/-. In hindbrain/brainstem tissue of Tgf-β2-/- mice, KCC2 phosphorylation at T1007 is increased and approximately half of pre-Bötzinger-complex neurons lack membrane KCC2 phenotypes rescued through exogenous TGF-β2. These results demonstrate that TGF-β2 regulates KCC2 transcription in immature neurons, possibly acting upstream of AP2β, and contributes to the developmental dephosphorylation of KCC2 at T1007. The present work suggests multiple and divergent roles for TGF-β2 on KCC2 during neuronal maturation and provides novel mechanistic insights for TGF-β2-mediated regulation of KCC2 gene expression, posttranslational modification and surface expression. We propose TGF-β2 as a major regulator of KCC2 with putative implications for pathophysiological conditions.
    Keywords:  GABA; chloride homeostasis; growth factors; neurotrophins; pre-Bötzinger complex
  47. Acta Biochim Biophys Sin (Shanghai). 2022 Nov 25. 54(12): 1-10
      Sepsis is a life-threatening condition manifested by concurrent inflammation and immunosuppression. Ubiquitin-specific peptidase 9, X-linked (USP9x), is a USP domain-containing deubiquitinase which is required in T-cell development. In the present study, we investigate whether USP9x plays a role in hepatic CD8 + T-cell dysfunction in septic mice. We find that CD8 + T cells are decreased in the blood of septic patients with liver injury compared with those without liver injury, the CD4/CD8 ratio is increased, and the levels of cytolytic factors, granzyme B and perforin are downregulated. The number of hepatic CD8 + T cells and USP9x expression are both increased 24 h after cecal ligation and puncture-induced sepsis in a mouse model, a pattern similar to liver injury. The mechanism involves promotion of CD8 + T-cell dysfunction by USP9x associated with suppression of cell cytolytic activity via autophagy inhibition, which is reversed by the USP9x inhibitor WP1130. In the in vivo studies, autophagy is significantly increased in hepatic CD8 + T cells of septic mice with conditional knockout of mammalian target of rapamycin. This study shows that USP9x has the potential to be used as a therapeutic target in septic liver injury.
    Keywords:  CD8 T cells; USP9x; autophagy; liver injury; sepsis
  48. Cell Death Dis. 2022 Dec 15. 13(12): 1045
      Owing to its ability to induce cellular senescence, inhibit PCNA, and arrest cell division cycle by negatively regulating CDKs as well as being a primary target of p53, p21 is traditionally considered a tumor suppressor. Nonetheless, several reports in recent years demonstrated its pro-oncogenic activities such as apoptosis inhibition by cytosolic p21, stimulation of cell motility, and promoting assembly of cyclin D-CDK4/6 complex. These opposing effects of p21 on cell proliferation, supported by the observations of its inconsistent expression in human cancers, led to the emergence of the concept of "antagonistic duality" of p21 in cancer progression. Here we demonstrate that p21 negatively regulates basal autophagy at physiological concentration. Akt activation, upon p21 attenuation, driven ROS accumulation appears to be the major underlying mechanism in p21-mediated modulation of autophagy. We also find p21, as a physiological inhibitor of autophagy, to have oncogenic activity during early events of tumor development while its inhibition favors survival and growth of cancer cells in the established tumor. Our data, thereby, reveal the potential role of autophagy in antagonistic functional duality of p21 in cancer.
  49. Cells. 2022 Nov 30. pii: 3842. [Epub ahead of print]11(23):
      Orofacial neuropathic pain indicates pain caused by a lesion or diseases of the somatosensory nervous system. It is challenging for the clinician to diagnose and manage orofacial neuropathic pain conditions due to the considerable variability between individual clinical presentations and a lack of understanding of the mechanisms underlying the etiology and pathogenesis. In the last few decades, researchers have developed diagnostic criteria, questionnaires, and clinical assessment methods for the diagnosis of orofacial neuropathic pain. Recently, researchers have observed the role of autophagy in neuronal dysfunction as well as in the modulation of neuropathic pain. On this basis, in the present review, we highlight the characteristics, classification, and clinical assessment of orofacial neuropathic pain. Additionally, we introduce autophagy and its potential role in the modulation of orofacial neuropathic pain, along with a brief overview of the pathogenesis, which in future may reveal new possible targets for treating this condition.
    Keywords:  autophagy; nerve injury; orofacial neuropathic pain; somatosensory
  50. EMBO Rep. 2022 Dec 12. e55472
      The transcription factor EB (TFEB) regulates energy homeostasis and cellular response to a wide variety of stress conditions, including nutrient deprivation, oxidative stress, organelle damage, and pathogens. Here we identify S401 as a novel phosphorylation site within the TFEB proline-rich domain. Phosphorylation of S401 increases significantly in response to oxidative stress, UVC light, growth factors, and LPS, whereas this increase is prevented by p38 MAPK inhibition or depletion, revealing a new role for p38 MAPK in TFEB regulation. Mutation of S401 in THP1 cells demonstrates that the p38 MAPK/TFEB pathway plays a particularly relevant role during monocyte differentiation into macrophages. TFEB-S401A monocytes fail to upregulate the expression of multiple immune genes in response to PMA-induced differentiation, including critical cytokines, chemokines, and growth factors. Polarization of M0 macrophages into M1 inflammatory macrophages is also aberrant in TFEB-S401A cells. These results indicate that TFEB-S401 phosphorylation links differentiation signals to the transcriptional control of monocyte differentiation.
    Keywords:  TFEB; autophagy; lysosomes; monocytes; p38 MAPK
  51. Autophagy Rep. 2022 ;1(1): 83-87
      IRF3 (interferon regulatory factor 3) is a critical component of the antiviral innate immune response. IRF3 deficiency causes detrimental effects to the host during virus infection. Dysregulation of IRF3 functions is associated with viral, inflammatory, and hepatic diseases. Both transcriptional and pro-apoptotic activities of IRF3 are involved in the exacerbated inflammation and apoptosis in liver injury induced by ethanol and high-fat diets. Therefore, regulation of IRF3 activities has consequences, and it is a potential therapeutic target for infectious and inflammatory diseases. We recently revealed that IRF3 is degraded by a small molecule, auranofin, by activating the cellular macroautophagy/autophagy pathway. Autophagy is a catabolic pathway that contributes to cellular homeostasis and antiviral host defense. Degradation of IRF3 by autophagy may be a novel strategy used by the viruses to their benefit. In addition, IRF3 functions are harmful in other diseases, including liver injury and bacterial infection. A better understanding of the role of autophagy in regulating IRF3 functions has significant implications in developing therapeutic strategies. Therefore, autophagy provides checks and balances in the innate immune response.
    Keywords:  Alcoholic liver diseases; IRF3; antiviral; auranofin; autophagy; degradation; innate response; interferon
  52. Front Cell Dev Biol. 2022 ;10 1036225
      Mitochondrial and endoplasmic reticulum (ER) are important intracellular organelles. The sites that mitochondrial and ER are closely related in structure and function are called Mitochondria-ER contacts (MERCs). MERCs are involved in a variety of biological processes, including calcium signaling, lipid synthesis and transport, autophagy, mitochondrial dynamics, ER stress, and inflammation. Sepsis-induced myocardial dysfunction (SIMD) is a vital organ damage caused by sepsis, which is closely associated with mitochondrial and ER dysfunction. Growing evidence strongly supports the role of MERCs in the pathogenesis of SIMD. In this review, we summarize the biological functions of MERCs and the roles of MERCs proteins in SIMD.
    Keywords:  ER stress; autophagy; calcium signaling; inflammation; mitochondria-ER contacts; mitochondrial dynamics; sepsis-induced myocardial dysfunction
  53. Hum Mol Genet. 2022 Dec 15. pii: ddac297. [Epub ahead of print]
      Abnormal lipid homeostasis has been observed in the brain of Parkinson's disease (PD) patients and experimental models, although the mechanism underlying this phenomenon is unclear. Notably, previous studies have reported that the PD-linked protein Parkin functionally interacts with important lipid regulators, including Sterol Regulatory Element Binding Proteins (SREBPs) and Cluster of differentiation 36 (CD36). Here, we demonstrate a functional relationship between Parkin and Lipoprotein Lipase (LPL), a triglyceride lipase that is widely expressed in the brain. Using a human neuroblastoma cell line and a Parkin knockout (KO) mouse model, we demonstrate that Parkin expression level positively correlates with neuronal LPL protein level and activity. Importantly, our study identified SREBP2, a major regulator of sterol and fatty acid synthesis, as a potential mediator between Parkin and LPL. Supporting this, SREBP2 genetic ablation abolished Parkin effect on LPL expression. We further demonstrate that Parkin-LPL pathway regulates the formation of intracellular lipid droplets, and that this pathway is upregulated upon exposure to PD-linked oxidative stress induced by rotenone. Finally, we show that inhibition of either LPL or SREBP2 exacerbates rotenone-induced cell death. Taken together, our findings reveal a novel pathway linking Parkin, SREBP2, and LPL in neuronal lipid homeostasis that may be relevant to the pathogenesis of PD.
  54. Nat Struct Mol Biol. 2022 Dec;29(12): 1196-1207
      Leucine-rich repeat kinase 2 (LRRK2) is one of the most commonly mutated genes in familial Parkinson's disease (PD). Under some circumstances, LRRK2 co-localizes with microtubules in cells, an association enhanced by PD mutations. We report a cryo-EM structure of the catalytic half of LRRK2, containing its kinase, in a closed conformation, and GTPase domains, bound to microtubules. We also report a structure of the catalytic half of LRRK1, which is closely related to LRRK2 but is not linked to PD. Although LRRK1's structure is similar to that of LRRK2, we find that LRRK1 does not interact with microtubules. Guided by these structures, we identify amino acids in LRRK2's GTPase that mediate microtubule binding; mutating them disrupts microtubule binding in vitro and in cells, without affecting LRRK2's kinase activity. Our results have implications for the design of therapeutic LRRK2 kinase inhibitors.
  55. Cell Death Dis. 2022 Dec 16. 13(12): 1047
      Increased brain iron content has been consistently reported in sporadic Parkinson's disease (PD) patients, and an increase in cytosolic free iron is known to cause oxidative stress and cell death. However, whether iron also accumulates in susceptible brain areas in humans or in mouse models of familial PD remains unknown. In addition, whilst the lysosome functions as a critical intracellular iron storage organelle, little is known about the mechanisms underlying lysosomal iron release and how this process is influenced by lysosome biogenesis and/or lysosomal exocytosis. Here, we report an increase in brain iron content also in PD patients due to the common G2019S-LRRK2 mutation as compared to healthy age-matched controls, whilst differences in iron content are not observed in G2019S-LRRK2 knockin as compared to control mice. Chemically triggering iron overload in cultured cells causes cytotoxicity via the endolysosomal release of iron which is mediated by TRPML1. TFEB expression reverts the iron overload-associated cytotoxicity by causing lysosomal exocytosis, which is dependent on a TRPML1-mediated increase in cytosolic calcium levels. Therefore, approaches aimed at increasing TFEB levels, or pharmacological TRPML1 activation in conjunction with iron chelation may prove beneficial against cell death associated with iron overload conditions such as those associated with PD.
  56. Int J Mol Sci. 2022 Nov 29. pii: 14945. [Epub ahead of print]23(23):
      Glucose is a direct energy source for eukaryotic cells, and its deficiency elicits complex stress responses and diverse cellular outcomes. Although several signaling pathways involved have been identified, how they coordinately dictate the cell fate remains obscure. We propose a minimal network model for the cellular response to glucose restriction, characterizing the glucose uptake and signaling of the AMPK, Akt, mTOR, and p53 pathways. We demonstrate that in the presence of sufficient growth factors and amino acids, cells may undergo proliferation, senescence, or apoptosis, depending on the extracellular glucose level. AMPK is first activated upon glucose limitation, activating p53 to induce cell-cycle arrest; possibly, cells resume proliferation after timely glucose restoration. For long-term energy stress, cell senescence is maintained by low/intermediate levels of p53 and persistent activation of mTOR and Akt, or cells commit apoptosis when the proteins undergo biphasic dynamics, e.g., p53 switches from intermediate levels to high levels while mTOR and Akt become inactivated in the later phase. The biphasic dynamics of p53 are associated with flipping of two bistable switches. Appropriate mTOR levels are required for optimal cell-fate decision. This work suggests that senescence and apoptosis occur sequentially in glucose-depleted cells, and a theoretical framework is provided for exploring the cellular response to energy stress.
    Keywords:  apoptosis; biphasic dynamics; cell-fate decision; glucose starvation; network modeling; senescence
  57. Am J Pathol. 2022 Dec 09. pii: S0002-9440(22)00394-7. [Epub ahead of print]
      The intestines play a crucial role in the development of sepsis. The balance between autophagy and apoptosis in intestinal epithelial cells is dynamic and determines intestinal permeability. The present study focused on the potential role of autophagy in sepsis-induced intestinal barrier dysfunction and explored the mechanisms in vivo and in vitro. Excessive apoptosis in intestinal epithelia and a disrupted intestinal barrier were observed in septic mice. Promoting autophagy with rapamycin reduced intestinal epithelial apoptosis and restored intestinal barrier function, presenting as decreased serum DAO and FD40 levels and increased expression of ZO-1 and Occludin. PLK1 knockdown in mice ameliorated intestinal epithelial apoptosis and the intestinal barrier during sepsis, while these effects were reduced with chloroquine and enhanced with rapamycin. PLK1 also promotes cell autophagy and improves LPS-induced apoptosis and high permeability in vitro. Moreover, PLK1 physically interacted with mTOR and participated in reciprocal regulatory crosstalk in intestinal epithelial cells during sepsis. Our studies provide novel insight into the role of autophagy in sepsis-induced intestinal barrier dysfunction and indicate that the PLK1-mTOR axis may be a promising therapeutic target for sepsis.
    Keywords:  PLK1; apoptosis; autophagy; intestinal barrier; mTOR; sepsis
  58. Cells. 2022 Dec 03. pii: 3918. [Epub ahead of print]11(23):
      Progerin, a permanently farnesylated prelamin A protein in cell nuclei, is potentially implicated in the defenestration of liver sinusoidal endothelial cells (LSECs) and liver fibrogenesis. Autophagy regulates the degradation of nuclear components, called nucleophagy, in response to damage. However, little is known about the role of nucleophagy in LSEC defenestration. Herein, we aim to dissect the underlying mechanism of progerin and nucleophagy in LSEC phenotype. We found an abnormal accumulation of progerin and a loss of SIRT1 in the nucleus of intrahepatic cells in human fibrotic liver tissue. In vivo, nuclear progerin abnormally accumulated in defenestrated LSECs, along with a depletion of SIRT1 and Cav-1 during liver fibrogenesis, whereas these effects were reversed by the overexpression of SIRT1 with the adenovirus vector. In vitro, H2O2 induced the excessive accumulation of progeirn, with the depletion of Lamin B1 and Cav-1 to aggravate LSEC defenestration. NAC and mito-TEMPO, classical antioxidants, inhibited NOX2- and NOX4-dependent oxidative stress to improve the depletion of Lamin B1 and Cav-1 and promoted progerin-related nucleophagy, leading to a reverse in H2O2-induced LSEC defenestration. However, rapamycin aggravated the H2O2-induced depletion of Lamin B1 and Cav-1 due to excessive autophagy, despite promoting progerin nucleophagic degradation. In addition, overexpressing SIRT1 with the adenovirus vector inhibited oxidative stress to rescue the production of Lamin B1 and Cav-1. Moreover, the SIRT1-mediated deacetylation of nuclear LC3 promoted progerin nucleophagic degradation and subsequently inhibited the degradation of Lamin B1 and Cav-1, as well as improved F-actin remodeling, contributing to maintaining LSEC fenestrae. Hence, our findings indicate a new strategy for reversing LSEC defenestration by promoting progerin clearance via the SIRT1-mediated deacetylation of nuclear LC3.
    Keywords:  LC3; Sirtuin 1; defenestration; liver sinusoidal endothelial cell; progerin
  59. Int J Mol Sci. 2022 Nov 28. pii: 14890. [Epub ahead of print]23(23):
      Mitochondria play a central role in the pathophysiology of inflammatory bowel disease (IBD) and colorectal cancer (CRC). The maintenance of mitochondrial function is necessary for a stable immune system. Mitochondrial dysfunction in the gastrointestinal system leads to the excessive activation of multiple inflammatory signaling pathways, leading to IBD and increased severity of CRC. In this review, we focus on the mitochondria and inflammatory signaling pathways and its related gastrointestinal diseases.
    Keywords:  biogenesis; colorectal cancer; inflammatory bowel disease; mitochondria; mitophagy
  60. Hum Mol Genet. 2022 Dec 15. pii: ddac299. [Epub ahead of print]
      Infantile Krabbe disease is a rapidly progressive and fatal disorder of myelin, caused by inherited deficiency of the lysosomal enzyme β-galactocerebrosidase. Affected children lose their motor skills and other faculties; uncontrolled seizures are a frequent terminal event. Overexpression of the sphingolipid metabolite psychosine is a pathogenic factor, but does not fully account for the pleiotropic manifestations and there is a clear need to investigate additional pathological mechanisms. We examined innate immunity, caspase-11 and associated inflammatory pathways in twitcher mice, an authentic model of Krabbe disease. Combined use of molecular tools, RNAscope in situ hybridization and immunohistochemical staining established that the expression of pro-inflammatory non-canonical caspase-11, canonical caspase-1, gasdermin D and cognate genes is induced in nervous tissue. Early onset and progressive upregulation of these genes accompanies demyelination and gliosis and while the molecules are scant in healthy tissue, abundance of the respective translation products is greatly increased in diseased animals. Caspase-11 is found in reactive microglia/macrophages as well as astrocytes but caspase-1 and gasdermin D are restricted to reactive microglia/macrophages. The inflammasome signature is not unique to Krabbe disease; to varying degrees, this signature is also prominent in other lysosomal diseases, Sandhoff and Niemann-Pick Type-C1, and the lysolecithin toxin model of focal demyelination. Given the potent inflammatory response here identified in Krabbe disease and the other neurodegenerative disorders studied, a broad induction of inflammasomes is likely to be a dominant factor in the pathogenesis, and thus represents a platform for therapeutic exploration.