bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2022‒08‒14
fifty-five papers selected by
Viktor Korolchuk
Newcastle University

  1. Elife. 2022 Aug 08. pii: e78923. [Epub ahead of print]11
      Monitoring autophagic flux is necessary for most autophagy studies. The autophagic flux assays currently available for mammalian cells are generally complicated and do not yield highly quantitative results. Yeast autophagic flux is routinely monitored with the GFP-based processing assay, whereby the amount of GFP proteolytically released from GFP-containing reporters (e.g., GFP-Atg8), detected by immunoblotting, reflects autophagic flux. However, this simple and effective assay is typically inapplicable to mammalian cells because GFP is efficiently degraded in lysosomes while the more proteolytically resistant RFP accumulates in lysosomes under basal conditions. Here, we report a HaloTag (Halo)-based reporter processing assay to monitor mammalian autophagic flux. We found that Halo is sensitive to lysosomal proteolysis but becomes resistant upon ligand binding. When delivered into lysosomes by autophagy, pulse-labeled Halo-based reporters (e.g., Halo-LC3 and Halo-GFP) are proteolytically processed to generate Haloligand when delivered into lysosomes by autophagy. Hence, the amount of free Haloligand detected by immunoblotting or in-gel fluorescence imaging reflects autophagic flux. We demonstrate the applications of this assay by monitoring the autophagy pathways, macroautophagy, selective autophagy, and even bulk nonselective autophagy. With the Halo-based processing assay, mammalian autophagic flux and lysosome-mediated degradation can be monitored easily and precisely.
    Keywords:  cell biology; human; mouse
  2. Int J Mol Sci. 2022 Aug 06. pii: 8747. [Epub ahead of print]23(15):
      Decreased content and activity of the mechanistic target of rapamycin (mTOR) signalling pathway, as well as the mTOR complex 1 (mTORC1) itself, are key traits for animal species and human longevity. Since mTORC1 acts as a master regulator of intracellular metabolism, it is responsible, at least in part, for the longevous phenotype. Conversely, increased content and activity of mTOR signalling and mTORC1 are hallmarks of ageing. Additionally, constitutive and aberrant activity of mTORC1 is also found in age-related diseases such as Alzheimer's disease (AD) and cancer. The downstream processes regulated through this network are diverse, and depend upon nutrient availability. Hence, multiple nutritional strategies capable of regulating mTORC1 activity and, consequently, delaying the ageing process and the development of age-related diseases, are under continuous study. Among these, the restriction of calories is still the most studied and robust intervention capable of downregulating mTOR signalling and feasible for application in the human population.
    Keywords:  age-related diseases; ageing; longevity; mTORC1; metabolism
  3. Nat Commun. 2022 Aug 09. 13(1): 4665
      Tuberous Sclerosis Complex (TSC) is a neurodevelopmental disorder caused by mutations in the TSC1 or TSC2 genes, which encode proteins that negatively regulate mTOR complex 1 (mTORC1) signaling. Current treatment strategies focus on mTOR inhibition with rapamycin and its derivatives. While effective at improving some aspects of TSC, chronic rapamycin inhibits both mTORC1 and mTORC2 and is associated with systemic side-effects. It is currently unknown which mTOR complex is most relevant for TSC-related brain phenotypes. Here we used genetic strategies to selectively reduce neuronal mTORC1 or mTORC2 activity in mouse models of TSC. We find that reduction of the mTORC1 component Raptor, but not the mTORC2 component Rictor, rebalanced mTOR signaling in Tsc1 knock-out neurons. Raptor reduction was sufficient to improve several TSC-related phenotypes including neuronal hypertrophy, macrocephaly, impaired myelination, network hyperactivity, and premature mortality. Raptor downregulation represents a promising potential therapeutic intervention for the neurological manifestations of TSC.
  4. Nat Commun. 2022 Aug 10. 13(1): 4685
      The protein kinase mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth and proliferation, supporting anabolic reactions and inhibiting catabolic pathways like autophagy. Its hyperactivation is a frequent event in cancer promoting tumor cell proliferation. Several intracellular membrane-associated mTORC1 pools have been identified, linking its function to distinct subcellular localizations. Here, we characterize the N-terminal kinase-like protein SCYL1 as a Golgi-localized target through which mTORC1 controls organelle distribution and extracellular vesicle secretion in breast cancer cells. Under growth conditions, SCYL1 is phosphorylated by mTORC1 on Ser754, supporting Golgi localization. Upon mTORC1 inhibition, Ser754 dephosphorylation leads to SCYL1 displacement to endosomes. Peripheral, dephosphorylated SCYL1 causes Golgi enlargement, redistribution of early and late endosomes and increased extracellular vesicle release. Thus, the mTORC1-controlled phosphorylation status of SCYL1 is an important determinant regulating subcellular distribution and function of endolysosomal compartments. It may also explain the pathophysiology underlying human genetic diseases such as CALFAN syndrome, which is caused by loss-of-function of SCYL1.
  5. J Virol. 2022 Aug 10. e0083622
      The mechanism by which avian reovirus (ARV)-modulated suppression of mTORC1 triggers autophagy remains largely unknown. In this work, we determined that p17 functions as a negative regulator of mTORC1. This study suggest novel mechanisms whereby p17-modulated inhibition of mTORC1 occurs via upregulation of p53, inactivation of Akt, and enhancement of binding of the endogenous mTORC1 inhibitors (PRAS40, FKBP38, and FKPP12) to mTORC1 to disrupt its assembly and accumulation on lysosomes. p17-modulated inhibition of Akt leads to activation of the downstream targets PRAS40 and TSC2, which results in mTORC1 inhibition, thereby triggering autophagy and translation shutoff, which is favorable for virus replication. p17 impairs the interaction of mTORC1 with its activator Rheb, which promotes FKBP38 interaction with mTORC1. It is worth noting that p17 activates ULK1 and Beclin1 and increases the formation of the Beclin 1/class III PI3K complex. These effects could be reversed in the presence of insulin or depletion of p53. Furthermore, we found that p17 induces autophagy in cancer cell lines by upregulating the p53/PTEN pathway, which inactivates Akt and mTORC1. This study highlights p17-modulated inhibition of Akt and mTORC1, which triggers autophagy and translation shutoff by positively modulating the tumor suppressors p53 and TSC2 and endogenous mTORC1 inhibitors. IMPORTANCE The mechanisms by which p17-modulated inhibition of mTORC1 induces autophagy and translation shutoff is elucidated. In this work, we determined that p17 serves as a negative regulator of mTORC1. This study provides several lines of conclusive evidence demonstrating that p17-modulated inhibition of mTORC1 occurs via upregulation of the p53/PTEN pathway, downregulation of the Akt/Rheb/mTORC1 pathway, enhancement of binding of the endogenous mTORC1 inhibitors to mTORC1 to disrupt its assembly, and suppression of mTORC1 accumulation on lysosomes. This work provides valuable information for better insights into p17-modulated inhibition of mTORC1, which induces autophagy and translation shutoff to benefit virus replication.
    Keywords:  Akt; PRAS40; Rheb; TSC2; autophagy; avian reovirus; mTORC1; p17; p53; translation shutoff
  6. Autophagy. 2022 Aug 08. 1-2
      Mitophagy neutralizes defective mitochondria via lysosomal elimination. Increased levels of mitophagy hallmark metabolic transitions and are induced by iron depletion, yet its metabolic basis has not been studied in-depth. How mitophagy integrates with different homeostatic mechanisms to support metabolic integrity is incompletely understood. We examined metabolic adaptations in cells treated with deferiprone (DFP), a therapeutic iron chelator known to induce PINK1-PRKN-independent mitophagy. We found that iron depletion profoundly rewired the cellular metabolome, remodeling lipid metabolism within minutes of treatment. DGAT1-dependent lipid droplet biosynthesis occurs upstream of mitochondrial turnover, with many LDs bordering mitochondria upon iron chelation. Surprisingly, DGAT1 inhibition restricts mitophagy in vitro by lysosomal dysfunction. Genetic depletion of mdy/DGAT1 in vivo impairs neuronal mitophagy and locomotor function in Drosophila, demonstrating the physiological relevance of our findings.
    Keywords:  DGAT1; iron; lipid droplet; metabolism; mitophagy
  7. Cold Spring Harb Perspect Biol. 2022 Aug 08. pii: a041256. [Epub ahead of print]
      The endoplasmic reticulum (ER) is the largest organelle and has multiple roles in various cellular processes such as protein secretion, lipid synthesis, calcium storage, and organelle biogenesis. The quantity and quality of this organelle are controlled by the ubiquitin-proteasome system and autophagy (termed "ER-phagy"). ER-phagy is defined as the degradation of part of the ER by the vacuole or lysosomes, and there are at least two types of ER-phagy: macro-ER-phagy and micro-ER-phagy. In macro-ER-phagy, ER fragments are enclosed by autophagosomes, which is mediated by ER-phagy receptors. In micro-ER-phagy, a portion of the ER is engulfed directly by the vacuole or lysosomes. In these two pathways, some proteins in the ER lumen can be recognized selectively and subjected to ER-phagy. This review summarizes our current knowledge of ER-phagy, focusing on its membrane dynamics, molecular mechanisms, substrate specificity, and physiological significance.
  8. Autophagy. 2022 Aug 10.
      Macroautophagy (hereafter "autophagy") is a membrane-mediated biological process that involves engulfing and delivering cytoplasmic components to lysosomes for degradation. In addition to autophagy's pro-survival effect during nutrient starvation, excessive activation of autophagy machinery can also cause regulated cell death, especially iron-dependent ferroptosis. Here, we report a key role for TMEM164 (transmembrane protein 164) in selectively mediating ATG5 (autophagy related 5)-dependent autophagosome formation during ferroptosis, rather than during starvation. In contrast, the membrane protein ATG9A (autophagy related 9A) is dispensable for the formation of autophagosomes during ferroptosis. TMEM164-mediated autophagy degrades ferritin, GPX4 (glutathione peroxidase 4), and lipid droplets to increase iron accumulation and lipid peroxidation, thereby promoting ferroptotic cell death. Consequently, the loss of TMEM164 limits the anticancer activity of ferroptosis-mediated cytotoxicity in mice. High TMEM164 expression is associated with improved survival and increased immune cell infiltration in patients with pancreatic cancer. These findings establish a new mode of autophagy-dependent ferroptosis.
    Keywords:  Autophagy; cell death; ferroptosis; membrane protein; tumor immunity
  9. NPJ Parkinsons Dis. 2022 Aug 06. 8(1): 100
      The abnormal accumulation of α-synuclein (α-syn) is a crucial factor for the onset and pathogenesis of Parkinson's disease (PD), and the autophagy-lysosome pathway (ALP) contributes to α-syn turnover. AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR) regulate autophagy by initiating the macroautophagy cascade and promoting lysosomal biogenesis via increased transcription factor EB (TFEB) activity. Hence, activation of AMPK-mTOR-TFEB axis-mediated autophagy might promote α-syn clearance in PD. Harmol is a β-carboline alkaloid that has been extensively studied in a variety of diseases but rarely in PD models. In this study, we aimed to evaluate the effect and underlying mechanism of harmol in PD models in vitro and in vivo. We show that harmol reduces α-syn via ALP in a dose- and time-dependent manner in cell model that overexpressed human A53T mutant α-syn. We also demonstrate that harmol promotes the translocation of TFEB into the nucleus and accompanies the restoration of autophagic flux and lysosomal biogenesis. Importantly, harmol improves motor impairment and down-regulates α-syn levels in the substantia nigra and prefrontal cortex in the α-syn transgenic mice model. Further studies revealed that harmol might activate ALP through AMPK-mTOR-TFEB to promote α-syn clearance. These in vitro and in vivo improvements demonstrate that harmol activates the AMPK-mTOR-TFEB mediated ALP pathway, resulting in reduced α-syn, and suggesting the potential benefit of harmol in the treatment of PD.
  10. Autophagy. 2022 Aug 10.
      Genetic evidence has increasingly linked lysosome dysfunction to an impaired autophagy-lysosomal pathway (ALP) flux in Alzheimer disease (AD) although the relationship of these abnormalities to other pathologies is unclear. In our recent investigation on the origin of impaired autophagic flux in AD, we established the critical early role of defective lysosomes in 5 mouse AD models. To assess in vivo alterations of autophagy and ALP vesicle acidification, we expressed eGFP-mRFP-LC3 specifically in neurons. We discovered that autophagy dysfunction in these models arises from exceptionally early failure of autolysosome/lysosome acidification, which then drives downstream AD pathogenesis. Extreme autophagic stress in compromised but still intact neurons causes AVs containing toxic APP metabolites, Aβ/β-CTFs, to pack into huge blebs and protrude from the perikaryon membrane. Most notably, AVs also coalesce with ER tubules and yield fibrillar β-amyloid within these tubules. Collectively, amyloid immunoreactivity within these intact neurons assumes the appearance of amyloid-plaques and, indeed, their eventual death transforms them into extracellular plaque lesions. Quantitative analysis confirms that neurons undergoing this transformation are the principal source of β-amyloid-plaques in APP-AD models. These findings prompt reconsideration of the conventionally accepted sequence of events in plaque formation and may help explain the inefficacy of Aβ/amyloid vaccine therapies.
    Keywords:  APP-βCTF; Alzheimer’s disease; Aβ; LC3; acidification; autophagy; lysosome; neuritic plaque; perikaryal blebbing
  11. Mol Psychiatry. 2022 Aug 10.
      Alzheimer's Disease (AD) is a progressive neurodegenerative disorder, which is characterized by cognitive deficit due to synaptic loss and neuronal death. Extracellular amyloid β plaques are one of the pathological hallmarks of AD. The autophagic lysosomal pathway is the essential mechanism to maintain cellular homeostasis by driving clearance of protein aggregates and is dysfunctional in AD. Here, we showed that inhibiting MEK/ERK signaling using a clinically available MEK1/2 inhibitor, trametinib (GSK1120212, SNR1611), induces the protection of neurons through autophagic lysosomal activation mediated by transcription factor EB (TFEB) in a model of AD. Orally administered trametinib recovered impaired neural structures, cognitive functions, and hippocampal long-term potentiation (LTP) in 5XFAD mice. Trametinib also reduced Aβ deposition via induction of autophagic lysosomal activation. RNA-sequencing analysis revealed upregulation of autophagic lysosomal genes by trametinib administration. In addition, trametinib inhibited TFEB phosphorylation at Ser142 and promoted its nuclear translocation, which in turn induced autophagic lysosomal related genes, indicating that trametinib activates the autophagic lysosomal process through TFEB activation. From these observations, we concluded that MEK inhibition provides neuronal protection from the Aβ burden by increasing autophagic lysosomal activity. Thus, MEK inhibition may be an effective therapeutic strategy for AD.
  12. Curr Med Chem. 2022 Aug 11.
      The process by which cells selectively remove damaged organelles or proteins is called autophagy. Chaperone-mediated autophagy (CMA) is a type of autophagy that degrades proteins containing the KFERQ pentapeptide in cells. CMA can degrade damaged or excess proteins and therefore plays an important role in maintaining protein balance in cells. CMA can also play a regulatory role by degrading key proteins in life activities, such as lipid and glucose metabolism. In this review, we introduce the CMA process and described the current commonly used CMA detection methods. In addition, we describe the role of CMA in glucose and lipid metabolism. Finally, we summarize the current role of CMA in metabolic diseases such as diabetic nephropathy (DN), alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) and discuss the role of CMA as a potential therapeutic target for metabolic diseases.
    Keywords:  Autophagy; Chaperone-mediated autophagy (CMA); Diabetic nephropathy (DN); HSC70; LAMP2A; Metabolic diseases
  13. Natl Sci Rev. 2022 Jul;9(7): nwab194
      Endoplasmic reticulum (ER) degradation by autophagy (ER-phagy) is a recently revealed selective autophagy pathway that plays important roles in organelle turnover and protein degradation, but the biological functions of ER-phagy are largely unknown. Here, we present an ER-targeting Re(I) tricarbonyl complex (Re-ERLAD) that can accumulate in the ER, induce ER-to-lysosome-associated degradation (ERLAD) upon visible light irradiation, and label ER buds and track their morphological alterations during ER-phagy. The emission of Re-ERLAD is sensitive to viscosity, which is a key parameter reflecting the amount of unfolded protein in the ER. Quantitative detection using two-photon fluorescence lifetime imaging microscopy shows that ER viscosity initially increases and then decreases during ERLAD, which reveals that ERLAD is a pathway for alleviating ER stress caused by unfolded proteins. In conclusion, our work presents the first specific photoinducer and tracker of ERLAD, which can be used in studying the regulatory mechanism and function of this process.
    Keywords:  ER-phagy; TPFLIM; rhenium; viscosity
  14. Autophagy. 2022 Aug 11. 1-2
      The selective macroautophagy/autophagy pathway is an important pathway of protein degradation, regulating signal transduction pathways via selective degradation of certain signaling complexes. TBK1 functions as a key protein in innate immunity or metabolic-associated fatty liver disease (MAFLD); however, the degradation of TBK1 has not been fully investigated. Recently, we have found that HNF1A functions as a novel cargo receptor to bridge TBK1 and MAP1LC3/LC3, hence promoting the degradation of TBK1 and regulating antiviral innate immunity and MAFLD.
    Keywords:  Cargo receptor; HNF1A; MAFLD; TBK1; selective autophagy
  15. Proc Natl Acad Sci U S A. 2022 Aug 16. 119(33): e2207489119
      The mechanistic target of rapamycin (mTOR) is assembled into signaling complexes of mTORC1 or mTORC2, and plays key roles in cell metabolism, stress response, and nutrient and growth factor sensing. Accumulating evidence from human and animal model studies has demonstrated a pathogenic role of hyperactive mTORC1 in age-related macular degeneration (AMD). The retinal pigment epithelium (RPE) is a primary injury site in AMD. In mouse models of RPE-specific deletion of Tuberous sclerosis 1 (Tsc1), which encodes an upstream suppressor of mTORC1, the hyperactivated mTORC1 metabolically reprogrammed the RPE and led to the degeneration of the outer retina and choroid (CH). In the current study, we use single-cell RNA sequencing (scRNA-seq) to identify an RPE mTORC1 downstream protein, dopamine- and cyclic AMP-regulated phosphoprotein of molecular weight 32,000 (DARPP-32). DARPP-32 was not found in healthy RPE but localized to drusen and basal linear deposits in human AMD eyes. In animal models, overexpressing DARPP-32 by adeno-associated virus (AAV) led to abnormal RPE structure and function. The data indicate that DARPP-32 is a previously unidentified signaling protein subjected to mTORC1 regulation and may contribute to RPE degeneration in AMD.
    Keywords:  RPE; age-related macular degeneration; drusen; mTORC1
  16. Autophagy. 2022 Aug 08. 1-17
      TFEB (transcription factor EB) regulates multiple genes involved in the process of macroautophagy/autophagy and plays a critical role in lifespan determination. However, the detailed mechanisms that regulate TFEB activity are not fully clear. In this study, we identified a role for HSP90AA1 in modulating TFEB. HSP90AA1 was phosphorylated by CDK5 at Ser 595 under basal condition. This phosphorylation inhibited HSP90AA1, disrupted its binding to TFEB, and impeded TFEB's nuclear localization and subsequent autophagy induction. Pro-autophagy signaling attenuated CDK5 activity and enhanced TFEB function in an HSP90AA1-dependent manner. Inhibition of HSP90AA1 function or decrease in its expression significantly attenuated TFEB's nuclear localization and transcriptional function following autophagy induction. HSP90AA1-mediated regulation of a TFEB ortholog was involved in the extended lifespan of Caenorhabditis elegans in the absence of its food source bacteria. Collectively, these findings reveal that this regulatory process plays an important role in modulation of TFEB, autophagy, and longevity.Abbreviations : AL: autolysosome; AP: autophagosome; ATG: autophagy related; BafA1: bafilomycin A1; CDK5: cyclin-dependent kinase 5; CDK5R1: cyclin dependent kinase 5 regulatory subunit 1; CR: calorie restriction; FUDR: 5-fluorodeoxyuridine; HSP90AA1: heat shock protein 90 alpha family class A member 1; MAP1LC3: microtubule associated protein 1 light chain 3; NB: novobiocin sodium; SQSTM1: sequestosome 1; TFEB: transcription factor EB; WT: wild type.
    Keywords:  Aging; CDK5; macroautophagy; phosphorylation; transcriptional factor
  17. Front Microbiol. 2022 ;13 935547
      Although autophagy can eliminate some intracellular pathogens, others, e.g., Staphylococcus aureus, Salmonella, Mycoplasma bovis, can evade it. The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway, a key regulator of autophagy, is involved in initiation and promotion of a range of pathological diseases. As the effects of M. bovis on the autophagic pathway are not well documented, our objective was to elucidate the effects of M. bovis infection on the PI3K-Akt-mTOR cellular autophagic pathway in bovine mammary epithelial cells (bMECs). Ultrastructure of bMECs infected with M. bovis was assessed with transmission electron microscopy, co-localization of LC3 puncta with M. bovis was confirmed by laser confocal microscopy, and autophagy-related indicators were quantified with Western blotting and RT-PCR. In M. bovis-infected bMECs, intracellular M. bovis was encapsulated by membrane-like structures, the expression level of LC3-II and Beclin1 protein decreased at the middle stage of infection, degradation of SQSTM1/P62 was blocked, autophagy of bMECs was inhibited, and PI3K-Akt-mTOR protein was activated by phosphorylation. Furthermore, the tumor suppressor PTEN can inhibit the PI3K-Akt signaling pathway through dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate and may be important for cellular resistance to infection. In the present study, the number of intracellular M. bovis was inversely related to the change in the level of autophagy markers (e.g., LC3-II, SQSTM1/P62) within host cells induced by the low knockdown of Akt or PTEN. We concluded that M. bovis-infected bMECs alleviated cellular autophagy through a PI3K-Akt-mTOR pathway, and that PTEN acted as a protective gene regulating autophagy, a key step in controlling infection.
    Keywords:  Mycoplasma bovis; PI3K-Akt-mTOR pathway; PTEN; autophagy; bovine mammary epithelial cells
  18. Trends Cell Biol. 2022 Aug 06. pii: S0962-8924(22)00175-1. [Epub ahead of print]
      The N-degron pathway is a degradative system in which the N-terminal residues of proteins modulate the half-lives of proteins and other cellular materials. The majority of amino acids in the genetic code have the potential to induce cis or trans degradation in diverse processes, which requires selective recognition between N-degrons and cognate N-recognins. Of particular interest is the Cys/N-degron branch, in which the N-terminal cysteine (Nt-Cys) induces proteolysis via either the ubiquitin (Ub)-proteasome system (UPS) or the autophagy-lysosome pathway (ALP), depending on physiological conditions. Recent studies provided new insights into the central role of Nt-Cys in sensing the fluctuating levels of oxygen and reactive oxygen species (ROS). Here, we discuss the components, regulations, and functions of the Cys/N-degron pathway.
    Keywords:  N-recognin; N-terminal oxidation; autophagy; oxygen sensor; proteolysis; the N-degron pathway
  19. Cold Spring Harb Perspect Biol. 2022 Aug 08. pii: a041254. [Epub ahead of print]
      Autophagy is an intracellular degradation system involving de novo generation of autophagosomes, which function as a transporting vesicle of cytoplasmic components to lysosomes for degradation. Isolation membranes (IMs) or phagophores, the precursor membranes of autophagosomes, require millions of phospholipids to expand and transform into autophagosomes, with the endoplasmic reticulum (ER) being the primary lipid source. Recent advances in structural and biochemical studies of autophagy-related proteins have revealed their lipid transport activities: Atg2 at the interface between IM and ER possesses intermembrane lipid transfer activities, while Atg9 at IM and VMP1 and TMEM41B at ER possess lipid scrambling activities. In this review, we summarize recent advances in the establishment of the lipid transport activities of these proteins and their collaboration mechanisms for lipid transport between the ER and IM, and further discuss how unidirectional lipid transport from the ER to IM occurs during autophagosome formation.
  20. Front Oncol. 2022 ;12 903874
      AXL receptor tyrosine kinase promotes an invasive phenotype and chemotherapy resistance in esophageal adenocarcinoma (EAC). AXL has been implicated in the regulation of autophagy, but the underlying molecular mechanism remains poorly understood. Herein, we investigate the mechanistic role of AXL in autophagy as well as metformin-induced effects on the growth and survival of EAC. We demonstrate that AXL mediates autophagic flux through activation of AMPK-ULK1 signaling in a reactive oxygen species (ROS)-dependent mechanism by glucose starvation. AXL positively regulates basal cellular ROS levels without significantly affecting mitochondrial ROS production in EAC cells. Pharmacological inhibition of cellular ROS using Trolox abrogates glucose starvation-induced AMPK signaling and autophagy. We demonstrate that AXL expression is required for metformin-induced apoptosis in EAC cells in vitro. The apoptosis induction by metformin is markedly attenuated by inhibition of autophagy through genetic silencing of Beclin1 or ATG7 autophagy mediators, thereby confirming the requirement of intact autophagy for enhancing metformin-induced apoptosis in EAC cells. Our data indicate that metformin-induced autophagy displays a pro-apoptotic function in EAC cells. We show that the metformin-induced suppression of tumor growth in vivo is highly dependent on AXL expression in a tumor xenograft mouse model of EAC. We demonstrate that AXL promotes metformin-induced apoptosis through activation of autophagy in EAC. AXL may be a valuable biomarker to identify tumors that are sensitive to metformin. Therefore, AXL expression could inform the selection of patients for future clinical trials to evaluate the therapeutic efficacy of metformin in EAC.
    Keywords:  AMPK; ATG7; Barrett’s esophagus; Beclin1; autophagic flux; glucose starvation; proliferation; reactive oxygen species
  21. Cells. 2022 Aug 05. pii: 2426. [Epub ahead of print]11(15):
      Loss of either PINK1 or PRKN causes an early onset Parkinson's disease (PD) phenotype. Functionally, PINK1 and PRKN work together to mediate stress-activated mitochondrial quality control. Upon mitochondrial damage, PINK1, a ubiquitin kinase and PRKN, a ubiquitin ligase, decorate damaged organelles with phosphorylated ubiquitin for sequestration and degradation in lysosomes, a process known as mitophagy. While several genetic mutations are established to result in loss of mitophagy function, many others have not been extensively characterized and are of unknown significance. Here, we analyzed a set of twenty variants, ten in each gene, focusing on understudied variants mostly from the Parkinson's progressive marker initiative, with sensitive assays to define potential functional deficits. Our results nominate specific rare genetic PINK1 and PRKN variants that cause loss of enzymatic function in line with a potential causative role for PD. Additionally, we identify several variants with intermediate phenotypes and follow up on two of them by gene editing midbrain-derived neuronal precursor cells. Thereof derived isogenic neurons show a stability defect of the rare PINK1 D525N mutation, while the common PINK1 Q115L substitution results in reduced kinase activity. Our strategy to analyze variants with sensitive functional readouts will help aid diagnostics and disease treatment in line with current genomic and therapeutic advances.
    Keywords:  PD genes; PINK1; PRKN; Parkin; Parkinson; mitophagy; ubiquitin
  22. Cells. 2022 Jul 28. pii: 2324. [Epub ahead of print]11(15):
      Autophagy, a lysosome-mediated cellular degradation pathway, recycles intracellular components to maintain metabolic balance and survival. Autophagy plays an important role in tumor immunotherapy as a "double-edged sword" that can both promote and inhibit tumor progression. Autophagy acts on innate and adaptive immunity and interacts with immune cells to modulate tumor immunotherapy. The discovery of autophagy inducers and autophagy inhibitors also provides new insights for clinical anti-tumor therapy. However, there are also difficulties in the application of autophagy-related regulators, such as low bioavailability and the lack of efficient selectivity. This review focuses on autophagy-related immunogenic regulation and its application in cancer therapy.
    Keywords:  autophagy; cancer therapy; immunity
  23. Autophagy. 2022 Aug 10.
      Brown adipose tissue (BAT) thermogenesis affects energy balance, and thereby it has the potential to induce weight loss and to prevent obesity. Here we document a macroautophagic/autophagic-dependent mechanism of PPARG activity regulation that induces brown adipose differentiation and thermogenesis, and that is mediated by TP53INP2. Disruption of TP53INP2-dependent autophagy reduced brown adipogenesis in cultured cells. In vivo specific-tp53inp2 ablation in brown precursor cells or in adult mice decreased the expression of thermogenic and mature adipocytes genes in BAT. As a result, TP53INP2-deficient mice had reduced UCP1 content in BAT and impaired maximal thermogenic capacity, leading to lipid accumulation and to positive energy balance. Mechanistically, TP53INP2 stimulates PPARG activity and adipogenesis in brown adipose cells by promoting the autophagic degradation of NCOR1, a PPARG co-repressor. Moreover, the modulation of TP53INP2 expression in BAT and in human brown adipocytes suggest that this protein increases PPARG activity during metabolic activation of brown fat. In all, we have identified a novel molecular explanation to the contribution of autophagy to BAT energy metabolism that could facilitate the design of therapeutic strategies against obesity and its metabolic complications.
    Keywords:  Autophagy; brown adipose tissue; metabolism; obesity; thermogenesis
  24. Exp Biol Med (Maywood). 2022 Aug 11. 15353702221116879
      Morroniside is known to improve osteoporosis by promoting osteoblastogenesis. The activation of PI3K/Akt/mTOR signaling is a significant mechanism in morroniside-promoted osteoblastogenesis. It is well known that protective autophagy is an important factor in osteoblastogenesis. However, the activation of mTOR signaling can inhibit autophagy. This study aimed to investigate the relationship between mTOR signaling and autophagy in morroniside-regulated osteoblastogenesis. In this study, we investigated the effect of morroniside on the autophagic activity (LC3 conversion rate, LC3-puncta formation, and autophagosome number) of differentiated osteoblast precursors (MC3T3-E1 cells). Then, we identified the roles of mTOR knockdown in morroniside-regulated alterations of autophagy and osteogenic parameters in MC3T3-E1 cells. Next, mTOR knockdown and overexpression were used to observe the roles of mTOR in morroniside-regulated alterations of autophagic molecules (Atg7, Atg13, and Beclin1). Subsequently, the additional value of the above autophagic molecules on morroniside-regulated osteogenic parameters in MC3T3-E1 cells was analyzed based on lentiviral transduction. Finally, combined with morroniside and TAT-Beclin1, the roles of Beclin1 upregulation in the in vivo effects of morroniside was investigated. Our experimental data showed that morroniside promoted both the mTOR activity and autophagy in MC3T3-E1 cells. Morroniside-upregulated autophagic activity and Atg13 or Beclin1 protein level in MC3T3-E1 cells were enhanced by mTOR knockdown. Furthermore, Morroniside-upregulated Atg13 and Beclin1 expression was reversed by mTOR overexpression. Importantly, autophagy upregulation with overexpression of the autophagic gene, Atg13 or BECN1 (gene form of Beclin1), significantly promoted osteoblastogenesis regulated by morroniside. The promotional effect of morroniside on bone microarchitecture, bone mass, and bone parameters (including trabecular bone area and OCN expression in trabecular bone) in ovariectomized (OVX) mice was enhanced by TAT-Beclin1 administration. In conclusion, the autophagy-enhancing drugs related to Beclin1 or Atg13 may be an effective adjuvant therapy in the treatment of osteoporosis with morroniside.
    Keywords:  Atg13; Beclin1; Morroniside; Osteoblast; mTOR
  25. Front Cell Dev Biol. 2022 ;10 950973
      The epidermis, the outmost layer of the skin, is a stratified squamous epithelium that protects the body from the external world. The epidermis and its appendages need constantly renew themselves and replace the damaged tissues caused by environmental assaults. The mechanistic target of rapamycin (mTOR) signaling is a central controller of cell growth and metabolism that plays a critical role in development, homeostasis and diseases. Recent findings suggest that mTOR signaling is activated in a spatiotemporal and context-dependent manner in the epidermis, coordinating diverse skin homeostatic processes. Dysregulation of mTOR signaling underlies the pathogenesis of skin diseases, including psoriasis and skin cancer. In this review, we discuss the role of epidermal mTOR signaling activity and function in skin, with a focus on skin barrier formation, hair regeneration, wound repair, as well as skin pathological disorders. We propose that fine-tuned control of mTOR signaling is essential for epidermal structural and functional integrity.
    Keywords:  epidermis; keratinocytes; mTOR; metabolism; wound healing
  26. Int J Mol Sci. 2022 Aug 03. pii: 8634. [Epub ahead of print]23(15):
      Deficiency in scavenger receptor class B, member 2 (SCARB2) is related to both Gaucher disease (GD) and Parkinson's disease (PD), which are both neurodegenerative-related diseases without cure. Although both diseases lead to weight loss, which affects the quality of life and the progress of diseases, the underlying molecular mechanism is still unclear. In this study, we found that Scarb2-/- mice showed significantly reduced lipid storage in white fat tissues (WAT) compared to WT mice on a regular chow diet. However, the phenotype is independent of heat production, activity, food intake or energy absorption. Furthermore, adipocyte differentiation and cholesterol homeostasis were unaffected. We found that the impaired lipid accumulation of Adiponectin-cre; Scarb2fl/fl mice was due to the imbalance between glycolysis and oxidative phosphorylation (OXPHOS). Mechanistically, the mechanistic target of rapamycin complex 1 (mTORC1)/ eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1) pathway was down-regulated in Scarb2 deficient adipocytes, leading to impaired mitochondrial respiration and enhanced glycolysis. Altogether, we reveal the role of SCARB2 in metabolism regulation besides the nervous system, which provides a theoretical basis for weight loss treatment of patients with neurodegenerative diseases.
    Keywords:  LIMP-2 (SCARB2); OXPHOS; glycolysis; lysosomes; mTORC1/4E-BP1; mitochondria
  27. Cells. 2022 Aug 02. pii: 2385. [Epub ahead of print]11(15):
      BACKGROUND: Posterior capsule opacification (PCO) is the most common complication after cataract surgery, in which increased levels of transforming growth factor-beta 2 (TGF-β2) accelerate PCO formation; however, the pathological mechanisms are not fully understood. This study aims to explore the regulation mechanism of TGF-β2 in PCO formation via its autophagic functions.METHODS: The autophagic effect of TGF-β2 was detected by transmission electron microscopy (TEM), Western blotting, and immunofluorescence analysis. The association between autophagy and the epithelial-mesenchymal transition (EMT) was evaluated by qPCR and Western blotting. The transcriptome analysis was used to uncover the molecular mechanism of TGF-β2-induced PCO formation.
    RESULTS: TGF-β2 specifically promotes autophagy flux in human lens epithelial cells. The activation of autophagy by rapamycin can promote EMT marker synthesis and improve cell migration. However, the inhibition of autophagy by 3-MA attenuates EMT. To uncover the molecular mechanisms, we performed RNA sequencing and found that TGF-β2 elevated tumor protein p53-inducible nuclear protein2 (TP53INP2) expression, which was accompanied by a nuclear-to-cytoplasm translocation. Moreover, the knockdown of TP53INP2 blocked the TGF-β2-induced autophagy and EMT processes, revealing that TP53INP2 plays an important role in TGF-β2-induced autophagy during EMT.
    CONCLUSIONS: Taken together, the results of this study suggested that TP53INP2 was a novel regulator of PCO development by TGF-β2, and notably, TP53INP2, may be a potential target for the pharmacological treatment of PCO.
    Keywords:  TGF-β2; TP53INP2; autophagy; epithelial–mesenchymal transition; posterior capsule opacification
  28. Autophagy. 2022 Aug 11. 1-10
      The COVID-19 pandemic has caused substantial losses worldwide in people's lives, health, and property. Currently, COVID-19 is still prominent worldwide without any specific drug treatment. The SARS-CoV-2 pathogen is the cause of various systemic diseases, mainly acute pneumonia. Within the pathological process, neutrophils are recruited to infected sites, especially in the lungs, for the first stage of removing invading SARS-CoV-2 through a range of mechanisms. Macroautophagy/autophagy, a conserved autodegradation process in neutrophils, plays a crucial role in the neutrophil phagocytosis of pathogens. NETosis refers to neutrophil cell death, while auto-inflammatory factors and antigens release NETs. This review summarizes the latest research progress and provides an in-depth explanation of the underlying mechanisms of autophagy and NETosis in COVID-19. Furthermore, after exploring the relationship between autophagy and NETosis, we discuss potential targets and treatment options. This review keeps up with the latest research on COVID-19 from neutrophil autophagy and NETosis with a new perspective, which can guide the urgent development of antiviral drugs and provide guidance for the clinical treatment of COVID-19.Abbreviations: AKT1: AKT serine/threonine kinase 1; AMPK: AMP-activated protein kinase; AP: autophagosome; ARDS: acute respiratory distress syndrome; ATG: autophagy related; BECN1: beclin 1; cfDNA: cell-free DNA; COVID-19: coronavirus disease 2019; CQ: chloroquine; DMVs: double-membrane vesicles; ELANE/NE: elastase, neutrophil expressed; F3: coagulation factor III, tissue factor; HCQ: hydroxychloroquine; MAP1LC3/LC3: microtubule associated protein 1 light chain of 3; MPO: myeloperoxidase; MTORC1: mechanistic target of rapamycin kinase complex 1; NETs: neutrophil traps; NSP: nonstructural protein; PI3K: class I phosphoinositide 3-kinase; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; ROS: reactive oxygen species; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SKP2: S-phase kinase associated protein 2; TCC: terminal complement complex; ULK1: unc-51 like.
    Keywords:  Autophagy; COVID-19; NETosis; biomarkers; clinical treatments; neutrophil
  29. Int J Mol Sci. 2022 Jul 28. pii: 8366. [Epub ahead of print]23(15):
      Plant diseases cause substantial loss to crops all over the world, reducing the quality and quantity of agricultural goods significantly. One of the world's most damaging plant diseases, rice blast poses a substantial threat to global food security. Magnaporthe oryzae causes rice blast disease, which challenges world food security by causing substantial damage in rice production annually. Autophagy is an evolutionarily conserved breakdown and recycling system in eukaryotes that regulate homeostasis, stress adaption, and programmed cell death. Recently, new studies found that the autophagy process plays a vital role in the pathogenicity of M. oryzae and the regulation mechanisms are gradually clarified. Here we present a brief summary of the recent advances, concentrating on the new findings of autophagy regulation mechanisms and summarize some autophagy-related techniques in rice blast fungus. This review will help readers to better understand the relationship between autophagy and the virulence of plant pathogenic fungi.
    Keywords:  Magnaporthe oryzae; appressorium; autophagosome; autophagy; autophagy-related techniques; pathogenesis; phagophore
  30. J Immunol Res. 2022 ;2022 9822157
      Objectives: Intestinal epithelial barrier function is an important mechanical barrier to maintain intestinal homeostasis and resist the invasion of intestinal pathogens and microorganisms. However, intestinal epithelial barrier function is vulnerable to damage under intestinal ischemia-reperfusion (I/R) injury. Under a category of pathophysiological conditions, including I/R, autophagy plays a crucial role. This study is aimed at discussing the role of autophagy inhibitors and activators in intestinal epithelial barrier function after intestinal I/R by changing autophagy levels.Methods: Mice with intestinal IR underwent 45 minutes of surgery for superior mesenteric artery occlusion. The autophagy inhibitor 3-MA and the autophagy inducer rapamycin (RAP) were used to change the level of autophagy, and then, the expressions of tight junction proteins and intestinal barrier function were detected.
    Results: The results showed that the autophagy inhibitor 3-MA aggravated intestinal epithelial barrier dysfunction, while the autophagy inducer RAP attenuated intestinal epithelial barrier dysfunction. In addition, promoting autophagy may promote occludin expression by inhibiting claudin-2 expression.
    Conclusion: Upregulation of autophagy levels by autophagy inducers can enhance intestinal epithelial barrier function after intestinal I/R.
  31. Cells. 2022 Aug 04. pii: 2416. [Epub ahead of print]11(15):
      Dysfunctional mitochondrial quality control (MQC) is implicated in the pathogenesis of Parkinson's disease (PD). The improper selection of mitochondria for mitophagy increases reactive oxygen species (ROS) levels and lowers ATP levels. The downstream effects include oxidative damage, failure to maintain proteostasis and ion gradients, and decreased NAD+ and NADPH levels, resulting in insufficient energy metabolism and neurotransmitter synthesis. A ketosis-based metabolic therapy that increases the levels of (R)-3-hydroxybutyrate (BHB) may reverse the dysfunctional MQC by partially replacing glucose as an energy source, by stimulating mitophagy, and by decreasing inflammation. Fasting can potentially raise cytoplasmic NADPH levels by increasing the mitochondrial export and cytoplasmic metabolism of ketone body-derived citrate that increases flux through isocitrate dehydrogenase 1 (IDH1). NADPH is an essential cofactor for nitric oxide synthase, and the nitric oxide synthesized can diffuse into the mitochondrial matrix and react with electron transport chain-synthesized superoxide to form peroxynitrite. Excessive superoxide and peroxynitrite production can cause the opening of the mitochondrial permeability transition pore (mPTP) to depolarize the mitochondria and activate PINK1-dependent mitophagy. Both fasting and exercise increase ketogenesis and increase the cellular NAD+/NADH ratio, both of which are beneficial for neuronal metabolism. In addition, both fasting and exercise engage the adaptive cellular stress response signaling pathways that protect neurons against the oxidative and proteotoxic stress implicated in PD. Here, we discuss how intermittent fasting from the evening meal through to the next-day lunch together with morning exercise, when circadian NAD+/NADH is most oxidized, circadian NADP+/NADPH is most reduced, and circadian mitophagy gene expression is high, may slow the progression of PD.
    Keywords:  DJ-1; IDH1; NAD; NADPH; PINK1; Parkin; Parkinson’s disease; circadian; coffee; exercise; fasting; metabolic therapy; mitochondrial biogenesis; mitochondrial quality control; mitophagy; nicotinamide adenine dinucleotide; nicotinamide adenine dinucleotide phosphate
  32. Geroscience. 2022 Aug 10.
      Mitochondrial dysfunction is a well-known contributor to aging and age-related diseases. The precise mechanisms through which mitochondria impact human lifespan, however, remain unclear. We hypothesize that humans with exceptional longevity harbor rare variants in nuclear-encoded mitochondrial genes (mitonuclear genes) that confer resistance against age-related mitochondrial dysfunction. Here we report an integrated functional genomics study to identify rare functional variants in ~ 660 mitonuclear candidate genes discovered by target capture sequencing analysis of 496 centenarians and 572 controls of Ashkenazi Jewish descent. We identify and prioritize longevity-associated variants, genes, and mitochondrial pathways that are enriched with rare variants. We provide functional gene variants such as those in MTOR (Y2396Lfs*29), CPS1 (T1406N), and MFN2 (G548*) as well as LRPPRC (S1378G) that is predicted to affect mitochondrial translation. Taken together, our results suggest a functional role for specific mitonuclear genes and pathways in human longevity.
    Keywords:  Aging; Centenarian; Genetic variant; Longevity; Mitochondria
  33. Cells. 2022 Aug 04. pii: 2415. [Epub ahead of print]11(15):
      Proper homeostasis of the proteome, referred to as proteostasis, is maintained by chaperone-dependent refolding of misfolded proteins and by protein degradation via the ubiquitin-proteasome system and the autophagic machinery. This review will discuss a crosstalk between biomolecular condensates and proteostasis, whereby the crowding of proteostasis factors into macromolecular assemblies is often established by phase separation of membraneless biomolecular condensates. Specifically, ubiquitin and other posttranslational modifications come into play as agents of phase separation, essential for the formation of condensates and for ubiquitin-proteasome system activity. Furthermore, an intriguing connection associates malfunction of the same pathways to the accumulation of misfolded and ubiquitinated proteins in aberrant condensates, the formation of protein aggregates, and finally, to the pathogenesis of neurodegenerative diseases. The crosstalk between biomolecular condensates and proteostasis is an emerging theme in cellular and disease biology and further studies will focus on delineating specific molecular pathways involved in the pathogenesis of amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases.
    Keywords:  ALS; amyotrophic lateral sclerosis; biomolecular condensation; membraneless organelles; neurodegeneration; proteostasis; ubiquitin proteasome system
  34. Cell Mol Neurobiol. 2022 Aug 12.
      Autophagy is a highly evolutionary conserved process that degrades cytosolic macromolecules or damaged organelles (e.g., mitochondria), as well as intracellular pathogens for energy and survival. Dysfunction of autophagy has been associated with the pathologies of Alzheimer's disease (AD), including Aβ plaques and neurofibrillary tangles. Recently, the presence of sustained immune response in the brain has been considered a new core pathology in AD. Accumulating evidence suggests that autophagy activation may suppress inflammation response through degrading inflammasomes or pro-inflammatory cytokines and improving immune system function in both clinical trials and preclinical studies. This review provides an overview of updated information on autophagy and inflammation and their potential mediators in AD. In summary, we believe that understanding the relationship between autophagy and inflammation will provide insightful knowledge for future therapeutic implications in AD.
    Keywords:  Alzheimer’s disease; Autophagy; Genetic factors; Inflammation; Microglia; NLRP3 inflammasomes
  35. Pancreatology. 2022 Aug 03. pii: S1424-3903(22)00466-5. [Epub ahead of print]
      Acute pancreatitis is characterized by necrosis of its parenchymal cells and influx and activation of inflammatory cells that further promote injury and necrosis. This review is intended to discuss the central role of disorders of calcium metabolism and mitochondrial dysfunction in the mechanism of pancreatitis development. The disorders are placed in context of calcium and mitochondria in physiologic function of the pancreas. Moreover, we discuss potential therapeutics for preventing pathologic calcium signals that injure mitochondria and interventions that promote the removal of injured mitochondria and regenerate new and heathy populations of mitochondria.
    Keywords:  Acute pancreatitis; Autophagy; Calcium; Inflammation; Mitochondria; Mitophagy; Necrosis
  36. Clin Transl Discov. 2022 Jun;2(2): e68
      In this commentary, we highlight autophagy's important function, while identifying potential therapeutic targets for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the elderly. Autophagy's decline in the elderly causes increased cell senescence and a dysregulated immune system. As this demographic often faces decreased vaccine-provided immunity, coronavirus disease 2019 treatments must be developed. We discuss a recent study by Acharya et al. (2022) that found that SF2523 induced autophagy, reducing SARS-CoV-2 replication. Furthermore, across varying dosages, SF2523 was shown to have a synergistic effect with remdesivir or MU-UNMC. Consequently, we believe that SF2523, alone or with other anti-virals, is a promising potential therapeutic for preventing SARS-CoV-2-related mortalities.
  37. Int J Mol Sci. 2022 Aug 08. pii: 8798. [Epub ahead of print]23(15):
      Phosphatidylethanolamine binding protein 4 (PEBP4) is an understudied multifunctional small protein. Previous studies have shown that the expression of PEBP4 is increased in many cancer specimens, which correlates to cancer progression. The present study explored the mechanism by which PEBP4 regulates the growth and progression of hepatocellular carcinoma cells. Thus, we showed that knockdown of PEBP4 in MHCC97H cells, where its expression was relatively high, diminished activities of serine/threonine protein kinase B (PKB, also known as Akt), mammalian target of rapamycin complex 1(mTORC1), and mTORC2, events that were not restored by insulin-like growth factor 1 (IGF-1). Conversely, overexpression of PEBP4 in MHCC97L cells with the low endogenous level yielded opposite effects. Furthermore, physical association of PEBP4 with Akt, mTORC1, and mTORC2 was observed. Interestingly, introduction of AktS473D mutant, bypassing phosphorylation by mTORC2, rescued mTORC1 activity, but without effects on mTORC2 signaling. In contrast, the effect of PEBP4 overexpression on the activity of mTORC1 but not that of mTORC2 was suppressed by MK2206, a specific inhibitor of Akt. In conjunction, PEBP4 knockdown-engendered reduction of cell proliferation, migration and invasion was partially rescued by Akt S473D while increases in these parameters induced by overexpression of PEBP4 were completely abolished by MK2206, although the expression of epithelial mesenchymal transition (EMT) markers appeared to be fully regulated by the active mutant of Akt. Finally, knockdown of PEBP4 diminished the growth of tumor and metastasis, whereas they were enhanced by overexpression of PEBP4. Altogether, our study suggests that increased expression of PEBP4 exacerbates malignant behaviors of hepatocellular cancer cells through cooperative participation of mTORC1 and mTORC2.
    Keywords:  Akt; HCC; PEBP4; mTORC1; mTORC2
  38. Mol Neurobiol. 2022 Aug 13.
      In attempts to develop effective therapeutic strategies to limit post-ischemic injury, mitochondria emerge as a key element determining neuronal fate. Mitochondrial damage can be alleviated by various mechanisms including mitochondrial network remodelling, mitochondrial elimination and mitochondrial protein biogenesis. However, the mechanisms regulating relationships between these phenomena are poorly understood. We hypothesized that mitofusin 2 (Mfn2), a mitochondrial GTPase involved in mitochondrial fusion, mitochondria trafficking and mitochondria and endoplasmic reticulum (ER) tethering, may act as one of linking and regulatory factors in neurons following ischemic insult. To verify this assumption, we performed temporal oxygen and glucose deprivation (OGD/R) on rat cortical primary culture to determine whether Mfn2 protein reduction affected the onset of mitophagy, subsequent mitochondrial biogenesis and thus neuronal survival. We found that Mfn2 knockdown increased neuronal susceptibility to OGD/R, prevented mitochondrial network remodelling and resulted in prolonged mitophagosomes formation in response to the insult. Next, Mfn2 knockdown was observed to be accompanied by reduced Parkin protein levels and increased Parkin accumulation on mitochondria. As for wild-type neurons, OGD/R insult was followed by an elevated mtDNA content and an increase in respiratory chain proteins. Neither of these phenomena were observed for Mfn2 knockdown neurons. Collectively, our findings showed that Mfn2 in neurons affected their response to mild and transient OGD stress, balancing the extent of defective mitochondria elimination and positively influencing mitochondrial respiratory protein levels. Our study suggests that Mfn2 is one of essential elements for neuronal response to ischemic insult, necessary for neuronal survival.
    Keywords:  Brain ischemia; Mitochondria; Mitochondrial DNA; Mitochondrial biogenesis; Mitofusin 2; Mitophagy; Primary neurons
  39. Mol Genet Metab. 2022 Jul 30. pii: S1096-7192(22)00381-X. [Epub ahead of print]137(1-2): 81-91
    Keywords:  Glycosphingolipidoses; Lyso-lipids; Mucopolysaccharidoses; Pompe disease; mTORC1
  40. Virus Res. 2022 Aug 07. pii: S0168-1702(22)00214-3. [Epub ahead of print] 198886
      The classical swine fever virus (CSFV) is one of the most harmful pathogens of swine and causes considerable economic loss. Mitophagy is a selective form of autophagy that degrades damaged mitochondria by combining with lysosomes. Previous studies have been reported that CSFV infection can induce mitophagy, but which effector protein is responsible for this process remains unclear. Herein, we revealed here that the CSFV nonstructural protein 5A (NS5A) plays a critical role in inducing cellular mitophagy. Specifically, the expression of CSFV NS5A in the PK-15 cells induces membrane potential loss and mitochondrial fission, and the quantities of mitophagosomes, the expression of Parkin and PINK1 were significantly increased compared with mock cells. Intriguingly, we found that Parkin-overexpression promotes CSFV propagation. Furthermore, the expression level of reactive oxygen species (ROS) was increased by CSFV NS5A protein, while NS5A-induced mitophagy correlated with the quantity of ROS production. In summary, our results reveal a new function of NS5A in inducing cellular mitophagy and broaden our understanding of the mechanism of CSFV-induced mitophagy, which may provide a new way to develop an antiviral strategy.
    Keywords:  CSFV; NS5A; Parkin; mitophagy; replication
  41. FASEB J. 2022 Sep;36(9): e22491
      Accumulation of lipid substances decreased the activity of osteoblasts. Trehalose is a typical stress metabolite to form a protective membrane on cell surface which has been demonstrated to regulate lipid metabolism. This activity of Trehalose indicates the potential effect of osteoporosis treatment. Our study aimed to determine the therapeutic effect of Trehalose in high fat-induced osteoporosis. We used palmitic acid (PA) to mimic the state of high fat and observed the apoptosis ratio of osteoblasts increased. After adding Trehalose, the apoptosis ratio decreased obviously. Autophagy is a regulatory means involved in the process of apoptosis. We detected the autophagy protein and found that the expression of Beclin-1, Atg5, and LC3 II increased, and p62 decreased after Trehalose treatment. When adding an autophagy inhibitor (3-MA), the expression of Beclin-1, Atg5, and LC3 II decreased, and p62 increased. These results indicated autophagy was an important factor involved in the preventive effect of Trehalose in PA-induced apoptosis. SIRT3 is a mitochondrial gene that can inhibit apoptosis, which has been reported to promote autophagy. We used SIRT3-siRNA to silence the expression of SIRT3 and found the effect of Trehalose was counteracted. The apoptosis ratio increased and the expression of Beclin-1, Atg5, and LC3 II decreased, p62 increased. Additionally, we also fed the mice with a high-fat diet (HFD) and intragastrical Trehalose. The results showed that Trehalose could inhibit the bone mass loss with HFD. Our study revealed the effect and mechanism of Trehalose in the treatment of osteoporosis.
    Keywords:  SIRT3; Trehalose; autophagy; lipotoxicity; palmitic acid
  42. Front Mol Biosci. 2022 ;9 952608
      Niemann-Pick type C disease (NPCD) is a rare genetic syndrome characterized by cholesterol accumulation in multiple organelles. NPCD is mainly caused by gene deficiency of NPC intracellular cholesterol transporter 1 (NPC1). It has been reported that some of the NPCD patients exhibit clinical features of progressive hearing loss at high frequency and iron disorder, but the underlying relationship is unknown. A recent study has reported that ferroptosis contributes to the impairment of cochlear hair cells that are related to sensory hearing. In this study, we generated NPC1-deficient HEI-OC1 cells to show the effect of NPC1 deficiency on cochlear outer hair cells. We found that NPC1 deficiency enhances autophagy-dependent ferritinophagy to release Fe (II). Our work provides important insights into the effect of NPC1 deficiency in auditory cells, indicating that it induces ferroptosis and results in hearing loss.
    Keywords:  NCOA4; NPC1 deficiency; Niemann–Pick type C disease; ferroptosis; hearing loss
  43. Chin Med J (Engl). 2022 Aug 11.
      ABSTRACT: Non-alcoholic fatty liver disease (NAFLD) is a disorder of lipid metabolism. The lipotoxic intermediates of lipid metabolism cause mitochondrial dysfunction and endoplasmic reticulum stress. Organelle-specific autophagy is responsible for the removal of dysfunctional organelles to maintain intracellular homeostasis. Lipophagy contributes to lipid turnover by degrading lipid droplets. The level of autophagy changes during the course of NAFLD, and the activation of hepatocyte autophagy might represent a method of treating NAFLD.
  44. Neurochem Res. 2022 Aug 12.
      Astrocytes act as "housekeeping cells" for maintaining cerebral homeostasis and play an important role in many disorders. Recent studies further highlight the contribution of autophagy to astrocytic functions, including astrogenesis, the astrocytic removal of neurotoxins or stressors, and astrocytic polarization. More importantly, genetic and pharmacological approaches have provided evidence that outlines the contributions of astrocytic autophagy to several brain disorders, including neurodegeneration, cerebral ischemia, and depression. In this study, we summarize the emerging role of autophagy in regulating astrocytic functions and discuss the contributions of astrocytic autophagy to different CNS disorders.
    Keywords:  Astrocyte; Autophagy; Cerebral ischemia; Depression; Neurodegeneration
  45. Cell Rep. 2022 Aug 09. pii: S2211-1247(22)00988-3. [Epub ahead of print]40(6): 111175
      Protein degradation is fundamentally important to ensure cell homeostasis. In the endoplasmic reticulum (ER), the ER-associated degradation (ERAD) pathway targets incorrectly folded and unassembled proteins for turnover by the cytoplasmic proteasome. Previously, we showed that the rhomboid protease RHBDL4, together with p97, mediates membrane protein degradation. However, whether RHBDL4 acts in concert with additional ERAD components is unclear, and its full substrate spectrum remains to be defined. Here, we show that, in addition to membrane proteins, RHBDL4 cleaves aggregation-prone luminal ERAD substrates. Since mutations of the RHBDL4 rhomboid domain led to stabilization of substrates at the cytoplasmic side, we hypothesize that, analogous to the homolog ERAD factor derlin, RHBDL4 is directly involved in substrate retrotranslocation. RHBDL4's interaction with the erlin ERAD complex and reciprocal interaction of rhomboid substrates with erlins suggest that RHBDL4 and erlins form a complex that clips substrates and thereby rescues aggregation-prone peptides in the ER from aggregation.
    Keywords:  CP: Cell biology; CP: Molecular biology; ER-associated protein degradation; intramembrane proteolysis; prohibitin family proteins Erlin1 and Erlin2; protein aggregates; rhomboid family protein
  46. Int J Mol Sci. 2022 Aug 08. pii: 8811. [Epub ahead of print]23(15):
      Zinc is a trace metal vital for various functions in nerve cells, although the effect of zinc deficiency on neuronal autophagy remains unclear. This study aimed to elucidate whether zinc deficiency induced by treatment with N, N, N', N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a zinc chelator, affects and alters autophagy activity. In cell viability assays, TPEN showed cytotoxicity in HT-22 cells. TPEN treatment also increased LC3-II levels and the ratio of LC3-II to LC3-I. Western blot analysis showed that phospho-AMP-activated protein kinase levels and the ratio of phospho-AMP-activated protein kinase to total AMP-activated protein kinase increased. Protein levels of the mammalian target of rapamycin and sirtuin 1 decreased following TPEN treatment. When TPEN-treated HT-22 cells were cotreated with autophagy inhibitors, 3-methyladenine (1 mM), or bafilomycin A1 (3 nM), the TPEN-induced decrease in cell viability was exacerbated. Cotreatment with chloroquine (10 μM) partially restored cell viability. The study showed that zinc deficiency induces autophagy and may be cytoprotective in neurons. We expect our results to add a new perspective to our understanding of the neuronal pathology related to zinc deficiency.
    Keywords:  AMPK; SIRT1; autophagy; mTOR; zinc; zinc deficiency
  47. Life Sci. 2022 Aug 07. pii: S0024-3205(22)00570-7. [Epub ahead of print] 120870
      Sirtuins perform an important effect on the neural cell fate following stroke. Several mechanisms that have been correlated with stroke are oxidative stress, apoptosis, necrosis and autophagy. Autophagy is usually regarded as unitary of the neural cell survival mechanisms. Recently, the importance of the sirtuins effect on autophagy by antioxidant agents for stroke treatment mentioned in various studies. One of these agents is melatonin. Melatonin can modulate autophagy by changing on sirtuin pathways. Melatonin and its metabolites adjust various sirtuins pathways related to apoptosis, proliferation, metastases, autophagy and inflammation in case of stroke. In this review, we will discuss about the modulation of autophagy by melatonin via sirtuins in stroke.
    Keywords:  Autophagy; Cerebrovascular disease; Melatonin; Sirtuins; Stroke
  48. Cells. 2022 Aug 04. pii: 2401. [Epub ahead of print]11(15):
      The NRF2-KEAP1 system is a fundamental component of the cellular response that controls a great variety of transcriptional targets that are mainly involved in the regulation of redox homeostasis and multiple cytoprotective mechanisms that confer adaptation to the stress conditions. The pleiotropic response orchestrated by NRF2 is particularly relevant in the context of oncogenic activation, wherein this transcription factor acts as a key driver of tumor progression and cancer cells' resistance to treatment. For this reason, NRF2 has emerged as a promising therapeutic target in cancer cells, stimulating extensive research aimed at the identification of natural, as well as chemical, NRF2 inhibitors. Excitingly, the influence of NRF2 on cancer cells' biology extends far beyond its mere antioxidant function and rather encompasses a functional crosstalk with the mitochondrial network that can influence crucial aspects of mitochondrial homeostasis, including biogenesis, oxidative phosphorylation, metabolic reprogramming, and mitophagy. In the present review, we summarize the current knowledge of the reciprocal interrelation between NRF2 and mitochondria, with a focus on malignant tumors and cancer stem cells.
    Keywords:  NRF2–KEAP1 pathway; ROS; cancer; cancer stem cells; mitochondria; oxidative stress
  49. BMC Vet Res. 2022 Aug 11. 18(1): 307
      BACKGROUND: Aside respiratory diseases, beef cattle may also suffer from serious kidney diseases after transportation. Hyperglycemia and gram-negative bacterial infection may be the main reasons why bovine is prone to severe kidney disease during transportation stress, however, the precise mechanism is still unclear. The purpose of the current study is to explore whether the combined treatment of high glucose (HG) and lipopolysaccharide (LPS) could induce madin-darby bovine kidney (MDBK) cells injury and autophagy, as well as investigate the potential molecular mechanisms involved.RESULTS: As we discovered, the combined effect of HG and LPS decreased MDBK cells viability. And, HG and LPS combination also induced autophagy in MDBK cells, which was characterized by increasing the expression of LC3-II/I and Beclin1 and decreasing p62 expression. LC3 fluorescence signal formation was also significantly increased by HG and LPS combination treatment. Furthermore, we measured whether the mammalian target of rapamycin (mTOR) and the Notch3 signaling pathways were involved in HG and LPS-induced autophagy. The results showed that the combination of HG and LPS significantly increased the protein expression of Notch3 and decreased protein expression of p-mTOR, indicating that Notch3 and mTOR signaling pathways were activated. However, co-treatment with the Notch3 inhibitor (DAPT) could reverse the induction of autophagy, and increased the protein expression of p-mTOR.
    CONCLUSIONS: This study demonstrated that the combination effect of HG and LPS could induce autophagy in MDBK cells, and the Notch3/mTOR signaling pathway was involved in HG and LPS-induced autophagy.
    Keywords:  Autophagy; High glucose; LPS; Notch3; mTOR
  50. Front Cell Dev Biol. 2022 ;10 918943
      Mitophagy plays a vital role in the selective elimination of dysfunctional and unwanted mitochondria. As a receptor of mitophagy, FUN14 domain containing 1 (FUNDC1) is attracting considerably critical attention. FUNDC1 is involved in the mitochondria fission, the clearance of unfolded protein, iron metabolism in mitochondria, and the crosstalk between mitochondria and endoplasmic reticulum besides mitophagy. Studies have demonstrated that FUNDC1 is associated with the progression of ischemic disease, cancer, and metabolic disease. In this review, we systematically examine the recent advancements in FUNDC1 and the implications of this protein in health and disease.
    Keywords:  FUNDC1; I/R injury; endoplasmic reticulum; mitochondrial fission; mitophagy
  51. Mol Med. 2022 Aug 12. 28(1): 94
      BACKGROUND: The proliferation ability and autophagy level of pulmonary artery endothelial cells (PAECs) play an important role in promoting the development of pulmonary artery hypertension (PAH), and there is still no effective treatment for PAH. Farnesyl diphosphate synthase (FDPS) is a key enzyme in the mevalonate pathway. The intermediate metabolites of this pathway are closely related to the activity of autophagy-associated small G proteins, including Ras-related C3 botulinum toxin substrate 1 (Rac1). Studies have shown that the mevalonate pathway affects the activation levels of different small G proteins, autophagy signaling pathways, vascular endothelial function, and so on. However, the exact relationship between them is still unclear in PAH.METHOD: In vitro, western blotting and mRFP-GFP-LC3 puncta formation assays were used to observe the expression of FDPS and the level of autophagy in PAECs treated with monocrotaline pyrrole (MCTP). In addition, cell proliferation and migration assays were used to assess the effect of FDPS on endothelial function, and Rac1 activity assays were used to evaluate the effect of Rac1 activation on PAEC autophagy via the PI3K/AKT/mTOR signaling pathway. In vivo, the right heart catheterization method, hematoxylin and eosin (H&E) staining and western blotting were used to determine the effect of FDPS on PAEC autophagy and monocrotaline (MCT)-induced PAH.
    RESULTS: We show that the expression of FDPS is increased in the PAH module in vitro and in vivo, concomitant with the induction of autophagy and the activation of Rac1. Our data demonstrate that inhibition of FDPS ameliorates endothelial function and decreases MCT-induced autophagy levels. Mechanistically, we found that FDPS promotes autophagy, Rac1 activity and endothelial disfunction through the PI3K/AKT/mTOR signaling pathway.
    CONCLUSION: Our study suggests that FDPS contributes to active small G protein-induced autophagy during MCT-induced PAH, which may serve as a potential therapeutic target against PAH.
    Keywords:  Autophagy; Endothelial; Farnesyl diphosphate synthase; Proliferation; Pulmonary artery hypertension; Ras-related C3 botulinum toxin substrate 1
  52. Hum Mol Genet. 2022 Aug 12. pii: ddac197. [Epub ahead of print]
      Type Ib glycogen storage disease (GSD-Ib) is caused by a deficiency in the G6P transporter (G6PT) that translocates G6P from the cytoplasm into the endoplasmic reticulum lumen, where the intraluminal G6P is hydrolyzed to glucose by glucose-6-phosphatase-α (G6Pase-α). Clinically, GSD-Ib patients manifest a metabolic phenotype of impaired blood glucose homeostasis and a long-term risk of hepatocellular adenoma/carcinoma (HCA/HCC). Studies have shown that autophagy deficiency contributes to hepatocarcinogenesis. In this study, we show that G6PT deficiency leads to impaired hepatic autophagy evident from attenuated expression of many components of the autophagy network, decreased autophagosome formation, and reduced autophagy flux. The G6PT-deficient liver displayed impaired SIRT1 and AMP-activated protein kinase (AMPK) signaling, along with reduced expression of SIRT1, forkhead boxO3a (FoxO3a), liver kinase B-1 (LKB1), and the active p-AMPK. Importantly, we show that overexpression of either SIRT1 or LKB1 in G6PT-deficient liver restored autophagy and SIRT1/FoxO3a and LKB1/AMPK signaling. The hepatosteatosis in G6PT-deficient liver decreased SIRT1 expression. LKB1 overexpression reduced hepatic triglycerides levels, providing a potential link between LKB1/AMPK signaling upregulation and the increase in SIRT1 expression. In conclusion, downregulation of SIRT1/FoxO3a and LKB1/AMPK signaling underlies impaired hepatic autophagy which may contribute to HCA/HCC development in GSD-Ib. Understanding this mechanism may guide future therapies.
  53. J Integr Plant Biol. 2022 Aug 13.
      Autophagy is an evolutionarily conserved degradation pathway in eukaryotes; it plays a critical role in nutritional stress tolerance. The circadian clock is an endogenous timekeeping system that generates biological rhythms to adapt to daily changes in the environment. Accumulating evidence indicates that the circadian clock and autophagy are intimately interwoven in animals. However, the role of the circadian clock in regulating autophagy has been poorly elucidated in plants. Here, we show that autophagy exhibits a robust circadian rhythm in both light/dark cycle (LD) and in constant light (LL) in Arabidopsis. However, autophagy rhythm showed a different pattern with a phase-advance shift and a lower amplitude in LL compared to LD. Moreover, mutation of the transcription factor LUX ARRHYTHMO (LUX) removed autophagy rhythm in LL and led to an enhanced amplitude in LD. LUX represses expression of the core autophagy genes ATG2, ATG8a, and ATG11 by directly binding to their promoters. Phenotypic analysis revealed that LUX is responsible for improved resistance of plants to carbon starvation, which is dependent on moderate autophagy activity. Comprehensive transcriptomic analysis revealed that the autophagy rhythm is ubiquitous in plants. Taken together, our findings demonstrate that the LUX-mediated circadian clock regulates plant autophagy rhythms. This article is protected by copyright. All rights reserved.
    Keywords:  LUX; autophagy; carbon starvation; circadian clock; rhythm
  54. Front Aging. 2022 ;3 927630
      In this review, we discuss in detail the most relevant proteolytic systems that together with chaperones contribute to creating the proteostasis network that is kept in dynamic balance to maintain overall functionality of cellular proteomes. Data accumulated over decades demonstrate that the effectiveness of elements of the proteostasis network declines with age. In this scenario, failure to degrade misfolded or faulty proteins increases the risk of protein aggregation, chronic inflammation, and the development of age-related diseases. This is especially important in the context of aging-related modification of functions of the immune system.
    Keywords:  aging; autophagy; chaperones; lysosome; proteases; proteostasis; ubiquitin-proteasome system