bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2021‒09‒05
twenty-nine papers selected by
Viktor Korolchuk
Newcastle University

  1. J Cell Biol. 2021 Nov 01. pii: e202104073. [Epub ahead of print]220(11):
      Defects in autophagy cause problems in metabolism, development, and disease. The autophagic clearance of mitochondria, mitophagy, is impaired by the loss of Vps13D. Here, we discover that Vps13D regulates mitophagy in a pathway that depends on the core autophagy machinery by regulating Atg8a and ubiquitin localization. This process is Pink1 dependent, with loss of pink1 having similar autophagy and mitochondrial defects as loss of vps13d. The role of Pink1 has largely been studied in tandem with Park/Parkin, an E3 ubiquitin ligase that is widely considered to be crucial in Pink1-dependent mitophagy. Surprisingly, we find that loss of park does not exhibit the same autophagy and mitochondrial deficiencies as vps13d and pink1 mutant cells and contributes to mitochondrial clearance through a pathway that is parallel to vps13d. These findings provide a Park-independent pathway for Pink1-regulated mitophagy and help to explain how Vps13D regulates autophagy and mitochondrial morphology and contributes to neurodegenerative diseases.
  2. Autophagy. 2021 Sep 01. 1-3
      A progressive decline in the macroautophagic/autophagic flux is a hallmark of pancreatic β-cell failure in type 2 diabetes (T2D) but the responsible intrinsic factors and underlying molecular mechanisms are incompletely understood. A stress-sensitive multicomponent cellular loop of the Hippo pathway kinase LATS2 (large tumor suppressor 2), MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) and autophagy regulates β-cell survival and metabolic adaptation. Chronic metabolic stress leads to LATS2 hyperactivation which then induces MTORC1, subsequently impairing the cellular autophagic flux and consequently triggering β-cell death. Reciprocally, under physiological conditions, autophagy controls β-cell survival by lysosomal degradation of LATS2. These signaling cross-talks and the interaction between autophagy and LATS2 are important for the regulation of β-cell turnover and functional compensation under metabolic stress.
    Keywords:  Autophagy; LATS2; MTORC1; beta cells; diabetes; type 2 diabetes
  3. Nat Commun. 2021 Sep 01. 12(1): 5212
      The autophagic degradation of misfolded and ubiquitinated proteins is important for cellular homeostasis. In this process, which is governed by cargo receptors, ubiquitinated proteins are condensed into larger structures and subsequently become targets for the autophagy machinery. Here we employ in vitro reconstitution and cell biology to define the roles of the human cargo receptors p62/SQSTM1, NBR1 and TAX1BP1 in the selective autophagy of ubiquitinated substrates. We show that p62 is the major driver of ubiquitin condensate formation. NBR1 promotes condensate formation by equipping the p62-NBR1 heterooligomeric complex with a high-affinity UBA domain. Additionally, NBR1 recruits TAX1BP1 to the ubiquitin condensates formed by p62. While all three receptors interact with FIP200, TAX1BP1 is the main driver of FIP200 recruitment and thus the autophagic degradation of p62-ubiquitin condensates. In summary, our study defines the roles of all three receptors in the selective autophagy of ubiquitin condensates.
  4. EMBO J. 2021 Aug 30. e108863
      Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.
    Keywords:  aging; cancer; inflammation; metabolic syndromes; neurodegeneration
  5. Cell Res. 2021 Sep 03.
      Primary cilia extending from mother centrioles are essential for vertebrate development and homeostasis maintenance. Centriolar coiled-coil protein 110 (CP110) has been reported to suppress ciliogenesis initiation by capping the distal ends of mother centrioles. However, the mechanism underlying the specific degradation of mother centriole-capping CP110 to promote cilia initiation remains unknown. Here, we find that autophagy is crucial for CP110 degradation at mother centrioles after serum starvation in MEF cells. We further identify NudC-like protein 2 (NudCL2) as a novel selective autophagy receptor at mother centrioles, which contains an LC3-interacting region (LIR) motif mediating the association of CP110 and the autophagosome marker LC3. Knockout of NudCL2 induces defects in the removal of CP110 from mother centrioles and ciliogenesis, which are rescued by wild-type NudCL2 but not its LIR motif mutant. Knockdown of CP110 significantly attenuates ciliogenesis defects in NudCL2-deficient cells. In addition, NudCL2 morphants exhibit ciliation-related phenotypes in zebrafish, which are reversed by wild-type NudCL2, but not its LIR motif mutant. Importantly, CP110 depletion significantly reverses these ciliary phenotypes in NudCL2 morphants. Taken together, our data suggest that NudCL2 functions as an autophagy receptor mediating the selective degradation of mother centriole-capping CP110 to promote ciliogenesis, which is indispensable for embryo development in vertebrates.
  6. Front Cell Dev Biol. 2021 ;9 709398
      Autophagy, a highly conserved intracellular process, has been identified as a novel mechanism regulating T lymphocyte homeostasis. Herein, we demonstrate that both starvation- and T cell receptor-mediated autophagy induction requires class I phosphatidylinositol-3 kinases to produce PI(3)P. In contrast, common gamma chain cytokines are suppressors of autophagy despite their ability to activate the PI3K pathway. T cells lacking the PI3KI regulatory subunits, p85 and p55, were almost completely unable to activate TCR-mediated autophagy and had concurrent defects in PI(3)P production. Additionally, T lymphocytes upregulate polyinositol phosphatases in response to autophagic stimuli, and the activity of the inositol phosphatases Inpp4 and SHIP are required for TCR-mediated autophagy induction. Addition of exogenous PI(3,4)P2 can supplement cellular PI(3)P and accelerate the outcome of activation-induced autophagy. TCR-mediated autophagy also requires internalization of the TCR complex, suggesting that this kinase/phosphatase activity is localized in internalized vesicles. Finally, HIV-induced bystander CD4+ T cell autophagy is dependent upon PI3KI. Overall, our data elucidate an important pathway linking TCR activation to autophagy, via induction of PI3KI activity and inositol phosphatase upregulation to produce PI(3)P.
    Keywords:  HIV; PI3K I; T cells; autophagy; cytokines; lipid kinase; lipid phosphatase
  7. Autophagy. 2021 Sep 01. 1-2
      Growing evidence demonstrates that macroautophagy/autophagy in the host stroma influences the tumor microenvironment. We have uncovered that autophagy in host stromal fibroblasts is compulsory to initiate and maintain the desmoplastic fibrotic response that fosters mammary tumor progression. Genetic loss of fibroblast autophagy impedes COL1A/type 1 collagen secretion, which is required for the development of a stiff tissue matrix permissive for mammary tumor growth. As a result, stromal fibroblast autophagy deficiency impairs mammary tumor progression in vivo, even when the cancer cells themselves remain autophagy competent. Our results provide unique conceptual insight into how the autophagy pathway can be modulated to abolish the desmoplastic response required for cancer progression.
    Keywords:  Autophagy; cancer associated fibroblasts; collagen; desmoplasia; tumor microenvironment
  8. Cell Death Dis. 2021 Aug 30. 12(9): 822
      The Hippo and mammalian target of rapamycin complex 1 (mTORC1) pathways are the two predominant pathways that regulate tumour growth and metastasis. Therefore, we explored the potential crosstalk between these two functionally relevant pathways to coordinate their tumour growth-control functions. We found that a Hippo pathway-related long noncoding RNA, HPR, directly interacts with Raptor, an essential component of mTORC1, to upregulate mTORC1 activation by impairing the phosphorylation of Raptor by AMPK. Knockdown or knockout of HPR in breast cancer and cholangiocarcinoma cells led to a reduction in tumour growth. Compared with HPR WT cells, HPR-overexpressing cells exhibited nuclear accumulation of YAP1, and significantly blocked the downregulation of mTORC1 signalling induced by energy stress. Thus, our study reveals a direct link between the Hippo and mTORC1 pathways in the control of tumour growth.
  9. Galen Med J. 2020 ;9 e1681
      Abnormal deposition of misfolded proteins is a neuropathological characteristic shared by many neurodegenerative disorders including Alzheimer's disease (AD). Generation of excessive amounts of aggregated proteins and impairment of degradation systems for misfolded proteins such as autophagy can lead to accumulation of proteins in diseased neurons. Molecules that contribute to both these effects are emerging as critical players in disease pathogenesis. Furthermore, impairment of autophagy under disease conditions can be both a cause and a consequence of abnormal protein accumulation. Specifically, disease-causing proteins can impair autophagy, which further enhances the accumulation of abnormal proteins. In this short review, we focus on the relationship between the microtubule-associated protein tau and autophagy to highlight a feed-forward mechanism in disease pathogenesis.
    Keywords:  Autophagy; Microtubule Binding Protein; Neurodegenerative Diseases; Phosphorylation; Tau; Tauopathy; Vesicle Trafficking
  10. Int J Mol Med. 2021 Oct;pii: 195. [Epub ahead of print]48(4):
      The autophagy‑lysosome system allows cells to adapt to environmental changes by regulating the degradation and recycling of cellular components, and to maintain homeostasis by removing aggregated proteins and defective organelles. Cyclin G‑associated kinase (GAK) is involved in the regulation of clathrin‑dependent endocytosis and cell cycle progression. In addition, a single nucleotide polymorphism at the GAK locus has been reported as a risk factor for Parkinson's disease. However, the roles of GAK in the autophagy‑lysosome system are not completely understood, thus the present study aimed to clarify this. In the present study, under genetic disruption or chemical inhibition of GAK, analyzing autophagic flux and observing morphological changes of autophagosomes and autolysosomes revealed that GAK controlled lysosomal dynamics via actomyosin regulation, resulting in a steady progression of autophagy. GAK knockout (KO) in A549 cells impaired autophagosome‑lysosome fusion and autophagic lysosome reformation, which resulted in the accumulation of enlarged autophagosomes and autolysosomes during prolonged starvation. The stagnation of autophagic flux accompanied by these phenomena was also observed with the addition of a GAK inhibitor. Furthermore, the addition of Rho‑associated protein kinase (ROCK) inhibitor or ROCK1 knockdown mitigated GAK KO‑mediated effects. The results suggested a vital role of GAK in controlling lysosomal dynamics via maintaining lysosomal homeostasis during autophagy.
    Keywords:  Rho‑associated protein kinase; actomyosin; autophagic lysosome reformation; autophagosome‑lysosome fusion; autophagy; cyclin G‑associated kinase
  11. Autophagy. 2021 Aug 30. 1-2
      Nonalcoholic fatty liver disease (NAFLD) affects a quarter of the global population. However, its pathogenesis is not completely understood. In our recent study, we have demonstrated that in a high-fat diet-induced liver steatosis model, the activation of SREBF1/SREBP-1c (sterol regulatory element binding transcription factor 1) directly upregulates Mir216a transcription, which inhibits CTH/CSE (cystathionase (cystathionine gamma-lyase)) expression and its function in hydrogen sulfide (H2S) production. Reduced H2S production suppresses the sulfhydration of ULK1 (unc-51 like autophagy activating kinase 1), consequently inhibiting autophagic flux and lipid droplet turnover. A single substitution mutation (C951S) in ULK1 or the silencing of CTH impairs ULK1 sulfhydration-mediated lipophagy, thereby promoting hepatic steatosis in mice. Interestingly, the sulfhydration of ULK1 increases its intrinsic kinase activity to modulate autophagy at both initiation and progression stages of autophagic catabolic flux. This study reveals that SREBF1/SREBP-1c contributes to hepatic lipid accumulation through its combined effect of increased lipid synthesis coupled with decreased lipid degradation mediated by autophagic dysregulation.
    Keywords:  Autophagy; SREBP-1C; ULK1; hepatic steatosis; hydrogen sulfide; sulfhydration
  12. Neural Regen Res. 2022 Apr;17(4): 741-747
      Mitochondria play a multidimensional role in the function and the vitality of the neurological system. From the generation of neural stem cells to the maintenance of neurons and their ultimate demise, mitochondria play a critical role in regulating our neural pathways' homeostasis, a task that is critical to our cognitive health and neurological well-being. Mitochondria provide energy via oxidative phosphorylation for the neurotransmission and generation of an action potential along the neuron's axon. This paper will first review and examine the molecular subtleties of the mitochondria's role in neurogenesis and neuron vitality, as well as outlining the impact of defective mitochondria in neural aging. The authors will then summarize neurodegenerative diseases related to either neurogenesis or homeostatic dysfunction. Because of the significant detriment neurodegenerative diseases have on the quality of life, it is essential to understand their etiology and ongoing molecular mechanics. The mitochondrial role in neurogenesis and neuron vitality is essential. Dissecting and understanding this organelle's role in the genesis and homeostasis of neurons should assist in finding pharmaceutical targets for neurodegenerative diseases.
    Keywords:  Alzheimer’s disease; PINK1; Parkin; Parkinson’s disease; autophagy; mitochondria; mitophagy; neural stem cells; neurodegenerative diseases; neurogenesis
  13. Mitochondrion. 2021 Aug 25. pii: S1567-7249(21)00115-X. [Epub ahead of print]
      Altered insulin signaling and insulin resistance are considered the link between Alzheimer's disease (AD) and metabolic syndrome. Here, by using an in vitro and an in vivo model, we investigated the relationship between these disorders focusing on neuronal mitochondrial dysfunction and mitophagy. In vitro Aβ insult induced the opening of mitochondrial permeability transition pore (mPTP), mitochondrial membrane potential (ΔΨm) loss, and apoptosis while insulin addition ameliorated these dysfunctions. The same alterations were detected in a 16 weeks of age mouse model of diet-induced obesity and insulin resistance. In addition, we detected an increase of fission related proteins and activation of mitophagy, proved by the rise of PINK1 and Parkin proteins. Nevertheless, in vitro, the increase of p62 and LC3 indicated an alteration in autophagy, while, in vivo decreased expression of p62 and increase of LC3 suggested removing of damaged mitochondria. Finally, in aged mice (28 and 48 weeks), the data indicated impairment of mitophagy and suggested the accumulation of damaged mitochondria. Taken together these outcomes indicate that alteration of the insulin pathway affects mitochondrial integrity, and effective mitophagy is age-dependent.
    Keywords:  aging; insulin pathway; metabolic diseases; mitochondrion; mitophagy; neurodegeneration
  14. Nat Cancer. 2020 Sep;1(9): 923-934
      Macroautophagy (hereafter autophagy) degrades and recycles intracellular components to sustain metabolism and survival during starvation. Host autophagy promotes tumor growth by providing essential tumor nutrients. Autophagy also regulates immune cell homeostasis and function and suppresses inflammation. Although host autophagy does not promote a T-cell anti-tumor immune response in tumors with low tumor mutational burden (TMB), whether this was the case in tumors with high TMB was not known. Here we show that autophagy, especially in the liver, promotes tumor immune tolerance by enabling regulatory T-cell function and limiting stimulator of interferon genes, T-cell response and interferon-γ, which enables growth of high-TMB tumors. We have designated this as hepatic autophagy immune tolerance. Autophagy thereby promotes tumor growth through both metabolic and immune mechanisms depending on mutational load and autophagy inhibition is an effective means to promote an antitumor T-cell response in high-TMB tumors.
  15. Proc Natl Acad Sci U S A. 2021 Sep 07. pii: e2101410118. [Epub ahead of print]118(36):
      In human neurodegenerative diseases, neurons can transfer toxic protein aggregates to surrounding cells, promoting pathology via poorly understood mechanisms. In Caenorhabditis elegans, proteostressed neurons can expel neurotoxic proteins in large, membrane-bound vesicles called exophers. We investigated how specific stresses impact neuronal trash expulsion to show that neuronal exopher production can be markedly elevated by oxidative and osmotic stress. Unexpectedly, we also found that fasting dramatically increases exophergenesis. Mechanistic dissection focused on identifying nonautonomous factors that sense and activate the fasting-induced exopher response revealed that DAF16/FOXO-dependent and -independent processes are engaged. Fasting-induced exopher elevation requires the intestinal peptide transporter PEPT-1, lipid synthesis transcription factors Mediator complex MDT-15 and SBP-1/SREPB1, and fatty acid synthase FASN-1, implicating remotely initiated lipid signaling in neuronal trash elimination. A conserved fibroblast growth factor (FGF)/RAS/MAPK signaling pathway that acts downstream of, or in parallel to, lipid signaling also promotes fasting-induced neuronal exopher elevation. A germline-based epidermal growth factor (EGF) signal that acts through neurons is also required for exopher production. Our data define a nonautonomous network that links food availability changes to remote, and extreme, neuronal homeostasis responses relevant to aggregate transfer biology.
    Keywords:  MAP kinase; exopher; fasting; neurology; stress
  16. Neurochem Res. 2021 Sep 02.
      Mutations in P/Q type voltage gated calcium channel (VGCC) lead severe human neurological diseases such as episodic ataxia 2, familial hemiplegic migraine 1, absence epilepsy, progressive ataxia and spinocerebellar ataxia 6. The pathogenesis of these diseases remains unclear. Mice with spontaneous mutation in the Cacna1a gene encoding the pore-forming subunit of P/Q type VGCC also exhibit ataxia, epilepsy and neurodegeneration. Based on the previous work showing that the P/Q type VGCC in neurons regulates lysosomal fusion through its calcium channel activity on lysosomes, we utilized CACNA1A mutant mice to further investigate the mechanism by which P/Q-type VGCCs regulate lysosomal function and neuronal homeostasis. We found CACNA1A mutant neurons have reduced lysosomal calcium storage without changing the resting calcium concentration in cytoplasm and the acidification of lysosomes. Immunohistochemistry and transmission electron microscopy reveal axonal degeneration due to lysosome dysfunction in the CACNA1A mutant cerebella. The calcium modulating drug thapsigargin, by depleting the ER calcium store, which locally increases the calcium concentration can alleviate the defective lysosomal fusion in mutant neurons. We propose a model that in cerebellar neurons, P/Q-type VGCC maintains the integrity of the nervous system by regulating lysosomal calcium homeostasis to affect lysosomal fusion, which in turn regulates multiple important cellular processes such as autophagy and endocytosis. This study helps us to better understand the pathogenesis of P/Q-type VGCC related neurodegenerative diseases and provides a feasible direction for future pharmacological treatment.
    Keywords:  Calcium homeostasis; LAMP1; Lysosome; Neurodegeneration; P/Q-type voltage gated calcium channel
  17. Cell Immunol. 2021 Aug 24. pii: S0008-8749(21)00145-3. [Epub ahead of print]369 104426
      Myeloid-derived suppressor cells (MDSC) are induced during active TB disease to restore immune homeostasis but instead exacerbate disease outcome due to chronic inflammation. Autophagy, in conventional phagocytes, ensures successful clearance of M.tb. However, autophagy has been demonstrated to induce prolonged MDSC survival. Here we investigate the relationship between autophagy mediators and MDSC in the context of active TB disease and during anti-TB therapy. We demonstrate a significant increase in MDSC frequencies in untreated active TB cases with these MDSC expressing TLR4 and significantly more mTOR and IL-6 than healthy controls, with mTOR levels decreasing during anti-TB therapy. Finally, we show that HMGB1 serum concentrations decrease in parallel with mTOR. These findings suggest a complex interplay between MDSC and autophagic mediators, potentially dependent on cellular localisation and M.tb infection state.
    Keywords:  Autophagy; High mobility group box protein 1; Mycobacterium tuberculosis; Myeloid-derived suppressor cells; Tuberculosis
  18. Cell Mol Gastroenterol Hepatol. 2021 Aug 27. pii: S2352-345X(21)00173-9. [Epub ahead of print]
  19. Life Sci. 2021 Aug 31. pii: S0024-3205(21)00907-3. [Epub ahead of print] 119920
      AIMS: The sustained activation of intestinal mechanistic target of rapamycin complex 1 (mTORC1) brought about by repeated mucosal insult or injury has been linked to escalation of gut inflammatory response, which may progress to damage the epithelium if not controlled. This study investigated the role of mTORC1 in the response of macrophage and enterocyte to inflammatory stimuli.MATERIALS AND METHODS: We genetically manipulated human THP-1 monocytes and epithelial intestinal Caco-2 cells to generate stable cell lines with baseline, low or high mTORC1 kinase activity. The effects of THP-1 macrophage secretions onto Caco-2 cells were investigated by means of conditioned media transfer experiments.
    KEY FINDINGS: The priming of mTORC1 for activation promoted lipopolysaccharide (LPS)-mediated THP-1 macrophage immune response as evidenced by the stimulation of inflammatory mediators (TNFα, IL-6, IL-8, IL-1β and IL-10). The treatment of THP-1 macrophages with LPS more than the manipulated level of mTORC1 activity of macrophages determined whether cytokine gene expression was induced in Caco-2 cells. LPS carry over was not responsible for the stimulation of Caco-2 cells' cytokine response. Knocking down Raptor in Caco-2 cells or treating Caco-2 cells with rapamycin enhanced Caco-2 TNFα gene expression revealing the anti-inflammatory role of a functional mTORC1 in intestinal epithelial cells exposed to macrophage-derived pro-inflammatory stimuli.
    SIGNIFICANCE: Taken together, mTORC1 differentially impacts the immune responses of THP-1-derived macrophages and Caco-2 epithelial cells when placed in a pro-inflammatory microenvironment.
    Keywords:  Cell differentiation; Endotoxin; Gut innate immunity; Interleukin; Rapamycin; Tuberous sclerosis complex
  20. Cell Rep. 2021 Aug 31. pii: S2211-1247(21)00975-X. [Epub ahead of print]36(9): 109541
      The regulation of lipid homeostasis is not well understood. Using forward genetic screening, we demonstrate that the loss of dTBC1D22, an essential gene that encodes a Tre2-Bub2-Cdc16 (TBC) domain-containing protein, results in lipid droplet accumulation in multiple tissues. We observe that dTBC1D22 interacts with Rab40 and exhibits GTPase activating protein (GAP) activity. Overexpression of either the GTP- or GDP-binding-mimic form of Rab40 results in lipid droplet accumulation. We observe that Rab40 mutant flies are defective in lipid mobilization. The lipid depletion induced by overexpression of Brummer, a triglyceride lipase, is dependent on Rab40. Rab40 mutant flies exhibit decreased lipophagy and small size of autolysosomal structures, which may be due to the defective Golgi functions. Finally, we demonstrate that Rab40 physically interacts with Lamp1, and Rab40 is required for the distribution of Lamp1 during starvation. We propose that dTBC1D22 functions as a GAP for Rab40 to regulate lipophagy.
    Keywords:  Drosophila; GTPase-activating proteins (GAPs); Golgi; Rab GTPase; Rab40; TBC domain-containing protein; autophagy; lipophagy; lysosome
  21. J Cell Sci. 2021 Sep 01. pii: jcs258589. [Epub ahead of print]134(17):
      Physical constraints, such as compression, shear stress, stretching and tension, play major roles during development, tissue homeostasis, immune responses and pathologies. Cells and organelles also face mechanical forces during migration and extravasation, and investigations into how mechanical forces are translated into a wide panel of biological responses, including changes in cell morphology, membrane transport, metabolism, energy production and gene expression, is a flourishing field. Recent studies demonstrate the role of macroautophagy in the integration of physical constraints. The aim of this Review is to summarize and discuss our knowledge of the role of macroautophagy in controlling a large panel of cell responses, from morphological and metabolic changes, to inflammation and senescence, for the integration of mechanical forces. Moreover, wherever possible, we also discuss the cell surface molecules and structures that sense mechanical forces upstream of macroautophagy.
    Keywords:  Macroautophagy; Mechanical forces; Mechanosensing; Signaling
  22. Biochem Cell Biol. 2021 Aug 31. 1-8
      Tuberous sclerosis complex (TSC), an inherited neurocutaneous disease, is caused by mutations in either the TSC1 or TSC2 gene. This genetic disorder is characterized by the growth of benign tumors in the brain, kidneys, and other organs. As a member of the orphan nuclear receptor family, nuclear receptor related 1 (Nurr1) plays a vital role in some neuropathological diseases and several types of benign or malignant tumors. Here, we explored the potential regulatory role of TSC1/2 signaling in Nurr1 and the effect of Nurr1 in TSC-related tumors. We found that Nurr1 expression was drastically decreased by the disruption of the TSC1/2 complex in Tsc2-null cells, genetically modified mouse models of TSC, cortical tubers of TSC patients, and kidney tumor tissue obtained from a TSC patient. Deficient TSC1/2 complex downregulated Nurr1 expression in an mTOR-dependent manner. Moreover, hyperactivation of mTOR reduced Nurr1 expression via suppression of autophagy. In addition, Nurr1 overexpression inhibited cell proliferation and suppressed cell cycle progression. Therefore, TSC/mTOR/autophagy/Nurr1 signaling is partially responsible for the tumorigenesis of TSC. Taken together, Nurr1 may be a novel therapeutic target for TSC-associated tumors, and Nurr1 agonists or reagents that induce Nurr1 expression may be used for the treatment of TSC.
    Keywords:  Nurr1; autophagie; autophagy; cell proliferation; cible de la rapamycine mTOR; mechanistic target of rapamycin; prolifération cellulaire; sclérose tubéreuse de Bourneville; tuberous sclerosis complex
  23. Cell Rep Med. 2021 Aug 17. 2(8): 100370
      LPIN1 mutations are responsible for inherited recurrent rhabdomyolysis, a life-threatening condition with no efficient therapeutic intervention. Here, we conduct a bedside-to-bench-and-back investigation to study the pathophysiology of lipin1 deficiency. We find that lipin1-deficient myoblasts exhibit a reduction in phosphatidylinositol-3-phosphate close to autophagosomes and late endosomes that prevents the recruitment of the GTPase Armus, locks Rab7 in the active state, inhibits vesicle clearance by fusion with lysosomes, and alters their positioning and function. Oxidized mitochondrial DNA accumulates in late endosomes, where it activates Toll-like receptor 9 (TLR9) and triggers inflammatory signaling and caspase-dependent myolysis. Hydroxychloroquine blocks TLR9 activation by mitochondrial DNA in vitro and may attenuate flares of rhabdomyolysis in 6 patients treated. We suggest a critical role for defective clearance of oxidized mitochondrial DNA that activates TLR9-restricted inflammation in lipin1-related rhabdomyolysis. Interventions blocking TLR9 activation or inflammation can improve patient care in vivo.
    Keywords:  Toll-like receptor 9; autophagosome; hydroxychloroquine; inflammation; late endosome; lipin1; mitochondrial quality control; rhabdomyolysis
  24. Clin Cancer Res. 2021 Sep 01. pii: clincanres.2574.2021. [Epub ahead of print]
      Cellular therapies have demonstrated limited efficacy thus far in acute myeloid leukemia (AML). A recent study shows that mTORC1 activation down-regulated CXCR4 reducing marrow infiltration of EpCAM-targeting CAR-T cells in AML. Abrogating mTOR signaling by co-treatment with mTOR inhibitors during IL2-mediated ex vivo expansion upregulated CXCR4 and bolstered bone marrow migration and AML elimination by CAR-T cells.
  25. Mol Omics. 2021 Sep 03.
      Lysosomes are the main degradative organelles of almost all eukaryotic cells. They fulfil a crucial function in cellular homeostasis, and impairments in lysosomal function are connected to a continuously increasing number of pathological conditions. In recent years, lysosomes are furthermore emerging as control centers of cellular metabolism, and major regulators of cellular signaling were shown to be activated at the lysosomal surface. To date, >300 proteins were demonstrated to be located in/at the lysosome, and the lysosomal proteome and interactome is constantly growing. For the identification of these proteins, and their involvement in cellular mechanisms or disease progression, mass spectrometry (MS)-based proteomics has proven its worth in a large number of studies. In this review, we are recapitulating the application of MS-based approaches for the investigation of the lysosomal proteome, and their application to a diverse set of research questions. Numerous strategies were applied for the enrichment of lysosomes or lysosomal proteins and their identification by MS-based methods. This allowed for the characterization of the lysosomal proteome, the investigation of lysosome-related disorders, the utilization of lysosomal proteins as biomarkers for diseases, and the characterization of lysosome-related cellular mechanisms. While these >60 studies provide a comprehensive picture of the lysosomal proteome across several model organisms and pathological conditions, various proteomics approaches have not been applied to lysosomes yet, and a large number of questions are still left unanswered.
  26. Adv Exp Med Biol. 2021 Sep 05.
      The bone marrow serves as a reservoir for a multifunctional assortment of stem, progenitor, and mature cells, located in functional anatomical micro-areas termed niches. Within the niche, hematopoietic and mesenchymal progenies establish a symbiotic relationship characterized by interdependency and interconnectedness. The fine-tuned physical and molecular interactions that occur in the niches guarantee physiological bone turnover, blood cell maturation and egression, and moderation of inflammatory and oxidative intramural stressful conditions. The disruption of bone marrow niche integrity causes severe local and systemic pathological settings, and thus bone marrow inhabitants have been the object of extensive study. In this context, research has revealed the importance of the autophagic apparatus for niche homeostatic maintenance. Archetypal autophagic players such as the p62 and the Atg family proteins have been found to exert a variety of actions, some autophagy-related and others not; they moderate the essential features of mesenchymal and hematopoietic stem cells and switch their operational schedules. This chapter focuses on our current understanding of bone marrow functionality and the role of the executive autophagic apparatus in the niche framework. Autophagic mediators such as p62 and Atg7 are currently considered the most important orchestrators of stem and mature cell dynamics in the bone marrow.
    Keywords:  Atg7; Autophagy; Bone marrow; Hematopoietic stem cells; Mesenchymal stem cells; p62
  27. Exp Hematol. 2021 Aug 28. pii: S0301-472X(21)00289-7. [Epub ahead of print]
      Hematopoietic stem cells (HSCs) are immature blood cells that exhibit multi-lineage differentiation capacity. Homeostasis is critical for HSC potential and life-long hematopoiesis, and HSC homeostasis is tightly governed by both intrinsic molecular networks and microenvironmental signals. The evolutionarily conserved serine/threonine protein kinase B (PKB, also referred to as Akt) -mammalian target of rapamycin (mTOR) pathway is universal to nearly all multicellular organisms and plays an integral role in most cellular processes. Emerging evidence has revealed a central role of the Akt-mTOR network in HSC homeostasis, as it responses to multiple intracellular and extracellular signals and regulates various downstream targets, eventually affecting several cellular processes, including the cell cycle, mitochondrial metabolism, and protein synthesis. The dysregulated Akt-mTOR signaling greatly affects HSC self-renewal, maintenance, differentiation, survival, and autophagy, and aging, as well as transformation of HSCs to leukemia stem cells (LSCs). Here, we review recent works and provide an advanced understanding of how the Akt-mTOR network regulates HSC homeostasis, thus offering insights for future clinical applications.
    Keywords:  Akt-mTOR; Hematopoietic stem cells; Homeostasis; Leukemia stem cells
  28. Autophagy. 2021 Sep 01. 1-14
      ABBREVIATIONS: ATG14: autophagy related 14; CDH2: cadherin 2; ChIP-qPCR: chromatin immunoprecipitation quantitative polymerase chain reaction; CQ: chloroquine; ECAR: extracellular acidification rate; EMT: epithelial-mesenchymal transition; EPCAM: epithelial cell adhesion molecule; MAP1LC3A/LC3A: microtubule associated protein 1 light chain 3 alpha; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAP1LC3C/LC3C: microtubule associated protein 1 light chain 3 gamma; NDUFV2: NADH:ubiquinone oxidoreductase core subunit V2; OCR: oxygen consumption rate; ROS: reactive oxygen species; RT-qPCR: reverse-transcriptase quantitative polymerase chain reaction; SC: scrambled control; shRNA: short hairpin RNA; SNAI2: snail family transcriptional repressor 2; SOX2: SRY-box transcription factor 2; SQSTM1/p62: sequestosome 1; TGFB/TGF-β: transforming growth factor beta; TOMM20: translocase of outer mitochondrial membrane 20; ZEB1: zinc finger E-box binding homeobox 1.
    Keywords:  Autophagy; LC3A; SOX2; cancer cell plasticity; lung cancer; mitochondria dynamics
  29. J Neurosci. 2021 Sep 02. pii: JN-RM-0783-21. [Epub ahead of print]
      In the vertebrate central nervous system, oligodendrocytes produce myelin, a specialized membrane, to insulate and support axons. Individual oligodendrocytes wrap multiple axons with myelin sheaths of variable lengths and thicknesses. Myelin grows at the distal ends of oligodendrocyte processes and multiple lines of work have provided evidence that mRNAs and RNA binding proteins localize to myelin, together supporting a model where local translation controls myelin sheath growth. What signal transduction mechanisms could control this? One strong candidate is the Akt-mTOR pathway, a major cellular signaling hub that coordinates transcription, translation, metabolism, and cytoskeletal organization. Here, using zebrafish as a model system, we found that Akt-mTOR signaling promotes myelin sheath growth and stability during development. Through cell-specific manipulations to oligodendrocytes, we show that the Akt-mTOR pathway drives cap-dependent translation to promote myelination and that restoration of cap-dependent translation is sufficient to rescue myelin deficits in mTOR loss-of-function animals. Moreover, an mTOR-dependent translational regulator was phosphorylated and co-localized with mRNA encoding a canonically myelin-translated protein in vivo and bioinformatic investigation revealed numerous putative translational targets in the myelin transcriptome. Together, these data raise the possibility that Akt-mTOR signaling in nascent myelin sheaths promotes sheath growth via translation of myelin-resident mRNAs during development.SIGNIFICANCE STATEMENTIn the brain and spinal cord oligodendrocytes extend processes that tightly wrap axons with myelin, a protein and lipid rich membrane that increases electrical impulses and provides trophic support. Myelin membrane grows dramatically following initial axon wrapping in a process that demands protein and lipid synthesis. How protein and lipid synthesis is coordinated with the need for myelin to be generated in certain locations remains unknown. Our study reveals that the Akt-mTOR signaling pathway promotes myelin sheath growth by regulating protein translation. Because we found translational regulators of the Akt-mTOR pathway in myelin, our data raise the possibility Akt-mTOR activity regulates translation in myelin sheaths to deliver myelin on demand to the places it is needed.