bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2021‒09‒26
38 papers selected by
Viktor Korolchuk
Newcastle University

  1. Biochem J. 2021 Sep 30. 478(18): 3395-3421
      The ubiquitin-proteasome pathway (UPP) and autophagy play integral roles in cellular homeostasis. As part of their normal life cycle, most proteins undergo ubiquitination for some form of redistribution, localization and/or functional modulation. However, ubiquitination is also important to the UPP and several autophagic processes. The UPP is initiated after specific lysine residues of short-lived, damaged or misfolded proteins are conjugated to ubiquitin, which targets these proteins to proteasomes. Autophagy is the endosomal/lysosomal-dependent degradation of organelles, invading microbes, zymogen granules and macromolecules such as protein, carbohydrates and lipids. Autophagy can be broadly separated into three distinct subtypes termed microautophagy, chaperone-mediated autophagy and macroautophagy. Although autophagy was once thought of as non-selective bulk degradation, advancements in the field have led to the discovery of several selective forms of autophagy. Here, we focus on the mechanisms of primary and selective mammalian autophagy pathways and highlight the current knowledge gaps in these molecular pathways.
    Keywords:  lysosomes; macroautophagy; microautophagy
  2. J Mol Cell Biol. 2021 Sep 25. pii: mjab059. [Epub ahead of print]
      The biogenesis of autophagosomes provides the basis for macroautophagy to capture and degrade intracellular cargoes. Binding of the autophagy-related protein ATG8/LC3 to autophagic membranes is essential to autophagosome formation, which involves the specific and dynamic processing of ATG8/LC3 by cysteine protease ATG4. However, to date, the mechanism whereby ATG4 is recruited to the membranes, the interaction of ATG4 and ATG8/LC3 on the membranes, and its role in the growth of phagophore are not completely understood. Here, we used fluorescence recovery after photobleaching to monitor the turnover of GFP-tagged ATG4B and LC3B in living animal cells. The data show that ATG4B localizes to early autophagic membranes in an LC3B-dependent manner. During autophagy, ATG4B and LC3B undergo rapid cytosol/isolation membrane exchange but not at the cytosol/completed autophagosome. In addition, ATG4B activity controls the efficiency of autophagosome formation by impacting the membrane binding/dissociation of LC3B. These data suggest that ATG4 and LC3 play interdependent roles in the formation of autophagosomes.
    Keywords:  ATG4; LC3; autophagosome biogenesis; autophagy; live-cell imaging; membrane binding kinetics
  3. Angew Chem Int Ed Engl. 2021 Sep 22.
      Mammalian cell nuclei contain copper, and cancer cells are known to accumulate aberrantly high copper levels, yet the mechanisms underlying nuclear accumulation and copper's broader functional significance remain poorly understood. Here, by combining APEX2-based proximity labeling focused on the copper chaperone Atox1 with mass spectrometry we identified a previously unrecognized nuclear copper binding protein, Cysteine-rich protein 2 (CRIP2), that interacts with Atox1 in the nucleus. We show that Atox1 transfers copper to CRIP2, which induces a change in CRIP2's secondary structure that ultimately promotes its ubiquitin-mediated proteasomal degradation. Finally, we demonstrate that depletion of CRIP2-as well as copper-induced CRIP2 degradation-elevates ROS levels and activates autophagy in H1299 cells. Thus, our study establishes that CRIP2 as an autophagic suppressor protein and implicates CRIP2-mediated copper metabolism in the activation of autophagy in cancer cells.
    Keywords:  Copper * An engineered ascorbate peroxidase (APEX2) * Atox1 * Cysteine-rich protein 2 (CRIP2) * Autophagy
  4. Cell Signal. 2021 Sep 18. pii: S0898-6568(21)00239-4. [Epub ahead of print] 110150
      Autophagy is an extremely essential cellular process aimed to clear redundant and damaged materials, namely organelles, protein aggregates, invading pathogens, etc. through the formation of autophagosomes which are ultimately targeted to lysosomal degradation. In this study, we demonstrated that mTOR dependent classical autophagy is ubiquitously triggered in differentiating monocytes. Moreover, autophagy plays a decisive role in sustaining the process of monocyte to macrophage differentiation. We have delved deeper into understanding the underlying mechanistic complexities that trigger autophagy during differentiation. Intrigued by the significant difference between the protein profiles of monocytes and macrophages, we investigated to learn that autophagy directs monocyte differentiation via protein degradation. Further, we delineated the complex cross-talk between autophagy and cell-cycle arrest in differentiating monocytes. This study also inspects the contribution of adhesion on various steps of autophagy and its ultimate impact on monocyte differentiation. Our study reveals new mechanistic insights into the process of autophagy associated with monocyte differentiation and would undoubtedly help to understand the intricacies of the process better for the effective design of therapeutics as autophagy and autophagy-related processes have enormous importance in human patho-physiology.
    Keywords:  Adhesion; Autophagy; Differentiation; Macrophage; Monocyte
  5. Hepatol Commun. 2021 Aug 24.
      Lysosomes are intracellular acidic organelles with catabolic functions that contribute to the activation of autophagy. Although autophagy abnormality is associated with defects in lysosomal acidification during the progression of nonalcoholic fatty liver disease (NAFLD), the mechanisms of control of lysosomal acidification are not well understood at the molecular level. Thus, we aimed to elucidate the role of the orphan nuclear receptor retinoic acid-related orphan receptor α (RORα) in lysosomal acidification and autophagic flux, particularly in nutrition-enriched hepatocytes. First, lysosomal acidity was much lower in the hepatocytes obtained from hepatocyte-specific RORα-deleted (RORα-LKO) mice, whereas the infusion of an adenovirus encoding RORα in wild-type hepatocytes increased lysosomal acidity, as determined by LysoSensor. Second, the lysosomal translocation of the mechanistic target of rapamycin was increased and immature cathepsin D was accumulated in the liver of RORα-LKO mice. Third, the accumulation of LC3-II, p62/sequestosome 1 (SQSTM1), and neighbor of BRCA1 gene 1 (NBR1) was increased in the livers of RORα-LKO mice, indicating an impaired autophagic flux in the livers. Consistently, the number of autolysosomes containing mitochondria and lipid droplets was dramatically reduced in the RORα-deleted hepatocytes. Finally, we found that RORα induced the transcription of genes involved in lysosomal function, such as Atp6v1g1, a vacuolar H+ -ATPase (v-ATPase) subunit, which were largely down-regulated in the livers of mice with high-fat diet-induced NAFLD and patients with hepatitis. Conclusion: Targeting RORα may be a potential therapeutic strategy to restore lysosomal acidification, which inhibits the progression of NAFLD.
  6. Stem Cell Rev Rep. 2021 Sep 21.
      Adult neurogenesis is the ongoing generation of functional new neurons from neural progenitor cells (NPCs) in the mammalian brain. However, this process declines with aging, which is implicated in the recession of brain function and neurodegeneration. Understanding the mechanism of adult neurogenesis and stimulating neurogenesis will benefit the mitigation of neurodegenerative diseases. Autophagy, a highly conserved process of cellular degradation, is essential for maintaining cellular homeostasis and normal function. Whether and how autophagy affects adult neurogenesis remains poorly understood. In present study, we revealed a close connection between impaired autophagy and adult neurogenetic decline. Expression of autophagy-related genes and autophagic activity were significantly declined in the middle-adult subventricular/subgranular zone (SVZ/SGZ) homogenates and cultured NPCs, and inhibiting autophagy by siRNA interference resulted in impaired proliferation and differentiation of NPCs. Conversely, stimulating autophagy by rapamycin not only revitalized the viability of middle-adult NPCs, but also facilitated the neurogenesis in middle-adult SVZ/SGZ. More importantly, autophagic activation by rapamycin also ameliorated the olfactory sensitivity and cognitional capacities in middle-adult mice. Taken together, our results reveal that compromised autophagy is involved in the decline of adult neurogenesis, which could be reversed by autophagy activation. It also shed light on the regulation of adult neurogenesis and paves the way for developing a therapeutic strategy for aging and neurodegenerative diseases.
    Keywords:  Adult neurogenesis; Autophagy; Neural progenitor cell; Rapamycin; mTOR
  7. FASEB J. 2021 Oct;35(10): e21909
      Metabolic stress contributes to the regulation of cell death in normal and diseased tissues. While different forms of cell death are known to be regulated by metabolic stress, how the cell engulfment and killing mechanism entosis is regulated is not well understood. Here we find that the death of entotic cells is regulated by the presence of amino acids and activity of the mechanistic target of rapamycin (mTOR). Amino acid withdrawal or mTOR inhibition induces apoptosis of engulfed cells and blocks entotic cell death that is associated with the lipidation of the autophagy protein microtubule-associated protein light chain 3 (LC3) to entotic vacuoles. Two other live cell engulfment programs, homotypic cell cannibalism (HoCC) and anti-CD47 antibody-mediated phagocytosis, known as phagoptosis, also undergo a similar vacuole maturation sequence involving LC3 lipidation and lysosome fusion, but only HoCC involves mTOR-dependent regulation of vacuole maturation and engulfed cell death similar to entosis. We further find that the regulation of cell death by mTOR is independent of autophagy activation and instead involves the 4E-BP1/2 proteins that are known regulators of mRNA translation. Depletion of 4E-BP1/2 proteins can restore the mTOR-regulated changes of entotic death and apoptosis rates of engulfed cells. These results identify amino acid signaling and the mTOR-4E-BP1/2 pathway as an upstream regulation mechanism for the fate of live engulfed cells formed by entosis and HoCC.
    Keywords:  amino acids; cell death; entosis; mTOR; metabolism
  8. Mol Cell. 2021 Sep 18. pii: S1097-2765(21)00729-2. [Epub ahead of print]
      The interferon (IFN) pathway is critical for cytotoxic T cell activation, which is central to tumor immunosurveillance and successful immunotherapy. We demonstrate here that PKCλ/ι inactivation results in the hyper-stimulation of the IFN cascade and the enhanced recruitment of CD8+ T cells that impaired the growth of intestinal tumors. PKCλ/ι directly phosphorylates and represses the activity of ULK2, promoting its degradation through an endosomal microautophagy-driven ubiquitin-dependent mechanism. Loss of PKCλ/ι results in increased levels of enzymatically active ULK2, which, by direct phosphorylation, activates TBK1 to foster the activation of the STING-mediated IFN response. PKCλ/ι inactivation also triggers autophagy, which prevents STING degradation by chaperone-mediated autophagy. Thus, PKCλ/ι is a hub regulating the IFN pathway and three autophagic mechanisms that serve to maintain its homeostatic control. Importantly, single-cell multiplex imaging and bioinformatics analysis demonstrated that low PKCλ/ι levels correlate with enhanced IFN signaling and good prognosis in colorectal cancer patients.
    Keywords:  STING; ULK1/2; atypical PKC; autophagy; chaperone-mediated autophagy; colorectal cancer; immunosuppression; immunosurveillance; immunotherapy; interferon
  9. Antioxid Redox Signal. 2021 Sep 21.
      SIGNIFICANCE: Despite the many efforts put into understanding diabetic nephropathy (DN), direct treatments for DN have yet to be discovered. Understanding the mechanisms behind DN is an essential step in the development of novel therapeutic regimens. The mTOR pathway has emerged as an important candidate in the quest for drug discovery because of its role in regulating growth, proliferation, as well as protein and lipid metabolism. Recent Advances: Kidney cells have been found to rely on basal autophagy for survival and for conserving kidney integrity. Recent studies have shown that diabetes induces renal autophagy deregulation, leading to kidney injury. Hyper-activation of the mTOR pathway and oxidative stress have been suggested to play a role in diabetes-induced autophagy imbalance.CRITICAL ISSUES: A detailed understanding of the role of mTOR signaling in diabetes-associated complications is of major importance in the search for a cure. In this review, we provide evidence that mTOR is heavily implicated in diabetes-induced kidney injury. We suggest possible mechanisms through which mTOR exerts its negative effects by increasing insulin resistance, upregulating oxidative stress, and inhibiting autophagy.
    FUTURE DIRECTIONS: Increased oxidative stress and autophagy deregulation are both deeply embedded in DN. However, the mechanisms controlling oxidative stress and autophagy are not well understood. While Akt/mTOR signaling seems to play an important role in oxidative stress and autophagy, further investigation is required to uncover the details of this signaling pathway.
  10. Oxid Med Cell Longev. 2021 ;2021 6347792
      Autophagy is an essential cellular process that involves the transport of cytoplasmic content in double-membraned vesicles to lysosomes for degradation. Neurons do not undergo cytokinesis, and thus, the cell division process cannot reduce levels of unnecessary proteins. The primary cause of neurodegenerative disorders (NDs) is the abnormal deposition of proteins inside neuronal cells, and this could be averted by autophagic degradation. Thus, autophagy is an important consideration when considering means of developing treatments for NDs. Various pharmacological studies have reported that the active components in herbal medicines exhibit therapeutic benefits in NDs, for example, by inhibiting cholinesterase activity and modulating amyloid beta levels, and α-synuclein metabolism. A variety of bioactive constituents from medicinal plants are viewed as promising autophagy controllers and are revealed to recover the NDs by targeting the autophagic pathway. In the present review, we discuss the role of autophagy in the therapeutic management of several NDs. The molecular process responsible for autophagy and its importance in various NDs and the beneficial effects of medicinal plants in NDs by targeting autophagy are also discussed.
  11. Front Cell Dev Biol. 2021 ;9 723108
      Mitochondria are important organelles whose primary function is energy production; in addition, they serve as signaling platforms for apoptosis and antiviral immunity. The central role of mitochondria in oxidative phosphorylation and apoptosis requires their quality to be tightly regulated. Mitophagy is the main cellular process responsible for mitochondrial quality control. It selectively sends damaged or excess mitochondria to the lysosomes for degradation and plays a critical role in maintaining cellular homeostasis. However, increasing evidence shows that viruses utilize mitophagy to promote their survival. Viruses use various strategies to manipulate mitophagy to eliminate critical, mitochondria-localized immune molecules in order to escape host immune attacks. In this article, we will review the scientific advances in mitophagy in viral infections and summarize how the host immune system responds to viral infection and how viruses manipulate host mitophagy to evade the host immune system.
    Keywords:  autophagy; immune; infection; mitochondria; mitophagy; virus
  12. Mol Cell. 2021 Sep 16. pii: S1097-2765(21)00688-2. [Epub ahead of print]81(18): 3786-3802.e13
      Amino acids are essential building blocks of life. However, increasing evidence suggests that elevated amino acids cause cellular toxicity associated with numerous metabolic disorders. How cells cope with elevated amino acids remains poorly understood. Here, we show that a previously identified cellular structure, the mitochondrial-derived compartment (MDC), functions to protect cells from amino acid stress. In response to amino acid elevation, MDCs are generated from mitochondria, where they selectively sequester and deplete SLC25A nutrient carriers and their associated import receptor Tom70 from the organelle. Generation of MDCs promotes amino acid catabolism, and their formation occurs simultaneously with transporter removal at the plasma membrane via the multivesicular body (MVB) pathway. The combined loss of vacuolar amino acid storage, MVBs, and MDCs renders cells sensitive to high amino acid stress. Thus, we propose that MDCs operate as part of a coordinated cell network that facilitates amino acid homeostasis through post-translational nutrient transporter remodeling.
    Keywords:  MDC; Tom70; amino acid; lysosome; mitochondria; nutrient carrier; vacuole
  13. Trends Endocrinol Metab. 2021 Sep 21. pii: S1043-2760(21)00203-4. [Epub ahead of print]
      Lipophagy is the process of selective degradation of lipid droplets (LDs) by autophagy. Several studies have highlighted the importance of lipophagy in regulating cellular lipid levels in various tissues and disease conditions. In recent years, disruption of autophagy and accumulation of LDs have been reported as pathological hallmarks in several neurodegenerative and neuroinflammatory diseases, raising the question whether lipophagy is a process that is important in the progression of these disorders. This supports the growing interest in lipid metabolism as a major player in neurodegeneration, and the emerging understanding of several neurological pathologies as not only proteinopathies but also lipidopathies. In this review we discuss the importance of lipophagy in the most common central nervous system diseases. We examine the latest evidence for the reported interplay between abnormalities in lipid accumulation and autophagy, and propose lipophagy as a potentially important mechanism in neurodegeneration.
  14. Chem Biol Interact. 2021 Sep 16. pii: S0009-2797(21)00297-0. [Epub ahead of print]349 109659
      Fluorine is an essential trace element for human health. However, excessive fluoride intake causes skeletal fluorosis which affects cartilage development. Fluoride inhibited chondrocyte proliferation which is the initial and critical step of endochondral ossification, but the underlying mechanism has not been clearly illustrated. Mammalian target of rapamycin (mTOR) is an important protein kinase which modulates various cellular processes and is believed to be a central regulator of chondrocyte proliferation and autophagy. In this study, we explored the effect of fluoride on the proliferation and autophagy of chondrocytes and the regulatory role of mTOR signaling pathway. Our results suggested that NaF inhibited the protein expressions of proliferating cell nuclear antigen (PCNA) and pS6 in cultured fetal rat tibias. Furthermore, NaF significantly downregulated the expressions of mTOR signaling pathway-related genes, including PI3K, AKT, mTOR, 4EBP1 and S6K1 in mouse ATDC5 chondrogenic cell line. We also found that NaF increased autophagy in ATDC5 cells. The mRNA and protein levels of autophagy-related genes LC3, Beclin1 and p62 were significantly changed after NaF treatment. Further studies demonstrated that MHY1485, a small-molecular mTOR activator, totally reversed fluoride-induced promotion of autophagy. MHY1485 also recovered the downregulation of proliferative chondrocytes markers Sox9 and Type Ⅱ Collagen (Col2a1) induced by fluoride in ATDC5 cells. Taken together, our result demonstrate that fluoride suppressed proliferation and facilitated autophagy via PI3K/AKT/mTOR signaling pathway in chondrogenesis.
    Keywords:  ATDC5 cells; Autophagy; Fluoride; Proliferation; mTOR
  15. Mol Cell. 2021 Sep 14. pii: S1097-2765(21)00735-8. [Epub ahead of print]
      AKT is a serine/threonine kinase that plays an important role in metabolism, cell growth, and cytoskeletal dynamics. AKT is activated by two kinases, PDK1 and mTORC2. Although the regulation of PDK1 is well understood, the mechanism that controls mTORC2 is unknown. Here, by investigating insulin receptor signaling in human cells and biochemical reconstitution, we found that insulin induces the activation of mTORC2 toward AKT by assembling a supercomplex with KRAS4B and RHOA GTPases, termed KARATE (KRAS4B-RHOA-mTORC2 Ensemble). Insulin-induced KARATE assembly is controlled via phosphorylation of GTP-bound KRAS4B at S181 and GDP-bound RHOA at S188 by protein kinase A. By developing a KARATE inhibitor, we demonstrate that KRAS4B-RHOA interaction drives KARATE formation. In adipocytes, KARATE controls insulin-dependent translocation of the glucose transporter GLUT4 to the plasma membrane for glucose uptake. Thus, our work reveals a fundamental mechanism that activates mTORC2 toward AKT in insulin-regulated glucose homeostasis.
    Keywords:  AKT; KRAS GTPase; PKA; RHOA GTPase; insulin; mTORC2
  16. J Virol. 2021 Sep 22. JVI0153721
      Autophagy is thought to be involved in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. However, how SARS-CoV-2 interferes with the autophagic pathway and whether autophagy contributes to virus infection in vivo is unclear. Here, we identified SARS-CoV-2-triggered autophagy in animal models including the long tailed or crab eating macaque (Macaca fascicularis), hACE2 transgenic mice and xenografted human lung tissues. In Vero E6 and Huh-7 cells, SARS-CoV-2 induces autophagosome formation, accompanied by consistent autophagic events, including inhibition of the Akt-mTOR pathway, and activation of the ULK-1-Atg13 and VPS34-VPS15-Beclin1 complexes, but blocks autophagosome-lysosome fusion. Modulation of autophagic elements, including the VPS34 complex and Atg14, but not Atg5, inhibits SARS-CoV-2 replication. Moreover, this study represents the first to demonstrate that the mouse bearing xenografted human lung tissue is a suitable model for SARS-CoV-2 infection and that autophagy inhibition suppresses SARS-CoV-2 replication and ameliorates virus-associated pneumonia in human lung tissues. We also observed a critical role of autophagy in SARS-CoV-2 infection in an hACE2 transgenic mouse model. This study, therefore, gives insights into the mechanisms by which SARS-CoV-2 manipulates autophagosome formation and we suggest that autophagy-inhibiting agents might be useful as therapeutic agents against SARS-CoV-2 infection. IMPORTANCE: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) caused a global pandemic with limited therapeutics. Insights into the virus-host interactions contributes substantially. The novelty of this report is the use of a new animal model: mice xenografted with human lung tissues. Using a combination of the in vitro and in vivo studies, we have provided experimental evidence that induction of autophagy contributes to SARS-CoV-2 infection and improves our understanding of potential therapeutic targets for SARS-CoV-2.
  17. Front Cell Dev Biol. 2021 ;9 737071
      WIPIs are a conserved family of proteins with a characteristic 7-bladed β-propeller structure. They play a prominent role in autophagy, but also in other membrane trafficking processes. Mutations in human WIPI4 cause several neurodegenerative diseases. One of them is BPAN, a rare disease characterized by developmental delay, motor disorders, and seizures. Autophagy dysfunction is thought to play an important role in this disease but the precise pathological consequences of the mutations are not well established. The use of simple models such as the yeast Saccharomyces cerevisiae and the social amoeba Dictyostelium discoideum provides valuable information on the molecular and cellular function of these proteins, but also sheds light on possible pathways that may be relevant in the search for potential therapies. Here, we review the function of WIPIs as well as disease-causing mutations with a special focus on the information provided by these simple models.
    Keywords:  BPAN; Dictyostelium discoideum; PROPPIN; Saccharomyces cerevisiae; Vmp1; WDR45; WIPI; autophagy
  18. Cell Res. 2021 Sep 24.
      Under stress, the endomembrane system undergoes reorganization to support autophagosome biogenesis, which is a central step in autophagy. How the endomembrane system remodels has been poorly understood. Here we identify a new type of membrane contact formed between the ER-Golgi intermediate compartment (ERGIC) and the ER-exit site (ERES) in the ER-Golgi system, which is essential for promoting autophagosome biogenesis induced by different stress stimuli. The ERGIC-ERES contact is established by the interaction between TMED9 and SEC12 which generates a short distance opposition (as close as 2-5 nm) between the two compartments. The tight membrane contact allows the ERES-located SEC12 to transactivate COPII assembly on the ERGIC. In addition, a portion of SEC12 also relocates to the ERGIC. Through both mechanisms, the ERGIC-ERES contact promotes formation of the ERGIC-derived COPII vesicle, a membrane precursor of the autophagosome. The ERGIC-ERES contact is physically and functionally different from the TFG-mediated ERGIC-ERES adjunction involved in secretory protein transport, and therefore defines a unique endomembrane structure generated upon stress conditions for autophagic membrane formation.
  19. Ageing Res Rev. 2021 Sep 19. pii: S1568-1637(21)00211-7. [Epub ahead of print] 101464
      Alzheimer's disease (AD) is a complex neurodegenerative disease in the elderly and the most common cause of human dementia. AD is characterized by accumulation of abnormal protein aggregates including amyloid plaques (composed of beta-amyloid (Aβ) peptides) and neurofibrillary tangles (formed by hyper-phosphorylated tau protein). Synaptic plasticity, neuroinflammation, calcium signaling etc. also show dysfunction in AD patients. Autophagy is an evolutionarily conserved lysosome-dependent cellular event in eukaryotes. It is closely linked to modulation of protein metabolism, through which damaged organelles and mis-folded proteins are degraded and then recycled to maintain protein homeostasis. Accumulating evidence has shown that impaired autophagy also contributes to AD pathogenesis. In the present review, we highlight the role of autophagy, including bulk and selective autophagy, in regulating metabolic circuits in AD pathogenesis. We also discuss the potential and future perspectives of autophagy-inducing strategies in AD therapeutics.
  20. Cell Res. 2021 Sep 24.
      The AMP-activated protein kinase (AMPK) is a central regulator of energy homeostasis. Although much has been learned on how low energy status and glucose starvation activate AMPK, how AMPK activity is properly controlled in vivo is still poorly understood. Here we report that UHRF1, an epigenetic regulator highly expressed in proliferating and cancer cells, interacts with AMPK and serves to suppress AMPK activity under both basal and stressed conditions. As a nuclear protein, UHRF1 promotes AMPK nuclear retention and strongly suppresses nuclear AMPK activity toward substrates H2B and EZH2. Importantly, we demonstrate that UHRF1 also robustly inhibits AMPK activity in the cytoplasm compartment, most likely as a consequence of AMPK nucleocytoplasmic shuttling. Mechanistically, we found that UHRF1 has no obvious effect on AMPK activation by upstream kinases LKB1 and CAMKK2 but inhibits AMPK activity by acting as a bridging factor targeting phosphatase PP2A to dephosphorylate AMPK. Hepatic overexpression of UHRF1 showed profound effects on glucose and lipid metabolism in wild-type mice but not in those with the liver-specific knockout of AMPKα1/α2, whereas knockdown of UHRF1 in adipose tissue led to AMPK activation and reduced sizes of adipocytes and lipogenic activity, highlighting the physiological significance of this regulation in glucose and lipid metabolism. Thus, our study identifies UHRF1 as a novel AMPK gate-keeper with critical roles in cellular metabolism.
  21. J Biol Chem. 2021 Sep 21. pii: S0021-9258(21)01025-5. [Epub ahead of print] 101222
      Intraneuronal neurofibrillary tangles composed of Tau aggregates have been widely accepted as an important pathological hallmark of Alzheimer's disease. A current therapeutic avenue for treating Alzheimer's disease is aimed at inhibiting Tau accumulation with small molecules such as natural flavonoids. Liquid-liquid phase separation (LLPS) of Tau can lead to its aggregation, and Tau aggregates can then be degraded by autophagy. However, it is unclear whether natural flavonoids modulate the formation of phase-separated Tau droplets or promote autophagy and Tau clearance. Here, using confocal microscopy and fluorescence recovery after photobleaching assays, we report that a natural antioxidant flavonoid compound myricetin slows LLPS of full-length human Tau, shifting the equilibrium phase boundary to a higher protein concentration. This natural flavonoid also significantly inhibits pathological phosphorylation and abnormal aggregation of Tau in neuronal cells, and blocks mitochondrial damage and apoptosis induced by Tau aggregation. Importantly, using co-immunoprecipitation and Western blotting, we show that treatment of cells with myricetin stabilizes the interaction between Tau and autophagy-related protein 5 (ATG5) to promote clearance of phosphorylated Tau to indirectly limit its aggregation. Consistently, this natural flavonoid inhibits mTOR pathway, activates ATG5-dependent Tau autophagy, and almost completely suppresses Tau toxicity in neuronal cells. Collectively, these results demonstrate how LLPS and abnormal aggregation of Tau are inhibited by natural flavonoids, bridging the gap between Tau LLPS and aggregation in neuronal cells, and also establish that myricetin could act as an ATG5-dependent autophagic activator to ameliorate the pathogenesis of Alzheimer's disease.
    Keywords:  Alzheimer’s disease; Myricetin; Protein aggregation; Protein liquid-liquid phase separation; Tau protein; Tau toxicity
  22. Cancer Lett. 2021 Sep 21. pii: S0304-3835(21)00464-X. [Epub ahead of print]
      Mechanistic target of rapamycin (mTOR) forms two distinct complexes, mTOR complex 1 (mTORC1) and mTORC2. Here we investigated the antitumor effect of dual mTORC1/2 inhibitor AZD2014 on epithelial ovarian cancer (EOC) and its potential effect on immunosuppressive myeloid-derived suppressor cells (MDSCs). Immunohistochemical analysis of mTORC1 and mTORC2 was performed on a human ovarian cancer tissue microarray. High mTORC2 expression level was associated with shorter survival in EOC, whereas mTORC1 was not correlate with patients' prognosis. AZD2014 suppressed mTOR signaling pathway in ovarian cancer cells, inhibited proliferation and induced G1-phase cell cycle arrest and apoptosis. In tumor-bearing mice, AZD2014 treatment limited tumor growth, reduced peritoneal ascites, and prolonged survival. AZD2014 specifically reduced MDSCs migration and accumulation in EOC peritoneal fluid but not in the spleen. Moreover, subsequent AZD2014 treatment after cisplatin chemotherapy delayed EOC recurrence. Collectively, we observed that high mTORC2 expression level in EOC indicated a poor prognosis. Remarkably, in tumor-bearing mice, AZD2014 diminished MDSC accumulation and delayed tumor growth and recurrence.
    Keywords:  MDSC; Ovarian cancer; mTOR inhibitor
  23. Circ Res. 2021 Sep 22.
      Rationale: Nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS) protects against myocardial ischemia-reperfusion injury (I/R). However, reperfusion of myocardium results in superoxide (O2•-) generation, which promotes eNOS glutathionylation that produces O2•- instead of NO. It is unclear whether glutathionylated eNOS (SG-eNOS) continues to produce O2•- indefinitely or undergoes a time-dependent degradation. Objective: To determine whether SG-eNOS continues to produce O2•- in I/R for a prolonged period causing accentuated I/R injury or it undergoes a time-dependent degradation. Methods and Results: Since SG-eNOS produces significant O2•- instead of NO, we sought to determine the time-course of SG-eNOS levels in the HCAEC in hypoxia/reoxygenation (H/R) by western analysis and immunoprecipitation. SG-eNOS was degraded by chaperone-mediated autophagy (CMA), as inhibitors of CMA rescued eNOS expression. We further confirmed CMA by high resolution confocal and electron microscopy. We showed that SG-eNOS is targeted by HSC70 chaperone via its interaction with glutathionylated-cysteine 691 and 910. Glutathionylation of cysteine 691 residue in H/R exposes 735QRYRL739 motif for interaction with HSC70, and consequent transportation to LAMP2A vesicle, where it is degraded by lysosomal proteases. Mutagenesis of these residues in eNOS inhibited its CMA. Using contrast echocardiography and electron paramagnetic resonance spectrometry (EPR), we found that Trx-Tg mice show improved myocardial perfusion and decreased myocardial apoptosis in I/R due to deglutathionylation of SG-eNOS and restoration of NO generation. Further, WT mice treated with recombinant human Trx (rhTrx) were protected against eNOS CMA, and restored NO production with improved myocardial perfusion and decreased I/R injury. Conclusions: SG-eNOS undergoes degradation via CMA, following prolonged retention in the cytosol. CMA of SG-eNOS terminates O2•- generation preventing further tissue damage but causes irreversible loss of eNOS and NO availability. Prompt deglutathionylation of SG-eNOS prevents CMA, promotes NO production, and improved myocardial perfusion, resulting in amelioration of reperfusion injury.
  24. Front Cell Dev Biol. 2021 ;9 738932
      Autophagy, an essential biological process that affects immunity, is a powerful tool that host cells can use to defend against infections caused by pathogenic microorganisms. Autophagy can not only initiate innate immune responses but also degrade the cellular components that provide the conditions for removing the invaders. However, hyperactivated or inhibited autophagy leads to mitochondrial dysfunction, which is harmful to the host itself and is involved in many types of diseases. Mitochondria perform the functions of biological oxidation and energy exchange. In addition, mitochondrial functions are closely related to cell death, oxygen radical formation, and disease. Accumulation of mitochondrial metabolites affects survival of intracellular pathogens. In this mini-review, we focus on the crosstalk between autophagy and mitochondrial homeostasis during infection.
    Keywords:  autophagy; dual role; homeostasis; mitochondria; pathogen infection
  25. J Extracell Vesicles. 2021 Sep;10(11): e12146
      Cancer-associated fibroblasts (CAFs) as a predominant cell component in the tumour microenvironment (TME) play an essential role in tumour progression. Our earlier studies revealed oxidized ATM activation in breast CAFs, which is independent of DNA double-strand breaks (DSBs). Oxidized ATM has been found to serve as a redox sensor to maintain cellular redox homeostasis. However, whether and how oxidized ATM in breast CAFs regulates breast cancer progression remains poorly understood. In this study, we found that oxidized ATM phosphorylates BNIP3 to induce autophagosome accumulation and exosome release from hypoxic breast CAFs. Inhibition of oxidized ATM kinase by KU60019 (a small-molecule inhibitor of activated ATM) or shRNA-mediated knockdown of endogenous ATM or BNIP3 blocks autophagy and exosome release from hypoxic CAFs. We also show that oxidized ATM phosphorylates ATP6V1G1, a core proton pump in maintaining lysosomal acidification, leading to lysosomal dysfunction and autophagosome fusion with multi-vesicular bodies (MVB) but not lysosomes to facilitate exosome release. Furthermore, autophagy-associated GPR64 is enriched in hypoxic CAFs-derived exosomes, which stimulates the non-canonical NF-κB signalling to upregulate MMP9 and IL-8 in recipient breast cancer cells, enabling cancer cells to acquire enhanced invasive abilities. Collectively, these results provide novel insights into the role of stromal CAFs in promoting tumour progression and reveal a new function of oxidized ATM in regulating autophagy and exosome release.
    Keywords:  autophagy; cancer-associated fibroblasts; exosomes; invasion; oxidized ATM
  26. Aging Cell. 2021 Sep 23. e13467
      Protein quality control mechanisms decline during the process of cardiac aging. This enables the accumulation of protein aggregates and damaged organelles that contribute to age-associated cardiac dysfunction. Macroautophagy is the process by which post-mitotic cells such as cardiomyocytes clear defective proteins and organelles. We hypothesized that late-in-life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs. adult mice. As expected, 24-month-old male C57BL/6J mice (old) exhibited repressed autophagosome formation and protein aggregate accumulation in the heart, systolic and diastolic dysfunction, and reduced exercise capacity vs. 8-month-old (adult) mice (all p < 0.05). To investigate the influence of late-in-life exercise training, additional cohorts of 21-month-old mice did (old-ETR) or did not (old-SED) complete a 3-month progressive resistance treadmill running program. Body composition, exercise capacity, and soleus muscle citrate synthase activity improved in old-ETR vs. old-SED mice at 24 months (all p < 0.05). Importantly, protein expression of autophagy markers indicate trafficking of the autophagosome to the lysosome increased, protein aggregate clearance improved, and overall function was enhanced (all p < 0.05) in hearts from old-ETR vs. old-SED mice. These data provide the first evidence that a physiological intervention initiated late-in-life improves autophagic flux, protein aggregate clearance, and contractile performance in mouse hearts.
    Keywords:  aging; cardiac function; exercise; protein aggregates
  27. Mol Ther. 2021 Sep 18. pii: S1525-0016(21)00471-8. [Epub ahead of print]
      N6-methyladenosine (m6A) mRNA modification plays critical roles in various biological events and involves in multiple complex diseases. However, the role of m6A modification in autophagy in nonalcoholic fatty liver disease (NAFLD) remains largely unknown. Here, we report that m6A modification was increased in livers of NAFLD mouse models and in free fatty acids (FFAs)-treated hepatocytes, and the abnormal m6A modification was attributed to the upregulation of methyltransferase like 3 (METTL3) induced by lipotoxicity. Knockdown of METTL3 promoted hepatic autophagic flux and lipid drops (LDs) clearance, while overexpression METTL3 inhibited these process. Mechanistically, METTL3 directly bound to Rubicon mRNA and mediated the m6A modification. While YTH N6-methyladenosine RNA binding protein 1 (YTHDF1), as a partner of METTL3, interacted with the m6A-marked Rubicon mRNA and promoted its stability. Subsequently, RUBICON inhibited autophagosome-lysosome fusion and further blocked LDs clearance. Together, our results showed a critical role of METTL3 and YTHDF1 in regulating lipid metabolism via autophagy pathway and provided a novel insight into m6A mRNA methylation in NAFLD.
    Keywords:  METTL3; NAFLD; YTHDF1; autophagy; m(6)A modification
  28. J Med Chem. 2021 Sep 24.
      Autophagy is upregulated in response to metabolic stress, a hypoxic tumor microenvironment, and therapeutic stress in various cancers and mediates tumor progression and resistance to cancer therapy. Herein, we identified a cinchona alkaloid derivative containing urea (C1), which exhibited potential cytotoxicity and inhibited autophagy in hepatocellular carcinoma (HCC) cells. We showed that C1 not only induced apoptosis but also blocked autophagy in HCC cells, as indicated by the increased expression of LC3-II and p62, inhibition of autophagosome-lysosome fusion, and suppression of the Akt/mTOR/S6k pathway in the HCC cells. Finally, to improve its solubility and efficacy, we encapsulated C1 into PEGylated lipid-poly(lactic-co-glycolic acid) (PLGA) nanoscale drug carriers. Systemic administration of nanoscale C1 significantly suppressed primary tumor growth and prevented distant metastasis while maintaining a desirable safety profile. Our findings demonstrate that C1 combines autophagy modulation and apoptosis induction in a single molecule, making it a promising therapeutic option for HCC.
  29. Hum Gene Ther. 2021 Sep 24.
      The efficiency of recombinant Adeno-associated virus vectors (AAV) transducing host cells is very low, limiting their therapeutic potential in patients. There are several cellular pathways interacting and interfering with the journey of the AAV from the cell surface to the nucleus, opening the possibility to enhance AAV transduction by modifying these interactions. In this study, we explored the results of AAV hepatic transduction when different mTOR inhibitors.- rapamycin, MLN0128, RapaLink-1 -were used in preconditioned juvenile and adult mice. We confirmed rapamycin as an AAV hepatic transduction enhancer in juvenile and adult mice; however, RapaLink-1, a stronger mTOR inhibitor and a clear hepatic autophagy inducer, had no positive effect. Moreover, MLN0128 reduced AAV hepatic transduction. Therefore, our results show a complex interaction between the mTOR pathway and AAV-mediated hepatic transduction and indicate that mTOR inhibition is not a straightforward strategy for improving AAV transduction. More studies are necessary to elucidate the molecular mechanisms involve in the positive and negative effects of mTOR inhibitors on AAV transduction efficiency.
  30. Toxicology. 2021 Sep 21. pii: S0300-483X(21)00285-7. [Epub ahead of print] 152963
      As a promising class of bioactive marine pyrrole alkaloids, lamellarins reportedly act on multiple targets to suppress the vitality of various cancer cell lines. Nevertheless, an in-depth understanding of the molecular mechanisms governing their cytotoxicity is still in demand. Here we report that while activating intrinsic apoptosis, up to 5 μM of lamellarins and their lactam-containing analogs, azalamellarins, also induced mitochondrial stress responses and autophagy in HeLa cervical cancer cells. Detailed characterization of the mitochondria in the treated cells revealed shifted abundance of the two optic atrophy protein 1 (Opa1) isoforms, disturbed morphology, and dissipated membrane potential, leading to PTEN-induced kinase-1 (PINK1) and microtubule-associated protein 1 light chain 3-II (LC3-II) accumulation as a molecular signature of mitophagy. Furthermore, an acute treatment with lamellarins also modulated cellular autophagy flux as evidenced by elevated LC3-II levels, LC3 puncta formation, and p62 degradation. Surprisingly, clustered regularly interspaced short palindromic repeats (CRISPR)-based suppression of autophagy transiently affected the number of apoptotic cells induced by these compounds. Our findings illustrate the potential of these alkaloids for further development into prospective anti-cancer agents.
    Keywords:  Autophagy; lamellarin pyrrole alkaloids; mitochondrial apoptosis; mitochondrial quality control; mitochondrial stress responses
  31. Mol Cell. 2021 Sep 16. pii: S1097-2765(21)00692-4. [Epub ahead of print]81(18): 3803-3819.e7
      Mitochondrial dynamics regulated by mitochondrial fusion and fission maintain mitochondrial functions, whose alterations underline various human diseases. Here, we show that inositol is a critical metabolite directly restricting AMPK-dependent mitochondrial fission independently of its classical mode as a precursor for phosphoinositide generation. Inositol decline by IMPA1/2 deficiency elicits AMPK activation and mitochondrial fission without affecting ATP level, whereas inositol accumulation prevents AMPK-dependent mitochondrial fission. Metabolic stress or mitochondrial damage causes inositol decline in cells and mice to elicit AMPK-dependent mitochondrial fission. Inositol directly binds to AMPKγ and competes with AMP for AMPKγ binding, leading to restriction of AMPK activation and mitochondrial fission. Our study suggests that the AMP/inositol ratio is a critical determinant for AMPK activation and establishes a model in which AMPK activation requires inositol decline to release AMPKγ for AMP binding. Hence, AMPK is an inositol sensor, whose inactivation by inositol serves as a mechanism to restrict mitochondrial fission.
    Keywords:  AMP; AMPK; IMPA1; energy stress; glucose deprivation; inosiotl sensor; inositol; inositol/AMP ratio; mitochondrial fission; mitocondrial dynamics
  32. Mitochondrion. 2021 Sep 15. pii: S1567-7249(21)00121-5. [Epub ahead of print]
      Mitochondria are dynamic, interactive organelles that connect cellular signaling and whole-cell homeostasis. This "mitochatting" allows the cell to receive information about the mitochondria's condition before accommodating energy demands. Mitofusin 2 (Mfn2), an outer mitochondrial membrane fusion protein specializes in mediating mitochondrial homeostasis. Early studies defined the biological significance of Mfn2, latter studies highlighted its role in substrate metabolism. However, determining Mfn2 potential to contribute to energy homeostasis needs study. This review summarizes current literature on mitochondrial metabolic processes, dynamics, and evidence of interactions among Mfn2 and regulatory processes that may link Mfn2's role in maintaining mitochondrial function and substrate metabolism.
    Keywords:  fatty acid oxidation; fission; fusion; glycolysis; mitochondrial dynamics; mitophagy
  33. Am J Physiol Renal Physiol. 2021 Sep 20.
      Receptor-mediated albumin transport in proximal tubule epithelial cells (PTECs) is important to control proteinuria. Autophagy is an evolutionarily conserved degradation pathway and its role in intracellular trafficking through interaction with the endocytic pathway has recently been highlighted. Here, we determined whether autophagy regulates albumin transcytosis in PTECs and suppresses albumin-induced cytotoxicity using human proximal tubule (HK-2) cells. Neonatal Fc-receptor (FcRn), a receptor for albumin transcytosis, partially co-localized with autophagosomes. Recycling of FcRn was attenuated and FcRn accumulated in autophagy related 7 (ATG7) knockdown HK-2 cells. Co-localization of FcRn with RAB7-positive late endosomes and RAB11-positive recycling endosomes was reduced in ATG7 knockdown cells, resulting in decreased recycling of FcRn to the plasma membrane. In ATG7 knockdown cells, albumin transcytosis was significantly reduced and intracellular albumin accumulation was increased. Finally, release of KIM-1, a marker of tubule injury, from ATG7 knockdown cells was increased in response to excess albumin. In conclusion, suppression of autophagy in tubules impairs FcRn transport, thereby inhibiting albumin transcytosis. The resulting accumulation of albumin induces cytotoxicity in tubules.
    Keywords:  Atg7; albumin; autophagy; neonatal Fc receptor; transcytosis
  34. Cell Death Dis. 2021 Sep 23. 12(10): 865
      Osteoarthritis (OA) is a complex condition that involves both apoptosis and senescence and currently cannot be cured. Fibroblast growth factor 21 (FGF21), known for its role as a potent regulator of glucose and energy metabolism, protects from various diseases, possibly by mediating autophagy. In the present study, the role of FGF21 in the progression of OA was investigated in both in vitro and in vivo experiments. In vitro, the results revealed that FGF21 administration alleviated apoptosis, senescence, and extracellular matrix (ECM) catabolism of the chondrocytes induced by tert-butyl hydroperoxide (TBHP) by mediating autophagy flux. Furthermore, CQ, an autophagy flux inhibitor, could reverse the protective effect of FGF21. It was observed that the FGF21-induced autophagy flux enhancement was mediated by the nuclear translocation of TFEB, which occurs due to the activation of the SIRT1-mTOR signaling pathway. The in vivo experiments demonstrated that FGF21 treatment could reduce OA in the DMM model. Taken together, these findings suggest that FGF21 protects chondrocytes from apoptosis, senescence, and ECM catabolism via autophagy flux upregulation and also reduces OA development in vivo, demonstrating its potential as a therapeutic agent in OA.
  35. Brain Commun. 2021 ;3(3): fcab183
      WIPI2 is a member of the human WIPI protein family (seven-bladed b-propeller proteins binding phosphatidylinositols, PROPPINs), which play a pivotal role in autophagy and has been implicated in the pathogenesis of several neurological conditions. The homozygous WIPI2 variant c.745G>A; p.(Val249Met) (NM_015610.4) has recently been associated with a neurodevelopmental disorder in a single family. Using exome sequencing and Sanger segregation analysis, here, two novel homozygous WIPI2 variants [c.551T>G; p.(Val184Gly) and c.724C>T; p.(Arg242Trp) (NM_015610.4)] were identified in four individuals of two consanguineous families. Additionally, follow-up clinical data were sought from the previously reported family. Three non-ambulant affected siblings of the first family harbouring the p.(Val184Gly) missense variant presented with microcephaly, profound global developmental delay/intellectual disability, refractory infantile/childhood-onset epilepsy, progressive tetraplegia with joint contractures and dyskinesia. In contrast, the proband of the second family carrying the p.(Arg242Trp) missense variant, similar to the initially reported WIPI2 cases, presented with a milder phenotype, encompassing moderate intellectual disability, speech and visual impairment, autistic features, and an ataxic gait. Brain MR imaging in five patients showed prominent white matter involvement with a global reduction in volume, posterior corpus callosum hypoplasia, abnormal dentate nuclei and hypoplasia of the inferior cerebellar vermis. To investigate the functional impact of these novel WIPI2 variants, we overexpressed both in WIPI2-knockout HEK293A cells. In comparison to wildtype, expression of the Val166Gly WIPI2b mutant resulted in a deficient rescue of LC3 lipidation whereas Arg224Trp mutant increased LC3 lipidation, in line with the previously reported Val231Met variant. These findings support a dysregulation of the early steps of the autophagy pathway. Collectively, our findings provide evidence that biallelic WIPI2 variants cause a neurodevelopmental disorder of variable severity and disease course. Our report expands the clinical spectrum and establishes WIPI2-related disorder as a congenital disorders of autophagy.
    Keywords:  WIPI2; WIPI2b; autophagy; congenital disorders of autophagy; neurodevelopmental disorder
  36. Sci Rep. 2021 Sep 22. 11(1): 18809
      Autophagy is a lysosomal degradation pathway of cellular components that regulates macrophage properties. Macrophages are critically involved in tumor growth, metastasis, angiogenesis and immune suppression. Here, we investigated whether macrophage autophagy may protect against hepatocellular carcinoma (HCC). Experiments were performed in mice with deletion of the autophagy gene Atg5 in the myeloid lineage (ATG5Mye-/- mice) and their wild-type (WT) littermates. As compared to WT, ATG5Mye-/- mice were more susceptible to diethylnitrosamine (DEN)-induced hepatocarcinogenesis, as shown by enhanced tumor number and volume. Moreover, DEN-treated ATG5Mye-/- mice exhibited compromised immune cell recruitment and activation in the liver, suggesting that macrophage autophagy invalidation altered the antitumoral immune response. RNA sequencing showed that autophagy-deficient macrophages sorted from DEN mice are characterized by an enhanced expression of immunosuppressive markers. In vitro studies demonstrated that hepatoma cells impair the autophagy flux of macrophages and stimulate their expression of programmed cell death-ligand 1 (PD-L1), a major regulator of the immune checkpoint. Moreover, pharmacological activation of autophagy reduces hepatoma cell-induced PD-L1 expression in cultured macrophages while inhibition of autophagy further increases PD-L1 expression suggesting that autophagy invalidation in macrophages induces an immunosuppressive phenotype. These results uncover macrophage autophagy as a novel protective pathway regulating liver carcinogenesis.
  37. FASEB J. 2021 Oct;35(10): e21933
      In obesity, skeletal muscle mitochondrial activity changes to cope with increased nutrient availability. Autophagy has been proposed as an essential mechanism involved in the regulation of mitochondrial metabolism. Still, the contribution of autophagy to mitochondrial adaptations in skeletal muscle during obesity is unknown. Here, we show that in response to high-fat diet (HFD) feeding, distinct skeletal muscles in mice exhibit differentially regulated autophagy that may modulate mitochondrial activity. We observed that after 4 and 40 weeks of high-fat diet feeding, OXPHOS subunits and mitochondrial DNA content increased in the oxidative soleus muscle. However, in gastrocnemius muscle, which has a mixed fiber-type composition, the mitochondrial mass increased only after 40 weeks of HFD feeding. Interestingly, fatty acid-supported mitochondrial respiration was enhanced in gastrocnemius, but not in soleus muscle after a 4-week HFD feeding. This increased metabolic profile in gastrocnemius was paralleled by preserving autophagy flux, while autophagy flux in soleus was reduced. To determine the role of autophagy in this differential response, we used an autophagy-deficient mouse model with partial deletion of Atg7 specifically in skeletal muscle (SkM-Atg7+/- mice). We observed that Atg7 reduction resulted in diminished autophagic flux in skeletal muscle, alongside blunting the HFD-induced increase in fatty acid-supported mitochondrial respiration observed in gastrocnemius. Remarkably, SkM-Atg7+/- mice did not present increased mitochondria accumulation. Altogether, our results show that HFD triggers specific mitochondrial adaptations in skeletal muscles with different fiber type compositions, and that Atg7-mediated autophagy modulates mitochondrial respiratory capacity but not its content in response to an obesogenic diet.
    Keywords:  Atg7; fatty acids; obesity; skeletal muscle fiber