bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2020‒11‒08
forty papers selected by
Viktor Korolchuk
Newcastle University

  1. Mol Cell. 2020 Nov 05. pii: S1097-2765(20)30687-0. [Epub ahead of print]80(3): 437-451.e6
      Amino-acid-induced lysosomal mechanistic target of rapamycin complex 1 (mTORC1) localization through the Rag GTPases is a critical step for its activation by Rheb GTPase. However, how the mTORC1 interacts with Rheb on the lysosome remains elusive. We report that amino acids enhance the polyubiquitination of Rheb (Ub-Rheb), which shows a strong binding preference for mTORC1 and supports its activation, while the Ub-Rheb is subjected to subsequent degradation. Mechanistically, we identified ATXN3 as a Ub-Rheb deubiquitinase whose lysosomal localization is blocked by active Rag heterodimer in response to amino acid stimulation. Consistently, cells lacking functional Rag heterodimer on the lysosome accumulate Ub-Rheb, and blockade of its degradation instigates robust lysosomal mTORC1 localization and its activation without the Ragulator-Rag system. Thus, polyubiquitination of Rheb is an important post-translational modification, which facilitates the binding of mTORC1 to Rheb on the lysosome and is another crosstalk between the amino acid and growth factor signaling for mTORC1 activation.
    Keywords:  ATXN3; Rag; Ragulator; Rheb; amino acids; deubiquitination; lysosome; mTORC1; ubiquitin
  2. Elife. 2020 Nov 03. pii: e61245. [Epub ahead of print]9
      Degradation of mitochondria through mitophagy contributes to the maintenance of mitochondrial function. In this study, we identified that Atg43, a mitochondrial outer membrane protein, serves as a mitophagy receptor in the model organism Schizosaccharomyces pombe to promote the selective degradation of mitochondria. Atg43 contains an Atg8-family-interacting motif essential for mitophagy. Forced recruitment of Atg8 to mitochondria restores mitophagy in Atg43-deficient cells, suggesting that Atg43 tethers expanding isolation membranes to mitochondria. We found that the mitochondrial import factors, including the Mim1-Mim2 complex and Tom70, are crucial for mitophagy. Artificial mitochondrial loading of Atg43 bypasses the requirement of the import factors, suggesting that they contribute to mitophagy through Atg43. Atg43 not only maintains growth ability during starvation but also facilitates vegetative growth through its mitophagy-independent function. Thus, Atg43 is a useful model to study the mechanism and physiological roles, as well as the origin and evolution, of mitophagy in eukaryotes.
    Keywords:  Atg43; MIM complex; S. pombe; autophagy; cell biology; mitochondria; mitophagy; receptor
  3. Mov Disord. 2020 Nov 03.
      BACKGROUND: VPS35 is part of the retromer complex and is responsible for the trafficking and recycling of proteins implicated in autophagy and lysosomal degradation, but also takes part in the degradation of mitochondrial proteins via mitochondria-derived vesicles. The p.D620N mutation of VPS35 causes an autosomal-dominant form of Parkinson's disease (PD), clinically representing typical PD.OBJECTIVE: Most of the studies on p.D620N VPS35 were performed on human tumor cell lines, rodent models overexpressing mutant VPS35, or in patient-derived fibroblasts. Here, based on identified target proteins, we investigated the implication of mutant VPS35 in autophagy, lysosomal degradation, and mitochondrial function in induced pluripotent stem cell-derived neurons from a patient harboring the p.D620N mutation.
    METHODS: We reprogrammed fibroblasts from a PD patient carrying the p.D620N mutation in the VPS35 gene and from two healthy donors in induced pluripotent stem cells. These were subsequently differentiated into neuronal precursor cells to finally generate midbrain dopaminergic neurons.
    RESULTS: We observed a decreased autophagic flux and lysosomal mass associated with an accumulation of α-synuclein in patient-derived neurons compared to controls. Moreover, patient-derived neurons presented a mitochondrial dysfunction with decreased membrane potential, impaired mitochondrial respiration, and increased production of reactive oxygen species associated with a defect in mitochondrial quality control via mitophagy.
    CONCLUSION: We describe for the first time the impact of the p.D620N VPS35 mutation on autophago-lysosome pathway and mitochondrial function in stem cell-derived neurons from an affected p.D620N carrier and define neuronal phenotypes for future pharmacological interventions. © 2020 International Parkinson and Movement Disorder Society.
    Keywords:  Parkinson's disease; VPS35; induced pluripotent stem cells; mitochondrial impairment; α-synuclein
  4. Int J Mol Sci. 2020 Nov 04. pii: E8259. [Epub ahead of print]21(21):
      The target of rapamycin (TOR) is an evolutionarily-conserved serine/threonine kinase that senses and integrates signals from the environment to coordinate developmental and metabolic processes. TOR senses nutrients, hormones, metabolites, and stress signals to promote cell and organ growth when conditions are favorable. However, TOR is inhibited when conditions are unfavorable, promoting catabolic processes such as autophagy. Autophagy is a macromolecular degradation pathway by which cells degrade and recycle cytoplasmic materials. TOR negatively regulates autophagy through phosphorylation of ATG13, preventing activation of the autophagy-initiating ATG1-ATG13 kinase complex. Here we review TOR complex composition and function in photosynthetic and non-photosynthetic organisms. We also review recent developments in the identification of upstream TOR activators and downstream effectors of TOR. Finally, we discuss recent developments in our understanding of the regulation of autophagy by TOR in photosynthetic organisms.
    Keywords:  TOR signaling; TORC1; autophagy; plant growth; target of rapamycin (TOR)
  5. Elife. 2020 Nov 02. pii: e55547. [Epub ahead of print]9
      The actin cytoskeletal regulator Wiskott Aldrich syndrome protein (WASp) has been implicated in maintenance of the autophagy-inflammasome axis in innate murine immune cells. Here, we show that WASp deficiency is associated with impaired rapamycin-induced autophagosome formation and trafficking to lysosomes in primary human monocyte-derived macrophages (MDMs). WASp reconstitution in vitro and in WAS patients following clinical gene therapy restores autophagic flux and is dependent on the actin-related protein complex ARP2/3. Induction of mitochondrial damage with CCCP, as a model of selective autophagy, also reveals a novel ARP2/3-dependent role for WASp in formation of sequestrating actin cages and maintenance of mitochondrial network integrity. Furthermore, mitochondrial respiration is suppressed in WAS patient MDMs and unable to achieve normal maximal activity when stressed, indicating profound intrinsic metabolic dysfunction. Taken together, we provide evidence of new and important roles of human WASp in autophagic processes and immunometabolic regulation, which may mechanistically contribute to the complex WAS immunophenotype.
    Keywords:  cell biology; human; immunology; inflammation; mouse
  6. Autophagy. 2020 Nov 05.
      Lysosomes are digestive organelles in cells containing many hydrolases, and also serve as a signaling hub to integrate intracellular and extracellular inputs; therefore, the integrity of lysosomes is critical for cellular homeostasis. Many agents and conditions can damage lysosomal membranes, which lead to leakage of lysosomal acidic contents into the cytosol thus becoming harmful for cells. Accordingly, cells have developed several defense systems to cope with damaged lysosomes, but underlying mechanisms of each system and their cross-talks are unclear. In our recent study, we found that a master transcription factor regulating autophagy and lysosomal biogenesis, TFEB (transcription factor EB) is activated during lysosomal damage, and this activation depends on an autophagy-independent function of lipidated LC3, which localizes on lysosomes. We further showed that this regulatory mechanism is essential to prevent the progression of the crystal nephropathy that accompanies lysosomal damage.
    Keywords:  Autophagy; LC3; TFEB; TRPML1; lysosome
  7. Cells. 2020 Nov 04. pii: E2416. [Epub ahead of print]9(11):
      The multifunctional HSP70 co-chaperone BAG3 (BCL-2-associated athanogene 3) represents a key player in the quality control of the cellular proteostasis network. In response to stress, BAG3 specifically targets aggregation-prone proteins to the perinuclear aggresome and promotes their degradation via BAG3-mediated selective macroautophagy. To adapt cellular homeostasis to stress, BAG3 modulates and functions in various cellular processes and signaling pathways. Noteworthy, dysfunction and deregulation of BAG3 and its pathway are pathophysiologically linked to myopathies, cancer, and neurodegenerative disorders. Here, we report a BAG3 proteomic signature under proteostasis stress. To elucidate the dynamic and multifunctional action of BAG3 in response to stress, we established BAG3 interactomes under basal and proteostasis stress conditions by employing affinity purification combined with quantitative mass spectrometry. In addition to the identification of novel potential BAG3 interactors, we defined proteins whose interaction with BAG3 was altered upon stress. By functional annotation and protein-protein interaction enrichment analysis of the identified potential BAG3 interactors, we confirmed the multifunctionality of BAG3 and highlighted its crucial role in diverse cellular signaling pathways and processes, ensuring cellular proteostasis and cell viability. These include protein folding and degradation, gene expression, cytoskeleton dynamics (including cell cycle and transport), as well as granulostasis, in particular.
    Keywords:  BAG3; autophagy; interactome; protein quality control; proteostasis; stress response
  8. Int J Mol Sci. 2020 Nov 02. pii: E8196. [Epub ahead of print]21(21):
      In recent years, the study of single nucleotide polymorphisms (SNPs) has gained increasing importance in biomedical research, as they can either be at the molecular origin of a determined disorder or directly affect the efficiency of a given treatment. In this regard, sequence variations in genes involved in pro-survival cellular pathways are commonly associated with pathologies, as the alteration of these routes compromises cellular homeostasis. This is the case of autophagy, an evolutionarily conserved pathway that counteracts extracellular and intracellular stressors by mediating the turnover of cytosolic components through lysosomal degradation. Accordingly, autophagy dysregulation has been extensively described in a wide range of human pathologies, including cancer, neurodegeneration, or inflammatory alterations. Thus, it is not surprising that pathogenic gene variants in genes encoding crucial effectors of the autophagosome/lysosome axis are increasingly being identified. In this review, we present a comprehensive list of clinically relevant SNPs in autophagy-related genes, highlighting the scope and relevance of autophagy alterations in human disease.
    Keywords:  ATGs; SNPs; autophagic receptors; autophagy; lysosomes; pathology; polymorphisms; variants
  9. Mol Cell Biol. 2020 Nov 02. pii: MCB.00389-20. [Epub ahead of print]
      Besides the ubiquitin-proteasome-system, autophagy is a major degradation pathway within cells. It delivers invading pathogens, damaged organelles, aggregated proteins and other macromolecules from the cytosol to the lysosome for bulk degradation. This so-called canonical autophagy activity contributes to the maintenance of organelle, protein and metabolite homeostasis as well as innate immunity. Over the past years, numerous studies rapidly deepened our knowledge on the autophagy machinery and its regulation; driven by the fact that impairment of autophagy is associated with several human pathologies including cancer, immune diseases and neurodegenerative disorders. Unexpectedly, components of the autophagic machinery were also found to participate in various processes that did not involve lysosomal delivery of cytosolic constituents. These functions are hereafter defined as non-canonical autophagy. Regarding neurodegenerative diseases, most research was performed in neurons, while for a long-time microglia received considerably less attention. Concomitant with the notion that microglia greatly contribute to brain health, the understanding of the role of autophagy in microglia expanded. To facilitate an overview of the current knowledge, we present herein the fundamentals as well as the recent advances of canonical and non-canonical autophagy functions in microglia.
  10. Ageing Res Rev. 2020 Oct 29. pii: S1568-1637(20)30338-X. [Epub ahead of print] 101203
      Dysregulated proteostasis is one of the hallmarks of ageing. Damaged proteins may impair cellular function and their accumulation may lead to tissue dysfunction and disease. This is why protective mechanisms to safeguard the cell proteome have evolved. These mechanisms consist of cellular machineries involved in protein quality control, including regulators of protein translation, folding, trafficking and degradation. In eukaryotic cells, protein degradation occurs via two main pathways: the ubiquitin-proteasome system (UPS) and the autophagy-lysosome pathway. Although distinct pathways, they are not isolated systems and have a complementary nature, as evidenced by recent studies. These findings raise the question of how autophagy and the proteasome crosstalk. In this review we address how the two degradation pathways impact each other, thereby adding a new layer of regulation to protein degradation. We also analyze the implications of the UPS and autophagy in ageing.
    Keywords:  Ageing; UPS-autophagy crosstalk; autophagy; proteostasis; ubiquitin-proteasome system
  11. Pharmacol Ther. 2020 Oct 24. pii: S0163-7258(20)30244-8. [Epub ahead of print] 107713
      The old Greek saying "Panta Rhei" ("everything flows") is true for all life and all living things in general. It also becomes nicely evident when looking closely into cells. There, material from the extracellular space is taken up by endocytic processes and transported to endosomes where it is sorted either for recycling or degradation. Cargo is also packaged for export through exocytosis involving the Golgi network, lysosomes and other organelles. Everything in this system is in constant motion and many proteins are necessary to coordinate transport along the different intracellular pathways to avoid chaos. Among these proteins are ion channels., in particular TRPML channels (mucolipins) and two-pore channels (TPCs) which reside on endosomal and lysosomal membranes to speed up movement between organelles, e.g. by regulating fusion and fission; they help readjust pH and osmolarity changes due to such processes, or they promote exocytosis of export material. Pathophysiologically, these channels are involved in neurodegenerative, metabolic, retinal and infectious diseases, cancer, pigmentation defects, and immune cell function, and thus have been proposed as novel pharmacological targets, e.g. for the treatment of lysosomal storage disorders, Duchenne muscular dystrophy, or different types of cancer. Here, we discuss the similarities but also differences of TPCs and TRPMLs in regulating phagocytosis, autophagy and lysosomal exocytosis, and we address the contradictions and open questions in the field relating to the roles TPCs and TRPMLs play in these different processes.
    Keywords:  Autophagy; Calcium; Endo-lysosomal cation channel; Endocytic pathway; Lysosomal exocytosis; MCOLN; Neurodegeneration; TPC; TPCN; TRPML
  12. Curr Biol. 2020 Oct 30. pii: S0960-9822(20)31530-X. [Epub ahead of print]
      Organelles of the endomembrane system maintain their identity and integrity during growth or stress conditions by homeostatic mechanisms that regulate membrane flux and biogenesis. At lysosomes and endosomes, the Fab1 lipid kinase complex and the nutrient-regulated target of rapamycin complex 1 (TORC1) control the integrity of the endolysosomal homeostasis and cellular metabolism. Both complexes are functionally connected as Fab1-dependent generation of PI(3,5)P2 supports TORC1 activity. Here, we identify Fab1 as a target of TORC1 on signaling endosomes, which are distinct from multivesicular bodies, and provide mechanistic insight into their crosstalk. Accordingly, TORC1 can phosphorylate Fab1 proximal to its PI3P-interacting FYVE domain, which causes Fab1 to shift to signaling endosomes, where it generates PI(3,5)P2. This, in turn, regulates (1) vacuole morphology, (2) recruitment of TORC1 and the TORC1-regulatory Rag GTPase-containing EGO complex to signaling endosomes, and (3) TORC1 activity. Thus, our study unravels a regulatory feedback loop between TORC1 and the Fab1 complex that controls signaling at endolysosomes.
    Keywords:  Fab1; PI(3,5)P2; TORC1; cellular signaling; late endosome; lipid kinase; lysosome; phosphoinositide; signaling endosome; vacuole
  13. Protein Cell. 2020 Nov 05.
      Autophagy is essential for the maintenance of cellular homeostasis and its dysfunction has been linked to various diseases. Autophagy is a membrane driven process and tightly regulated by membrane-associated proteins. Here, we summarized membrane lipid composition, and membrane-associated proteins relevant to autophagy from a spatiotemporal perspective. In particular, we focused on three important membrane remodeling processes in autophagy, lipid transfer for phagophore elongation, membrane scission for phagophore closure, and autophagosome-lysosome membrane fusion. We discussed the significance of the discoveries in this field and possible avenues to follow for future studies. Finally, we summarized the membrane-associated biochemical techniques and assays used to study membrane properties, with a discussion of their applications in autophagy.
    Keywords:  ATG2; ESCRT; autophagy; elongation; fusion; lipid transfer; membrane-associated biochemistry assays; membrane-associated proteins; scission
  14. PLoS Genet. 2020 Nov 02. 16(11): e1009196
      The Target of rapamycin (TOR) protein kinase forms part of TOR complex 1 (TORC1) and TOR complex 2 (TORC2), two multi-subunit protein complexes that regulate growth, proliferation, survival and developmental processes by phosphorylation and activation of AGC-family kinases. In the fission yeast, Schizosaccharomyces pombe, TORC2 and its target, the AGC kinase Gad8 (an orthologue of human AKT or SGK1) are required for viability under stress conditions and for developmental processes in response to starvation cues. In this study, we describe the isolation of gad8 mutant alleles that bypass the requirement for TORC2 and reveal a separation of function of TORC2 and Gad8 under stress conditions. In particular, osmotic and nutritional stress responses appear to form a separate branch from genotoxic stress responses downstream of TORC2-Gad8. Interestingly, TORC2-independent mutations map into the regulatory PIF pocket of Gad8, a highly conserved motif in AGC kinases that regulates substrate binding in PDK1 (phosphoinositide dependent kinase-1) and kinase activity in several AGC kinases. Gad8 activation is thought to require a two-step mechanism, in which phosphorylation by TORC2 allows further phosphorylation and activation by Ksg1 (an orthologue of PDK1). We focus on the Gad8-K263C mutation and demonstrate that it renders the Gad8 kinase activity independent of TORC2 in vitro and independent of the phosphorylation sites of TORC2 in vivo. Molecular dynamics simulations of Gad8-K263C revealed abnormal high flexibility at T387, the phosphorylation site for Ksg1, suggesting a mechanism for the TORC2-independent Gad8 activity. Significantly, the K263 residue is highly conserved in the family of AGC-kinases, which may suggest a general way of keeping their activity in check when acting downstream of TOR complexes.
  15. Clin Transl Med. 2020 Oct;10(6): e208
      BACKGROUND: Autophagy is an intracellular degradation pathway conserved in eukaryotes. ANXA6 (annexin A6) belongs to a family of calcium-dependent membrane and phospholipid-binding proteins. Here, we identify ANXA6 as a newly synthesized protein in starvation-induced autophagy and validate it as a novel autophagy modulator that regulates autophagosome formation.RESULTS: ANXA6 knockdown attenuates starvation-induced autophagy, while restoration of its expression enhances autophagy. GO (gene ontology) analysis of ANXA6 targets showed that ANXA6 interacts with many RAB GTPases and targets endocytosis and phagocytosis pathways, indicating that ANXA6 exerts its function through protein trafficking. ATG9A (autophagy-related 9A) is the sole multispanning transmembrane protein and its trafficking through recycling endosomes is an essential step for autophagosome formation. Our results showed that ANXA6 enables appropriate ATG9A+ vesicle trafficking from endosomes to autophagosomes through RAB proteins or F-actin. In addition, restoration of ANXA6 expression suppresses mTOR (mammalian target of rapamycin) activity through the inhibition of the PI3K (phosphoinositide 3-kinase)-AKT and ERK (extracellular signal-regulated kinase) signaling pathways, which is a negative regulator of autophagy. Functionally, ANXA6 expression is correlated with LC3 (microtubule-associated protein 1 light chain 3) expression in cervical cancer, and ANXA6 inhibits tumorigenesis through autophagy induction.
    CONCLUSIONS: Our results reveal an important mechanism for ANXA6 in tumor suppression and autophagy regulation.
    Keywords:  ANXA6; ATG9A; ERK; autophagy; cervical cancer; mTOR
  16. Int J Mol Sci. 2020 Oct 30. pii: E8135. [Epub ahead of print]21(21):
      Organotin compounds represent potential cancer therapeutics due to their pro-apoptotic action. We recently synthesized the novel organotin ferulic acid derivative tributyltin (IV) ferulate (TBT-F) and demonstrated that it displays anti-tumor properties in colon cancer cells related with autophagic cell death. The purpose of the present study was to elucidate the mechanism of TBT-F action in colon cancer cells. We specifically show that TBT-F-dependent autophagy is determined by a rapid generation of reactive oxygen species (ROS) and correlated with endoplasmic reticulum (ER) stress. TBT-F evoked nuclear factor erythroid-2 related factor 2 (Nrf2)-mediated antioxidant response and Nrf2 silencing by RNA interference markedly increased the anti-tumor efficacy of the compound. Moreover, as a consequence of ROS production, TBT-F increased the levels of glucose regulated protein 78 (Grp78) and C/EBP homologous protein (CHOP), two ER stress markers. Interestingly, Grp78 silencing produced significant decreasing effects on the levels of the autophagic proteins p62 and LC3-II, while only p62 decreased in CHOP-silenced cells. Taken together, these results indicate that ROS-dependent ER stress and autophagy play a major role in the TBT-F action mechanism in colon cancer cells and open a new perspective to consider the compound as a potential candidate for colon cancer treatment.
    Keywords:  ROS; autophagic cell death; endoplasmic reticulum stress; oxidative stress; tributyltin (IV) derivative
  17. FEBS J. 2020 Nov 01.
      Protein misfolding is a major driver of ageing-associated frailty and disease pathology. Although all cells possess multiple, well-characterised protein quality control systems to mitigate the toxicity of misfolded proteins, how they are integrated to maintain protein homeostasis ('proteostasis') in health-and how their dis-integration contributes to disease-is still an exciting and fast-paced area of research. Under physiological conditions, the predominant route for misfolded protein clearance involves ubiquitylation and proteasome-mediated degradation. When the capacity of this route is overwhelmed-as happens during conditions of acute environmental stress, or chronic ageing-related decline-alternative routes for protein quality control are activated. In this review, we summarise our current understanding of how proteasome-targeted misfolded proteins are re-trafficked to alternative protein quality control routes such as juxta-nuclear sequestration and selective autophagy when the ubiquitin-proteasome system is compromised. We also discuss the molecular determinants of these alternative protein quality control systems, attempt to clarify distinctions between various cytoplasmic spatial quality control inclusion bodies (e.g., Q-bodies, p62-bodies, JUNQ, aggresomes, and aggresome-like induced structures 'ALIS'), and speculate on emerging concepts in the field that we hope will spur future research-with the potential to benefit the rational development of healthy ageing strategies.
    Keywords:  PQC; cancer; chaperone; heat shock protein; neurodegeneration; protein aggregate; protein degradation; protein triage; ubiquitin; ubiquitination
  18. Mol Psychiatry. 2020 Nov 06.
      Although the activities of many signaling pathways are dysregulated during the progression of neurodegenerative and muscle degeneration disorders, the precise sequence of cellular events leading to degeneration has not been fully elucidated. Two kinases of particular interest, the growth-promoting Tor kinase and the energy sensor AMPK, appear to show reciprocal changes in activity during degeneration, with increased Tor activity and decreased AMPK activity reported. These changes in activity have been predicted to cause degeneration by attenuating autophagy, leading to the accumulation of unfolded protein aggregates and dysfunctional mitochondria, the consequent increased production of reactive oxygen species (ROS), and ultimately oxidative damage. Here we propose that this increased ROS production not only causes oxidative damage but also ultimately induces an oxidative stress response that reactivates the redox-sensitive AMPK and activates the redox-sensitive stress kinase JNK. Activation of these kinases reactivates autophagy. Because at this late stage, cells have become filled with dysfunctional mitochondria and protein aggregates, which are autophagy targets, this autophagy reactivation induces degeneration. The mechanism proposed here emphasizes that the process of degeneration is dynamic, that dysregulated signaling pathways change over time and can transition from deleterious to beneficial and vice versa as degeneration progresses.
  19. Cells. 2020 Nov 02. pii: E2399. [Epub ahead of print]9(11):
      Lysosomal function has a central role in maintaining neuronal homeostasis, and, accordingly, lysosomal dysfunction has been linked to neurodegeneration and particularly to Parkinson's disease (PD). Lysosomes are the converging step where the substrates delivered by autophagy and endocytosis are degraded in order to recycle their primary components to rebuild new macromolecules. Genetic studies have revealed the important link between the lysosomal function and PD; several of the autosomal dominant and recessive genes associated with PD as well as several genetic risk factors encode for lysosomal, autophagic, and endosomal proteins. Mutations in these PD-associated genes can cause lysosomal dysfunction, and since α-synuclein degradation is mostly lysosomal-dependent, among other consequences, lysosomal impairment can affect α-synuclein turnover, contributing to increase its intracellular levels and therefore promoting its accumulation and aggregation. Recent studies have also highlighted the bidirectional link between Parkinson's disease and lysosomal storage diseases (LSD); evidence includes the presence of α-synuclein inclusions in the brain regions of patients with LSD and the identification of several lysosomal genes involved in LSD as genetic risk factors to develop PD.
    Keywords:  Parkinson’s disease; autophagy; endocytosis; glucocerebrosidase; lysosomal storage diseases; lysosomes; α-synuclein
  20. Int J Mol Sci. 2020 Oct 30. pii: E8105. [Epub ahead of print]21(21):
      Doxorubicin (DOX) is a highly effective chemotherapeutic agent used in the treatment of various cancer types. Nevertheless, it is well known that DOX promotes the development of severe cardiovascular complications. Therefore, investigation into the underlying mechanisms that drive DOX-induced cardiotoxicity is necessary to develop therapeutic countermeasures. In this regard, autophagy is a complex catabolic process that is increased in the heart following DOX exposure. However, conflicting evidence exists regarding the role of autophagy dysregulation in the etiology of DOX-induced cardiac dysfunction. This study aimed to clarify the contribution of autophagy to DOX-induced cardiotoxicity by specifically inhibiting autophagosome formation using a dominant negative autophagy gene 5 (ATG5) adeno-associated virus construct (rAAV-dnATG5). Acute (2-day) and delayed (9-day) effects of DOX (20 mg/kg intraperitoneal injection (i.p.)) on the hearts of female Sprague-Dawley rats were assessed. Our data confirm established detrimental effects of DOX on left ventricular function, redox balance and mitochondrial function. Interestingly, targeted inhibition of autophagy in the heart via rAAV-dnATG5 in DOX-treated rats ameliorated the increase in mitochondrial reactive oxygen species emission and the attenuation of cardiac and mitochondrial function, but only at the acute timepoint. Deviation in the effects of autophagy inhibition at the 2- and 9-day timepoints appeared related to differences in ATG5-ATG12 conjugation, as this marker of autophagosome formation was significantly elevated 2 days following DOX exposure but returned to baseline at day 9. DOX exposure may transiently upregulate autophagy signaling in the rat heart; thus, long-term inhibition of autophagy may result in pathological consequences.
    Keywords:  adriamycin; anthracycline; cardiotoxicity; chemotherapy; oxidative stress
  21. Cells. 2020 Nov 04. pii: E2413. [Epub ahead of print]9(11):
      Over the past 20 years, there has been a drastically increased understanding of the genetic basis of Amyotrophic Lateral Sclerosis. Despite the identification of more than 40 different ALS-causing mutations, the accumulation of neurotoxic misfolded proteins, inclusions, and aggregates within motor neurons is the main pathological hallmark in all cases of ALS. These protein aggregates are proposed to disrupt cellular processes and ultimately result in neurodegeneration. One of the main reasons implicated in the accumulation of protein aggregates may be defective autophagy, a highly conserved intracellular "clearance" system delivering misfolded proteins, aggregates, and damaged organelles to lysosomes for degradation. Autophagy is one of the primary stress response mechanisms activated in highly sensitive and specialised neurons following insult to ensure their survival. The upregulation of autophagy through pharmacological autophagy-inducing agents has largely been shown to reduce intracellular protein aggregate levels and disease phenotypes in different in vitro and in vivo models of neurodegenerative diseases. In this review, we explore the intriguing interface between ALS and autophagy, provide a most comprehensive summary of autophagy-targeted drugs that have been examined or are being developed as potential treatments for ALS to date, and discuss potential therapeutic strategies for targeting autophagy in ALS.
    Keywords:  amyotrophic lateral sclerosis; autophagy; motor neuron disease; therapeutics
  22. Ageing Res Rev. 2020 Oct 31. pii: S1568-1637(20)30342-1. [Epub ahead of print] 101207
      In mammals, the Keap1-Nrf2-ARE pathway (henceforth, "the Nrf2 pathway") and autophagy are major intracellular defence systems that combat oxidative damage and maintain homeostasis. p62/SQSTM1, a ubiquitin-binding autophagy receptor protein, links the Nrf2 pathway and autophagy. Phosphorylation of p62 dramatically enhances its affinity for Keap1, which induces Keap1 to release Nrf2, and the p62-Keap1 heterodimer recruits LC3 and mediates the permanent degradation of Keap1 in the selective autophagy pathway. Eventually, Nrf2 accumulates in the cytoplasm and then translocates into the nucleus to activate the transcription of downstream genes that encode antioxidant enzymes, which protect cells from oxidative damage. Since Nrf2 also upregulates the expression of the p62 gene, a p62-Keap1-Nrf2 positive feedback loop is created that further enhances the protective effect on cells. Studies have shown that the p62-activated noncanonical Nrf2 pathway is an important marker of neurodegenerative diseases. The p62-Keap1-Nrf2 positive feedback loop and the Nrf2 pathway are involved in eliminating the ROS and protein aggregates induced by AD. Therefore, maintaining the homeostasis of the p62-Keap1-Nrf2 positive feedback loop, which is a bridge between the Nrf2 pathway and autophagy, may be a potential target for the treatment of AD.
    Keywords:  .; Alzheimer; Autophagy; Nrf2 pathway; Oxidative stress; p62-Keap1-Nrf2; positive feedback loop; s disease; ’
  23. Front Cell Dev Biol. 2020 ;8 580933
      The induction of autophagy, the catabolic pathway by which damaged or unnecessary cellular components are subjected to lysosome-mediated degradation and recycling, is impaired in Collagen VI (COL6) null mice and COL6-related myopathies. This autophagic impairment causes an accumulation of dysfunctional mitochondria, which in turn leads to myofiber degeneration. Our previous work showed that reactivation of autophagy in COL6-related myopathies is beneficial for muscle structure and function both in the animal model and in patients. Here we show that pterostilbene (Pt)-a non-toxic polyphenol, chemically similar to resveratrol but with a higher bioavailability and metabolic stability-strongly promotes in vivo autophagic flux in the skeletal muscle of both wild-type and COL6 null mice. Reactivation of autophagy in COL6-deficient muscles was also paralleled by several beneficial effects, including significantly decreased incidence of spontaneous apoptosis, recovery of ultrastructural defects and muscle remodeling. These findings point at Pt as an effective autophagy-inducing nutraceutical for skeletal muscle with great potential in counteracting the major pathogenic hallmarks of COL6-related myopathies, a valuable feature that may be also beneficial in other muscle pathologies characterized by defective regulation of the autophagic machinery.
    Keywords:  Collagen VI; autophagy; congenital muscular dystrophies; muscle remodeling; nutraceutical agent; skeletal muscle
  24. Nat Commun. 2020 11 03. 11(1): 5559
      Cholesterol import in mammalian cells is mediated by the LDL receptor pathway. Here, we perform a genome-wide CRISPR screen using an endogenous cholesterol reporter and identify >100 genes involved in LDL-cholesterol import. We characterise C18orf8 as a core subunit of the mammalian Mon1-Ccz1 guanidine exchange factor (GEF) for Rab7, required for complex stability and function. C18orf8-deficient cells lack Rab7 activation and show severe defects in late endosome morphology and endosomal LDL trafficking, resulting in cellular cholesterol deficiency. Unexpectedly, free cholesterol accumulates within swollen lysosomes, suggesting a critical defect in lysosomal cholesterol export. We find that active Rab7 interacts with the NPC1 cholesterol transporter and licenses lysosomal cholesterol export. This process is abolished in C18orf8-, Ccz1- and Mon1A/B-deficient cells and restored by a constitutively active Rab7. The trimeric Mon1-Ccz1-C18orf8 (MCC) GEF therefore plays a central role in cellular cholesterol homeostasis coordinating Rab7 activation, endosomal LDL trafficking and NPC1-dependent lysosomal cholesterol export.
  25. J Mol Med (Berl). 2020 Oct 31.
      Toll-interacting protein (TOLLIP) is a ubiquitous intracellular adaptor protein involved in multiple intracellular signaling pathways. It plays a key role in mediating inflammatory intracellular responses, promoting autophagy, and enabling vacuole transport within the cell. TOLLIP is being increasingly recognized for its role in disease pathophysiology through involvement in these three primary pathways. Recent research also indicates that TOLLIP is involved in nuclear-cytoplasmic transfer, although this area requires further exploration. TOLLIP is involved in the pathophysiologic pathways associated with neurodegenerative diseases, pulmonary diseases, cardiovascular disease, inflammatory bowel disease, and malignancy. We postulate that TOLLIP plays an integral role in the disease pathophysiology of other conditions involved in vacuole trafficking and autophagy. We suggest that future research in this field should investigate the role of TOLLIP in the pathogenesis of these multiple conditions. This research has the potential to inform disease mechanisms and identify novel opportunities for therapeutic advances in multiple disease processes.
    Keywords:  Idiopathic pulmonary fibrosis; Inflammatory bowel disease; Neoplasms; Neurodegenerative diseases; TOLLIP
  26. PLoS One. 2020 ;15(11): e0239119
      Autophagy is an important factor in liver ischemia-reperfusion injury. In the current study we investigate the function of interferon regulatory factor-1 (IRF1) in regulating autophagy to promote hepatic ischemia reperfusion injury (IR). The high expression of IRF1 during hepatic IR exhibited increased liver damage and was associated with activation of autophagy shown by Western blot markers, as well as immunofluorescent staining for autophagosomes. These effects were diminished by IRF1 deficiency in IRF1 knock out (KO) mice. Moreover, the autophagy inhibitor 3-MA decreased IR-induced liver necrosis and markedly abrogated the rise in liver injury tests (AST/ALT). β-catenin expression decreased during liver IR and was increased in the IRF1 KO mice. Immunoprecipitation assay showed the binding between IRF1 and β-catenin. Overexpression of IRF1 induced autophagy and also inhibited the expression of β-catenin. β-catenin inhibitor increased autophagy while β-catenin agonist suppressed autophagy in primary mouse hepatocytes. These results indicate that IRF1 induced autophagy aggravates hepatic IR injury in part by inhibiting β-catenin and suggests that targeting IRF1 may be an effective strategy in reducing hepatic IR injury.
  27. Nat Commun. 2020 Nov 06. 11(1): 5640
      Lymphangioleiomyomatosis (LAM) is a rare fatal cystic lung disease due to bi-allelic inactivating mutations in tuberous sclerosis complex (TSC1/TSC2) genes coding for suppressors of the mechanistic target of rapamycin complex 1 (mTORC1). The origin of LAM cells is still unknown. Here, we profile a LAM lung compared to an age- and sex-matched healthy control lung as a hypothesis-generating approach to identify cell subtypes that are specific to LAM. Our single-cell RNA sequencing (scRNA-seq) analysis reveals novel mesenchymal and transitional alveolar epithelial states unique to LAM lung. This analysis identifies a mesenchymal cell hub coordinating the LAM disease phenotype. Mesenchymal-restricted deletion of Tsc2 in the mouse lung produces a mTORC1-driven pulmonary phenotype, with a progressive disruption of alveolar structure, a decline in pulmonary function, increase of rapamycin-sensitive expression of WNT ligands, and profound female-specific changes in mesenchymal and epithelial lung cell gene expression. Genetic inactivation of WNT signaling reverses age-dependent changes of mTORC1-driven lung phenotype, but WNT activation alone in lung mesenchyme is not sufficient for the development of mouse LAM-like phenotype. The alterations in gene expression are driven by distinctive crosstalk between mesenchymal and epithelial subsets of cells observed in mesenchymal Tsc2-deficient lungs. This study identifies sex- and age-specific gene changes in the mTORC1-activated lung mesenchyme and establishes the importance of the WNT signaling pathway in the mTORC1-driven lung phenotype.
  28. J Cardiovasc Pharmacol. 2020 Oct 27.
      Foam cells are the main pathological components of atherosclerosis. Therapies reducing foam cell formation can effectively prevent atherosclerotic diseases and cardiovascular events. Beyond lowering plasma cholesterol levels, the pleiotropic functions of statins in atherosclerosis have not been fully elucidated. In the present study, atorvastatin reduced cholesterol content and increased cholesterol efflux from foam cells in a concentration-dependent manner. Atorvastatin (10μM) inhibited foam cell formation within 48 h. Furthermore, we found that atorvastatin inhibited foam cell formation by promoting lipophagy, which was manifested by increased autophagy-related gene 5 (Atg5) expression, elevated ratio of microtubule-associated protein1 light chain 3 (LC3) II to LC3I, reduced p62 expression, and increased LC3 and lipid droplets (LD) colocalization in foam cells treated with atorvastatin. The autophagy inducer, rapamycin (Rap), did not increase the lipophagy enhancement effect of atorvastatin, but the autophagy inhibitor, 3-methyladenine (3-MA), suppressed the effect of atorvastatin on Atg5 expression and the LC3II/LC3I ratio, as well as the increased p62 expression, suppressed lipophagy, attenuated cholesterol efflux and increased cholesterol content in foam cells. Further analysis revealed that atorvastatin promoted lipophagy by upregulating AMP-activated protein kinase (AMPK) phosphorylation, and downregulating mammalian target of rapamycin (mTOR) phosphorylation, whereas the AMPK inhibiter, compound C, attenuated these effects. In conclusion, atorvastatin reduced lipid accumulation and promoted cholesterol efflux by enhancing lipophagy in foam cells and thereby inhibited foam cell formation. The enhanced lipophagy of foam cells was exerted through the AMPK/mTOR signaling pathway.
  29. FASEB J. 2020 Nov 01.
      The impairment of autophagy can cause cellular metabolic perturbations involved in endothelial-to-mesenchymal transition (EndoMT). However, the interplay between the cellular autophagy machinery and endothelial metabolism remains elusive. Sirtuin 3 (SIRT3), an NAD-dependent deacetylase, is a major cellular sensor of energy metabolism. The aim of this work was to determine the role of SIRT3-mediated autophagy in cellular metabolism and the process of EndoMT. We demonstrated that Angiotensin II (Ang II) led to defective autophagic flux and high levels of glycolysis in endothelial cells (ECs) accompanied by a loss of mitochondrial SIRT3 during EndoMT. The loss of SIRT3 further induced the hyperacetylation of endogenous autophagy-regulated gene 5 (ATG5), which in turn inhibited autophagosome maturation and increased pyruvate kinase M2 (PKM2) dimer expression. The M2 dimer is the less active form of PKM2, which drives glucose through aerobic glycolysis. Additionally, TEPP-46, a selective PKM2 tetramer activator, produced lower concentrations of lactate and led to the reduction of EndoMT both in vitro and in vivo. In parallel, the blockade of lactate influx from ECs into vascular smooth muscle cells (VSMCs) downregulated synthetic VSMC markers. EC-specific SIRT3 transgenic mice exhibited reduced endothelial cell transition but partial rescue of vascular fibrosis and collagen accumulation. Taken together, these findings reveal that SIRT3 regulates EndoMT by improving the autophagic degradation of PKM2. Pharmacological targeting of glycolysis metabolism may, therefore, represent an effective therapeutic strategy for hypertensive vascular remodeling.
    Keywords:  PKM2; SIRT3; autophagy; endothelial-to-mesenchymal transition; glycolysis
  30. Biochim Biophys Acta Rev Cancer. 2020 Oct 22. pii: S0304-419X(20)30174-8. [Epub ahead of print]1875(1): 188455
      Dysregulation of mRNA translation is involved in the onset and progression of different types of cancer. To gain insight into novel genetic strategies to avoid this malady, we reviewed the available genomic, transcriptomic, and proteomic data about the translational machinery from the naked-mole rat (NMR) Heterocephalus glaber, a new model of study that exhibits high resistance to cancer. The principal features that might confer cancer resistance are 28S rRNA fragmentation, RPL26 and eIF4G overexpression, global downregulation of mTOR pathway, specific amino acid residues in RAPTOR (P908) and RICTOR (V1695), and the absence of 4E-BP3. These features are not only associated with cancer but also might couple longevity and adaptation to hypoxia. We propose that the regulation of translation is among the strategies endowing NMR cancer resistance.
    Keywords:  Cancer; Heterocephalus glaber; Hypoxia; Naked mole-rat; Translational control; mTOR
  31. Neuron. 2020 Oct 28. pii: S0896-6273(20)30773-X. [Epub ahead of print]
      Neurons are known to rely on autophagy for removal of defective proteins or organelles to maintain synaptic neurotransmission and counteract neurodegeneration. In spite of its importance for neuronal health, the physiological substrates of neuronal autophagy in the absence of proteotoxic challenge have remained largely elusive. We use knockout mice conditionally lacking the essential autophagy protein ATG5 and quantitative proteomics to demonstrate that loss of neuronal autophagy causes selective accumulation of tubular endoplasmic reticulum (ER) in axons, resulting in increased excitatory neurotransmission and compromised postnatal viability in vivo. The gain in excitatory neurotransmission is shown to be a consequence of elevated calcium release from ER stores via ryanodine receptors accumulated in axons and at presynaptic sites. We propose a model where neuronal autophagy controls axonal ER calcium stores to regulate neurotransmission in healthy neurons and in the brain.
    Keywords:  autophagy, ERphagy, presynapse, neurotransmission, endoplasmic reticulum, calcium, ryanodine receptor
  32. Cells. 2020 Oct 29. pii: E2372. [Epub ahead of print]9(11):
      Modeling human infectious diseases using the early life stages of zebrafish provides unprecedented opportunities for visualizing and studying the interaction between pathogens and phagocytic cells of the innate immune system. Intracellular pathogens use phagocytes or other host cells, like gut epithelial cells, as a replication niche. The intracellular growth of these pathogens can be counteracted by host defense mechanisms that rely on the autophagy machinery. In recent years, zebrafish embryo infection models have provided in vivo evidence for the significance of the autophagic defenses and these models are now being used to explore autophagy as a therapeutic target. In line with studies in mammalian models, research in zebrafish has shown that selective autophagy mediated by ubiquitin receptors, such as p62, is important for host resistance against several bacterial pathogens, including Shigella flexneri, Mycobacterium marinum, and Staphylococcus aureus. Furthermore, an autophagy related process, Lc3-associated phagocytosis (LAP), proved host beneficial in the case of Salmonella Typhimurium infection but host detrimental in the case of S. aureus infection, where LAP delivers the pathogen to a replication niche. These studies provide valuable information for developing novel therapeutic strategies aimed at directing the autophagy machinery towards bacterial degradation.
    Keywords:  Cyba; Dram1; LAP; Optn; Rubcn; autophagy; innate immunity; p62; tuberculosis zebrafish
  33. EMBO Rep. 2020 Nov 05. 21(11): e51652
      Mitochondrial homeostasis is necessary for the maintenance of cellular function and neuronal survival. Mitochondrial quality is tightly regulated by mitophagy, in which defective/superfluous mitochondria are degraded and recycled. Here, Hara et al demonstrate that induction of mitophagy via iron depletion suppresses the development of hepatocellular carcinoma (HCC). This work suggests turning up mitophagy as a potential therapeutic strategy against liver cancer.
  34. Carcinogenesis. 2020 Nov 04. pii: bgaa114. [Epub ahead of print]
      Age and DNA repair deficiencies are strong risk factors for developing cancer. This is reflected in the comorbidity of cancer with premature aging diseases associated with DNA damage repair deficiencies. Recent research has suggested that DNA damage accumulation, telomere dysfunction, and the accompanying mitochondrial dysfunction exacerbate the aging process and may increase the risk of cancer development. Thus, an area of interest in both cancer and aging research is the elucidation of the dynamic crosstalk between the nucleus and the mitochondria. In this review, we discuss current research on aging and cancer with specific focus on the role of mitochondrial dysfunction in cancer and aging as well as how nuclear to mitochondrial DNA damage signaling may be a driving factor in the increased cancer incidence with aging. We suggest that therapeutic interventions aimed at induction of autophagy and mediation of nuclear to mitochondrial signaling may provide a mechanism for healthier aging and reduced tumorigenesis.
  35. Redox Biol. 2020 Oct 23. pii: S2213-2317(20)30972-1. [Epub ahead of print]38 101767
      Sepsis is the major cause of acute kidney injury (AKI) associated with high mortality rates. Mitochondrial dysfunction contributes to the pathophysiology of septic AKI. Mitophagy is an important mitochondrial quality control mechanism that selectively eliminates damaged mitochondria, but its role and regulation in septic AKI remain largely unknown. Here, we demonstrate the induction of mitophagy in mouse models of septic AKI induced by lipopolysaccharide (LPS) treatment or by cecal ligation and puncture. Mitophagy was also induced in cultured proximal tubular epithelial cells exposed to LPS. Induction of mitophagy under these experimental setting was suppressed by pink1 or park2 knockout, indicating the role of the PINK1/PARK2 pathway of mitophagy in septic AKI. In addition, sepsis induced more severe kidney injury and cell apoptosis in pink1 or park2 knockout mice than in wild-type mice, suggesting a beneficial role of mitophagy in septic AKI. Furthermore, in cultured renal tubular cells treated with LPS, knockdown of pink1 or park2 inhibited mitochondrial accumulation of the autophagy adaptor optineurin (OPTN) and silencing Optn inhibited LPS-induced mitophagy. Taken together, these findings suggest that the PINK1/PARK2 pathway of mitophagy plays an important role in mitochondrial quality control, tubular cell survival, and renal function in septic AKI.
    Keywords:  Acute kidney injury; Mitophgay; Optineurin; PARK2; PINK1; Sepsis
  36. Chem Soc Rev. 2020 Nov 06.
      As a ubiquitous degradation process in cells, autophagy plays important roles in various biological activities. However, the abnormality of autophagy is closely related to many diseases, such as aging, neurological disorder, and cancer. Thus, monitoring the process of autophagy in living cells has high significance in biological studies and diagnosis of related diseases. In order to real-time and in situ monitor the process of autophagy, various organic fluorescent probes have been explored in recent years owing to the advantages such as handy staining processes, flexible molecular design strategies, and near-nondestructive detection. However, this interesting and frontier topic has not been reviewed so far. In this tutorial review, we will focus on the latest breakthrough results of organic fluorescent probes in monitoring autophagy of living cells, especially the probe design strategies based on the several microenvironment changes of the autophagy process, and the responding mechanisms and bio-imaging applications in the autophagy process. In addition, we will discuss the shortcomings and limitations of the probes developed, such as susceptible to interference, unable to monitor the whole process, and lack of clinical applications. Finally, we will highlight some challenges and further opportunities in this field. This tutorial review may promote the development of more robust fluorescent probes to further reveal the mechanisms of autophagy, which is the basis of degradation and recycling of cell components.
  37. EMBO Rep. 2020 Nov 02. e51462
      The ER-bound kinase/endoribonuclease (RNase), inositol-requiring enzyme-1 (IRE1), regulates the phylogenetically most conserved arm of the unfolded protein response (UPR). However, the complex biology and pathology regulated by mammalian IRE1 cannot be fully explained by IRE1's one known, specific RNA target, X box-binding protein-1 (XBP1) or the RNA substrates of IRE1-dependent RNA degradation (RIDD) activity. Investigating other specific substrates of IRE1 kinase and RNase activities may illuminate how it performs these diverse functions in mammalian cells. We report that macrophage IRE1 plays an unprecedented role in regulating phosphatidylinositide-derived signaling lipid metabolites and has profound impact on the downstream signaling mediated by the mammalian target of rapamycin (mTOR). This cross-talk between UPR and mTOR pathways occurs through the unconventional maturation of microRNA (miR) 2137 by IRE1's RNase activity. Furthermore, phosphatidylinositol (3,4,5) phosphate (PI(3,4,5)P3 ) 5-phosphatase-2 (INPPL1) is a direct target of miR-2137, which controls PI(3,4,5)P3 levels in macrophages. The modulation of cellular PI(3,4,5)P3 /PIP2 ratio and anabolic mTOR signaling by the IRE1-induced miR-2137 demonstrates how the ER can provide a critical input into cell growth decisions.
    Keywords:  ER stress; hyperlipidemia; mTOR signaling; macrophage; microRNA
  38. J Pathol. 2020 Nov 02.
      Autophagy is a constitutive process that degrades, recycles and clears damaged proteins or organelles, yet, despite activation of this pathway abnormal proteins accumulate in neurons in neurodegenerative diseases, and in oligodendrocytes in white matter disorders. Here, we discuss the role of autophagy in white matter disorders including neurotropic infections, inflammatory diseases such as multiple sclerosis, and in hereditary metabolic disorders and acquired toxic-metabolic disorders. Once triggered due to cell stress, autophagy can enhance cell survival or cell death that may contribute to oligodendrocyte damage and myelin loss in white matter diseases. For some disorders, the mechanisms leading to myelin loss are clear while the aetiological agent and pathological mechanisms are unknown for other myelin disorders, although emerging studies indicate that a common mechanism underlying these disorders is dysregulation of autophagic pathways. In this review we discuss the alterations in the autophagic process in white matter disorders and the potential use of autophagy modulating agents as therapeutic approaches in these pathological conditions. This article is protected by copyright. All rights reserved.
    Keywords:  White matter disorders; autophagy; demyelinating disease; demyelination; leukodystrophy; multiple sclerosis; therapy
  39. J Cell Mol Med. 2020 Nov 01.
      Aseptic prosthetic loosening due to wear particle-induced inflammatory osteolysis is the main cause of failure for artificial joint replacement. The inflammatory response and the production of pro-osteoclastic factors lead to elevation of osteoclast formation and excessive activity results in extensive bone destruction around the bone-implant interface. Here we showed that Nepetin, a natural bioactive flavonoid with proven anti-inflammatory and anti-proliferative properties, potently inhibited RANKL-induced osteoclast differentiation, formation and bone resorption in vitro, and protected mice against the deleterious effects of titanium particle-induced calvarial osteolysis in vivo. Mechanistically, Nepetin attenuated RANKL-induced activation of NF-κB and MAPK signalling pathways and TRAF6-dependent ubiquitination of Beclin 1 which is necessary for the induction of autophagy. In brief, our study demonstrates the potential therapeutic application of Nepetin against osteoclast-mediated osteolytic diseases.
    Keywords:  TRAF6; bone destruction; nepetin; osteoclasts
  40. Proc Natl Acad Sci U S A. 2020 Nov 05. pii: 201920323. [Epub ahead of print]
      Members of the tripartite motif (TRIM) protein family have been shown to assemble into structures in both the nucleus and cytoplasm. One TRIM protein family member, TRIM5α, has been shown to form cytoplasmic bodies involved in restricting retroviruses such as HIV-1. Here we applied cryogenic correlated light and electron microscopy, combined with electron cryo-tomography, to intact mammalian cells expressing YFP-rhTRIM5α and found the presence of hexagonal nets whose arm lengths were similar to those of the hexagonal nets formed by purified TRIM5α in vitro. We also observed YFP-rhTRIM5α within a diversity of structures with characteristics expected for organelles involved in different stages of macroautophagy, including disorganized protein aggregations (sequestosomes), sequestosomes flanked by flat double-membraned vesicles (sequestosome:phagophore complexes), sequestosomes within double-membraned vesicles (autophagosomes), and sequestosomes within multivesicular autophagic vacuoles (amphisomes or autolysosomes). Vaults were also seen in these structures, consistent with their role in autophagy. Our data 1) support recent reports that TRIM5α can form both well-organized signaling complexes and nonsignaling aggregates, 2) offer images of the macroautophagy pathway in a near-native state, and 3) reveal that vaults arrive early in macroautophagy.
    Keywords:  TRIM5α-body; autophagy; cryo-CLEM/ECT; endoplasmic reticulum; hexagonal nets