bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2020‒09‒13
forty-nine papers selected by
Viktor Korolchuk
Newcastle University


  1. Genes (Basel). 2020 Sep 03. pii: E1043. [Epub ahead of print]11(9):
    Bjedov I, Rallis C.
      Ageing is a complex trait controlled by genes and the environment. The highly conserved mechanistic target of rapamycin signalling pathway (mTOR) is a major regulator of lifespan in all eukaryotes and is thought to be mediating some of the effects of dietary restriction. mTOR is a rheostat of energy sensing diverse inputs such as amino acids, oxygen, hormones, and stress and regulates lifespan by tuning cellular functions such as gene expression, ribosome biogenesis, proteostasis, and mitochondrial metabolism. Deregulation of the mTOR signalling pathway is implicated in multiple age-related diseases such as cancer, neurodegeneration, and auto-immunity. In this review, we briefly summarise some of the workings of mTOR in lifespan and ageing through the processes of transcription, translation, autophagy, and metabolism. A good understanding of the pathway's outputs and connectivity is paramount towards our ability for genetic and pharmacological interventions for healthy ageing and amelioration of age-related disease.
    Keywords:  Drosophila; TORC1; TORC2; ageing; autophagy; metabolism; nutrient-response; transcription; translation; yeast
    DOI:  https://doi.org/10.3390/genes11091043
  2. J Mol Biol. 2020 Sep 04. pii: S0022-2836(20)30528-3. [Epub ahead of print]
    Margolis HK, Katzenell S, Leary KA, Ragusa MJ.
      Selective autophagy is the capture of specific cytosolic contents in double membrane vesicles that subsequently fuse with the vacuole or lysosome, thereby delivering cargo for degradation. Selective autophagy receptors (SARs) mark the cargo for degradation and, in yeast, recruit Atg11, the scaffolding protein for selective autophagy initiation. The mitochondrial protein Atg32 is the yeast SAR that mediates mitophagy, the selective autophagic capture of mitochondria. Atg11-Atg32 interactions concentrate Atg32 into puncta that are thought to represent sites of mitophagy initiation. However, it is unclear how Atg11 concentrates Atg32 to generate mitophagy initiation sites. We show here that the coiled coil 3 (CC3) domain of Atg11 is required for concentrating Atg32 into puncta. We determined the structure of the majority of the CC3, demonstrating that the CC3 forms a parallel homodimer whose dimer interface is formed by a small number of hydrophobic residues. We further show that the CC3 interface is not required for Atg11 dimerization but is required for shaping Atg32 into functional mitophagy initiation sites and for delivery of mitochondria to the vacuole. Our findings suggest that Atg11 self-interactions help concentrate SARs as a necessary precondition for cargo capture.
    Keywords:  Atg11; Autophagy; Crystal structure; Mitophagy
    DOI:  https://doi.org/10.1016/j.jmb.2020.08.025
  3. Autophagy. 2020 Sep 07. 1-3
    Yamano K, Youle RJ.
      PINK1 and PRKN, proteins mutated in Parkinson disease, selectively amplify ubiquitin signals on damaged mitochondria for elimination via mitophagy. Because all five macroautophagy/autophagy receptors in mammals possess domains binding to ubiquitin and Atg8-family proteins, they were thought to recruit Atg8-family protein labeled phagophores from a cytosolic pool. However, our recent findings show that, in addition to Atg8-family protein binding, two of the receptors CALCOCO2 and OPTN interact with RB1CC1 and ATG9A, respectively, indicating that two different axes, CALCOCO2-RB1CC1 and OPTN-ATG9A, can initiate de novo biogenesis of autophagic membranes on ubiquitin-coated damaged mitochondria. These results explain the critical roles of the autophagy receptors CALCOCO2 and OPTN in mitochondrial degradation, and their abilities to simultaneously bind multiple autophagy core proteins propose a new function, i.e. a scaffold to build multivalent interactions for the orchestrated assembly of autophagy proteins near the ubiquitinated cargo.ABBREVIATIONS: ATG: autophagy-related; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CRABP2: cellular retinoic acid binding protein 2; LIR: MAP1LC3/LC3-interacting region; MAP1LC3: microtubule associated protein 1 light chain 3; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RB1CC1/FIP200: RB1 inducible coiled-coil 1; SNIPER: specific and nongenetic IAP-dependent protein eraser; SQSTM1/p62: sequestosome 1; ULK: unc-51 like autophagy activating kinase.
    Keywords:  Mitochondria; PINK1; Parkin; Parkinson’s disease; ubiquitin
    DOI:  https://doi.org/10.1080/15548627.2020.1815457
  4. Dev Cell. 2020 Aug 31. pii: S1534-5807(20)30666-3. [Epub ahead of print]
    Lee C, Lamech L, Johns E, Overholtzer M.
      Lysosome function is essential for cellular homeostasis, but quality-control mechanisms that maintain healthy lysosomes remain poorly characterized. Here, we developed a method to measure lysosome turnover and use this to identify a selective mechanism of membrane degradation that involves lipidation of the autophagy protein LC3 onto lysosomal membranes and the formation of intraluminal vesicles through microautophagy. This mechanism is induced in response to metabolic stress resulting from glucose starvation or by treatment with pharmacological agents that induce osmotic stress on lysosomes. Cells lacking ATG5, an essential component of the LC3 lipidation machinery, show reduced ability to regulate lysosome size and degradative capacity in response to activation of this mechanism. These findings identify a selective mechanism of lysosome membrane turnover that is induced by stress and uncover a function for LC3 lipidation in regulating lysosome size and activity through microautophagy.
    Keywords:  ATG5; LAP; LC3; ammonium; autophagy; glucose; glutamine; lysosome; metabolism; microautophagy
    DOI:  https://doi.org/10.1016/j.devcel.2020.08.008
  5. Nat Commun. 2020 09 08. 11(1): 4480
    Ogasawara Y, Cheng J, Tatematsu T, Uchida M, Murase O, Yoshikawa S, Ohsaki Y, Fujimoto T.
      Macroautophagy initiates by formation of isolation membranes, but the source of phospholipids for the membrane biogenesis remains elusive. Here, we show that autophagic membranes incorporate newly synthesized phosphatidylcholine, and that CTP:phosphocholine cytidylyltransferase β3 (CCTβ3), an isoform of the rate-limiting enzyme in the Kennedy pathway, plays an essential role. In starved mouse embryo fibroblasts, CCTβ3 is initially recruited to autophagic membranes, but upon prolonged starvation, it concentrates on lipid droplets that are generated from autophagic degradation products. Omegasomes and isolation membranes emanate from around those lipid droplets. Autophagy in prolonged starvation is suppressed by knockdown of CCTβ3 and is enhanced by its overexpression. This CCTβ3-dependent mechanism is also present in U2OS, an osteosarcoma cell line, and autophagy and cell survival in starvation are decreased by CCTβ3 depletion. The results demonstrate that phosphatidylcholine synthesis through CCTβ3 activation on lipid droplets is crucial for sustaining autophagy and long-term cell survival.
    DOI:  https://doi.org/10.1038/s41467-020-18153-w
  6. iScience. 2020 Aug 15. pii: S2589-0042(20)30658-1. [Epub ahead of print]23(9): 101466
    Sakai Y, Koyama-Honda I, Tachikawa M, Knorr RL, Mizushima N.
      Autophagy is an intracellular degradation process that is mediated by de novo formation of autophagosomes. Autophagosome formation involves dynamic morphological changes; a disk-shaped membrane cisterna grows, bends to become a cup-shaped structure, and finally develops into a spherical autophagosome. We have constructed a theoretical model that integrates the membrane morphological change and entropic partitioning of putative curvature generators, which we have used to investigate the autophagosome formation process quantitatively. We show that the membrane curvature and the distribution of the curvature generators stabilize disk- and cup-shaped intermediate structures during autophagosome formation, which is quantitatively consistent with in vivo observations. These results suggest that various autophagy proteins with membrane curvature-sensing properties control morphological change by stabilizing these intermediate structures. Our model provides a framework for understanding autophagosome formation.
    Keywords:  Biophysics; Cell Biology; Membrane Architecture; Molecular Biology
    DOI:  https://doi.org/10.1016/j.isci.2020.101466
  7. Front Neurosci. 2020 ;14 775
    Norwitz NG, Querfurth H.
      The mechanistic target of rapamycin protein complex, mTORC1, has received attention in recent years for its role in aging and neurodegenerative diseases, such as Alzheimer's disease. Numerous excellent reviews have been written on the pathways and drug targeting of this keystone regulator of metabolism. However, none have specifically highlighted several important nuances of mTOR regulation as relates to neurodegeneration. Herein, we focus on six such nuances/open questions: (1) "Antagonistic pleiotropy" - Should we weigh the beneficial anabolic functions of mTORC1 against its harmful inhibition of autophagy? (2) "Early/late-stage specificity" - Does the relative importance of these neuroprotective/neurotoxic actions change as a disease progresses? (3) "Regional specificity" - Does mTOR signaling respond differently to the same interventions in different brain regions? (4) "Disease specificity" - Could the same intervention to inhibit mTORC1 help in one disease and cause harm in another disease? (5) "Personalized therapy" - Might genetically-informed personalized therapies that inhibit particular nodes in the mTORC1 regulatory network be more effective than generalized therapies? (6) "Lifestyle interventions" - Could specific diets, micronutrients, or exercise alter mTORC1 signaling to prevent or improve the progression neurodegenerative diseases? This manuscript is devoted to discussing recent research findings that offer insights into these gaps in the literature, with the aim of inspiring further inquiry.
    Keywords:  Alzheimer’s disease; Parkinson’s disease; antagonistic pleiotropy; autophagy; insulin/Akt; mTOR
    DOI:  https://doi.org/10.3389/fnins.2020.00775
  8. Genes (Basel). 2020 Sep 04. pii: E1045. [Epub ahead of print]11(9):
    Fu W, Hall MN.
      Mammalian target of rapamycin (mTOR), a serine/threonine protein kinase and a master regulator of cell growth and metabolism, forms two structurally and functionally distinct complexes, mTOR complex 1 (mTORC1) and mTORC2. While mTORC1 signaling is well characterized, mTORC2 is relatively poorly understood. mTORC2 appears to exist in functionally distinct pools, but few mTORC2 effectors/substrates have been identified. Here, we review recent advances in our understanding of mTORC2 signaling, with particular emphasis on factors that control mTORC2 activity.
    Keywords:  Akt; mTOR; mTORC2 signaling; signaling crosstalk
    DOI:  https://doi.org/10.3390/genes11091045
  9. IUBMB Life. 2020 Sep 07.
    Nourbakhsh F, Read MI, Barreto GE, Sahebkar A.
      The lysosome is a membrane-enclosed organelle in eukaryotic cells, which has basic pattern recognition for nutrient-dependent signal transduction. In Alzheimer's disease, the already declining autophagy-lysosomal function is exacerbated by an increased need for clearance of damaged proteins and organelles in aged cells. Recent evidence suggests that numerous diseases are linked to impaired autophagy upstream of lysosomes. In this way, a comprehensive survey on the pathophysiology of the disease seems necessary. Hence, in the first section of this review, we will discuss the ultimate findings in lysosomal signaling functions and how they affect cellular metabolism and trafficking under neurodegenerative conditions, specifically Alzheimer's disease. In the second section, we focus on how natural products and their derivatives are involved in the regulation of inflammation and lysosomal dysfunction pathways, including how these should be considered a crucial target for Alzheimer's disease therapeutics.
    Keywords:  Alzheimer's disease; lysosomal dysfunction; natural products; neurodegenerative diseases
    DOI:  https://doi.org/10.1002/iub.2369
  10. Autophagy. 2020 Sep 10.
    Tian J, Kou X, Wang R, Jing H, Chen C, Tang J, Mao X, Zhao B, Wei X, Shi S.
      Mesenchymal stem cell transplantation (MSCT) has been applied to treat a variety of autoimmune and inflammatory diseases. Psychosocial stress can aggravate disease progression in chronic inflammatory patients. Whether psychological stress affects MSCT is largely unknown. In this study we show that psychological stress attenuates therapeutic effects of MSCT in a DSS-induced colitis mouse model by elevating the levels of exosomal Mir7k/mmu-let-7k (microRNA 7k) in circulation. Mechanistically, Mir7k inhibits STAT3 pathway in donor MSCs, leading to upregulated expression of BECN1 (beclin 1, autophagy related) and, thus, activation of macroautophagy/autophagy. Inhibition of autophagy by blocking Mir7k or activating STAT3 signaling can restore MSCT-mediated therapy in psychologically stressed colitis mice. Our study identifies a previously unknown role of autophagy in regulating MSCT therapy via exosomal miRNA Mir7k.
    Keywords:   Mir7k miRNA; Autophagy; colitis; exosomes; mesenchymal stem cell; psychological stress
    DOI:  https://doi.org/10.1080/15548627.2020.1821547
  11. J Cell Biol. 2020 Nov 02. pii: e201909073. [Epub ahead of print]219(11):
    Allen EA, Amato C, Fortier TM, Velentzas P, Wood W, Baehrecke EH.
      Macroautophagy (autophagy) targets cytoplasmic cargoes to the lysosome for degradation. Like all vesicle trafficking, autophagy relies on phosphoinositide identity, concentration, and localization to execute multiple steps in this catabolic process. Here, we screen for phosphoinositide phosphatases that influence autophagy in Drosophila and identify CG3530. CG3530 is homologous to the human MTMR6 subfamily of myotubularin-related 3-phosphatases, and therefore, we named it dMtmr6. dMtmr6, which is required for development and viability in Drosophila, functions as a regulator of autophagic flux in multiple Drosophila cell types. The MTMR6 family member MTMR8 has a similar function in autophagy of higher animal cells. Decreased dMtmr6 and MTMR8 function results in autophagic vesicle accumulation and influences endolysosomal homeostasis.
    DOI:  https://doi.org/10.1083/jcb.201909073
  12. Histochem Cell Biol. 2020 Sep 11.
    Moss JJ, Hammond CL, Lane JD.
      In the last twenty years, research using zebrafish as a model organism has increased immensely. With the many advantages that zebrafish offer such as high fecundity, optical transparency, ex vivo development, and genetic tractability, they are well suited to studying developmental processes and the effect of genetic mutations. More recently, zebrafish models have been used to study autophagy. This important protein degradation pathway is needed for cell and tissue homeostasis in a variety of contexts. Correspondingly, its dysregulation has been implicated in multiple diseases including skeletal disorders. In this review, we explore how zebrafish are being used to study autophagy in the context of skeletal development and disease, and the ways these areas are intersecting to help identify potential therapeutic targets for skeletal disorders.
    Keywords:  Autophagy; Bone; Development; Tools; Zebrafish
    DOI:  https://doi.org/10.1007/s00418-020-01917-2
  13. Int J Mol Sci. 2020 Sep 04. pii: E6476. [Epub ahead of print]21(18):
    Lee DS, Kim JE.
      Recently, we have reported that blockade/deletion of P2X7 receptor (P2X7R), an ATP-gated ion channel, exacerbates heat shock protein 25 (HSP25)-mediated astroglial autophagy (clasmatodendrosis) following kainic acid (KA) injection. In P2X7R knockout (KO) mice, prolonged astroglial HSP25 induction exerts 5' adenosine monophosphate-activated protein kinase/unc-51 like autophagy activating kinase 1-mediated autophagic pathway independent of mammalian target of rapamycin (mTOR) activity following KA injection. Sustained HSP25 expression also enhances AKT-serine (S) 473 phosphorylation leading to astroglial autophagy via glycogen synthase kinase-3β/bax interacting factor 1 signaling pathway. However, it is unanswered how P2X7R deletion induces AKT-S473 hyperphosphorylation during autophagic process in astrocytes. In the present study, we found that AKT-S473 phosphorylation was increased by enhancing activity of focal adhesion kinase (FAK), independent of mTOR complex (mTORC) 1 and 2 activities in isolated astrocytes of P2X7R knockout (KO) mice following KA injection. In addition, HSP25 overexpression in P2X7R KO mice acted as a chaperone of AKT, which retained AKT-S473 phosphorylation by inhibiting the pleckstrin homology domain and leucine-rich repeat protein phosphatase (PHLPP) 1- and 2-binding to AKT. Therefore, our findings suggest that P2X7R may be a fine-tuner of AKT-S473 activity during astroglial autophagy by regulating FAK phosphorylation and HSP25-mediated inhibition of PHLPP1/2-AKT binding following KA treatment.
    Keywords:  Bif-1; FAK inhibitor 14; LAMP1; PRAS40; Raptor; Rictor; p70S6K; siRNA
    DOI:  https://doi.org/10.3390/ijms21186476
  14. Cell Signal. 2020 Sep 08. pii: S0898-6568(20)30251-5. [Epub ahead of print] 109774
    Suzuki K, Honda T, Akatsu A, Yamaguchi N, Yamaguchi N.
      Src-family kinases (SFKs), such as c-Src, Lyn and Fyn, belong to non-receptor-type tyrosine kinases and play key roles in cell proliferation, adhesion, and migration. SFKs are anchored to the plasma membrane, Golgi membranes and lysosomal membranes through lipid modifications. Although the functions of SFKs being localized to the plasma membrane are intensively studied, those of SFKs being localized to organelle membranes are poorly understood. Here, we show that, among SFKs, c-Src in particular is involved in a decrease in the amount of LC3-II. c-Src and non-palmitoylated Lyn [Lyn(C3S) (cysteine-3 → serine-3)], which are localized onto lysosomes, decrease the amount of LC3-II and treatment with SFK inhibitors increases the amount of LC3-II, suggesting the importance of SFKs' lysosomal localization for a change of autophagic flux in a kinase activity-dependent manner. Colocalization of LC3-II with the lysosome-associated membrane protein LAMP1 shows that lysosome-localized SFKs promote the fusion of autophagosomes with lysosomes. Lysosome-localized SFKs play a positive role in the maintenance of cell viability under starvation conditions, which is further supported by knockdown of c-Src. Therefore, our results suggest that autophagosome-lysosome fusion is promoted by lysosome-localized c-Src, leading to cell survival under starvation conditions.
    Keywords:  Autophagosome; Autophagy; C-Src; LC-3; Lysosome; Src-family tyrosine kinase
    DOI:  https://doi.org/10.1016/j.cellsig.2020.109774
  15. Biochem Soc Trans. 2020 Sep 08. pii: BST20200130. [Epub ahead of print]
    Alam JM, Noda NN.
      Autophagy is a lysosomal degradation system that involves de novo autophagosome formation. A lot of factors are involved in autophagosome formation, including dozens of Atg proteins that form supramolecular complexes, membrane structures including vesicles and organelles, and even membraneless organelles. Because these diverse higher-order structural components cooperate to mediate de novo formation of autophagosomes, it is too complicated to be elaborated only by cell biological approaches. Recent trials to regenerate each step of this phenomenon in vitro have started to elaborate on the molecular mechanisms of such a complicated process by simplification. In this review article, we outline the in vitro reconstitution trials in autophagosome formation, mainly focusing on the reports in the past few years and discussing the molecular mechanisms of autophagosome formation by comparing in vitro and in vivo observations.
    Keywords:   in vitro reconstitution; autophagy; phase separation
    DOI:  https://doi.org/10.1042/BST20200130
  16. Nat Commun. 2020 Sep 09. 11(1): 4510
    Ham DJ, Börsch A, Lin S, Thürkauf M, Weihrauch M, Reinhard JR, Delezie J, Battilana F, Wang X, Kaiser MS, Guridi M, Sinnreich M, Rich MM, Mittal N, Tintignac LA, Handschin C, Zavolan M, Rüegg MA.
      With human median lifespan extending into the 80s in many developed countries, the societal burden of age-related muscle loss (sarcopenia) is increasing. mTORC1 promotes skeletal muscle hypertrophy, but also drives organismal aging. Here, we address the question of whether mTORC1 activation or suppression is beneficial for skeletal muscle aging. We demonstrate that chronic mTORC1 inhibition with rapamycin is overwhelmingly, but not entirely, positive for aging mouse skeletal muscle, while genetic, muscle fiber-specific activation of mTORC1 is sufficient to induce molecular signatures of sarcopenia. Through integration of comprehensive physiological and extensive gene expression profiling in young and old mice, and following genetic activation or pharmacological inhibition of mTORC1, we establish the phenotypically-backed, mTORC1-focused, multi-muscle gene expression atlas, SarcoAtlas (https://sarcoatlas.scicore.unibas.ch/), as a user-friendly gene discovery tool. We uncover inter-muscle divergence in the primary drivers of sarcopenia and identify the neuromuscular junction as a focal point of mTORC1-driven muscle aging.
    DOI:  https://doi.org/10.1038/s41467-020-18140-1
  17. Biochem Biophys Res Commun. 2020 Sep 08. pii: S0006-291X(20)31725-3. [Epub ahead of print]
    Tokumura K, Iwahashi S, Park G, Ochiai S, Okayama Y, Fusawa H, Fukasawa K, Iezaki T, Hinoi E.
      The mechanistic/mammalian target of rapamycin (mTOR) regulates various cellular processes, in part through incorporation into distinct protein complexes. The mTOR complex 1 (mTORC1) contains the Raptor subunit, while mTORC2 specifically contains the Rictor subunit. Mouse genetic studies, including ours, have revealed a critical role for mTOR in skeletogenesis through its expression in undifferentiated mesenchymal cells. In addition, we have recently revealed that mTORC1 expression in chondrocytes is crucial for skeletogenesis. Recent work indicates that mTOR regulates cellular functions, depending on the context, through both complex-dependent (canonical pathway) and complex-independent roles (noncanonical pathway). Here, we determined that mTOR regulates skeletal development through the noncanonical pathway, as well as the canonical pathway, in a cell-type and context-specific manner. Inactivation of Mtor in undifferentiated mesenchymal cells or chondrocytes led to either severe hypoplasia in appendicular skeletons or a severe and generalized chondrodysplasia, respectively. Moreover, Rictor deletion in undifferentiated mesenchymal cells or chondrocytes led to mineralization defects in some skeletal components. Finally, we revealed that simultaneous deletion of Raptor and Rictor in undifferentiated mesenchymal cells recapitulated the appendicular skeletal phenotypes of Mtor deficiency, whereas chondrocyte-specific Raptor and Rictor double-mutants exhibited milder hypoplasia of appendicular and axial skeletons than those seen upon Mtor deletion. These findings indicate that mTOR regulates skeletal development mainly through the canonical pathway in undifferentiated mesenchymal cells, but at least in part through the noncanonical pathway in chondrocytes.
    Keywords:  Canonical pathway; Chondrocytes; Mesenchymal cells; Noncanonical pathway; Skeletogenesis; mTOR
    DOI:  https://doi.org/10.1016/j.bbrc.2020.09.002
  18. Dev Cell. 2020 Sep 03. pii: S1534-5807(20)30630-4. [Epub ahead of print]
    Yang S, Zhang Y, Ting CY, Bettedi L, Kim K, Ghaniam E, Lilly MA.
      The dysregulation of the metabolic regulator TOR complex I (TORC1) contributes to a wide array of human pathologies. Tuberous sclerosis complex (TSC) is a potent inhibitor of TORC1. Here, we demonstrate that the Rag GTPase acts in both the amino-acid-sensing and growth factor signaling pathways to control TORC1 activity through the regulation of TSC dynamics in HeLa cells and Drosophila. We find that TSC lysosomal-cytosolic exchange increases in response to both amino acid and growth factor restriction. Moreover, the rate of exchange mirrors TSC function, with depletions of the Rag GTPase blocking TSC lysosomal mobility and rescuing TORC1 activity. Finally, we show that the GATOR2 complex controls the phosphorylation of TSC2, which is essential for TSC exchange. Our data support the model that the amino acid and growth factor signaling pathways converge on the Rag GTPase to inhibit TORC1 activity through the regulation of TSC dynamics.
    Keywords:  AKT1; Drosophila; GATOR2; HeLa cell; Rag GTPase; TORC1; TSC; amino acid signaling; growth factor signaling; lysosome
    DOI:  https://doi.org/10.1016/j.devcel.2020.08.006
  19. J Neurosci. 2020 Sep 11. pii: JN-RM-1759-19. [Epub ahead of print]
    Adnan G, Rubikaite A, Khan M, Reber M, Suetterlin P, Hindges R, Drescher U.
      Interstitial axon branching is an essential step during the establishment of neuronal connectivity. However, the exact mechanisms on how the number and position of branches are determined are still not fully understood. Here, we investigated the role of Arl8B, an adaptor molecule between lysosomes and kinesins. In chick retinal ganglion cells, downregulation of Arl8B reduces axon branch density and shifts their location more proximally, while Arl8B overexpression leads to increased density and more distal positions of branches. These alterations correlate with changes in the location and density of lysosomes and autophagosomes along the axon shaft. Diminishing autophagy directly by knockdown of atg7, a key autophagy gene, reduces branch density, while induction of autophagy by rapamycin increases axon branching, indicating that autophagy plays a prominent role in axon branch formation. In vivo, local inactivation of autophagy in the retina using a mouse conditional knockout approach disturbs retino-collicular map formation which is dependent on the formation of interstitial axon branches. These data suggest that Arl8B plays a principal role in the positioning of axon branches by spatially controlling autophagy, thus directly controlling formation of neural connectivity in the brain.SIGNIFICANCE STATEMENTThe formation of interstitial axonal branches plays a prominent role in numerous places of the developing brain during neural circuit establishment. We show here that the GTPase Arl8B controls density and location of interstitial axon branches, and at the same time controls also density and location of the autophagy machinery. Up- or down-regulation of autophagy in vitro promotes or inhibits axon branching. Local disruption of autophagy in vivo disturbs retino-collicular mapping. Our data suggest that Arl8B controls axon branching by controlling locally autophagy. This work is one of the first reports showing a role of autophagy during early neural circuit development and suggests that autophagy in general plays a much more prominent role during brain development than previously anticipated.
    DOI:  https://doi.org/10.1523/JNEUROSCI.1759-19.2020
  20. Cancer Sci. 2020 Sep 08.
    Torii S, Honda S, Murohashi M, Yamaguchi H, Shimizu S.
      Various clinical and experimental findings have revealed the causal relationship between autophagy failure and oncogenesis, and several mechanisms have been suggested to explain this relationship. We recently proposed two additional mechanisms: centrosome number dysregulation and the failure of autophagic cell death. Here, we detail the mechanical relationship between autophagy failure and oncogenesis.
    Keywords:  Alternative autophagy; Autophagic cell death; Autophagy; Centrosome; Oncogenesis
    DOI:  https://doi.org/10.1111/cas.14646
  21. Neurobiol Aging. 2020 Aug 04. pii: S0197-4580(20)30245-1. [Epub ahead of print]
    Liu X, He J, Chen L, Zhang N, Tang L, Liu X, Ma Y, Fan D.
      TBK1 has been reported as a risk gene of amyotrophic lateral sclerosis (ALS). We screened TBK1 variants in 69 familial ALS patients and 608 sporadic ALS patients from mainland China. All 20 coding exons and the exon-intron flanking regions of TBK1 were amplified and sequenced using Sanger sequencing. In total, we identified eight missense variants and one suspicious splice site mutation. The patient with K291R had a family history of ALS. Other variants were detected in sALS patients. Interestingly, 2 patients with variants in TBK1 carried another variant in other genes related to autophagy: G175S in TBK1 and P392L in SQSTM1; and D534H in TBK1 and E372D in SQSTM1. We concluded that TBK1 variants account for approximately 1.3% of Chinese ALS patients. Screening for this gene in ALS patients is necessary, especially in the group with variants in other genes related to the autophagy pathway.
    Keywords:  Amyotrophic lateral sclerosis; China; Genetics; TBK1
    DOI:  https://doi.org/10.1016/j.neurobiolaging.2020.07.028
  22. Int Immunol. 2020 Sep 10. pii: dxaa062. [Epub ahead of print]
    Honjo H, Watanabe T, Arai Y, Kamata K, Minaga K, Komeda Y, Yamashita K, Kudo M.
      Polymorphisms in the autophagy-related protein 16 like 1 (ATG16L1) and nucleotide-binding oligomerization domain 2 (NOD2) genes are associated with Crohn's disease (CD). Impaired interaction between ATG16L1 and NOD2 underlies CD immunopathogenesis. Although activation of the receptor-interacting serine/threonine kinase (RICK, also known as RIP2), a downstream signaling molecule for NOD2 and multiple toll-like receptors (TLRs), plays a pathogenic role in the development of inflammatory bowel disease, the molecular interaction between ATG16L1 and RICK/RIP2 remains poorly understood. In this study, we examined the physical interaction between ATG16L1 and RICK/RIP2 in human embryonic kidney 293 (HEK293) cells and human monocyte-derived dendritic cells (DCs) expressing excessive and endogenous levels of these proteins, respectively. We established that ATG16L1 binds to RICK/RIP2 kinase domain and negatively regulates TLR2-mediated nuclear factor-kappa B (NF-κB) activation and proinflammatory cytokine responses by inhibiting the interaction between TLR2 and RICK/RIP2. Binding of ATG16L1 to RICK/RIP2 suppressed NF-κB activation by downregulating RICK/RIP2 polyubiquitination. Notably, the percentage of colonic DCs expressing ATG16L1 inversely correlated with IL-6 and TNF-α expression levels in the colon of CD patients. These data suggest that the interaction between ATG16L1 and RICK/RIP2 maintains intestinal homeostasis via the downregulation of TLR-mediated proinflammatory cytokine responses.
    Keywords:  ATG16L1; Crohn’s disease; RICK/RIP2
    DOI:  https://doi.org/10.1093/intimm/dxaa062
  23. J Physiol. 2020 Sep 07.
    Ogasawara R, Knudsen JR, Li J, Ato S, Jensen TE.
      KEY POINTS: Muscle contractions increase protein synthesis in a mechanistic target of rapamycin (mTOR)-dependent manner, yet it is unclear which/how mTOR complexes regulate muscle protein synthesis. We investigated the requirement of mTOR Complex 2 (mTORC2) in contraction-stimulated muscle protein synthesis. mTORC2 inhibition by muscle-specific Rictor knockout (Rictor mKO) did not prevent contraction-induced muscle protein synthesis. Rapamycin prevented contraction-induced muscle protein synthesis in Rictor mKO but not wild-type mice.ABSTRACT: Protein synthesis increases following muscle contractions. Previous studies showed that the mechanistic target of rapamycin complex 1 (mTORC1) inhibition suppressed the early but not late muscle protein synthesis-response, while the inhibition of both mTORC1 and mTORC2 abolished both effects. Therefore, we hypothesized that mTORC2 regulates muscle protein synthesis following muscle contractions. To test this, we investigated the effect of mTORC2 inhibition by mouse muscle-specific Rictor knockout (Rictor mKO) on muscle protein synthesis 3h post-contraction. The right gastrocnemius muscles of Rictor mKO mice and wild-type (WT) mice were isometrically contracted using percutaneous electrical stimulation, while the left gastrocnemius muscles served as controls. Vehicle or the mTORC1 inhibitor rapamycin (1.5 mg/kg) was injected intraperitoneally 1 h before contraction. Treatment of WT mice with rapamycin and Rictor mKO lowered protein synthesis in general, but the response to contractions was intact 3h post contractions in both conditions. Rapamycin treatment in Rictor mKO prevented contraction-stimulated muscle protein synthesis. Notably, signalling traditionally associated with mTORC1 was increased by muscle contractions despite rapamycin treatment. In rapamycin-treated Rictor mKO mice, the same mTORC1 signalling was blocked following contractions. Our results indicate that although neither rapamycin-sensitive mTOR/mTORC1 nor mTORC2 regulates contraction-induced muscle protein synthesis, combined inhibition of rapamycin-sensitive mTOR/mTORC1 and mTORC2 synergistically inhibits contraction-induced muscle protein synthesis. This article is protected by copyright. All rights reserved.
    Keywords:  cell signalling; exercisemTORC1; mTORC2; protein translation
    DOI:  https://doi.org/10.1113/JP280528
  24. Curr Opin Cell Biol. 2020 Sep 02. pii: S0955-0674(20)30101-0. [Epub ahead of print]67 46-55
    Llamas E, Alirzayeva H, Loureiro R, Vilchez D.
      The proteostasis network adjusts protein composition and maintains protein integrity, which are essential processes for cell function and viability. Current efforts, given their intrinsic characteristics, regenerative potential and fundamental biological functions, have been directed to define proteostasis of stem cells. These insights demonstrate that embryonic stem cells and induced pluripotent stem cells exhibit an endogenous proteostasis network that not only modulates their pluripotency and differentiation but also provides a striking ability to suppress aggregation of disease-related proteins. Moreover, recent findings establish a central role of enhanced proteostasis to prevent the aging of somatic stem cells in adult organisms. Notably, proteostasis is also required for the biological purpose of adult germline stem cells, that is to be passed from one generation to the next. Beyond these links between proteostasis and stem cell function, we also discuss the implications of these findings for disease, aging, and reproduction.
    Keywords:  Adult somatic stem cells; Aging; Autophagy; Cell reprogramming; Differentiation; Embryonic stem cells; Germline stem cells; Hematopoietic stem cells; Induced pluripotent stem cells; Muscle stem cells; Neural stem cells; Protein chaperones; Protein synthesis; Proteostasis; RNA-binding proteins; Ubiquitin proteasome system
    DOI:  https://doi.org/10.1016/j.ceb.2020.08.005
  25. Mol Med Rep. 2020 Sep 09.
    Chen W, Lv L, Nong Z, Chen X, Pan X, Chen C.
      Our previous study demonstrated that hyperbaric oxygen (HBO) improves heart function predominantly through reducing oxygen stress, modulating energy metabolism and inhibiting cell apoptosis. The present study aimed to investigate the protective effects of HBO on mitochondrial function and autophagy using rats with a ligated left anterior descending artery. The cardioprotective effects of HBO were mainly evaluated using ELISA, fluorescent probes, transmission electron microscopy and reverse transcription‑quantitative PCR (RT‑qPCR). HBO pretreatment for 14 days (once a day) using a 0.25 MPa chamber improved mitochondrial morphology and decreased the number of autophagic vesicles, as observed using a transmission electron microscope. HBO pretreatment significantly increased the levels of ATP, ADP, energy charge and the opening of the mitochondrial permeability transition pore, but decreased the levels of AMP, cytochrome c and reactive oxygen species. Moreover, HBO pretreatment significantly increased the gene or protein expression levels of eIF4E‑binding protein 1, mammalian target of rapamycin (mTOR), mitochondrial DNA, NADH dehydrogenase subunit 1, mitofusin 1 and mitofusin 2, whereas it decreased the gene or protein expression levels of autophagy‑related 5 (Atg5), cytochrome c, dynamin‑related protein 1 and p53, as determined using RT‑qPCR or immunohistochemistry. In conclusion, HBO treatment was observed to protect cardiomyocytes during myocardial ischemia‑reperfusion injury (MIRI) by preventing mitochondrial dysfunction and inhibiting autophagy. Thus, these results provide novel evidence to support the use of HBO as a potential agent for the mitigation of MIRI.
    DOI:  https://doi.org/10.3892/mmr.2020.11497
  26. Cell Rep. 2020 Sep 08. pii: S2211-1247(20)31114-1. [Epub ahead of print]32(10): 108125
    Burkewitz K, Feng G, Dutta S, Kelley CA, Steinbaugh M, Cram EJ, Mair WB.
      Individually, dysfunction of both the endoplasmic reticulum (ER) and mitochondria has been linked to aging, but how communication between these organelles might be targeted to promote longevity is unclear. Here, we provide evidence that, in Caenorhabditis elegans, inhibition of the conserved unfolded protein response (UPRER) mediator, activating transcription factor (atf)-6, increases lifespan by modulating calcium homeostasis and signaling to mitochondria. Atf-6 loss confers longevity via downregulation of the ER calcium buffer, calreticulin. ER calcium release via the inositol triphosphate receptor (IP3R/itr-1) is required for longevity, while IP3R/itr-1 gain of function is sufficient to extend lifespan. Highlighting coordination between organelles, the mitochondrial calcium import channel mcu-1 is also required for atf-6 longevity. IP3R inhibition leads to impaired mitochondrial bioenergetics and hyperfusion, which is sufficient to suppress long life in atf-6 mutants. This study reveals the importance of organellar calcium handling as a critical output for the UPRER in determining the quality of aging.
    Keywords:  InsP3R; UPR; aging; calreticulin; interorganelle communication; longevity
    DOI:  https://doi.org/10.1016/j.celrep.2020.108125
  27. J Cell Sci. 2020 Sep 09. pii: jcs246322. [Epub ahead of print]133(17):
    Schuck S.
      Autophagy is fundamental for cell and organismal health. Two types of autophagy are conserved in eukaryotes: macroautophagy and microautophagy. During macroautophagy, autophagosomes deliver cytoplasmic constituents to endosomes or lysosomes, whereas during microautophagy lytic organelles take up cytoplasm directly. While macroautophagy has been investigated extensively, microautophagy has received much less attention. Nonetheless, it has become clear that microautophagy has a broad range of functions in biosynthetic transport, metabolic adaptation, organelle remodeling and quality control. This Review discusses the selective and non-selective microautophagic processes known in yeast, plants and animals. Based on the molecular mechanisms for the uptake of microautophagic cargo into lytic organelles, I propose to distinguish between fission-type microautophagy, which depends on ESCRT proteins, and fusion-type microautophagy, which requires the core autophagy machinery and SNARE proteins. Many questions remain to be explored, but the functional versatility and mechanistic diversity of microautophagy are beginning to emerge.
    Keywords:  Core autophagy machinery; ESCRT machinery; Membrane fission; Membrane fusion; Microautophagy; SNAREs
    DOI:  https://doi.org/10.1242/jcs.246322
  28. FASEB J. 2020 Sep 06.
    Wang X, Lin Y, Liu S, Zhu Y, Lu K, Broering R, Lu M.
      O-GlcNAcylation is a form of posttranslational modification, and serves various functions, including modulation of location, stability, and activity for the modified proteins. O-linked-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is an essential cellular enzyme that posttranslationally modifies the cellular proteins with O-GlcNAc moiety. Early studies reported that the decreased O-GlcNAcylation regulates cellular autophagy, a process relevant for hepatitis B virus replication (HBV) and assembly. Therefore, we addressed the question how O-GlcNAcylation regulates cellular autophagy and HBV replication. Inhibition of OGT activity with a small molecule inhibitor OSMI-1 or silencing OGT significantly enhanced HBV replication and HBsAg production in hepatoma cells and primary human hepatocytes (PHHs). Western blotting analysis showed that inhibition of O-GlcNAcylation-induced endoplasmic reticulum (ER) stress and cellular autophagy, two processes subsequently leading to enhanced HBV replication. Importantly, the numbers of autophagosomes and the levels of autophagic markers LC3-II and SQSTM1/p62 in hepatoma cells were elevated after inhibition of O-GlcNAcylation. Further analysis revealed that inhibition of O-GlcNAcylation blocked autophagosome-lysosome fusion and thereby prevented autophagic degradation of HBV virions and proteins. Moreover, OSMI-1 further promoted HBV replication by inducing autophagosome formation via inhibiting the O-GlcNAcylation of Akt and mTOR. In conclusion, decreased O-GlcNAcylation enhanced HBV replication through increasing autophagosome formation at multiple levels, including triggering ER-stress, Akt/mTOR inhibition, and blockade of autophagosome-lysosome fusion.
    Keywords:   O-GlcNAcylation ; Akt/mTOR signaling; ER stress; HBV; autophagosome-lysosome fusion; autophagy
    DOI:  https://doi.org/10.1096/fj.202001168RR
  29. Eur J Med Chem. 2020 Jul 19. pii: S0223-5234(20)30466-9. [Epub ahead of print]206 112494
    Yin L, Hu Q.
      Ubiquitin-proteasome system, autophagy-lysosome pathway and N-end rule pathway are crucial protein quality control mechanisms in human body. Hijacking these endogenous protein degrading measures by chimera degraders could be a revolutionary strategy for the discovery of small-molecule drugs. As the most advanced chimera degraders, PROTACs have demonstrated the potential by delivering two drug candidates into clinical trials. The development of chimera degraders exploiting these three pathways are reviewed, a focus is given on the chemical structures and their influences on biological effects from a viewpoint of medicinal chemistry.
    Keywords:  Autophagy-lysosome pathway; Chimera degraders; Drug discovery; N-end rule; PROTACs; Ubiquitin–proteasome system
    DOI:  https://doi.org/10.1016/j.ejmech.2020.112494
  30. J Cell Mol Med. 2020 Sep 11.
    Zhu MJ, Liu BY, Shi L, Wang X, Wang Y.
      It is growingly concerned about methamphetamine (MA)-induced lung toxicity. IMP1 is identified as a key molecule for cell life processes, but the role of IMP1 in MA-induced senescence remains unclear. The purpose of this study was to investigate whether chronic exposure to MA can cause autophagy and senescence of the lungs, whether there are interactions between Mammalian target of rapamycin (mTOR) and IMP1 and whether IMP1 is involved in pulmonary senescence promoted by mTOR-autophagy. The rats were randomly divided into control group and MA group, following by H&E staining, immunohistochemistry staining and Western blot. The alveolar epithelial cells were proceeded by ß-galactosidase staining, cell cycle detection, transfection and co-immunoprecipitation. Long-term exposure to MA led to the thickening of alveolar septum and more compact lungs. MA promoted the conversion of LC3-I to LC3-II and inhibited the activation of mTOR to induce autophagy. Bioinformatics and co-immunoprecipitation results presented the interactions between IMP1 and mTOR. MA induced cell senescence by decreasing IMP1, up-regulating p21 and p53, arresting cell cycle and increasing SA-β-gal. Overexpression of IMP1 reduced p21 and SA-β-gal to inhibit the senescence of alveolar epithelial cells. These results demonstrated that mTOR-autophagy promotes pulmonary senescence through IMP1 in chronic toxicity of methamphetamine.
    Keywords:  IMP1; autophagy; mTOR; methamphetamine; pulmonary; senescence
    DOI:  https://doi.org/10.1111/jcmm.15841
  31. FASEB J. 2020 Sep 12.
    Kurano M, Tsukamoto K, Hara M, Tsuneyama K, Nishikawa T, Ikeda H, Yatomi Y.
      Hepatobiliary cholesterol handling, mediated by Niemann-Pick C1-like 1 protein (NPC1L1) and ABCG5/8, is well-known to contribute to the homeostasis of cholesterol. We attempted to elucidate the impact of hepatobiliary cholesterol handling on the homeostasis of sphingolipids and lysophospholipids, especially sphingosine 1-phosphate (S1P). We induced the overexpression of NPC1L1 or ABCG5/8 in the mouse liver. Hepatic NPC1L1 overexpression increased the plasma and hepatic S1P levels, while it decreased the biliary S1P levels, and all of these changes were inhibited by ezetimibe. The ability of HDL to activate Akt in the endothelial cells was augmented by hepatic NPC1L1 overexpression. NPC1L1-mediated S1P transport was confirmed by both in vitro and in vivo studies conducted using C17 S1P, an exogenous S1P analog. Upregulation of apolipoprotein M (apoM) was involved in these modulations, although apoM was not necessary for these modulations. Moreover, the increase in the plasma S1P levels also observed in ABCG5/8-overexpressing mice was dependent on the elevation of the plasma apoM levels. In regard to other sphingolipids and lysophospholipids, ceramides were similarly modulated by NPC1L1 to S1P, while other lipids were differently influenced by NPC1L1 or ABCG5/8 from S1P. Hepatobiliary cholesterol handling might also regulate the functional lipids, such as S1P.
    Keywords:  ABCG5/8; Niemann-Pick C1-like 1 protein; apolipoprotein M; ceramides; glycero-lysophospholipids; hepatobiliary cholesterol handling; sphingosine 1-phosphate
    DOI:  https://doi.org/10.1096/fj.202001397R
  32. EMBO Rep. 2020 Sep 07. e50845
    Malecki M, Kamrad S, Ralser M, Bähler J.
      When glucose is available, many organisms repress mitochondrial respiration in favour of aerobic glycolysis, or fermentation in yeast, that suffices for ATP production. Fission yeast cells, however, rely partially on respiration for rapid proliferation under fermentative conditions. Here, we determined the limiting factors that require respiratory function during fermentation. When inhibiting the electron transport chain, supplementation with arginine was necessary and sufficient to restore rapid proliferation. Accordingly, a systematic screen for mutants growing poorly without arginine identified mutants defective in mitochondrial oxidative metabolism. Genetic or pharmacological inhibition of respiration triggered a drop in intracellular levels of arginine and amino acids derived from the Krebs cycle metabolite alpha-ketoglutarate: glutamine, lysine and glutamic acid. Conversion of arginine into these amino acids was required for rapid proliferation when blocking the respiratory chain. The respiratory block triggered an immediate gene expression response diagnostic of TOR inhibition, which was muted by arginine supplementation or without the AMPK-activating kinase Ssp1. The TOR-controlled proteins featured biased composition of amino acids reflecting their shortage after respiratory inhibition. We conclude that respiration supports rapid proliferation in fermenting fission yeast cells by boosting the supply of Krebs cycle-derived amino acids.
    Keywords:   S. pombe ; arginine; cellular metabolism; fermentation; respiration
    DOI:  https://doi.org/10.15252/embr.202050845
  33. Cell Signal. 2020 Sep 04. pii: S0898-6568(20)30245-X. [Epub ahead of print] 109768
    Li J, Ye W, Xu W, Chang T, Zhang L, Ma J, Pei R, He M, Zhou J.
      Subcapsular cataracts are common phenotype of diabetic cataracts, and abnormal lens epithelial cells (LECs) under the lens capsules have been considered to involve in the pathogenesis. Our previous studies have shown that the epithelial to mesenchymal transition (EMT), which is responsible for the LECs to lose their original polarity and tight junctions, occurs in a diabetic cataract mouse model. Autophagy is known to function in the EMT process in multiple tissues. However, the relationship between autophagy and EMT process in LECs has not yet been fully demonstrated. We found that high glucose retreatment reducing expression level of E-cadherin, an epithelial marker, but increasing that of α-smooth muscle actin (α-SMA), a mesenchymal marker, by Western blot and immunoflurence staining assays, and increased the cell migration by Transwell assay in human lens epithelial cell line HLE-B3. High glucose retreatment also led to impairment of autophagy, representing by downregulation of Beclin, LC3II/LC3I, and reducing the number of autophagosomes. Activation of autophagy by rapamycin could prevent high glucose-induced EMT. In addition, the levels of p62 and Snail were increased in high glucose-treated HLE-B3 cells, and their interactions were demonstrated by co-immunoprecipitation and immunoflurence staining, but all these changes were attenuated by application of rapamycin. These findings delineated a novel autophagy-mediated mechanism, p62 might mediate Snail underlying high glucose-induced EMT in LECs, suggesting a potential therapeutic approach for diabetic cataract by regulating autophagy.
    Keywords:  Autophagy; Epithelial to mesenchymal transition; High glucose; Lens epithelial cells; Snail; p62
    DOI:  https://doi.org/10.1016/j.cellsig.2020.109768
  34. Cancers (Basel). 2020 Sep 04. pii: E2515. [Epub ahead of print]12(9):
    Shin J, Bae J, Park S, Kang HG, Shin SM, Won G, Kim JS, Cho SG, Choi Y, Oh SM, Shin J, Kim JS, Park HW.
      Oncogenic activation of the mammalian target of rapamycin complex 1 (mTORC1) leads to endometrial cancer cell growth and proliferation. Sestrin2 (SESN2), a highly conserved stress-inducible protein, is involved in homeostatic regulation via inhibition of reactive oxygen species (ROS) and mTORC1. However, the role of SESN2 in human endometrial cancer remains to be investigated. Here, we investigated expression, clinical significance, and underlying mechanisms of SESN2 in endometrial cancer. SESN2 was upregulated more in endometrial cancer tissues than in normal endometrial tissues. Furthermore, upregulation of SESN2 statistically correlated with shorter overall survival and disease-free survival in patients with endometrial cancer. SESN2 expression strongly correlated with mTORC1 activity, suggesting its impact on prognosis in endometrial cancer. Additionally, knockdown of SESN2 promoted cell proliferation, migration, and ROS production in endometrial cancer cell lines HEC-1A and Ishikawa. Treatment of these cells with mTOR inhibitors reversed endometrial cancer cell proliferation, migration, and epithelial-mesenchymal transition (EMT) marker expression. Moreover, in a xenograft nude mice model, endometrial cancer growth increased by SESN2 knockdown. Thus, our study provides evidence for the prognostic significance of SESN2, and a relationship between SESN2, the mTORC1 pathway, and endometrial cancer growth, suggesting SESN2 as a potential therapeutic target in endometrial cancer.
    Keywords:  endometrial cancer; mTORC1; migration; proliferation; reactive oxygen species (ROS); sestrin2
    DOI:  https://doi.org/10.3390/cancers12092515
  35. Elife. 2020 Sep 10. pii: e58073. [Epub ahead of print]9
    Pan ZQ, Shao GC, Liu XM, Chen Q, Dong MQ, Du LL.
      Autophagy is a proteolytic pathway conserved from yeasts to mammals. Atg1 kinase is essential for autophagy but how its activity is controlled remains insufficiently understood. Here, we show that, in the fission yeast Schizosaccharomyces pombe, Atg1 kinase activity requires Atg11, the ortholog of mammalian FIP200/RB1CC1, but does not require Atg13, Atg17, or Atg101. Remarkably, a 62-amino-acid region of Atg11 is sufficient for the autophagy function of Atg11 and for supporting the Atg1 kinase activity. This region harbors an Atg1-binding domain and a homodimerization domain. Dimerizing Atg1 is the main role of Atg11, as it can be bypassed by artificially dimerizing Atg1. In an Atg1 dimer, only one Atg1 molecule needs to be catalytically active, suggesting that Atg1 activation can be achieved through cis-autophosphorylation. We propose that mediating Atg1 oligomerization and activation may be a conserved function of Atg11/FIP200 family proteins and cis-autophosphorylation may be a general mechanism of Atg1 activation.
    Keywords:  S. pombe; cell biology
    DOI:  https://doi.org/10.7554/eLife.58073
  36. Am J Transl Res. 2020 ;12(8): 4807-4818
    Guan X, Shen J, Xu Y, Feng X, Zhou R.
      Lead (Pb), a highly poisonous heavy metal and an important occupational hazard, is currently a widespread environmental pollutant. The kidney is especially susceptible to the toxic effects of Pb because of its major role in Pb excretion. Heme oxygenase-1 (HO-1) is an inducible antioxidant enzyme that can mitigate cellular injury. However, its role in Pb-elicited nephrotoxicity remains uncertain. This study was designed to examine the role of HO-1 in lead acetate (PbAc)-induced renal tubular cell injury in vitro. PbAc injury was found to suppress HO-1 expression and impair cell viability, with concomitant depletion of the autophagy proteins LC3-II and Beclin 1. Overexpression of HO-1 dramatically restored autophagy and protected cells against PbAc-induced apoptosis. In addition, pretreatment with 3-methyladenine, an inhibitor of autophagy, aggravated apoptosis and abolished renoprotection by HO-1, suggesting that the anti-apoptotic effect of HO-1 in Pb-induced nephrotoxicity is dependent on enhanced autophagy. Furthermore, HO-1 overexpression abrogated the inhibitory effect of PbAc on the adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTORC1) signaling pathway. Pretreatment with an AMPK agonist, 5-aminoimidazole-4-carboxamide-1-β-D ribofuranoside, markedly enhanced autophagic activity and diminished apoptosis. Conversely, inhibition of AMPK phosphorylation abolished the pro-autophagic and anti-apoptotic effects of HO-1 in PbAc-injured cells. Our findings suggest that HO-1 alleviates Pb-induced nephrotoxicity via enhanced autophagy, which involves activation of the AMPK/mTORC1 signaling pathway.
    Keywords:  AMPK; Heme oxygenase-1; autophagy; lead acetate; mTORC1; nephrotoxicity
  37. J Exp Bot. 2020 Sep 09. pii: eraa410. [Epub ahead of print]
    Kazibwe Z, Soto-Burgos J, MacIntosh GC, Bassham DC.
      The Arabidopsis thaliana T2 family endoribonuclease RNS2 localizes to the vacuole and functions in rRNA degradation. Loss of RNS2 activity impairs rRNA turnover and leads to constitutive autophagy, a process for degradation of cellular components. Autophagy is normally activated during environmental stress and is important for stress tolerance and homeostasis. Here we show that restoration of cytosolic purine nucleotide levels rescues the constitutive autophagy phenotype of rns2-2 seedlings, whereas inhibition of purine synthesis induces autophagy in wild-type seedlings. rns2-2 seedlings have reduced activity of the target of rapamycin (TOR) kinase complex, a negative regulator of autophagy, and this phenotype is rescued by addition of inosine to increase purine levels. Activation of TOR in rns2-2 by exogenous auxin blocks the enhanced autophagy, indicating a possible involvement of the TOR signaling pathway in the activation of autophagy in the rns2-2 mutant. Our data suggest a model in which loss of rRNA degradation in rns2-2 leads to a reduction in cytoplasmic nucleotide concentrations, which in turn inhibits TOR activity, leading to activation of autophagy to restore homeostasis.
    Keywords:  Arabidopsis; RNS2; TOR; autophagy; inosine; nucleotides; rRNA; ribonuclease
    DOI:  https://doi.org/10.1093/jxb/eraa410
  38. Nat Commun. 2020 Sep 08. 11(1): 4496
    Shi D, Xia X, Cui A, Xiong Z, Yan Y, Luo J, Chen G, Zeng Y, Cai D, Hou L, McDermott J, Li Y, Zhang H, Han JJ.
      Aging is characterized by the loss of homeostasis and the general decline of physiological functions, accompanied by various degenerative diseases and increased rates of mortality. Aging targeting small molecule screens have been performed many times, however, few have focused on endogenous metabolic intermediates-metabolites. Here, using C. elegans lifespan assays, we conducted a worm metabolite screen and identified an eukaryotes conserved metabolite, myo-inositol (MI), to extend lifespan, increase mobility and reduce fat content. Genetic analysis of enzymes in MI metabolic pathway suggest that MI alleviates aging through its derivative PI(4,5)P2. MI and PI(4,5)P2 are precursors of PI(3,4,5)P3, which is negatively related to longevity. The longevity effect of MI is dependent on the tumor suppressor gene, daf-18 (homologous to mouse Pten), independent of its classical pathway downstream genes, akt or daf-16. Furthermore, we found MI effects on aging and lifespan act through mitophagy regulator PTEN induced kinase-1 (pink-1) and mitophagy. MI's anti-aging effect is also conserved in mouse, indicating a conserved mechanism in mammals.
    DOI:  https://doi.org/10.1038/s41467-020-18280-4
  39. Oncol Rep. 2020 Sep 09.
    Xu W, Huang Z, Gan Y, Chen R, Huang Y, Xue B, Jiang S, Yu Z, Yu K, Zhang S.
      Enhancement of autophagy serves as a promising therapeutic strategy for cancer, including acute myeloid leukemia (AML). Casein kinase 1α (CK1α), encoded by CSNK1A1, regulates Wnt/β‑catenin, p53 and other key signaling pathways, and is critically involved in tumor progression. However, the relationship and mechanism of CK1α with autophagy in AML still remain unclear. In the present study, it was found that AML patients had higher expression of CSNK1A1 mRNA than healthy donors. Furthermore, we analyzed 163 cases of AML patients in the LAML database of TCGA and found that AML patients with high CSNK1A1 had shorter overall survival than those with low or medium CSNK1A1 expression. Furthermore, we demonstrated that CK1α was a negative regulator of autophagy and apoptosis. Pharmacologic inhibition of CK1α using D4476 or CK1α knockdown via lentivirus‑mediated shRNA suppressed proliferation and the clone formation by enhancing autophagic flux and apoptosis in AML cell lines as well as in patient blast cells. Intriguingly, D4476‑induced cell death was aggravated in combination with an autophagy inhibitor, Spautin‑1, suggesting that autophagy may be a pro‑survival signaling. CK1α interacted with murine double minute 2 (MDM2) and p53, and CK1α inhibitor D4476 significantly upregulated p53 and phosphorylated 5' AMP‑activated protein kinase (AMPK), and substantially inhibited the phosphorylation of mammalian target of rapamycin (mTOR). Our findings indicate that CK1α promotes AML by suppressing p53 downstream of MDM2‑mediated autophagy and apoptosis, suggesting that targeting CK1α provides a therapeutic opportunity to treat AML.
    DOI:  https://doi.org/10.3892/or.2020.7760
  40. Exp Mol Med. 2020 Sep 11.
    Jo DS, Park NY, Cho DH.
      In recent decades, the role of the peroxisome in physiology and disease conditions has become increasingly important. Together with the mitochondria and other cellular organelles, peroxisomes support key metabolic platforms for the oxidation of various fatty acids and regulate redox conditions. In addition, peroxisomes contribute to the biosynthesis of essential lipid molecules, such as bile acid, cholesterol, docosahexaenoic acid, and plasmalogen. Therefore, the quality control mechanisms that regulate peroxisome biogenesis and degradation are important for cellular homeostasis. Current evidence indicates that peroxisomal function is often reduced or dysregulated in various human disease conditions, such as neurodegenerative diseases. Here, we review the recent progress that has been made toward understanding the quality control systems that regulate peroxisomes and their pathological implications.
    DOI:  https://doi.org/10.1038/s12276-020-00503-9
  41. Oxid Med Cell Longev. 2020 ;2020 9738143
    Wang Y, Peng X, Zhang M, Jia Y, Yu B, Tian J.
      Ferroptosis was recently identified as an iron-dependent regulatory necrosis process mediated by polyunsaturated fatty acid (PUFA) peroxidation. The pivotal events related to oxidative stress in ferroptosis include direct or indirect glutathione peroxidase 4 (GPX4) inhibition, ferrous iron overload, and lipid peroxidation. The links between ferroptosis and multiple pathological processes including tumor and cardiovascular system disease have become increasingly apparent, and the mechanisms and compounds involved in ferroptosis, such as reduction of coenzyme Q10 (ubiquinone/CoQ10), are gradually emerging. Current reports have revealed crossroads between ferroptosis and other multiple responses. This overview of the current research illuminates the mechanisms involving ferroptosis-related compounds and emphasizes the crosstalk between ferroptosis and other responses, including mitochondrial damage, endoplasmic reticulum stress (ER stress), autophagy, and the release of damage-associated molecular patterns (DAMPs), to reveal the intersections of regulatory mechanisms. This review also outlines the discovery, characterization, and pathological relevance of ferroptosis and notes controversial elements in ferroptosis-related mechanisms, such as nuclear factor E2-related factor 2 (Nrf2), sequestosome 1 (p62/SQSTM1), and heat shock protein family A member 5 (HSPA5). We hope our inferences will supply a partial reference for disorder prevention and treatment.
    DOI:  https://doi.org/10.1155/2020/9738143
  42. Neuropharmacology. 2020 Sep 02. pii: S0028-3908(20)30365-8. [Epub ahead of print] 108297
    Theilmann W, Gericke B, Schidlitzki A, Muneeb Anjum SM, Borsdorf S, Harries T, Roberds SL, Aguiar DJ, Brunner D, Leiser SC, Song D, Fabbro D, Hillmann P, Wymann MP, Löscher W.
      Mechanistic target of rapamycin (mTOR) regulates cell proliferation, growth and survival, and is activated in cancer and neurological disorders, including epilepsy. The rapamycin derivative ("rapalog") everolimus, which allosterically inhibits the mTOR pathway, is approved for the treatment of partial epilepsy with spontaneous recurrent seizures (SRS) in individuals with tuberous sclerosis complex (TSC). In contrast to the efficacy in TSC, the efficacy of rapalogs on SRS in other types of epilepsy is equivocal. Furthermore, rapalogs only poorly penetrate into the brain and are associated with peripheral adverse effects, which may compromise their therapeutic efficacy. Here we compare the antiseizure efficacy of three novel, brain-permeable ATP-competitive and selective mTORC1/2 inhibitors PQR620 and PQR626, and the selective dual pan-PI3K/mTORC1/2 inhibitor PQR530 in two mouse models of chronic epilepsy with SRS, the intrahippocampal kainate (IHK) mouse model of acquired temporal lobe epilepsy and Tsc1GFAP CKO mice, a well-characterized mouse model of epilepsy in TSC. During prolonged treatment of IHK mice with rapamycin, everolimus, PQR620, PQR626, or PQR530; only PQR620 exerted a transient antiseizure effect on SRS, at well tolerated doses whereas the other compounds were ineffective. In contrast, all of the examined compounds markedly suppressed SRS in Tsc1GFAP CKO mice during chronic treatment at well tolerated doses. Thus, against our expectation, no clear differences in antiseizure efficacy were found across the three classes of mTOR inhibitors examined in mouse models of genetic and acquired epilepsies. The main advantage of the novel 1,3,5-triazine derivatives is their excellent tolerability compared to rapalogs, which would favor their development as new therapies for TORopathies such as TSC.
    Keywords:  Acquired epilepsies; Antiseizure drugs; Genetic epilepsies; TORopathies; Tolerability
    DOI:  https://doi.org/10.1016/j.neuropharm.2020.108297
  43. Sci Rep. 2020 Sep 10. 10(1): 14874
    Kumar M, Papaleo E.
      Autophagy is a key clearance process to recycle damaged cellular components. One important upstream regulator of autophagy is ULK1 kinase. Several three-dimensional structures of the ULK1 catalytic domain are available, but a comprehensive study, including molecular dynamics, is missing. Also, an exhaustive description of ULK1 alterations found in cancer samples is presently lacking. We here applied a framework which links -omics data to structural protein ensembles to study ULK1 alterations from genomics data available for more than 30 cancer types. We predicted the effects of mutations on ULK1 function and structural stability, accounting for protein dynamics, and the different layers of changes that a mutation can induce in a protein at the functional and structural level. ULK1 is down-regulated in gynecological tumors. In other cancer types, ULK2 could compensate for ULK1 downregulation and, in the majority of the cases, no marked changes in expression have been found. 36 missense mutations of ULK1, not limited to the catalytic domain, are co-occurring with mutations in a large number of ULK1 interactors or substrates, suggesting a pronounced effect of the upstream steps of autophagy in many cancer types. Moreover, our results pinpoint that more than 50% of the mutations in the kinase domain of ULK1, here investigated, are predicted to affect protein stability. Three mutations (S184F, D102N, and A28V) are predicted with only impact on kinase activity, either modifying the functional dynamics or the capability to exert effects from distal sites to the functional and catalytic regions. The framework here applied could be extended to other protein targets to aid the classification of missense mutations from cancer genomics studies, as well as to prioritize variants for experimental validation, or to select the appropriate biological readouts for experiments.
    DOI:  https://doi.org/10.1038/s41598-020-71527-4
  44. Aging (Albany NY). 2020 Sep 09. 12
    Yang X, Zhang M, Dai Y, Sun Y, Aman Y, Xu Y, Yu P, Zheng Y, Yang J, Zhu X.
      Aging is the primary driver of various diseases, including common neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Currently there is no cure for AD and PD, and the development of novel drug candidates is demanding. Spermidine is a small anti-aging molecule with elimination of damaged mitochondria via the process of mitophagy identified as a molecular mechanism of action. Here, we show that spermidine inhibits memory loss in AD worms and improves behavioral performance, e.g., locomotor capacity, in a PD worm model, both via the PINK1-PDR1-dependent mitophagy pathway. Additionally, spermidine delays accelerated aging and improves healthspan in the DNA repair-deficient premature aging Werner syndrome (WS) worm model. While possible intertwined interactions between mitophagy/autophagy induction and DNA repair by spermidine are to be determined, our data support further translation of spermidine as a possible therapeutic intervention for such diseases.
    Keywords:  aging; caenorhabditis elegans; mitophagy; neurodegenerative diseases; spermidine
    DOI:  https://doi.org/10.18632/aging.103578
  45. Cell Metab. 2020 Aug 31. pii: S1550-4131(20)30424-1. [Epub ahead of print]
    Kim CS, Ding X, Allmeroth K, Biggs LC, Kolenc OI, L'Hoest N, Chacón-Martínez CA, Edlich-Muth C, Giavalisco P, Quinn KP, Denzel MS, Eming SA, Wickström SA.
      Stem cells reside in specialized niches that are critical for their function. Upon activation, hair follicle stem cells (HFSCs) exit their niche to generate the outer root sheath (ORS), but a subset of ORS progeny returns to the niche to resume an SC state. Mechanisms of this fate reversibility are unclear. We show that the ability of ORS cells to return to the SC state requires suppression of a metabolic switch from glycolysis to oxidative phosphorylation and glutamine metabolism that occurs during early HFSC lineage progression. HFSC fate reversibility and glutamine metabolism are regulated by the mammalian target of rapamycin complex 2 (mTORC2)-Akt signaling axis within the niche. Deletion of mTORC2 results in a failure to re-establish the HFSC niche, defective hair follicle regeneration, and compromised long-term maintenance of HFSCs. These findings highlight the importance of spatiotemporal control of SC metabolic states in organ homeostasis.
    Keywords:  Akt; Hif1; cell fate; glutamine; hair follicle; hypoxia; mTOR; mTORC2; metabolism; stem cell
    DOI:  https://doi.org/10.1016/j.cmet.2020.08.011
  46. Aging (Albany NY). 2020 Sep 09. 12
    Chen Y, Zhang P, Lin X, Zhang H, Miao J, Zhou Y, Chen G.
      Postoperative cognitive dysfunction (POCD) is frequently observed in elderly patients following anesthesia, but its pathophysiological mechanisms have not been fully elucidated. Sevoflurane was reported to repress autophagy in aged rat neurons; however, the role of mitophagy, which is crucial for the control of mitochondrial quality and neuronal health, in sevoflurane-induced POCD in aged rats remains undetermined. Therefore, this study investigated whether mitophagy impairment is involved in sevoflurane-induced cognitive dysfunction. We found sevoflurane treatment inhibited mitochondrial respiration and mitophagic flux, changes in mitochondria morphology, impaired lysosomal acidification, and increased Tomm20 and deceased LAMP1 accumulation were observed in H4 cell and aged rat models. Rapamycin counteracted ROS induced by sevoflurane, restored mitophagy and improved mitochondrial function. Furthermore, rapamycin ameliorated the cognitive deficits observed in aged rats given sevoflurane anesthesia as determined by the Morris water maze test; this improvement was associated with an increased number of dendritic spines and pyramidal neurons. Overexpression of PARK2, but not mutant PARK2 lacking enzyme activity, in H4 cells decreased ROS and Tomm20 accumulation and reversed mitophagy dysfunction after sevoflurane treatment. These findings suggest that mitophagy dysfunction could be a mechanism underlying sevoflurane-induced POCD and that activating mitophagy may provide a new strategy to rescue cognitive deficits.
    Keywords:  aged rat; mitophagy; postoperative cognitive dysfunction; rapamycin; sevoflurane
    DOI:  https://doi.org/10.18632/aging.103673
  47. Redox Biol. 2020 Aug 22. pii: S2213-2317(20)30900-9. [Epub ahead of print]37 101695
    Van Laar VS, Chen J, Zharikov AD, Bai Q, Di Maio R, Dukes AA, Hastings TG, Watkins SC, Greenamyre JT, St Croix CM, Burton EA.
      Convergent evidence implicates impaired mitochondrial function and α-Synuclein accumulation as critical upstream events in the pathogenesis of Parkinson's disease, but comparatively little is known about how these factors interact to provoke neurodegeneration. We previously showed that α-Synuclein knockdown protected rat substantia nigra dopaminergic neurons from systemic exposure to the mitochondrial complex I inhibitor rotenone. Here we show that motor abnormalities prior to neuronal loss in this model are associated with extensive α-Synuclein-dependent cellular thiol oxidation. In order to elucidate the underlying events in vivo we constructed novel transgenic zebrafish that co-express, in dopaminergic neurons: (i) human α-Synuclein at levels insufficient to provoke neurodegeneration or neurobehavioral abnormalities; and (ii) genetically-encoded ratiometric fluorescent biosensors to detect cytoplasmic peroxide flux and glutathione oxidation. Live intravital imaging of the intact zebrafish CNS at cellular resolution showed unequivocally that α-Synuclein amplified dynamic cytoplasmic peroxide flux in dopaminergic neurons following exposure to the mitochondrial complex I inhibitors MPP+ or rotenone. This effect was robust and clearly evident following either acute or prolonged exposure to each inhibitor. In addition, disturbance of the resting glutathione redox potential following exogenous hydrogen peroxide challenge was augmented by α-Synuclein. Together these data show that α-Synuclein is a critical determinant of the redox consequences of mitochondrial dysfunction in dopaminergic neurons. The findings are important because the mechanisms underlying α-Synuclein-dependent reactive oxygen species fluxes and antioxidant suppression might provide a pharmacological target in Parkinson's disease to prevent progression from mitochondrial dysfunction and oxidative stress to cell death.
    Keywords:  Dopaminergic neuron; Glutathione; Parkinson's disease; Peroxide; Zebrafish; α-Synuclein
    DOI:  https://doi.org/10.1016/j.redox.2020.101695
  48. J Cancer. 2020 ;11(19): 5802-5811
    Liu J, Liang H, Khilji S, Li H, Song D, Chen C, Wang X, Zhang Y, Zhao N, Li X, Gao A.
      Moxidectin (MOX), a broad-spectrum antiparasitic drug, has been characterized as a potential anti-glioma agent. The main objective of this study was to explore autophagy induced by MOX in glioma U251 and C6 cells, and the deep underlying molecular mechanisms. In addition, the effects of autophagy on apoptosis in glioma cells were tested. Autophagy was measured by transmission electron microscopy (TEM), immunofluorescence, western blot and immunohistochemistry. Cell viability was detected with MTT and colony formation assay. The apoptosis rate was measured by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL). Additonally, autophagy inhibition was achieved by using 3-Methyladenine (3-MA) and chloroquine (CQ). U251-derived xenografts were established for examination of MOX-induced autophagy on glioma in vivo. Firstly, our research found that MOX stimulated autophagy of glioma cells in a dose-dependent manner. Secondly, we found that MOX induced autophagy by inhibiting the AKT/mTOR signalling pathway. Thirdly, inhibition of autophagy could reduce apoptosis in MOX-treated glioma cells. Finally, MOX induced autophagy, and autophagy increased the apoptosis effect of MOX on U251 in vivo. In conclusion, our data provide evidence that MOX can induce autophagy in glioma cells, and autophagy could increase MOX-induced apoptosis through inhibiting the AKT/mTOR signalling pathway. These findings provided a new prospect for the application of MOX and a novel targeted therapy for the treatment of gliomas.
    Keywords:  AKT/mTOR; Autophagy; Glioma; Moxidectin
    DOI:  https://doi.org/10.7150/jca.46697
  49. Neurochem Res. 2020 Sep 11.
    Nascimento AC, Erustes AG, Reckziegel P, Bincoletto C, Ureshino RP, Pereira GJS, Smaili SS.
      Although the etiology of Parkinson's disease (PD) is multifactorial, it has been linked to abnormal accumulation of α-synuclein (α-syn) in dopaminergic neurons, which could lead to dysfunctions on intracellular organelles, with potential neurodegeneration. Patients with familial early-onset PD frequently present mutation in the α-syn gene (SNCA), which encodes mutant α-syn forms, such as A30P and A53T, which potentially regulate Ca2+ unbalance. Here we investigated the effects of overexpression of wild-type α-syn (WT) and the mutant forms A30P and A53T, on modulation of lysosomal Ca2+ stores and further autophagy activation. We found that in α-syn-overexpressing cells, there was a decrease in Ca2+ released from endoplasmic reticulum (ER) which is related to the increase in lysosomal Ca2+ release, coupled to lysosomal pH alkalization. Interestingly, α-syn-overexpressing cells showed lower LAMP1 levels, and a disruption of lysosomal morphology and distribution, affecting autophagy. Interestingly, all these effects were more evident with A53T mutant isoform when compared to A30P and WT α-syn types, indicating that the pathogenic phenotype for PD is potentially related to impairment of α-syn degradation. Taken together, these events directly impact PD-related dysfunctions, being considered possible molecular targets for neuroprotection.
    Keywords:  Calcium; Lysosomes; Parkinson’s disease; α-Synuclein
    DOI:  https://doi.org/10.1007/s11064-020-03126-8