bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2020‒05‒10
38 papers selected by
Viktor Korolchuk
Newcastle University


  1. Nat Rev Mol Cell Biol. 2020 May 05.
    Nakatogawa H.
      Autophagosomes are double-membrane vesicles newly formed during autophagy to engulf a wide range of intracellular material and transport this autophagic cargo to lysosomes (or vacuoles in yeasts and plants) for subsequent degradation. Autophagosome biogenesis responds to a plethora of signals and involves unique and dynamic membrane processes. Autophagy is an important cellular mechanism allowing the cell to meet various demands, and its disruption compromises homeostasis and leads to various diseases, including metabolic disorders, neurodegeneration and cancer. Thus, not surprisingly, the elucidation of the molecular mechanisms governing autophagosome biogenesis has attracted considerable interest. Key molecules and organelles involved in autophagosome biogenesis, including autophagy-related (ATG) proteins and the endoplasmic reticulum, have been discovered, and their roles and relationships have been investigated intensely. However, several fundamental questions, such as what supplies membranes/lipids to build the autophagosome and how the membrane nucleates, expands, bends into a spherical shape and finally closes, have proven difficult to address. Nonetheless, owing to recent studies with new approaches and technologies, we have begun to unveil the mechanisms underlying these processes on a molecular level. We now know that autophagosome biogenesis is a highly complex process, in which multiple proteins and lipids from various membrane sources, supported by the formation of membrane contact sites, cooperate with biophysical phenomena, including membrane shaping and liquid-liquid phase separation, to ensure seamless segregation of the autophagic cargo. Together, these studies pave the way to obtaining a holistic view of autophagosome biogenesis.
    DOI:  https://doi.org/10.1038/s41580-020-0241-0
  2. Autophagy. 2020 May 05.
    Yang Y, White E.
      Macroautophagy (hereafter autophagy) plays an important role in maintaining cellular homeostasis under stress conditions. We previously demonstrated that conditional autophagy deficiency in adult mice causes selective tissue damage, is lethal upon fasting, and shortens lifespan to less than three months primarily due to neurodegeneration, but not all the mechanisms are known. We conditionally deleted Trp53/p53 and/or the essential autophagy gene Atg7 throughout adult mice to test whether TRP53 is responsible for any of these phenotypes. atg7Δ/Δ trp53Δ/Δ mice have extended lifespan due to delayed tissue damage and neurodegeneration, and are resistant to death upon fasting compared to atg7Δ/Δ mice. Atg7 also suppresses apoptosis induced by the TRP53 activator Nutlin-3 in liver and brain. We then deleted Atg7 in the presence or absence of the master regulator of antioxidant defense NFE2L2/NRF2 (nuclear factor, erythroid derived 2, like 2) to test if increased oxidative stress causes TRP53 activation in atg7Δ/Δ mice. nfe2l2-/-atg7Δ/Δ mice die rapidly due to intestinal damage, which is not rescued by trp53 co-deletion. Therefore, these data demonstrate the tissue specificities and functional dependencies between autophagy, TRP53 and NFE2L2 stress response mechanisms.
    Keywords:  ATG7; DNA damage; NRF2; apoptosis; autophagy; brain; intestine; liver; oxidative stress; p53
    DOI:  https://doi.org/10.1080/15548627.2020.1765522
  3. Elife. 2020 May 04. pii: e56590. [Epub ahead of print]9
    Hoffmann-Conaway S, Brockmann MM, Schneider K, Annamneedi A, Rahman KA, Bruns C, Textoris-Taube K, Trimbuch T, Smalla KH, Rosenmund C, Gundelfinger ED, Garner CC, Montenegro-Venegas C.
      Mechanisms regulating the turnover of synaptic vesicle (SV) proteins are not well understood. They are thought to require poly-ubiquitination and degradation through proteasome, endo-lysosomal or autophagy-related pathways. Bassoon was shown to negatively regulate presynaptic autophagy in part by scaffolding Atg5. Here, we show that increased autophagy in Bassoon knockout neurons depends on poly-ubiquitination and that the loss of Bassoon leads to elevated levels of ubiquitinated synaptic proteins per se. Our data show that Bassoon knockout neurons have a smaller SV pool size and a higher turnover rate as indicated by a younger pool of SV2. The E3 ligase Parkin is required for increased autophagy in Bassoon-deficient neurons as the knockdown of Parkin normalized autophagy and SV protein levels and rescued impaired SV recycling. These data indicate that Bassoon is a key regulator of SV proteostasis and that Parkin is a key E3 ligase in the autophagy-mediated clearance of SV proteins.
    Keywords:  mouse; neuroscience
    DOI:  https://doi.org/10.7554/eLife.56590
  4. Front Cell Dev Biol. 2020 ;8 239
    Bakula D, Scheibye-Knudsen M.
      Maintaining mitochondrial health is emerging as a keystone in aging and associated diseases. The selective degradation of mitochondria by mitophagy is of particular importance in keeping a pristine mitochondrial pool. Indeed, inherited monogenic diseases with defects in mitophagy display complex multisystem pathologies but particularly progressive neurodegeneration. Fortunately, therapies are being developed that target mitophagy allowing new hope for treatments for previously incurable diseases. Herein, we describe mitophagy and associated diseases, coin the term mitophaging and describe new small molecule interventions that target different steps in the mitophagic pathway. Consequently, several age-associated diseases may be treated by targeting mitophagy.
    Keywords:  aging; autophagy; interventions; mitophaging; mitophagy; monogenic disorders
    DOI:  https://doi.org/10.3389/fcell.2020.00239
  5. Cells. 2020 May 04. pii: E1131. [Epub ahead of print]9(5):
    Trivedi PC, Bartlett JJ, Pulinilkunnil T.
      Lysosomes are the main proteolytic compartments of mammalian cells comprising of a battery of hydrolases. Lysosomes dispose and recycle extracellular or intracellular macromolecules by fusing with endosomes or autophagosomes through specific waste clearance processes such as chaperone-mediated autophagy or microautophagy. The proteolytic end product is transported out of lysosomes via transporters or vesicular membrane trafficking. Recent studies have demonstrated lysosomes as a signaling node which sense, adapt and respond to changes in substrate metabolism to maintain cellular function. Lysosomal dysfunction not only influence pathways mediating membrane trafficking that culminate in the lysosome but also govern metabolic and signaling processes regulating protein sorting and targeting. In this review, we describe the current knowledge of lysosome in influencing sorting and nutrient signaling. We further present a mechanistic overview of intra-lysosomal processes, along with extra-lysosomal processes, governing lysosomal fusion and fission, exocytosis, positioning and membrane contact site formation. This review compiles existing knowledge in the field of lysosomal biology by describing various lysosomal events necessary to maintain cellular homeostasis facilitating development of therapies maintaining lysosomal function.
    Keywords:  autophagy; calcium; cathepsin; endocytosis; lysosome; mannose-6-phosphate; metabolism; proton
    DOI:  https://doi.org/10.3390/cells9051131
  6. J Biol Chem. 2020 May 08. pii: jbc.RA120.012659. [Epub ahead of print]
    Newton J, Palladino END, Weigel C, Maceyka M, Gräler MH, Senkal CE, Enriz RD, Marvanova P, Jampilek J, Lima S, Milstien S, Spiegel S.
      Niemann-Pick type C (NPC) disease is a lysosomal storage disorder arising from mutations in the cholesterol-trafficking proteins NPC1 (95%) or NPC2 (5%). These mutations result in accumulation of low-density lipoprotein-derived cholesterol in late endosomes/lysosomes, disruption of endocytic trafficking, and stalled autophagic flux. Additionally, NPC disease results in sphingolipid accumulation, yet it is unique among the sphingolipidoses because of the absence of mutations in the enzymes responsible for sphingolipid degradation. In this work, we examined the cause for sphingosine and sphingolipid accumulation in multiple cellular models of NPC disease and observed that the activity of sphingosine kinase 1 (SphK1), one of the two isoenzymes that phosphorylate sphingoid bases, was markedly reduced in both NPC1 mutant and NPC1 knockout cells. Conversely, SphK1 inhibition with the isotype-specific inhibitor SK1-I in wild type cells induced accumulation of cholesterol and reduced cholesterol esterification. Of note, a novel SphK1 activator (SK1-A) that we have characterized decreased sphingoid base and complex sphingolipid accumulation and ameliorated autophagic defects in both NPC1 mutant and NPC1 knockout cells. Remarkably, in these cells, SK1-A also reduced cholesterol accumulation and increased cholesterol ester formation. Our results indicate that a SphK1 activator rescues aberrant cholesterol and sphingolipid storage and trafficking in NPC1 mutant cells. These observations highlight a previously unknown link between SphK1 activity, NPC1, and cholesterol trafficking and metabolism.
    Keywords:  NPC1; Sphingosine kinase (SphK); cholesterol; lipid metabolism; sphingolipid; sphingosine-1-phosphate (S1P)
    DOI:  https://doi.org/10.1074/jbc.RA120.012659
  7. Autophagy. 2020 May 06. 1-14
    Brattås PL, Hersbach BA, Madsen S, Petri R, Jakobsson J, Pircs K.
      Activation of macroautophagy/autophagy, a key mechanism involved in the degradation and removal of aggregated proteins, can successfully reverse Huntington disease phenotypes in various model systems. How neuronal autophagy impairments need to be considered in Huntington disease progression to achieve a therapeutic effect is currently not known. In this study, we used a mouse model of HTT (huntingtin) protein aggregation to investigate how different methods and timing of autophagy activation influence the efficacy of autophagy-activating treatment in vivo. We found that overexpression of human TFEB, a master regulator of autophagy, did not decrease mutant HTT aggregation. On the other hand, Becn1 overexpression, an autophagic regulator that plays a key role in autophagosome formation, partially cleared mutant HTT aggregates and restored neuronal pathology, but only when administered early in the disease progression. When Becn1 was administered at a later stage, when prominent mutant HTT accumulation and autophagy impairments have occurred, Becn1 overexpression did not rescue the mutant HTT-associated phenotypes. Together, these results demonstrate that the targets used to activate autophagy, as well as the timing of autophagy activation, are crucial for achieving efficient therapeutic effects.Abbreviations: AAV: adeno-associated viral vectors; ACTB: actin beta; BECN1: beclin 1, autophagy related; DAPI: 4',6-diamidino-2-phenylindole; GO: gene ontology; HD: Huntington disease; HTT: huntingtin; ICQ: Li's intensity correlation quotient; IHC: immunohistochemistry; LAMP1: lysosomal-associated membrane protein 1; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mHTT: mutant huntingtin; PCA: principal component analysis; PPP1R1B/DARPP-32: protein phosphatase 1 regulatory inhibitor subunit 1B; SQSTM1: sequestosome 1; TFEB: transcription factor EB; WB: western blot; WT: wild-type.
    Keywords:  Adeno-associated viral vectors; BECN1/beclin-1; Huntington disease; TFEB; autophagy; macroautophagy; neurodegeneration
    DOI:  https://doi.org/10.1080/15548627.2020.1760014
  8. Cell Discov. 2020 ;6 23
    Martens S, Fracchiolla D.
      ATG8 family proteins are evolutionary conserved ubiquitin-like modifiers, which become attached to the headgroup of the membrane lipid phosphatidylethanolamine in a process referred to as lipidation. This reaction is carried out analogous to the conjugation of ubiquitin to its target proteins, involving the E1-like ATG7, the E2-like ATG3 and the E3-like ATG12-ATG5-ATG16 complex, which determines the site of lipidation. ATG8 lipidation is a hallmark of autophagy where these proteins are involved in autophagosome formation, the fusion of autophagosomes with lysosomes and cargo selection. However, it has become evident that ATG8 lipidation also occurs in processes that are not directly related to autophagy. Here we discuss recent insights into the targeting of ATG8 lipidation in autophagy and other pathways with special emphasis on the recruitment and activation of the E3-like complex.
    Keywords:  Macroautophagy; Phagocytosis
    DOI:  https://doi.org/10.1038/s41421-020-0155-1
  9. J Clin Invest. 2020 May 04. pii: 132366. [Epub ahead of print]
    Nah J, Zhai P, Huang CY, Fernández ÁF, Mareedu S, Levine B, Sadoshima J.
      Although autophagy is generally protective, uncontrolled or excessive activation of autophagy can be detrimental. However, it is often difficult to distinguish death by autophagy from death with autophagy, and whether autophagy contributes to death in cardiomyocytes (CMs) is still controversial. Excessive activation of autophagy induces a morphologically and biochemically defined form of cell death termed autosis. Whether autosis is involved in tissue injury induced under pathologically relevant conditions is poorly understood. In the present study, myocardial ischemia/reperfusion (I/R) induced autosis in CMs, as evidenced by cell death with numerous vacuoles and perinuclear spaces, and depleted intracellular membranes. Autosis was observed frequently after 6 hours of reperfusion, accompanied by upregulation of Rubicon, attenuation of autophagic flux, and marked accumulation of autophagosomes. Genetic downregulation of Rubicon inhibited autosis and reduced I/R injury, whereas stimulation of autosis during the late phase of I/R with Tat-Beclin 1 exacerbated injury. Suppression of autosis by ouabain, a cardiac glycoside, in humanized Na+,K+-ATPase-knockin mice reduced I/R injury. Taken together, these results demonstrate that autosis is significantly involved in I/R injury in the heart and triggered by dysregulated accumulation of autophagosomes due to upregulation of Rubicon.
    Keywords:  Autophagy; Cardiology; Cell Biology; Signal transduction
    DOI:  https://doi.org/10.1172/JCI132366
  10. Biomed Pharmacother. 2020 Apr 28. pii: S0753-3322(20)30317-6. [Epub ahead of print]127 110125
    Wang X, Feng L, Xin M, Hao Y, Wang X, Shang P, Zhao M, Hou S, Zhang Y, Xiao Y, Ma D, Feng J.
      Connexin-43 (Cx43) is the most abundant gap junction protein in the nervous system. It enables cell communication and has important physiological roles including ion transport and substrate exchange, all of which have been implicated in cerebral ischemia injury. Our previous in vitro and in vivo studies have demonstrated that Cx43 is internalized and degraded during ischemia stress. However, the significance of ischemia-induced degradation of Cx43 remains unclear. Herein, we demonstrated that Cx43 degradation during ischemia injury is mediated by selective autophagy; additionally, we identified two related autophagy receptors-OPTN and NDP52. Cx43 degradation during ischemia requires its phosphorylation and ubiquitination, which are mediated by PKC, Src kinases, and ubiquitin kinase PINK1. Using point mutagenesis, we identified three phosphorylation sites underlying Cx43 autophagy degradation under ischemic stress. Cx43 degradation inhibition promoted the transition of astrocytes from a pro-inflammatory to an anti-inflammatory status, based on the levels of IL-10 and TNF in ischemia. Knockdown or accelerated degradation of Cx43 protected astrocytes from apoptosis under ischemic stress. These findings elucidate the underlying mechanism of astrocytic Cx43 autophagic degradation during ischemia. The study has identified potentially novel therapeutic strategies against ischemic stroke and evidence of crosstalk between autophagic degradation of Cx43, astrocytic apoptosis, and neuroinflammation.
    Keywords:  Astrocytes; Autophagy; Cx43; NDP52; OPTN; Oxygen-glucose deprivation; PINK1; Phosphorylation
    DOI:  https://doi.org/10.1016/j.biopha.2020.110125
  11. J Cell Sci. 2020 May 06. pii: jcs.239822. [Epub ahead of print]
    O'Loughlin T, Kruppa AJ, Ribeiro ALR, Edgar JR, Ghannam A, Smith AM, Buss F.
      Optineurin (OPTN) is a multifunctional protein involved in autophagy, secretion as well as NF-κB and IRF3 signalling and OPTN mutations are associated with several human diseases. Here we show that, in response to viral RNA, OPTN translocates to foci in the perinuclear region, where it negatively regulates NF-κB and IRF3 signalling pathways and downstream pro-inflammatory cytokine secretion. These OPTN foci consist of a tight cluster of small membrane vesicles, which are positive for ATG9A. Disease mutations linked to POAG cause aberrant foci formation in the absence of stimuli, which correlates with the ability of OPTN to inhibit signalling. Using proximity labelling proteomics, we identify the LUBAC complex, CYLD and TBK1 as part of the OPTN interactome and show that these proteins are recruited to this OPTN-positive perinuclear compartment. Our work uncovers a crucial role for OPTN in dampening NF-κB and IRF3 signalling through the sequestration of LUBAC and other positive regulators in this viral RNA-induced compartment leading to altered pro-inflammatory cytokine secretion.
    Keywords:  ATG9A; BioID; Functional proteomics; IFN; LUBAC; Linear ubiquitin; NF-κB; OPTN; TBK1
    DOI:  https://doi.org/10.1242/jcs.239822
  12. JCI Insight. 2020 May 07. pii: 128820. [Epub ahead of print]5(9):
    Kanno A, Asahara SI, Furubayashi A, Masuda K, Yoshitomi R, Suzuki E, Takai T, Kimura-Koyanagi M, Matsuda T, Bartolome A, Hirota Y, Yokoi N, Inaba Y, Inoue H, Matsumoto M, Inoue K, Abe T, Wei FY, Tomizawa K, Ogawa W, Seino S, Kasuga M, Kido Y.
      EIF2AK4, which encodes the amino acid deficiency-sensing protein GCN2, has been implicated as a susceptibility gene for type 2 diabetes in the Japanese population. However, the mechanism by which GCN2 affects glucose homeostasis is unclear. Here, we show that insulin secretion is reduced in individuals harboring the risk allele of EIF2AK4 and that maintenance of GCN2-deficient mice on a high-fat diet results in a loss of pancreatic β cell mass. Our data suggest that GCN2 senses amino acid deficiency in β cells and limits signaling by mechanistic target of rapamycin complex 1 to prevent β cell failure during the consumption of a high-fat diet.
    Keywords:  Endocrinology; Insulin signaling; Islet cells; Metabolism
    DOI:  https://doi.org/10.1172/jci.insight.128820
  13. J Biol Chem. 2020 May 08. pii: jbc.RA119.011650. [Epub ahead of print]
    Lautenschläger J, Wagner-Valladolid S, Stephens AD, Fernández-Villegas A, Hockings C, Mishra A, Manton JD, Fantham MJ, Lu M, Rees EJ, Kaminski CF, Kaminski Schierle GS.
      Mitochondrial dysfunction has long been implicated in the neurodegenerative disorder Parkinson's disease (PD); however, it is unclear how mitochondrial impairment and α-synuclein pathology are coupled. Using specific mitochondrial inhibitors, EM analysis, and biochemical assays, we report here that intramitochondrial protein homeostasis plays a major role in α-synuclein aggregation. We found that interference with intramitochondrial proteases, such as HtrA2 and Lon protease, and mitochondrial protein import significantly aggravates α-synuclein seeding. In contrast, direct inhibition of mitochondrial complex I, an increase in intracellular calcium concentration, or formation of reactive oxygen species (ROS), all of which have been associated with mitochondrial stress, did not affect α-synuclein pathology. We further demonstrate that similar mechanisms are involved in amyloid β 1-42 (Aβ42) aggregation. Our results suggest that, in addition to other protein quality-control pathways such as the ubiquitin-proteasome system, mitochondria per se can influence protein homeostasis of cytosolic aggregation-prone proteins.  We propose that approaches that seek to maintain mitochondrial fitness, rather than target downstream mitochondrial dysfunction, may aid in the search for therapeutic strategies to manage PD and related neuropathologies.
    Keywords:  HtrA serine peptidase 2; HtrA2/Omi; Lon peptidase 1 mitochondrial; Lon protease; Parkinson disease; alpha-synuclein (a-synuclein); amyloid-beta (AB); mitochondria; neurodegeneration; neurodegenerative disease; protein aggregation; protein homeostasis
    DOI:  https://doi.org/10.1074/jbc.RA119.011650
  14. Cell. 2020 Apr 30. pii: S0092-8674(20)30336-6. [Epub ahead of print]181(3): 748-748.e1
    Holland LKK, Nielsen IØ, Maeda K, Jäättelä M.
      In addition to their well-defined recycling function, lysosomes act as metabolic signaling hubs that adjust cellular metabolism according to the availability of nutrients and growth factors by regulating metabolic kinases and transcription factors on their surface. Moreover, lysosomal hydrolases and ions released to cytosol or extracellular space have recently emerged as important regulators of various cellular processes from cell death to cell division. To view this SnapShot, open or download the PDF.
    DOI:  https://doi.org/10.1016/j.cell.2020.03.043
  15. Int J Mol Sci. 2020 May 06. pii: E3289. [Epub ahead of print]21(9):
    Yun HR, Jo YH, Kim J, Shin Y, Kim SS, Choi TG.
      Autophagy is a catabolic process for unnecessary or dysfunctional cytoplasmic contents by lysosomal degradation pathways. Autophagy is implicated in various biological processes such as programmed cell death, stress responses, elimination of damaged organelles and development. The role of autophagy as a crucial mediator has been clarified and expanded in the pathological response to redox signalling. Autophagy is a major sensor of the redox signalling. Reactive oxygen species (ROS) are highly reactive molecules that are generated as by-products of cellular metabolism, principally by mitochondria. Mitochondrial ROS (mROS) are beneficial or detrimental to cells depending on their concentration and location. mROS function as redox messengers in intracellular signalling at physiologically low level, whereas excessive production of mROS causes oxidative damage to cellular constituents and thus incurs cell death. Hence, the balance of autophagy-related stress adaptation and cell death is important to comprehend redox signalling-related pathogenesis. In this review, we attempt to provide an overview the basic mechanism and function of autophagy in the context of response to oxidative stress and redox signalling in pathology.
    Keywords:  autophagy; oxidative stress; reactive oxygen species
    DOI:  https://doi.org/10.3390/ijms21093289
  16. Clin Chim Acta. 2020 Apr 30. pii: S0009-8981(20)30192-3. [Epub ahead of print]
    Zhou H, He L, Xu G, Chen L.
      Cardiovascular disease (CVD) leads to high morbidity and mortality rates worldwide. Accumulating evidence has revealed that mitochondria dysfunction is implicated in CVD, such as atherosclerosis (AS), hypertension, myocardial ischemia-reperfusion (MI/R) injury, myocardial infarction (MI), cardiac hypertrophy, heart failure (HF), dilated cardiomyopathy (DCM) and so on. Mitophagy is a mitochondrial quality control mechanism that eliminates damaged or superfluous mitochondria to maintain cardiac function in response to various stress and cardiac disease conditions. This article reviews the latest findings regarding the mechanistic, functional, and potential role of mitophagy in the pathogenesis of CVD. Moreover, various drugs can target mitophagy activity during CVD progression. Thus, the modulation of the mitophagy pathway provides a potential therapeutic strategy for CVD management.
    DOI:  https://doi.org/10.1016/j.cca.2020.04.033
  17. Cell Discov. 2020 ;6 24
    Stamatakou E, Wróbel L, Hill SM, Puri C, Son SM, Fujimaki M, Zhu Y, Siddiqi F, Fernandez-Estevez M, Manni MM, Park SJ, Villeneuve J, Rubinsztein DC.
      The lysosomal degradation pathway of macroautophagy (herein referred to as autophagy) plays a crucial role in cellular physiology by regulating the removal of unwanted cargoes such as protein aggregates and damaged organelles. Over the last five decades, significant progress has been made in understanding the molecular mechanisms that regulate autophagy and its roles in human physiology and diseases. These advances, together with discoveries in human genetics linking autophagy-related gene mutations to specific diseases, provide a better understanding of the mechanisms by which autophagy-dependent pathways can be potentially targeted for treating human diseases. Here, we review mutations that have been identified in genes involved in autophagy and their associations with neurodegenerative diseases.
    Keywords:  Macroautophagy; Mechanisms of disease
    DOI:  https://doi.org/10.1038/s41421-020-0158-y
  18. Neurosci Res. 2020 Apr 29. pii: S0168-0102(20)30176-0. [Epub ahead of print]
    Sato S, Noda S, Hattori N.
      In 2018, we summarized Parkin mutation analysis over the 20 years since its discovery. As a strategy for treating Parkinson's disease (PD), disease-modifying therapies based on the overall picture of PD, including pathological studies of hereditary PD, have been developed. With the discovery of Parkin, research on PD accelerated explosively around the world. Several PD mouse models were generated to investigate the pathology of PD. Recently, we reported dopaminergic neuron-specific autophagy-deficient mice as a model of sporadic PD. These mice exhibit Lewy pathology and motor dysfunction, and provide in vivo evidence for Lewy body formation. In these animals, synuclein deposition is preceded by p62, resulting in the formation of inclusions containing both proteins. The number and size of these inclusions increase gradually with aging. Consequently, dopaminergic (DA) neuron loss and motor dysfunction are observed in 120-week-old mice. To assess the critical role of Parkin in vivo, we characterized Parkin-knockout mice over a long period of time. At the age of 110 weeks, Parkin-knockout mice exhibited locomotor impairments, including hindlimb defects and neuronal loss, and fragmented mitochondria with abnormal internal structures accumulated in their DA neurons. Age-related motor dysfunction and damaged mitochondria were observed in Parkin-deficient mice.
    Keywords:  Parkin; Parkinson’s disease; aging; dopaminergic neuron; mitochondria; mitophagy
    DOI:  https://doi.org/10.1016/j.neures.2020.03.014
  19. Int Rev Cell Mol Biol. 2020 ;pii: S1937-6448(19)30124-8. [Epub ahead of print]353 255-284
    Rasmussen ML, Gama V.
      The B cell CLL/lymphoma-2 (BCL-2) family of proteins control the mitochondrial pathway of apoptosis, also known as intrinsic apoptosis. Direct binding between members of the BCL-2 family regulates mitochondrial outer membrane permeabilization (MOMP) after an apoptotic insult. The ability of the cell to sense stress and translate it into a death signal has been a major theme of research for nearly three decades; however, other mechanisms by which the BCL-2 family coordinates cellular homeostasis beyond its role in initiating apoptosis are emerging. One developing area of research is understanding how the BCL-2 family of proteins regulate development using pluripotent stem cells as a model system. Understanding BCL-2 family-mediated regulation of mitochondrial homeostasis in cell death and beyond would uncover new facets of stem cell maintenance and differentiation potential.
    Keywords:  Apoptosis; BCL-2 family; Mitochondria; Mitochondrial dynamics; Pluripotency; Stem cells
    DOI:  https://doi.org/10.1016/bs.ircmb.2019.12.005
  20. Aging (Albany NY). 2020 May 04. 12
    Wang S, Wu YY, Wang X, Shen P, Jia Q, Yu S, Wang Y, Li X, Chen W, Wang A, Lu Y.
      Biologically active natural products have been used for the chemoprevention of cutaneous tumors. Lycopene is the main active phytochemical in tomatoes. We herein aimed to assess the cancer preventive effects of lycopene and to find potential molecular targets. In chemically-induced cutaneous tumor mice and cell models, lycopene attenuated cutaneous tumor incidence and multiplicity as well as the tumorigenesis of normal cutaneous cells in phase-selectivity (only in the promotion phase) manners. By utilizing a comprehensive approach combining bioinformatics with network pharmacology, we predicted that intracellular autophagy and redox status were associated with lycopene's preventive effect on cutaneous tumors. Lycopene stimulated the activation of antioxidant enzymes and the translocation of the transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) that predominantly maintained intracellular redox equilibrium. The cancer chemopreventive effects were mediated by Nrf2. Further, lycopene enhanced the expression of autophagy protein p62. Therefore this led to the degradation of Keap1(Kelch ECH associating protein 1), the main protein locking Nrf2 in cytoplasm. In conclusion, our study provides preclinical evidence of the chemopreventive effects of lycopene on cutaneous tumors and reveals the mechanistic link between lycopene's stimulation of Nrf2 signaling pathway and p62-mediated degradation of Keap1 via the autophagy-lysosomal pathway.
    Keywords:  Nrf2; autophagy; chemoprevention; cutaneous tumor; lycopene
    DOI:  https://doi.org/10.18632/aging.103132
  21. Cell Death Discov. 2020 ;6 32
    Zhang W, Li X, Wang S, Chen Y, Liu H.
      The transcription factor EB (TFEB) regulates the expression of target genes bearing the Coordinated Lysosomal Expression and Regulation (CLEAR) motif, thereby modulating autophagy and lysosomal biogenesis. Furthermore, TFEB can bind to the promoter of autophagy-associated genes and induce the formation of autophagosomes, autophagosome-lysosome fusion, and lysosomal cargo degradation. An increasing number of studies have shown that TFEB stimulates the intracellular clearance of pathogenic factors by enhancing autophagy and lysosomal function in multiple kidney diseases, such as cystinosis, acute kidney injury, and diabetic nephropathy. Taken together, this highlights the importance of developing novel therapeutic strategies against kidney diseases based on TFEB regulation. In this review, we present an overview of the current data on TFEB and its implication in kidney disease.
    Keywords:  Acute kidney injury; Nephrons
    DOI:  https://doi.org/10.1038/s41420-020-0265-4
  22. EMBO J. 2020 May 05. e103181
    Lin Z, Niu Y, Wan A, Chen D, Liang H, Chen X, Sun L, Zhan S, Chen L, Cheng C, Zhang X, Bu X, He W, Wan G.
      N6-methyladenosine (m6 A) is an abundant nucleotide modification in mRNA, known to regulate mRNA stability, splicing, and translation, but it is unclear whether it is also has a physiological role in the intratumoral microenvironment and cancer drug resistance. Here, we find that METTL3, a primary m6 A methyltransferase, is significantly down-regulated in human sorafenib-resistant hepatocellular carcinoma (HCC). Depletion of METTL3 under hypoxia promotes sorafenib resistance and expression of angiogenesis genes in cultured HCC cells and activates autophagy-associated pathways. Mechanistically, we have identified FOXO3 as a key downstream target of METTL3, with m6 A modification of the FOXO3 mRNA 3'-untranslated region increasing its stability through a YTHDF1-dependent mechanism. Analysis of clinical samples furthermore showed that METTL3 and FOXO3 levels are tightly correlated in HCC patients. In mouse xenograft models, METTL3 depletion significantly enhances sorafenib resistance of HCC by abolishing the identified METTL3-mediated FOXO3 mRNA stabilization, and overexpression of FOXO3 restores m6 A-dependent sorafenib sensitivity. Collectively, our work reveals a critical function for METTL3-mediated m6 A modification in the hypoxic tumor microenvironment and identifies FOXO3 as an important target of m6 A modification in the resistance of HCC to sorafenib therapy.
    Keywords:  FOXO3; METTL3; N6-methyladenosine; autophagy; hypoxia
    DOI:  https://doi.org/10.15252/embj.2019103181
  23. EMBO Rep. 2020 May 05. e48950
    Choi YR, Kim JB, Kang SJ, Noh HR, Jou I, Joe EH, Park SM.
      Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons located in the substantia nigra pars compacta and the presence of proteinaceous inclusions called Lewy bodies and Lewy neurites in numerous brain regions. Increasing evidence indicates that Lewy pathology progressively involves additional regions of the nervous system as the disease advances, and the prion-like propagation of α-synuclein (α-syn) pathology promotes PD progression. Accordingly, the modulation of α-syn transmission may be important for the development of disease-modifying therapies in patients with PD. Here, we demonstrate that α-syn fibrils induce c-src activation in neurons, which depends on the FcγRIIb-SHP-1/-2-c-src pathway and enhances signals for the uptake of α-syn into neurons. Blockade of c-src activation inhibits the uptake of α-syn and the formation of Lewy body-like inclusions. Furthermore, the blockade of c-src activation also inhibits the release of α-syn via activation of autophagy. The brain-permeable c-src inhibitor, saracatinib, efficiently reduces α-syn propagation into neighboring regions in an in vivo model system. These results suggest a new therapeutic target against progressive PD.
    Keywords:  Parkinson's disease; c-src; prion; α-synuclein
    DOI:  https://doi.org/10.15252/embr.201948950
  24. Mol Psychiatry. 2020 May 04.
    Xu Y, Du S, Marsh JA, Horie K, Sato C, Ballabio A, Karch CM, Holtzman DM, Zheng H.
      Neurofibrillary tangles (NFTs) composed of hyperphosphorylated and misfolded tau protein are a pathological hallmark of Alzheimer's disease and other tauopathy conditions. Tau is predominantly an intraneuronal protein but is also secreted in physiological and pathological conditions. The extracellular tau has been implicated in the seeding and propagation of tau pathology and is the prime target of the current tau immunotherapy. However, truncated tau species lacking the microtubule-binding repeat (MTBR) domains essential for seeding have been shown to undergo active secretion and the mechanisms and functional consequences of the various extracellular tau are poorly understood. We report here that the transcription factor EB (TFEB), a master regulator of lysosomal biogenesis, plays an essential role in the lysosomal exocytosis of selected tau species. TFEB loss of function significantly reduced the levels of interstitial fluid (ISF) tau in PS19 mice expressing P301S mutant tau and in conditioned media of mutant tau expressing primary neurons, while the secretion of endogenous wild-type tau was not affected. Mechanistically we found that TFEB regulates the secretion of truncated mutant tau lacking MTBR and this process is dependent on the lysosomal calcium channel TRPML1. Consistent with the seeding-incompetent nature of the truncated tau and supporting the concept that TFEB-mediated lysosomal exocytosis promotes cellular clearance, we show that reduced ISF tau in the absence of TFEB is associated with enhanced intraneuronal pathology and accelerated spreading. Our results support the idea that TFEB-mediated tau exocytosis serves as a clearance mechanism to reduce intracellular tau under pathological conditions and that effective tau immunotherapy should devoid targeting these extracellular tau species.
    DOI:  https://doi.org/10.1038/s41380-020-0738-0
  25. Proc Natl Acad Sci U S A. 2020 May 05. pii: 201917174. [Epub ahead of print]
    Trentesaux C, Fraudeau M, Pitasi CL, Lemarchand J, Jacques S, Duche A, Letourneur F, Naser E, Bailly K, Schmitt A, Perret C, Romagnolo B.
      The intestinal epithelium acts as a barrier between the organism and its microenvironment, including the gut microbiota. It is the most rapidly regenerating tissue in the human body thanks to a pool of intestinal stem cells (ISCs) expressing Lgr5 The intestinal epithelium has to cope with continuous stress linked to its digestive and barrier functions. Epithelial repair is crucial to maintain its integrity, and Lgr5-positive intestinal stem cell (Lgr5+ISC) resilience following cytotoxic stresses is central to this repair stage. We show here that autophagy, a pathway allowing the lysosomal degradation of intracellular components, plays a crucial role in the maintenance and genetic integrity of Lgr5+ISC under physiological and stress conditions. Using conditional mice models lacking the autophagy gene Atg7 specifically in all intestinal epithelial cells or in Lgr5+ISC, we show that loss of Atg7 induces the p53-mediated apoptosis of Lgr5+ISC. Mechanistically, this is due to increasing oxidative stress, alterations to interactions with the microbiota, and defective DNA repair. Following irradiation, we show that Lgr5+ISC repair DNA damage more efficiently than their progenitors and that this protection is Atg7 dependent. Accordingly, we found that the stimulation of autophagy on fasting protects Lgr5+ISC against DNA damage and cell death mediated by oxaliplatin and doxorubicin treatments. Finally, p53 deletion prevents the death of Atg7-deficient Lgr5+ISC but promotes genetic instability and tumor formation. Altogether, our findings provide insights into the mechanisms underlying maintenance and integrity of ISC and highlight the key functions of Atg7 and p53.
    Keywords:  Atg7; DNA repair; autophagy; intestinal stem cells
    DOI:  https://doi.org/10.1073/pnas.1917174117
  26. Front Cell Dev Biol. 2020 ;8 191
    Zhang X, Li L, Zhang Q, Wei Q, Lin J, Jia J, Zhang J, Yan T, Lv Y, Jiang X, Zhang P, Song H, Zhang D, Huang Y.
      Induced autophagy is protective against myocardial hypoxia/ischemia (H/I) injury, but evidence regarding the extent of autophagic clearance under H/I and the molecular mechanisms that influence autophagic flux has scarcely been presented. Here, we report that CD38 knockout improved cardiac function and autophagic flux in CD38-/- mice and CD38-/- neonatal cardiomyocytes (CMs) under H/I conditions. Mechanistic studies demonstrated that overexpression of CD38 specifically downregulated the expression of Rab7 and its adaptor protein pleckstrin homology domain-containing protein family member 1 (PLEKHM1) through nicotinamide adenine dinucleotide (NAD)-dependent and non-NAD-dependent pathways, respectively. Loss of Rab7/PLEKHM1 impaired the fusion of autophagosomes and lysosomes, resulting in autophagosome accumulation in the myocardium and consequent cardiac dysfunction under H/I conditions. Thus, CD38 mediated autophagic flux blockade and cardiac dysfunction in a Rab7/PLEKHM1-dependent manner. These findings suggest a potential therapeutic strategy involving targeted suppression of CD38 expression.
    Keywords:  Rab7; autophagosome–lysosome fusion; heart disease; nicotinamide adenine dinucleotide; pleckstrin homology domain-containing protein family member 1
    DOI:  https://doi.org/10.3389/fcell.2020.00191
  27. Cell Rep. 2020 May 05. pii: S2211-1247(20)30563-5. [Epub ahead of print]31(5): 107614
    Beilina A, Bonet-Ponce L, Kumaran R, Kordich JJ, Ishida M, Mamais A, Kaganovich A, Saez-Atienzar S, Gershlick DC, Roosen DA, Pellegrini L, Malkov V, Fell MJ, Harvey K, Bonifacino JS, Moore DJ, Cookson MR.
      Mutations in Leucine-rich repeat kinase 2 (LRRK2) cause Parkinson's disease (PD). However, the precise function of LRRK2 remains unclear. We report an interaction between LRRK2 and VPS52, a subunit of the Golgi-associated retrograde protein (GARP) complex that identifies a function of LRRK2 in regulating membrane fusion at the trans-Golgi network (TGN). At the TGN, LRRK2 further interacts with the Golgi SNAREs VAMP4 and Syntaxin-6 and acts as a scaffolding platform that stabilizes the GARP-SNAREs complex formation. Therefore, LRRK2 influences both retrograde and post-Golgi trafficking pathways in a manner dependent on its GTP binding and kinase activity. This action is exaggerated by mutations associated with Parkinson's disease and can be blocked by kinase inhibitors. Disruption of GARP sensitizes dopamine neurons to mutant LRRK2 toxicity in C. elegans, showing that these pathways are interlinked in vivo and suggesting a link in PD.
    Keywords:  Leucine-rich repeat kinase 2; RAB29; RAB7L1; VPS52; endosome; lysosome; membrane trafficking; neurodegeneration; neurodegenerative disease; neuroscience
    DOI:  https://doi.org/10.1016/j.celrep.2020.107614
  28. Oncol Rep. 2020 May 04.
    Wu G, Long Y, Lu Y, Feng Y, Yang X, Xu X, Yao D.
      Kindlin‑2 plays a carcinogenic or tumor‑suppressor role in various tumors. However, its role in cervical cancer remains unclear. In the present study, kindlin‑2 expression was first analyzed using public expression data and clinical specimens. It was revealed that kindlin‑2 was downregulated in cervical cancer tissues, and low expression of kindlin‑2 was associated with poor disease‑free survival. In addition, kindlin‑2 was overexpressed and knocked down in two cell lines to study its effect in cervical cancer cells. The results revealed that kindlin‑2 promoted cell autophagy and inactivated AKT/mTOR signaling. Rescue experiments indicated that the regulation of autophagy by kindlin‑2 was dependent on the AKT/mTOR signaling pathway. Furthermore, it was revealed that kindlin‑2 inhibited cell migration, and autophagy was required for this process. Collectively, these findings revealed the role and mechanism of kindlin‑2 in the autophagy and migration of cervical cancer cells.
    DOI:  https://doi.org/10.3892/or.2020.7603
  29. Int Rev Cell Mol Biol. 2020 ;pii: S1937-6448(19)30125-X. [Epub ahead of print]353 31-82
    Dionísio PA, Amaral JD, Rodrigues CMP.
      Necroptosis is a regulated cell death pathway morphologically similar to necrosis that depends on the kinase activity of receptor interacting protein 3 (RIP3) and the subsequent activation of the pseudokinase mixed lineage kinase domain-like protein (MLKL), being also generally dependent on RIP1 kinase activity. Necroptosis can be recruited during pathological conditions, usually following the activation of death receptors under specific cellular contexts. In this regard, necroptosis has been implicated in the pathogenesis of multiple disorders, including acute and chronic neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases, and multiple sclerosis. Here, we summarize the molecular mechanisms regulating the induction of necroptosis and downstream effectors of this form of cell death, besides exploring non-necroptotic roles for necroptosis-related proteins that may impact on alternative cell death pathways and inflammatory mechanisms in disease. Finally, we outline the recent evidence implicating necroptosis in neurodegenerative conditions and the emerging therapeutic perspectives targeting necroptosis in these diseases.
    Keywords:  MLKL; Mitochondria; Necroptosis; Neurodegenerative diseases; RIP1/RIPK1; RIP3/RIPK3; ROS; TNF-α
    DOI:  https://doi.org/10.1016/bs.ircmb.2019.12.006
  30. Sci Rep. 2020 May 04. 10(1): 7468
    Arjunan P, Swaminathan R, Yuan J, Al-Shabrawey M, Espinosa-Heidmann DG, Nussbaum J, Martin PM, Cutler CW.
      Recent epidemiological  studies link Periodontal disease(PD) to age-related macular degeneration (AMD). We documented earlier that Porphyromonas gingivalis(Pg), keystone oral-pathobiont, causative of PD, efficiently invades human gingival epithelial and blood-dendritic cells. Here, we investigated the ability of dysbiotic Pg-strains to invade human-retinal pigment epithelial cells(ARPE-19), their survival, intracellular localization, and the pathological effects, as dysfunction of RPEs leads to AMD. We show that live, but not heat-killed Pg-strains adhere to and invade ARPEs. This involves early adhesion to ARPE cell membrane, internalization and localization of Pg within single-membrane vacuoles or cytosol, with some nuclear localization apparent. No degradation of Pg or localization inside double-membrane autophagosomes was evident, with dividing Pg suggesting a metabolically active state during invasion. We found significant downregulation of autophagy-related genes particularly, autophagosome complex. Antibiotic protection-based recovery assay further confirmed distinct processes of adhesion, invasion and amplification of Pg within ARPE cells. This is the first study to demonstrate invasion of human-RPEs, begin to characterize intracellular localization and survival of Pg within these cells. Collectively, invasion of RPE by Pg and its prolonged survival by autophagy evasion within these cells suggest a strong rationale for studying the link between oral infection and AMD pathogenesis in individuals with periodontitis.
    DOI:  https://doi.org/10.1038/s41598-020-64449-8
  31. FASEB J. 2020 May 08.
    Machiela E, Liontis T, Dues DJ, Rudich PD, Traa A, Wyman L, Kaufman C, Cooper JF, Lew L, Nadarajan S, Senchuk MM, Van Raamsdonk JM.
      Mitochondria are dynamic organelles that can change shape and size depending on the needs of the cell through the processes of mitochondrial fission and fusion. In this work, we investigated the role of mitochondrial dynamics in organismal stress response. By using C. elegans as a genetic model, we could visualize mitochondrial morphology in a live organism with well-established stress assays and well-characterized stress response pathways. We found that disrupting mitochondrial fission (DRP1/drp-1) or fusion (OPA1/eat-3, MFN/fzo-1) genes caused alterations in mitochondrial morphology that impacted both mitochondrial function and physiologic rates. While both mitochondrial fission and mitochondrial fusion mutants showed increased sensitivity to osmotic stress and anoxia, surprisingly we found that the mitochondrial fusion mutants eat-3 and fzo-1 are more resistant to both heat stress and oxidative stress. In exploring the mechanism of increased stress resistance, we found that disruption of mitochondrial fusion genes resulted in the upregulation of multiple stress response pathways. Overall, this work demonstrates that disrupting mitochondrial dynamics can have opposite effects on resistance to different types of stress. Our results suggest that disruption of mitochondrial fusion activates multiple stress response pathways that enhance resistance to specific stresses.
    Keywords:   C. elegans ; genetics; mitochondria; mitochondrial dynamics; stress resistance
    DOI:  https://doi.org/10.1096/fj.201903235R
  32. Acta Neuropathol Commun. 2020 May 06. 8(1): 63
    Smolders S, Van Broeckhoven C.
      Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection.Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.
    Keywords:  Lysosomal dysfunction; Lysosomal storage disorder genes; Mitochondrial dysfunction; Oligogenic and polygenic inheritance; Parkinson’s disease; Vesicular trafficking defects
    DOI:  https://doi.org/10.1186/s40478-020-00935-4
  33. J Physiol. 2020 May 05.
    Knudsen JR, Li Z, Persson KW, Li J, Henriquez-Olguin C, Jensen TE.
      HIGHLIGHTS: AMPK-dependent Raptor Ser792 phosphorylation does not influence mTORC1-S6K1 activation by intense muscle contraction. α2 -AMPK activity-deficient mice have lower contraction-stimulated protein synthesis Increasing glycogen activates mTORC1-S6K1 independently of AMPK α2 Normalizing muscle glycogen content rescues reduced protein synthesis in AMPK-deficient mice ABSTRACT: Objective The mammalian Target of Rapamycin Complex 1 (mTORC1)-S6K1 signalling pathway regulates muscle growth-related protein synthesis and is antagonized by AMP-activated protein kinase (AMPK) in multiple cell types. Resistance exercise stimulates skeletal muscle mTORC1-S6K1 and AMPK signalling and post-contraction protein synthesis. Glycogen inhibits AMPK and has been proposed as a pro-anabolic stimulus. The aim of this study was to investigate how muscle mTORC1-S6K1 signalling and protein synthesis respond to resistance exercise-mimicking contraction in the absence of AMPK and with glycogen-manipulation. Methods Resistance exercise-mimicking unilateral in situ contraction of m. quadriceps femoris on anaesthetized wild-type and dominant negative α2 AMPK kinase dead transgenic (KD-AMPK) mice, measuring muscle mTORC1 and AMPK signalling immediately (0h) and 4h post-contraction, and protein-synthesis at 4h. Muscle glycogen manipulation by 5-day oral gavage of the glycogen phosphorylase inhibitor CP316819 and sucrose (80 g L-1 ) in the drinking water prior to in situ contraction. Results The mTORC1-S6K1 and AMPK signalling axes were co-activated immediately post-contraction, despite potent AMPK-dependent Raptor Ser792 phosphorylation on the mTORC1 subunit Raptor. KD-AMPK muscles displayed normal mTORC1-S6K1 activation at 0h and 4h post-exercise, but impaired contraction-stimulated protein synthesis 4h post-contraction. Pharmacological/dietary elevation of muscle glycogen content augmented contraction-stimulated mTORC1-S6K1-S6 signalling and rescued the reduced protein synthesis-response in KD-AMPK to WT levels. Conclusions mTORC-S6K1 signalling is not influenced by α2 -AMPK during or after intense muscle contraction. Elevated glycogen augments mTORC1-S6K1 signalling. α2 -AMPK-deficient KD-AMPK mice display impaired contraction-induced muscle protein synthesis, which can be rescued by normalizing muscle glycogen content. This article is protected by copyright. All rights reserved.
    DOI:  https://doi.org/10.1113/JP279780
  34. Cell Rep. 2020 May 05. pii: S2211-1247(20)30562-3. [Epub ahead of print]31(5): 107613
    Erra Díaz F, Ochoa V, Merlotti A, Dantas E, Mazzitelli I, Gonzalez Polo V, Sabatté J, Amigorena S, Segura E, Geffner J.
      During inflammation, recruited monocytes can differentiate either into macrophages or dendritic cells (DCs); however, little is known about the environmental factors that determine this cell fate decision. Low extracellular pH is a hallmark of a variety of inflammatory processes and solid tumors. Here, we report that low pH dramatically promotes the differentiation of monocytes into DCs (monocyte-derived DCs [mo-DCs]). This process is associated with a reduction in glucose consumption and lactate production, the upregulation of mitochondrial respiratory chain genes, and the inhibition of mTORC1 activity. Interestingly, we also find that both serum starvation and pharmacological inhibition of mTORC1 markedly promote the differentiation of mo-DCs. Our study contributes to better understanding the mechanisms that govern the differentiation of monocytes into DCs and reveals the role of both extracellular pH and mTORC1 as master regulators of monocyte cell fate.
    Keywords:  Monocytes; acidosis; dendritic cells; differentiation; inflammation; low pH; mTOR; metabolism; starvation
    DOI:  https://doi.org/10.1016/j.celrep.2020.107613
  35. Front Cell Dev Biol. 2020 ;8 225
    Li T, Zhang G, Wang L, Li S, Xu X, Gao Y.
      Background and Aims: Mammalian target of rapamycin complex 1 (mTORC1) is frequently hyperactivated in hepatocellular carcinoma (HCC). Cases of HCC without inflammation and cirrhosis are not rarely seen in clinics. However, the molecular basis of non-inflammatory HCC remains unclear.Methods: Spontaneous non-inflammatory HCC in mice was triggered by constitutive elevation of mTORC1 by liver-specific TSC1 knockout (LTsc1KO). A multi-omics approach was utilized on tumor tissues to better understand the molecular basis for the development of HCC in the LTsc1KO model.
    Results: We showed that LTsc1KO in mice triggered spontaneous non-inflammatory HCC, with molecular characteristics similar to those of diethylnitrosamine-mediated non-cirrhotic HCC. Mitochondrial and autophagy defects, as well as hepatic metabolic disorder were manifested in HCC development by LTsc1KO. mTORC1 activation on its own regulated an oncogenic network (DNA-damage-inducible transcript 4, nuclear protein 1, and fibroblast growth factor 21), and mTORC1-signal transducer and activator of transcription pathway crosstalk that altered specific metabolic pathways contributed to the development of non-inflammatory HCC.
    Conclusion: Our findings reveal the mechanisms of mTORC1-driven non-inflammatory HCC and provide insight into further development of a protective strategy against non-inflammatory HCC.
    Keywords:  carcinogenesis; gene network; metabolic disorder; mouse model; non-inflammation
    DOI:  https://doi.org/10.3389/fcell.2020.00225
  36. Nat Commun. 2020 May 08. 11(1): 2300
    Rambur A, Lours-Calet C, Beaudoin C, Buñay J, Vialat M, Mirouse V, Trousson A, Renaud Y, Lobaccaro JA, Baron S, Morel L, de Joussineau C.
      One of the most important but less understood step of epithelial tumourigenesis occurs when cells acquire the ability to leave their epithelial compartment. This phenomenon, described as basal epithelial cell extrusion (basal extrusion), represents the first step of tumour invasion. However, due to lack of adequate in vivo model, implication of emblematic signalling pathways such as Ras/Mitogen-Activated Protein Kinase (MAPK) and phosphoinositide 3 kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signalling pathways, is scarcely described in this phenomenon. We have developed a unique model of basal extrusion in the Drosophila accessory gland. There, we demonstrate that both Ras/MAPK and PI3K/AKT/mTOR pathways are necessary for basal extrusion. Furthermore, as in prostate cancer, we show that these pathways are co-activated. This occurs through set up of Epidermal Growth Factor Receptor (EGFR) and Insulin Receptor (InR) dependent autocrine loops, a phenomenon that, considering human data, could be relevant for prostate cancer.
    DOI:  https://doi.org/10.1038/s41467-020-16123-w
  37. Cell Rep. 2020 May 05. pii: S2211-1247(20)30565-9. [Epub ahead of print]31(5): 107616
    Todd TW, McEachin ZT, Chew J, Burch AR, Jansen-West K, Tong J, Yue M, Song Y, Castanedes-Casey M, Kurti A, Dunmore JH, Fryer JD, Zhang YJ, San Millan B, Teijeira Bautista S, Arias M, Dickson D, Gendron TF, Sobrido MJ, Disney MD, Bassell GJ, Rossoll W, Petrucelli L.
      A G4C2 hexanucleotide repeat expansion in an intron of C9orf72 is the most common cause of frontal temporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). A remarkably similar intronic TG3C2 repeat expansion is associated with spinocerebellar ataxia 36 (SCA36). Both expansions are widely expressed, form RNA foci, and can undergo repeat-associated non-ATG (RAN) translation to form similar dipeptide repeat proteins (DPRs). Yet, these diseases result in the degeneration of distinct subsets of neurons. We show that the expression of these repeat expansions in mice is sufficient to recapitulate the unique features of each disease, including this selective neuronal vulnerability. Furthermore, only the G4C2 repeat induces the formation of aberrant stress granules and pTDP-43 inclusions. Overall, our results demonstrate that the pathomechanisms responsible for each disease are intrinsic to the individual repeat sequence, highlighting the importance of sequence-specific RNA-mediated toxicity in each disorder.
    Keywords:  ALS; C9orf72; FTD; RAN translation; RNA foci; SCA36; TDP-43; mouse; poly(GP); poly(PR)
    DOI:  https://doi.org/10.1016/j.celrep.2020.107616
  38. Cells. 2020 May 06. pii: E1142. [Epub ahead of print]9(5):
    Kim MJ, Min Y, Im JS, Son J, Lee JS, Lee KY.
      Toll-like receptors (TLRs) induce the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and autophagy through the TNF (Tumor necrosis factor) receptor-associated factor 6 (TRAF6)-evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) and TRAF6-BECN1 signaling axes, respectively. Having shown that p62 negatively regulates Toll-like receptor 4 (TLR4)-mediated signaling via TRAF6-ECSIT signaling axis, we herein investigated whether p62 is functionally implicated in the TRAF6-BECN1 signaling axis, thereby regulating cancer cell migration and invasion. p62 interacted with TRAF6 and BECN1, to interrupt the functional associations required for TRAF6-BECN1 complex formation, leading to inhibitions of BECN1 ubiquitination and autophagy activation. Importantly, p62-deficient cancer cells, such as p62-knockdown (p62KD) SK-HEP-1, p62KD MDA-MB-231, and p62-knockout (p62KO) A549 cells, showed increased activation of autophagy induced by TLR4 stimulation, suggesting that p62 negatively regulates autophagy activation. Moreover, these p62-deficient cancer cells exhibited marked increases in cell migration and invasion in response to TLR4 stimulation. Collectively, these results suggest that p62 is negatively implicated in the TRAF6-BECN1 signaling axis, thereby inhibiting cancer cell migration and invasion regulated by autophagy activation in response to TLR4 stimulation.
    Keywords:  BECN1; TRAF6; autophagy; p62; toll-like receptor 4
    DOI:  https://doi.org/10.3390/cells9051142