bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2022‒05‒08
fifty-four papers selected by
Viktor Korolchuk
Newcastle University

  1. Autophagy. 2022 May 06. 1-15
      Macroautophagy/autophagy, an evolutionarily conserved degradation system, serves to clear intracellular components through the lysosomal pathway. Mounting evidence has revealed cytoprotective roles of autophagy; however, the intracellular causes of overactivated autophagy, which has cytotoxic effects, remain elusive. Here we show that sustained proteotoxic stress induced by loss of the RING and Kelch repeat-containing protein C53A5.6/RIKE-1 induces sequestration of LET-363/MTOR complex and overactivation of autophagy, and consequently impairs epithelial integrity in C. elegans. In C53A5.6/RIKE-1-deficient animals, blocking autophagosome formation effectively prevents excessive endosomal degradation, mitigates mislocalization of intestinal membrane components and restores intestinal lumen morphology. However, autophagy inhibition does not affect LET-363/MTOR aggregation in animals with compromised C53A5.6/RIKE-1 function. Improving proteostasis capacity by reducing DAF-2 insulin/IGF1 signaling markedly relieves the aggregation of LET-363/MTOR and alleviates autophagy overactivation, which in turn reverses derailed endosomal trafficking and rescues epithelial morphogenesis defects in C53A5.6/RIKE-1-deficient animals. Hence, our studies reveal that C53A5.6/RIKE-1-mediated proteostasis is critical for maintaining the basal level of autophagy and epithelial integrity.Abbreviations: ACT-5: actin 5; ACTB: actin beta; ALs: autolysosomes; APs: autophagosomes; AJM-1: apical junction molecule; ATG: autophagy related; C. elegans: Caenorhabditis elegans; CPL-1: cathepsin L family; DAF: abnormal dauer formation; DLG-1: Drosophila discs large homolog; ERM-1: ezrin/radixin/moesin; EPG: ectopic P granule; GFP: freen fluorescent protein; HLH-30: helix loop helix; HSP: heat shock protein; LAAT-1: lysosome associated amino acid transporter; LET: lethal; LGG-1: LC3, GABARAP and GATE-16 family; LMP-1: LAMP (lysosome-associated membrane protein) homolog; MTOR: mechanistic target of rapamycin kinase; NUC-1: abnormal nuclease; PEPT-1/OPT-2: Peptide transporter family; PGP-1: P-glycoprotein related; RAB: RAB family; RIKE-1: RING and Kelch repeat-containing protein; SLCF-1: solute carrier family; SQST-1: sequestosome related; SPTL-1: serine palmitoyl transferase family.
    Keywords:  Autophagy; C. elegans; LET-363/MTOR; endosomal degradation; epithelial morphogenesis; proteostasis
  2. Autophagy. 2022 May 06. 1-3
      Accumulating evidence suggests that macroautophagy/autophagy dysfunction plays a critical role in myocardial ischemia-reperfusion (I/R) injury. However, the underlying mechanisms responsible for malfunctional autophagy in cardiomyocytes subjected to I/R are poorly understood. As a result, there are no effective therapeutic options that target autophagy to prevent myocardial I/R injury. We recently revealed that MCOLN1/TRPML1, a lysosomal cationic channel, directly contributes to the inhibition of autophagic flux in cardiomyocytes post I/R. We found that MCOLN1 is activated secondary to reactive oxygen species (ROS) elevation following I/R, which in turn induces the release of lysosomal zinc into the cytosol. This ultimately blocks autophagic flux in cardiomyocytes by disrupting the fusion between autophagosomes containing engulfed mitochondria and lysosomes. Furthermore, we discovered that the MCOLN1-mediated inhibition of autophagy induced by I/R impairs mitochondrial function, which results in further detrimental ROS release that directly contributes to cardiomyocyte death. More importantly, restoration of blocked autophagic flux in cardiomyocytes subjected to I/R achieved by blocking MCOLN1 channels significantly rescues cardiomyocyte death in vitro and greatly improves cardiac function of mice subjected to I/R in vivo. Therefore, targeting MCOLN1 represents a novel therapeutic strategy to protect against myocardial I/R injury.Abbreviations: I/R: ischemia-reperfusion; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MCOLN1/TRPML1: mucolipin TRP cation channel 1; ROS: reactive oxygen species; SQSTM1/p62: sequestosome 1.
    Keywords:  Autophagy inhibition; MCOLN1; cardiomyocyte death; ischemia-reperfusion injury; mitochondria turnover
  3. Life Sci. 2022 Apr 30. pii: S0024-3205(22)00295-8. [Epub ahead of print] 120595
      Autophagy is a highly evolutionarily conserved process in the eukaryotic cellular system by which dysfunctional organelles are selectively degraded through a series of processes of lysosomal activity and then returned to the cytoplasm for reuse. All cells require this process to maintain cellular homeostasis and promote cell survival during stress responses such as deprivation and hypoxia. Osteoblasts and osteoclasts are two cellular phenotypes in the bone that mediate bone homeostasis. However, an imbalance between osteoblastic bone formation and osteoclastic bone resorption contributes to the onset of bone diseases. A recent study suggests that autophagy, mitophagy, and selective mitochondrial autophagy may play an essential role in regulating osteoblast differentiation and osteoclast maturation. Autophagic activity dysregulation alters the equilibrium between osteoblastic bone creation and osteoclastic bone resorption, allowing bone disorders like osteoporosis to develop more easily. The current review emphasizes the role of autophagy and mitophagy and their related molecular mechanisms in bone metabolic disorders. In the current review, we emphasize the role of autophagy and mitophagy as well as their related molecular mechanism in bone metabolic disorders. Furthermore, we will discuss its potential as a new molecular target for the treating of metabolic bone disease and future application in therapeutic translational research.
    Keywords:  Autophagy; Epigenetics; Mitophagy; Osteoporosis; miRNA regulation
  4. Autophagy Rep. 2022 ;1(1): 79-82
      In the final critical step for autophagic degradation, lysosomes fuse with autophagosomes to form autolysosomes. Although recent research has suggested that soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins are important for lysosome-autophagosome fusion, neither the architecture of the prefusion state nor the regulatory mechanisms have been identified. In our study, using structured illumination microscopy, we observed that lysosomes formed clusters around individual autophagosomes, thereby setting the stage for membrane fusion. Moreover, VAMP8 (vesicle-associated membrane protein 8) assists in forming the prefusion state of these clusters. We also found that VAMP8 phosphorylation reduces spontaneous lysosome-autophagosome fusion, whereas its dephosphorylation promotes fusion events between lysosomes and autophagosomes in both normal and autophagy-induced conditions. Our data thus suggest a key role of VAMP8 phosphorylation in the regulation of lysosome-autophagosome fusion.
    Keywords:  Autophagy; VAMP8; fusion; lysosomes; phosphorylation
  5. Autophagy. 2022 May 04. 1-20
      Mutations in DNAJC5/CSPα are associated with adult neuronal ceroid lipofuscinosis (ANCL), a dominant-inherited neurodegenerative disease featuring lysosome-derived autofluorescent storage materials (AFSMs) termed lipofuscin. Functionally, DNAJC5 has been implicated in chaperoning synaptic proteins and in misfolding-associated protein secretion (MAPS), but how DNAJC5 dysfunction causes lipofuscinosis and neurodegeneration is unclear. Here we report two functionally distinct but coupled chaperoning activities of DNAJC5, which jointly regulate lysosomal homeostasis: While endolysosome-associated DNAJC5 promotes ESCRT-dependent microautophagy, a fraction of perinuclear and non-lysosomal DNAJC5 mediates MAPS. Functional proteomics identifies a previously unknown DNAJC5 interactor SLC3A2/CD98hc that is essential for the perinuclear DNAJC5 localization and MAPS but dispensable for microautophagy. Importantly, uncoupling these two processes, as seen in cells lacking SLC3A2 or expressing ANCL-associated DNAJC5 mutants, generates DNAJC5-containing AFSMs resembling NCL patient-derived lipofuscin and induces neurodegeneration in a Drosophila ANCL model. These findings suggest that MAPS safeguards microautophagy to avoid DNAJC5-associated lipofuscinosis and neurodegeneration.Abbreviations: 3-MA: 3-methyladenine; ACTB: actin beta; AFSM: autofluorescent storage materials; ANCL: adult neuronal ceroid lipofuscinosis; Baf. A1: bafilomycin A1; CLN: ceroid lipofuscinosis neuronal; CLU: clusterin; CS: cysteine string domain of DNAJC5/CSPα; CUPS: compartment for unconventional protein secretion; DN: dominant negative; DNAJC5/CSPα: DnaJ heat shock protein family (Hsp40) member C5; eMI: endosomal microautophagy; ESCRT: endosomal sorting complex required for transport; GFP: green fluorescent protein; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; INCL: infant neuronal ceroid lipofuscinosis; JNCL: juvenile neuronal ceroid lipofuscinosis; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LAPTM4B: lysosomal protein transmembrane 4 beta; LN: linker domain of DNAJC5/CSPα; MAPS: misfolding-associated protein secretion; mCh/Ch: mCherry; mCi/Ci: mCitrine; MTOR: mechanistic target of rapamycin kinase; NCL: neuronal ceroid lipofuscinosis; PPT1: palmitoyl-protein thioesterase 1; PQC: protein quality control; SBP: streptavidin binding protein; SGT: small glutamine-rich tetratricopeptide repeat; shRNA: short hairpin RNA; SLC3A2/CD98hc: solute carrier family 3 member 2; SNCA/α-synuclein: synuclein alpha; TMED10: transmembrane p24 trafficking protein 10; UV: ultraviolet; VPS4: vacuolar protein sorting 4 homolog; WT: wild type.
    Keywords:  CLN4; DNAJC5/CSPα; ESCRT; cysteine string protein α; lysobody; lysosome/endolysosome; microautophagy/eMI; misfolding-associated protein secretion/MAPS; neuronal ceroid lipofuscinosis/NCL; protein quality control/PQC; unconventional protein secretion/UPS
  6. J Cell Biol. 2022 Jul 04. pii: e202202060. [Epub ahead of print]221(7):
      The stimulator of interferon genes (STING) plays a critical role in innate immunity. Emerging evidence suggests that STING is important for DNA or cGAMP-induced non-canonical autophagy, which is independent of a large part of canonical autophagy machineries. Here, we report that, in the absence of STING, energy stress-induced autophagy is upregulated rather than downregulated. Depletion of STING in Drosophila fat cells enhances basal- and starvation-induced autophagic flux. During acute exercise, STING knockout mice show increased autophagy flux, exercise endurance, and altered glucose metabolism. Mechanistically, these observations could be explained by the STING-STX17 interaction. STING physically interacts with STX17, a SNARE that is essential for autophagosome biogenesis and autophagosome-lysosome fusion. Energy crisis and TBK1-mediated phosphorylation both disrupt the STING-STX17 interaction, allow different pools of STX17 to translocate to phagophores and mature autophagosomes, and promote autophagic flux. Taken together, we demonstrate a heretofore unexpected function of STING in energy stress-induced autophagy through spatial regulation of autophagic SNARE STX17.
  7. Autophagy. 2022 May 04. 1-26
      Macroautophagy/autophagy is an essential process for cellular survival and is implicated in many diseases. A critical step in autophagy is the transport of the transcription factor TFEB from the cytosol into the nucleus, through the nuclear pore (NP) by KPNB1/importinβ1. In the C9orf72 subtype of amyotrophic lateral sclerosis-frontotemporal lobar degeneration (ALS-FTD), the hexanucleotide (G4C2)RNA expansion (HRE) disrupts the nucleocytoplasmic transport of TFEB, compromising autophagy. Here we show that a molecular chaperone, the SIGMAR1/Sigma-1 receptor (sigma non-opioid intracellular receptor 1), facilitates TFEB transport into the nucleus by chaperoning the NP protein (i.e., nucleoporin) POM121 which recruits KPNB1. In NSC34 cells, HRE reduces TFEB transport by interfering with the association between SIGMAR1 and POM121, resulting in reduced nuclear levels of TFEB, KPNB1, and the autophagy marker LC3-II. Overexpression of SIGMAR1 or POM121, or treatment with the highly selective and potent SIGMAR1 agonist pridopidine, currently in phase 2/3 clinical trials for ALS and Huntington disease, rescues all of these deficits. Our results implicate nucleoporin POM121 not merely as a structural nucleoporin, but also as a chaperone-operated signaling molecule enabling TFEB-mediated autophagy. Our data suggest the use of SIGMAR1 agonists, such as pridopidine, for therapeutic development of diseases in which autophagy is impaired.Abbreviations: ALS-FTD, amyotrophic lateral sclerosis-frontotemporal dementiaC9ALS-FTD, C9orf72 subtype of amyotrophic lateral sclerosis-frontotemporal dementiaCS, citrate synthaseER, endoplasmic reticulumGSS, glutathione synthetaseHRE, hexanucleotide repeat expansionHSPA5/BiP, heat shock protein 5LAMP1, lysosomal-associated membrane protein 1MAM, mitochondria-associated endoplasmic reticulum membraneMAP1LC3/LC3, microtubule-associated protein 1 light chain 3NP, nuclear poreNSC34, mouse motor neuron-like hybrid cell lineNUPs, nucleoporinsPOM121, nuclear pore membrane protein 121SIGMAR1/Sigma-1R, sigma non-opioid intracellular receptor 1TFEB, transcription factor EBTMEM97/Sigma-2R, transmembrane protein 97.
    Keywords:  ALS/FTD; KPNB1/importinβ1; SIGMAR1; TFEB; c9orf72; chaperone; nucleocytoplasmic transport; nucleoporin POM121; pridopidine; sigma-1 receptor
  8. Vet Res. 2022 May 03. 53(1): 33
      Autophagy has been demonstrated to play important roles in the infection and pathogenesis of many viruses. We previously found that porcine parvovirus (PPV) infection can induce autophagy in porcine placental trophoblast cells (PTCs), but its underlying mechanism has not yet been fully revealed. In this study, we showed that PPV infection inhibited the activation of mTORC1 and promoted the expression of Beclin 1 and LC3II in PTCs. Treatment with a mTOR activator inhibited the expression of Beclin 1 and LC3II, as well as autophagy formation, and reduced viral replication in PPV-infected PTCs. Furthermore, we found that inhibition of AMPK expression, but not the inhibition of PI3K/Akt, p53, or MAPK/ERK1/2 pathway activation, can significantly increase mTOR phosphorylation in PPV-infected PTCs. Then, we found that the regulation of mTOR phosphorylation by AMPK was mediated by Raptor. AMPK expression knockout inhibited the activation of Raptor, decreased the expression of Beclin 1 and LC3II, suppressed the formation of autophagosomes, and reduced viral replication during PPV infection. Together, our results showed that PPV infection induces autophagy to promote viral replication by inhibiting the activation of mTORC1 through activation of the AMPK/Raptor pathway. These findings provide information to understand the molecular mechanisms of PPV-induced autophagy.
    Keywords:  Porcine parvovirus; autophagy; placental trophoblast cells; signalling pathway
  9. J Cell Biol. 2022 Jun 06. pii: e202105112. [Epub ahead of print]221(6):
      Non-canonical autophagy is a key cellular pathway in immunity, cancer, and neurodegeneration, characterized by conjugation of ATG8 to endolysosomal single membranes (CASM). CASM is activated by engulfment (endocytosis, phagocytosis), agonists (STING, TRPML1), and infection (influenza), dependent on K490 in the ATG16L1 WD40-domain. However, factors associated with non-canonical ATG16L1 recruitment and CASM induction remain unknown. Here, using pharmacological inhibitors, we investigate a role for V-ATPase during non-canonical autophagy. We report that increased V0-V1 engagement is associated with, and sufficient for, CASM activation. Upon V0-V1 binding, V-ATPase recruits ATG16L1, via K490, during LC3-associated phagocytosis (LAP), STING- and drug-induced CASM, indicating a common mechanism. Furthermore, during LAP, key molecular players, including NADPH oxidase/ROS, converge on V-ATPase. Finally, we show that LAP is sensitive to Salmonella SopF, which disrupts the V-ATPase-ATG16L1 axis and provide evidence that CASM contributes to the Salmonella host response. Together, these data identify V-ATPase as a universal regulator of CASM and indicate that SopF evolved in part to evade non-canonical autophagy.
  10. Neuropathol Appl Neurobiol. 2022 May 02. e12818
      AIM: Mutations in the Valosin-containing protein (VCP) gene cause various lethal proteinopathies that mainly include inclusion body myopathy with Paget's disease of bone frontotemporal dementia (IBMPFD) and amyotrophic lateral sclerosis (ALS). Different pathological mechanisms have been proposed. Here, we define the impact of VCP mutants on lysosomes and how cellular homeostasis is restored by inducing autophagy in the presence of lysosomal damage.METHODS: By electron microscopy, we studied lysosomal morphology in VCP animal and motoneuronal models. Using western blotting, RT-qPCR, immunofluorescence, and filter trap assay, we evaluated the effect of selected VCP mutants in neuronal cells on lysosome size and activity, lysosomal membrane permeabilization, and their impact on autophagy.
    RESULTS: We found that VCP mutants induced aberrant multilamellar organelles in VCP animal and cell models similar to those found in patients with VCP mutations or with lysosomal storage disorders. In neuronal cells, we found altered lysosomal activity characterized by membrane permeabilization with galectin-3 redistribution and activation of PPP3CB. This selectively activated the autophagy/lysosomal transcriptional regulator TFE3, but not TFEB, and enhanced both SQSTM1/p62 and lipidated MAP 1LC3B levels inducing autophagy. Moreover, we found that WT VCP, but not the mutants, counteracted lysosomal damage induced either by trehalose or by a mutant form of SOD1 (G93A), also blocking the formation of its insoluble intracellular aggregates. Thus, chronic activation of autophagy might fuel the formation of multilamellar bodies.
    CONCLUSION: Together, our findings provide insights into the pathogenesis of VCP-related diseases, by proposing a novel mechanism of multilamellar body formation induced by VCP mutants that involves lysosomal damage and induction of lysophagy.
    Keywords:  ALS; PQC; TFE3; lysosome; neurodegeneration; p97
  11. Biol Futur. 2022 May 04.
      Lysosomal degradation of cytoplasmic components by autophagy ensures the continuous turnover of proteins and organelles and aids cellular survival during nutrient deprivation and other stress conditions. Lysosomal targeting of cytoplasmic proteins and organelles requires the concerted action of several proteins and multisubunit complexes. The core components of this machinery are conserved from yeast to humans and many of them are well-characterized; however, novel molecular players have been recently discovered and are waiting for detailed analysis. The osteopetrosis-linked PLEKHM1 protein is a lysosomal adaptor involved in autophagosome and endosome to lysosome fusion events and its role in lysosomal positioning in osteoclasts was reported together with its proposed binding partner, the relatively uncharacterized DEF8 protein. Here, we report the generation and subsequent analysis of novel mutant alleles of Drosophila plekhm1 and def8. Interestingly, the CRISPR-generated null mutations of these genes do not have any obvious effects on autophagy in Drosophila tissues, even though RNAi knockdown of these genes seems to perturb autophagy. Although these results are quite surprising and raise the possibility of compensatory changes in the case of null mutants, the new alleles will be valuable tools in future studies to understand the cellular functions of Drosophila Plekhm1 and Def8 proteins.
    Keywords:  Autophagy; Def8; Drosophila; Lysosome; Plekhm1
  12. Biochem Biophys Res Commun. 2022 Apr 25. pii: S0006-291X(22)00634-9. [Epub ahead of print]612 99-104
      Autophagy is known to play an essential role in intracellular quality control through the degradation of damaged organelles and components. We previously demonstrated that β-cell-specific autophagy deficient mice, which lack Atg7, exhibited impaired glucose tolerance, accompanied by the accumulation of sequestosome 1/p62 (hereafter referred to as p62). Whereas p62 has been reported to play essential roles in regulating cellular homeostasis in the liver and adipose tissue, we previously showed that β-cell-specific p62 deficiency does not cause any apparent impairment in glucose metabolism. In the present study, we investigated the roles of p62 in β cells under autophagy-deficient conditions, by simultaneously inactivating both Atg7 and p62 in a β-cell specific manner. Whereas p62 accumulation was substantially reduced in the islets of Atg7 and p62 double-deficient mice, glucose tolerance and insulin secretion were comparable to Atg7 single-deficient mice. Taken together, these findings suggest that the p62 accumulation appears to have little effect on β-cell function under conditions of autophagy inhibition.
    Keywords:  Atg7; Autophagy; Diabetes; p62/SQSTM1; β cell
  13. Int Rev Mov Disord. 2021 ;2 221-244
      Parkinson's disease is a sporadic and common neurodegenerative movement disorder resulting from the complex interplay between genetic risk, aging and environmental exposure. Familial forms of PD account for ~10% of cases and are known to result from the inheritance of mutations in at least 15 genes. Mutations in the vacuolar protein sorting 35 ortholog (VPS35) gene cause late-onset, autosomal dominant familial PD. VPS35 is a key suunit of the pentameric retromer complex that plays a role in the retrograde sorting and recycling of transmembrane cargo proteins from endosomes to the plasma membrane and trans-Golgi network. A single heterozygous Asp620Asn (D620N) mutation in VPS35 has been identified in multiple families that segregates with PD, and a number of experimental cellular and animal models have been developed to understand its pathogenic effects. At the molecular level, the D620N mutation has been shown to impair the interaction of VPS35 with the WASH complex, that plays an accessory function in retromer-dependent sorting. In addition, the D620N mutation has been linked to the abnormal sorting of retromer cargo, including CI-M6PR, AMPA receptor subunits, MUL1, LAMP2a and ATG9A, as well as to LRRK2 hyperactivation. At the cellular level, data support an impact of D620N VPS35 on mitochondrial function, the autophagy-lysosomal pathway, Wnt signaling and neurotransmission via altered endosomal sorting. The relevance of abnormal retromer sorting and cellular pathways to PD-related neurodegenerative phenotypes induced by D620N VPS35 in rodent models is not yet clear. There is also uncertainty regarding the mechanism-of-action of the D620N mutation and whether it manifests pathogenic effects in animal models and PD through a gain-of-function and/or a partial dominant-negative mechanism. Here, we discuss the emerging molecular and cellular mechanisms underlying PD induced by familial VPS35 mutations, going from structure to cellular function to neuropathology. We further discuss studies linking reduced retromer function to other neurodegenerative diseases and potential therapeutic strategies to normalize retromer function to mitigate disease.
    Keywords:  Golgi; LRRK2; Lysosome; Mitochondria; Parkinson’s disease (PD); VPS35; endosome; retromer; vesicular sorting
  14. Biol Futur. 2022 May 02.
      Lysosomal-dependent self-degradative (autophagic) mechanisms are essential for the maintenance of normal homeostasis in all eukaryotic cells. Several types of such self-degradative and recycling pathways have been identified, based on how the cellular self material can incorporate into the lysosomal lumen. Ubiquitination, a well-known and frequently occurred posttranslational modification has essential role in all cell biological processes, thus in autophagy too. The second most common type of polyubiquitin chain is the K63-linked polyubiquitin, which strongly connects to some self-degradative mechanisms in the cells. In this review, we discuss the role of this type of polyubiquitin pattern in numerous autophagic processes.
    Keywords:  Lysine 63 linkage specific ubiquitin; Lysosome; Vesicular trafficking
  15. Nat Commun. 2022 May 03. 13(1): 2412
      Human neurodegenerative disorders often exhibit similar pathologies, suggesting a shared aetiology. Key pathological features of Parkinson's disease (PD) are also observed in other neurodegenerative diseases. Pantothenate Kinase-Associated Neurodegeneration (PKAN) is caused by mutations in the human PANK2 gene, which catalyzes the initial step of de novo CoA synthesis. Here, we show that fumble (fbl), the human PANK2 homolog in Drosophila, interacts with PINK1 genetically. fbl and PINK1 mutants display similar mitochondrial abnormalities, and overexpression of mitochondrial Fbl rescues PINK1 loss-of-function (LOF) defects. Dietary vitamin B5 derivatives effectively rescue CoA/acetyl-CoA levels and mitochondrial function, reversing the PINK1 deficiency phenotype. Mechanistically, Fbl regulates Ref(2)P (p62/SQSTM1 homolog) by acetylation to promote mitophagy, whereas PINK1 regulates fbl translation by anchoring mRNA molecules to the outer mitochondrial membrane. In conclusion, Fbl (or PANK2) acts downstream of PINK1, regulating CoA/acetyl-CoA metabolism to promote mitophagy, uncovering a potential therapeutic intervention strategy in PD treatment.
  16. EMBO J. 2022 May 02. e109460
      PINK1 and parkin constitute a mitochondrial quality control system mutated in Parkinson's disease. PINK1, a kinase, phosphorylates ubiquitin to recruit parkin, an E3 ubiquitin ligase, to mitochondria. PINK1 controls both parkin localization and activity through phosphorylation of both ubiquitin and the ubiquitin-like (Ubl) domain of parkin. Here, we observed that phospho-ubiquitin can bind to two distinct sites on parkin, a high-affinity site on RING1 that controls parkin localization and a low-affinity site on RING0 that releases parkin autoinhibition. Surprisingly, ubiquitin vinyl sulfone assays, ITC, and NMR titrations showed that the RING0 site has higher affinity for phospho-ubiquitin than phosphorylated Ubl in trans. We observed parkin activation by micromolar concentrations of tetra-phospho-ubiquitin chains that mimic mitochondria bearing multiple phosphorylated ubiquitins. A chimeric form of parkin with the Ubl domain replaced by ubiquitin was readily activated by PINK1 phosphorylation. In all cases, mutation of the binding site on RING0 abolished parkin activation. The feedforward mechanism of parkin activation confers robustness and rapidity to the PINK1-parkin pathway and likely represents an intermediate step in its evolutionary development.
    Keywords:  Parkinson's disease; autophagy; mitophagy; open-loop control; ubiquitin
  17. Mol Cell. 2022 May 05. pii: S1097-2765(22)00375-6. [Epub ahead of print]82(9): 1613-1615
      Jouandin et al. (2022) show that lysosomal-derived cysteine serves as a signal to promote the tricarboxylic acid (TCA) cycle and suppress TORC1 signaling for Drosophila to endure starvation periods.
  18. Trends Cell Biol. 2022 Apr 27. pii: S0962-8924(22)00089-7. [Epub ahead of print]
      Pluripotent stem cells (PSCs) can self-renew indefinitely in culture while retaining the potential to differentiate into virtually all normal cell types in the adult animal. Due to these remarkable properties, PSCs not only provide a superb system to investigate mammalian development and model diseases, but also hold promise for regenerative therapies. Autophagy is a self-digestive process that targets proteins, organelles, and other cellular contents for lysosomal degradation. Here, we review recent literature on the mechanistic role of different types of autophagy in embryonic development, embryonic stem cells (ESCs), and induced PSCs (iPSCs), focusing on their remodeling functions on protein, metabolism, and epigenetics. We present a perspective on unsolved issues and propose that autophagy is a promising target to modulate acquisition, maintenance, and directed differentiation of PSCs.
    Keywords:  autophagy; chaperone-mediated autophagy; differentiation; embryonic stem cells; induced pluripotent stem cells; macroautophagy; microautophagy; self-renewal
  19. Nat Rev Neurosci. 2022 May 03.
      Macroautophagy is an evolutionarily conserved process that delivers diverse cellular contents to lysosomes for degradation. As our understanding of this pathway grows, so does our appreciation for its importance in disorders of the CNS. Once implicated primarily in neurodegenerative events owing to acute injury and ageing, macroautophagy is now also linked to disorders of neurodevelopment, indicating that it is essential for both the formation and maintenance of a healthy CNS. In parallel to understanding the significance of macroautophagy across contexts, we have gained a greater mechanistic insight into its physiological regulation and the breadth of cargoes it can degrade. Macroautophagy is a broadly used homeostatic process, giving rise to questions surrounding how defects in this single pathway could cause diseases with distinct clinical and pathological signatures. To address this complexity, we herein review macroautophagy in the mammalian CNS by examining three key features of the process and its relationship to disease: how it functions at a basal level in the discrete cell types of the brain and spinal cord; which cargoes are being degraded in physiological and pathological settings; and how the different stages of the macroautophagy pathway intersect with diseases of neurodevelopment and adult-onset neurodegeneration.
  20. J Biol Chem. 2022 May 02. pii: S0021-9258(22)00448-3. [Epub ahead of print] 102008
      Mitochondrial ATPase ATAD3A is essential for cholesterol transport, mitochondrial structure, and cell survival. However, the relationship between ATAD3A and non-alcoholic fatty liver disease (NAFLD) is largely unknown. In this study, we found that ATAD3A was upregulated in the progression of NAFLD in livers from rats with diet-induced non-alcoholic steatohepatitis and in human livers from patients diagnosed with NAFLD. We used CRISPR-Cas9 to delete ATAD3A in Huh7 human hepatocellular carcinoma cells, and used RNAi to silence ATAD3A expression in human hepatocytes isolated from humanized liver-chimeric mice to assess the influence of ATAD3A deletion on liver cells with free cholesterol (FC) overload induced by treatment with cholesterol plus 58035, an inhibitor of acetyl-CoA acetyltransferase. Our results showed that ATAD3A KO exacerbated FC accumulation under FC overload in Huh7 cells, and also that triglyceride (TG) levels were significantly increased in ATAD3A KO Huh7 cells following inhibition of lipolysis mediated by upregulation of lipid droplet-binding protein perilipin-2. Moreover, loss of ATAD3A upregulated autophagosome-associated light chain 3-II protein and p62 in Huh7 cells and fresh human hepatocytes through blockage of autophagosome degradation. Finally, we show the mitophagy mediator, PTEN-induced kinase 1, was downregulated in ATAD3A KO Huh7 cells, suggesting that ATAD3A KO inhibits mitophagy. These results also showed that loss of ATAD3A impaired mitochondrial basal respiration and ATP production in Huh7 cells under FC overload, accompanied by downregulation of mitochondrial ATP synthase. Taken together, we conclude that loss of ATAD3A promotes the progression of NAFLD through the accumulation of FC, TG, and damaged mitochondria in hepatocytes.
    Keywords:  ATAD3A; NAFLD; autophagy; cholesterol; fatty acid oxidation; free fatty acid; mitochondrial respiration; mitophagy; triglyceride
  21. Nat Rev Cardiol. 2022 May 06.
      Mitochondria are organelles involved in the regulation of various important cellular processes, ranging from ATP generation to immune activation. A healthy mitochondrial network is essential for cardiovascular function and adaptation to pathological stressors. Mitochondria undergo fission or fusion in response to various environmental cues, and these dynamic changes are vital for mitochondrial function and health. In particular, mitochondrial fission is closely coordinated with the cell cycle and is linked to changes in mitochondrial respiration and membrane permeability. Another key function of fission is the segregation of damaged mitochondrial components for degradation by mitochondrial autophagy (mitophagy). Mitochondrial fission is induced by the large GTPase dynamin-related protein 1 (DRP1) and is subject to sophisticated regulation. Activation requires various post-translational modifications of DRP1, actin polymerization and the involvement of other organelles such as the endoplasmic reticulum, Golgi apparatus and lysosomes. A decrease in mitochondrial fusion can also shift the balance towards mitochondrial fission. Although mitochondrial fission is necessary for cellular homeostasis, this process is often aberrantly activated in cardiovascular disease. Indeed, strong evidence exists that abnormal mitochondrial fission directly contributes to disease development. In this Review, we compare the physiological and pathophysiological roles of mitochondrial fission and discuss the therapeutic potential of preventing excessive mitochondrial fission in the heart and vasculature.
  22. Exp Eye Res. 2022 Apr 28. pii: S0014-4835(22)00175-0. [Epub ahead of print] 109095
      Diabetic retinopathy (DR) is a potentially blinding complication resulting from diabetes mellitus (DM). Retinal vascular endothelial cells (RMECs) dysfunction occupies an important position in the pathogenesis of DR, and mitochondrial disorders play a vital role in RMECs dysfunction. However, the detailed mechanisms underlying DR-induced mitochondrial disorders in RMECs remain elusive. In the present study, we used High glucose (HG)-induced RMECs in vitro and streptozotocin (STZ)-induced Sprague-Dawley rats in vivo to explore the related mechanisms. We found that HG-induced mitochondrial dysfunction via mitochondrial Dynamin-related protein 1(Drp1)-mediated mitochondrial fission. Drp1 inhibitor, Mdivi-1, rescued HG-induced mitochondrial dysfunction. Protein Kinase Cδ (PKCδ) could induce phosphorylation of Drp1, and we found that HG induced phosphorylation of PKCδ. PKCδ inhibitor (Go 6983) or PKCδ siRNA reversed HG-induced phosphorylation of Drp1 and further mitochondrial dysfunction. The above studies indicated that HG increases mitochondrial fission via promoting PKCδ/Drp1 signaling. Drp1 induces excessive mitochondrial fission and produces damaged mitochondrial, and mitophagy plays a key role in clearing damaged mitochondrial. Our study showed that HG suppressed mitophagy via inhibiting LC3B-II formation and p62 degradation. 3-MA (autophagy inhibitor) aggravated HG-induced RMECs damage, while rapamycin (autophagy agonist) rescued the above phenomenon. Further studies were identified that HG inhibited mitophagy by down-regulation of the PINK1/Parkin signaling pathway, and PINK1 siRNA aggravated HG-induced RMECs damage. Further in-depth study, we propose that Drp1 promotion of Hexokinase II (HK-II) separation from mitochondria, thus inhibiting HK-II-PINK1-mediated mitophagy. In vivo, we found that intraretinal microvascular abnormalities (IRMA), including retinal vascular leakage, acellular capillaries, and apoptosis were increased in STZ-induced DR rats, which were reversed by pretreatment with Mdivi-1 or Rapamycin. Altogether, our findings provide new insight into the mechanisms underlying the regulation of mitochondrial homeostasis and provide a potential treatment strategy for Diabetic retinopathy.
    Keywords:  Diabetic retinopathy; Drp1; Mitochondrial fission; Mitophagy; PINK1
  23. Anal Chem. 2022 May 03.
      Autophagy, a widespread degradation system in eukaryotes, plays an important role in maintaining the homeostasis of the cellular environment and the recycling of substances. Optical probes for the tracking of autophagy can be used as an effective tool not only to visualize the autophagy process but also to study autophagy-targeted drugs. Various molecule probes for autophagy of cancer cells emerge but are very limited for that of fungal cells, resulting in the lack of research on antifungal drugs targeting autophagy. To address this issue, we report an azole NIR fluorescence-based theranostic probe AF-1 with antifungal activity that is sensitive to autophagy-associated pH. The unique design of this probe lies in the introduction of both the pH-sensitive fluorophore with a detection range matching the pH range of the autophagy process and the conserved core structural fragment of azole drugs, providing a strategy to investigate the relationship between antifungal drug action and autophagy. As such, AF-1 exhibited excellent spectral properties and was found to target and induce the autophagy of the fungal cell membrane while maintaining moderate antifungal activity. Of note, using this theranostic probe as both a dye and drug, the autophagy process of fungi was visualized in a ratiometric manner, revealing the role of azole antifungal drugs in promoting autophagy to induce fungal cell apoptosis.
  24. Stem Cell Res Ther. 2022 May 03. 13(1): 174
      BACKGROUND: Ocular surface and retinal diseases are widespread problems that cannot be ignored in today's society. However, existing prevention and treatment still have many shortcomings and limitations, and fail to effectively hinder the occurrence and development of them.MAIN BODY: The purpose of this review is to give a detailed description of the potential mechanism of exosomes and autophagy. The eukaryotic endomembrane system refers to a range of membrane-bound organelles in the cytoplasm that are interconnected structurally and functionally, which regionalize and functionalize the cytoplasm to meet the needs of cells under different conditions. Exosomal biogenesis and autophagy are two important components of this system and are connected by lysosomal pathways. Exosomes are extracellular vesicles that contain multiple signaling molecules produced by multivesicular bodies derived from endosomes. Autophagy includes lysosome-dependent degradation and recycling pathways of cells or organelles. Recent studies have revealed that there is a common molecular mechanism between exosomes and autophagy, which have been, respectively, confirmed to involve in ocular surface and retinal diseases.
    CONCLUSION: The relationship between exosomes and autophagy and is mostly focused on fundus diseases, while a deeper understanding of them will provide new directions for the pathological mechanism, diagnosis, and treatment of ocular surface and retinal diseases.
    Keywords:  Autophagy; Exosomes; Extracellular vesicles; Ocular pathophysiology; Ocular surface diseases; Retinal diseases
  25. iScience. 2022 May 20. 25(5): 104249
      L3MBTL2 is a crucial component of ncPRC1.6 and has been implicated in transcriptional repression and chromatin compaction. However, the repression mechanism of L3MBTL2 and its biological functions are largely undefined. Here, we found that L3MBTL2 plays a distinct oncogenic role in tumor development. We demonstrated that L3MBTL2 repressed downstream CGA through an H2AK119ub1-dependent mechanism. Importantly, the binding of the MGA/MAX heterodimer to the E-box on the CGA promoter enhanced the specific selective repression of CGA by L3MBTL2. CGA encodes the alpha subunit of glycoprotein hormones; however, we showed that CGA plays an individual tumor suppressor role in PDAC. Moreover, CGA-transcript1 (T1) was identified as the major transcript, and the tumor suppression function of CGA-T1 depends on its own glycosylation. Furthermore, glycosylated CGA-T1 inhibited PDAC, partly by repression of autophagy through multiple pathways, including PI3K/Akt/mTOR and TP53INP2 pathways. These findings reveal the important roles of L3MBTL2 and CGA in tumor development.
    Keywords:  Biological sciences; Cancer; Cell biology
  26. Mol Metab. 2022 May 02. pii: S2212-8778(22)00077-1. [Epub ahead of print] 101508
      OBJECTIVE: Brown adipocytes play a key role in maintaining body temperature as well as glucose and lipid homeostasis. However, brown adipocytes need to adapt their thermogenic activity and substrate utilization to changes in nutrient availability. Amongst the multiple factors influencing brown adipocyte activity, autophagy is an important regulatory element of thermogenic capacity and activity. Nevertheless, a specific sensing mechanism of extracellular amino acid availability linking autophagy to nutrient availability in brown adipocytes is unknown.METHODS: To characterize the role of the amino acid transporter PAT2/SLC36A2 in brown adipocytes, loss or gain of function of PAT2 were studied with respect to differentiation, subcellular localization, lysosomal activity and autophagy. Activity of vATPase was evaluated by quenching of EGFP fused to LC3 or FITC-dextran loaded lysosomes in brown adipocytes upon amino acid starvation, whereas the effect of PAT2 on assembly of the vATPase was investigated by Native-PAGE.
    RESULTS: We show that PAT2 translocates from the plasma membrane to the lysosome in response to amino acid withdrawal. Loss or overexpression of PAT2 impair lysosomal acidification and starvation induced S6K re-phosphorylation, as PAT2 facilitates the assembly of the lysosomal vATPase, by recruitment of the cytoplasmic V1 subunit to the lysosome.
    CONCLUSION: PAT2 is an important sensor of extracellular amino acids and regulator of lysosomal acidification in brown adipocytes.
    Keywords:  Brown adipocytes; Lysosomal acidification; Proton-coupled amino acid transporter; Transporter translocation across membranes; V-ATPase assembly
  27. J Cell Biochem. 2022 May 01.
      Macroautophagy (hereafter autophagy) is one of the adaptive pathways that contribute to cancer cell chemoresistance. Despite the fact that autophagy can both promote and inhibit cell death, there is mounting evidence that in the context of anticancer treatment, it predominantly functions as a cell survival mechanism. Therefore, silencing of key autophagy genes emerges as a potent strategy to reduce chemoresistance. Though the importance of autophagy in chemoresistance is established, the changes in autophagy in the case of acquired chemoresistance are poorly understood. In this study, we aimed to determine the changes of autophagy in the cellular model of acquired chemoresistance of colorectal cancer cell lines HCT116 and SW620, induced by 5-fluorouracil (5-FU) or oxaliplatin (OxaPt) treatment, and determine the susceptible factors for autophagy inhibition. Our results demonstrate that in the context of autophagy, 5-FU and OxaPt have different effects on HCT116 and SW620 cell lines and their chemoresistant sublines. 5-FU inhibits autophagic flux, while changes in the flux after OxaPt treatment are cell type- and dose-dependent, inducing autophagy reduction or increase. The chemoresistant subline of HCT116 cells derived by OxaPt differs from the subline derived by 5-FU treatment - it responds to OxaPt by upregulating ATG7 protein level and autophagic flux, in contrast to downregulation in cells derived by 5-FU. Moreover, 5-FU and OxaPt treatments significantly modulate protein levels of core-autophagy proteins ATG7 and ATG12. The potential effects of 5-FU and OxaPt on ATG protein levels should be taken into account to reduce chemoresistance by applying small interferingRNAs, targeting ATG proteins.
    Keywords:  5-fluorouracil; ATG12; ATG7; autophagy; chemoresistance; colorectal cancer; oxaliplatin
  28. Cancer Gene Ther. 2022 May 03.
      Transmembrane ATPases are membrane-bound enzyme complexes and ion transporters that can be divided into F-, V-, and A-ATPases according to their structure. The V-ATPases, also known as H+-ATPases, are large multi-subunit protein complexes composed of a peripheral domain (V1) responsible for the hydrolysis of ATP and a membrane-integrated domain (V0) that transports protons across plasma membrane or organelle membrane. V-ATPases play a fundamental role in maintaining pH homeostasis through lysosomal acidification and are involved in modulating various physiological and pathological processes, such as macropinocytosis, autophagy, cell invasion, and cell death (e.g., apoptosis, anoikis, alkaliptosis, ferroptosis, and lysosome-dependent cell death). In addition to participating in embryonic development, V-ATPase pathways, when dysfunctional, are implicated in human diseases, such as neurodegenerative diseases, osteopetrosis, distal renal tubular acidosis, and cancer. In this review, we summarize the structure and regulation of isoforms of V-ATPase subunits and discuss their context-dependent roles in cancer biology and cell death. Updated knowledge about V-ATPases may enable us to design new anticancer drugs or strategies.
  29. Clin Transl Med. 2022 May;12(5): e825
      AIMS: MORC family CW-type zinc finger 2 (MORC2), a GHKL-type ATPase, is aberrantly upregulated in multiple types of human tumors with profound effects on cancer aggressiveness, therapeutic resistance, and clinical outcome, thus making it an attractive drug target for anticancer therapy. However, the antagonists of MORC2 have not yet been documented.METHODS AND RESULTS: We report that MORC2 is a relatively stable protein, and the N-terminal homodimerization but not ATP binding and hydrolysis is crucial for its stability through immunoblotting analysis and Quantitative real-time PCR. The N-terminal but not C-terminal inhibitors of heat shock protein 90 (HSP90) destabilize MORC2 in multiple cancer cell lines, and strikingly, this process is independent on HSP90. Mechanistical investigations revealed that HSP90 N-terminal inhibitors disrupt MORC2 homodimer formation without affecting its ATPase activities, and promote its lysosomal degradation through the chaperone-mediated autophagy pathway. Consequently, HSP90 inhibitor 17-AAG effectively blocks the growth and metastatic potential of MORC2-expressing breast cancer cells both in vitro and in vivo, and these noted effects are not due to HSP90 inhibition.
    CONCLUSION: We uncover a previously unknown role for HSP90 N-terminal inhibitors in promoting MORC2 degradation in a HSP90-indepentent manner and support the potential application of these inhibitors for treating MORC2-overexpressing tumors, even those with low or absent HSP90 expression. These results also provide new clue for further design of novel small-molecule inhibitors of MORC2 for anticancer therapeutic application.
    Keywords:  HSP90 inhibitor; MORC2; breast cancer; chaperone-mediated autophagy; protein degradation
  30. Autophagy. 2022 May 01.
      Following acute kidney injury (AKI), renal tubular cells may stimulate fibroblasts in a paracrine fashion leading to interstitial fibrosis, but the paracrine factors and their regulation under this condition remain elusive. Here we identify a macroautophagy/autophagy-dependent FGF2 (fibroblast growth factor 2) production in tubular cells. Upon induction, FGF2 acts as a key paracrine factor to activate fibroblasts for renal fibrosis. After ischemic AKI in mice, autophagy activation persisted for weeks in renal tubular cells. In inducible, renal tubule-specific atg7 (autophagy related 7) knockout (iRT-atg7-KO) mice, autophagy deficiency induced after AKI suppressed the pro-fibrotic phenotype in tubular cells and reduced fibrosis. Among the major cytokines, tubular autophagy deficiency in iRT-atg7-KO mice specifically diminished FGF2. Autophagy inhibition also attenuated FGF2 expression in TGFB1/TGF-β1 (transforming growth factor, beta 1)-treated renal tubular cells. Consistent with a paracrine action, the culture medium of TGFB1-treated tubular cells stimulated renal fibroblasts, and this effect was suppressed by FGF2 neutralizing antibody and also by fgf2- or atg7-deletion in tubular cells. In human, compared with non-AKI, the renal biopsies from post-AKI patients had higher levels of autophagy and FGF2 in tubular cells, which showed significant correlations with renal fibrosis. These results indicate that persistent autophagy after AKI induces pro-fibrotic phenotype transformation in tubular cells leading to the expression and secretion of FGF2, which activates fibroblasts for renal fibrosis during maladaptive kidney repair.
    Keywords:  Autophagy; FGF2; interstitial fibrosis; kidney repair; proximal tubule; renal ischemia-reperfusion
  31. Front Endocrinol (Lausanne). 2022 ;13 874748
      Testosterone (T) administration has previously been shown to improve muscle size and oxidative capacity. However, the molecular mechanisms underlying these adaptations in human skeletal muscle remain to be determined. Here, we examined the effect of moderate-dose T administration on molecular regulators of muscle protein turnover and mitochondrial remodeling in muscle samples collected from young women. Forty-eight healthy, physically active, young women (28 ± 4 years) were assigned in a random double-blind fashion to receive either T (10 mg/day) or placebo for 10-weeks. Muscle biopsies collected before and after the intervention period were divided into sub-cellular fractions and total protein levels of molecular regulators of muscle protein turnover and mitochondrial remodeling were analyzed using Western blotting. T administration had no effect on androgen receptor or 5α-reductase levels, nor on proteins involved in the mTORC1-signaling pathway (mTOR, S6K1, eEF2 and RPS6). Neither did it affect the abundance of proteins associated with proteasomal protein degradation (MAFbx, MuRF-1 and UBR5) and autophagy-lysosomal degradation (AMPK, ULK1 and p62). T administration also had no effect on proteins in the mitochondria enriched fraction regulating mitophagy (Beclin, BNIP3, LC3B-I, LC3B-II and LC3B-II/I ratio) and morphology (Mitofilin), and it did not alter the expression of mitochondrial fission- (FIS1 and DRP1) or fusion factors (OPA1 and MFN2). In summary, these data indicate that improvements in muscle size and oxidative capacity in young women in response to moderate-dose T administration cannot be explained by alterations in total expression of molecular factors known to regulate muscle protein turnover or mitochondrial remodeling.
    Keywords:  androgen receptor; fission; fusion; mTORC1-signaling; ubiquitin-proteasome system
  32. J Ginseng Res. 2022 Mar;46(2): 266-274
      Colon cancer, the third most frequent occurred cancer, has high mortality and extremely poor prognosis. Ginsenoside, the active components of traditional Chinese herbal medicine Panax ginseng, exerts antitumor effect in various cancers, including colon cancer. However, the detailed molecular mechanism of Ginsenoside in the tumor suppression have not been fully elucidated. Here, we chose the representative ginsenoside Rg3 and reported for the first time that Rg3 induces mitophagy in human colon cancer cells, which is responsible for its anticancer effect. Rg3 treatment leads to mitochondria damage and the formation of mitophagosome; when autophagy is inhibited, the clearance of damaged mitochondria can be reversed. Next, our results showed that Rg3 treatment activates the PINK1-Parkin signaling pathway and recruits Parkin and ubiquitin proteins to mitochondria to induce mitophagy. GO analysis of Parkin targets showed that Parkin interacts with a large number of mitochondrial proteins and regulates the molecular function of mitochondria. The cellular energy metabolism enzyme GAPDH is validated as a novel substrate of Parkin, which is ubiquitinated by Parkin. Moreover, GAPDH participates in the Rg3-induced mitophagy and regulates the translocation of Parkin to mitochondria. Functionally, Rg3 exerts the inhibitory effect through regulating the nonglycolytic activity of GAPDH, which could be associated with the cellular oxidative stress. Thus, our results revealed GAPDH ubiquitination by Parkin as a crucial mechanism for mitophagy induction that contributes to the tumor-suppressive function of ginsenoside, which could be a novel treatment strategy for colon cancer.
    Keywords:  BNIP3, BCL2 interacting protein 3; COX Ⅳ, cytochrome c oxidase Ⅳ; GAPDH; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GSH, glutathione; Gensinoside; HSP60, heat shock protein 60 KDa; LC3, microtubule-associated proteins 1A/1B light chain 3; MFN2, mitofusion 2; Mitophagy; PARK2, Parkin; PHGDH, phosphoglycerate dehydrogenase; PINK1, PTEN induced putative kinase 1; Parkin; ROS; SQSTM1, sequestosome 1; TIM23, translocase of the inner membrane 23; TOMM20, translocase of outer mitochondrial membrane 20; Ubiquitination; VDAC1, voltage-dependent anion-selective channel protein 1
  33. Autophagy. 2022 May 03. 1-17
      Dietary restriction (DR) is known to promote autophagy to exert its longevity effect. While SAMS-1 (S-adenosyl methionine synthetase-1) has been shown to be a key mediator of the DR response, little is known about the roles of S-adenosyl methionine (SAM) and SAM-dependent methyltransferase in autophagy and DR-induced longevity. In this study, we show that DR and SAMS-1 repress the activity of SET-2, a histone H3K4 methyltransferase, by limiting the availability of SAM. Consequently, the reduced H3K4me3 levels promote the expression and activity of two transcription factors, HLH-30/TFEB and PHA-4/FOXA, which both regulate the transcription of autophagy-related genes. We then find that HLH-30/TFEB and PHA-4/FOXA act collaboratively on their common target genes to mediate the transcriptional response of autophagy-related genes and consequently the lifespan of the animals. Our study thus shows that the SAMS-1-SET-2 axis serves as a nutrient-sensing module to epigenetically coordinate the activation of HLH-30/TFEB and PHA-4/FOXA transcription factors to control macroautophagy/autophagy and longevity in response to DR.
    Keywords:  Aging; Caenorhabditis. elegans; HLH-30/TFEB; PHA-4/FOXA; S-adenosyl methionine; SET-2 histone methyltransferase; dietary restriction; histone methylation
  34. Autophagy Rep. 2022 ;1(1): 143-160
      Equilibration of phospholipids between the two monolayers of the lipid bilayer of cellular membranes is mediated by scramblases acting as phospholipid shuttling proteins that are critical for cellular function, particularly during inter-organelle contact. Recent work has identified several protein scramblases, including TMEM41B, VMP1 and ATG9 that are critical in autophagy. More recently, ATG9, TMEM41B, and VMP1 have also been discovered to be important regulators of cellular lipid homeostasis. In vivo mouse models involving ablation of TMEM41B in liver have shown that knockout of these proteins can lead to rapid development of non-alcoholic steatohepatitis (NASH) and systemic dyslipidemia, though this has not been explored yet with ATG9. The resulting phenotype is likely due to the combined effects of a severe lipid secretion defect caused by stalled neutral lipids export from the endoplasmic reticulum (ER) membrane bilayer coupled with increased lipogenesis. Here we briefly discuss recent exciting findings on the topic of scramblases in autophagy, their relevance to human non-alcoholic fatty liver disease (NAFLD)/NASH, as well as future directions in this research.
    Keywords:  NASH; TMEM41B; VLDL; VMP1; autophagy
  35. ACS Appl Mater Interfaces. 2022 May 04.
      Autophagy is an important protective mechanism in maintaining or restoring cell homeostasis under physiological and pathological conditions. Nanoparticles (NPs) with certain components and morphologies can induce autophagic responses in cancer cells, providing a new perspective for establishing cancer therapy strategies. Herein, a novel nanodrug system, cell membranes-coated zeolitic imidazolate framework-8 (ZIF-8) NPs encapsulating chloroquine (CQ) and glucose oxidase (GOx) (defined as mCG@ZIF), is designed to achieve an enhanced anticancer effect with the combination of starvation therapy and an autophagy regulation strategy. It is found that ZIF-8 as a nanocarrier can induce autophagy to promote survival of cancer cells via the upstream Zn2+-stimulated mitochondrial reactive oxygen species (ROS) so that the anticancer effect is directly achieved by inhibiting this pro-survival autophagy using CQ released from mCG@ZIF under a tumor acidic microenvironment. Moreover, a cancer cell under starvation caused by GOx harnesses autophagy to maintain intracellular ATP levels and resist starvation therapy. The released CQ further inhibits the starvation-induced pro-survival autophagy and cuts off the protective pathway of cancer cells, enhancing the anticancer efficiency of GOx-based starvation therapy. Significantly, the cell membrane coating endows mCG@ZIF with excellent in vivo homotypic targeting ability. Both in vitro and in vivo results have confirmed the enhanced anticancer effect achieved by mCG@ZIF with a negligible side effect.
    Keywords:  ZIF-8; autophagy inhibition; nanocarrier; pro-survival autophagy; starvation therapy
  36. Cell Death Differ. 2022 May 06.
      Autophagy targets cytoplasmic materials for degradation, and influences cell health. Alterations in Atg6/Beclin-1, a key regulator of autophagy, are associated with multiple diseases. While the role of Atg6 in autophagy regulation is heavily studied, the role of Atg6 in organism health and disease progression remains poorly understood. Here, we discover that loss of Atg6 in Drosophila results in various alterations to stress, metabolic and immune signaling pathways. We find that the increased levels of circulating blood cells and tumor-like masses in atg6 mutants vary depending on tissue-specific function of Atg6, with contributions from intestine and hematopoietic cells. These phenotypes are suppressed by decreased function of macrophage and inflammatory response receptors crq and drpr. Thus, these findings provide a basis for understanding how Atg6 systemically regulates cell health within multiple organs, and highlight the importance of Atg6 in inflammation to organismal health.
  37. Ageing Res Rev. 2022 Apr 28. pii: S1568-1637(22)00078-2. [Epub ahead of print] 101636
      Adult neurogenesis, the process by which neurons are generated in certain areas of the adult brain, declines in an age-dependent manner and is one potential target for extending cognitive healthspan. Aging is a major risk factor for neurodegenerative diseases and, as lifespans are increasing, these health challenges are becoming more prevalent. An age-associated loss in neural stem cell number and/or activity could cause this decline in brain function, so interventions that reverse aging in stem cells might increase the human cognitive healthspan. In this review, we describe the involvement of adult neurogenesis in neurodegenerative diseases and address the molecular mechanistic aspects of neurogenesis that involve some of the key aggregation-prone proteins in the brain (i.e., tau, Aβ, α-synuclein, …). We summarize the research pertaining to interventions that increase neurogenesis and regulate known targets in aging research, such as mTOR and sirtuins. Lastly, we share our outlook on restoring the levels of neurogenesis to physiological levels in elderly individuals and those with neurodegeneration. We suggest that modulating neurogenesis represents a potential target for interventions that could help in the fight against neurodegeneration and cognitive decline.
    Keywords:  Neurogenesis; aging; dentate gyrus; hippocampus; memory; neurodegeneration
  38. ACS Chem Neurosci. 2022 May 06.
      Lysosomes are intracellular organelles responsible for the degradation of diverse macromolecules in a cell. A highly acidic pH is required for the optimal functioning of lysosomal enzymes. Loss of lysosomal intralumenal acidity can disrupt cellular protein homeostasis and is linked to age-related diseases such as neurodegeneration. Using a new robust lysosomal pH biosensor (FIRE-pHLy), we developed a cell-based fluorescence assay for high-throughput screening (HTS) and applied it to differentiated SH-SY5Y neuroblastoma cells. The goal of this study was twofold: (1) to screen for small molecules that acidify lysosomal pH and (2) to identify molecular targets and pathways that regulate lysosomal pH. We conducted a screen of 1835 bioactive compounds with annotated target information to identify lysosomal pH modulators (both acidifiers and alkalinizers). Forty-five compounds passed the initial hit selection criteria, using a combined analysis approach of population-based and object-based data. Twenty-three compounds were retested in dose-response assays and two compounds, OSI-027 and PP242, were identified as top acidifying hits. Overall, data from this phenotypic HTS screen may be used to explore novel regulatory pathways of lysosomal pH regulation. Additionally, OSI-027 and PP242 may serve as useful tool compounds to enable mechanistic studies of autophagy activation and lysosomal acidification as potential therapeutic pathways for neurodegenerative diseases.
    Keywords:  high-content analysis; lysosomal pH; lysosomes; neurons; pH biosensor; phenotypic screening
  39. Respir Res. 2022 May 04. 23(1): 110
      BACKGROUND: Retinoid-related orphan receptor-α (RORα) and autophagy dysregulation are involved in the pathophysiology of chronic obstructive pulmonary disease (COPD), but little is known regarding their association. We investigated the role of RORα in COPD-related autophagy.METHODS: The lung tissues and cells from a mouse model were analyzed for autophagy markers by using western blot analysis and transmission electron microscopy.
    RESULTS: Cigarette smoke increased the LC3-II level and decreased the p62 level in whole lung homogenates of a chronic cigarette smoking mouse model. Although cigarette smoke did not affect the levels of p62 in Staggerer mutant mice (RORαsg/sg), the baseline expression levels of p62 were significantly higher than those in wild type (WT) mice. Autophagy was induced by cigarette smoke extract (CSE) in Beas-2B cells and in primary fibroblasts from WT mice. In contrast, fibroblasts from RORαsg/sg mice failed to show CSE-induced autophagy and exhibited fewer autophagosomes, lower LC3-II levels, and higher p62 levels than fibroblasts from WT mice. Damage-regulated autophagy modulator (DRAM), a p53-induced modulator of autophagy, was expressed at significantly lower levels in the fibroblasts from RORαsg/sg mice than in those from WT mice. DRAM knockdown using siRNA in Beas-2B cells inhibited CSE-induced autophagy and cell death. Furthermore, RORα co-immunoprecipitated with p53 and the interaction increased p53 reporter gene activity.
    CONCLUSIONS: Our findings suggest that RORα promotes autophagy and contributes to COPD pathogenesis via regulation of the RORα-p53-DRAM pathway.
    Keywords:  Autophagy; Chronic obstructive pulmonary disease; Damage-regulated autophagy modulator; Retinoid-related orphan receptor-α; p53
  40. ACS Chem Neurosci. 2022 May 05.
      Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by upper and lower motor neuron loss. The pathomechanisms of ALS are still poorly understood with current hypotheses involving genetic mutations, excitotoxicity, and reactive oxygen species formation. In the absence of a disease-altering clinically approved therapeutic, there is an ever-increasing need to identify new targets to develop drugs that delay disease onset and/or progression. The purinergic P2X7 receptor (P2X7R) has been implicated widely across the ALS realm, providing a potential therapeutic strategy. This review summarizes the current understanding of ALS, the P2X7R and its role in ALS, the current landscape of P2X7R antagonists, and the in vivo potential of these antagonists in preclinical ALS models.
    Keywords:  Amyotrophic lateral sclerosis; P2X7; P2X7 receptor antagonists; autophagy; neuroinflammation; purinergic
  41. Sci Rep. 2022 May 06. 12(1): 7439
      A complex link exists between HIV-1 and autophagy, and discordant results have been reported in different in vitro models regarding the way HIV and autophagy modulate each other. Despite this, there is very limited knowledge about the interplay between HIV and autophagy in vivo in lymphoid tissue, due in part by the lack of cell models that recapitulate the in vivo setting. Here, we evaluate the interrelationship between HIV and autophagy using human ex vivo lymphoid tissue cultures as an HIV infection model. Our results showed that human lymphoid aggregated cultures (HLACs) from tonsillar tissue displayed fully functional autophagic activity. In this system, HIV infection resulted in an increase in autophagy. Notably, we observed that both, autophagy-enhancing (rapamycin) or blocking drugs (3-methyladenine, chloroquine and bafilomycin), were able to decrease HIV-DNA levels and HIV replication. Therefore, efficient HIV-1 replication requires a fine-tuned level of autophagy, so modifications of this balance will have a negative impact on its replication. Therefore, targeting the autophagic pathway could be a new therapeutic approach to be explored to treat HIV-1 infection. Ex vivo cultures of human lymphoid tissue are a suitable model to obtain further insights into HIV and its intricate relationship with autophagy.
  42. Biol Futur. 2022 May 02.
      In this review, we present recent scientific advances about integrin trafficking in the endo-lysosomal system. In the last few years, plenty of new information has emerged about the endo-lysosomal system, integrins, and the mechanism, how exactly the intracellular trafficking of integrins is regulated. We review the internalization and recycling pathways of integrins, and we provide information about the possible ways of lysosomal degradation through the endosomal and autophagic system. The regulation of integrin internalization and recycling proved to be a complex process worth studying. Trafficking of integrins, together with the regulation of their gene expression, defines cellular adhesion and cellular migration through bidirectional signalization and ligand binding. Thus, any malfunction in this system can potentially (but not necessarily) lead to tumorigenesis or metastasis. Hence, extensive examinations of integrins in the endo-lysosomal system raise the possibility to identify potential new medical targets. Furthermore, this knowledge can also serve as a basis for further determination of integrin signaling- and adhesion-related processes.
    Keywords:  Endo-lysosomal system; Integrin; Internalization and recycling pathway; Lysosomal degradation
  43. J Adv Res. 2022 03;37 107-117
      Introduction: Leucine-rich repetitive kinase-2 (LRRK2) is a Parkinson's disease-related gene that also participates in many inflammatory diseases. However, the functional role of LRRK2 in cardiovascular disease is not clear.Objective: In this study, we aimed to elucidate the role of LRRK2 in cardiac remodelling under pressure overload.
    Methods: Aortic banding surgery was performed to induce cardiac remodelling in a LRRK2 knockout mouse model. A cardiomyocyte remodelling model was established by phenylephrine (PE) stimulation in neonatal rat cardiomyocytes.
    Results: LRRK2 was upregulated in remodelled mouse hearts and cardiomyocytes. Cardiac hypertrophy, fibrosis and dysfunction were ameliorated in LRRK2 knockout mice. LRRK2 silencing protected against the PE-induced cardiomyocyte hypertrophic response, while LRRK2 over-expression worsened the PE-induced hypertrophic response in cardiomyocytes. Decreased autophagy was observed in remodelled cardiomyocytes, whereas LRRK2 silencing increased autophagy levels and LRRK2 overexpression reduced autophagy levels. The autophagy inhibitors 3-MA, bafilomycin and chloroquine reversed the protective effects of LRRK2 deficiency. The autophagy activator rapamycin reversed the deleterious effects of LRRK2 overexpression. We found that LRRK2 inhibited Bcl-2 phosphorylation, thus decreasing the phosphorylation of Beclin1. The protective effects of LRRK2 knockout were partly counteracted by Beclin1(+/-) in vivo and Beclin1 silencing in vitro. We also observed an interaction between LRRK2 and Rab7, an autolysosome degradation-associated protein, which caused Rab7 downregulation. Rab7 knockdown almost completely reversed LRRK2 silencing-induced protection of cardiomyocytes.
    Conclusion: LRRK2 deficiency protected against cardiac remodelling under pressure overload by increasing Bcl-2/Beclin1 and Rab7-regulated autophagy levels in the heart.
    Keywords:  Autophagy; Bcl-2; Beclin1; Cardiac remodelling; Leucine-rich repeat kinase-2; Rab7
  44. iScience. 2022 May 20. 25(5): 104238
      The TORC1 (Target of Rapamycin Complex 1) kinase complex plays a pivotal role in controlling cell growth in probably all eukaryotic species. The signals and mechanisms regulating TORC1 have been intensely studied in mammals but those of fungi and plants are much less known. We have previously reported that the yeast plasma membrane H+-ATPase Pma1 promotes TORC1 activation when stimulated by cytosolic acidification or nutrient-uptake-coupled H+ influx. Furthermore, a homologous plant H+-ATPase can substitute for yeast Pma1 to promote this H+-elicited TORC1 activation. We here report that TORC1 activity in Nicotiana tabacum BY-2 cells is also strongly influenced by the activity of plasma membrane H+-ATPases. In particular, stimulation of H+-ATPases by fusicoccin activates TORC1, and this response is also observed in cells transferred to a nutrient-free and auxin-free medium. Our results suggest that plant H+-ATPases, known to be regulated by practically all factors controlling cell growth, contribute to TOR signaling.
    Keywords:  Biological sciences; Molecular plant pathology; Plant biology
  45. Proc Natl Acad Sci U S A. 2022 May 10. 119(19): e2121244119
      SignificanceDisease resistance and tolerance are evolutionarily conserved yet distinct defense strategies that protect the host against microbial infection. Here, we report that taurolidine administered before the start of infection confers protection against polymicrobial sepsis by promoting resistance and tolerance. Notably, taurolidine given after the onset of infection also rescues mice from sepsis-associated lethality by enhancing disease tolerance to organ damage. This protection relies on an intact autophagy pathway, as taurolidine fails to protect autophagy-deficient mice against microbial sepsis. Specifically, taurolidine induces light chain 3-associated phagocytosis, but not xenophagy, in macrophages, resulting in an augmented bactericidal activity with enhanced cellular resistance to infection. These results highlight the importance of autophagy induction for taurolidine-augmented host resistance and disease tolerance and subsequent protection.
    Keywords:  autophagy; disease tolerance; host resistance; microbial sepsis
  46. RSC Adv. 2020 Oct 01. 10(60): 36317-36336
      The skin acts as both physical as well as an immunological barrier against hazardous agents from the outside environment and protects the internal organs against damage. Skin ageing is a dynamic process caused by the influence of various external factors, including damage from ultraviolet (UV-B) radiation, which is known as photo-ageing, and due to internal chronological mechanisms. A normal ageing process requires several orchestrated defense mechanisms to diverse types of stress responses, the concomitant renewal of cellular characteristics, and the homeostasis of different cell types that directly or indirectly protect the integrity of skin. Cumulative oxidative and endoplasmic reticulum (ER) stress responses and their adverse impact on biological systems in the skin are a common mechanism of the ageing process, negatively impacting DNA by causing mutations that lead to many physiological, functional, and aesthetic changes in the skin, culminating in the development of many diseases, including photo-damage and photo-carcinogenesis. Exposure of the skin to ultraviolet-(B) elicits the activation of signal transduction pathways, including DNA damage response, autophagy, and checkpoint signal adaptations associated with clearing radiation-induced DNA damage. Recent experimental reports suggest that autophagy is involved in maintaining skin homeostasis upon encountering different stresses, notably genotoxic stress. It has also been revealed that autophagy positively regulates the recognition of DNA damage by nucleotide excision repair and that skin ageing is associated with defects in the autophagy process. Moreover, autophagy is constitutively active in the skin epithelium, imparting protection to skin cells against a diverse range of outside insults, thus increasing resistance to environmental stressors. It has also been found that the stress-induced suppression of the autophagy response in experimental settings leads to enhanced apoptosis during photo-ageing upon UV-B exposure and that the maintenance of homeostasis depends on cellular autophagy levels. More recent reports in this domain claim that relieving the oxidative-stress-mediated induction of the ER stress response upon UV-B irradiation protects skin cells from photo-damage effects. The integration of autophagy and the DNA damage response under genotoxic stress is being considered as a meaningful partnership for finding novel molecular targets and devising suitable therapeutic strategies against photo-ageing disorders. Here, we summarize and review the current understanding of the mechanisms governing the intricate interplay between autophagy and the DNA damage response and its regulation by UV-B, the roles of autophagy in regulating the cellular response to UV-B-induced photodamage, and the implications of the modulation of autophagy as a meaningful partnership in the treatment and prevention of photoaging disorders.
  47. Life Sci Alliance. 2022 Sep;pii: e202101346. [Epub ahead of print]5(9):
      Rab40c is a SOCS box-containing protein which binds Cullin5 to form a ubiquitin E3 ligase complex (Rab40c/CRL5) to regulate protein ubiquitylation. However, the exact functions of Rab40c remain to be determined, and what proteins are the targets of Rab40c-Cullin5-mediated ubiquitylation in mammalian cells are unknown. Here we showed that in migrating MDA-MB-231 cells Rab40c regulates focal adhesion's number, size, and distribution. Mechanistically, we found that Rab40c binds the protein phosphatase 6 (PP6) complex and ubiquitylates one of its subunits, ankyrin repeat domain 28 (ANKRD28), thus leading to its lysosomal degradation. Furthermore, we identified that phosphorylation of FAK and MOB1 is decreased in Rab40c knock-out cells, which may contribute to focal adhesion site regulation by Rab40c. Thus, we propose a model where Rab40c/CRL5 regulates ANKRD28 ubiquitylation and degradation, leading to a decrease in PP6 activity, which ultimately affects FAK and Hippo pathway signaling to alter focal adhesion dynamics.
  48. Proc Natl Acad Sci U S A. 2022 May 03. 119(18): e2201646119
      SignificanceNiemann-Pick type C disease (NPCD) is an incurable genetic neurological disorder. Cells with NPC mutations fail to export cholesterol from endosomal organelle to multiple other organelles. ACAT1 is an enzyme that converts cholesterol to cholesteryl esters for storage. In mutant NPC cells, cholesterol storage still occurs, although at reduced rate. Here we show that in mutant NPC cells, ACAT1 blockade (A1B) decreases cholesterol storage such that it can be utilized to fulfill cholesterol needs in multiple organelles. In mutant NPC1 mice, Acat1 gene knockout reduces pathological onset and prolongs the lifespan by 34%. This work identifies ACAT1 as a target to treat NPCD and may help to explain why A1B has been reported to ameliorate preclinical models for Alzheimer's disease.
    Keywords:  Niemann-Pick disease type C; acyl-coenzyme A:cholesterol acyltransferase; cholesterol esterification
  49. Cell Death Dis. 2022 Apr 30. 13(4): 418
      Iron deposits are neuropathological hallmark of Parkinson's disease (PD). Iron regulatory protein 2 (IRP2) is a key factor in regulating brain iron homeostasis. Although two ubiquitin ligases that promote IRP2 degradation have been identified, the deubiquitylase for stabilization of IRP2 in PD remains undefined. Here, we report OTUD3 (OTU domain-containing protein 3) functions as a deubiquitylase for IRP2, interacts with IRP2 in the cytoplasm, de-polyubiquitylates, and stabilizes IRP2 protein in an iron-independent manner. Depletion of OTUD3 results in a disorder of iron metabolism. OTUD3 knockout mice display nigral iron accumulation, motor deficits, and nigrostriatal dopaminergic neurodegeneration, which resembles the pathology of PD. Consistently, decreased levels of OTUD3 are detected in transgenic PD mice expressing A53T mutant of human α-synuclein. Five single nucleotide polymorphism mutations of OTUD3 are present in cases of sporadic PD or controls, although no significant associations of OTUD3 SNPs with sporadic PD are detected. Taken together, these findings demonstrate that OTUD3 is a bona fide deubiquitylase for IRP2 and plays a critical role in the nigral iron deposits in PD.
  50. Cell Rep. 2022 05 03. pii: S2211-1247(22)00540-X. [Epub ahead of print]39(5): 110776
      Assemblies of tau can transit between neurons, seeding aggregation in a prion-like manner. To accomplish this, tau must cross cell-limiting membranes, a process that is poorly understood. Here, we establish assays for the study of tau entry into the cytosol as a phenomenon distinct from uptake, in real time, and at physiological concentrations. The entry pathway of tau is cell type specific and, in neurons, highly sensitive to cholesterol. Depletion of the cholesterol transporter Niemann-Pick type C1 or extraction of membrane cholesterol renders neurons highly permissive to tau entry and potentiates seeding even at low levels of exogenous tau assemblies. Conversely, cholesterol supplementation reduces entry and almost completely blocks seeded aggregation. Our findings establish entry as a rate-limiting step to seeded aggregation and demonstrate that dysregulated cholesterol, a feature of several neurodegenerative diseases, potentiates tau aggregation by promoting entry of tau assemblies into the cell interior.
    Keywords:  Alzheimer’s disease; CP: Metabolism; CP: Neuroscience; Niemann-Pick disease; cholesterol; endocytosis; neurodegeneration; seeded aggregation; tau
  51. Proc Natl Acad Sci U S A. 2022 May 10. 119(19): e2119990119
      SignificanceBoth the mTORC2 and Ras-ERK pathways respond to growth factor stimulation and play critical roles in cell growth and proliferation, disarray of these pathways leads to many diseases, especially cancer. These two signaling pathways crosstalk at many levels; recently it's become clear that the SIN1 component of mTORC2 could interact with Ras family small GTPases, but how these two proteins interact at the molecular level and the functional outcomes of this interaction remain to be addressed. In this work we determined the high-resolution structure of Ras-SIN1 complexes and revealed the detailed interaction mechanism. We also showed that Ras-SIN1 association inhibits insulin-induced ERK activation. Insights from this work could improve our understanding of the disease-causing mechanism of errant mTORC2 or Ras proteins.
    Keywords:  PI3K; Ras; SIN1; insulin; mTORC2
  52. Mol Neurobiol. 2022 May 03.
      Over the last decade, researchers have discovered that  a group of apparently unrelated neurodegenerative disorders, such as Parkinson's disease, have remarkable cellular and molecular biology similarities. Protein misfolding and aggregation are involved in all of the neurodegenerative conditions; as a result, inclusion bodies aggregation starts in the cells. Chaperone proteins and ubiquitin (26S proteasome's proteolysis signal), which aid in refolding misfolded proteins, are frequently found in these aggregates. The discovery of disease-causing gene alterations that code for multiple ubiquitin-proteasome pathway proteins in Parkinson's disease has strengthened the relationship between the ubiquitin-proteasome system and neurodegeneration. The specific molecular linkages between these systems and pathogenesis, on the other hand, are unknown and controversial. We outline the current level of knowledge in this article, focusing on important unanswered problems.
    Keywords:  Neurodegeneration; Parkinson's disease; Proteolysis; UPS; α-synuclein
  53. Transl Psychiatry. 2022 May 04. 12(1): 184
      Bipolar disorder (BPD) is a severe mental illness characterized by episodes of depression and mania. To investigate the molecular mechanisms underlying the pathophysiology of bipolar disorder, we performed transcriptome studies using RNA-seq data from the prefrontal cortex (PFC) of individuals with BPD and matched controls, as well as data from cell culture and animal model studies. We found 879 differentially expressed genes that were also replicated in an independent cohort of post-mortem samples. Genes involving the mechanistic target of rapamycine (mTOR) pathway were down-regulated, while genes interrelated with the mTOR pathway such as Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway were up-regulated. Gene co-expression network analyses identified a module related to the mTOR pathway that was up-regulated in BPD and also enriched for markers of endothelial cells. We also found a down-regulated co-expression module enriched for genes involved in mTOR signalling and in mTOR related pathways and enriched with neuronal markers. The mTOR related modules were also replicated in the independent cohort of samples. To investigate whether the expression of the modules related to mTOR signalling pathway could be differentially regulated in different cell types we performed comparative network analyses in experimental models. We found both up-regulated modules in the PFC significantly overlapped with an up-regulated module in the brain endothelial cells from mice treated with lipopolysaccharides (LPS) and mTOR related pathways such as JAK-STAT, PI3K-Akt and ribosome were enriched in the common genes. In addition, the down-regulated module in the PFC significantly overlapped with a down-regulated module from neurons treated with the mTOR inhibitor, Torin1 and mTOR signalling, autophagy, and synaptic vesicle cycles were significantly enriched in the common genes. These results suggest that co-expression networks related to mTOR signalling pathways may be up- or down-regulated in different cell types in the PFC of BPD. These results provide novel insights into the molecular mechanisms underlying the pathophysiology of BPD.