bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2020‒09‒20
27 papers selected by
Viktor Korolchuk
Newcastle University

  1. Autophagy. 2020 Sep 14.
    Tian X, Teng J, Chen J.
      Macroautophagy/autophagy refers to the engulfment of cellular contents selected for lysosomal degradation. The final step in autophagy is the fusion of autophagosome with the lysosome, which is mediated by SNARE proteins. Of the SNAREs, autophagosome-localized Q-SNAREs, such as STX17 and SNAP29, and lysosome-localized R-SNAREs, such as VAMP8 or VAMP7, have been reported to be involved. Recent studies also reveal participation of the R-SNARE, YKT6, in autophagosome-lysosome fusion. These SNAREs, with the help of other regulatory factors, act coordinately to spatiotemporally control the fusion process. Besides regulating autophagosome-lysosome fusion, some SNAREs, such as STX17, also function in other autophagic processes, including autophagosome formation and mitophagy. A better understanding of the functions of SNAREs will shed light on the molecular mechanisms of autophagosome-lysosome fusion as well as on the mechanisms by which autophagy is globally regulated.
    Keywords:  Autophagosome-lysosome fusion; SNARE; STX17; autophagy; mitophagy
  2. Sci Adv. 2020 Jul;pii: eaay9131. [Epub ahead of print]6(31):
    Shin SH, Lee JS, Zhang JM, Choi S, Boskovic ZV, Zhao R, Song M, Wang R, Tian J, Lee MH, Kim JH, Jeong M, Lee JH, Petukhov M, Lee SW, Kim SG, Zou L, Byun S.
      Despite considerable efforts, mTOR inhibitors have produced limited success in the clinic. To define the vulnerabilities of mTORC1-addicted cancer cells and to find previously unknown therapeutic targets, we investigated the mechanism of piperlongumine, a small molecule identified in a chemical library screen to specifically target cancer cells with a hyperactive mTORC1 phenotype. Sensitivity to piperlongumine was dependent on its ability to suppress RUVBL1/2-TTT, a complex involved in chromatin remodeling and DNA repair. Cancer cells with high mTORC1 activity are subjected to higher levels of DNA damage stress via c-Myc and displayed an increased dependency on RUVBL1/2 for survival and counteracting genotoxic stress. Examination of clinical cancer tissues also demonstrated that high mTORC1 activity was accompanied by high RUVBL2 expression. Our findings reveal a previously unknown role for RUVBL1/2 in cell survival, where it acts as a functional chaperone to mitigate stress levels induced in the mTORC1-Myc-DNA damage axis.
  3. Sci Adv. 2020 Jun;pii: eabb1989. [Epub ahead of print]6(25):
    Huang CS, Yu X, Fordstrom P, Choi K, Chung BC, Roh SH, Chiu W, Zhou M, Min X, Wang Z.
      The intestinal absorption of cholesterol is mediated by a multipass membrane protein, Niemann-Pick C1-Like 1 (NPC1L1), the molecular target of a cholesterol lowering therapy ezetimibe. While ezetimibe gained Food and Drug Administration approval in 2002, its mechanism of action has remained unclear. Here, we present two cryo-electron microscopy structures of NPC1L1, one in its apo form and the other complexed with ezetimibe. The apo form represents an open state in which the N-terminal domain (NTD) interacts loosely with the rest of NPC1L1, leaving the NTD central cavity accessible for cholesterol loading. The ezetimibe-bound form signifies a closed state in which the NTD rotates ~60°, creating a continuous tunnel enabling cholesterol movement into the plasma membrane. Ezetimibe blocks cholesterol transport by occluding the tunnel instead of competing with cholesterol binding. These findings provide insight into the molecular mechanisms of NPC1L1-mediated cholesterol transport and ezetimibe inhibition, paving the way for more effective therapeutic development.
  4. Sci Adv. 2020 Jul;pii: eabb8725. [Epub ahead of print]6(31):
    Xu F, Li X, Huang X, Pan J, Wang Y, Zhou S.
      Autophagy is involved in the occurrence and development of tumors. Here, a pH-responsive polymersome codelivering hydroxychloroquine (HCQ) and tunicamycin (Tuni) drugs is developed to simultaneously induce endoplasmic reticulum (ER) stress and autophagic flux blockade for achieving an antitumor effect and inhibiting tumor metastasis. The pH response of poly(β-amino ester) and HCQ synergistically deacidifies the lysosomes, thereby blocking the fusion of autophagosomes and lysosomes and lastly blocking autophagic flux. The function mechanism of regulating autophagy was systematically investigated on orthotopic luciferase gene-transfected, 4T1 tumor-bearing BALB/c mice through Western blot and immunohistochemistry analyses. The Tuni triggers ER stress to regulate the PERK/Akt signaling pathway to increase the autophagic level. The "autophagic stress" generated by triggering ER stress-induced autophagy and blocking autophagic flux is effective against tumors. The reduced expression of matrix metalloproteinase-2 due to ER stress and reduced focal adhesions turnover due to the blockade of autophagic flux synergistically inhibit tumor metastasis.
  5. Biochim Biophys Acta Mol Cell Res. 2020 Sep 11. pii: S0167-4889(20)30210-X. [Epub ahead of print] 118852
    Mattam U, Talari NK, Paripati AK, Krishnamoorthy T, Sepuri NBV.
      It has become amply clear that mitochondrial function defined by quality, quantity, dynamics, homeostasis, and regulated by mitophagy and mitochondrial biogenesis is a critical metric of human aging and disease. As a consequence, therapeutic interventions that can improve mitochondrial function can have a profound impact on human health and longevity. Kisspeptins are neuropeptides belonging to the family of metastasis suppressors that are known to regulate functions like fertility, reproduction, and metabolism. Using SKNSH cell line, hippocampus explant cultures and hippocampus of aging Wistar rat models, we show that Kisspeptin-10 (Kp) induces autophagy and mitophagy via calcium, Ca2+/CaM-dependent protein kinase kinase β (CaMKKβ), AMP-activated protein kinase (AMPK), and Unc-51 like autophagy activating kinase (ULK1) signaling pathway that is independent of mammalian target of rapamycin (mTOR). Intriguingly, Kp administration in vivo also results in the enhancement of mitochondrial number, complex I activity, and Adenosine Triphosphate (ATP) levels. This study uncovers potential effects of Kp in protecting mitochondrial health and as a possible therapeutic intervention to hippocampus associated impairments such as memory, cognitive aging, and other diseases linked to mitochondrial dysfunction.
    Keywords:  Autophagy; Kisspeptin; Mitophagy and Mitochondrial biogenesis; SKNSH; hippocampus
  6. JCI Insight. 2020 Sep 15. pii: 136676. [Epub ahead of print]
    Liu EA, Schultz ML, Mochida C, Chung C, Paulson HL, Lieberman AP.
      A critical response to lysosomal membrane permeabilization (LMP) is the clearance of damaged lysosomes through a selective form of macroautophagy known as lysophagy. Although regulators of this process are emerging, whether organ and cell specific components contribute to the control of lysophagy remains incompletely understood. Here, we examine LMP and lysophagy in Niemann-Pick type C disease (NPC), an autosomal recessive disorder characterized by the accumulation of unesterified cholesterol within late endosomes and lysosomes, leading to neurodegeneration and early death. We demonstrate that NPC patient fibroblasts show enhanced sensitivity to lysosomal damage as a consequence of lipid storage. Moreover, we describe a role for the glycan binding F-box protein Fbxo2 in CNS lysophagy. Fbxo2 functions as a component of the SCF ubiquitin ligase complex. Loss of Fbxo2 in mouse primary cortical cultures delays clearance of damaged lysosomes and decreases viability following lysosomal damage. Moreover, Fbxo2 deficiency in a mouse model of NPC exacerbates deficits in motor function, enhances neurodegeneration, and reduces survival. Collectively, our data identify a role for Fbxo2 in CNS lysophagy and establish its functional importance in NPC.
    Keywords:  Autophagy; Lysosomes; Neurodegeneration; Neuroscience
  7. EMBO Rep. 2020 Sep 14. e50241
    Werner G, Damme M, Schludi M, Gnörich J, Wind K, Fellerer K, Wefers B, Wurst W, Edbauer D, Brendel M, Haass C, Capell A.
      Single nucleotide polymorphisms (SNPs) in TMEM106B encoding the lysosomal type II transmembrane protein 106B increase the risk for frontotemporal lobar degeneration (FTLD) of GRN (progranulin gene) mutation carriers. Currently, it is unclear if progranulin (PGRN) and TMEM106B are synergistically linked and if a gain or a loss of function of TMEM106B is responsible for the increased disease risk of patients with GRN haploinsufficiency. We therefore compare behavioral abnormalities, gene expression patterns, lysosomal activity, and TDP-43 pathology in single and double knockout animals. Grn-/- /Tmem106b-/- mice show a strongly reduced life span and massive motor deficits. Gene expression analysis reveals an upregulation of molecular signature characteristic for disease-associated microglia and autophagy. Dysregulation of maturation of lysosomal proteins as well as an accumulation of ubiquitinated proteins and widespread p62 deposition suggest that proteostasis is impaired. Moreover, while single Grn-/- knockouts only occasionally show TDP-43 pathology, the double knockout mice exhibit deposition of phosphorylated TDP-43. Thus, a loss of function of TMEM106B may enhance the risk for GRN-associated FTLD by reduced protein turnover in the lysosomal/autophagic system.
    Keywords:   FTD ; TDP-43; TMEM106B; neurodegeneration; progranulin
  8. Mol Genet Metab. 2020 Sep 04. pii: S1096-7192(20)30190-6. [Epub ahead of print]
    Schwarz JM, Pedrazza L, Stenzel W, Rosa JL, Schuelke M, Straussberg R.
      The giant 532 kDa HERC1 protein is a ubiquitin ligase that interacts with tuberous sclerosis complex subunit 2 (TSC2), a negative upstream regulator of the mammalian target of rapamycin complex 1 (mTORC1). TSC2 regulates anabolic cell growth through its influence on protein synthesis, cell growth, proliferation, autophagy, and differentiation. TSC subunit 1 (TSC1) stabilizes TSC2 by inhibiting the interaction between TSC2 and HERC1, forming a TSC1-TSC2 complex that negatively regulates mTORC1. HERC1-TSC2 interaction destabilizes and degrades TSC2. Recessive mutations in HERC1 have been reported in patients with intellectual disability. Some patients exhibit epilepsy, macrocephaly, somatic overgrowth, and dysmorphic facial features as well. Here we describe two sisters from a consanguineous marriage with a novel homozygous missense variant in the C-terminal HECT domain of HERC1 [chr15:g63,907,989C>G GRCh37.p11 | c.14,072G>C NM_003922 | p.(Arg4,691Pro)]. Symptoms compris global developmental delay, macrocephaly, somatic overgrowth, intellectual disability, seizures, schizoaffective disorder, and pyramidal tract signs. We functionally assessed the HERC1 mutation by investigation of patient and control fibroblasts under normal and nutrient starving conditions. During catabolic state, mTORC1 activity remained high in patient fibroblasts, which stands in stark contrast to its downregulation in controls. This was corroborated by an abnormally high phosphorylation of S6K1-kinase, a direct downstream target of mTORC1, in patients. Moreover, autophagy, usually enhanced in catabolic states, was down-regulated in patient fibroblasts. These data confirm that the missense variant found in both patients results in a gain-of-function for the mutant HERC1 protein.
    Keywords:  Autophagy; MDFPMR; Next generation sequencing; Seizures; Tuberous sclerosis complex; Ubiquitination; mTORC1
  9. Biochim Biophys Acta Mol Cell Res. 2020 Sep 11. pii: S0167-4889(20)30213-5. [Epub ahead of print] 118855
    Li HP, Liu JT, Chen YX, Wang WB, Han Y, Yao QP, Qi YX.
      Dysfunctions of vascular smooth cells (VSMCs) play crucial roles in vascular remodeling in hypertension, which correlates with pathologically elevated cyclic stretch due to increased arterial pressure. Recent researches reported that autophagy, a life-sustaining process, was increased in hypertension. However, the mechanobiological mechanism of VSMC autophagy and its potential roles in vascular remodeling are still unclear. Using renal hypertensive rats in vivo and FX5000 stretch application Unit in vitro, the autophagy of VSMCs was detected. The results showed that LC3II remarkably enhanced in hypertensive rats and 15% cyclic stretch (mimic the pathologically increased mechanical stretch in hypertension), and the activity of mammalian target of rapamycin (mTOR) was suppressed in 15% cyclic stretch. Administration of autophagy inhibitors, bafilomycin A1 and chloroquine, repressed VSMC proliferation efficiently, but did not affect the degradation of two important nuclear envelope (NE) proteins, lamin A/C and emerin. Using RNA interference to decline the expression of lamin A/C and emerin, respectively, we discovered that autophagy was upregulated under both static and 5% cyclic stretch conditions, accompanying with the decreased mTOR activity. During 15% cyclic stretch application, mTOR inhibition was responsible for autophagy elevation. Chloroquine administration in vivo inhibited the expression of PCNA (marker of proliferation) of abdominal aorta in hypertensive rats. Altogether, these results demonstrated that pathological cyclic stretch suppresses the expression of lamin A/C and emerin which subsequently represses mTOR pathway so as to induce autophagy activation. Blocking autophagic flux may be a practicable way to relieve the pathological vascular remodeling in hypertensive.
    Keywords:  Autophagy; Cyclic stretch; Mechanobiology; Nuclear envelope proteins; Vascular smooth muscle cells
  10. Cells. 2020 Sep 10. pii: E2072. [Epub ahead of print]9(9):
    Guijarro MV, Danielson LS, Cañamero M, Nawab A, Abrahan C, Hernando E, Palmer GD.
      TSC1 is a tumor suppressor that inhibits cell growth via negative regulation of the mammalian target of rapamycin complex (mTORC1). TSC1 mutations are associated with Tuberous Sclerosis Complex (TSC), characterized by multiple benign tumors of mesenchymal and epithelial origin. TSC1 modulates self-renewal and differentiation in hematopoietic stem cells; however, its effects on mesenchymal stem cells (MSCs) are unknown. We investigated the impact of Tsc1 inactivation in murine bone marrow (BM)-MSCs, using tissue-specific, transgelin (Tagln)-mediated cre-recombination, targeting both BM-MSCs and smooth muscle cells. Tsc1 mutants were viable, but homozygous inactivation led to a dwarfed appearance with TSC-like pathologies in multiple organs and reduced survival. In young (28 day old) mice, Tsc1 deficiency-induced significant cell expansion of non-hematopoietic BM in vivo, and MSC colony-forming potential in vitro, that was normalized upon treatment with the mTOR inhibitor, everolimus. The hyperproliferative BM-MSC phenotype was lost in aged (1.5 yr) mice, and Tsc1 inactivation was also accompanied by elevated ROS and increased senescence. ShRNA-mediated knockdown of Tsc1 in BM-MSCs replicated the hyperproliferative BM-MSC phenotype and led to impaired adipogenic and myogenic differentiation. Our data show that Tsc1 is a negative regulator of BM-MSC proliferation and support a pivotal role for the Tsc1-mTOR axis in the maintenance of the mesenchymal progenitor pool.
    Keywords:  TSC1; mammalian target of rapamycin (mTOR); mesenchymal stem cell; senescence; stem cell proliferation; tuberous sclerosis
  11. Cells. 2020 Sep 15. pii: E2101. [Epub ahead of print]9(9):
    Lin Y, Zhao Z, Huang A, Lu M.
      Autophagy, a conserved process in which cells break down and destroy old, damaged, or abnormal proteins and other substances in the cytoplasm through lysosomal degradation, occurs via autophagosome formation and aids in the maintenance of intracellular homeostasis. Autophagy is closely associated with hepatitis B virus (HBV) replication and assembly. Currently, HBV infection is still one of the most serious public health issues worldwide. The unavailability of satisfactory therapeutic strategies for chronic HBV infection indicates an urgent need to elucidate the mechanisms underlying the pathogenesis of HBV infection. Increasing evidence has shown that HBV not only possesses the ability to induce incomplete autophagy but also evades autophagic degradation, indicating that HBV utilizes or hijacks the autophagy machinery for its own replication. Therefore, autophagy might be a crucial target pathway for controlling HBV infection. The definite molecular mechanisms underlying the association between cellular autophagy and HBV replication require further clarification. In this review, we have summarized and discussed the latest findings on the interplay between autophagy and HBV replication.
    Keywords:  HBs; HBx; autophagosome; autophagy; hepatitis B virus; viral replication
  12. Neurobiol Dis. 2020 Sep 09. pii: S0969-9961(20)30356-9. [Epub ahead of print] 105081
    Kuwahara T, Funakawa K, Komori T, Sakurai M, Yoshii G, Eguchi T, Fukuda M, Iwatsubo T.
      Leucine-rich repeat kinase 2 (LRRK2), the major causative gene product of autosomal-dominant Parkinson's disease, is a protein kinase that phosphorylates a subset of Rab GTPases. Since pathogenic LRRK2 mutations increase its ability to phosphorylate Rab GTPases, elucidating the mechanisms of how Rab phosphorylation is regulated by LRRK2 is of great importance. We have previously reported that chloroquine-induced lysosomal stress facilitates LRRK2 phosphorylation of Rab10 to maintain lysosomal homeostasis. Here we reveal that Rab10 phosphorylation by LRRK2 is potently stimulated by treatment of cells with a set of lysosome stressors and clinically used lysosomotropic drugs. These agents commonly promoted the formation of LRRK2-coated enlarged lysosomes and extracellular release of lysosomal enzyme cathepsin B, the latter being dependent on LRRK2 kinase activity. In contrast to the increase in Rab10 phosphorylation, treatment with lysosomotropic drugs did not increase the enzymatic activity of LRRK2, as monitored by its autophosphorylation at Ser1292 residue, but rather enhanced the molecular proximity between LRRK2 and its substrate Rab GTPases on the cytosolic surface of lysosomes. Lysosomotropic drug-induced upregulation of Rab10 phosphorylation was likely a downstream event of Rab29 (Rab7L1)-mediated enzymatic activation of LRRK2. These results suggest a regulated process of Rab10 phosphorylation by LRRK2 that is associated with lysosomal overload stress, and provide insights into the novel strategies to halt the aberrant upregulation of LRRK2 kinase activity.
    Keywords:  LRRK2; Lysosome; Lysosomotropic agents; Parkinson's disease; Phosphorylation; Rab
  13. Anal Methods. 2020 Jun 18. 12(23): 2978-2984
    Li L, Xiong Z, Dang Y, Li Y, Zhang A, Ding C, Xu Z, Zhang W.
      Visual detection of pH changes in lysosomes is critical because lysosomes not only play an important role in diverse cellular functions but also are closely related to various physiological and pathological processes. Herein, we disclose a donor-acceptor-donor (D-A-D) type fluorescent probe DBTD for detecting pH fluctuation in lysosomes. DBTD was rationally designed by using benzothiadiazole as the electron acceptor and N,N-diethylamino groups as the electron donor. Owing to its unique D-A-D structure, DBTD displayed a red-emission centered at 614 nm. It showed a sensitive and a linear response to pH from 4.5 to 5.2 with a pKa of 5.0, which is very suitable for lysosomal pH imaging. The response was based on the intramolecular charge transfer (ICT) effect owing to the protonation of the diethylamino group. Furthermore, DBTD could accurately monitor lysosomal pH variations in SGC-7901 cells. More importantly, it was able to image the pH change in lysosomes during the autophagy process successfully, suggesting the great potential of DBTD acting as a powerful tool for monitoring lysosomal pH-related biological processes.
  14. Mol Cell Oncol. 2020 ;7(5): 1769434
    Sica V, Kroemer G.
      When the orthologue of tumor suppressor protein p53 (TP53), cep-1, is inactivated in Caenorhabditis elegans, the nematodes manifest an autophagy-dependent increase in lifespan. A recent paper by Yang et al. demonstrates that accelerated aging phenotype of autophagy-deficient mice can be reduced by the knockout (KO) of Trp53. These findings point to a complex bidirectional crosstalk between autophagy and TP53 that has vast implications for the aging process.
  15. Sci Signal. 2020 Sep 15. pii: eaba5665. [Epub ahead of print]13(649):
    De Zan E, van Stiphout R, Gapp BV, Blomen VA, Brummelkamp TR, Nijman SMB.
      Forward genetic screens in mammalian cell lines, such as RNAi and CRISPR-Cas9 screens, have made major contributions to the elucidation of diverse signaling pathways. Here, we exploited human haploid cells as a robust comparative screening platform and report a set of quantitative forward genetic screens for identifying regulatory mechanisms of mTORC1 signaling, a key growth control pathway that senses diverse metabolic states. Selected chemical and genetic perturbations in this screening platform, including rapamycin treatment and genetic ablation of the Ragulator subunit LAMTOR4, revealed the known core mTORC1 regulatory signaling complexes and the intimate interplay of the mTORC1 pathway with lysosomal function, validating the approach. In addition, we identified a differential requirement for LAMTOR4 and LAMTOR5 in regulating the mTORC1 pathway under fed and starved conditions. Furthermore, we uncovered a previously unknown "synthetic-sick" interaction between the tumor suppressor folliculin and LAMTOR4, which may have therapeutic implications in cancer treatment. Together, our study demonstrates the use of iterative "perturb and observe" genetic screens to uncover regulatory mechanisms driving complex mammalian signaling networks.
  16. PLoS One. 2020 ;15(9): e0239019
    Park HJ, Jo DS, Choi H, Bae JE, Park NY, Kim JB, Choi JY, Kim YH, Oh GS, Chang JH, Kim HJ, Cho DH.
      The melanosome is a specialized membrane-bound organelle that is involved in melanin synthesis, storage, and transportation. In contrast to melanosome biogenesis, the processes underlying melanosome degradation remain largely unknown. Autophagy is a process that promotes degradation of intracellular components' cooperative process between autophagosomes and lysosomes, and its role for process of melanosome degradation remains unclear. Here, we assessed the regulation of autophagy and its contributions to depigmentation associated with Melasolv (3,4,5-trimethoxycinnamate thymol ester). B16F1 cells-treated with Melasolv suppressed the α-MSH-stimulated increase of melanin content and resulted in the activation of autophagy. However, introduction of bafilomycin A1 strongly suppressed melanosome degradation in Melasolv-treated cells. Furthermore, inhibition of autophagy by ATG5 resulted in significant suppression of Melasolv-mediated depigmentation in α-MSH-treated cells. Taken together, our results suggest that treatment with Melasolv inhibits skin pigmentation by promoting melanosome degradation via autophagy activation.
  17. J Cell Mol Med. 2020 Sep 17.
    Zhang X, Jing Y, Qin C, Liu C, Yang D, Gao F, Yang M, Du L, Li J.
      Increased mechanical stress after spinal cord injury (SCI) expands the scope of nerve tissue damage and exacerbates nerve function defects. Surgical decompression after SCI is a conventional therapeutic strategy and has been proven to have neuroprotective effects. However, the mechanisms of the interaction between mechanical stress and neurons are currently unknown. In this study, we monitored intramedullary pressure (IMP) and investigated the therapeutic benefit of decompression (including durotomy and piotomy) after injury and its underlying mechanisms in SCI. We found that decreased IMP promotes the generation and degradation of LC3 II, promotes the degradation of p62 and enhances autophagic flux to alleviate apoptosis. The lysosomal dysfunction was reduced after decompression. Piotomy was better than durotomy for the histological repair of spinal cord tissue after SCI. However, the autophagy-lysosomal pathway inhibitor chloroquine (CQ) partially reversed the apoptosis inhibition caused by piotomy after SCI, and the structural damage was also aggravated after CQ administration. An antibody microarray analysis showed that decompression may reverse the up-regulated abundance of p-PI3K, p-AKT and p-mTOR caused by SCI. Our findings may contribute to a better understanding of the mechanism of decompression and the effects of mechanical stress on autophagy after SCI.
    Keywords:  apoptosis; autophagic flux; decompression; mTOR; mechanical stress; spinal cord injury
  18. Mol Cell Oncol. 2020 ;7(4): 1754723
    Cassidy LD, Narita M.
      Reduced autophagy has been implicated in aging, yet whether its loss can promote aging phenotypes and pathologies in mammals, and how reversible this process is, has never been fully explored. Using inducible short hairpin RNA (shRNA) mouse models, we have recently shown that autophagy inhibition accelerates aging, and that even a temporary block in autophagy can create irreversible damage that increases a cancer risk.
    Keywords:  Autophagy; aging; cancer; senescence
  19. FASEB J. 2020 Sep 16.
    Guo X, Zhang W, Wang C, Zhang B, Li R, Zhang L, Zhao K, Li Y, Tian L, Li B, Cheng H, Li L, Pei C, Xu H.
      Mitochondria is a double membrane-bound cellular organelle that generates energy to maintain the homeostasis of cells. Immunity-related GTPase M (IRGM) in human locates at the inner membrane of mitochondria and is best known for its role in regulating autophagy against intracellular pathogens. Previous studies have shown that IRGM is crucial for the normal function of mitochondria, yet, the molecular mechanisms underlying IRGM-mediated quality control of mitochondria are still not fully understood. In this study, we showed that knocking-down IRGM inhibits CCCP induced mitophagy in SH-SY5Y cells. Furthermore, we reported that IRGM decreases the stability of Mitofilin (IMMT, MIC60) in the damaged mitochondria. Knocking down Mitofilin rescues the loss of mitophagy that is observed in the IRGM KD cells, suggesting that IRGM regulates mitophagy through the inhibition of Mitofilin. These data together provide molecular insight regarding how IRGM regulates mitophagy to control the quality of mitochondria.
    Keywords:  IRGM; PINK1; mitochondria; mitofilin; mitophagy
  20. J Immunol. 2020 Sep 18. pii: ji2000048. [Epub ahead of print]
    Hos NJ, Fischer J, Hos D, Hejazi Z, Calabrese C, Ganesan R, Murthy AMV, Rybniker J, Kumar S, Krönke M, Robinson N.
      Salmonella enterica serovar Typhimurium (S Typhimurium) is a Gram-negative bacterium that induces cell death of macrophages as a key virulence strategy. We have previously demonstrated that the induction of macrophage death is dependent on the host's type I IFN (IFN-I) response. IFN-I signaling has been shown to induce tripartite motif (TRIM) 21, an E3 ubiquitin ligase with critical functions in autoimmune disease and antiviral immunity. However, the importance and regulation of TRIM21 during bacterial infection remains poorly understood. In this study, we investigated the role of TRIM21 upon S Typhimurium infection of murine bone marrow-derived macrophages. Although Trim21 expression was induced in an IFN-I-dependent manner, we found that TRIM21 levels were mainly regulated posttranscriptionally. Following TLR4 activation, TRIM21 was transiently degraded via the lysosomal pathway by chaperone-mediated autophagy (CMA). However, S Typhimurium-induced mTORC2 signaling led to phosphorylation of Akt at S473, which subsequently impaired TRIM21 degradation by attenuating CMA. Elevated TRIM21 levels promoted macrophage death associated with reduced transcription of NF erythroid 2-related factor 2 (NRF2)-dependent antioxidative genes. Collectively, our results identify IFN-I-inducible TRIM21 as a negative regulator of innate immune responses to S Typhimurium and a previously unrecognized substrate of CMA. To our knowledge, this is the first study reporting that a member of the TRIM family is degraded by the lysosomal pathway.
  21. Sci Adv. 2020 Aug;6(35): eaba8271
    Motori E, Atanassov I, Kochan SMV, Folz-Donahue K, Sakthivelu V, Giavalisco P, Toni N, Puyal J, Larsson NG.
      Neurodegeneration in mitochondrial disorders is considered irreversible because of limited metabolic plasticity in neurons, yet the cell-autonomous implications of mitochondrial dysfunction for neuronal metabolism in vivo are poorly understood. Here, we profiled the cell-specific proteome of Purkinje neurons undergoing progressive OXPHOS deficiency caused by disrupted mitochondrial fusion dynamics. We found that mitochondrial dysfunction triggers a profound rewiring of the proteomic landscape, culminating in the sequential activation of precise metabolic programs preceding cell death. Unexpectedly, we identified a marked induction of pyruvate carboxylase (PCx) and other anaplerotic enzymes involved in replenishing tricarboxylic acid cycle intermediates. Suppression of PCx aggravated oxidative stress and neurodegeneration, showing that anaplerosis is protective in OXPHOS-deficient neurons. Restoration of mitochondrial fusion in end-stage degenerating neurons fully reversed these metabolic hallmarks, thereby preventing cell death. Our findings identify a previously unappreciated pathway conferring resilience to mitochondrial dysfunction and show that neurodegeneration can be reversed even at advanced disease stages.
  22. Cell Death Dis. 2020 Sep 15. 11(9): 755
    Wei C, Pan Y, Zhang Y, Dai Y, Jiang L, Shi L, Yang W, Xu S, Zhang Y, Xu W, Zhang Y, Lin X, Zhang S.
      Autophagy can be dynamically induced in response to stresses and is an essential, ubiquitous intracellular recycling system that impacts the fate of damaged resident cells, thereby influencing wound healing. Endometrial fibrosis is a form of abnormal wound healing that causes intrauterine adhesion (IUA) and infertility. We previously demonstrated that overactivated sonic hedgehog (SHH) signaling exacerbated endometrial fibrosis, but the role of autophagy in this process is still unknown. Here, we report that impaired autophagy participates in SHH pathway-induced endometrial fibrosis. Endometrial stroma-myofibroblast transition accompanied by autophagy dysfunction was present in both endometrial biopsies of IUA patients and Amhr2cre/+ R26-SmoM2+/- (AM2) transgenic mouse. Mechanistically, SHH pathway negatively regulated autophagy through pAKT-mTORC1 in a human endometrial stromal cell line (T-HESCs). Furthermore, SHH pathway-mediated fibrosis was partly counteracted by autophagy modulation in both T-HESCs and the murine IUA model. Specifically, the impact of SHH pathway inhibition (GANT61) was reversed by the pharmacological autophagy inhibitor chloroquine (CQ) or RNA interference of autophagy-related gene ATG5 or ATG7. Similar results were obtained from the murine IUA model treated with GANT61 and CQ. Moreover, promoting autophagy with rapamycin reduced fibrosis in the AM2 IUA model to baseline levels. In summary, defective autophagy is involved in SHH pathway-driven endometrial fibrosis, suggesting a potential novel molecular target for IUA treatment.
  23. J Cell Biol. 2020 Nov 02. pii: e202004029. [Epub ahead of print]219(11):
    Killackey SA, Philpott DJ, Girardin SE.
      Mitophagy is an evolutionarily conserved process involving the autophagic targeting and clearance of mitochondria destined for removal. Recent insights into the complex nature of the overlapping pathways regulating mitophagy illustrate mitophagy's essential role in maintaining the health of the mitochondrial network. In this review, we highlight recent studies that have changed the way mitophagy is understood, from initiation through lysosomal degradation. We outline the numerous mitophagic receptors and triggers, with a focus on basal and physiologically relevant cues, offering insight into why they lead to mitochondrial removal. We also explore how mitophagy maintains mitochondrial homeostasis at the organ and system levels and how a loss of mitophagy may play a role in a diverse group of diseases, including cardiovascular, metabolic, and neurodegenerative diseases. With disrupted mitophagy affecting such a wide array of physiological processes, a deeper understanding of how to modulate mitophagy could provide avenues for numerous therapies.
  24. Front Genet. 2020 ;11 930
    Zhang W, Zhang S, Guan W, Huang Z, Kong J, Huang C, Wang H, Yang S.
      Accumulating evidence show that Poly C Binding Protein 1 (PCBP1) is deleted in distinct types of tumors as a novel tumor suppressor, but its tumor suppression mechanism remains elusive. Here, we firstly describe that downregulation of PCBP1 is significantly associated with clinical ovarian tumor progression. Mechanistically, PCBP1 overexpression affects various autophagy-related genes expression at various expression levels to attenuate the intrinsic cell autophagy, including the autophagy-initiating ULK, ATG12, ATG7 as well as the bona fide marker of autophagosome, LC3B. Accordingly, knockdown of the endogenous PCBP1 in turn enhances autophagy and less cell death. Meanwhile, PCBP1 upregulates p62/SQSTM1 via inhibition p62/SQSTM1 autophagolysome and proteasome degradation as well as its mRNA stability, consequently accompanying with the caspase 3 or 8 activation for tumor cell apoptosis. Importantly, clinical ovary cancer sample analysis consistently validates the relevance of PCBP1 expression to both p62/SQSTM1 and caspase-8 to overall survival, and indicates PCBP1 may be a master player to repress tumor initiation. Taken together, our results uncover the tumorigenic mechanism of PCBP1 depletion and suggest that inhibition of tumor cell autophagy with autophagic inhibitors could be an effective therapeutical strategy for PCBP1-deficient tumor.
    Keywords:  PCBP1; apoptosis; autophagy; caspase-8; colon cancer; ovary cancer; p62/SQSTM1
  25. Nat Commun. 2020 Sep 17. 11(1): 4684
    Gremke N, Polo P, Dort A, Schneikert J, Elmshäuser S, Brehm C, Klingmüller U, Schmitt A, Reinhardt HC, Timofeev O, Wanzel M, Stiewe T.
      Cancer cells have a characteristic metabolism, mostly caused by alterations in signal transduction networks rather than mutations in metabolic enzymes. For metabolic drugs to be cancer-selective, signaling alterations need to be identified that confer a druggable vulnerability. Here, we demonstrate that many tumor cells with an acquired cancer drug resistance exhibit increased sensitivity to mechanistically distinct inhibitors of cancer metabolism. We demonstrate that this metabolic vulnerability is driven by mTORC1, which promotes resistance to chemotherapy and targeted cancer drugs, but simultaneously suppresses autophagy. We show that autophagy is essential for tumor cells to cope with therapeutic perturbation of metabolism and that mTORC1-mediated suppression of autophagy is required and sufficient for generating a metabolic vulnerability leading to energy crisis and apoptosis. Our study links mTOR-induced cancer drug resistance to autophagy defects as a cause of a metabolic liability and opens a therapeutic window for the treatment of otherwise therapy-refractory tumor patients.
  26. Diabetes. 2020 Sep 18. pii: db191176. [Epub ahead of print]
    Zang H, Wu W, Qi L, Tan W, Nagarkatti P, Nagarkatti M, Wang X, Cui T.
      Nuclear factor-erythroid factor 2-related factor 2 (Nrf2) may either ameliorate or worsen diabetic cardiomyopathy. However, the underlying mechanisms are poorly understood. Herein we report a novel mechanism of Nrf2-mediated myocardial damage in type 1 diabetes (T1D). Global Nrf2 knockout (Nrf2KO) hardly affected the onset of cardiac dysfunction induced by T1D but slowed down its progression in mice independent of sex. In addition, Nrf2KO inhibited cardiac pathological remodeling, apoptosis and oxidative stress associated with both onset and advancement of cardiac dysfunction in T1D. Such Nrf2-mediated progression of diabetic cardiomyopathy was confirmed by cardiomyocyte-restricted (CR) Nrf2 transgenic (Tg) approach in mice. Moreover, cardiac autophagy inhibition via CR KO of autophagy related 5 gene (CR-Atg5KO) led to early onset and accelerated development of cardiomyopathy in T1D, and CR-Atg5KO-induced adverse phenotypes were rescued by additional Nrf2KO. Mechanistically, chronic T1D leads to glucolipotoxicity inhibiting autolysosome efflux, which in turn intensifies Nrf2-driven transcription to fuel lipid peroxidation while inactivating Nrf2-mediated antioxidant defense and impairing Nrf2-coordinated iron metabolism, thereby leading to ferroptosis in cardiomyocytes. These results demonstrate that diabetes over time causes autophagy deficiency, which turns off Nrf2-mediated defense while switching on Nrf2-operated pathological program toward ferroptosis in cardiomyocytes, thereby worsening the progression of diabetic cardiomyopathy.
  27. Exp Cell Res. 2020 Sep 09. pii: S0014-4827(20)30525-5. [Epub ahead of print]396(1): 112276
    Reggio A, Buonomo V, Grumati P.
      Autophagy is an evolutionary conserved catabolic process devoted to the removal of unnecessary and harmful cellular components. In its general form, autophagy governs cellular lifecycle through the formation of double membrane vesicles, termed autophagosomes, that enwrap and deliver unwanted intracellular components to lysosomes. In addition to this omniscient role, forms of selective autophagy, relying on specialized receptors for cargo recognition, exert fine-tuned control over cellular homeostasis. In this regard, xenophagy plays a pivotal role in restricting the replication of intracellular pathogens, thus acting as an ancient innate defense system against infections. Recently, selective autophagy of the endoplasmic reticulum (ER), more simply ER-phagy, has been uncovered as a critical mechanism governing ER network shape and function. Six ER-resident proteins have been characterized as ER-phagy receptors and their orchestrated function enables ER homeostasis and turnover overtime. Unfortunately, ER is also the preferred site for viral replication and several viruses hijack ER machinery for their needs. Thus, it is not surprising that some ER-phagy receptors can act to counteract viral replication and minimize the spread of infection throughout the organism. On the other hand, evolutionary pressure has armed pathogens with strategies to evade and subvert xenophagy and ER-phagy. Although ER-phagy biology is still in its infancy, the present review aims to summarize recent ER-phagy literature, with a special focus on its role in counteracting viral infections. Moreover, we aim to offer some hints for future targeted approaches to counteract host-pathogen interactions by modulating xenophagy and ER-phagy pathways.
    Keywords:  Autophagy; ER-phagy; Virophagy; Virus; Xenophagy