Role for Rab7 in maturation of late autophagic vacuoles

Effects of botulinum neurotoxin-associated proteins on cellular organelle dynamics in NRK-52E cells

Clostridium botulinum produces seven distinct serotypes (A-G) of botulinum neurotoxin (BoNT), a potent biological toxin that affects the nervous system. In its natural state, BoNT forms a progenitor toxin complex with neurotoxin-associated proteins (NAPs), substantially enhancing its stability and oral toxicity. Recent studies have shown that NAPs in certain serotypes induce vacuolation and death in various epithelial cell types. In this study, we examined the effects of the serotype D NAPs complex (NAPs/D) on intracellular organelles in NRK-52E cells, a rat kidney cell line. NRK-52E cells were selected because they exhibit a unique response, showing vacuolation without undergoing cell death upon exposure to NAPs/D. Our findings indicated that NAPs/D-induced vacuole formation was associated with the reduced size of the Golgi apparatus. Additionally, vacuoles were associated with endocytic vesicles, implying that NAPs/D modulate endocytic pathways and affect intracellular transport. Furthermore, NAPs/D exposure activated early autophagic signaling, as evidenced by increased LC3 expression, although vacuole formation appeared to occur independently of the complete autophagy process. These findings provide valuable insights into the cellular mechanisms underlying BoNT toxicity and highlight the complex interplay between NAPs/D-induced vacuolation, endocytosis, and autophagy. This study highlights potential therapeutic approaches to mitigate the effects of botulism by targeting these pathways.

Unraveling the functional and molecular interplay between cellular senescence and the unfolded protein response

Senescence is a complex cellular state that can be considered as a stress response phenotype. A decade ago, we suggested the intricate connections between unfolded protein response (UPR) signaling and the development of the senescent phenotype. Over the past ten years, significant advances have been made in understanding the multifaceted role of the UPR in regulating cellular senescence, highlighting its contribution to biological processes such as oxidative stress and autophagy. In this updated review, we expand these interconnections with the benefit of new insights, and we suggest that targeting specific components of the UPR could provide novel therapeutic strategies to mitigate the deleterious effects of senescence, with significant implications for age-related pathologies and geroscience.

EPG-5 regulates TGFB/TGF-β and WNT signalling by modulating retrograde endocytic trafficking

The Vici syndrome protein EPG5 acts as a tethering factor determining the fusion specificity of autophagosomes with late endosomes/lysosomes. Here we demonstrated that during C. elegans development, EPG-5 modulates SMA and MAB TGFB/TGF-β signaling in controlling body size and also WNT signaling in regulating cell migration. EPG-5 is required for retrograde trafficking of the TGFB receptor SMA-6 and WLS/Wntless homolog MIG-14. In epg-5 mutants, SMA-6 and MIG-14 are trapped within hybrid endosomal structures, which colocalize with SNX-1- and SNX-3-labeled vesicles, respectively. Basolateral recycling processes of transmembrane cargos H.s.TFR/hTfR and H.s.IL2RA/hTAC are also defective in epg-5 mutants. Depletion of EPG-5 causes defective RAB-5 and RAB-7, and RAB-5 and RAB-10 conversion, leading to the formation of these hybrid vesicles. The defects in endocytic trafficking and autophagy in epg-5 mutants are ameliorated by knocking down components of the HOPS complex. Our study demonstrates the intersection between the autophagy pathway and the endocytic pathway, providing insights into the pathogenesis of amyotrophic lateral sclerosis (ALS) and Vici syndrome.Abbreviations: ALM: anterior lateral microtubule; ATG: autophagy related; AVM: anterior ventral microtubule; CORVET: class C core vacuole/endosome tethering; DAF-4: abnormal dauer formation 4; DIC: differential interference contrast; EPG: ectopic PGL granules; EPG-5: ectopic P granules 5; GAP: GTPase activating protein; GFP: green fluorescent protein; HOPS: homotypic fusion and vacuole protein sorting; H.s.IL2RA/hTAC: human interleukin 2 receptor subunit alpha; H.s.TFR/hTfR: human transferrin receptor; L1/L4: the first/fourth larval; mCh: mCherry; MIG-14: abnormal cell migration 14; PLM: posterior lateral microtubule; PVM: posterior ventral microtubule; RAB: ras-related protein; RFP: red fluorescent protein; RME-1: receptor mediated endocytosis 1; SMA-6: small 6; SNARE: soluble N-ethylmaleimide-sensitive factor attachment protein receptor; SNX: sorting nexin; TBC-2: TBC1 (Tre-2/Bub2/Cdc16) domain family 2; TGFB/TGF-β: transforming growth factor beta; TGN: trans-Golgi network; VPS: related to yeast vacuolar protein sorting factor; WT: wild type.

USP4 depletion-driven RAB7A ubiquitylation impairs autophagosome-lysosome fusion and aggravates periodontitis

Periodontitis, a prevalent and chronic inflammatory disease, is intricately linked with macroautophagy/autophagy, which has a dual role in maintaining periodontal homeostasis. Despite its importance, the precise interplay between autophagy and periodontitis pathogenesis remains to be fully elucidated. In this study, our investigation revealed that the ubiquitination of RAB7A, mediated by reduced levels of the deubiquitinating enzyme USP4 (ubiquitin specific peptidase 4), disrupts normal lysosomal trafficking and autophagosome-lysosome fusion, thereby contributing significantly to periodontitis progression. Specifically, through genomic and histological analysis of clinical gingival samples, we observed a decreased RAB7A expression and impaired autophagic activity in periodontitis. This was further substantiated through experimental periodontitis mice, where RAB7A inactivation was shown to directly affect autophagy efficiency and drive periodontitis progression. Next, we explored the function of active RAB7A to promote lysosomal trafficking dynamics and autophagosome-lysosome fusion, which was inhibited by RAB7A ubiquitination in macrophages stimulated by Porphyromonas gingivalis (P. g.), one of the keystone pathogens of periodontitis. Last, by proteomics analysis, we revealed that the ubiquitination of RAB7A was mediated by USP4 and validated that upregulation of USP4 could attenuate periodontitis in vivo. In conclusion, these findings highlight the interaction between USP4 and RAB7A as a promising target for therapeutic intervention in managing periodontal diseases.Abbreviation: 3-MA: 3-methyladenine; Baf A1:bafilomycin A1; BECN1: beclin 1, autophagy related; CEJ-ABC: cementoenamel junctionto alveolar bone crest; IL1B/IL-1β: interleukin 1 beta; KD:knockdown; LPS: lipopolysaccharide; MOI: multiplicity of infection;OE: overexpression; P.g.: Porphyromonasgingivalis; RILP: Rabinteracting lysosomal protein; ScRNA-seq: single-cell RNA sequencing; SQSTM1/p62: sequestosome 1; S.s.: Streptococcus sanguinis; USP4:ubiquitin specific peptidase 4.

The primate-specific Nedd4-1(NE) localizes to late endosomes in response to amino acids to suppress autophagy

The ubiquitin ligase Nedd4 (Nedd4-1), comprised of C2-WW(n)-HECT domains, regulates protein trafficking. We recently described a primate-specific Nedd4-1 splice isoform with an extended N-terminus replacing the C2 domain, called Nedd4-1(NE). Here, we show that while canonical Nedd4-1 is primarily localized to the cytosol, Nedd4-1(NE) localizes to late endosomes. This localization is mediated by the NE region, is dependent on amino acid availability, is independent of mTORC1, and is inhibited by the autophagy inducer IKKβ. We further demonstrate that VPS16B, which regulates late endosome to lysosome maturation, is a unique Nedd4-1(NE) substrate that co-localizes with Nedd4-1(NE) in the presence of nutrients. Importantly, a potentially pathogenic homozygous variant identified in the NE region (E70Q) of a patient with lymphangiectasia and protein-losing enteropathy leads to reduced VPS16B ubiquitination by Nedd4-1(NE). Finally, we report that Nedd4-1(NE) inhibits autophagy, likely by disrupting late endosome to autophagosome maturation. This work identified an mTORC1-independent, IKK-driven mechanism to regulate Nedd4-1(NE) localization to late endosomes in primates in response to nutrient availability, and uncovered suppression of autophagy by this ubiquitin ligase.

Autophagy regulates cellular senescence by mediating the degradation of CDKN1A/p21 and CDKN2A/p16 through SQSTM1/p62-mediated selective autophagy in myxomatous mitral valve degeneration

Myxomatous mitral valve degeneration (MMVD) is one of the most important age-dependent degenerative heart valve disorders in both humans and dogs. It is characterized by the aberrant remodeling of extracellular matrix (ECM), regulated by senescent myofibroblasts (aVICs) transitioning from quiescent valve interstitial cells (qVICs), primarily under TGFB1/TGF-β1 control. In the present study, we found senescent aVICs exhibited impaired macroautophagy/autophagy as evidenced by compromised autophagy flux and immature autophagosomes. MTOR-dependent autophagy induced by rapamycin and torin-1 attenuated cell senescence and decreased the expression of cyclin-dependent kinase inhibitors (CDKIs) CDKN2A/p16INK4A and CDKN1A/p21CIP1. Furthermore, induction of autophagy in aVICs by ATG (autophagy related) gene overexpression restored autophagy flux, with a concomitant reduction in CDKN1A and CDKN2A expression and senescence-associated secretory phenotype (SASP). Conversely, autophagy deficiency induced CDKN1A and CDKN2A accumulation and SASP, whereas ATG re-expression alleviated senescent phenotypic transformation. Notably, CDKN1A and CDKN2A localized to autophagosomes and lysosomes following MTOR antagonism or MG132 treatment. SQSTM1/p62 was identified as the autophagy receptor to selectively sequester CDKN1A and CDKN2A cargoes for autophagic degradation. Our findings are the first demonstration that CDKN1A and CDKN2A are degraded through SQSTM1-mediated selective autophagy, independent of the ubiquitin-proteasome pathway. These data will inform development of therapeutic strategies for the treatment of canine and human MMVD, and for the treatment of Alzheimer disease, Parkinson disease and other age-related degenerative disorders.Abbreviations: ACTA2/α-SMA: actin alpha 2, smooth muscle; AKT: AKT serine/threonine kinase; aVICs: activated valve interstitial cells; ATG: autophagy related; baf-A1: bafilomycin A1; BrdU, bromodeoxyuridine; BSA: bovine serum albumin; CDKIs, cyclin-dependent kinase inhibitors; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; CDKN2A/p16: cyclin dependent kinase inhibitor 2A; co-IP: co-immunoprecipitation; DMSO: dimethylsulfoxide; ECM, extracellular matrix; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; eGFP: green fluorescent protein; ELISA: enzyme-linked immunosorbent assay; HEK-293T, human embryonic kidney 293T; HRP: horseradish peroxidase; KO: knockout; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; LIR: MAP1LC3/LC3-interacting region; MFS: Marfan syndrome; MKI67/Ki-67: marker of proliferation Ki-67; MMVD: myxomatous mitral valve degeneration; MTOR: mechanistic target of rapamycin kinase; MTORC: MTOR complex; OE: overexpression; PBST, phosphate-buffered saline with 0.1% Tween-20; PCNA: proliferating cell nuclear antigen; PIK3CA/PI3K: phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha; PLA: proximity ligation assays; PSMA1: proteasome 20S subunit alpha 1; PSMB5: proteasome 20S subunit beta 5; qVICs: quiescent valve interstitial cells; qRT-PCR: quantitative real-time PCR; SA-GLB1/β-gal: SA-senescence-associated GLB1/β-galactosidase; ROS: reactive oxygen species; SASP: senescence-associated secretory phenotype; RPS6KB1/p70 S6K: ribosomal protein S6 kinase B1; SMAD: SMAD family member; SQSTM1/p62: sequestosome 1; STEM: scanning transmission electron microscopy; TGFB: transforming growth factor beta; TGFBR: transforming growth factor beta receptor; TP53/p53: tumor protein p53; UPS: ubiquitin-proteasome system; WT, wild-type.

E3 ubiquitin ligase RNF128 promotes Lys63-linked polyubiquitination on SRB1 in macrophages and aggravates atherosclerosis

Macrophage-derived foam cell formation is the hallmark of atherosclerotic plaques prominently attributed to excessive lipid uptake and metabolic disorders. As a classic membrane-localized ubiquitin ligase, the role of RNF128 in atherosclerosis remains unknown. We discover that RNF128 is specifically expressed in macrophages of the lipid core based on single-cell RNA sequencing data and persistent hyperlipidemia induces the high expression of RNF128 in macrophages. RNF128 ablation in macrophages ameliorates atherosclerosis in both male and female mice under the background of ApoE and LDLR deficiency. Mechanistically, RNF128 directly binds to scavenger receptor B1 (SRB1), preventing its degradation through the lysosomal system and promoting oxidized low-density lipoprotein (oxLDL)-induced foam cell formation and inflammatory response in macrophages. In addition, RNF128 catalyzes Lys63-linked polyubiquitination on the cytoplasmic C-terminus of the SRB1 at lysine 478, which promotes the endosome SRB1 recycling to the cell membrane with the assistance of Rab11, instead of entering the lysosome for degradation.

Autophagy and Cancer: Insights into Molecular Mechanisms and Therapeutic Approaches for Chronic Myeloid Leukemia

Autophagy is a critical cellular process that maintains homeostasis by recycling damaged or aberrant components. This process is orchestrated by a network of proteins that form autophagosomes, which engulf and degrade intracellular material. In cancer, autophagy plays a dual role: it suppresses tumor initiation in the early stages but supports tumor growth and survival in advanced stages. Chronic myeloid leukemia (CML), a hematological malignancy, is characterized by the Philadelphia chromosome, a chromosomal abnormality resulting from a translocation between chromosomes 9 and 22. Autophagy has emerged as a key factor in CML pathogenesis, promoting cancer cell survival and contributing to resistance against tyrosine kinase inhibitors (TKIs), the primary treatment for CML. Targeting autophagic pathways is being actively explored as a therapeutic approach to overcome drug resistance and enhance cancer cell death. Recent research highlights the intricate interplay between autophagy and CML progression, underscoring its role in disease biology and treatment outcomes. This review aims to provide a comprehensive analysis of the molecular and cellular mechanisms underlying CML, with a focus on the therapeutic potential of targeting autophagy.

Lipid droplets in central nervous system and functional profiles of brain cells containing lipid droplets in various diseases

Lipid droplets (LDs), serving as the convergence point of energy metabolism and multiple signaling pathways, have garnered increasing attention in recent years. Different cell types within the central nervous system (CNS) can regulate energy metabolism to generate or degrade LDs in response to diverse pathological stimuli. This article provides a comprehensive review on the composition of LDs in CNS, their generation and degradation processes, their interaction mechanisms with mitochondria, the distribution among different cell types, and the roles played by these cells-particularly microglia and astrocytes-in various prevalent neurological disorders. Additionally, we also emphasize the paradoxical role of LDs in post-cerebral ischemia inflammation and explore potential underlying mechanisms, aiming to identify novel therapeutic targets for this disease.

Cholesterol deficiency directs autophagy-dependent secretion of extracellular vesicles

Extracellular vesicle (EV) secretion is an important, though not fully understood, intercellular communication process. Lipid metabolism has been shown to regulate EV activity, though the impact of specific lipid classes is unclear. Through analysis of small EVs (sEVs), we observe aberrant increases in sEV release within genetic models of cholesterol biosynthesis disorders, where cellular cholesterol is diminished. Inhibition of cholesterol synthesis at multiple synthetic steps mimics genetic models in terms of cholesterol reduction and sEVs secreted. Further analyses of sEVs from cholesterol-depleted cells revealed structural deficits and altered surface marker expression, though these sEVs were also more easily internalized by recipient cells. Transmission electron microscopy of cells with impaired cholesterol biosynthesis demonstrated multivesicular and multilamellar structures potentially associated with autophagic defects. We further found autophagic vesicles being redirected toward late endosomes at the expense of autophagolysosomes. Through CRISPR-mediated inhibition of autophagosome formation, we mechanistically determined that release of sEVs after cholesterol depletion is autophagy dependent. We conclude that cholesterol imbalance initiates autophagosome-dependent secretion of sEVs, which may have pathological relevance in diseases of cholesterol disequilibrium.

Tacrolimus regulates extracellular vesicle secretion from T cells via autophagy-lysosomal pathway

Extracellular vesicles (EVs) derived from T cells have been proposed to mediate intercellular communication and orchestrate immune responses. The immunosuppressive drug, tacrolimus (TAC), suppresses T cell activity; however, the impact of TAC on T cell-derived EVs remains primarily unexplored. In this study, human primary T cells purified from healthy donors were used to investigate TAC-mediated regulation of EV secretion by T cells. Using size exclusion chromatography (SEC) to isolate EVs released by T cells, we found that the number of released EVs was increased upon anti-CD3/CD28 bead-mediated activation. Furthermore, pre-treatment with TAC before activation had a potentiating effect on EV release, as evidenced by western blot analysis of EV markers and small particle flow cytometry. In addition, we showed that EVs isolated from the plasma of TAC-treated kidney transplant patients were increased compared to those observed with pre-transplant plasma. Upon examining the mechanism underlying the action of TAC, we found that TAC impaired autophagy-lysosome-mediated degradation by inhibiting the nuclear translocation of transcription factor EB, a master regulator of lysosomal biogenesis. Notably, the addition of trehalose, an autophagy inducer, abrogated the TAC-induced EV release, indicating that TAC regulated EV secretion via the autophagy-lysosomal pathway. At the functional level, we demonstrated that EVs from TAC-treated T cells carried a decreased amount of CD40L, a protein critical for the activation of the adaptive immune response. Collectively, these findings demonstrate that an overall increase in EV production and decreased CD40L levels in EVs are characteristic responses of T cells to TAC.

Autophagy in cancer development, immune evasion, and drug resistance

Macroautophagy/autophagy is a highly conserved evolutionary mechanism involving lysosomes for the degradation of cytoplasmic components including organelles. The constitutive, basal level of autophagy is fundamental for preserving cellular homeostasis; however, alterations in autophagy can cause disease pathogenesis, including cancer. The role of autophagy in cancer is particularly complicated, since this process acts both as a tumor suppressor in precancerous stages but facilitates tumor progression during carcinogenesis and later stages of cancer progression. This shift between anti-tumor and pro-tumor roles may be influenced by genetic and environmental factors modulating key pathways such as those involving autophagy-related proteins, the PI3K-AKT-MTOR axis, and AMPK, which often show dysregulation in tumors. Autophagy regulates various cellular functions, including metabolism of glucose, glutamine, and lipids, cell proliferation, metastasis, and several types of cell death (apoptosis, ferroptosis, necroptosis and immunogenic cell death). These multifaceted roles demonstrate the potential of autophagy to affect DNA damage repair, cell death pathways, proliferation and survival, which are critical in determining cancer cells' response to chemotherapy. Therefore, targeting autophagy pathways presents a promising strategy to combat chemoresistance, as one of the major reasons for the failure in cancer patient treatment. Furthermore, autophagy modulates immune evasion and the function of immune cells such as T cells and dendritic cells, influencing the tumor microenvironment and cancer's biological behavior. However, the therapeutic targeting of autophagy is complex due to its dual role in promoting survival and inducing cell death in cancer cells, highlighting the need for strategies that consider both the beneficial and detrimental effects of autophagy modulation in cancer therapy. Hence, both inducers and inhibitors of autophagy have been introduced for the treatment of cancer. This review emphasizes the intricate interplay between autophagy, tumor biology, and immune responses, offering insights into potential therapeutic approaches that deploy autophagy in the cancer suppression.

Comprehensive knockout analysis of the RAB family small GTPases reveals an overlapping role of RAB2 and RAB14 in autophagosome maturation

Macroautophagy, simply referred to below as autophagy, is an intracellular degradation system that is highly conserved in eukaryotes. Since the processes involved in autophagy are accompanied by membrane dynamics, RAB small GTPases, key regulators of membrane trafficking, are generally thought to regulate the membrane dynamics of autophagy. Although more than half of the mammalian RABs have been reported to be involved in canonical and selective autophagy, no consensus has been reached in regard to the role of RABs in mammalian autophagy. Here, we comprehensively analyzed a rab-knockout (KO) library of MDCK cells to reevaluate the requirement for each RAB isoform in basal and starvation-induced autophagy. The results revealed clear alteration of the MAP1LC3/LC3-II level in only four rab-KO cells (rab1-KO, rab2-KO, rab7a-KO, and rab14-KO cells) and identified RAB14 as a new regulator of autophagy, specifically at the autophagosome maturation step. The autophagy-defective phenotype of two of these rab-KO cells, rab2-KO and rab14-KO cells, was very mild, but double KO of rab2 and rab14 caused a severer autophagy-defective phenotype (greater LC3 accumulation than in single-KO cells, indicating an overlapping role of RAB2 and RAB14 during autophagosome maturation. We also found that RAB14 is phylogenetically similar to RAB2 and that it possesses the same properties as RAB2, i.e. autophagosome localization and interaction with the HOPS subunits VPS39 and VPS41. Our findings suggest that RAB2 and RAB14 overlappingly regulate the autophagosome maturation step through recruitment of the HOPS complex to the autophagosome.Abbreviation: AID2: auxin-inducible degron 2; ATG: autophagy related; BafA1: bafilomycin A1; CKO: conditional knockout; EBSS: Earle's balanced salt solution; EEA1: early endosome antigen 1; HOPS: homotypic fusion and protein sorting; HRP: horseradish peroxidase; IP: immunoprecipitation; KD: knockdown; KO: knockout; LAMP2: lysosomal-associated membrane protein 2; MDCK: Madin-Darby canine kidney; mAb: monoclonal antibody; MEF: mouse embryonic fibroblast; MTORC1: mechanistic target of rapamycin kinase complex 1; 5-Ph-IAA: 5-phenyl-indole-3-acetic acid; pAb: polyclonal antibody; siRNA: small interfering RNA; SNARE: soluble NSF-attachment protein receptor; TF: transferrin; WT: wild-type.

SIRT1-FOXOs signaling pathway: A potential target for attenuating cardiomyopathy

Cardiomyopathy constitutes a global health burden. It refers to myocardial injury that causes alterations in cardiac structure and function, ultimately leading to heart failure. Currently, there is no definitive treatment for cardiomyopathy. This is because existing treatments primarily focus on drug interventions to attenuate symptoms rather than addressing the underlying causes of the disease. Notably, the cardiomyocyte loss is one of the key risk factors for cardiomyopathy. This loss can occur through various mechanisms such as metabolic disturbances, cardiac stress (e.g., oxidative stress), apoptosis as well as cell death resulting from disorders in autophagic flux, etc. Sirtuins (SIRTs) are categorized as class III histone deacetylases, with their enzyme activity primarily reliant on the substrate nicotinamide adenine dinucleotide (NAD (+)). Among them, Sirtuin 1 (SIRT1) is the most intensively studied in the cardiovascular system. Forkhead O transcription factors (FOXOs) are the downstream effectors of SIRT1. Several reports have shown that SIRT1 can form a signaling pathway with FOXOs in myocardial tissue, and this pathway plays a key regulatory role in cell loss. Thus, this review describes the basic mechanism of SIRT1-FOXOs in inhibiting cardiomyocyte loss and its favorable role in cardiomyopathy. Additionally, we summarized the SIRT1-FOXOs related regulation factor and prospects the SIRT1-FOXOs potential clinical application, which provide reference for the development of cardiomyopathy treatment.

Autophagy and cancer therapy

Autophagy is an intracellular degradation process that sequesters cytoplasmic components in double-membrane vesicles known as autophagosomes, which are degraded upon fusion with lysosomes. This pathway maintains the integrity of proteins and organelles while providing energy and nutrients to cells, particularly under nutrient deprivation. Deregulation of autophagy can cause genomic instability, low protein quality, and DNA damage, all of which can contribute to cancer. Autophagy can also be overactivated in cancer cells to aid in cancer cell survival and drug resistance. Emerging evidence indicates that autophagy has functions beyond cargo degradation, including roles in tumor immunity and cancer stem cell survival. Additionally, autophagy can also influence the tumor microenvironment. This feature warrants further investigation of the role of autophagy in cancer, in which autophagy manipulation can improve cancer therapies, including cancer immunotherapy. This review discusses recent findings on the regulation of autophagy and its role in cancer therapy and drug resistance.

Acetylation of FOXO1 is involved in cadmium-induced rat kidney injury via mediating autophagosome-lysosome fusion blockade and autophagy inhibition

Cadmium (Cd), a potentially toxic elements, has the potential to cause harm to the kidneys. Studies has demonstrated that autophagosome-lysosome fusion blockade and consequent autophagy inhibition is related to Cd-induced kidney injury. Studies indicate that acetylation of forkhead box protein O1 (FOXO1) as a transcriptional factor of lysosomal and autophagy genes, but its roles in Cd-exposed kidney tissues remains unclear till now. Therefore, the present study was conducted to elucidate this issue. Data found that Cd enhances the acetylation level of FOXO1 and inhibits the expression level of silent information regulator 1 (Sirt1, deacetylase of FOXO1). Pharmacological activation of Sirt1 (SRT2104 treatment) decreases Cd-increased acetylation level of FOXO1, enhances Cd-inhibited transcription level of Ras-related protein 7 (Rab7), restores Cd-blocked fusion of autophagosome and lysosome, and alleviates Cd-induced autophagy inhibition. Moreover, data corroborated that inhibiting the acetylation level of FOXO1 is conductive to mitigating Cd-induced kidney injury. Collectively, these results demonstrate that acetylation of FOXO1 mediates the autophagosome-lysosome fusion blockade and autophagy inhibition during Cd-induced kidney injury, while regulating the acetylation level of FOXO1 may be a potential mechanism of treating nephrotoxicity after Cd exposure.

Functional Role of Hepatitis C Virus NS5A in the Regulation of Autophagy

Many types of RNA viruses, including the hepatitis C virus (HCV), activate autophagy in infected cells to promote viral growth and counteract the host defense response. Autophagy acts as a catabolic pathway in which unnecessary materials are removed via the lysosome, thus maintaining cellular homeostasis. The HCV non-structural 5A (NS5A) protein is a phosphoprotein required for viral RNA replication, virion assembly, and the determination of interferon (IFN) sensitivity. Recently, increasing evidence has shown that HCV NS5A can induce autophagy to promote mitochondrial turnover and the degradation of hepatocyte nuclear factor 1 alpha (HNF-1α) and diacylglycerol acyltransferase 1 (DGAT1). In this review, we summarize recent progress in understanding the detailed mechanism by which HCV NS5A triggers autophagy, and outline the physiological significance of the balance between host-virus interactions.

Force-induced dephosphorylation activates the cochaperone BAG3 to coordinate protein homeostasis and membrane traffic

Proteome maintenance in contracting skeletal and cardiac muscles depends on the chaperone-regulating protein BAG3. Reduced BAG3 activity leads to muscle weakness and heart failure in animal models and patients. BAG3 and its chaperone partners recognize mechanically damaged muscle proteins and initiate their disposal through chaperone-assisted selective autophagy (CASA). However, molecular details of the force-dependent regulation of BAG3 have remained elusive so far. Here, we demonstrate that mechanical stress triggers the dephosphorylation of BAG3 in human muscle and in isolated cells. We identify force-regulated phospho-switches in BAG3 that control CASA complex assembly and CASA activity. Differential proteomics reveal RAB GTPases, which organize membrane traffic and fusion, as dephosphorylation-dependent interactors of BAG3. In fact, RAB7A and RAB11B are shown here to be essential for CASA in skeletal muscle cells. Moreover, BAG3 dephosphorylation is also observed upon induction of mitophagy, suggesting an involvement of the cochaperone in the RAB7A-dependent autophagic engulfment of damaged mitochondria in exercised muscle. Cooperation of BAG3 with RAB7A relies on a direct interaction of both proteins, which is regulated by the nucleotide state of the GTPase and by association with the autophagosome membrane protein LC3B. Finally, we provide evidence that BAG3 and RAB7A also cooperate in non-muscle cells and propose that overactivation of CASA in RAB7A-L129F patients contributes to the loss of peripheral neurons in Charcot-Marie-Tooth neuropathy.

Downregulation of O-GlcNAc transferase activity impairs basal autophagy and late endosome positioning under nutrient-rich conditions in human colon cells

Autophagy is a critical catabolic pathway that enables cells to survive and adapt to stressful conditions, especially nutrient deprivation. The fusion of autophagic vacuoles with lysosomes is the final step of autophagy, which degrades the engulfed contents into metabolic precursors for re-use by the cell. O-GlcNAc transferase (OGT) plays a crucial role in regulating autophagy flux in response to nutrient stress, particularly by targeting key proteins involved in autophagosome-lysosome fusion. However, the role of OGT in basal autophagy, which occurs at a low and constitutive levels under growth conditions, remains poorly understood. Silencing or inhibition of OGT was used to compare the effect of OGT downregulation on autophagy flux in the non-cancerous CCD841CoN and cancerous HCT116 human colon cell lines under nutrient-rich conditions. We provide evidence that the reduction of OGT activity impairs the maturation of autophagosomes, thereby blocking the completion of basal autophagy in both cell lines. Additionally, OGT inhibition results in the accumulation of lysosomes and enlarged late endosomes in the perinuclear region, as demonstrated by confocal imaging. This is associated with a defect in the localization of the small GTPase Rab7 to these organelles. The regulation of transport and fusion events between the endosomal and lysosomal compartments is crucial for maintaining the autophagic flux. These findings suggest an interplay between OGT and the homeostasis of the endolysosomal network in human cells.

Autophagy in glioblastoma: A mechanistic perspective

Glioblastoma (GBM) is one of the most lethal malignancies in humans. Even after surgical resection and aggressive radio- or chemotherapies, patients with GBM can survive for less than 14 months. Extreme inter-tumor and intra-tumor heterogeneity of GBM poses a challenge for resolving recalcitrant GBM pathophysiology. GBM tumor microenvironment (TME) exhibits diverse heterogeneity in cellular composition and processes contributing to tumor progression and therapeutic resistance. Autophagy is such a cellular process; that demonstrates a cell-specific and TME context-dependent role in GBM progression, leading to either the promotion or suppression of GBM progression. Autophagy can regulate GBM cell function directly via regulation of survival, migration, and invasion, or indirectly by affecting GBM TME composition such as immune cell population, tumor metabolism, and glioma stem cells. This review comprehensively investigates the role of autophagy in GBM pathophysiology.

SIRT5-Mediated Desuccinylation of RAB7A Protects Against Cadmium-Induced Alzheimer's Disease-Like Pathology by Restoring Autophagic Flux

Cadmium (Cd) is a neurotoxic contaminant that induces cognitive decline similar to that observed in Alzheimer's disease (AD). Autophagic flux dysfunction is attributed to the pathogenesis of AD, and this study aimed to investigate the effect of autophagy on environmental Cd-induced AD progression and the underlying mechanism. Here, Cd exposure inhibited autophagosome-lysosome fusion and impaired lysosomal function, leading to defects in autophagic clearance and then to APP accumulation and nerve cell death. Proteomic analysis coupled with Ingenuity Pathway Analysis (IPA) identified SIRT5 as an essential molecular target in Cd-impaired autophagic flux. Mechanistically, Cd exposure hampered the expression of SIRT5, thus increasing the succinylation of RAB7A at lysine 31 and inhibiting RAB7A activity, which contributed to autophagic flux blockade. Importantly, SIRT5 overexpression led to the restoration of autophagic flux blockade, the alleviation of Aβ deposition and memory deficits, and the desuccinylation of RAB7A in Cd-exposed FAD4T mice. Additionally, SIRT5 levels decrease mainly in neurons but not in other cell clusters in the brains of AD patients according to single-nucleus RNA sequencing data from the public dataset GSE188545. This study reveals that SIRT5-catalysed RAB7A desuccinylation is an essential adaptive mechanism for the amelioration of Cd-induced autophagic flux blockade and AD-like pathogenesis.

The vesicle trafficking gene, OsRab7, is critical for pollen development and male fertility in cytoplasmic male-sterility rice

Rice cytoplasmic male sterility (CMS) provides an exceptional model for studying genetic interaction within plant nuclei given its inheritable trait of non-functional male gametophyte. Gaining a comprehensive understanding of the genes and pathways associated with the CMS mechanism is imperative for improving the vigor of hybrid rice agronomically, such as its productivity. Here, we observed a significant decrease in the expression of a gene named OsRab7 in the anther of the CMS line (SJA) compared to the maintainer line (SJB). OsRab7 is responsible for vesicle trafficking and loss function of OsRab7 significantly reduced pollen fertility and setting rate relative to the wild type. Meanwhile, over-expression of OsRab7 enhanced pollen fertility in the SJA line while a decrease in its expression in the SJB line led to the reduced pollen fertility. Premature tapetum and abnormal development of microspores were observed in the rab7 mutant. The expression of critical genes involved in tapetum development (OsMYB103, OsPTC1, OsEAT1 and OsAP25) and pollen development (OsMSP1, OsDTM1 and OsC4) decreased significantly in the anther of rab7 mutant. Reduced activities of the pDR5::GUS marker in the young panicle and anther of the rab7 mutant were also observed. Furthermore, the mRNA levels of genes involved in auxin biosynthesis (YUCCAs), auxin transport (PINs), auxin response factors (ARFs), and members of the IAA family (IAAs) were all downregulated in the rab7 mutant, indicating its impact on auxin signaling and distribution. In summary, these findings underscore the importance of OsRab7 in rice pollen development and its potential link to cytoplasmic male sterility.

Illuminating intercellular autophagy: A comprehensive review of cell non-autonomous autophagy

Macro-autophagy (autophagy hereafter) is an evolutionarily conserved cellular process that has long been recognized as an intracellular mechanism for maintaining cellular homeostasis. It involves the formation of a membraned structure called the autophagosome, which carries cargo that includes toxic protein aggregates and dysfunctional organelles to the lysosome for degradation and recycling. Autophagy is primarily considered and studied as a cell-autonomous mechanism. However, recent studies have illuminated an underappreciated facet of autophagy, i.e., non-autonomously regulated autophagy. Non-autonomously regulated autophagy involves the degradation of autophagic components, including organelles, cargo, and signaling molecules, and is induced in neighboring cells by signals from primary adjacent or distant cells/tissues/organs. This review provides insight into the complex molecular mechanisms governing non-autonomously regulated autophagy, highlighting the dynamic interplay between cells within tissue/organ or distinct cell types in different tissues/organs. Emphasis is placed on modes of intercellular communication that include secreted molecules, including microRNAs, and their regulatory roles in orchestrating this phenomenon. Furthermore, we explore the multidimensional roles of non-autonomously regulated autophagy in various physiological contexts, spanning tissue development and aging, as well as its importance in diverse pathological conditions, including cancer and neurodegeneration. By studying the complexities of non-autonomously regulated autophagy, we hope to gain insights into the sophisticated intercellular dynamics within multicellular organisms, including mammals. These studies will uncover novel avenues for therapeutic intervention to modulate intercellular autophagic pathways in altered human physiology.

Effect of MEHP on testosterone synthesis via Sirt1/Foxo1/Rab7 signaling pathway inhibition of lipophagy in TM3 cells

Mono-2-ethylhexyl phthalic acid (MEHP) is the most toxic metabolite of the plasticizer di-2-ethylhexyl phthalic acid (DEHP), and studies have shown that MEHP causes serious reproductive effects. However, its exact mechanisms of action remain elusive. In this study, we aimed to investigate the reproductive effects of MEHP and preliminarily explore its underlying molecular mechanisms. We found that TM3 cells gradually secreted less testosterone and intracellular free cholesterol with increasing MEHP exposure. MEHP exposure inhibited lipophagy and the Sirt1/Foxo1/Rab7 signaling pathway in TM3 cells, causing aberrant accumulation of intracellular lipid droplets. Addition of the Sirt1 agonist SRT1720 and Rab7 agonist ML-098 alleviated the inhibition of lipophagy and increased free cholesterol and testosterone contents in TM3 cells. SRT1720 alleviated the inhibitory effect of MEHP on the Sirt1/Foxo1/Rab7 signaling pathway, whereas ML-098 only alleviated the inhibition of Rab7 protein expression by MEHP and had no effect on Sirt1 and Foxo1 protein expression. This suggests that MEHP inhibits lipophagy in TM3 cells by suppressing the Sirt1/Foxo1/Rab7 signaling pathway, ultimately leading to a further decrease in cellular testosterone secretion. This study improves our current understanding of the toxicity and molecular mechanisms of action of MEHP and provides new insights into the reproductive effects of phthalic acid esters.

Deregulated expression of autophagy genes; PIK3C3 and RAB7A in COVID-19 patients

BACKGROUND

The role of autophagy in coronaviruses infection and replication has a lot of debate. Autophagy involves the catalytic breakdown of intracellular components to be subsequently recycled by the lysosome. The aim of the study was to evaluate autophagy genes; PIK3C3 and RAB7A expressions in COVID-19 patients, and identify if PIK3C3 and RAB7A can be used as markers for monitoring COVID-19 patients.

METHODS

A case-control study was carried out on 50 patients and 50 healthy controls. Genes expression was performed using quantitative real-time polymerase chain reaction.

RESULTS

Compared to controls, PIK3C3 and RAB7A gene expression levels were significantly lower in patients (p < 0.001) with approximately with 9.4 and 2.3 decreased fold in PIK3C3 and RAB7A respectively. The ROC curve of PIK3C3 and RAB7A expressions showed sensitivity of 84 % and 74 % and specificity of 98 % and 78 % respectively. There was a positive correlation between PIK3C3 expression and WBCs, absolute neutrophil count, interleukin-6, D-dimer, and ALT among patients and between RAB7A expression and WBCs, CRP, IL-6, D-dimer and ALT in patients.

CONCLUSIONS

The study showed reduction of PIK3C3 and RAB7A expressions in COVID-19 patients. However, further studies are recommended to clarify their roles in the disease pathogenies as autophagy genes.

Identification of secretory autophagy as a mechanism modulating activity-induced synaptic remodeling

The ability of neurons to rapidly remodel their synaptic structure and strength in response to neuronal activity is highly conserved across species and crucial for complex brain functions. However, mechanisms required to elicit and coordinate the acute, activity-dependent structural changes across synapses are not well understood, as neurodevelopment and structural plasticity are tightly linked. Here, using an RNAi screen in Drosophila against genes affecting nervous system functions in humans, we uncouple cellular processes important for synaptic plasticity and synapse development. We find mutations associated with neurodegenerative and mental health disorders are 2-times more likely to affect activity-induced synaptic remodeling than synapse development. We report that while both synapse development and activity-induced synaptic remodeling at the fly NMJ require macroautophagy (hereafter referred to as autophagy), bifurcation in the autophagy pathway differentially impacts development and synaptic plasticity. We demonstrate that neuronal activity enhances autophagy activation but diminishes degradative autophagy, thereby driving the pathway towards autophagy-based secretion. Presynaptic knockdown of Snap29, Sec22, or Rab8, proteins implicated in the secretory autophagy pathway, is sufficient to abolish activity-induced synaptic remodeling. This study uncovers secretory autophagy as a transsynaptic signaling mechanism modulating synaptic plasticity.

Regulation of Autophagosome-Lysosome Fusion by Human Viral Infections

Autophagy plays a fundamental role in maintaining cellular homeostasis by eliminating intracellular components via lysosomes. Successful degradation through autophagy relies on the fusion of autophagosomes to lysosomes, which leads to the formation of autolysosomes containing acidic proteases that degrade the sequestered materials. Viral infections can exploit autophagy in infected cells to balance virus-host cell interactions by degrading the invading virus or promoting viral growth. In recent years, cumulative studies have indicated that viral infections may interfere with the fusion of autophagosomes and lysosomes, thus benefiting viral replication and associated pathogenesis. In this review, I provide an overview of the current understanding of the molecular mechanism by which human viral infections deregulate autophagosome-lysosome fusion and summarize the physiological significance in the virus life cycle and host cell damage.

Molecular Mechanism of Autophagosome-Lysosome Fusion in Mammalian Cells

In eukaryotes, targeting intracellular components for lysosomal degradation by autophagy represents a catabolic process that evolutionarily regulates cellular homeostasis. The successful completion of autophagy initiates the engulfment of cytoplasmic materials within double-membrane autophagosomes and subsequent delivery to autolysosomes for degradation by acidic proteases. The formation of autolysosomes relies on the precise fusion of autophagosomes with lysosomes. In recent decades, numerous studies have provided insights into the molecular regulation of autophagosome-lysosome fusion. In this review, an overview of the molecules that function in the fusion of autophagosomes with lysosomes is provided. Moreover, the molecular mechanism underlying how these functional molecules regulate autophagosome-lysosome fusion is summarized.

Autophagy as a new player in the regulation of clock neurons physiology of Drosophila melanogaster

Axonal terminals of the small ventral lateral neurons (sLNvs), the circadian clock neurons of Drosophila, show daily changes in their arborization complexity, with many branches in the morning and their shrinkage during the night. This complex phenomenon is precisely regulated by several mechanisms. In the present study we describe that one of them is autophagy, a self-degradative process, also involved in changes of cell membrane size and shape. Our results showed that autophagosome formation and processing in PDF-expressing neurons (both sLNv and lLNv) are rhythmic and they have different patterns in the cell bodies and terminals. These rhythmic changes in the autophagy activity seem to be important for neuronal plasticity. We found that autophagosome cargos are different during the day and night, and more proteins involved in membrane remodeling are present in autophagosomes in the morning. In addition, we described for the first time that Atg8-positive vesicles are also present outside the sLNv terminals, which suggests that secretory autophagy might be involved in regulating the clock signaling network. Our data indicate that rhythmic autophagy in clock neurons affect the pacemaker function, through remodeling of terminal membrane and secretion of specific proteins from sLNvs.

The multiple roles of autophagy in uveal melanoma and the microenvironment

PURPOSE

Uveal melanoma (UM) is the most common primary malignant intraocular tumor in adults, and effective clinical treatment strategies are still lacking. Autophagy is a lysosome-dependent degradation system that can encapsulate abnormal proteins, damaged organelles. However, dysfunctional autophagy has multiple types and plays a complex role in tumorigenicity depending on many factors, such as tumor stage, microenvironment, signaling pathway activation, and application of autophagic drugs.

METHODS

A systematic review of the literature was conducted to analyze the role of autophagy in UM, as well as describing the development of autophagic drugs and the link between autophagy and the tumor microenvironment.

RESULTS

In this review, we summarize current research advances regarding the types of autophagy, the mechanisms of autophagy, the application of autophagy inhibitors or agonists, autophagy and the tumor microenvironment. Finally, we also discuss the relationship between autophagy and UM.

CONCLUSION

Understanding the molecular mechanisms of how autophagy differentially affects tumor progression may help to design better therapeutic regimens to prevent and treat UM.

Astrocytes: The Stars in Neurodegeneration?

Today, neurodegenerative disorders like Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) affect millions of people worldwide, and as the average human lifespan increases, similarly grows the number of patients. For many decades, cognitive and motoric decline has been explained by the very apparent deterioration of neurons in various regions of the brain and spinal cord. However, more recent studies show that disease progression is greatly influenced by the vast population of glial cells. Astrocytes are traditionally considered star-shaped cells on which neurons rely heavily for their optimal homeostasis and survival. Increasing amounts of evidence depict how astrocytes lose their supportive functions while simultaneously gaining toxic properties during neurodegeneration. Many of these changes are similar across various neurodegenerative diseases, and in this review, we highlight these commonalities. We discuss how astrocyte dysfunction drives neuronal demise across a wide range of neurodegenerative diseases, but rather than categorizing based on disease, we aim to provide an overview based on currently known mechanisms. As such, this review delivers a different perspective on the disease causes of neurodegeneration in the hope to encourage further cross-disease studies into shared disease mechanisms, which might ultimately disclose potentially common therapeutic entry points across a wide panel of neurodegenerative diseases.

The human OPA1delTTAG mutation induces adult onset and progressive auditory neuropathy in mice

Dominant optic atrophy (DOA) is one of the most prevalent forms of hereditary optic neuropathies and is mainly caused by heterozygous variants in OPA1, encoding a mitochondrial dynamin-related large GTPase. The clinical spectrum of DOA has been extended to a wide variety of syndromic presentations, called DOAplus, including deafness as the main secondary symptom associated to vision impairment. To date, the pathophysiological mechanisms underlying the deafness in DOA remain unknown. To gain insights into the process leading to hearing impairment, we have analyzed the Opa1delTTAG mouse model that recapitulates the DOAplus syndrome through complementary approaches combining morpho-physiology, biochemistry, and cellular and molecular biology. We found that Opa1delTTAG mutation leads an adult-onset progressive auditory neuropathy in mice, as attested by the auditory brainstem response threshold shift over time. However, the mutant mice harbored larger otoacoustic emissions in comparison to wild-type littermates, whereas the endocochlear potential, which is a proxy for the functional state of the stria vascularis, was comparable between both genotypes. Ultrastructural examination of the mutant mice revealed a selective loss of sensory inner hair cells, together with a progressive degeneration of the axons and myelin sheaths of the afferent terminals of the spiral ganglion neurons, supporting an auditory neuropathy spectrum disorder (ANSD). Molecular assessment of cochlea demonstrated a reduction of Opa1 mRNA level by greater than 40%, supporting haploinsufficiency as the disease mechanism. In addition, we evidenced an early increase in Sirtuin 3 level and in Beclin1 activity, and subsequently an age-related mtDNA depletion, increased oxidative stress, mitophagy as well as an impaired autophagic flux. Together, these results support a novel role for OPA1 in the maintenance of inner hair cells and auditory neural structures, addressing new challenges for the exploration and treatment of OPA1-linked ANSD in patients.

ER stress elicits non-canonical CASP8 (caspase 8) activation on autophagosomal membranes to induce apoptosis

The VPS37A gene encodes a subunit of the endosomal sorting complex required for transport (ESCRT)-I complex that is frequently lost in a wide variety of human solid cancers. We have previously demonstrated the role of VPS37A in directing the ESCRT membrane scission machinery to seal the phagophore for autophagosome completion. Here, we report that VPS37A-deficient cells exhibit an accumulation of the apoptotic initiator CASP8 (caspase 8) on the phagophore and are primed to undergo rapid apoptosis through the intracellular death-inducing signaling complex (iDISC)-mediated CASP8 activation upon exposure to endoplasmic reticulum (ER) stress. Using CRISPR-Cas9 gene editing and comparative transcriptome analysis, we identified the ATF4-mediated stress response pathway as a crucial mediator to elicit iDISC-mediated apoptosis following the inhibition of autophagosome closure. Notably, ATF4-mediated iDISC activation occurred independently of the death receptor TNFRSF10B/DR5 upregulation but required the pro-apoptotic transcriptional factor DDIT3/CHOP to enhance the mitochondrial amplification pathway for full-activation of CASP8 in VPS37A-deficient cells stimulated with ER stress inducers. Our analysis also revealed the upregulation of NFKB/NF-kB signaling as a potential mechanism responsible for restraining iDISC activation and promoting cell survival upon VPS37A depletion. These findings have important implications for the future development of new strategies to treat human cancers, especially those with VPS37A loss.Abbreviations: ATG: autophagy related; BMS: BMS-345541; CASP: caspase; CHMP: charged multivesicular body protein; DKO: double knockout; Dox: doxycycline; ER: endoplasmic reticulum; ESCRT: endosomal sorting complex required for transport; gRNA: guide RNA; GSEA: gene set enrichment analysis; GSK157: GSK2656157; iDISC: intracellular death-inducing signaling complex; IKK: inhibitor of NFKB kinase; IPA: ingenuity pathway analysis; KO: knockout; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; NFKB/NF-kB: nuclear factor kappa B; OZ: 5Z-7-oxozeaenol; RNA-seq: RNA sequencing; UPR: unfolded protein response; TFT: transcription factor target; THG: thapsigargin; TUN: tunicamycin; VPS: vacuolar protein sorting.

Recent advances of vacuolar protein-sorting 34 inhibitors targeting autophagy

Autophagy is a ubiquitous pathological/physiological antioxidant cellular reaction in eukaryotic cells. Vacuolar protein sorting 34 (Vps34 or PIK3C3), which plays a crucial role in autophagy, has received much attention. As the only Class III phosphatidylinositol-3 kinase in mammals, Vps34 participates in vesicular transport, nutrient signaling and autophagy. Dysfunctionality of Vps34 induces carcinogenesis, and abnormal autophagy mediated by dysfunction of Vps34 is closely related to the pathological progression of various human diseases, which makes Vps34 a novel target for tumor immunotherapy. In this review, we summarize the molecular mechanisms underlying macroautophagy, and further discuss the structure-activity relationship of Vps34 inhibitors that have been reported in the past decade as well as their potential roles in anticancer immunotherapy to better understand the antitumor mechanism underlying the effects of these inhibitors.

Pathogenesis underlying hexanucleotide repeat expansions in C9orf72 gene in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disorder. Mutations in C9orf72 and the resulting hexanucleotide repeat (GGGGCC) expansion (HRE) has been identified as a major cause of familial ALS, accounting for about 40 % of familial and 6 % of sporadic cases of ALS in Western patients. The pathological outcomes of HRE expansion in ALS have been recognized as the results of two mechanisms that include both the toxic gain-of-function and loss-of-function of C9ORF72. The gain of toxicity results from RNA and dipeptide repeats (DPRs). The HRE can be bidirectionally transcribed into RNA foci, which can bind to and disrupt RNA splicing, transport, and translation. The DPRs that include poly-glycine-alanine, poly-glycine-proline, poly-glycine- arginine, poly-proline-alanine, and poly-proline-arginine can induce toxicity by direct binding and sequestrating other proteins to interfere rRNA synthesis, ribosome biogenesis, translation, and nucleocytoplasmic transport. The C9ORF72 functions through binding to its partners-Smith-Magenis chromosome regions 8 (SMCR8) and WD repeat-containing protein (WDR41). Loss of C9ORF72 function results in impairment of autophagy, deregulation of autoimmunity, increased stress, and disruption of nucleocytoplasmic transport. Further insight into the mechanism in C9ORF72 HRE pathogenesis will facilitate identifying novel and effective therapeutic targets for ALS.

Unexpected inhibition of the lipid kinase PIKfyve reveals an epistatic role for p38 MAPKs in endolysosomal fission and volume control

p38 mitogen-activated protein kinases (MAPKs) participate in autophagic signaling; and previous reports suggest that pyridinyl imidazole p38 MAPK inhibitors, including SB203580 and SB202190, induce cell death in some cancer cell-types through unrestrained autophagy. Subsequent studies, however, have suggested that the associated cytoplasmic vacuolation resulted from off-target inhibition of an unidentified enzyme. Herein, we report that SB203580-induced vacuolation is rapid, reversible, and relies on the class III phosphatidylinositol 3-kinase (PIK3C3) complex and the production of phosphatidylinositol 3-phosphate [PI(3)P] but not on autophagy per se. Rather, vacuolation resulted from the accumulation of Rab7 on late endosome and lysosome (LEL) membranes, combined with an osmotic imbalance that triggered severe swelling in these organelles. Inhibition of PIKfyve, the lipid kinase that converts PI(3)P to PI(3,5)P2 on LEL membranes, produced a similar phenotype in cells; therefore, we performed in vitro kinase assays and discovered that both SB203580 and SB202190 directly inhibited recombinant PIKfyve. Cancer cells treated with either drug likewise displayed significant reductions in the endogenous levels of PI(3,5)P2. Despite these results, SB203580-induced vacuolation was not entirely due to off-target inhibition of PIKfyve, as a drug-resistant p38α mutant suppressed vacuolation; and combined genetic deletion of both p38α and p38β dramatically sensitized cells to established PIKfyve inhibitors, including YM201636 and apilimod. The rate of vacuole dissolution (i.e., LEL fission), following the removal of apilimod, was also significantly reduced in cells treated with BIRB-796, a structurally unrelated p38 MAPK inhibitor. Thus, our studies indicate that pyridinyl imidazole p38 MAPK inhibitors induce cytoplasmic vacuolation through the combined inhibition of both PIKfyve and p38 MAPKs, and more generally, that p38 MAPKs act epistatically to PIKfyve, most likely to promote LEL fission.

Role of autophagy in cancer-associated fibroblast activation, signaling and metabolic reprograming

Tumors not only consist of cancerous cells, but they also harbor several normal-like cell types and non-cellular components. cancer-associated fibroblasts (CAFs) are one of these cellular components that are found predominantly in the tumor stroma. Autophagy is an intracellular degradation and quality control mechanism, and recent studies provided evidence that autophagy played a critical role in CAF formation, metabolic reprograming and tumor-stroma crosstalk. Therefore, shedding light on the autophagy and its role in CAF biology might help us better understand the roles of CAFs and the TME in cancer progression and may facilitate the exploitation of more efficient cancer diagnosis and treatment. Here, we provide an overview about the involvement of autophagy in CAF-related pathways, including transdifferentiation and activation of CAFs, and further discuss the implications of targeting tumor stroma as a treatment option.

The Small GTPase Rab7 Regulates Antigen Processing in B Cells in a Possible Interplay with Autophagy Machinery

In B cells, antigen processing and peptide-antigen (pAg) presentation is essential to ignite high-affinity antibody responses with the help of cognate T cells. B cells efficiently internalize and direct specific antigens for processing and loading onto MHCII. This critical step, which enables pAg presentation, occurs in MHCII compartments (MIICs) which possess the enzymatic machinery for pAg loading on MHCII. The intracellular transport systems that guide antigen and maintain this unique compartment remain enigmatic. Here, we probed the possible functional role of two known endosomal proteins, the Rab family small GTPases Rab7 and Rab9, that are both reported to colocalize with internalized antigen. As compared to Rab9, we found Rab7 to exhibit a higher overlap with antigen and MIIC components. Rab7 also showed a higher association with antigen degradation. The inhibition of Rab7 drastically decreased pAg presentation. Additionally, we detected the strong colocalization of perinuclearly clustered and presumably MIIC-associated antigen with autophagy protein LC3. When we pharmacologically inhibited autophagy, pAg presentation was inhibited. Together, our data promote Rab7 as an important regulator of antigen processing and, considering the previously reported functions of Rab7 in autophagy, this also raises the possibility of the involvement of autophagy-related machinery in this process.

Identification of secretory autophagy as a novel mechanism modulating activity-induced synaptic remodeling

The ability of neurons to rapidly remodel their synaptic structure and strength in response to neuronal activity is highly conserved across species and crucial for complex brain functions. However, mechanisms required to elicit and coordinate the acute, activity-dependent structural changes across synapses are not well understood. Here, using an RNAi screen in Drosophila against genes affecting nervous system functions in humans, we uncouple cellular processes important for synaptic plasticity from synapse development. We find mutations associated with neurodegenerative and mental health disorders are 2-times more likely to affect activity-induced synaptic remodeling than synapse development. We further demonstrate that neuronal activity stimulates autophagy activation but diminishes degradative autophagy, thereby driving the pathway towards autophagy-based secretion. Presynaptic knockdown of Snap29, Sec22, or Rab8, proteins implicated in the secretory autophagy pathway, is sufficient to abolish activity-induced synaptic remodeling. This study uncovers secretory autophagy as a novel trans-synaptic signaling mechanism modulating structural plasticity.

Encapsulation of Nano-Bortezomib in Apoptotic Stem Cell-Derived Vesicles for the Treatment of Multiple Myeloma

Extracellular vesicles (EVs) are lipid bilayer nanovesicles released from living or apoptotic cells that can transport DNA, RNA, protein, and lipid cargo. EVs play critical roles in cell-cell communication and tissue homeostasis, and have numerous therapeutic uses including serving as carriers for nanodrug delivery. There are multiple ways to load EVs with nanodrugs, such as electroporation, extrusion, and ultrasound. However, these approaches may have limited drug-loading rates, poor EV membrane stability, and high cost for large-scale production. Here, it is shown that apoptotic mesenchymal stem cells (MSCs) can encapsulate exogenously added nanoparticles into apoptotic vesicles (apoVs) with a high loading efficiency. When nano-bortezomib is incorporated into apoVs in culture-expanded apoptotic MSCs, nano-bortezomib-apoVs show a synergistic combination effect of bortezomib and apoVs to ameliorate multiple myeloma (MM) in a mouse model, along with significantly reduced side effects of nano-bortezomib. Moreover, it is shown that Rab7 regulates the nanoparticle encapsulation efficiency in apoptotic MSCs and that activation of Rab7 can increase nanoparticle-apoV production. In this study, a previously unknown mechanism to naturally synthesize nano-bortezomib-apoVs to improve MM therapy is revealed.

Bidirectional interplay between SARS-CoV-2 and autophagy

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as the causative agent of the recent COVID-19 pandemic, continues representing one of the main health concerns worldwide. Autophagy, in addition to its role in cellular homeostasis and metabolism, plays an important part for the host antiviral immunity. However, viruses including SARS-CoV-2 have evolved diverse mechanisms to not only overcome autophagy's antiviral pressure but also manipulate its machinery in order to enhance viral replication and propagation. Here, we discuss our current knowledge on the impact that autophagy exerts on SARS-CoV-2 replication, as well as the different counteracting measures that this virus has developed to manipulate autophagy's complex machinery. Some of the elements regarding this interplay may become future therapeutic targets in the fight against SARS-CoV-2.

Lysosomes, curcumin, and anti-tumor effects: how are they linked?

Curcumin is a natural active ingredient from traditional Chinese medicine (TCM) that has multi-target characteristics to exert extensive pharmacological activities and thus has been applied in the treatment of various diseases such as cancer, cardiovascular diseases, nervous system, and autoimmune disorders. As an important class of membranous organelles in the intracellular membrane system, lysosomes are involved in biological processes such as programmed cell death, cell metabolism, and immune regulation, thus affecting tumor initiation and progression. It has been shown that curcumin can modulate lysosomal function through the aforementioned pathways, thereby affecting tumor proliferation, invasion, metastasis, drug resistance, and immune function. This review briefly elaborated the regulatory mechanisms of lysosome biogenesis and summarized curcumin-related studies with its anti-tumor effect, providing a reference for the clinical application of curcumin and anti-tumor research targeting lysosomes.

Potent New Targets for Autophagy Enhancement to Delay Neuronal Ageing

Autophagy is a lysosomal-dependent degradation process of eukaryotic cells responsible for breaking down unnecessary and damaged intracellular components. Autophagic activity gradually declines with age due to genetic control, and this change contributes to the accumulation of cellular damage at advanced ages, thereby causing cells to lose their functionality and viability. This could be particularly problematic in post-mitotic cells including neurons, the mass destruction of which leads to various neurodegenerative diseases. Here, we aim to uncover new regulatory points where autophagy could be specifically activated and test these potential drug targets in neurodegenerative disease models of Drosophila melanogaster. One possible way to activate autophagy is by enhancing autophagosome-lysosome fusion that creates the autolysosome in which the enzymatic degradation happens. The HOPS (homotypic fusion and protein sorting) and SNARE (Snap receptor) protein complexes regulate the fusion process. The HOPS complex forms a bridge between the lysosome and autophagosome with the assistance of small GTPase proteins. Thus, small GTPases are essential for autolysosome maturation, and among these proteins, Rab2 (Ras-associated binding 2), Rab7, and Arl8 (Arf-like 8) are required to degrade the autophagic cargo. For our experiments, we used Drosophila melanogaster as a model organism. Nerve-specific small GTPases were silenced and overexpressed. We examined the effects of these genetic interventions on lifespan, climbing ability, and autophagy. Finally, we also studied the activation of small GTPases in a Parkinson's disease model. Our results revealed that GTP-locked, constitutively active Rab2 (Rab2-CA) and Arl8 (Arl8-CA) expression reduces the levels of the autophagic substrate p62/Ref(2)P in neurons, extends lifespan, and improves the climbing ability of animals during ageing. However, Rab7-CA expression dramatically shortens lifespan and inhibits autophagy. Rab2-CA expression also increases lifespan in a Parkinson's disease model fly strain overexpressing human mutant (A53T) α-synuclein protein. Data provided by this study suggests that Rab2 and Arl8 serve as potential targets for autophagy enhancement in the Drosophila nervous system. In the future, it might be interesting to assess the effect of Rab2 and Arl8 coactivation on autophagy, and it would also be worthwhile to validate these findings in a mammalian model and human cell lines. Molecules that specifically inhibit Rab2 or Arl8 serve as potent drug candidates to modulate the activity of the autophagic process in treating neurodegenerative pathologies. In the future, it would be reasonable to investigate which GAP enzyme can inhibit Rab2 or Arl8 specifically, but not affect Rab7, with similar medical purposes.

Autophagy Regulators in Cancer

Autophagy plays a complex impact role in tumor initiation and development. It serves as a double-edged sword by supporting cell survival in certain situations while also triggering autophagic cell death in specific cellular contexts. Understanding the intricate functions and mechanisms of autophagy in tumors is crucial for guiding clinical approaches to cancer treatment. Recent studies highlight its significance in various aspects of cancer biology. Autophagy enables cancer cells to adapt to and survive unfavorable conditions by recycling cellular components. However, excessive or prolonged autophagy can lead to the self-destruction of cancer cells via a process known as autophagic cell death. Unraveling the molecular mechanisms underlying autophagy regulation in cancer is crucial for the development of targeted therapeutic interventions. In this review, we seek to present a comprehensive summary of current knowledge regarding autophagy, its impact on cancer cell survival and death, and the molecular mechanisms involved in the modulation of autophagy for cancer therapy.

Exercise against nonalcoholic fatty liver disease: Possible role and mechanism of lipophagy

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease worldwide. NAFLD is prevalent in about 30% of people worldwide. The lack of physical activity is considered as one of the risks for NAFLD, and approximately one-third of NAFLD patients hardly engage in physical activity. It is acknowledged that exercise is one of the optimal non-pharmacological methods for preventing and treating NAFLD. Different forms of exercise such as aerobic exercise, resistance exercise and even simply physical activity in a higher level can be beneficial in reducing liver lipid accumulation and disease progression for NAFLD patients. In NAFLD patients, exercise is helpful in lowering steatosis and enhancing liver function. The mechanisms underlying the prevention and treatment of NAFLD by exercise are various and complex. Current studies on the mechanisms have focused on the pro-lipolytic, anti-inflammatory, and antioxidant and lipophagy. Promotion of lipophagy is regarded as an important mechanism for prevention and improvement of NAFLD by exercise. Recent studies have investigated the above mechanism, yet the potential mechanism has not been completely elucidated. Thus, in this review, we cover the recent advances of exercise-promoted lipophagy in NAFLD treatment and prevention. Furthermore, given the fact that exercise activates SIRT1, we discuss the possible regulatory mechanisms of lipophagy by SIRT1 during exercise. These mechanisms need to be verified by further experimental studies.

Systematic Transmission Electron Microscopy-Based Identification and 3D Reconstruction of Cellular Degradation Machinery

Various intracellular degradation organelles, including autophagosomes, lysosomes, and endosomes, work in tandem to perform autophagy, which is crucial for cellular homeostasis. Altered autophagy contributes to the pathophysiology of various diseases, including cancers and metabolic diseases. This paper aims to describe an approach to reproducibly identify and distinguish subcellular structures involved in macroautophagy. Methods are provided that help avoid common pitfalls. How to distinguish between lysosomes, lipid droplets, autolysosomes, autophagosomes, and inclusion bodies are also discussed. These methods use transmission electron microscopy (TEM), which is able to generate nanometer-scale micrographs of cellular degradation components in a fixed sample. Serial block face-scanning electron microscopy is also used to visualize the 3D morphology of degradation machinery using the Amira software. In addition to TEM and 3D reconstruction, other imaging techniques are discussed, such as immunofluorescence and immunogold labeling, which can be used to classify cellular organelles, reliably and accurately. Results show how these methods may be used to accurately quantify cellular degradation machinery under various conditions, such as treatment with the endoplasmic reticulum stressor thapsigargin or ablation of the dynamin-related protein 1.

Puerarin Prevents Cadmium-Induced Neuronal Injury by Alleviating Autophagic Dysfunction in Rat Cerebral Cortical Neurons

Autophagic dysfunction is one of the main mechanisms of cadmium (Cd)-induced neurotoxicity. Puerarin (Pue) is a natural antioxidant extracted from the medicinal and edible homologous plant Pueraria lobata. Studies have shown that Pue has neuroprotective effects in a variety of brain injuries, including Cd-induced neuronal injury. However, the role of Pue in the regulation of autophagy to alleviate Cd-induced injury in rat cerebral cortical neurons remains unclear. This study aimed to elucidate the protective mechanism of Pue in alleviating Cd-induced injury in rat cerebral cortical neurons by targeting autophagy. Our results showed that Pue alleviated Cd-induced injury in rat cerebral cortical neurons in vitro and in vivo. Pue activates autophagy and alleviates Cd-induced autophagic blockade in rat cerebral cortical neurons. Further studies have shown that Pue alleviates the Cd-induced inhibition of autophagosome-lysosome fusion, as well as the inhibition of lysosomal degradation. The specific mechanism is related to Pue alleviating the inhibition of Cd on the expression levels of the key proteins Rab7, VPS41, and SNAP29, which regulate autophagosome-lysosome fusion, as well as the lysosome-related proteins LAMP2, CTSB, and CTSD. In summary, these results indicate that Pue alleviates Cd-induced autophagic dysfunction in rat cerebral cortical neurons by alleviating autophagosome-lysosome fusion dysfunction and lysosomal degradation dysfunction, thereby alleviating Cd-induced neuronal injury.

Role of Microbiota-Modified Bile Acids in the Regulation of Intracellular Organelles and Neurodegenerative Diseases

Bile acids (BAs) are amphiphilic steroidal molecules generated from cholesterol in the liver and facilitate the digestion and absorption of fat-soluble substances in the gut. Some BAs in the intestine are modified by the gut microbiota. Because BAs are modified in a variety of ways by different types of bacteria present in the gut microbiota, changes in the gut microbiota can affect the metabolism of BAs in the host. Although most BAs absorbed from the gut are transferred to the liver, some are transferred to the systemic circulation. Furthermore, BAs have also been detected in the brain and are thought to migrate into the brain through the systemic circulation. Although BAs are known to affect a variety of physiological functions by acting as ligands for various nuclear and cell-surface receptors, BAs have also been found to act on mitochondria and autophagy in the cell. This review focuses on the BAs modified by the gut microbiota and their roles in intracellular organelles and neurodegenerative diseases.

Diabetes influences the fusion of autophagosomes with lysosomes in SH-SY5Y cells and induces Aβ deposition and cognitive dysfunction in STZ-induced diabetic rats

Diabetes has been regarded as an independent risk factor for Alzheimer's disease (AD). Our previous study found that diabetes activated autophagy, but lysosome function was impaired. Autophagy-lysosome dysfunction may be involved in Aβ deposition in diabetic cognitive impairment. In the present study, we used STZ-induced diabetic rats and SH-SY5Y cells to investigate whether diabetes inhibits autophagosome fusion with lysosomes. We found that in the in vivo study, STZ-induced diabetic rats exhibited cognitive dysfunction, and the lysosome function-related factors CTSL, CTSD, and Rab7 were decreased (P < 0.05). In an in vitro study, the mRFP-GFP-LC3 assay showed that the fusion of autophagosomes with lysosomes was partly blocked in SH-SY5Y cells. High glucose treatment downregulated the number of autophagolysosomes, downregulated CTSD, CTSL, and Rab7 expression (P < 0.05), and then influenced the function of ACP2 to partly block the fusion of autophagosomes and lysosomes to inhibit Aβ clearance. These findings indicate that high glucose treatment affected lysosome function, interfered with the fusion of autophagosomes with lysosomes, and partly blocked autophagic flux to influence Aβ clearance.

Crosstalk between Autophagy and RLR Signaling

Autophagy plays a homeostatic role in regulating cellular metabolism by degrading unwanted intracellular materials and acts as a host defense mechanism by eliminating infecting pathogens, such as viruses. Upon viral infection, host cells often activate retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling to induce the transcription of type I interferons, thus establishing the first line of the innate antiviral response. In recent years, numerous studies have shown that virus-mediated autophagy activation may benefit viral replication through different actions on host cellular processes, including the modulation of RLR-mediated innate immunity. Here, an overview of the functional molecules and regulatory mechanism of the RLR antiviral immune response as well as autophagy is presented. Moreover, a summary of the current knowledge on the biological role of autophagy in regulating RLR antiviral signaling is provided. The molecular mechanisms underlying the crosstalk between autophagy and RLR innate immunity are also discussed.