ATG14 promotes membrane tethering and fusion of autophagosomes to endolysosomes

Spautin-1 promotes PINK1-PRKN-dependent mitophagy and improves associative learning capability in an alzheimer disease animal model

Spautin-1 is a well-known macroautophagy/autophagy inhibitor via suppressing the deubiquitinases USP10 and USP13 and promoting the degradation of the PIK3C3/VPS34-BECN1 complex, while its effect on selective autophagy remains poorly understood. Mitophagy is a selective form of autophagy for removal of damaged and superfluous mitochondria via the autophagy-lysosome pathway. Here, we report a surprising discovery that, while spautin-1 remains as an effective autophagy inhibitor, it promotes PINK1-PRKN-dependent mitophagy induced by mitochondrial damage agents. Mechanistically, spautin-1 facilitates the stabilization and activation of the full-length PINK1 at the outer mitochondrial membrane (OMM) via binding to components of the TOMM complex (TOMM70 and TOMM20), leading to the disruption of the mitochondrial import of PINK1 and prevention of PARL-mediated PINK1 cleavage. Moreover, spautin-1 induces neuronal mitophagy in Caenorhabditis elegans (C. elegans) in a PINK-1-PDR-1-dependent manner. Functionally, spautin-1 is capable of improving associative learning capability in an Alzheimer disease (AD) C. elegans model. In summary, we report a novel function of spautin-1 in promoting mitophagy via the PINK1-PRKN pathway. As deficiency of mitophagy is closely implicated in the pathogenesis of neurodegenerative disorders, the pro-mitophagy function of spautin-1 might suggest its therapeutic potential in neurodegenerative disorders such as AD.Abbreviations: AD, Alzheimer disease; ATG, autophagy related; BafA1, bafilomycin A1; CALCOCO2/NDP52, calcium binding and coiled-coil domain 2; CCCP, carbonyl cyanide m-chlorophenyl hydrazone; COX4/COX IV, cytochrome c oxidase subunit 4; EBSS, Earle's balanced salt; ECAR, extracellular acidification rate; GFP, green fluorescent protein; IA, isoamyl alcohol; IMM, inner mitochondrial membrane; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; MMP, mitochondrial membrane potential; mtDNA, mitochondrial DNA; nDNA, nuclear DNA; O/A, oligomycin-antimycin; OCR, oxygen consumption rate; OMM, outer mitochondrial membrane; OPTN, optineurin; PARL, presenilin associated rhomboid like; PINK1, PTEN induced kinase 1; PRKN, parkin RBR E3 ubiquitin protein ligase; p-Ser65-Ub, phosphorylation of Ub at Ser65; TIMM23, translocase of inner mitochondrial membrane 23; TOMM, translocase of outer mitochondrial membrane; USP10, ubiquitin specific peptidase 10; USP13, ubiquitin specific peptidase 13; VAL, valinomycin; YFP, yellow fluorescent protein.

The matrix protein of lyssavirus hijacks autophagosome for efficient egress by recruiting NEDD4 through its PPxY motif

Lyssaviruses are well-known worldwide and often cause fatal encephalitis. Previous studies have shown that autophagy is beneficial for the replication of rabies virus (RABV), the representative lyssavirus, but the detailed mechanism remains obscure. In this study, we showed that the rabies virus matrix protein (RABV-M) used its PPxY motif to interact with the E3 ubiquitin-protein ligase NEDD4. NEDD4 then recruited MAP1LC3/LC3 via its LC3-interacting region (LIR). Interestingly, after binding to the ubiquitinated RABV-M, NEDD4 could bind more LC3 and enhance autophagosome accumulation, while NEDD4 knockdown significantly reduced M-induced autophagosome accumulation. Further study revealed that RABV-M prevented autophagosome-lysosome fusion and facilitated viral budding. Inhibition of RABV-M-induced autophagosome accumulation reduced the production of extracellular virus-like particles. We also found that M proteins of most lyssaviruses share the same mechanism to accumulate autophagosome by hijacking NEDD4. Collectively, this study revealed a novel strategy for lyssaviruses to achieve efficient viral replication by exploiting the host autophagy system.Abbreviations: ABLV: Australian bat lyssavirus; ATG5: autophagy related 5; Baf A1:bafilomycin A1;co-IP: co-immunoprecipitation; CQ: chloroquine; DAPI:4',6-diamidino-2'-phenylindole; DMSO: dimethyl sulfoxide; EBLV:European bat lyssavirus; GFP: green fluorescent protein; GST:glutathione S-transferase; hpi: hours post-infection; hpt: hourspost-transfection; LIR: LC3-interactingregion;MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; mCherry:red fluorescent protein; MOI: multiplicity of infection; NC: negativecontrol; MVB: multivesicular body; NEDD4: neural precursorcell-expressed developmentally down-regulated 4; RABV: rabies virus;SQSTM1/p62: sequestosome 1; VLP: virus-like particle; VPS4B: vacuolarprotein sorting 4B; TEM: transmission electron microscopy; WB:western blotting; WT: wild-type; μm: micrometer; μM: micromole.

Lassa virus Z protein hijacks the autophagy machinery for efficient transportation by interrupting CCT2-mediated cytoskeleton network formation

The Lassa virus (LASV) is a widely recognized virulent pathogen that frequently results in lethal viral hemorrhagic fever (VHF). Earlier research has indicated that macroautophagy/autophagy plays a role in LASV replication, but, the precise mechanism is unknown. In this present study, we show that LASV matrix protein (LASV-Z) is essential for blocking intracellular autophagic flux. LASV-Z hinders actin and tubulin folding by interacting with CCT2, a component of the chaperonin-containing T-complexes (TRiC). When the cytoskeleton is disrupted, lysosomal enzyme transit is hampered. In addition, cytoskeleton disruption inhibits the merge of autophagosomes with lysosomes, resulting in autophagosome accumulation that promotes the budding of LASV virus-like particles (VLPs). Inhibition of LASV-Z-induced autophagosome accumulation blocks the LASV VLP budding process. Furthermore, it is found that glutamine at position 29 and tyrosine at position 48 on LASV-Z are important in interacting with CCT2. When these two sites are mutated, LASV-mut interacts with CCT2 less efficiently and can no longer inhibit the autophagic flux. These findings demonstrate a novel strategy for LASV-Z to hijack the host autophagy machinery to accomplish effective transportation.Abbreviation: 3-MA: 3-methyladenine; ATG5: autophagy related 5; ATG7: autophagy related 7; Baf-A1: bafilomycin A1; CCT2: chaperonin containing TCP1 subunit 2; co-IP: co-immunoprecipitation; CTSD: cathepsin D; DAPI: 4',6-diamidino-2'-phenylindole; DMSO: dimethyl sulfoxide; EGFR: epidermal growth factor receptor; GFP: green fluorescent protein; hpi: hours post-infection; hpt: hours post-transfection; LAMP1: lysosomal-associated membrane protein 1; LASV: lassa virus; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; mCherry: red fluorescent protein; PM: plasma membrane; SQSTM1/p62: sequestosome 1; STX6: syntaxin 6; VLP: virus-like particle; TEM: transmission electron microscopy; TRiC: chaperonin-containing T-complex; WB: western blotting; μm: micrometer; μM: micromole.

MAMs and Mitochondrial Quality Control: Overview and Their Role in Alzheimer's Disease

Alzheimer's disease (AD) represents the most widespread neurodegenerative disorder, distinguished by a gradual onset and slow progression, presenting a substantial challenge to global public health. The mitochondrial-associated membrane (MAMs) functions as a crucial center for signal transduction and material transport between mitochondria and the endoplasmic reticulum, playing a pivotal role in various pathological mechanisms of AD. The dysregulation of mitochondrial quality control systems is considered a fundamental factor in the development of AD, leading to mitochondrial dysfunction and subsequent neurodegenerative events. Recent studies have emphasized the role of MAMs in regulating mitochondrial quality control. This review will delve into the molecular mechanisms underlying the imbalance in mitochondrial quality control in AD and provide a comprehensive overview of the role of MAMs in regulating mitochondrial quality control.

Role of O-linked N-acetylglucosamine protein modification in oxidative stress-induced autophagy: a novel target for bone remodeling

O-linked N-acetylglucosamine protein modification (O-GlcNAcylation) is a dynamic post-translational modification (PTM) involving the covalent binding of serine and/or threonine residues, which regulates bone cell homeostasis. Reactive oxygen species (ROS) are increased due to oxidative stress in various pathological contexts related to bone remodeling, such as osteoporosis, arthritis, and bone fracture. Autophagy serves as a scavenger for ROS within bone marrow-derived mesenchymal stem cells, osteoclasts, and osteoblasts. However, oxidative stress-induced autophagy is affected by the metabolic status, leading to unfavorable clinical outcomes. O-GlcNAcylation can regulate the autophagy process both directly and indirectly through oxidative stress-related signaling pathways, ultimately improving bone remodeling. The present interventions for the bone remodeling process often focus on promoting osteogenesis or inhibiting osteoclast absorption, ignoring the effect of PTM on the overall process of bone remodeling. This review explores how O-GlcNAcylation synergizes with autophagy to exert multiple regulatory effects on bone remodeling under oxidative stress stimulation, indicating the application of O-GlcNAcylation as a new molecular target in the field of bone remodeling.

Interactions Between Extracellular Vesicles and Autophagy in Neuroimmune Disorders

Neuroimmune disorders, such as multiple sclerosis, neuromyelitis optica spectrum disorder, myasthenia gravis, and Guillain-Barré syndrome, are characterized by the dysfunction of both the immune system and the nervous system. Increasing evidence suggests that extracellular vesicles and autophagy are closely associated with the pathogenesis of these disorders. In this review, we summarize the current understanding of the interactions between extracellular vesicles and autophagy in neuroimmune disorders and discuss their potential diagnostic and therapeutic applications. Here we highlight the need for further research to fully understand the mechanisms underlying these disorders, and to develop new diagnostic and therapeutic strategies.

PtdIns4P is required for the autophagosomal recruitment of STX17 (syntaxin 17) to promote lysosomal fusion

The autophagosomal SNARE STX17 (syntaxin 17) promotes lysosomal fusion and degradation, but its autophagosomal recruitment is incompletely understood. Notably, PtdIns4P is generated on autophagosomes and promotes fusion through an unknown mechanism. Here we show that soluble recombinant STX17 is spontaneously recruited to negatively charged liposomes and adding PtdIns4P to liposomes containing neutral lipids is sufficient for its recruitment. Consistently, STX17 colocalizes with PtdIns4P-positive autophagosomes in cells, and specific inhibition of PtdIns4P synthesis on autophagosomes prevents its loading. Molecular dynamics simulations indicate that C-terminal positively charged amino acids establish contact with membrane bilayers containing negatively charged PtdIns4P. Accordingly, Ala substitution of Lys and Arg residues in the C terminus of STX17 abolishes membrane binding and impairs its autophagosomal recruitment. Finally, only wild type but not Ala substituted STX17 expression rescues the autophagosome-lysosome fusion defect of STX17 loss-of-function cells. We thus identify a key step of autophagosome maturation that promotes lysosomal fusion.Abbreviations: Cardiolipin: 1',3'-bis[1-palmitoyl-2-oleoyl-sn-glycero-3-phospho]-glycerol; DMSO: dimethyl sulfoxide; GST: glutathione S-transferase; GUV: giant unilamellar vesicles; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PA: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate; PC/POPC: 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine; PG: 1-palmitoyl-2-linoleoyl-sn-glycero-3-phospho-(1'-rac-glycerol); PI: L-α-phosphatidylinositol; PI4K2A: phosphatidylinositol 4-kinase type 2 alpha; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; POPE/PE: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine; PS: 1-stearoyl-2-linoleoyl-sn-glycero-3-phospho-L-serine; PtdIns(3,5)P2: 1,2-dioleoyl-sn-glycero-3-phospho-(1"-myo-inositol-3',5'-bisphosphate); PtdIns3P: 1,2- dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol-3'-phosphate); PtdIns4P: 1,2-dioleoyl-sn-glycero-3-phospho-(1"-myo-inositol-4'-phosphate); SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; STX17: syntaxin 17.

Dialogue between mitochondria and endoplasmic reticulum-potential therapeutic targets for age-related cardiovascular diseases

Mitochondria-associated endoplasmic reticulum membranes (MAMs) act as physical membrane contact sites facilitating material exchange and signal transmission between mitochondria and endoplasmic reticulum (ER), thereby regulating processes such as Ca2+/lipid transport, mitochondrial dynamics, autophagy, ER stress, inflammation, and apoptosis, among other pathological mechanisms. Emerging evidence underscores the pivotal role of MAMs in cardiovascular diseases (CVDs), particularly in aging-related pathologies. Aging significantly influences the structure and function of the heart and the arterial system, possibly due to the accumulation of reactive oxygen species (ROS) resulting from reduced antioxidant capacity and the age-related decline in organelle function, including mitochondria. Therefore, this paper begins by describing the composition, structure, and function of MAMs, followed by an exploration of the degenerative changes in MAMs and the cardiovascular system during aging. Subsequently, it discusses the regulatory pathways and approaches targeting MAMs in aging-related CVDs, to provide novel treatment strategies for managing CVDs in aging populations.

Regulated cell death in hypoxic-ischaemic encephalopathy: recent development and mechanistic overview

Hypoxic-ischaemic encephalopathy (HIE) in termed infants remains a significant cause of morbidity and mortality worldwide despite the introduction of therapeutic hypothermia. Depending on the cell type, cellular context, metabolic predisposition and insult severity, cell death in the injured immature brain can be highly heterogenous. A continuum of cell death exists in the H/I-injured immature brain. Aside from apoptosis, emerging evidence supports the pathological activation of necroptosis, pyroptosis and ferroptosis as alternative regulated cell death (RCD) in HIE to trigger neuroinflammation and metabolic disturbances in addition to cell loss. Upregulation of autophagy and mitophagy in HIE represents an intrinsic neuroprotective strategy. Molecular crosstalk between RCD pathways implies one RCD mechanism may compensate for the loss of function of another. Moreover, mitochondrion was identified as the signalling "hub" where different RCD pathways converge. The highly-orchestrated nature of RCD makes them promising therapeutic targets. Better understanding of RCD mechanisms and crosstalk between RCD subtypes likely shed light on novel therapy development for HIE. The identification of a potential RCD converging node may open up the opportunity for simultaneous and synergistic inhibition of cell death in the immature brain.

SLC34A2 promotes cell proliferation by activating STX17-mediated autophagy in esophageal squamous cell carcinoma

BACKGROUND

Solute carrier family 34 member 2 (SLC34A2) has been implicated in the development of various malignancies. However, the clinical significance and underlying molecular mechanisms of SLC34A2 in esophageal squamous cell carcinoma (ESCC) remain elusive.

METHODS

Western blotting, quantitative real-time PCR and immunohistochemistry were utilized to evaluate the expression levels of SLC34A2 mRNA/protein in ESCC cell lines or tissues. Kaplan-Meier curves were employed for survival analysis. CCK-8, colony formation, EdU and xenograft tumor model assays were conducted to determine the impact of SLC34A2 on ESCC cell proliferation. Cell cycle was examined using flow cytometry. RNA-sequencing and enrichment analysis were carried out to explore the potential signaling pathways. The autophagic flux was evaluated by western blotting, mRFP-GFP-LC3 reporter system and transmission electron microscopy. Immunoprecipitation and mass spectrometry were utilized for identification of potential SLC34A2-interacting proteins. Cycloheximide (CHX) chase and ubiquitination assays were conducted to test the protein stability.

RESULTS

The expression of SLC34A2 was significantly upregulated in ESCC and correlated with unfavorable clinicopathologic characteristics particularly the Ki-67 labeling index and poor prognosis of ESCC patients. Overexpression of SLC34A2 promoted ESCC cell proliferation, while silencing SLC34A2 had the opposite effect. Moreover, SLC34A2 induced autophagy to promote ESCC cell proliferation, whereas inhibition of autophagy suppressed the proliferation of ESCC cells. Further studies showed that SLC34A2 interacted with an autophagy-related protein STX17 to promote autophagy and proliferation of ESCC cells by inhibiting the ubiquitination and degradation of STX17.

CONCLUSIONS

These findings indicate that SLC34A2 may serve as a prognostic biomarker for ESCC.

Pparα activation stimulates autophagic flux through lipid catabolism-independent route

Autophagy is a cellular process that involves the fusion of autophagosomes and lysosomes to degrade damaged proteins or organelles. Triglycerides are hydrolyzed by autophagy, releasing fatty acids for energy through mitochondrial fatty acid oxidation (FAO). Inhibited mitochondrial FAO induces autophagy, establishing a crosstalk between lipid catabolism and autophagy. Peroxisome proliferator-activated receptor α (PPARα), a transcription factor, stimulates lipid catabolism genes, including fatty acid transport and mitochondrial FAO, while also inducing autophagy through transcriptional regulation of transcription factor EB (TFEB). Therefore, the study explores whether PPARα regulates autophagy through TFEB transcriptional control or mitochondrial FAO. In aquaculture, addressing liver lipid accumulation in fish is crucial. Investigating the link between lipid catabolism and autophagy is significant for devising lipid-lowering strategies and maintaining fish health. The present study investigated the impact of dietary fenofibrate and L-carnitine on autophagy by activating Pparα and enhancing FAO in Nile tilapia (Oreochromis niloticus), respectively. The dietary fenofibrate and L-carnitine reduced liver lipid content and enhanced ATP production, particularly fenofibrate. FAO enhancement by L-carnitine showed no changes in autophagic protein levels and autophagic flux. Moreover, fenofibrate-activated Pparα promoted the expression and nuclear translocation of Tfeb, upregulating autophagic initiation and lysosomal biogenesis genes. Pparα activation exhibited an increasing trend of LC3II protein at the basal autophagy and cumulative p62 protein trends after autophagy inhibition in zebrafish liver cells. These data show that Pparα activation-induced autophagic flux should be independent of lipid catabolism.

Function of autophagy genes in innate immune defense against mucosal pathogens

Mucosal immunity is posed to constantly interact with commensal microbes and invading pathogens. As a fundamental cell biological pathway affecting immune response, autophagy regulates the interaction between mucosal immunity and microbes through multiple mechanisms, including direct elimination of microbes, control of inflammation, antigen presentation and lymphocyte homeostasis, and secretion of immune mediators. Some of these physiologically important functions do not involve canonical degradative autophagy but rely on certain autophagy genes and their 'autophagy gene-specific functions.' Here, we review the relationship between autophagy and important mucosal pathogens, including influenza virus, Mycobacterium tuberculosis, Salmonella enterica, Citrobacter rodentium, norovirus, and herpes simplex virus, with a particular focus on distinguishing the canonical versus gene-specific mechanisms of autophagy genes.

AMPK-mediated autophagy pathway activation promotes ΔFosB degradation to improve levodopa-induced dyskinesia

BACKGROUND

Parkinson's disease patients on chronic levodopa often suffer from motor complications, which tend to reduce their quality of life. Levodopa-induced dyskinesia (LID) is one of the most prevalent motor complications, often characterized by abnormal involuntary movements, and the pathogenesis of LID is still unclear but recent studies have suggested the involvement of autophagy.

METHODS

The onset of LID was mimicked by chronic levodopa treatment in a unilateral 6-hydroxydopamine (6-OHDA) -lesion rat model. Overexpression of ΔFosB in HEK293 cells to mimic the state of ΔFosB accumulation. The modulation of the AMP-activated protein kinase (AMPK)-mediated autophagy pathway using by metformin, AICAR (an AMPK activator), Compound C (an AMPK inhibitor) and chloroquine (an autophagy pathway inhibitor). The severity of LID was assessed by axial, limb, and orofacial (ALO) abnormal involuntary movements (AIMs) score and in vivo electrophysiology. The activity of AMPK pathway as well as autophagy markers and FosB-ΔFosB levels were detected by western blotting. RT-qPCR was performed to detect the transcription level of FosB-ΔFosB. The mechanism of autophagy dysfunction was further explored by immunofluorescence and transmission electron microscopy.

RESULTS

In vivo experiments demonstrated that chronic levodopa treatment reduced AMPK phosphorylation, impaired autophagosome-lysosomal fusion and caused FosB-ΔFosB accumulation in the striatum of PD rats. Long-term metformin intervention improved ALO AIMs scores as well as reduced the mean power of high gamma (hγ) oscillations and the proportion of striatal projection neurons unstable in response to dopamine for LID rats. Moreover, the intervention of metformin promoted AMPK phosphorylation, ameliorated the impairment of autophagosome-lysosomal fusion, thus, promoting FosB-ΔFosB degradation to attenuate its accumulation in the striatum of LID rats. However, the aforementioned roles of metformin were reversed by Compound C and chloroquine. The results of in vitro studies demonstrated the ability of metformin and AICAR to attenuate ΔFosB levels by promoting its degradation, while Compound C and chloroquine could block this effect.

CONCLUSIONS

In conclusion, our results suggest that long-term metformin treatment could promote ΔFosB degradation and thus attenuate the development of LID through activating the AMPK-mediated autophagy pathway. Overall, our results support the AMPK-mediated autophagy pathway as a novel therapeutic target for LID and also indicate that metformin is a promising therapeutic candidate for LID.

Hypoxia-associated autophagy flux dysregulation in human cancers

A general feature of cancer is hypoxia, determined as low oxygen levels. Low oxygen levels may cause cells to alter in ways that contribute to tumor growth and resistance to treatment. Hypoxia leads to variations in cancer cell metabolism, angiogenesis and metastasis. Furthermore, a hypoxic tumor microenvironment might induce immunosuppression. Moreover, hypoxia has the potential to impact cellular processes, such as autophagy. Autophagy refers to the catabolic process by which damaged organelles and toxic macromolecules are broken down. The abnormal activation of autophagy has been extensively recorded in human tumors and it serves as a regulator of cell growth, spread to other parts of the body, and resistance to treatment. There is a correlation between hypoxia and autophagy in human malignancies. Hypoxia can regulate the activity of AMPK, mTOR, Beclin-1, and ATGs to govern autophagy in human malignancies. Furthermore, HIF-1α, serving as an indicator of low oxygen levels, controls the process of autophagy. Hypoxia-induced autophagy has a crucial role in regulating the growth, spread, and resistance to treatment in human malignancies. Hypoxia-induced regulation of autophagy can impact other mechanisms of cell death, such as apoptosis. Chemoresistance and radioresistance have become significant challenges in recent years. Hypoxia-mediated autophagy plays a crucial role in determining the response to these therapeutic treatments.

Transcription factor FOXM1 specifies chromatin DNA to extracellular vesicles

Extracellular vesicle DNAs (evDNAs) hold significant diagnostic value for various diseases and facilitate transcellular transfer of genetic material. Our study identifies transcription factor FOXM1 as a mediator for directing chromatin genes or DNA fragments (termed FOXM1-chDNAs) to extracellular vesicles (EVs). FOXM1 binds to MAP1LC3/LC3 in the nucleus, and FOXM1-chDNAs, such as the DUX4 gene and telomere DNA, are designated by FOXM1 binding and translocated to the cytoplasm before being released to EVs through the secretory autophagy during lysosome inhibition (SALI) process involving LC3. Disrupting FOXM1 expression or the SALI process impairs FOXM1-chDNAs incorporation into EVs. FOXM1-chDNAs can be transmitted to recipient cells via EVs and expressed in recipient cells when they carry functional genes. This finding provides an example of how chromatin DNA fragments are specified to EVs by transcription factor FOXM1, revealing its contribution to the formation of evDNAs from nuclear chromatin. It provides a basis for further exploration of the roles of evDNAs in biological processes, such as horizontal gene transfer.Abbreviation: ATG5: autophagy related 5; CCFs: cytoplasmic chromatin fragments; ChIP: chromatin immunoprecipitation; cytoDNA: cytoplasmic DNA; CQ: chloroquine; FOXM1-DBD: FOXM1 DNA binding domain; DUX4:double homeobox 4; EVs: extracellular vesicles; evDNAs: extracellular vesicle DNAs; FOXM1: forkhead box M1; FOXM1-chDNAs: chromatin DNA fragments directed by FOXM1 to EVs; HGT: horizontal gene transfer; LC3-II: lipid modified LC3; LMNB1: lamin B1; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MVBs: multivesicular bodies; M1-binding DNA: a linear DNA containing 72× FOXM1 binding sites; SALI: secretory autophagy during lysosome inhibition; siRNA: small interfering RNA; TetO-DUX4: TetO array-containing DUX4 DNA; TetO: tet operator; TetR: tet repressor.

Molecular mechanisms in regulation of autophagy and apoptosis in view of epigenetic regulation of genes and involvement of liquid-liquid phase separation

Cellular physiology is critically regulated by multiple signaling nexuses, among which cell death mechanisms play crucial roles in controlling the homeostatic landscape at the tissue level within an organism. Apoptosis, also known as programmed cell death, can be induced by external and internal stimuli directing the cells to commit suicide in unfavourable conditions. In contrast, stress conditions like nutrient deprivation, infection and hypoxia trigger autophagy, which is lysosome-mediated processing of damaged cellular organelle for recycling of the degraded products, including amino acids. Apparently, apoptosis and autophagy both are catabolic and tumor-suppressive pathways; apoptosis is essential during development and cancer cell death, while autophagy promotes cell survival under stress. Moreover, autophagy plays dual role during cancer development and progression by facilitating the survival of cancer cells under stressed conditions and inducing death in extreme adversity. Despite having two different molecular mechanisms, both apoptosis and autophagy are interconnected by several crosslinking intermediates. Epigenetic modifications, such as DNA methylation, post-translational modification of histone tails, and miRNA play a pivotal role in regulating genes involved in both autophagy and apoptosis. Both autophagic and apoptotic genes can undergo various epigenetic modifications and promote or inhibit these processes under normal and cancerous conditions. Epigenetic modifiers are uniquely important in controlling the signaling pathways regulating autophagy and apoptosis. Therefore, these epigenetic modifiers of both autophagic and apoptotic genes can act as novel therapeutic targets against cancers. Additionally, liquid-liquid phase separation (LLPS) also modulates the aggregation of misfolded proteins and provokes autophagy in the cytosolic environment. This review deals with the molecular mechanisms of both autophagy and apoptosis including crosstalk between them; emphasizing epigenetic regulation, involvement of LLPS therein, and possible therapeutic approaches against cancers.

Mitochondrial derived vesicle-carrying protein MIGA2 promotes copper-induced autophagosomes-lysosomes fusion by regulating ATG14

As an environmental pollution metal, copper (Cu) exposure-induced toxicity is closely related to mitochondrial damage. Mitochondrial-derived vesicles (MDVs) plays an essential role in mitochondrial quality control and cellular metabolism. However, the mechanism by which MDVs are involved in cellular metabolism under Cu exposure remains unclear. Here, the MDV-carrying protein MIGA2 was identified as a crucial molecule involved in the Cu-induced autophagosomes-lysosomes fusion. Furthermore, Cu exposure significantly promoted MDVs secretion, accompanied by a markedly increased MIGA2 expression in MDVs, as well as accelerated the autophagosomes-lysosomes fusion. However, small RNA interference of SNX9 (the MDVs secretion inductor) and MIGA2 blocked autophagic flux induced by Cu, leading to failure of autophagosomes degradation. Co-immunoprecipitation assay further demonstrated that ATG14 was a regulation target protein of MIGA2. Overexpression and knockdown of ATG14 significantly affected the autophagosomes-lysosomes fusion induced by Cu. Meanwhile, knockdown of ATG14 dramatically reversed the effect of MIGA2-overexpression in promoting autophagosomes-lysosomes fusion, while overexpression of ATG14 shows the opposite effect. These results demonstrated that MDVs-carrying MIGA2 protein promoted autophagosomes-lysosomes fusion induced by Cu. This study demonstrated that MDVs is involved in regulating organelles-to-organelles communication, providing a new insight into the toxicity mechanism of Cu exposure on hepatocytes.

Recent progresses in the late stages of autophagy

Autophagy, a lysosome-dependent degradation process, plays a crucial role in maintaining cell homeostasis. It serves as a vital mechanism for adapting to stress and ensuring intracellular quality control. Autophagy deficiencies or defects are linked to numerous human disorders, especially those associated with neuronal degeneration or metabolic diseases. Yoshinori Ohsumi was honored with the Nobel Prize in Physiology or Medicine in 2016 for his groundbreaking discoveries regarding autophagy mechanisms. Over the past few decades, autophagy research has predominantly concentrated on the early stages of autophagy, with relatively limited attention given to the late stages. Nevertheless, recent studies have witnessed substantial advancements in understanding the molecular intricacies of the late stages, which follows autophagosome formation. This review provides a comprehensive summary of the recent progresses in comprehending the molecular mechanisms of the late stages of autophagy.

The role of autophagy in odontogenesis, dental implant surgery, periapical and periodontal diseases

Autophagy is a cellular process that is evolutionarily conserved, involving the sequestration of damaged organelles and proteins into autophagic vesicles, which subsequently fuse with lysosomes for degradation. Autophagy controls the development of many diseases by influencing apoptosis, inflammation, the immune response and different cellular processes. Autophagy plays a significant role in the aetiology of disorders associated with dentistry. Autophagy controls odontogenesis. Furthermore, it is implicated in the pathophysiology of pulpitis and periapical disorders. It enhances the survival, penetration and colonization of periodontal pathogenic bacteria into the host periodontal tissues and facilitates their escape from host defences. Autophagy plays a crucial role in mitigating exaggerated inflammatory reactions within the host's system during instances of infection and inflammation. Autophagy also plays a role in the relationship between periodontal disease and systemic diseases. Autophagy promotes wound healing and may enhance implant osseointegration. This study reviews autophagy's dento-alveolar effects, focusing on its role in odontogenesis, periapical diseases, periodontal diseases and dental implant surgery, providing valuable insights for dentists on tooth development and dental applications. A thorough examination of autophagy has the potential to discover novel and efficacious treatment targets within the field of dentistry.

Deciphering adipose development: Function, differentiation and regulation

The overdevelopment of adipose tissues, accompanied by excess lipid accumulation and energy storage, leads to adipose deposition and obesity. With the increasing incidence of obesity in recent years, obesity is becoming a major risk factor for human health, causing various relevant diseases (including hypertension, diabetes, osteoarthritis and cancers). Therefore, it is of significance to antagonize obesity to reduce the risk of obesity-related diseases. Excess lipid accumulation in adipose tissues is mediated by adipocyte hypertrophy (expansion of pre-existing adipocytes) or hyperplasia (increase of newly-formed adipocytes). It is necessary to prevent excessive accumulation of adipose tissues by controlling adipose development. Adipogenesis is exquisitely regulated by many factors in vivo and in vitro, including hormones, cytokines, gender and dietary components. The present review has concluded a comprehensive understanding of adipose development including its origin, classification, distribution, function, differentiation and molecular mechanisms underlying adipogenesis, which may provide potential therapeutic strategies for harnessing obesity without impairing adipose tissue function.

The autophagy protein, ATG14 safeguards against unscheduled pyroptosis activation to enable embryo transport during early pregnancy

Recurrent pregnancy loss (RPL), characterized by two or more failed clinical pregnancies, poses a significant challenge to reproductive health. In addition to embryo quality and endometrial function, proper oviduct function is also essential for successful pregnancy establishment. Therefore, structural abnormalities or inflammation resulting from infection in the oviduct may impede the transport of embryos to the endometrium, thereby increasing the risk of miscarriage. However, the precise cellular mechanisms that maintain the structural and functional integrity of the oviduct are not studied yet. Here, we report that autophagy is critical for maintaining the oviduct homeostasis and keeping the inflammation under check to enable embryo transport. Specifically, the loss of the autophagy-related gene, Atg14 in the oviduct causes severe structural abnormalities compromising its cellular plasticity and integrity leading to the retention of embryos. Interestingly, the selective loss of Atg14 in oviduct ciliary epithelial cells did not impact female fertility, highlighting the specificity of ATG14 function in distinct cell types within the oviduct. Mechanistically, loss of Atg14 triggered unscheduled pyroptosis leading to inappropriate embryo retention and impeded embryo transport in the oviduct. Finally, pharmacological activation of pyroptosis in pregnant mice led to an impairment in embryo transport. Together, we found that ATG14 safeguards against unscheduled pyroptosis activation to enable embryo transport from the oviduct to uterus for the successful implantation. Of clinical significance, these findings provide possible insights on the underlying mechanism(s) of early pregnancy loss and might aid in developing novel prevention strategies using autophagy modulators.

Long non-coding RNA MLLT4 antisense RNA 1 induces autophagy to inhibit tumorigenesis of cervical cancer through modulating the myosin-9/ATG14 axis

The regulatory mechanism of long non-coding RNAs (lncRNAs) in autophagy is as yet not well established. In this research, we show that the long non-coding RNA MLLT4 antisense RNA 1 (lncRNA MLLT4-AS1) is induced by the MTORC inhibitor PP242 and rapamycin in cervical cells. Overexpression of MLLT4-AS1 promotes autophagy and inhibits tumorigenesis and the migration of cervical cancer cells, whereas knockdown of MLLT4-AS1 attenuates PP242-induced autophagy. Mass spectrometry, RNA fluorescence in situ hybridization (RNA-FISH), and immunoprecipitation assays were performed to identify the direct interactions between MLLT4-AS1 and other associated targets, such as myosin-9 and autophagy-related 14(ATG14). MLLT4-AS1 was upregulated by H3K27ac modification with PP242 treatment, and knockdown of MLLT4-AS1 reversed autophagy by modulating ATG14 expression. Mechanically, MLLT4-AS1 was associated with the myosin-9 protein, which further promoted the transcription activity of the ATG14 gene. In conclusion, we demonstrated that MLLT4-AS1 acts as a potential tumor suppressor in cervical cancer by inducing autophagy, and H3K27ac modification-induced upregulation of MLLT4-AS1 could cause autophagy by associating with myosin-9 and promoting ATG14 transcription.

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.

VHL suppresses autophagy and tumor growth through PHD1-dependent Beclin1 hydroxylation

The Von Hippel-Lindau (VHL) protein, which is frequently mutated in clear-cell renal cell carcinoma (ccRCC), is a master regulator of hypoxia-inducible factor (HIF) that is involved in oxidative stresses. However, whether VHL possesses HIF-independent tumor-suppressing activity remains largely unclear. Here, we demonstrate that VHL suppresses nutrient stress-induced autophagy, and its deficiency in sporadic ccRCC specimens is linked to substantially elevated levels of autophagy and correlates with poorer patient prognosis. Mechanistically, VHL directly binds to the autophagy regulator Beclin1, after its PHD1-mediated hydroxylation on Pro54. This binding inhibits the association of Beclin1-VPS34 complexes with ATG14L, thereby inhibiting autophagy initiation in response to nutrient deficiency. Expression of non-hydroxylatable Beclin1 P54A abrogates VHL-mediated autophagy inhibition and significantly reduces the tumor-suppressing effect of VHL. In addition, Beclin1 P54-OH levels are inversely correlated with autophagy levels in wild-type VHL-expressing human ccRCC specimens, and with poor patient prognosis. Furthermore, combined treatment of VHL-deficient mouse tumors with autophagy inhibitors and HIF2α inhibitors suppresses tumor growth. These findings reveal an unexpected mechanism by which VHL suppresses tumor growth, and suggest a potential treatment for ccRCC through combined inhibition of both autophagy and HIF2α.

Lysosomes as coordinators of cellular catabolism, metabolic signalling and organ physiology

Every cell must satisfy basic requirements for nutrient sensing, utilization and recycling through macromolecular breakdown to coordinate programmes for growth, repair and stress adaptation. The lysosome orchestrates these key functions through the synchronised interplay between hydrolytic enzymes, nutrient transporters and signalling factors, which together enable metabolic coordination with other organelles and regulation of specific gene expression programmes. In this Review, we discuss recent findings on lysosome-dependent signalling pathways, focusing on how the lysosome senses nutrient availability through its physical and functional association with mechanistic target of rapamycin complex 1 (mTORC1) and how, in response, the microphthalmia/transcription factor E (MiT/TFE) transcription factors exert feedback regulation on lysosome biogenesis. We also highlight the emerging interactions of lysosomes with other organelles, which contribute to cellular homeostasis. Lastly, we discuss how lysosome dysfunction contributes to diverse disease pathologies and how inherited mutations that compromise lysosomal hydrolysis, transport or signalling components lead to multi-organ disorders with severe metabolic and neurological impact. A deeper comprehension of lysosomal composition and function, at both the cellular and organismal level, may uncover fundamental insights into human physiology and disease.

Ironing out the details of ferroptosis

Ferroptosis, spurred by excess labile iron and lipid peroxidation, is implicated in various diseases. Advances have been made in comprehending the lipid-peroxidation side of ferroptosis, but the exact role of iron in driving ferroptosis remains unknown. Although iron overload is characterized in multiple disease states, the potential role of ferroptosis within them remains undefined. This overview focuses on the 'ferro' side of ferroptosis, highlighting iron dysregulation in human diseases and potential therapeutic strategies targeting iron regulation and metabolism.

Human YKT6 forms priming complex with STX17 and SNAP29 to facilitate autophagosome-lysosome fusion

Autophagy is crucial for degrading and recycling cellular components. Fusion between autophagosomes and lysosomes is pivotal, directing autophagic cargo to degradation. This process is driven by STX17-SNAP29-VAMP8 and STX7-SNAP29-YKT6 in mammalian cells. However, the interaction between STX17 and YKT6 and its significance remain to be revealed. In this study, we challenge the notion that STX17 and YKT6 function independently in autophagosome-lysosome fusion. YKT6, through its SNARE domain, forms a complex with STX17 and SNAP29 on autophagosomes, enhancing autophagy flux. VAMP8 displaces YKT6 from this complex, leading to the formation of the fusogenic complex STX17-SNAP29-VAMP8. We demonstrated that the YKT6-SNAP29-STX17 complex facilitates both lipid and content mixing driven by STX17-SNAP29-VAMP8, suggesting a priming role of YKT6 for efficient membrane fusion. Our results provide a potential regulation mechanism of autophagosome-lysosome fusion, highlighting the importance of YKT6 and its interactions with STX17 and SNAP29 in promoting autophagy flux.

Targeting autophagy as a therapeutic strategy in pediatric acute lymphoblastic leukemia

Autophagy is activated in response to a variety of stress conditions including anti-cancer therapies, and tumors cells often depend on autophagy for survival. In this study, we have evaluated inhibition of autophagy as therapeutic strategy in acute lymphoblastic leukemia (ALL) in children, both as a single treatment and in combination with glucocorticoid (GC) Dexamethasone (Dexa). Analysis of proteomics and RNA-seq of ALL cell lines and primary samples identified an upregulation of Vps34 and ATG14 proteins and autophagy and lysosomal pathway enrichment in a genetic subgroup with a recurrent t(12;21) translocation. Cells from this sugbroup were also significantly more sensitive to the selective autophagy or lysosomal inhibitors than cells with other genetic rearrangements. Further, combination of Dexa with either lysosomal or autophagy inhibitors was either synergistic or additive in killing leukemic cells across various genetic and lineage backgrounds, for both cell lines and primary samples, as assessed using viability assays and SynergyFinder as well as apoptotic caspase 3/7-based live-cell assays. Our data demonstrate that targeting autophagy represents a promising strategy for the treatment of pediatric ALL, both as a selective modality for the t(12;21) pre-B-ALL subgroup, and in combination treatments to sensitize to GC-induced cytotoxicity.

NPFs-mediated actin cytoskeleton: a new viewpoint on autophagy regulation

Macroautophagy/autophagy is a lysosome-dependent catabolic process induced by various cellular stress conditions, maintaining the homeostasis of cells, tissues and organs. Autophagy is a series of membrane-related events involving multiple autophagy-related (ATG) proteins. Most studies to date have focused on various signaling pathways affecting ATG proteins to control autophagy. However, mounting evidence reveals that the actin cytoskeleton acts on autophagy-associated membranes to regulate different events of autophagy. The actin cytoskeleton assists in vesicle formation and provides the mechanical forces for cellular activities that involve membrane deformation. Although the interaction between the actin cytoskeleton and membrane makes the role of actin in autophagy recognized, how the actin cytoskeleton is recruited and assembles on membranes during autophagy needs to be detailed. Nucleation-promoting factors (NPFs) activate the Arp2/3 complex to produce actin cytoskeleton. In this review, we summarize the important roles of the actin cytoskeleton in autophagy regulation and focus on the effect of NPFs on actin cytoskeleton assembly during autophagy, providing new insights into the occurrence and regulatory mechanisms of autophagy. Video Abstract.

Molecular structures and function of the autophagosome-lysosome fusion machinery

Macroautophagy (also known as autophagy) plays a pivotal role in maintaining cellular homeostasis. The terminal step of the multi-step autophagy degradation pathway involves fusion between the cargo-laden, double-membraned autophagosome and the lytic organelle lysosome/vacuole. Over the past decade, various core components of the molecular machinery that execute this critical terminal autophagy event have been identified. This review highlights recent advances in understanding the molecular structures, biochemical functions, and regulatory mechanisms of key components of this highly sophisticated machinery including the SNARE fusogens, tethering factors, Rab GTPases and associated guanine nucleotide exchange factors, and other accessory factors.

Understanding the mechanisms of disease modifying effects of aerobic exercise in people with Alzheimer's disease

Alzheimer's disease (AD) is a very disabling disease. Pathologically, it is characterized by the presence of amyloid plaques and neurofibrillary tangles in the brain that results in neurodegeneration. Its clinical manifestations include progressive memory impairment, language decline and difficulty in carrying out activities of daily living (ADL). The disease is managed using interventions such as pharmacological interventions and aerobic exercise. Use of aerobic exercise has shown some promises in reducing the risk of developing AD, and improving cognitive function and the ability to carry out both basic and instrumental ADL. Although, the mechanisms through which aerobic exercise improves AD are poorly understood, improvement in vascular function, brain glucose metabolism and cardiorespiratory fitness, increase in antioxidant capacity and haemoglobin level, amelioration of immune-related and inflammatory responses, modulation of concentration of circulating Neurotrophins and peptides and decrease in concentration of tau protein and cortisol level among others seem to be the possible mechanisms. Therefore, understanding these mechanisms is important to help characterize the dose and the nature of the aerobic exercise to be given. In addition, they may also help in finding ways to optimize other interventions such as the pharmacological interventions. However, more quality studies are needed to verify the mechanisms.

The STX17-SNAP47-VAMP7/VAMP8 complex is the default SNARE complex mediating autophagosome-lysosome fusion

Autophagosome-lysosome fusion mediated by SNARE complexes is an essential step in autophagy. Two SNAP29-containing SNARE complexes have been extensively studied in starvation-induced bulk autophagy, while the relevant SNARE complexes in other types of autophagy occurring under non-starvation conditions have been overlooked. Here, we found that autophagosome-lysosome fusion in selective autophagy under non-starvation conditions does not require SNAP29-containing SNARE complexes, but requires the STX17-SNAP47-VAMP7/VAMP8 SNARE complex. Further, the STX17-SNAP47-VAMP7/VAMP8 SNARE complex also functions in starvation-induced autophagy. SNAP47 is recruited to autophagosomes following concurrent detection of ATG8s and PI(4,5)P2 via its Pleckstrin homology domain. By contrast, SNAP29-containing SNAREs are excluded from selective autophagy due to inactivation by O-GlcNAcylation under non-starvation conditions. These findings depict a previously unknown, default SNARE complex responsible for autophagosome-lysosome fusion in both selective and bulk autophagy, which could guide research and therapeutic development in autophagy-related diseases.

ATG14 targets lipid droplets and acts as an autophagic receptor for syntaxin18-regulated lipid droplet turnover

Lipid droplets (LDs) are dynamic lipid storage organelles that can be degraded by autophagy machinery to release neutral lipids, a process called lipophagy. However, specific receptors and regulation mechanisms for lipophagy remain largely unknown. Here, we identify that ATG14, the core unit of the PI3KC3-C1 complex, also targets LD and acts as an autophagic receptor that facilitates LD degradation. A negative regulator, Syntaxin18 (STX18) binds ATG14, disrupting the ATG14-ATG8 family members interactions and subverting the PI3KC3-C1 complex formation. Knockdown of STX18 activates lipophagy dependent on ATG14 not only as the core unit of PI3KC3-C1 complex but also as the autophagic receptor, resulting in the degradation of LD-associated anti-viral protein Viperin. Furthermore, coronavirus M protein binds STX18 and subverts the STX18-ATG14 interaction to induce lipophagy and degrade Viperin, facilitating virus production. Altogether, our data provide a previously undescribed mechanism for additional roles of ATG14 in lipid metabolism and virus production.

Organelle proteomic profiling reveals lysosomal heterogeneity in association with longevity

Lysosomes are active sites to integrate cellular metabolism and signal transduction. A collection of proteins associated with the lysosome mediate these metabolic and signaling functions. Both lysosomal metabolism and lysosomal signaling have been linked to longevity regulation; however, how lysosomes adjust their protein composition to accommodate this regulation remains unclear. Using deep proteomic profiling, we systemically profiled lysosome-associated proteins linked with four different longevity mechanisms. We discovered the lysosomal recruitment of AMP-activated protein kinase and nucleoporin proteins and their requirements for longevity in response to increased lysosomal lipolysis. Through comparative proteomic analyses of lysosomes from different tissues and labeled with different markers, we further elucidated lysosomal heterogeneity across tissues as well as the increased enrichment of the Ragulator complex on Cystinosin-positive lysosomes. Together, this work uncovers lysosomal proteome heterogeneity across multiple scales and provides resources for understanding the contribution of lysosomal protein dynamics to signal transduction, organelle crosstalk, and organism longevity.

Neuronal Autophagy: Regulations and Implications in Health and Disease

Autophagy is a major degradative pathway that plays a key role in sustaining cell homeostasis, integrity, and physiological functions. Macroautophagy, which ensures the clearance of cytoplasmic components engulfed in a double-membrane autophagosome that fuses with lysosomes, is orchestrated by a complex cascade of events. Autophagy has a particularly strong impact on the nervous system, and mutations in core components cause numerous neurological diseases. We first review the regulation of autophagy, from autophagosome biogenesis to lysosomal degradation and associated neurodevelopmental/neurodegenerative disorders. We then describe how this process is specifically regulated in the axon and in the somatodendritic compartment and how it is altered in diseases. In particular, we present the neuronal specificities of autophagy, with the spatial control of autophagosome biogenesis, the close relationship of maturation with axonal transport, and the regulation by synaptic activity. Finally, we discuss the physiological functions of autophagy in the nervous system, during development and in adulthood.

L-Dopa decarboxylase modulates autophagy in hepatocytes and is implicated in dengue virus-caused inhibition of autophagy completion

The enzyme L-Dopa Decarboxylase (DDC) synthesizes the catecholamine dopamine and the indolamine serotonin. Apart from its role in the brain as a neurotransmitter biosynthetic enzyme, DDC has been detected also in the liver and other peripheral organs, where it is implicated in cell proliferation, apoptosis, and host-virus interactions. Dengue virus (DENV) suppresses DDC expression at the later stages of infection, during which DENV also inhibits autophagosome-lysosome fusion. As dopamine affects autophagy in neuronal cells, we investigated the possible association of DDC with autophagy in human hepatocytes and examined whether DDC mediates the relationship between DENV infection and autophagy. We performed DDC silencing/overexpression and evaluated autophagic markers upon induction of autophagy, or suppression of autophagosome-lysosome fusion. Our results showed that DDC favored the autophagic process, at least in part, through its biosynthetic function, while knockdown of DDC or inhibition of DDC enzymatic activity prevented autophagy completion. In turn, autophagy induction upregulated DDC, while autophagy reduction by chemical or genetic (ATG14L knockout) ways caused the opposite effect. This study also implicated DDC with the cellular energetic status, as DDC silencing reduced the oxidative phosphorylation activity of the cell. We also report that upon DDC silencing, the repressive effect of DENV on the completion of autophagy was enhanced, and the inhibition of autolysosome formation did not exert an additive effect on viral proliferation. These data unravel a novel role of DDC in the autophagic process and suggest that DENV downregulates DDC expression to inhibit the completion of autophagy, reinforcing the importance of this protein in viral infections.

MK8722 initiates early-stage autophagy while inhibiting late-stage autophagy via FASN-dependent reprogramming of lipid metabolism

Background and objective: Epithelial ovarian cancer (EOC) is associated with latent onset and poor prognosis, with drug resistance being a main concern in improving the prognosis of these patients. The resistance of cancer cells to most chemotherapeutic agents can be related to autophagy mechanisms. This study aimed to assess the therapeutic effect of MK8722, a small-molecule compound that activates AMP-activated protein kinase (AMPK), on EOC cells and to propose a novel strategy for the treatment of EOC. Purpose: To explore the therapeutic effects of MK8722 on EOC cells, and to elucidate the underlying mechanism. Methods and results: It was found that MK8722 effectively inhibited the malignant biological behaviors of EOC cells. In vitro experiments showed that MK8722 targeted and decreased the lipid metabolic pathway-related fatty acid synthase (FASN) expression levels, causing the accumulation of lipid droplets. In addition, transmission electron microscopy revealed the presence of autophagosome-affected mitochondria. Western blotting confirmed that MK8722 plays a role in activating autophagy upstream (PI3K/AKT/mTOR) and inhibiting autophagy downstream via FASN-dependent reprogramming of lipid metabolism. Plasmid transient transfection demonstrated that MK8722 suppressed late-stage autophagy by blocking autophagosome-lysosome fusion. Immunofluorescence and gene silencing revealed that this effect was achieved by inhibiting the interaction of FASN with the SNARE complexes STX17-SNP29-VAMP8. Furthermore, the antitumor effect of MK8722 was verified using a subcutaneous xenograft mouse model. Conclusion: The findings suggest that using MK8722 may be a new strategy for treating EOC, as it has the potential to be a new autophagy/mitophagy inhibitor. Its target of action, FASN, is a molecular crosstalk between lipid metabolism and autophagy, and exploration of the underlying mechanism of FASN may provide a new research direction.

CREBH promotes autophagy to ameliorate NASH by regulating Coro1a

Dysfunctional autophagy aggravates oxidative stress and inflammation in hepatocytes and accelerates the progression of nonalcoholic steatohepatitis (NASH). Here, we demonstrated that cAMP-responsive element-binding protein H (CREBH) is a transcriptional regulator of hepatic autophagy in response to diet-induced NASH. The results showed that the upregulation of CREBH in lipid-overloaded hepatocytes improves cell damage, dysfunction of autophagic flux and associated abnormal accumulation of the autophagosome marker LC3-II and autophagic substrate p62. CREBH deficiency aggravated the dysfunctional autophagy and liver injury and even caused NASH-associated liver fibrosis. In addition, the changing trend of autolysosomes and lysosome membrane-associated protein (LAMP1) was consistent with the expression level of CREBH. This result indicated that CREBH might promote autophagic degradation by restoring the formation of autolysosomes, thereby improving the blocked autophagic flux. Moreover, we observed that CREBH inhibited the expression of Coronin 1a (Coro1a), an autophagosome-lysosome fusion-related gene, through transcriptional regulation. The overexpression of Coro1a in LO2 liver cells inhibited autophagic flux and elevated inflammatory cytokine levels upon palmitic acid (PA) stimulation. Overall, our findings provide new insights into the regulatory role of CREBH in the progression of NASH and reveal that Coro1a is a novel target gene of CREBH based on the autophagy pathway.

VAMP8 suppresses the metastasis via DDX5/β-catenin signal pathway in osteosarcoma

Osteosarcoma is a highly metastatic malignant bone tumor, necessitating the development of new treatments to target its metastasis. Recent studies have revealed the significance of VAMP8 in regulating various signaling pathways in various types of cancer. However, the specific functional role of VAMP8 in osteosarcoma progression remains unclear. In this study, we observed a significant downregulation of VAMP8 in osteosarcoma cells and tissues. Low levels of VAMP8 in osteosarcoma tissues were associated with patients' poor prognosis. VAMP8 inhibited the migration and invasion capability of osteosarcoma cells. Mechanically, we identified DDX5 as a novel interacting partner of VAMP8, and the conjunction of VAMP8 and DDX5 promoted the degradation of DDX5 via the ubiquitin-proteasome system. Moreover, reduced levels of DDX5 led to the downregulation of β-catenin, thereby suppressing the epithelial-mesenchymal transition (EMT). Additionally, VAMP8 promoted autophagy flux, which may contribute to the suppression of osteosarcoma metastasis. In conclusion, our study anticipated that VAMP8 inhibits osteosarcoma metastasis by promoting the proteasomal degradation of DDX5, consequently inhibiting WNT/β-catenin signaling and EMT. Dysregulation of autophagy by VAMP8 is also implicated as a potential mechanism. These findings provide new insights into the biological nature driving osteosarcoma metastasis and highlight the modulation of VAMP8 as a potential therapeutic strategy for targeting osteosarcoma metastasis.

AI-based AlphaFold2 significantly expands the structural space of the autophagy pathway

ABBREVIATIONS

AF2: AlphaFold2; AF2-Mult: AlphaFold2 multimer; ATG: autophagy-related; CTD: C-terminal domain; ECTD: extreme C-terminal domain; FR: flexible region; MD: molecular dynamics; NTD: N-terminal domain; pLDDT: predicted local distance difference test; UBL: ubiquitin-like.

Plant reoviruses hijack autophagy in insect vectors

Plant reoviruses, transmitted only by insect vectors, seriously threaten global cereal production. Understanding how insect vectors efficiently transmit the viruses is key to controlling the viral diseases. Autophagy commonly plays important roles in plant host defense against virus infection, but recent studies have shown that plant reoviruses can hijack the autophagy pathway in insect cells to enable their persistence in the insect and continued transmission to plants. Here, we summarize and discuss new insights on viral activation, evasion, regulation, and manipulation of autophagy within the insect vectors and the role of autophagy in virus survival in insect vectors. Deeper knowledge of the functions of autophagy in vectors may lead to novel strategies for blocking transmission of insect-borne plant viruses.

ATG14 plays a critical role in hepatic lipid droplet homeostasis

BACKGROUND & AIMS

Autophagy-related 14 (ATG14) is a key regulator of autophagy. ATG14 is also localized to lipid droplet; however, the function of ATG14 on lipid droplet remains unclear. In this study, we aimed to elucidate the role of ATG14 in lipid droplet homeostasis.

METHODS

ATG14 loss-of-function and gain-of-function in lipid droplet metabolism were analyzed by fluorescence imaging in ATG14 knockdown or overexpression hepatocytes. Specific domains involved in the ATG14 targeting to lipid droplets were analyzed by deletion or site-specific mutagenesis. ATG14-interacting proteins were analyzed by co-immunoprecipitation. The effect of ATG14 on lipolysis was analyzed in human hepatocytes and mouse livers that were deficient in ATG14, comparative gene identification-58 (CGI-58), or both.

RESULTS

Our data show that ATG14 is enriched on lipid droplets in hepatocytes. Mutagenesis analysis reveals that the Barkor/ATG14 autophagosome targeting sequence (BATS) domain of ATG14 is responsible for the ATG14 localization to lipid droplets. Co-immunoprecipitation analysis illustrates that ATG14 interacts with adipose triglyceride lipase (ATGL) and CGI-58. Moreover, ATG14 also enhances the interaction between ATGL and CGI-58. In vitro lipolysis analysis demonstrates that ATG14 deficiency remarkably decreases triglyceride hydrolysis.

CONCLUSIONS

Our data suggest that ATG14 can directly enhance lipid droplet breakdown through interactions with ATGL and CGI-58.

C9orf72-catalyzed GTP loading of Rab39A enables HOPS-mediated membrane tethering and fusion in mammalian autophagy

The multi-subunit homotypic fusion and vacuole protein sorting (HOPS) membrane-tethering complex is required for autophagosome-lysosome fusion in mammals, yet reconstituting the mammalian HOPS complex remains a challenge. Here we propose a "hook-up" model for mammalian HOPS complex assembly, which requires two HOPS sub-complexes docking on membranes via membrane-associated Rabs. We identify Rab39A as a key small GTPase that recruits HOPS onto autophagic vesicles. Proper pairing with Rab2 and Rab39A enables HOPS complex assembly between proteoliposomes for its tethering function, facilitating efficient membrane fusion. GTP loading of Rab39A is important for the recruitment of HOPS to autophagic membranes. Activation of Rab39A is catalyzed by C9orf72, a guanine exchange factor associated with amyotrophic lateral sclerosis and familial frontotemporal dementia. Constitutive activation of Rab39A can rescue autophagy defects caused by C9orf72 depletion. These results therefore reveal a crucial role for the C9orf72-Rab39A-HOPS axis in autophagosome-lysosome fusion.

RUNDC1 inhibits autolysosome formation and survival of zebrafish via clasping ATG14-STX17-SNAP29 complex

Autophagy serves as a pro-survival mechanism for a cell or a whole organism to cope with nutrient stress. Our understanding of the molecular regulation of this fusion event remains incomplete. Here, we identified RUNDC1 as a novel ATG14-interacting protein, which is highly conserved across vertebrates, including zebrafish and humans. By gain and loss of function studies, we demonstrate that RUNDC1 negatively modulates autophagy by blocking fusion between autophagosomes and lysosomes via inhibiting the assembly of the STX17-SNAP29-VAMP8 complex both in human cells and the zebrafish model. Moreover, RUNDC1 clasps the ATG14-STX17-SNAP29 complex via stimulating ATG14 homo-oligomerization to inhibit ATG14 dissociation. This also prevents VAMP8 from binding to STX17-SNAP29. We further identified that phosphorylation of RUNDC1 Ser379 is crucial to inhibit the assembly of the STX17-SNAP29-VAMP8 complex via promoting ATG14 homo-oligomerization. In line with our findings, RunDC1 is crucial for zebrafish in their response to nutrient-deficient conditions. Taken together, our findings demonstrate that RUNDC1 is a negative regulator of autophagy that restricts autophagosome fusion with lysosomes by clasping the ATG14-STX17-SNAP29 complex to hinder VAMP8 binding.

Near infrared in and out: Deep imaging for scrap leather induced autophagy in vivo by an ultrasensitive two-photon polarity probe

As one of the important means for eukaryotic cells to maintain homeostasis, autophagy allows for transporting deformed biomacromolecules and damaged organelles to lysosome for digestion and degradation. The process of autophagy entails the merging of autophagosomes and lysosomes, culminating in the breakdown of biomacromolecules. This, in turn, leads to a change in lysosomal polarity. Therefore, fully understanding the changes of lysosomal polarity during autophagy is of significance to the study of membrane fluidity and enzymatic reaction. However, the shorter emission wavelength has greatly damaged the imaging depth, thus seriously limiting its biological application. Therefore, in this work, a near infrared in and out lysosome-targeted polarity-sensitive probe NCIC-Pola was developed. The fluorescence intensity of NCIC-Pola showed an approximate 1160-fold increase when the polarity decreased under two-photon excitation (TPE). In addition, the excellent fluorescence emission wavelength (692 nm) enabled the deep imaging analysis of scrap leather induced autophagy in vivo.

MARCH7-mediated ubiquitination decreases the solubility of ATG14 to inhibit autophagy

Autophagy is a fundamental biological process critical to all eukaryotic cellular life. Although autophagy has been increasingly studied, how its process is precisely coordinated remains an open question. ATG14 (ATG14L/Barkor) is known to play a crucial role in both autophagosome formation and autophagosome-lysosome fusion. However, how ATG14 is regulated, especially at the post-translation level, is still not clear. Here, we report that MARCH7 (membrane-associated ring-CH-type finger 7), an E3 ubiquitin ligase, inhibits autophagy by ubiquitinating ATG14. MARCH7 significantly promotes K6-, K11-, and K63-linked mixed polyubiquitination on ATG14, triggering the aggregation of ATG14 and reducing its solubility in cells. Functionally, we find that MARCH7 depletion decreases the number of aggresome-like induced structures (ALISs). Mechanistically, we show that ubiquitinated ATG14 has fewer interactions with STX17, leading to the inhibition of autophagy flux. Collectively, our study reveals a mechanism in regulating autophagy and suggests a potential strategy for the treatment of autophagy-related diseases.

Interaction between Autophagy and Senescence in Pancreatic Beta Cells

Aging leads to an increase in cellular stress due to the fragility of the organism and the inability to cope with it. In this setting, there is a higher chance of developing different cardiometabolic diseases like diabetes. Cellular senescence and autophagy, both hallmarks of aging and stress-coping mechanisms, have gained increased attention for their role in the pathophysiology of diabetes. Studies show that impairing senescence dampens and even prevents diabetes while the role of autophagy is more contradictory, implying a context- and disease-stage-dependent effect. Reports show conflicting data about the effect of autophagy on senescence while the knowledge about this interaction in beta cells remains scarce. Elucidating this interaction between autophagy and senescence in pancreatic beta cells will lead to an identification of their respective roles and the extent of the effect each mechanism has on beta cells and open new horizons for developing novel therapeutic agents. To help illuminate this relationship we will review the latest findings of cellular senescence and autophagy with a special emphasis on pancreatic beta cells and diabetes.

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.

Regulation of Phosphoinositide Signaling by Scaffolds at Cytoplasmic Membranes

Cytoplasmic phosphoinositides (PI) are critical regulators of the membrane-cytosol interface that control a myriad of cellular functions despite their low abundance among phospholipids. The metabolic cycle that generates different PI species is crucial to their regulatory role, controlling membrane dynamics, vesicular trafficking, signal transduction, and other key cellular events. The synthesis of phosphatidylinositol (3,4,5)-triphosphate (PI3,4,5P3) in the cytoplamic PI3K/Akt pathway is central to the life and death of a cell. This review will focus on the emerging evidence that scaffold proteins regulate the PI3K/Akt pathway in distinct membrane structures in response to diverse stimuli, challenging the belief that the plasma membrane is the predominant site for PI3k/Akt signaling. In addition, we will discuss how PIs regulate the recruitment of specific scaffolding complexes to membrane structures to coordinate vesicle formation, fusion, and reformation during autophagy as well as a novel lysosome repair pathway.

Ubiquitination in the regulation of autophagy

Autophagy, an efficient and effective approach to clear rapidly damaged organelles, macromolecules, and other harmful cellular components, enables the recycling of nutrient materials and supply of nutrients to maintain cellular homeostasis. Ubiquitination plays an important regulatory role in autophagy. This paper summarizes the most recent progress in ubiquitin modification in various stages of autophagy, including initiation, elongation, and termination. Moreover, this paper shows that ubiquitination is an important way through which selective autophagy achieves substrate specificity. Furthermore, we note the distinction between monoubiquitination and polyubiquitination in the regulation of autophagy. Compared with monoubiquitination, polyubiquitination is a more common strategy to regulate the activity of the autophagy molecular machinery. In addition, the role of ubiquitination in the closure and fusion of autophagosomes warrants further study. This article not only clarifies the regulatory mechanism of autophagy but also contributes to a deeper understanding of the importance of ubiquitination modification.