Autophagy最新文献

Macroautophagy/autophagy is a conserved process in eukaryotes responsible for degrading unwanted or damaged macromolecules and organelles through the lysosome or vacuole for recycling and reutilization. Our previous studies revealed the degradation of chloroplast proteins through a pathway dependent on the ubiquitin proteasome system, known as CHLORAD. Recently, we demonstrated a role for selective autophagy in regulating chloroplast protein import and enhancing stress tolerance in plants. Specifically, we found that K63-ubiquitination of TOC components at the chloroplast outer envelope membrane is recognized by the selective autophagy adaptor NBR1, leading to the degradation of TOC proteins under UV-B irradiation and heat stresses in Arabidopsis. This process was shown to control chloroplast protein import and influence photosynthetic activity. Based on our results, we have, for the first time, demonstrated that selective autophagy plays a vital role in chloroplast protein degradation, specifically in response to certain abiotic stresses.

Differentiation and fate decisions are critical for the epithelial cells lining the proximal tubule (PT) of the kidney, but the signals involved remain unknown. Defective cystine mobilization from lysosomes through CTNS (cystinosin, lysosomal cystine transporter), which is mutated in cystinosis, triggers the dedifferentiation and dysfunction of the PT cells, causing kidney disease and severe metabolic complications. Using preclinical models and physiologically relevant cellular systems, along with functional assays and a generative artificial intelligence (AI)-powered engine, we found that cystine storage imparted by CTNS deficiency stimulates Ragulator-RRAG GTPase-dependent recruitment of MTORC1 and its constitutive activation. In turn, this diverts the catabolic trajectories and differentiating states of PT cells toward growth and proliferation, disrupting homeostasis and their specialized functions. Therapeutic MTORC1 inhibition by using low doses of rapamycin corrects lysosome function and differentiation downstream of cystine storage and ameliorates PT dysfunction in preclinical models of cystinosis. These discoveries suggest that cystine may act as a lysosomal fasting signal that tailors MTORC1 signaling to direct fate decisions in the kidney PT epithelium, highlighting novel therapeutic paradigms for cystinosis and other lysosome-related disorders.

Adult stem cells are long-lived and quiescent with unique metabolic requirements. Macroautophagy/autophagy is a fundamental survival mechanism that allows cells to adapt to metabolic changes by degrading and recycling intracellular components. Here we address why autophagy depletion leads to a drastic loss of the stem cell compartment. Using inducible deletion of autophagy specifically in adult hematopoietic stem cells (HSCs) and in mice chimeric for autophagy-deficient and normal HSCs, we demonstrate that the stem cell loss is cell-intrinsic. Mechanistically, autophagy-deficient HSCs showed higher expression of several amino acid transporters (AAT) when compared to autophagy-competent cells, resulting in increased amino acid (AA) uptake. This was followed by sustained MTOR (mechanistic target of rapamycin) activation, with enlarged cell size, glucose uptake and translation, which is detrimental to the quiescent HSCs. MTOR inhibition by rapamycin treatment in vivo was able to rescue autophagy-deficient HSC loss and bone marrow failure and resulted in better reconstitution after transplantation. Our results suggest that targeting MTOR may improve aged stem cell function, promote reprogramming and stem cell transplantation.List of abbreviations: 5FU: fluoracil; AA: amino acids; AKT/PKB: thymoma viral proto-oncogene 1; ATF4: activating transcription factor 4; BafA: bafilomycin A₁; BM: bone marrow; EIF2: eukaryotic initiation factor 2; EIF4EBP1/4EBP1: eukaryotic translation initiation factor 4E binding protein 1; KIT/CD117/c-Kit: KIT proto-oncogene receptor tyrosine kinase; HSCs: hematopoietic stem cells; HSPCs: hematopoietic stem and progenitor cells; Kyn: kynurenine; LSK: lineage^- (Lin^-), LY6A/Sca-1⁺, KIT/c-Kit/CD117⁺; LY6A/Sca-1: lymphocyte antigen 6 family member A; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; MTORC2: MTOR complex 2; OPP: O-propargyl-puromycin; PI3K: phosphoinositide 3-kinase; poly(I:C): polyinosinic:polycytidylic acid; RPS6/S6: ribosomal protein S6; tam: tamoxifen; TCA: tricarboxylic acid; TFEB: transcription factor EB; PTPRC/CD45: Protein Tyrosine Phosphatase Receptor Type C, CD45 antigen.

Over the past decade, accumulated studies have reported the presence of non-canonical macroautophagy/autophagy characterized by the shared usage of the autophagy machinery and distinct components that function in multiple scenarios but do not involve lysosomal degradation. One type of non-canonical autophagy is secretory autophagy, which facilitates the secretion of various cargoes. In a recent work from Gao et al. the ER-membrane protein STING1 has been identified as a novel substrate of secretory autophagy. The secretion of activated STING1 is mediated by its packing into the rafeesome, a newly identified organelle formed upon the fusion of RAB22A-mediated non-canonical autophagosome with an early endosome. Moreover, extracellular vesicles containing activated STING1 induce antitumor immunity in recipient cells, a process potentially promoted by RAB22A.

SnRK1 (SNF1-related protein kinase 1) is a plant ortholog of yeast Snf1 and mammalian adenosine monophosphate-activated protein kinase (AMPK) that acts as a positive regulator of macroautophagy/autophagy. However, whether and how the autophagy pathway modulates SnRK1 activity remains elusive. Recently, we identified a clade of plant-specific FLZ (FCS-like zinc finger) proteins as novel ATG8 (autophagy-related 8)-interacting partners in Arabidopsis thaliana. These AtFLZs, which mainly localize on the surface of mitochondria, can inhibit SnRK1 signaling by repressing the T-loop phosphorylation of its catalytic α subunits, thereby negatively regulating carbon starvation-induced autophagy and plant tolerance to energy deprivation. Upon energy starvation, autophagy is activated to mediate the degradation of these AtFLZs, thus relieving their repression of SnRK1. More importantly, the ATG8-FLZ-SnRK1 regulatory axis appears to be functionally conserved during seed plant evolution. These findings highlight the positive role of autophagy in SnRK1 signaling activation under energy-limiting conditions in plants.Abbreviations: ADS, AIMs docking site; AIM, ATG8-interacting motif; AMPK, adenosine monophosphate-activated protein kinase; ATG, autophagy-related; ESCRT, endosomal sorting complexes required for transport; FLZ, FCS-like zinc finger protein; FREE1, FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING 1; RAPTOR, REGULATORY-ASSOCIATED PROTEIN OF TOR; Snf1, SUCROSE NON-FERMENTING 1; SnRK1, SNF1-related kinase 1; TOR, TARGET OF RAPAMYCIN.

Macroautophagy/autophagy and lipid droplet (LD) biology are intricately linked, with autophagosome-dependent degradation of LDs in response to different signals. LDs play crucial roles in forming autophagosomes possibly by providing essential lipids and serving as a supportive autophagosome assembly platform at the endoplasmic reticulum (ER)-LD interface. LDs and autophagosomes share common proteins, such as VPS13, ATG2, ZFYVE1/DFCP1, and ATG14, but their dual functions remain poorly understood. In our recent study, we found that prolonged starvation leads to ATG3 localizing to large LDs and lipidating LC3B, revealing a non-canonical autophagic role on LDs. In vitro, ATG3 associates with purified and artificial LDs, and conjugated Atg8-family proteins. In long-term starved cells, only LC3B is found on the specific large LDs, positioned near LC3B-positive membranes that undergo lysosome-mediated acidification. This implies that LD-lipidated LC3B acts as a tethering factor, connecting phagophores to LDs and promoting degradation. Our data also support the notion that certain LD surfaces may function as lipidation stations for LC3B, which may move to nearby sites of autophagosome formation. Overall, our study unveils an unknown non-canonical implication of LDs in autophagy processes.Abbreviation: ATG: autophagy-related enzyme, ATP: adenosine triphosphate, E2 enzyme: ubiquitin-conjugating enzyme, ER: endoplasmic reticulum, LD: lipid droplet, LIR motif: LC3-interacting region, MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta, PE: phosphatidylethanolamine, PLIN1: perilipin 1, PNPLA2/ATGL: patatin-like phospholipase domain containing 2, SQSTM1/p62: sequestosome 1, VSP13: vacuolar protein sorting 13, ZFYVE1/DFCP1: zinc finger, FYVE domain containing 1.