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Journal of Biomedical Science Oct 2020Autophagy is a process in which a myriad membrane structures called autophagosomes are formed de novo in a single cell, which deliver the engulfed substrates into... (Review)
Review
Autophagy is a process in which a myriad membrane structures called autophagosomes are formed de novo in a single cell, which deliver the engulfed substrates into lysosomes for degradation. The size of the autophagosomes is relatively uniform in non-selective autophagy and variable in selective autophagy. It has been recently established that autophagosome formation occurs near the endoplasmic reticulum (ER). In this review, we have discussed recent advances in the relationship between autophagosome formation and endoplasmic reticulum. Autophagosome formation occurs near the ER subdomain enriched with phospholipid synthesizing enzymes like phosphatidylinositol synthase (PIS)/CDP-diacylglycerol-inositol 3-phosphatidyltransferase (CDIPT) and choline/ethanolamine phosphotransferase 1 (CEPT1). Autophagy-related protein 2 (Atg2), which is involved in autophagosome formation has a lipid transfer capacity and is proposed to directly transfer the lipid molecules from the ER to form autophagosomes. Vacuole membrane protein 1 (VMP1) and transmembrane protein 41b (TMEM41b) are ER membrane proteins that are associated with the formation of the subdomain. Recently, we have reported that an uncharacterized ER membrane protein possessing the DNAJ domain, called ERdj8/DNAJC16, is associated with the regulation of the size of autophagosomes. The localization of ERdj8/DNAJC16 partially overlaps with the PIS-enriched ER subdomain, thereby implying its association with autophagosome size determination.
Topics: Animals; Autophagosomes; Autophagy; Autophagy-Related Proteins; Endoplasmic Reticulum; Humans
PubMed: 33087127
DOI: 10.1186/s12929-020-00691-6 -
Neuroscience Letters Apr 2019Neurons are long-lived and highly polarized cells that depend on autophagy to maintain cellular homeostasis. The robust, constitutive biogenesis of autophagosomes in the... (Review)
Review
Neurons are long-lived and highly polarized cells that depend on autophagy to maintain cellular homeostasis. The robust, constitutive biogenesis of autophagosomes in the distal axon occurs via a conserved pathway that is required to maintain functional synapses and prevent axon degeneration. Autophagosomes are formed de novo at the axon terminal in a stepwise assembly process, engulfing mitochondrial fragments, aggregated proteins, and bulk cytosol in what appears to be a nonselective uptake mechanism. Following formation, autophagosomes fuse with late endosomes/lysosomes and then are rapidly and efficiently transported along the axon toward the soma, driven by the microtubule motor cytoplasmic dynein. Motile autophagosomes mature to autolysosomes in transit by fusing with additional late endosomes/lysosomes, arriving at the soma as fully competent degradative organelles. Misregulation of neuronal autophagy leads to axonal degeneration and synaptic destabilization, and has been implicated in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and ALS.
Topics: Animals; Autophagosomes; Autophagy; Axons; Central Nervous System; Endosomes; Homeostasis; Humans; Lysosomes; Neurodegenerative Diseases; Neurons; Protein Transport
PubMed: 29548988
DOI: 10.1016/j.neulet.2018.03.025 -
The Journal of Clinical Investigation Jun 2020Although autophagy is generally protective, uncontrolled or excessive activation of autophagy can be detrimental. However, it is often difficult to distinguish death by...
Although autophagy is generally protective, uncontrolled or excessive activation of autophagy can be detrimental. However, it is often difficult to distinguish death by autophagy from death with autophagy, and whether autophagy contributes to death in cardiomyocytes (CMs) is still controversial. Excessive activation of autophagy induces a morphologically and biochemically defined form of cell death termed autosis. Whether autosis is involved in tissue injury induced under pathologically relevant conditions is poorly understood. In the present study, myocardial ischemia/reperfusion (I/R) induced autosis in CMs, as evidenced by cell death with numerous vacuoles and perinuclear spaces, and depleted intracellular membranes. Autosis was observed frequently after 6 hours of reperfusion, accompanied by upregulation of Rubicon, attenuation of autophagic flux, and marked accumulation of autophagosomes. Genetic downregulation of Rubicon inhibited autosis and reduced I/R injury, whereas stimulation of autosis during the late phase of I/R with Tat-Beclin 1 exacerbated injury. Suppression of autosis by ouabain, a cardiac glycoside, in humanized Na+,K+-ATPase-knockin mice reduced I/R injury. Taken together, these results demonstrate that autosis is significantly involved in I/R injury in the heart and triggered by dysregulated accumulation of autophagosomes due to upregulation of Rubicon.
Topics: Animals; Autophagosomes; Autophagy; Intracellular Signaling Peptides and Proteins; Mice; Mice, Transgenic; Myocardial Reperfusion Injury; Myocardium; Up-Regulation
PubMed: 32364533
DOI: 10.1172/JCI132366 -
Trends in Biochemical Sciences Jun 2020Autophagy is traditionally depicted as a signaling cascade that culminates in the formation of an autophagosome that degrades cellular cargo. However, recent studies... (Review)
Review
Autophagy is traditionally depicted as a signaling cascade that culminates in the formation of an autophagosome that degrades cellular cargo. However, recent studies have identified myriad pathways and cellular organelles underlying the autophagy process, be it as signaling platforms or through the contribution of proteins and lipids. The Golgi complex is recognized as being a central transport hub in the cell, with a critical role in endocytic trafficking and endoplasmic reticulum (ER) to plasma membrane (PM) transport. However, the Golgi is also an important site of key autophagy regulators, including the protein autophagy-related (ATG)-9A and the lipid, phosphatidylinositol-4-phosphate [PI(4)P]. In this review, we highlight the central function of this organelle in autophagy as a transport hub supplying various components of autophagosome formation.
Topics: Autophagosomes; Autophagy; Autophagy-Related Proteins; Biological Transport; Endosomes; Golgi Apparatus; Humans; Lipid Metabolism; Membrane Proteins; Vesicular Transport Proteins
PubMed: 32307224
DOI: 10.1016/j.tibs.2020.03.010 -
Journal of Molecular Cell Biology Jan 2022The biogenesis of autophagosomes provides the basis for macroautophagy to capture and degrade intracellular cargoes. Binding of the autophagy-related protein ATG8/LC3 to...
The biogenesis of autophagosomes provides the basis for macroautophagy to capture and degrade intracellular cargoes. Binding of the autophagy-related protein ATG8/LC3 to autophagic membranes is essential to autophagosome formation, which involves the specific and dynamic processing of ATG8/LC3 by cysteine protease ATG4. However, to date, the mechanism whereby ATG4 is recruited to the membranes, the interaction of ATG4 and ATG8/LC3 on the membranes, and its role in the growth of phagophore are not completely understood. Here, we used fluorescence recovery after photobleaching to monitor the turnover of GFP-tagged ATG4B and LC3B in living animal cells. The data show that ATG4B localizes to early autophagic membranes in an LC3B-dependent manner. During autophagy, ATG4B and LC3B undergo rapid cytosol/isolation membrane exchange but not at the cytosol/completed autophagosome. In addition, ATG4B activity controls the efficiency of autophagosome formation by impacting the membrane binding/dissociation of LC3B. These data suggest that ATG4 and LC3 play interdependent roles in the formation of autophagosomes.
Topics: Animals; Autophagosomes; Autophagy; Autophagy-Related Proteins; Macroautophagy; Microtubule-Associated Proteins
PubMed: 34562084
DOI: 10.1093/jmcb/mjab059 -
Autophagy Aug 2021Parkinson disease (PD)-causing mutations in the (leucine rich repeat kinase 2) gene hyperactivate LRRK2 kinase activity. Here, we discuss our recent work linking LRRK2... (Review)
Review
Parkinson disease (PD)-causing mutations in the (leucine rich repeat kinase 2) gene hyperactivate LRRK2 kinase activity. Here, we discuss our recent work linking LRRK2 hyperactivation to defective axonal autophagosome transport in neurons. In three different models, we observed that expression of the most common causative mutation for PD, LRRK2, disrupts processive autophagosome transport in a kinase-dependent manner. Mechanistically, we found that hyperactive LRRK2 recruits SPAG9/JIP4, a motor adaptor known to bind to LRRK2-phosphorylated RAB proteins, to the autophagosomal membrane. Increased SPAG9/JIP4 levels induce abnormal recruitment and activation of kinesin-1, which we propose results in an unproductive tug-of-war between anterograde and retrograde motors bound to autophagosomes. Disruption of autophagosome transport correlates with defective autophagosome maturation, suggesting that hyperactive LRRK2 may impair efficient degradation of autophagosomal cargo. Our work demonstrates that LRRK2 hyperactivation is sufficient to induce defects in autophagosome transport and maturation, further establishing a role of defective autophagy in the pathogenesis of PD.
Topics: Adaptor Proteins, Signal Transducing; Animals; Autophagosomes; Autophagy; Axonal Transport; Axons; Humans; Leucine-Rich Repeat Serine-Threonine Protein Kinase-2
PubMed: 34110246
DOI: 10.1080/15548627.2021.1936933 -
FEBS Letters Sep 2022Plant selective (macro)autophagy is a highly regulated process where eukaryotic cells spatiotemporally degrade some of their constituents that have become superfluous or... (Review)
Review
Plant selective (macro)autophagy is a highly regulated process where eukaryotic cells spatiotemporally degrade some of their constituents that have become superfluous or harmful. The identification and characterization of the factors determining this selectivity make it possible to integrate selective (macro)autophagy into plant cell physiology and homeostasis. The specific cargo receptors and/or scaffold proteins involved in this pathway are generally not structurally conserved, as are the biochemical mechanisms underlying recognition and integration of a given cargo into the autophagosome in different cell types. This review discusses the few specific cargo receptors described in plant cells to highlight key features of selective autophagy in the plant kingdom and its integration with plant physiology, aiming to identify evolutionary convergence and knowledge gaps to be filled by future research.
Topics: Autophagosomes; Autophagy; Homeostasis; Plant Cells
PubMed: 35638898
DOI: 10.1002/1873-3468.14412 -
Science Signaling Jan 2023The degradation of macromolecules and organelles by the process of autophagy is critical for cellular homeostasis and is often compromised during aging and disease....
The degradation of macromolecules and organelles by the process of autophagy is critical for cellular homeostasis and is often compromised during aging and disease. Beclin1 and Beclin2 are implicated in autophagy induction, and these homologs share a high degree of amino acid sequence similarity but have divergent N-terminal regions. Here, we investigated the functions of the Beclin homologs in regulating autophagy and mitophagy, a specialized form of autophagy that targets mitochondria. Both Beclin homologs contributed to autophagosome formation, but a mechanism of autophagosome formation independent of either Beclin homolog occurred in response to starvation or mitochondrial damage. Mitophagy was compromised only in Beclin1-deficient HeLa cells and mouse embryonic fibroblasts because of defective autophagosomal engulfment of mitochondria, and the function of Beclin1 in mitophagy required the phosphorylation of the conserved Ser residue by the kinase Ulk1. Mitochondria-ER-associated membranes (MAMs) are important sites of autophagosome formation during mitophagy, and Beclin1, but not Beclin2 or a Beclin1 mutant that could not be phosphorylated at Ser, localized to MAMs during mitophagy. Our findings establish a regulatory role for Beclin1 in selective mitophagy by initiating autophagosome formation adjacent to mitochondria, a function facilitated by Ulk1-mediated phosphorylation of Ser in its distinct N-terminal region.
Topics: Animals; Humans; Mice; Autophagosomes; Autophagy; Beclin-1; Fibroblasts; HeLa Cells; Mitophagy
PubMed: 36719945
DOI: 10.1126/scisignal.abo4457 -
Autophagy Jun 2021In eukaryotes, ATG4/Atg4 is a critical regulator of macroautophagy/autophagy. The protease activity of Atg4/ATG4, involved in conjugation and deconjugation of...
In eukaryotes, ATG4/Atg4 is a critical regulator of macroautophagy/autophagy. The protease activity of Atg4/ATG4, involved in conjugation and deconjugation of Atg8-family proteins, was so far regarded as its sole functional contribution. However, the role of individual ATG4-family proteins during mammalian autophagy had previously not been examined . During their recent investigation, Nguyen et al. discovered a hitherto unexplored role for mammalian ATG4s during mitophagy - the recruitment of ATG9A-containing vesicles. Their article, highlighted here, discusses the finding, which uses a novel artificial intelligence (AI)-directed analysis technique for focused ion beam-scanning electron microscopy (FIB-SEM) imaging to demonstrate the role of ATG4s in promoting phagophore growth and establishing phagophore-ER contacts.
Topics: Animals; Apoptosis Regulatory Proteins; Artificial Intelligence; Autophagosomes; Autophagy; Autophagy-Related Proteins; Humans; Microtubule-Associated Proteins; Mitophagy
PubMed: 34011239
DOI: 10.1080/15548627.2021.1917284 -
Proceedings of the National Academy of... Sep 2022Autophagosomes are unique organelles that form de novo as double-membrane vesicles engulfing cytosolic material for destruction. Their biogenesis involves membrane...
Autophagosomes are unique organelles that form de novo as double-membrane vesicles engulfing cytosolic material for destruction. Their biogenesis involves membrane transformations of distinctly shaped intermediates whose ultrastructure is poorly understood. Here, we combine cell biology, correlative cryo-electron tomography (cryo-ET), and extensive data analysis to reveal the step-by-step structural progression of autophagosome biogenesis at high resolution directly within yeast cells. The analysis uncovers an unexpectedly thin intermembrane distance that is dilated at the phagophore rim. Mapping of individual autophagic structures onto a timeline based on geometric features reveals a dynamical change of membrane shape and curvature in growing phagophores. Moreover, our tomograms show the organelle interactome of growing autophagosomes, highlighting a polar organization of contact sites between the phagophore and organelles, such as the vacuole and the endoplasmic reticulum (ER). Collectively, these findings have important implications for the contribution of different membrane sources during autophagy and for the forces shaping and driving phagophores toward closure without a templating cargo.
Topics: Autophagosomes; Cell Membrane; Endoplasmic Reticulum; Macroautophagy; Saccharomyces cerevisiae; Vacuoles
PubMed: 36122245
DOI: 10.1073/pnas.2209823119