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Autophagy 2018The autophagy-lysosome pathway plays a fundamental role in the clearance of aggregated proteins and protection against cellular stress and neurodegenerative conditions....
UNLABELLED
The autophagy-lysosome pathway plays a fundamental role in the clearance of aggregated proteins and protection against cellular stress and neurodegenerative conditions. Alterations in autophagy processes, including macroautophagy and chaperone-mediated autophagy (CMA), have been described in Parkinson disease (PD). CMA is a selective autophagic process that depends on LAMP2A (lysosomal-associated membrane protein 2A), a mammal and bird-specific membrane glycoprotein that translocates cytosolic proteins containing a KFERQ-like peptide motif across the lysosomal membrane. Drosophila reportedly lack CMA and use endosomal microautophagy (eMI) as an alternative selective autophagic process. Here we report that neuronal expression of human LAMP2A protected Drosophila against starvation and oxidative stress, and delayed locomotor decline in aging flies without extending their lifespan. LAMP2A also prevented the progressive locomotor and oxidative defects induced by neuronal expression of PD-associated human SNCA (synuclein alpha) with alanine-to-proline mutation at position 30 (SNCA). Using KFERQ-tagged fluorescent biosensors, we observed that LAMP2A expression stimulated selective autophagy in the adult brain and not in the larval fat body, but did not increase this process under starvation conditions. Noteworthy, we found that neurally expressed LAMP2A markedly upregulated levels of Drosophila Atg5, a key macroautophagy initiation protein, and that it increased the density of Atg8a/LC3-positive puncta, which reflects the formation of autophagosomes. Furthermore, LAMP2A efficiently prevented accumulation of the autophagy defect marker Ref(2)P/p62 in the adult brain under acute oxidative stress. These results indicate that LAMP2A can potentiate autophagic flux in the Drosophila brain, leading to enhanced stress resistance and neuroprotection.
ABBREVIATIONS
Act5C: actin 5C; a.E.: after eclosion; Atg5: autophagy-related 5; Atg8a/LC3: autophagy-related 8a; CMA: chaperone-mediated autophagy; DHE: dihydroethidium; elav: embryonic lethal abnormal vision; eMI: endosomal microautophagy; ESCRT: endosomal sorting complexes required for transport; GABARAP: GABA typeA receptor-associated protein; Hsc70-4: heat shock protein cognate 4; HSPA8/Hsc70: heat shock protein family A (Hsp70) member 8; LAMP2: lysosomal associated membrane protein 2; MDA: malondialdehyde; PA-mCherry: photoactivable mCherry; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PD: Parkinson disease; Ref(2)P/p62: refractory to sigma P; ROS: reactive oxygen species; RpL32/rp49: ribosomal protein L32; RT-PCR: reverse transcription polymerase chain reaction; SING: startle-induced negative geotaxis; SNCA/α-synuclein: synuclein alpha; SQSTM1/p62: sequestosome 1; TBS: Tris-buffered saline; UAS: upstream activating sequence.
Topics: Animals; Animals, Genetically Modified; Autophagy; Brain; Disease Models, Animal; Drosophila; Humans; Locomotion; Lysosomal-Associated Membrane Protein 2; Neuroprotection; Oxidative Stress; Parkinson Disease; Phenotype; Signal Transduction; alpha-Synuclein
PubMed: 29989488
DOI: 10.1080/15548627.2018.1491489 -
Molecular Cell Mar 2021Autophagy deficiency in fed conditions leads to the formation of protein inclusions highlighting the contribution of this lysosomal delivery route to cellular...
Autophagy deficiency in fed conditions leads to the formation of protein inclusions highlighting the contribution of this lysosomal delivery route to cellular proteostasis. Selective autophagy pathways exist that clear accumulated and aggregated ubiquitinated proteins. Receptors for this type of autophagy (aggrephagy) include p62, NBR1, TOLLIP, and OPTN, which possess LC3-interacting regions and ubiquitin-binding domains (UBDs), thus working as a bridge between LC3/GABARAP proteins and ubiquitinated substrates. However, the identity of aggrephagy substrates and the redundancy of aggrephagy and related UBD-containing receptors remains elusive. Here, we combined proximity labeling and organelle enrichment with quantitative proteomics to systematically map the autophagic degradome targeted by UBD-containing receptors under basal and proteostasis-challenging conditions in human cell lines. We identified various autophagy substrates, some of which were differentially engulfed by autophagosomal and endosomal membranes via p62 and TOLLIP, respectively. Overall, this resource will allow dissection of the proteostasis contribution of autophagy to numerous individual proteins.
Topics: Autophagosomes; Autophagy; Autophagy-Related Proteins; HEK293 Cells; HeLa Cells; Humans; Protein Interaction Maps; Proteolysis; Proteomics; Proteostasis; Ubiquitination
PubMed: 33545068
DOI: 10.1016/j.molcel.2021.01.009 -
Molecular Cell Apr 2022Organelles are continuously turned over as part of cellular homeostasis and adaptation. Most organelles, even including the nucleus, are degraded by lysosomes via...
Organelles are continuously turned over as part of cellular homeostasis and adaptation. Most organelles, even including the nucleus, are degraded by lysosomes via different pathways, such as macroautophagy, microautophagy, organelle-derived vesicle degradation, and crinophagy. In some specific cases-for example, in lens fiber cells-organelles are degraded by cytosolic phospholipases. To view this SnapShot, open or download the PDF.
Topics: Autophagy; Cytosol; Lens, Crystalline; Lysosomes; Organelles
PubMed: 35452619
DOI: 10.1016/j.molcel.2022.03.015 -
Cellular and Molecular Life Sciences :... Apr 2012Microautophagy, the non-selective lysosomal degradative process, involves direct engulfment of cytoplasmic cargo at a boundary membrane by autophagic tubes, which... (Review)
Review
Microautophagy, the non-selective lysosomal degradative process, involves direct engulfment of cytoplasmic cargo at a boundary membrane by autophagic tubes, which mediate both invagination and vesicle scission into the lumen. With its constitutive characteristics, microautophagy of soluble substrates can be induced by nitrogen starvation or rapamycin via regulatory signaling complex pathways. The maintenance of organellar size, membrane homeostasis, and cell survival under nitrogen restriction are the main functions of microautophagy. In addition, microautophagy is coordinated with and complements macroautophagy, chaperone-mediated autophagy, and other self-eating pathways. Three forms of selective microautophagy, including micropexophagy, piecemeal microautophagy of the nucleus, and micromitophagy, share common ground with microautophagy to some degree. As the accumulation of experimental data, the precise mechanisms that govern microautophagy are becoming more appreciated. Here, we review the microautophagic molecular machinery, its physiological functions, and relevance to human diseases, especially in diseases involving multivesicular bodies and multivesicular lysosomes.
Topics: Animals; Autophagy; Cytoplasmic Vesicles; Homeostasis; Humans; Signal Transduction
PubMed: 22080117
DOI: 10.1007/s00018-011-0865-5 -
Current Genetics Aug 2020Proteasomes are highly abundant protein complexes that are responsible for most regulated protein degradation in cells under favorable growth conditions. When yeast... (Review)
Review
Proteasomes are highly abundant protein complexes that are responsible for most regulated protein degradation in cells under favorable growth conditions. When yeast cells are under nutritional stress, most proteasomes exit the nucleus and either accumulate in cytoplasmic condensates called proteasome storage granules (PSGs) or are directed to the vacuole by autophagy. Nitrogen starvation does not cause PSG formation but leads to degradation of proteasomes through the classical macroautophagy pathway. By contrast, carbon starvation or extended incubation in stationary phase results in both PSG formation and macroautophagy of proteasomes. Unexpectedly, we found that glucose limitation also causes proteasomes to be taken up directly into vacuoles by a microautophagy mechanism. Macro- and micro-autophagy occur in parallel in glucose-starved cells, and microautophagy appears biased toward aberrant or inactive proteasomes, leaving functional proteasomes to accumulate in PSGs. PSGs dissolve and proteasomes remobilize to the nucleus within minutes after glucose refeeding. We showed that AMP-activated protein kinase (AMPK) and endosomal-sorting-complex-required-for-transport (ESCRT) factors are required for proteasome microautophagy and also impact PSG dissipation and nuclear reimport of proteasomes after glucose refeeding. The insoluble protein deposit (IPOD) compartment provides an alternative means of proteasome homeostasis, including when microautophagy is impaired. Our findings reveal a surprising diversity of mechanisms for proteasome quality and quantity control during starvation. A mechanistic understanding of the AMPK-regulated ESCRT-mediated microautophagy pathway could provide new avenues for manipulating proteasome homeostasis and treating human disease.
Topics: AMP-Activated Protein Kinases; Cytoplasm; Glucose; Microautophagy; Proteasome Endopeptidase Complex; Proteostasis
PubMed: 32077993
DOI: 10.1007/s00294-020-01059-x -
Frontiers in Oncology 2022The endosomal sorting complex required for transport (ESCRT) machinery plays a key role in the repair of damaged plasma membranes with puncta form and removes pores from... (Review)
Review
The endosomal sorting complex required for transport (ESCRT) machinery plays a key role in the repair of damaged plasma membranes with puncta form and removes pores from the plasma membrane in regulated cell death, apoptosis, necroptosis, pyroptosis, ferroptosis, and autophagy. ESCRT-I overexpression and ESCRT-III-associated charged multivesicular body protein (CHMP) 4B participate in apoptosis, and the ESCRT-1 protein TSG 101 maintains low levels of ALIX and ALG-2 and prevents predisposition to apoptosis. The ESCRT-III components CHMP2A and CHMP4B are recruited to broken membrane bubble sites with the requirement of extracellular Ca, remove membrane vesicles from cells, and delay the time required for active MLKL to mediate necroptosis, thus preserving cell survival. CHMP4B disturbed pyroptosis by recruiting around the plasma membrane neck to remove the GSDMD pores and preserve plasma membrane integrity depending on Ca influx. The accumulation of the ESCRT-III subunits CHMP5 and CHMP6 in the plasma membrane is increased by the classical ferroptosis activators erastin-1 and ras-selective lethal small molecule 3 (RSL3) upon cytosolic calcium influx and repairs the ferroptotic plasma membrane. ESCRT-III- and VPS4-induced macroautophagy, ESCRT-0-initiated microautophagy. ESCRT-I, ESCRT-II, ESCRT-III, ALIX, and VPS4A are recruited to damaged lysosomes and precede lysophagy, indicating that ESCRT is a potential target to overcome drug resistance during tumor therapy.
PubMed: 36330465
DOI: 10.3389/fonc.2022.1007446 -
Cell Discovery 2020Autophagy is a major intracellular degradation system that derives its degradative abilities from the lysosome. The most well-studied form of autophagy is... (Review)
Review
Autophagy is a major intracellular degradation system that derives its degradative abilities from the lysosome. The most well-studied form of autophagy is macroautophagy, which delivers cytoplasmic material to lysosomes via the double-membraned autophagosome. Other forms of autophagy, namely chaperone-mediated autophagy and microautophagy, occur directly on the lysosome. Besides providing the means for degradation, lysosomes are also involved in autophagy regulation and can become substrates of autophagy when damaged. During autophagy, they exhibit notable changes, including increased acidification, enhanced enzymatic activity, and perinuclear localization. Despite their importance to autophagy, details on autophagy-specific regulation of lysosomes remain relatively scarce. This review aims to provide a summary of current understanding on the behaviour of lysosomes during autophagy and outline unexplored areas of autophagy-specific lysosome research.
PubMed: 32047650
DOI: 10.1038/s41421-020-0141-7 -
International Journal of Molecular... Sep 2019Peroxisomes are cell organelles that play an important role in plants in many physiological and developmental processes. The plant peroxisomes harbor enzymes of the... (Review)
Review
Peroxisomes are cell organelles that play an important role in plants in many physiological and developmental processes. The plant peroxisomes harbor enzymes of the β-oxidation of fatty acids and the glyoxylate cycle; photorespiration; detoxification of reactive oxygen and nitrogen species; as well as biosynthesis of hormones and signal molecules. The function of peroxisomes in plant cells changes during plant growth and development. They are transformed from organelles involved in storage lipid breakdown during seed germination and seedling growth into leaf peroxisomes involved in photorespiration in green parts of the plant. Additionally, intensive oxidative metabolism of peroxisomes causes damage to their components. Therefore, unnecessary or damaged peroxisomes are degraded by selective autophagy, called pexophagy. This is an important element of the quality control system of peroxisomes in plant cells. Despite the fact that the mechanism of pexophagy has already been described for yeasts and mammals, the molecular mechanisms by which plant cells recognize peroxisomes that will be degraded via pexophagy still remain unclear. It seems that a plant-specific mechanism exists for the selective degradation of peroxisomes. In this review, we describe the physiological role of pexophagy in plant cells and the current hypotheses concerning the mechanism of plant pexophagy.
Topics: Autophagy; Macroautophagy; Microautophagy; Oxidative Stress; Peroxisomes; Plant Physiological Phenomena; Plants; Sugars
PubMed: 31557865
DOI: 10.3390/ijms20194754 -
International Journal of Molecular... Jun 2020Nucleophagy, the selective subtype of autophagy that targets nuclear material for autophagic degradation, was not only shown to be a model system for the study of... (Review)
Review
Nucleophagy, the selective subtype of autophagy that targets nuclear material for autophagic degradation, was not only shown to be a model system for the study of selective macroautophagy, but also for elucidating the role of the core autophagic machinery within microautophagy. Nucleophagy also emerged as a system associated with a variety of disease conditions including cancer, neurodegeneration and ageing. Nucleophagic processes are part of natural cell development, but also act as a response to various stress conditions. Upon releasing small portions of nuclear material, micronuclei, the autophagic machinery transfers these micronuclei to the vacuole for subsequent degradation. Despite sharing many cargos and requiring the core autophagic machinery, recent investigations revealed the aspects that set macro- and micronucleophagy apart. Central to the discrepancies found between macro- and micronucleophagy is the nucleus vacuole junction, a large membrane contact site formed between nucleus and vacuole. Exclusion of nuclear pore complexes from the junction and its exclusive degradation by micronucleophagy reveal compositional differences in cargo. Regarding their shared reliance on the core autophagic machinery, micronucleophagy does not involve normal autophagosome biogenesis observed for macronucleophagy, but instead maintains a unique role in overall microautophagy, with the autophagic machinery accumulating at the neck of budding vesicles.
Topics: Animals; Autophagy; Cell Nucleus; Humans; Microautophagy; Nuclear Proteins; Vacuoles
PubMed: 32599961
DOI: 10.3390/ijms21124506 -
MedComm Oct 2023Chaperone-mediated autophagy (CMA) is a lysosomal degradation pathway that eliminates substrate proteins through heat-shock cognate protein 70 recognition and... (Review)
Review
Chaperone-mediated autophagy (CMA) is a lysosomal degradation pathway that eliminates substrate proteins through heat-shock cognate protein 70 recognition and lysosome-associated membrane protein type 2A-assisted translocation. It is distinct from macroautophagy and microautophagy. In recent years, the regulatory mechanisms of CMA have been gradually enriched, including the newly discovered NRF2 and p38-TFEB signaling, as positive and negative regulatory pathways of CMA, respectively. Normal CMA activity is involved in the regulation of metabolism, aging, immunity, cell cycle, and other physiological processes, while CMA dysfunction may be involved in the occurrence of neurodegenerative disorders, tumors, intestinal disorders, atherosclerosis, and so on, which provides potential targets for the treatment and prediction of related diseases. This article describes the general process of CMA and its role in physiological activities and summarizes the connection between CMA and macroautophagy. In addition, human diseases that concern the dysfunction or protective role of CMA are discussed. Our review deepens the understanding of the mechanisms and physiological functions of CMA and provides a summary of past CMA research and a vision of future directions.
PubMed: 37655052
DOI: 10.1002/mco2.347