Autophagy reports最新文献

The molecular and functional characterization of the thousands of uncoated intracellular transport vesicles inside cells is a major challenge. Intracellular nanovesicles (INVs) are a large and molecularly heterogenous family of uncoated transport vesicles, which are comprised of multiple subtypes. As a step to characterizing these subtypes, we recently published the first INV proteome and were intrigued by the enrichment of ATG9A in it. ATG9A is the only conserved transmembrane protein with a core function in macroautophagy/autophagy, and it is found on small, uncoated vesicles, termed "ATG9A-positive vesicles". We therefore, set out to disambiguate the relationship between these two types of vesicular carriers in cells. We showed that ATG9A-containing vesicles, rather than being a distinct vesicle class, represent one subset of the INV family. We also demonstrated that this relationship is functionally important and that perturbing INV-mediated trafficking impeded starvation-induced autophagy. Here, we briefly introduce INVs, summarize the evidence supporting our definition of ATG9A-flavor INVs and present our outlook on why we hope that this classification will help to consolidate efforts to understand the functions of these vesicles in autophagy and beyond.

Neurons, as post-mitotic and long-lived cells, rely heavily on autophagy to maintain cellular homoeostasis and ensure proper function. Huntingtin (HTT), a protein central to Huntington's disease (HD), has emerged as a putative multifunctional regulator within the neuronal autophagy-lysosome pathway. This review explores normal HTT's multifaceted role in neuronal autophagy, from its potential involvement in autophagy induction, its capacity to influence cargo recognition and autophagosome formation, and its contribution to autophagosome-lysosome fusion and transport. We also discuss the unique challenges that neurons face in maintaining proteostasis through autophagy, emphasising the need for specialised mechanisms like axonal transport of autophagosomes and distinct regulatory pathways. Furthermore, we highlight the spatial and temporal regulation of neuronal autophagy, particularly in the context of ageing and neuronal maturation, underscoring the importance of understanding HTT's role in different neuronal states. By elucidating the intricate relationship between HTT and neuronal autophagy, this review aims to shed light on specific mechanisms of action in autophagy that can be disrupted in neurodegenerative diseases including HD.

Quiescence is a conserved, reversible state of proliferative arrest, characterized by changes in cell physiology and metabolism. Many cells spend a considerable part of their lifetime in quiescence, including adult stem cells or microorganisms facing unfavorable environmental conditions. Cells can remain quiescent for long periods of time while retaining their viability and reproductive capacity, indicating a need to maintain protein homeostasis. Given the changes in intracellular organization, it has been unclear how protein quality control (PQC) functions in quiescent cells. In our recent study, we examined model misfolded proteins expressed in glucose-depleted quiescent yeast cells and found that quiescent cells maintain an active PQC that relies primarily on selective protein degradation, requiring the ubiquitin-proteasome system, intact nucleus-vacuole junctions and autophagy. Our results highlight the relevance of mitigating misfolded proteins in quiescence.

Monitoring the delivery of single proteins and protein complexes to the vacuole by autophagy or other processes in yeast Saccharomyces cerevisiae mainly relies on western blot or fluorescence microscopy analyses using endogenous tagging of the protein of interest with GFP. However, these approaches are semi-quantitative and next to impossible with proteins of low abundancy because of the insensitive nature of the methods. Here, we describe the creation of a new PCR-based integration cassette to endogenously tag specific proteins with the truncated version of the vacuolar phosphatase Pho8. The vacuolar activation of Pho8 allows the quantitative measurement of vacuolar delivery using a colorimetric enzymatic assay. This approach has the advantages of a more quantitative interpretation of data and relies on the appearance of a signal rather than its disappearance. As a proof-of-principle, we examined the vacuolar delivery of known cargoes of bulk autophagy and endocytosis. This new system will be of great value to the whole community working within the field of autophagy and other transport pathways to the vacuole.

Hydrolytic enzymes within lysosomes maintain cell and tissue homoeostasis by degrading macromolecules delivered by endocytosis and autophagy. The release of lysosomal enzymes into the cytosol can induce apoptosis and "lysosome-dependent cell death" making it important for damaged lysosomes to be repaired or removed. Extensive lysosome damage exposes luminal sugars to galectin-dependent autophagy pathways that use ATG16L1:ATG5-ATG12 complex to conjugate LC3/ATG8 to autophagosomes to facilitate removal by lysophagy. Sphingomyelin exposed on stressed lysosomes recruits the lysosome tethering protein TECPR1 (tectonin beta propeller repeat-containing protein) allowing an alternative TECRP1:ATG5-ATG12 complex to conjugate LC3 directly to lysosomes. Here we have used cells lacking ATG16L1 to follow the recruitment of TECPR1, galectin-3 and LC3/ATG8 to lysosomes in response to osmotic imbalance induced by chloroquine. TECPR1 was recruited to swollen lysosomes that exposed sphingomyelin. LC3II was absent from swollen lysosomes but located to small puncta that contained the V-ATPase and LAMP1. The presence of galectin-3 and PI4P in the small LC3 puncta suggested that the TECPR1:ATG5-ATG12 complex conjugates LC3 to lysosome remnants that have ruptured in response to osmotic imbalance.

The E3-like complex Atg12-Atg5-Atg16, which promotes Atg8 lipidation, is recruited to the autophagosomal membrane through the interaction of Atg16 with the PROPPIN/WIPI protein Atg21, as well as by the binding of Atg12 to Atg17, the scaffold protein of the Atg1 kinase complex in yeast. In order to gain insights into the molecular basis of Atg12-Atg17 interaction, we performed reverse two-hybrid screens to identify key-binding residues in both proteins and, based on these data, model the structure of this protein complex. Strikingly, we found that the Atg17 binding site in Atg12 overlaps with a PKA phosphorylation site and that PKA phosphorylation of Atg12 prevents Atg17 binding, revealing a new regulatory mechanism by which PKA regulates the assembly of the autophagy machinery.

Malaria parasites encounter diverse conditions as they transition between mosquito and mammalian hosts. A characteristic of the sporozoite stage of the parasite is that once it enters the hepatocyte, it changes its morphology and metabolism. Motile-elongated sporozoites transform into round trophozoites, discard unnecessary organelles, undergo extensive replication, and mature into hepatic merozoites. However, the mechanisms of superfluous organelle elimination and apicoplast biogenesis are unclear. In our latest study, using a conditional mutagenesis system, we clarified the role of Atg7 during parasite metamorphosis in the liver. We found that cytosolic Atg7 is essential for the localization of Atg8 on the membrane and the development of parasites in the blood and liver stages. Parasites lacking Atg7 fail to lipidate Atg8 on the membrane, which leads to impaired exocytosis of micronemes, and parasites eventually fail to mature into hepatic merozoites. This work provides insights into the essential role of Atg7 in maintaining parasite cellular homeostasis during liver stage development.

Autophagy has been implicated in various cellular processes, including non-conventional secretion. Our previous findings suggest that ATP is loaded into amphisomes and secreted upon autophagy stimulation at focal adhesion sites in a VAMP7-dependent manner. Here, we demonstrate that the knockout (KO) of VAMP7, along with its partners RAB21 and its guanine nucleotide exchange factor (GEF) VARP, inhibits ATP release, indicating a key role for this pathway in amphisome secretion. Constitutively inactive RAB21 also inhibited ATP secretion. RAB21 overexpression rescued starvation-induced ATP secretion in RAB21 KO, but not in VAMP7 or VARP KO cells. RAB21-LC3-positive vesicles redistributed to the cell periphery upon starvation. KO cells and overexpression experiments showed that RAB21 plays a positive role in autophagosome biogenesis, particularly in controlling the number of LC3-II- and DFCP1-positive structures upon starvation, suggesting a role in the early steps of autophagosome formation. Accordingly, VARP partially colocalized with LC3 upon starvation. Together, these findings identify a novel role for RAB21 in regulating autophagic ATP secretion likely in amphisome biogenesis and their localization in the cell periphery.

Alzheimer disease (AD) is the most common form of dementia with hallmarks of β-amyloid deposits, neurofilament tangles, synaptic loss and neuronal death in the patient's brain. AD is a heavy burden in an ageing society as there are no effective therapies in treating the causes or slowing down its progression. Autophagy is a conserved process through formation of double membrane structure, namely autophagosome which is delivered to lysosome to digest cellular disposals. Autophagy maintains homoeostasis in the brain and is generally considered to protect brain functions against ageing. The first evidence of autophagy involvement in AD is that there is decreased expression of autophagy essential genes in post-mortem AD brains. Autophagy is also believed to be protective in neurodegeneration. However, the molecular and cellular mechanisms for dysfunction of autophagy in AD are not fully understood. Recent studies of autophagy regulation in AD cover the findings not only in neurons, but also from fast growing evidence for their importance in glia and brain vascular system. Thus, this review composes pertinent information regarding the involvement of autophagy in neurons, glias (including microglia, astrocyte, and oligodendrocyte), and brain vascular cells in AD, and their unique cellular mechanisms of this connection in AD pathology. We will provide effectual insights both in investigating autophagy in AD pathological mechanisms and in establishing a strategic approach for developing autophagy-based AD therapies.

Cellular homeostasis depends on a multitude of cellular functions, which in turn depend on the clearance of damaged components for their maintenance. Lysosomes being one of the main sites of recycling, are at the frontline for cellular protein degradation, which leads to generation of protein building blocks, the amino acids (AAs), within the lysosomal lumen. However, the fate of these lysosomal pool of AAs are only partly known. Recently, studies from our and other groups have led to the finding that AA can be stored in lysosomes and revealed a homeostatic communication of these storages with the environment. Thus, lysosome appear to be a nutritional signaling hub that has a dual role. As a degradation-competent hydrolytic sack, lysosomes have a long-studied degradative function, additionally now they can either store or channel into utilization of the AAs generated through their proteolytic activity. Since the existence of a lysosomal AA storage pool has been determined by changing the levels of extracellular AAs, this indicates a multi-directional homeostatic communication between the lysosome and the extracellular environment. This Lysosomal homeostatic and adaptive response to the niche could be vital for life-threatening age-related degenerative disorders, where the lysosome-autophagy pathway and the microenvironmental cues play major roles in the disease progression, which will be discussed further in this piece.