Autophagy最新文献

Parkinson disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra, primarily due to mitochondria dysfunction. PRKN (parkin RBR E3 ubiquitin protein ligase) and PINK1 (PTEN induced kinase 1) are linked to early-onset cases of PD and essential for the clearance of damaged mitochondria via selective mitochondrial autophagy (mitophagy). In a recent publication, we detail how a small molecule can activate PRKN mutants that are unable to be phosphorylated, restoring mitophagy in cellular assays. These findings offer hope for the design of therapeutic drugs for some forms of PD.

Macroautophagy is a catabolic process that maintains cellular homeostasis by recycling intracellular material through the use of double-membrane vesicles called autophagosomes. In turn, autophagosomes fuse with vacuoles (in yeast and plants) or lysosomes (in metazoans), where resident hydrolases degrade the cargo. Given the conservation of autophagy, Saccharomyces cerevisiae is a valuable model organism for deciphering molecular details that define macroautophagy pathways. In yeast, macroautophagic pathways fall into two subclasses: selective and nonselective (bulk) autophagy. Bulk autophagy is predominantly upregulated following TORC1 inhibition, triggered by nutrient stress, and degrades superfluous random cytosolic proteins and organelles. In contrast, selective autophagy pathways maintain cellular homeostasis when TORC1 is active by degrading damaged organelles and dysfunctional proteins. Here, selective autophagy receptors mediate cargo delivery to the vacuole. Now, two groups have discovered a new hybrid autophagy mechanism, coined cargo hitchhiking autophagy (CHA), that uses autophagic receptor proteins to deliver selected cargo to phagophores built in response to nutrient stress for the random destruction of cytosolic contents. In CHA, various autophagic receptors link their cargos to lipidated Atg8, located on growing phagophores. In addition, the sorting nexin heterodimer Snx4-Atg20 assists in the degradation of cargo during CHA, possibly by aiding the delivery of cytoplasmic cargos to phagophores and/or by delaying the closure of expanding phagophores. This review will outline this new mechanism, also known as Snx4-assisted autophagy, that degrades an assortment of cargos in yeast, including transcription factors, glycogen, and a subset of ribosomal proteins.

DBI/ACBP is a phylogenetically ancient hormone that stimulates appetite and lipo-anabolism. In response to starvation, DBI/ACBP is secreted through a noncanonical, macroautophagy/autophagy-dependent pathway. The physiological hunger reflex involves starvation-induced secretion of DBI/ACBP from multiple cell types. DBI/ACBP concentrations subsequently increase in extracellular fluids to stimulate food intake. Recently, we observed that glucocorticoids, which are endogenous stress hormones as well as anti-inflammatory drugs, upregulate DBI/ACBP expression at the transcriptional level and stimulate autophagy in hepatocytes, thereby causing a surge in circulating DBI/ACBP levels. Prolonged increase in glucocorticoid concentrations causes an extreme form of metabolic syndrome, dubbed "Cushing syndrome", which is characterized by clinical features including hyperphagia, hyperdipsia, dyslipidemia, hyperinsulinemia, insulin resistance, lipodystrophy, visceral adiposity, steatosis, sarcopenia and osteoporosis. Mice and patients with Cushing syndrome exhibit supraphysiological DBI/ACBP plasma levels. Of note, neutralization of extracellular DBI/ACBP protein with antibodies or mutation of the DBI/ACBP receptor (i.e. the GABRG2 subunit of GABR [gamma-aminobutyric acid type A receptor]) renders mice resistant to the induction of Cushing syndrome. Similarly, knockout of Dbi/Acbp in hepatocytes suppresses the corticotherapy-induced surge in plasma DBI/ACBP concentrations and prevents the manifestation of most of the characteristics of Cushing syndrome. We conclude that autophagy-mediated secretion of DBI/ACBP by hepatocytes constitutes a critical step of the pathomechanism of Cushing syndrome. It is tempting to speculate that stress-induced chronic elevations of endogenous glucocorticoids also compromise human health due to the protracted augmentation of circulating DBI/ACBP concentrations.Abbreviations: DBI/ACBP: diazepam binding inhibitor, acyl-CoA binding protein; GABA: gamma-aminobutyric acid; GABAR: gamma-aminobutyric acid type A receptor; GABRG2: gamma-aminobutyric acid type A receptor subunit gamma2.

Recent key technological developments, such as super-resolution microscopy and microfabrication, enabled investigation of biological processes, including macroautophagy/autophagy, with unprecedented spatiotemporal resolution and control over experimental conditions. Such disruptive innovations deepened our capability to provide mechanistic understandings of the autophagic process and its causes. This addendum aims to expand the guidelines on autophagy in three key directions: optical methods enabling visualization of autophagic machinery beyond the diffraction-limited resolution; bioengineering enabling accurate designs and control over experimental conditions; and theoretical advances in mechanobiology connecting autophagy and mechanical processes of the cell. Abbreviation: 3D: three-dimensional; SIM: structured illumination microscopy; STORM: stochastic optical reconstruction microscopy.

Metabolic reprogramming is pivotal in cancer stem cell (CSC) self-renewal. However, the intricate regulatory mechanisms governing the crosstalk between metabolic reprogramming and liver CSCs remain elusive. Here, using a metabolic CRISPR-Cas9 knockout screen, we identify ATP6V1D, a subunit of the vacuolar-type H⁺-translocating ATPase (V-ATPase), as a key metabolic regulator of hepatocellular carcinoma (HCC) stemness. Elevated ATP6V1D expression correlates with poor clinical outcomes in HCC patients. ATP6V1D knockdown inhibits HCC stemness and malignant progression both in vitro and in vivo. Mechanistically, ATP6V1D enhances HCC stemness and progression by maintaining macroautophagic/autophagic flux. Specifically, ATP6V1D not only promotes lysosomal acidification, but also enhances the interaction between CHMP4B and IST1 to foster ESCRT-III complex assembly, thereby facilitating autophagosome-lysosome fusion to maintain autophagic flux. Moreover, silencing CHMP4B or IST1 attenuates HCC stemness and progression. Notably, low-dose bafilomycin A₁ targeting the V-ATPase complex shows promise as a potential therapeutic strategy for HCC. In conclusion, our study highlights the critical role of ATP6V1D in driving HCC stemness and progression via the autophagy-lysosomal pathway, providing novel therapeutic targets and approaches for HCC treatment.Abbreviations: 3-MA: 3-methyladenine; ANT: adjacent normal liver tissues; ATP6V1D: ATPase H+ transporting V1 subunit D; BafA1: bafilomycin A₁; CHMP: charged multivesicular body protein; co-IP: co-immunoprecipitation; CSC: cancer stem cell; ESCRT: endosomal sorting complex required for transport; HCC: hepatocellular carcinoma; IF: immunofluorescence; IHC: immunohistochemical; LCSCs: liver cancer stem cells; qRT-PCR: quantitative real time PCR; V-ATPase: vacuolar-type H⁺- translocating ATPase; WB: western blot.

Macroautophagy/autophagy is a highly conserved catabolic process in eukaryotes and plays pivotal roles in regulating male fertility and sexual reproduction. In metazoans, mutations in core ATG (autophagy related) proteins frequently result in severe defects in sperm formation and maturation, resulting in male sterility. In contrast, autophagy has traditionally been considered dispensable for reproduction in Arabidopsis thaliana, as most atg mutants can complete fertilization and produce viable progeny without apparent reproductive defects. We recently systematically re-assessed the role of autophagy in Arabidopsis male gametophyte development and fertility using atg5 and atg7 mutants, and the double mutant. These mutants exhibited partial defects in pollen germination, pollen tube growth and seed production compared to the wild type (WT). Furthermore, our findings reveal that autophagy is essential for modulating actin dynamic organization during sperm cell formation within pollen grains and for supporting pollen tube elongation. This is achieved through the selective degradation of actin depolymerizing factors ADF7 and PFN2/Profilin2. NBR1 is identified as a key receptor mediating this process. This study provides valuable insights into the evolutionary conservation and functional divergence of autophagy in modulating male fertility, highlighting distinctions between plant and mammalian systems.

Melanosomes play a pivotal role in skin color and photoprotection. In contrast to the well-elucidated pathway of melanosome biogenesis, the process of melanosome degradation, referred to as melanophagy, is largely unexplored. Previously, we discovered that 3,4,5-trimethoxycinnamate thymol ester (TCTE) effectively inhibits skin pigmentation by activating melanophagy. In this study, we discovered a new regulatory signaling cascade that controls melanophagy in TCTE-treated melanocytes. ITCH (itchy E3 ubiquitin protein ligase) facilitates ubiquitination of the melanosome membrane protein MLANA (melan-A) during TCTE-induced melanophagy. This ubiquitinated MLANA is then recognized by an autophagy receptor protein, OPTN (optineurin). Additionally, a phospho-kinase antibody array revealed that TCTE activates PTK2 (protein tyrosine kinase 2), which phosphorylates ITCH, enhancing the ubiquitination of MLANA. Furthermore, inhibition of either PTK2 or ITCH disrupts the ubiquitination of MLANA and the MLANA-OPTN interaction in TCTE-treated cells. Taken together, our findings highlight the critical role of the PTK2-ITCH-MLANA-OPTN cascade in orchestrating melanophagy progression.Abbreviations: α-MSH: alpha-melanocyte-stimulating hormone; dichlone: 2,3-dichloro-1,4-naphthoquinone; ITCH: itchy E3 ubiquitin protein ligase; MITF: melanocyte inducing transcription factor; MLANA: melan-A; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PINK1: PTEN induced kinase 1; PTK2: protein tyrosine kinase 2; SQSTM1/p62: sequestosome 1; TCTE: 3,4,5-trimethoxycinnamate thymol ester; TPC2: two pore segment channel 2; VDAC1: voltage dependent anion channel 1.

Intrinsically disordered regions (IDRs) are crucial to homeostatic and organellar remodeling pathways. In reticulophagy/ER-phagy, long cytosolic IDR-containing receptors (e.g. RETREG1/FAM134B) house the LC3-interacting region (LIR) motif to recruit the phagophore. The precise functions of the IDR beyond engaging the autophagic machinery are unclear. Here, we comment on the role of the RETREG1-IDR based on our recent computer modeling and molecular dynamics (MD) simulations. Extensive analysis of the RETREG1-IDR indicates a continuum of conformations between expanded and compact structures, displaying a Janus-like feature. Using an adapted MARTINI model, we find that the IDR ensemble properties vary widely depending on the membrane anchor. IDRs alone are sufficient to promote and sense membrane curvature and can act as entropic tethers. When anchored to the Reticulon homology domain (RHD), they adopt compact collapsed conformations, acting as effector scaffolds that amplify RHD membrane remodeling properties, enhancing receptor-clustering and accelerating spontaneous budding. These findings expand the operational scope of IDRs within reticulophagy, offering fresh insights into a mechanistic understanding of membrane remodeling.

Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB), remains a significant global health challenge. Mtb is transmitted by respiratory aerosols and infects a variety of myeloid populations. Our recent study shows that the Mtb virulence lipid phthiocerol dimycocerosate (PDIM) promotes the intracellular survival of Mtb in macrophages by inhibiting NADPH oxidase, thereby impairing LC3-associated phagocytosis, and in vivo PDIM also antagonizes canonical macroautophagy/autophagy. In addition, mice defective in autophagy in myeloid cells fail to develop B-cell follicles in the lungs during chronic infection. Here, we present a summary of our recent publication, highlighting the most significant findings and discussing how they provide new insight into the role of autophagy and the diversity of lung myeloid cells in the pathogenesis of Mtb.