Explore the vast range of titles available.

Selective autophagy ensures the removal of specific soluble proteins, protein aggregates, damaged mitochondria, and invasive bacteria from cells. Defective autophagy has been directly linked to metabolic disorders. However how selective autophagy regulates metabolism remains largely uncharacterized. Here we show that a deficiency in selective autophagy is associated with suppression of lipid oxidation. Hepatic loss of Atg7 or Atg5 significantly impairs the production of ketone bodies upon fasting, due to decreased expression of enzymes involved in β-oxidation following suppression of transactivation by PPARα. Mechanistically, nuclear receptor co-repressor 1 (NCoR1), which interacts with PPARα to suppress its transactivation, binds to the autophagosomal GABARAP family proteins and is degraded by autophagy. Consequently, loss of autophagy causes accumulation of NCoR1, suppressing PPARα activity and resulting in impaired lipid oxidation. These results suggest that autophagy contributes to PPARα activation upon fasting by promoting degradation of NCoR1 and thus regulates β-oxidation and ketone bodies production. Defective autophagy has been associated with metabolic disorders. Here Saito et al. show that autophagy promotes the selective degradation of NCoR1, a repressor of lipid metabolism regulator PPARα, in response to starvation, and thus induces the expression of enzymes involved in lipid oxidation and the production of ketone bodies.

Sensing and clearance of dysfunctional lysosomes is critical for cellular homeostasis. Here we show that transcription factor EB (TFEB)—a master transcriptional regulator of lysosomal biogenesis and autophagy—is activated during the lysosomal damage response, and its activation is dependent on the function of the ATG conjugation system, which mediates LC3 lipidation. In addition, lysosomal damage triggers LC3 recruitment on lysosomes, where lipidated LC3 interacts with the lysosomal calcium channel TRPML1, facilitating calcium efflux essential for TFEB activation. Furthermore, we demonstrate the presence and importance of this TFEB activation mechanism in kidneys in a mouse model of oxalate nephropathy accompanying lysosomal damage. A proximal tubule-specific TFEB-knockout mouse exhibited progression of kidney injury induced by oxalate crystals. Together, our results reveal unexpected mechanisms of TFEB activation by LC3 lipidation and their physiological relevance during the lysosomal damage response.Nakamura et al. find that the master transcriptional regulator of lysosomal biogenesis and autophagy TFEB is activated following LC3 lipidation during lysosomal damage and show the importance of this mechanism during kidney injury.

Cyclic GMP-AMP (cGAMP) synthase (cGAS) detects infections or tissue damage by binding to microbial or self DNA in the cytoplasm 1 . Upon binding DNA, cGAS produces cGAMP that binds to and activates the adaptor protein STING, which then activates the kinases IKK and TBK1 to induce interferons and other cytokines 2 – 6 . Here we report that STING also activates autophagy through a mechanism that is independent of TBK1 activation and interferon induction. Upon binding cGAMP, STING translocates to the endoplasmic reticulum–Golgi intermediate compartment (ERGIC) and the Golgi in a process that is dependent on the COP-II complex and ARF GTPases. STING-containing ERGIC serves as a membrane source for LC3 lipidation, which is a key step in autophagosome biogenesis. cGAMP induced LC3 lipidation through a pathway that is dependent on WIPI2 and ATG5 but independent of the ULK and VPS34–beclin kinase complexes. Furthermore, we show that cGAMP-induced autophagy is important for the clearance of DNA and viruses in the cytosol. Interestingly, STING from the sea anemone Nematostella vectensis induces autophagy but not interferons in response to stimulation by cGAMP, which suggests that induction of autophagy is a primordial function of the cGAS–STING pathway. The authors report that the cGAS–STING pathway drives a form of autophagy that is independent of interferon induction and distinct from the conventional autophagy.

Background/Aims: Recent studies have indicated that exosomes secreted from adipose-derived stem cells (ADSCs) have important effects in the treatment of ischemic injury. However, the treatment mechanism is unclear. This study aimed to investigate whether ADSC-derived exosomes enriched with microRNA (miR)-30d-5p have a protective effect on acute ischemic stroke (AIS). Methods: In the current study, inflammatory factors and miR-30d-5p expression were assessed in 70 subjects with AIS and 35 healthy controls. Exosomes were characterized by transmission electron microscopy and further examined using nanoparticle tracking analyses. A rat model of AIS and an in vitro model of oxygen- and glucose-deprived (OGD) primary microglia were established to study the protective mechanism of exosomes from miR-30d-5p-overexpressing ADSCs in ischemia-induced nerve injury. Results: The results showed that following AIS, the expression of inflammatory cytokines increased, while the anti-inflammatory cytokines IL-4, IL-10, and miR-30d-5p decreased both in patients and in animal models. Moreover, in vitro studies demonstrated that suppression of autophagy significantly reduced the OGD-induced inflammatory response. In addition, exosome treatment was more effective in suppressing the inflammatory response by reversing OGD-induced and autophagy-mediated microglial polarization to M1. Furthermore, in vivo studies showed that exosomes derived from ADSCs significantly decreased the cerebral injury area of infarction by suppressing autophagy and promoting M2 microglia/macrophage polarization. Conclusions: Our results suggest that miR-30d-5p-enhanced ADSC-derived exosomes prevent cerebral injury by inhibiting autophagy-mediated microglial polarization to M1.

ATG5 and ATG7 are considered to be essential molecules for the induction of autophagy. However, we found that cells lacking ATG5 or ATG7 can still form autophagosomes/autolysosomes and perform autophagic protein degradation when subjected to certain types of stress. Although the lipidation of LC3 is accepted as a good indicator of autophagy, this did not occur during ATG5/ATG7-independent alternative autophagy. Unlike conventional autophagy, autophagosomes appeared to be generated in a Rab9-dependent manner by the fusion of the phagophores with vesicles derived from the trans-Golgi and late endosomes. Therefore, mammalian autophagy can occur via at least two different pathways; the ATG5/ATG7-dependent conventional pathway and an ATG5/ATG7-independent alternative pathway.

Plant chloroplasts constantly accumulate damage caused by visible wavelengths of light during photosynthesis. Our previous study revealed that entire photodamaged chloroplasts are subjected to vacuolar digestion through an autophagy process termed chlorophagy; however, how this process is induced and executed remained poorly understood. In this study, we monitored intracellular induction of chlorophagy in Arabidopsis (Arabidopsis thaliana) leaves and found that mesophyll cells damaged by high visible light displayed abnormal chloroplasts with a swollen shape and 2.5 times the volume of normal chloroplasts. In wild-type plants, the activation of chlorophagy decreased the number of swollen chloroplasts. In the autophagy-deficient autophagy mutants, the swollen chloroplasts persisted, and dysfunctional chloroplasts that had lost chlorophyll fluorescence accumulated in the cytoplasm. Chloroplast swelling and subsequent induction of chlorophagy were suppressed by the application of exogenous mannitol to increase the osmotic pressure outside chloroplasts or by overexpression of VESICLE INDUCING PROTEIN IN PLASTID1, which maintains chloroplast envelope integrity. Microscopic observations of autophagy-related membranes showed that swollen chloroplasts were partly surrounded by autophagosomal structures and were engulfed directly by the tonoplast, as in microautophagy. Our results indicate that an elevation in osmotic potential inside the chloroplast due to high visible light-derived envelope damage results in chloroplast swelling and serves as an induction factor for chlorophagy, and this process mobilizes entire chloroplasts via tonoplast-mediated sequestering to avoid the cytosolic accumulation of dysfunctional chloroplasts.

Selective autophagy is mediated by cargo receptors that link the cargo to the isolation membrane via interactions with Atg8 proteins. Atg8 proteins are localized to the membrane in an ubiquitin-like conjugation reaction, but how this conjugation is coupled to the presence of the cargo is unclear. Here we show that the S. cerevisiae Atg19, Atg34 and the human p62, Optineurin and NDP52 cargo receptors interact with the E3-like enzyme Atg12~Atg5-Atg16, which stimulates Atg8 conjugation. The interaction of Atg19 with the Atg12~Atg5-Atg16 complex is mediated by its Atg8-interacting motifs (AIMs). We identify the AIM-binding sites in the Atg5 subunit and mutation of these sites impairs selective autophagy. In a reconstituted system the recruitment of the E3 to the prApe1 cargo is sufficient to drive accumulation of conjugated Atg8 at the cargo. The interaction of the Atg12~Atg5-Atg16 complex and Atg8 with Atg19 is mutually exclusive, which may confer directionality to the system. A living cell must remove unhealthy or excess material from its interior in order to remain healthy and operational. Cells pack this waste into membrane-bound compartments named autophagosomes in a process called autophagy. So-called autophagy proteins make sure that only the unwanted material is eliminated. However, it was not completely clear how these proteins achieve this. What was known was that proteins called cargo receptors recognize and bind to specific waste materials. At the same time, so-called autophagy enzymes tag the membranes of the autophagosome with a protein known as Atg8, so that cargo receptor molecules can bind this membrane. Now, Fracchiolla, Sawa-Makarska et al. report that, in yeast, an autophagy enzyme links these two events by binding to the cargo receptor and promoting the tagging of the autophagosome’s membrane at the same place. The enzyme in question is a complex made from three autophagy proteins (called Atg12, Atg5 and Atg16), and its activity ensures that the membrane is tagged only next to those materials that need to be disposed of. Although it is now clearer how a cell’s waste ends up in the autophagosome, it is still puzzling how this process is regulated and how the other autophagy-related components contribute to this highly coordinated process. In particular, an important next step will be to find out what is the source of membrane that gives rise to the autophagosome.

Current asthma therapies fail to target airway remodeling that correlates with asthma severity driving disease progression that ultimately leads to loss of lung function. Macroautophagy (hereinafter \"autophagy\") is a fundamental cell-recycling mechanism in all eukaryotic cells; emerging evidence suggests that it is dysregulated in asthma. We investigated the interrelationship between autophagy and airway remodeling and assessed preclinical efficacy of a known autophagy inhibitor in murine models of asthma. Human asthmatic and nonasthmatic lung tissues were histologically evaluated and were immunostained for key autophagy markers. The percentage area of positive staining was quantified in the epithelium and airway smooth muscle bundles using ImageJ software. Furthermore, the autophagy inhibitor chloroquine was tested intranasally in prophylactic (3 wk) and treatment (5 wk) models of allergic asthma in mice. Human asthmatic tissues showed greater tissue inflammation and demonstrated hallmark features of airway remodeling, displaying thickened epithelium (  < 0.001) and reticular basement membrane (  < 0.0001), greater lamina propria depth (  < 0.005), and increased airway smooth muscle bundles (  < 0.001) with higher expression of Beclin-1 (  < 0.01) and ATG5 (autophagy-related gene 5) (  < 0.05) together with reduced p62 (  < 0.05) compared with nonasthmatic control tissues. Beclin-1 expression was significantly higher in asthmatic epithelium and ciliated cells (  < 0.05), suggesting a potential role of ciliophagy in asthma. Murine asthma models demonstrated effective preclinical efficacy (reduced key features of allergic asthma: airway inflammation, airway hyperresponsiveness, and airway remodeling) of the autophagy inhibitor chloroquine. Our data demonstrate cell context-dependent and selective activation of autophagy in structural cells in asthma. Furthermore, this pathway can be effectively targeted to ameliorate airway remodeling in asthma.

Plasma membrane integrity is essential for the viability of eukaryotic cells. In response to bacterial pore-forming toxins, disrupted regions of the membrane are rapidly repaired. However, the pathways that mediate plasma membrane repair are unclear. Here we show that autophagy-related (ATG) protein ATG16L1 and its binding partners ATG5 and ATG12 are required for plasma membrane repair through a pathway independent of macroautophagy. ATG16L1 is required for lysosome fusion with the plasma membrane and blebbing responses that promote membrane repair. ATG16L1 deficiency causes accumulation of cholesterol in lysosomes that contributes to defective membrane repair. Cell-to-cell spread by Listeria monocytogenes requires membrane damage by the bacterial toxin listeriolysin O, which is restricted by ATG16L1-dependent membrane repair. Cells harbouring the ATG16L1 T300A allele associated with inflammatory bowel disease were also found to accumulate cholesterol and be defective in repair, linking a common inflammatory disease to plasma membrane integrity. Thus, plasma membrane repair could be an important therapeutic target for the treatment of bacterial infections and inflammatory disorders. Autophagy-related proteins ATG16L1, ATG5 and ATG12 are required for plasma membrane repair and help to restrict Listeria monocytogenes toxin-mediated cell-to-cell spread.

Here we have explored whether inhibition of autophagy can be used as a treatment strategy for acute myeloid leukemia (AML). Steady-state autophagy was measured in leukemic cell lines and primary human CD34 + AML cells with a large variability in basal autophagy between AMLs observed. The autophagy flux was higher in AMLs classified as poor risk, which are frequently associated with TP53 mutations (TP53 mut ), compared with favorable- and intermediate-risk AMLs. In addition, the higher flux was associated with a higher expression level of several autophagy genes, but was not affected by alterations in p53 expression by knocking down p53 or overexpression of wild-type p53 or p53 R273H . AML CD34 + cells were more sensitive to the autophagy inhibitor hydroxychloroquine (HCQ) than normal bone marrow CD34 + cells. Similar, inhibition of autophagy by knockdown of ATG5 or ATG7 triggered apoptosis, which coincided with increased expression of p53. In contrast to wild-type p53 AML (TP53 wt ), HCQ treatment did not trigger a BAX and PUMA-dependent apoptotic response in AMLs harboring TP53 mut . To further characterize autophagy in the leukemic stem cell-enriched cell fraction AML CD34 + cells were separated into ROS low and ROS high subfractions. The immature AML CD34 + -enriched ROS low cells maintained higher basal autophagy and showed reduced survival upon HCQ treatment compared with ROS high cells. Finally, knockdown of ATG5 inhibits in vivo maintenance of AML CD34 + cells in NSG mice. These results indicate that targeting autophagy might provide new therapeutic options for treatment of AML since it affects the immature AML subfraction.