Restoration Of Autophagic Flux Research Articles

ORMDL MISLOCALIZATION BY IMPAIRED AUTOPHAGY IN NIEMANN-PICK TYPE C DISEASE LEADS TO INCREASED DE NOVO SPHINGOLIPID BIOSYNTHESIS

Niemann-Pick type C1 (NPC1) disease is rare neurodegenerative cholesterol and sphingolipid storage disorder primarily due to mutations in the cholesterol-trafficking protein NPC1. In addition to catabolic-derived sphingolipids, NPC1 dysfunction also leads to an increase in de novo sphingolipid biosynthesis, yet little is known of the cellular mechanism involved. Although deletion of NPC1 or inhibition of the NPC1 sterol binding domain enhanced de novo sphingolipid biosynthesis, surprisingly levels of the ORMDLs, the regulatory subunits of serine palmitoyltransferase (SPT), the rate-limiting step in sphingolipid biosynthesis, were also greatly increased. Nevertheless, less ORMDL was bound in the SPT-ORMDL complex despite elevated ceramide levels. Instead, ORMDL colocalized with p62, the selective autophagy receptor, and accumulated in stalled autophagosomes due to defective autophagy in NPC1 disease cells. Restoration of autophagic flux with N-acetyl-L-leucine in NPC1 deleted cells decreased ORMDL accumulation in autophagosomes and reduced de novo sphingolipid biosynthesis and their accumulation. This study revealed a previously unknown link between de novo sphingolipid biosynthesis, ORMDL and autophagic defects present in NCP1 disease. In addition, we provide further evidence and mechanistic insight for the beneficial role of N-acetyl-L-leucine treatment for NPC1 disease that is presently awaiting approval from the Food and Drug Administration and the European Medicines Agency.

Rosmarinic acid alleviates toosendanin-induced liver injury through restoration of autophagic flux and lysosomal function by activating JAK2/STAT3/CTSC pathway

Ethnopharmacological relevanceRosmarinic acid (RA), a natural polyphenol abundant in numerous herbal remedies, has been attracting growing interest owing to its exceptional ability to protect the liver. Toosendanin (TSN), a prominent bioactive compound derived from Melia toosendan Siebold & Zucc., boasts diverse pharmacological properties. Nevertheless, TSN possesses remarkable hepatotoxicity. Intriguingly, the potential of RA to counteract TSN-induced liver damage and its probable mechanisms remain unexplored. Aim of the studyThis study is aimed at exploring whether RA can alleviate TSN-induced liver injury and the potential mechanisms involved autophagy. Materials and methodsCCK-8 and LDH leakage rate assay were used to evaluate cytotoxicity. Balb/c mice were intraperitoneally administered TSN (20 mg/kg) for 24 h after pretreatment with RA (0, 40, 80 mg/kg) by gavage for 5 days. The autophagic proteins P62 and LC3B expressions were detected using western blot and immunohistochemistry. RFP-GFP-LC3B and transmission electron microscopy were applied to observe the accumulation levels of autophagosomes and autolysosomes. LysoTracker Red and DQ-BSA staining were used to evaluate the lysosomal acidity and degradation ability respectively. Western blot, immunohistochemistry and immunofluorescence staining were employed to measure the expressions of JAK2/STAT3/CTSC pathway proteins. Dual-luciferase reporter gene was used to measure the transcriptional activity of CTSC and RT-PCR was used to detect its mRNA level. H&E staining and serum biochemical assay were employed to determine the degree of damage to the liver. ResultsTSN-induced damage to hepatocytes and livers was significantly alleviated by RA. RA markedly diminished the autophagic flux blockade and lysosomal dysfunction caused by TSN. Mechanically, RA alleviated TSN-induced down-regulation of CTSC by activating JAK2/STAT3 signaling pathway. ConclusionRA could protect against TSN-induced liver injury by activating the JAK2/STAT3/CTSC pathway-mediated autophagy and lysosomal function.

6PPDQ induces cardiomyocyte senescence via AhR/ROS-mediated autophagic flux blockage

Recently, attention has been drawn to the adverse outcomes of N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPDQ) on human health, but its cardiac toxicity has been relatively understudied. This work aims to investigate the effects of 6PPDQ on differentiated H9c2 cardiomyocytes. Our findings demonstrated that exposure to 6PPDQ altered cellular morphology and disrupted the expression of cardiac-specific markers. Significantly, 6PPDQ exposure led to cardiomyocyte senescence, characterized by elevated β-Galactosidase activity, upregulation of cell cycle inhibitor, induction of DNA double-strand breaks, and remodeling of Lamin B1. Furthermore, 6PPDQ hindered autophagy flux by promoting the formation of autophagosomes while inhibiting the degradation of autolysosomes. Remarkably, restoration of autophagic flux using rapamycin counteracted 6PPDQ-induced cardiomyocyte senescence. Additionally, our study revealed that 6PPDQ significantly increased the ROS production. However, ROS scavenger effectively reduced the blockage of autophagic flux and cardiomyocyte senescence caused by 6PPDQ. Furthermore, we discovered that 6PPDQ activated the Aryl hydrocarbon receptor (AhR) signaling pathway. AhR antagonist was found to reverse the blockage of autophagy and alleviate cardiac senescence, while also reducing ROS levels in 6PPDQ-treated group. In conclusion, our research unveils that exposure to 6PPDQ induces ROS overproduction through AhR activation, leading to disruption of autophagy flux and ultimately contributing to cardiomyocyte senescence.

The SLC38A9–mTOR axis is involved in autophagy in the juvenile yellow catfish (Pelteobagrus fulvidraco) under ammonia stress

The primary objective of this study was to examine the effect of acute ammonia stress on hepatic physiological alterations in yellow catfish by performing a comprehensive analysis of the metabolome and transcriptome. The present study showed that ammonia stress led to liver metabolic disruption, functional incapacitation, and oxidative damage. Transcriptomic and metabolomic analyses revealed transcriptional and metabolic differences in the liver of yellow catfish under control and high ammonia stress conditions. After 96 h of acute exposure to ammonia, the mRNA levels of 596 liver genes were upregulated, whereas those of 603 genes were downregulated. Enrichment analysis of the differentially expressed genes identified multiple signalling pathways associated with autophagy, including the endocytosis, autophagy-animal, and mammalian target of rapamycin signalling pathways. A total of 186 upregulated and 117 downregulated metabolites, primarily associated with amino acid biosynthesis pathways, were identified. Multi-omics integration revealed the solute carrier family 38 member 9 (SLC38A9)-mammalian target of rapamycin axis as a signalling nexus for amino acid-mediated modulation of autophagy flux, and q-PCR was used to assess the expression of autophagy-related genes (LC3a and sqstm1), revealing an initial inhibition followed by the restoration of autophagic flux during ammonia stress. Subsequent utilisation of arginine as a specific SLC38A9 activator during ammonia stress demonstrated that augmented SLC38A9 expression hindered autophagy, exacerbated ammonia toxicity, and caused a physiological decline (total cholesterol, total triglyceride, acid phosphatase, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase levels were significantly increased), oxidative stress, and apoptosis. Autophagy activation may be an adaptive mechanism to resist ammonia stress.

Melatonin Restores Autophagic Flux by Activating the Sirt3/TFEB Signaling Pathway to Attenuate Doxorubicin-Induced Cardiomyopathy.

Doxorubicin (DOX) chemotherapy in cancer patients increases the risk of the occurrence of cardiac dysfunction and even results in congestive heart failure. Despite the great progress of pathology in DOX-induced cardiomyopathy, the underlying molecular mechanisms remain elusive. Here, we investigate the protective effects and the underlying mechanisms of melatonin in DOX-induced cardiomyopathy. Our results clearly show that oral administration of melatonin prevented the deterioration of cardiac function caused by DOX treatment, which was evaluated by left ventricular ejection fraction and fractional shortening as well as cardiac fibrosis. The ejection fraction and fractional shortening in the DOX group were 49.48% and 25.5%, respectively, while melatonin treatment increased the ejection fraction and fractional shortening to 60.33 and 31.39 in wild-type mice. Cardiac fibrosis in the DOX group was 3.97%, while melatonin reduced cardiac fibrosis to 1.95% in wild-type mice. Sirt3 is a mitochondrial deacetylase and shows protective effects in diverse cardiovascular diseases. Therefore, to test whether Sirt3 is a key factor in protection, Sirt3 knockout mice were used, and it was found that the protective effects of melatonin in DOX-induced cardiomyopathy were partly abolished. Further analysis revealed that Sirt3 and its downstream molecule TFEB were downregulated in response to DOX treatment, while melatonin administration was able to significantly enhance the expressions of Sirt3 and TFEB. Our in vitro study demonstrated that melatonin enhanced lysosomal function by increasing the Sirt3-mediated increase at the TFEB level, and the accumulation of autolysosomes induced by DOX treatment was attenuated. Thus, autophagic flux disrupted by DOX treatment was restored by melatonin supplementation. In summary, our results demonstrate that melatonin protects the heart against DOX injury by the restoration of autophagic flux via the activation of the Sirt3/TFEB signaling pathway.

URB597 exerts neuroprotective effects against transient brain ischemia injury in mice by regulating autophagic flux and necroptosis

Ischemic stroke is a leading cause of death and disability, and medical treatments for ischemic stroke are very limited. URB597 is a potent and selective inhibitor of fatty acid amide hydrolase (FAAH). However, the effect of URB597 on ischemic stroke and the underlying molecular mechanisms remain little known. In this study, focal cerebral ischemia was induced by transient middle cerebral artery occlusion in mice. Our results showed that URB597 dose-dependently improved neurological function and reduced brain infarct volume and brain edema 24 h after brain ischemia. The most effective dose was 1 mg/kg and the therapeutic time window was within 3 h after ischemic stroke. To further investigate the underlying mechanism, necroptosis and autophagy flux were detected by Western blot and/or immunofluorescence staining with or without chloroquine, an autophagic flux inhibitor. Our results showed that URB597 promoted autophagic flux and reduced neuronal necroptosis after brain ischemia and these effects could be abolished by chloroquine. In addition, we found that peroxisome proliferator-activated receptor α (PPARα) antagonist GW6471 partly abolished the effect of URB597 against brain ischemia and URB597 upregulated the expressions of PPARα. In conclusion, URB597 exerts a neuroprotective effect in a dose- and time-dependent manner, and this effect may be related to its restoration of autophagic flux and inhibition of neuronal necroptosis. PPARα is involved in the neuroprotective effect of URB597. This study provides novel evidence that URB597 may be a promising agent for the clinical treatment of ischemic stroke.

Paeoniflorin, ferulic acid, and atractylenolide III improved LPS-induced neuroinflammation of BV2 microglia cells by enhancing autophagy

Microglia hyperactivation is an important cause of neuroinflammation in Alzheimer's disease (AD). Paeoniflorin (PF), ferulic acid (FA), and atractylenolide III (ATL) are potent in anti-inflammation and neuroprotection. Multiple components can act on different targets simultaneously to exert synergistic therapeutic effects and exploring the synergistic potential between compounds is an important area of research. We investigated the effects of PF, FA, and ATL, alone or in combination, on LPS-induced neuroinflammation and autophagy in BV2 microglia cells. We found that PF, FA, and ATL, alone or in combination, significantly reduced the production of inflammatory factors such as IL-6, IL-1β, and TNF-α, especially in the PF + FA + ATL group, which performed the best. In addition, the combination of PF, FA, and ATL significantly increased the expression of autophagy-related proteins p-AMPK, p-ULK1, Beclin1, LC3, and TFEB and decreased the expression of p62. Moreover, the restoration of autophagic flux by the combination of PF, FA, and ATL was abrogated by the addition of the autophagy inhibitor Wortmannin. In conclusion, PF, FA, and ATL have a synergistic effect in reducing LPS-induced inflammatory factor release from BV2 microglia cells, and its protective effect may be through activation of the AMPK/ULK1/TFEB autophagic signaling pathway.

Nano-selenium Alleviates Cadmium-Induced Mouse Leydig Cell Injury, via the Inhibition of Reactive Oxygen Species and the Restoration of Autophagic Flux.

Cadmium (Cd) is a well-known environmental pollutant that can contribute to male reproductive toxicity through oxidative stress. Nano-selenium (Nano-se) is an active single body of selenium with strong antioxidant properties and low toxicity. Some studies have addressed the potential ameliorative effect of Nano-se against Cd-induced testicular toxicity; however, the underlying mechanisms remain to be investigated. This study aimed to explore the protective effect of Nano-se on Cd-induced mouse testicular TM3 cell toxicity by regulating autophagy process. We showed that cadmium exposure to TM3 cells inhibited cell viability and elevated the level of reactive oxygen species (ROS) generation. Morphology observation by transmission electron microscope and the presence of mRFP-GFP-LC3 fluorescence puncta demonstrated that cadmium increased autophagosome formation and accumulation in TM3 cells, resulting in blocking the autophagic flux of TM3 cells. Meanwhile, cadmium remarkably increased the ratio of LC3-II to LC3-I protein expression (2.07 ± 0.31) and the Beclin-1 protein expression (1.97 ± 0.40) in TM3 cells (P < 0.01). Pretreatment with Nano-se significantly reduced Cd-induced TM3 cell toxicity (P < 0.01). Furthermore, Nano-se treatment reversed Cd-induced ROS production and autophagosome accumulation, and autophagy as evidenced by the ratio of LC3-II to LC3-I and Beclin-1 expression. In addition, ROS scavenger, N-acetyl-L-cysteine (NAC) or autophagy inhibitor, 3-methyladenine (3-MA) reversed cadmium-induced ROS generation, autophagosome accumulation, and autophagy-related protein expression levels, which confirmed that cadmium induced TM3 cell injury via ROS signal pathway and blockage of autophagic flux. Collectively, our results reveal that Nano-se attenuates Cd-induced TM3 cell toxicity through the inhibition of ROS production and the amelioration of autophagy disruption.

Autophagic flux restoration enhances the antitumor efficacy of tumor infiltrating lymphocytes

BackgroundAlthough adoptive cell therapy with tumor infiltrating lymphocytes (TILs) has mediated effective antitumor responses in several cancers, dysfunction and exhaustion of TILs significantly impair the therapeutic effect of TILs. Thus,...

Phloretin mitigates oxidative injury, inflammation, and fibrogenic responses via restoration of autophagic flux in in vitro and preclinical models of NAFLD

Nonalcoholic fatty liver disease (NAFLD) with growing incidences is a major health concern worldwide. Alteration in cellular redox homeostasis and autophagy plays a critical role in the progression of NAFLD to more severe outcomes. The lack of safe and effective therapy for the disease necessitates the exploration of new therapeutic compounds. Therefore, in the present study, we investigated the potential of phloretin to maintain redox equilibrium and prevent disease progression via modulation of autophagy in NAFLD. Free fatty acid exposed Huh7 cells were used to evaluate the efficacy of phloretin in vitro. Further, phloretin was administered orally to western diet induced NAFLD in C57BL/6J mice at different doses. The chronic exposure to fatty acids and the western diet triggered lipid accumulation in the Huh7 cells and western diet-fed mice liver, respectively. In addition, mitochondrial dysfunction, oxidative stress, inflammation and decreased hepatic autophagy were observed in disease condition. Phloretin encouraged autophagy mediated hepatic lipid clearance and restored mitochondrial membrane potential and redox homeostasis. It also reduced histological injury by reducing hepatic lipogenesis and facilitating fatty acid oxidation. Moreover, findings of the study also revealed the mitigatory effect of phloretin on inflammatory and fibrogenic markers. Altogether, the study suggested that phloretin effectively attenuates NAFLD progression via upregulating autophagy-mediated lipid breakdown and inhibits oxidative damage, hepatic inflammation and fibrosis.

Apigenin Alleviates Intervertebral Disc Degeneration via Restoring Autophagy Flux in Nucleus Pulposus Cells.

Oxidative stress–induced apoptosis and senescence of nucleus pulposus (NP) cells play a crucial role in the progression of intervertebral disc degeneration (IVDD). Accumulation of studies has shown that activated autophagy and enhanced autophagic flux can alleviate IVDD. In this study, we explored the effects of apigenin on IVDD in vitro and in vivo. Apigenin was found to inhibit tert-butyl hydroperoxide (TBHP)–induced apoptosis, senescence, and ECM degradation in NP cells. In addition, apigenin treatment can restore the autophagic flux blockage caused by TBHP. Mechanistically, we found that TBHP may induce autophagosome and lysosome fusion interruption and lysosomal dysfunction, while apigenin alleviates these phenomena by promoting the nuclear translocation of TFEB via the AMPK/mTOR signaling pathway. Furthermore, apigenin also exerts a protective effect against the progression of IVDD in the puncture-induced rat model. Taken together, these findings indicate that apigenin protects NP cells against TBHP-induced apoptosis, senescence, and ECM degradation via restoration of autophagic flux in vitro, and it also ameliorates IVDD progression in rats in vivo, demonstrating its potential for serving as an effective therapeutic agent for IVDD.

Autophagic flux restoration of senescent T cells improves antitumor activity of TCR-engineered T cells.

ObjectivesAlthough adoptive cell therapy with T‐cell receptor‐engineered T cells (TCR‐Ts) has mediated effective antitumor responses in several cancers, senescence of T cells could impair the therapeutic effect of TCR‐Ts. Thus, it is essential to elucidate the characteristics of senescent TCR‐Ts and how to subsequently improve their antitumor effect. Here, we focused on the influence of autophagy on TCR‐Ts, since autophagy is tightly associated with the regulation of T‐cell activation, proliferation and differentiation.MethodsWe first evaluated autophagy level of senescent TCR‐Ts, and then the senescent TCR‐Ts were expanded in vitro for 7 days with and without spermidine treatment, respectively. Furthermore, the proliferative potential, phenotypical characteristics and functionality of the propagated senescent TCR‐Ts were analysed in vitro and in vivo after 7‐day ex vivo expansion.ResultsWe found that autophagic flux of senescent TCR‐T cells was significantly impaired. The restoration of autophagic flux via spermidine treatment reduced the expression of inhibitory immunoreceptors (PD‐1, TIM‐3 or LAG‐3), enhanced proliferation and effector functions and subsequently demonstrated the superior in vitro and in vivo antitumor activity of TCR‐Ts.ConclusionThese data suggest that spermidine treatment presents an opportunity to improve the antitumor effect of TCR‐Ts for the treatment of solid tumors.

Epigenetic regulator BRD4 is involved in cadmium-induced acute kidney injury via contributing to lysosomal dysfunction, autophagy blockade and oxidative stress

Cadmium (Cd) is a known nephrotoxic heavy metal and proximal tubules are the major target of Cd-induced acute kidney injury (AKI). We previously demonstrated that lysosomal dysfunction and dysregulated autophagy contribute to Cd-induced AKI. Recent studies have revealed that bromodomain-containing protein 4 (BRD4) is a transcriptional repressor of autophagy and lysosomal function. Hence, in vivo and in vitro studies were performed to clarify the role of BRD4 in Cd-induced AKI. Firstly, Cd has no effect on BRD4 expression levels, but increases H4K16 acetylation. Resultantly, Cd promotes the recruitment of BRD4 to lysosomal gene promoter regions to make it as a transcriptional regulator. Pharmacological and genetic inhibition of BRD4 alleviates Cd-inhibited lysosomal gene transcript levels and lysosomal function, leading to the alleviation of Cd-induced autophagy inhibition. Moreover, inhibition of BRD4 relieves Cd-induced oxidative stress and concurrent cytotoxicity, which is counteracted by the inhibition of autophagy via Atg5 knockdown, indicating that alleviation of oxidative stress by BRD4 inhibition is ascribed to its restoration of autophagic flux. Collectively, these results demonstrate that BRD4 acts as a transcriptional repressor to mediate lysosomal dysfunction, autophagy blockade and oxidative stress during Cd exposure, which may be a potential therapeutic target for Cd-induced AKI.

Cardiac Shock Wave Therapy Alleviates Hypoxia/Reoxygenation-Induced Myocardial Necroptosis by Modulating Autophagy.

Regulated necrosis (necroptosis) is crucially involved in cardiac ischaemia-reperfusion injury (MIRI). The aim of our study is to investigate whether shock wave therapy (SWT) is capable of exerting protective effects by inhibiting necroptosis during myocardial ischaemia-reperfusion (I/R) injury and the possible role of autophagy in this process. We established a hypoxia/reoxygenation (H/R) model in vitro using HL-1 cells to simulate MIRI. MTS assays and LDH cytotoxicity assay were performed to measure cell viability and cell damage. Annexin V/PI staining was used to determine apoptosis and necrosis. Western blotting was performed to assess the changes in cell signaling pathways associated with autophagy, necroptosis, and apoptosis. Reactive oxygen species (ROS) production was detected using DHE staining. Autophagosome generation and degradation (autophagic flux) were analysed using GFP and RFP tandemly tagged LC3 (tfLC3). HL-1 cells were then transfected with p62/SQSTM1 siRNA in order to analyse its role in cardioprotection. Our results revealed that SWT increased cell viability in the H/R model and decreased receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and RIPK3 expression. ROS production was also inhibited by SWT. Moreover, SWT decreased Beclin1 expression and the ratio of LC3-II/LC3-I following H/R. Simultaneously, in the tfLC3 assay, the SWT provoked a decrease in the cumulative autophagosome abundance. siRNA-mediated knockdown of p62 attenuated H/R-induced necroptosis, and SWT did not exert additive effects. Taken together, SWT ameliorated H/R injury by inhibiting necroptosis. SWT also relieved the blockade of autophagic flux in response to H/R injury. The restoration of autophagic flux by SWT might contribute to its cardioprotective effect on necroptosis following H/R injury.

Sestrin2 regulates microglia polarization through mTOR-mediated autophagic flux to attenuate inflammation during experimental brain ischemia

BackgroundNeuroinflammation is the major pathogenesis of cerebral ischemia. Microglia are activated and polarized to either the pro-inflammatory M1 phenotype or anti-inflammatory M2 phenotype, which act as a critical mediator of neuroinflammation. Sestrin2 has pro-survival properties against ischemic brain injury. However, whether sestrin2 has an anti-inflammatory function by shifting microglia polarization and its underlying mechanism is unknown.MethodsAdult male C57BL/6 mice (N = 108) underwent transient middle cerebral artery occlusion (tMCAO) and were treated with exogenous sestrin2. Neurological deficit scores and infarct volume were determined. Cell apoptosis was examined by TUNEL staining and Western blotting. The expression of inflammatory mediators, M1/M2-specific markers, and signaling pathways were detected by reverse transcription-polymerase chain reaction, immunostaining, and Western blotting. To explore the underlying mechanism, primary neurons were subjected to oxygen-glucose deprivation (OGD) and then treated with oxygenated condition medium of BV2 cells incubated with different doses of sestrin2.ResultsSestrin2 attenuated the neurological deficits, infarction volume, and cell apoptosis after tMCAO compared to those in the control (p < 0.05). Sestrin2 had an anti-inflammatory effect and could suppress M1 microglia polarization and promote M2 microglia polarization. Condition medium from BV2 cells cultured with sestrin2 reduced neuronal apoptosis after OGD in vitro. Furthermore, we demonstrated that sestrin2 drives microglia to the M2 phenotype by inhibiting the mammalian target of rapamycin (mTOR) signaling pathway and restoring autophagic flux.ConclusionsSestrin2 exhibited neuroprotection by shifting microglia polarization from the M1 to M2 phenotype in ischemic mouse brain, which may be due to suppression of the mTOR signaling pathway and the restoration of autophagic flux.

Metformin reduces saturated fatty acid-induced lipid accumulation and inflammatory response by restoration of autophagic flux in endothelial cells

Autophagy, an integral part of the waste recycling process, plays an important role in cellular physiology and pathophysiology. Impaired autophagic flux causes ectopic lipid deposition, which is defined as the accumulation of lipids in non-adipose tissue. Ectopic lipid accumulation is observed in patients with cardiometabolic syndrome, including obesity, diabetes, insulin resistance, and cardiovascular complications. Metformin is the first line of treatment for type 2 diabetes, and one of the underlying mechanisms for the anti-diabetic effect of metformin is mediated by the stimulation of AMP-activated protein kinase (AMPK). Because the activation of AMPK is crucial for the initiation of autophagy, we hypothesize that metformin reduces the accumulation of lipid droplets by increasing autophagic flux in vascular endothelial cells. Incubation of vascular endothelial cells with saturated fatty acid (SFA) increased the accumulation of lipid droplets and impaired autophagic flux. We observed that the accumulation of lipid droplets was reduced, and the autophagic flux was enhanced by treatment with metformin. The knock-down of AMPKα by using siRNA blunted the effect of metformin. Furthermore, treatment with SFA or inhibition of autophagy increased leukocyte adhesion, whereas treatment with metformin decreased the SFA-induced leukocyte adhesion. The results suggest a novel mechanism by which metformin protects vascular endothelium from SFA-induced ectopic lipid accumulation and pro-inflammatory responses. In conclusion, improving autophagic flux may be a therapeutic strategy to protect endothelial function from dyslipidemia and diabetic complications.

\u03b1-Linolenic acid but not linolenic acid protects against hypertension: critical role of SIRT3 and autophagic flux

Although dietary α-linolenic acid (ALA) or linolenic acid (LA) intake was reported to be epidemiologically associated with a lower prevalence of hypertension, recent clinical trials have yielded conflicting results. Comparable experimental evidence for the roles of these two different fatty acids is still lacking and the underlying mechanisms need to be further elucidated. Our data showed that ALA but not LA supplementation alleviated systolic blood pressure elevation and improved ACh-induced, endothelium-dependent vasodilation in both spontaneously hypertensive rats (SHRs) and AngII-induced hypertensive mice. In addition, SHRs displayed reduced vascular Sirtuin 3 (SIRT3) expression, subsequent superoxide dismutase 2 (SOD2) hyperacetylation and mitochondrial ROS overproduction, all of which were ameliorated by ALA but not LA supplementation. In primary cultured endothelial cells, ALA treatment directly inhibited SIRT3 reduction, SOD2 hyperacetylation, mitochondrial ROS overproduction and alleviated autophagic flux impairment induced by AngII plus TNFα treatment. However, these beneficial effects of ALA were completely blocked by silencing SIRT3. Restoration of autophagic flux by rapamycin also inhibited mitochondrial ROS overproduction in endothelial cells exposed to AngII plus TNFα. More interestingly, SIRT3 KO mice developed severe hypertension in response to a low dose of AngII infusion, while ALA supplementation lost its anti-hypertensive and endothelium-protective effects on these mice. Our findings suggest that ALA but not LA supplementation improves endothelial dysfunction and diminishes experimental hypertension by rescuing SIRT3 impairment to restore autophagic flux and mitochondrial redox balance in endothelial cells.

P6273Inhibitory phosphorylation of RIP1 at Ser320 induces nuclear translocation of TFEB, leading to suppression of necroptosis in cardiomyocytes

Abstract Background Necroptosis, a form of programmed necrosis, has been shown to contribute to the pathogenesis of various diseases including ischemia/reperfusion injury and heart failure. We recently reported that necroptotic signals suppresses autophagy in cardiomyocytes and that rapamycin, an mTORC1 inhibitor, not only promotes autophagy but also protect the cells from necroptosis. Purpose We examined the mechanism by which rapamycin suppresses necroptosis of cardiomyocytes, focusing on regulation of RIP1 activity and autophagic flux. Methods and results In H9c2 cardiomyoblasts, necroptosis was induced by treatment with TNF and z-VAD-fmk (zVAD) for 24 h, and cell death was determined by LDH release (as % of total). The treatment with TNF/zVAD increased LDH release from 3.4±1.3% to 46.1±2.3%, and LDH release was suppressed by necrostatin-1 (5.9±0.9%), a RIP1 inhibitor, and by rapamycin (23.5±1.4%). The protective effect of rapamycin was mimicked by Ku-0063794, an mTORC1/2 inhibitor. TNF/zVAD induced RIP1-RIP3 complex formation, together with suppression of TNF-induced RIP1 cleavage, which was mitigated by rapamycin. In addition, rapamycin not only suppressed TNF/zVAD-induced phosphorylation of RIP1-Ser166, an index of RIP1 activation, but also increased phosphorylation of RIP1-Ser320, an inhibitory phosphorylation site. In cells transfected with RIP1-S320A, which lack Ser320 for inhibitory phosphorylation, rapamycin failed to suppress TNF/zVAD-induced RIP1-RIP3 binding and cell death. Immunoblot analyses showed that TNF/zVAD significantly increased level of LC3-II. The accumulation of LC3-II protein was not further increased by bafilomycin A1 (100 nM), an inhibitor of lysosomal protein degradation, indicating that accumulation of LC3-II by TNF/zVAD reflected suppression of autophagic flux. Inhibition of RIP1 by necrostatin-1 attenuated TNF/zVAD-induced accumulation of LC3 II. The restoration of autophagic flux in TNF/zVAD-treated cells by necrostatin-1 was confirmed by monitoring tandem RFP-GFP-LC3 transfected cells; necrostatin-1 increased a ratio of RFP-LC3-puncta (autolysosomes) to RFP-GFP-LC3-puncta (autophagosomes) in TNF/zVAD-treated cells. In addition, necrostatin-1 and rapamycin induced nuclear translocation of TFEB, a regulator of lysosome biogenesis, which was associated with upregulation of MCOLN1 mRNA, a downstream target of TFEB. Restoration of autophagic flux in TNF/zVAD-treated cells by necrostatin-1 was inhibited by siRNA-mediated knockdown of TFEB. Conclusion Activation of TFEB by inhibitiory phosphorylation of RIP1-Ser320 is a primary mechanism of cytoprotection afforded by mTORC1 inhibition against necroptosis.

P928MTORC1 inhibition suppresses necroptosis through restoration of autophagic flux by inhibitory phosphorylation of RIP1 in cardiomyocytes

P928MTORC1 inhibition suppresses necroptosis through restoration of autophagic flux by inhibitory phosphorylation of RIP1 in cardiomyocytes

Transcription factor E3 protects against cadmium-induced apoptosis by maintaining the lysosomal-mitochondrial axis but not autophagic flux in Neuro-2a cells

Cadmium (Cd), is a well-known environmental and occupational hazard with a potent neurotoxic action. However, the mechanism underlying cadmium-induced neurotoxicity remains unclear. Herein, we exposed Neuro-2a cells to different concentrations of cadmium chloride (CdCl2) (12.5, 25 and 50 μM) for 24 h and found that Cd significantly induced lysosomal membrane permeabilization (LMP) with the release of cathepsin B (CTSB) to the cytosol, which in turn caused the release of mitochondrial cytochrome c (Cyt c) and eventually triggered caspase-dependent apoptosis. Interestingly, Cd decreased TFE3 expression but induced the nuclear translocation of TFE3 and TFE3 target-gene expression, which might be associated with lysosomal stress mediated by Cd. Notably, Tfe3 overexpression protected against Cd-induced neurotoxicity by maintaining the lysosomal-mitochondrial axis, and the protective effect of TFE3 is not dependent on the restoration of autophagic flux. In conclusion, our study demonstrated for the first time that lysosomal-mitochondrial axis dependent apoptosis, a neglected mechanism, may be the most important reason for Cd-induced neurotoxicity and that manipulation of TFE3 signaling may be a potential therapeutic approach for treatment of Cd-induced neurotoxicity.