Autophagy protects against palmitate-induced apoptosis in hepatocytes

Expression, modulation, and clinical correlates of the autophagy protein Beclin-1 in esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) is characterized by rapidly increasing incidence and mortality rates and poor survival. Efficacious preventive and treatment options are urgently needed. An increasing number of pharmacologic agents targeting cancer cell death via autophagy mechanisms are being evaluated in hopes of circumventing apoptotic and therapeutic resistance. We report for the first time, loss of Beclin-1, a key mediator of autophagy, was significantly linked to prognostic factors in EAC. Specifically, Beclin-1 expression loss occurred in 49.0% of EAC patients versus 4.8% of controls. There was a significant inverse correlation between loss of Beclin-1 with histologic grade and tumor stage supporting a tumor suppressive role for Beclin-1. Autophagy modulation linked to cell death was examined in EAC cell lines following treatment with a proanthocyanidin-rich cranberry extract, C-PAC, and the commonly used autophagy inducer, rapamycin. C-PAC induced Beclin-1-independent autophagy in EAC cells characterized by reduced phosphorylation at serine 15 and 93, and significant cell death induction. In contrast, rapamycin-induced autophagy resulted in concomitant, increases in total Beclin-1 levels as well as Beclin-1-phosphorylation in a cell line specific manner, leading to long-term cell survival. Furthermore, autophagic LC3-II was induced by C-PAC following siRNA suppression of Beclin-1 in EAC cells. Together these data support a prognostic role of Beclin-1 in EAC with evidence that Beclin-dependent autophagy induction is agent specific. Future studies are necessary to fully interrogate the role autophagy plays in the progression of normal tissue to EAC and how specific agents targeting autophagic mechanisms can be efficaciously applied for cancer prevention or treatment. © 2015 Wiley Periodicals, Inc.

Bone marrow-derived mesenchymal stem cells ameliorate chronic high glucose-induced β-cell injury through modulation of autophagy

Chronic hyperglycemia causes a progressive decrease of β-cell function and mass in type 2 diabetic patients. Growing evidence suggests that augment of autophagy may be an effective approach to protect β cells against various extra-/intracellular stimuli. In this study, we thus investigated whether bone marrow-derived mesenchymal stem cells (BM-MSCs) could ameliorate chronic high glucose (HG)-induced β-cell injury through modulation of autophagy. Prolonged exposure to HG decreased cell viability, increased cell apoptosis and impaired basal insulin secretion and glucose-stimulated insulin secretion of INS-1 cells, but BM-MSC treatment significantly alleviated these glucotoxic alternations. In addition, western blotting displayed upregulated expression of Beclin1 and LC3-II in INS-1 cells co-cultured with BM-MSCs. Results from immunofluorescence staining and transmission electronic microscope analysis also revealed that BM-MSCs promoted autophagosomes and autolysosomes formation in HG-treated INS-1 cells. However, it should be noted that inhibition of autophagy significantly diminished the protective effects of BM-MSCs on HG-treated INS-1 cells, suggesting that the improvement of β-cell function and survival induced by BM-MSCs was mediated through autophagy. Furthermore, our results showed that BM-MSCs improved mitochondrial function and reduced reactive oxygen species production in HG-treated INS-1 cells, largely owing to autophagic clearance of impaired mitochondria. In vivo study was performed in rats with type 2 diabetes (T2D). BM-MSC infusion not only ameliorated hyperglycemia, but also promoted restoration of pancreatic β cells in T2D rats. Meanwhile, BM-MSC infusion upregulated LAMP2 expression and enhanced formation of autophagosomes and autolysosomes, combined with reduced β-cell apoptosis and increased number of insulin granules. These findings together indicated that BM-MSCs could protect β cells against chronic HG-induced injury through modulation of autophagy in vitro and in vivo. This study unveiled novel evidence of BM-MSCs as an ideal strategy to enhance autophagy for treatment of T2D mellitus.

The 2014 ming k jeang award for excellence in cell & bioscience

Three research groups led by Dr. Robert Clarke of Georgetown University Medical Center, Washington, DC, USA; Dr. Lixin Wei of Shanghai Jiaotong University, Shanghai, China; and Dr. Zhiming Zhang of Xiamen University, Xiamen, Fujian, China, won the 2014 Ming K Jeang Award for Excellence in Cell & Bioscience.

Autophagy in anti-apoptotic effect of augmenter of liver regeneration in HepG2 cells

AIM

To investigate the role of autophagy in the anti-apoptotic effect of augmenter of liver regeneration (ALR).

METHODS

Autophagy was induced through serum deprivation. An ALR-expressing plasmid was transfected into HepG2 cells, and autophagic flux was determined using fluorescence microscopy, electron microscopy, Western blot and quantitative polymerase chain reaction (qPCR) assays. After ALR-expressing plasmid transfection, an autophagy inhibitor [3-methyladenine (3-MA)] was added to HepG2 cells, and apoptosis was observed using fluorescence microscopy and flow cytometry.

RESULTS

Autophagy was activated in HepG2 cells, peaking at 24 h after serum deprivation. Microtubule-associated protein light chain three-II levels were higher in HepG2 cells treated with ALR than in control cells, fluorescence microscopy, electron microscopy and qPCR studies showed the similar trend, and p62 levels showed the opposite trend, which indicated that ALR may play an important role in increasing autophagy flux. The numbers of apoptotic cells were substantially higher in HepG2 cells treated with both ALR and 3-MA than in cells treated with ALR alone. Therefore, the protective effect of ALR was significantly attenuated or abolished when autophagy was inhibited, indicating that the anti-apoptotic effect of ALR may be related to autophagy.

CONCLUSION

ALR protects cells from apoptosis partly through increased autophagy in HepG2 cells and may be valuable as a new therapeutic treatment for liver disease.

New evidence for the role of ceramide in the development of hepatic insulin resistance

Aim

There are few and contradictory data on the role of excessive accumulation of intracellular sphingolipids, particularly ceramides, in the development of hepatic insulin resistance. In our study we assessed accumulated sphingolipid fractions and clarify the mechanisms of hepatic insulin resistance development as well as involvement of fatty acid and ceramide transporters in this process.

Methods

In culture of primary rat hepatocytes, exposed to high concentration of palmitic acid (0.75mM) during short and prolonged incubation, high performance liquid chromatography was used to assess intra- and extracellular sphingolipid fractions content. Degree of palmitate-induced insulin resistance was estimated by measuring changes in phosphorylation of insulin pathway proteins by western blotting as well as changes in expression of different type of transporters.

Results

In our study short and prolonged exposure of primary hepatocytes to palmitic acid resulted in increased intracellular accumulation of ceramide which inhibited insulin signaling pathway. We observed a significant increase in the expression of fatty-acid transport protein (FATP2) and ceramide transfer protein (CERT) what is consistent with enhanced intracellular ceramide content. The content of extracellular ceramide was increased nearly threefold after short and twofold after long incubation period. Expression of microsomal triglyceride transfer protein (MTP) and ATP-binding cassette transporter (ABCA1) was increased significantly mainly after short palmitate incubation.

Conclusion

Our data showed that increase in intarcellular ceramide content contributes to the development of hepatic insulin resistance. We suggest pivotal role of transporters in facilitating fatty acid influx (FATP2), accumulation of ceramides (CERT) and export to the media (MTP and ABCA1).

KEAP the balance between life and death

Hepatocyte apoptosis in association with oxidative stress represent key pathogenic factors involved in tumor development in patients with non-alcoholic fatty liver disease (NAFLD). In our recent study, we established that cellular degradation of Kelch-like ECH-associated protein 1 (KEAP1) through sequestrosome (SQSTM)1/p62-dependent autophagy activates c-Jun NH2 terminal kinase (JNK), upregulates expression of Bcl-2-interacting mediator (BIM) and p53 upregulated modulator of apoptosis (PUMA), and contributes to hepatocyte apoptosis induced by saturated free fatty acids. These findings raise the possibility that dysregulation of KEAP1 may contribute to liver cell death and tumorigenesis during chronic inflammatory liver disease.

Activation of autophagy in photoreceptor necroptosis after experimental retinal detachment

AIM

To investigate whether photoreceptor necroptosis induced by z-VAD-FMK (pan caspase inhibitor) was involved the activation of autophagy and whether Necrostatin-1, a specific necroptosis inhibitor, could inhibit this induction of autophagy after experimental retinal detachment.

METHODS

Experimental retinal detachment models were created in Sprague-Dawley rats by subretinal injection of sodium hyaluronate and subretinal injections of z-VAD-FMK, vehicle or z-VAD-FMK plus Necrostatin-1. Three days after retinal detachment, morphologic changes were observed by transmission electron microscopy. In other animals, retinas were subjected to immunoprecipitation and Western Blotting, then probed with anti-RIP1, phosphoserine, LC-3II or caspase 8 antibody.

RESULTS

It was proved by immunoprecipitation and western blotting, that photoreceptor necroptosis was mediated by caspase-8 inhibition and receptor interacting protein kinase (RIP1) phosphorylation activation. Transmission electron microscope and western blotting results indicated that photoreceptor necroptosis was involved the LC-3II and autophagosomes induction. We also discovered Necrostatin-1 could inhibit RIP1 phosphorylation and LC-3II induction.

CONCLUSION

These data firstly indicate photoreceptor necroptosis is associated with the activation of autophagy. Necrostatin-1 protects photoreceptors from necroptosis and autophagy by down-regulation of RIP1 phosphorylation and LC-3II.

Uncoupling protein 2 regulates palmitic acid-induced hepatoma cell autophagy

Mitochondrial uncoupling protein 2 (UCP2) is suggested to have a role in the development of nonalcoholic steatohepatitis (NASH). However, the mechanism remains unclear. Autophagy is an important mediator of many pathological responses. This study aims to investigate the relationship between UCP2 and hepatoma cells autophagy in palmitic acid- (PA-) induced lipotoxicity. H4IIE cells were treated with palmitic acid (PA), and cell autophagy and apoptosis were examined. UCP2 expression, in association with LC3-II and caspase-3, which are indicators of cell autophagy and apoptosis, respectively,was measured. Results demonstrated that UCP2 was associated with autophagy during PA-induced hepatic carcinoma cells injury. Tests on reactive oxygen species (ROS) showed that UCP2 overexpression strongly decreases PA-induced ROS production and apoptosis. Conversely, UCP2 inhibition by genipin or UCP2 mRNA silencing enhances PA-induced ROS production and apoptosis. Autophagy partially participates in this progress. Moreover, UCP2 was associated with ATP synthesis during PA-induced autophagy. In conclusion, increasing UCP2 expression in hepatoma cells may contribute to cell autophagy and antiapoptotic as result of fatty acid injury. Our results may bring new insights for potential NASH therapies.