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JunB protects ?-cells from lipotoxicity via the XBP1-AKT pathway.

ABSTRACT: Diets rich in saturated fats may contribute to the loss of pancreatic ?-cells in type 2 diabetes. JunB, a member of the activating protein 1 (AP-1) transcription factor family, promotes ?-cell survival and mediates part of the beneficial effects of GLP-1 agonists. In this study we interrogated the molecular mechanisms involved in JunB-mediated ?-cell protection from lipotoxicity. The saturated fatty acid palmitate decreased JunB expression, and this loss may contribute to ?-cell apoptosis, as overexpression of JunB protected cells from lipotoxicity. Array analysis of JunB-deficient ?-cells identified a gene expression signature of a downregulated endoplasmic reticulum (ER) stress response and inhibited AKT signaling. JunB stimulates XBP1 expression via the transcription factor c/EBP? during ER stress, and forced expression of XBP1s rescued the viability of JunB-deficient cells, constituting an important antiapoptotic mechanism. JunB silencing inhibited AKT activation and activated the proapoptotic Bcl-2 protein BAD via its dephosphorylation. BAD knockdown reversed lipotoxic ?-cell death potentiated by JunB siRNA. Interestingly, XBP1s links JunB and AKT signaling as XBP1 knockdown also reduced AKT phosphorylation. GLP-1 agonists induced cAMP-dependent AKT phosphorylation leading to ?-cell protection against palmitate-induced apoptosis. JunB and XBP1 knockdown or IRE1 inhibition decreased AKT activation by cAMP, leading to ?-cell apoptosis. In conclusion, JunB modulates the ?-cell ER stress response and AKT signaling via the induction of XBP1s. The activation of the JunB gene network and the crosstalk between the ER stress and AKT pathway constitute a crucial defense mechanism by which GLP-1 agonists protect against lipotoxic ?-cell death. These findings elucidate novel ?-cell-protective signal transduction in type 2 diabetes.

SUBMITTER: Cunha DA

PROVIDER: S-EPMC4085537 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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JunB protects β-cells from lipotoxicity via the XBP1-AKT pathway.

Cunha D A DA Gurzov E N EN Naamane N N Ortis F F Cardozo A K AK Bugliani M M Marchetti P P Eizirik D L DL Cnop M M

Cell death and differentiation 20140502 8

Diets rich in saturated fats may contribute to the loss of pancreatic β-cells in type 2 diabetes. JunB, a member of the activating protein 1 (AP-1) transcription factor family, promotes β-cell survival and mediates part of the beneficial effects of GLP-1 agonists. In this study we interrogated the molecular mechanisms involved in JunB-mediated β-cell protection from lipotoxicity. The saturated fatty acid palmitate decreased JunB expression, and this loss may contribute to β-cell apoptosis, as ov ...[more]

PMID: 24786832

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Project description:The detrimental role of hepatic lipotoxicity has been well-implicated in the pathogenesis of NAFLD. Previously, we reported that inhibiting autophagy aggravated saturated fatty acid (SFA)-induced hepatotoxicity. Insulin, a physiological inhibitor of autophagy, is commonly increased within NAFLD mainly caused by insulin resistance. We therefore hypothesized that insulin augments the sensitivity of hepatocyte to SFA-induced lipotoxicity. The present study was conducted via employing human and mouse hepatocytes, which were exposed to SFAs, insulin, or their combination. Unexpectedly, our results indicated that insulin protected hepatocytes against SFA-induced lipotoxicity, based on the LDH, MTT, and nuclear morphological measurements, and the detection from cleaved-Parp-1 and -caspase-3 expressions. We subsequently clarified that insulin led to a rapid and short-period inhibition of autophagy, which was gradually recovered after 1 h incubation in hepatocytes, and such extent of inhibition was insufficient to aggravate SFA-induced lipotoxicity. The mechanistic study revealed that insulin-induced alleviation of ER stress contributed to its hepatoprotective role. Pre-treating hepatocytes with insulin significantly stimulated phosphorylated-Akt and reversed SFA-induced up-regulation of p53. Chemical inhibition of p53 by pifithrin-? robustly prevented palmitate-induced cell death. The PI3K/Akt pathway blockade by its special antagonist abolished the protective role of insulin against SFA-induced lipotoxicity and p53 up-regulation. Furthermore, we observed that insulin promoted intracellular TG deposits in hepatocytes in the present of palmitate. However, blocking TG accumulation via genetically silencing DGAT-2 did not prevent insulin-protected lipotoxicity. Our study demonstrated that insulin strongly protected against SFA-induced lipotoxicity in hepatocytes mechanistically through alleviating ER stress via a PI3K/Akt/p53 involved pathway but independently from autophagy.

Project description:Background: Cardiovascular disease is the most common complication and leading cause of death in maintenance hemodialysis patients. Previous studies have found that disorders of cystathionine-gamma-lyase/hydrogen sulfide (CSE/H2S) system in maintenance hemodialysis patients are correlated with the risk of cardiovascular disease. Although the role of CSE/H2S system in UAAS has been preliminarily explored, the molecular mechanism of CSE/H2S is still not systematically elaborated, and the molecular mechanism of nPKCδ and its related signaling pathway in UAAS is still not thoroughly studied. Methods: Forty chronic kidney disease (CHD) patients were studied and the activation of nPKCδ in peripheral blood mononuclear cells (PBMCs) were detected. ApoE-/- mice aged 6 weeks were treated with 5/6 nephrectomy and high-fat diet to make UAAS model. They were divided into Sham group (Sham group), UAAS group (UAAS group), UAAS+L-cysteine group (UAAS+L-cys group), UAAS+sodium hydrosulfide group (UAAS+NaHS group) and UAAS+propargylglycine group (UAAS+PPG group). The UAAS+L-cys group, UAAS+NaHS group and UAAS+PPG group were respectively given L-cys, NaHS and PPG by intraperitoneal injection. The aorta was taken 6 weeks after surgery. Western blot was used to detect the activation of nPKCδ, the phosphorylation of Akt, and the expression of VCAM-1 in the aorta of mice. Results: The membrane translocation of nPKCδ in CHD patients with plaque was higher than that in CHD patients without plaque. The membrane translocation of nPKCδ and the expression of VCAM-1 in UAAS group was higher than sham group, L-cys or NaHS injection could suppress the membrane translocation of nPKCδ and the expression of VCAM-1, but PPG treatment resulted in more membrane translocation of nPKCδ and the expression of VCAM-1 (P<0.05, n=6 per group). Akt phosphorylation in UAAS group was lower than sham group, and L-cys or NaHS injection could suppress the degradation of Akt phosphorylation, but PPG treatment resulted in more decrease in the Akt phosphorylation (P<0.05, n=6 per group). Conclusion: Endogenous CSE/H2S system protected against the formation of UAAS via nPKCδ/Akt signal pathway. The imbalance of CSE/H2S system may participate in the formation of UAAS by affecting the expression of downstream molecule VCAM-1, which may be mediated by nPKCδ/Akt signaling pathway.

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JunB protects ?-cells from lipotoxicity via the XBP1-AKT pathway.

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JunB protects β-cells from lipotoxicity via the XBP1-AKT pathway.

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