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Mcl-1 downregulation by pro-inflammatory cytokines and palmitate is an early event contributing to ?-cell apoptosis.

ABSTRACT: Pancreatic ?-cell apoptosis is a key feature of diabetes mellitus and the mitochondrial pathway of apoptosis is a major mediator of ?-cell death. We presently evaluated the role of the myeloid cell leukemia sequence 1 (Mcl-1), an antiapoptotic protein of the Bcl-2 family, in ?-cells following exposure to well-defined ?-cell death effectors, for example, pro-inflammatory cytokines, palmitate and chemical endoplasmic reticulum (ER) stressors. All cytotoxic stresses rapidly and preferentially decreased Mcl-1 protein expression as compared with the late effect observed on the other antiapoptotic proteins, Bcl-2 and Bcl-xL. This was due to ER stress-mediated inhibition of translation through eIF2? phosphorylation for palmitate and ER stressors and through the combined action of translation inhibition and JNK activation for cytokines. Knocking down Mcl-1 using small interference RNAs increased apoptosis and caspase-3 cleavage induced by cytokines, palmitate or thapsigargin, whereas Mcl-1 overexpression partly prevented Bax translocation to the mitochondria, cytochrome c release, caspase-3 cleavage and apoptosis induced by the ?-cell death effectors. Altogether, our data suggest that Mcl-1 downregulation is a crucial event leading to ?-cell apoptosis and provide new insights into the mechanisms linking ER stress and the mitochondrial intrinsic pathway of apoptosis. Mcl-1 is therefore an attractive target for the design of new strategies in the treatment of diabetes.

SUBMITTER: Allagnat F

PROVIDER: S-EPMC3131897 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

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Mcl-1 downregulation by pro-inflammatory cytokines and palmitate is an early event contributing to β-cell apoptosis.

Allagnat F F Cunha D D Moore F F Vanderwinden J M JM Eizirik D L DL Cardozo A K AK

Cell death and differentiation 20100827 2

Pancreatic β-cell apoptosis is a key feature of diabetes mellitus and the mitochondrial pathway of apoptosis is a major mediator of β-cell death. We presently evaluated the role of the myeloid cell leukemia sequence 1 (Mcl-1), an antiapoptotic protein of the Bcl-2 family, in β-cells following exposure to well-defined β-cell death effectors, for example, pro-inflammatory cytokines, palmitate and chemical endoplasmic reticulum (ER) stressors. All cytotoxic stresses rapidly and preferentially decre ...[more]

PMID: 20798690

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Project description:BackgroundAdult human pancreatic beta cells are the "gold standard" for studies on diabetes pathogenesis, but their use is limited by insufficient availability and variable quality. An important effort has recently taken place to differentiate beta cells from human induced pluripotent stem cells (iPSCs) and validate their use for diabetes research. We presently used a 7-stage protocol to generate beta cells from human iPSC and evaluated whether these cells are responsive to the pro-inflammatory cytokines (IFN?, IL-1?, or IFN?) that play a role in type 1 diabetes.MethodsThe iPSC-derived islet-like cell clusters contained 40-50% beta and 10-15% alpha cells and expressed the receptors for IFN?, IL-1?, or IFN?. Cells were exposed to either IFN? (1000?U/mL)?+?IL-1? (50?U/mL) or IFN? alone (2000?U/mL) for 24/48?h. Apoptosis was quantified using Hoechst/propidium iodide staining or the RealTime Glo Apoptosis Kit (Promega). After treatment, CXCL10 secretion was quantified by ELISA. The expression of multiples genes (Ins, Gcg, Nkx2.2, Nkx6.1, Pdx1, Mafa, BiP, Chop, Atf3, CXCL10, CXCL9, CCL5, and HLA-ABC) was quantified by RT-qPCR. Phosphorylation state and total expression of STAT1/STAT2, as well as expression of PDL1 and of the ER chaperone BiP, were quantified by Western blotting. The co-localization of HLA-ABC or cleaved caspase-3 and Ins/Gcg expression was assessed by immunohistochemistry. The presence of HLA-ABC at the plasma membrane was measured by flow cytometry.ResultsIFN? + IL-1? and IFN? induced apoptosis of the cells after 48?h of exposure. Cleaved caspase-3 co-localized mostly but not exclusively with Ins+ cells. Exposure to IFN? + IL-1? induced a pro-inflammatory phenotype, including increased CXCL10, CXCL9, and CCL5 expression; CXCL10 secretion; and HLA-ABC expression. HLA overexpression was confirmed at the protein level by Western blotting and flow cytometry. Exposure to IFN? + IL-1? (but not IFN?) also induced beta cell dedifferentiation and endoplasmic reticulum stress (increase in BiP, Chop, and Atf3 mRNA expression). Phosphorylation of STAT1 was stimulated already after 1?h by IFN? + IL-1? and IFN?, while phosphorylation of STAT2 was only activated by IFN? at 1-4 h. PDL1 expression was increased by both IFN? + IL-1? and IFN?.ConclusionsOur data show that human iPSC-derived beta cells respond to pro-inflammatory cytokines IL-1? + IFN? and IFN?, by activating the same pathogenic processes as adult human primary beta cells. These cells thus represent a valuable tool for future research on the pathogenesis of type 1 diabetes.

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Mcl-1 downregulation by pro-inflammatory cytokines and palmitate is an early event contributing to ?-cell apoptosis.

Publications

Mcl-1 downregulation by pro-inflammatory cytokines and palmitate is an early event contributing to β-cell apoptosis.

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