The Na+/Ca2+ exchanger and the Plasma Membrane Ca2+-ATPase in β-cell function and diabetes

The rat pancreatic β-cell expresses 6 splice variants of the Plasma Membrane Ca2+-ATPase (PMCA) and two splice variants of the Na+/Ca2+ exchanger 1 (NCX1). In the β-cell Na+/Ca2+ exchange displays a high capacity, contributes to both Ca2+ outflow and influx and participates to the control of insulin release. Gain of function studies show that overexpression of PMCA2 or NCX1 leads to endoplasmic reticulum (ER) Ca2+ depletion with subsequent ER stress, decrease in β-cell proliferation and β-cell death by apoptosis. Loss of function studies show, on the contrary, that heterozygous inactivation of NCX1 (Ncx1+/−) leads to an increase in β-cell function and a 5 fold increase in both β-cell mass and proliferation. The mutation also increases β-cell resistance to hypoxia, and Ncx1+/− islets show a 2–4 times higher rate of diabetes cure than Ncx1+/+ islets when transplanted in diabetic animals. Thus, down-regulation of the Na+/Ca2+ exchanger leads to various changes in β-cell function that are opposite to the major abnormalities seen in diabetes. In addition, the β-cell includes the mutually exclusive exon B in the alternative splicing region of NCX1, which confers a high sensitivity of its NCX splice variants (NCX1.3 & 1.7) to the inhibitory action of compounds like KBR-7943. Heterozygous inactivation of PMCA2 leads to apparented, though not completely similar results.These provide 2 unique models for the prevention and treatment of β-cell dysfunction in diabetes and following islet transplantation.SCOPUS: re.jinfo:eu-repo/semantics/publishe

Cellules souches pluripotentes induites et technologies associées :de nouveaux outils performants permettant de tester les traitements liés au diabète et de mieux comprendre sa pathogenèse

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β-Cell preservation and regeneration in diabetes by modulation of β-cell Ca²⁺ homeostasis.

Ca(2+) extrusion from the β-cell is mediated by two processes the Na/Ca exchanger (NCX) and the plasma membrane Ca(2+) -ATPase (PMCA). Gain of function studies show that overexpression of NCX or PMCA leads to endoplasmic reticulum (ER) Ca(2+) depletion with subsequent ER stress, decrease in β-cell proliferation and β-cell death by apoptosis. Interestingly, chronic exposure to cytokines or high free fatty acid concentrations also induce ER Ca(2+) depletion and β-cell death in diabetes. Loss of function studies show, on the contrary, that heterozygous inactivation of NCX1 (Ncx1(+/-)) leads to an increase in β-cell function (insulin production and release), and a fivefold increase in both β-cell mass and proliferation. The mutation also increases β-cell resistance to hypoxia, and Ncx1(+/-) islets show a two to four times higher rate of diabetes cure than Ncx1(+/+) islets when transplanted in diabetic animals. Thus, down-regulation of the Na/Ca exchanger leads to various changes in β-cell function that are opposite to the major abnormalities seen in diabetes. This provides a unique model for the prevention and treatment of β-cell dysfunction in diabetes and following islet transplantation.Journal ArticleResearch Support, Non-U.S. Gov'tFLWINSCOPUS: re.jinfo:eu-repo/semantics/publishe

Heterozygous inactivation of plasma membrane Ca(2+)-ATPase in mice increases glucose-induced insulin release and beta cell proliferation, mass and viability

AIMS/HYPOTHESIS: Calcium plays an important role in the process of glucose-induced insulin release in pancreatic beta cells. These cells are equipped with a double system responsible for Ca(2+) extrusion--the Na/Ca exchanger (NCX) and the plasma membrane Ca(2+)-ATPase (PMCA). We have shown that heterozygous inactivation of NCX1 in mice increased glucose-induced insulin release and stimulated beta cell proliferation and mass. In the present study, we examined the effects of heterozygous inactivation of the PMCA on beta cell function. METHODS: Biological and morphological methods (Ca(2+) imaging, Ca(2+) uptake, glucose metabolism, insulin release and immunohistochemistry) were used to assess beta cell function and proliferation in Pmca2 (also known as Atp2b2) heterozygous mice and control littermates ex vivo. Blood glucose and insulin levels were also measured to assess glucose metabolism in vivo. RESULTS: Pmca (isoform 2) heterozygous inactivation increased intracellular Ca(2+) stores and glucose-induced insulin release. Moreover, increased beta cell proliferation, mass, viability and islet size were observed in Pmca2 heterozygous mice. However, no differences in beta cell glucose metabolism, proinsulin immunostaining and insulin content were observed. CONCLUSIONS/INTERPRETATION: The present data indicates that inhibition of Ca(2+) extrusion from the beta cell and its subsequent intracellular accumulation stimulates beta cell function, proliferation and mass. This is in agreement with our previous results observed in mice displaying heterozygous inactivation of NCX, and indicates that inhibition of Ca(2+) extrusion mechanisms by small molecules in beta cells may represent a new approach in the treatment of type 1 and type 2 diabetes

Mcl-1 is a key anti-apoptotic protein in human and rodent pancreatic beta cells

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MCL-1 is a Key Anti-Apoptotic Protein in Human and Rodent Pancreatic Beta cells.

Induction of endoplasmic reticulum stress and activation of the intrinsic apoptotic pathway is widely believed to contribute to β-cell death in type 1 diabetes (T1D). MCL-1 is an anti-apoptotic member of the BCL-2 protein family, whose depletion causes apoptosis in rodent β-cells in vitro. Importantly, decreased MCL-1 expression was observed in islets from T1D patients. We report here that MCL-1 downregulation is associated with cytokine-mediated killing of human β-cells, a process partially prevented by MCL-1 overexpression. By generating a β-cell specific Mcl-1 knockout mouse strain (βMcl-1KO), we observed that, surprisingly, MCL-1 ablation does not affect islet development and function. β-cells from βMcl-1KO mice were, however, more susceptible to cytokine-induced apoptosis. Moreover, βMcl-1KO mice displayed higher hyperglycaemia and lower pancreatic insulin content after multiple low dose streptozotocin treatment. We found that the kinase GSK3β, the E3 ligases MULE and βTrCP and the deubiquitinase USP9x, regulate cytokine-mediated MCL-1 protein turnover in rodent β-cells. Our results identify MCL-1 as a critical pro-survival protein for preventing β-cell death and clarify the mechanisms behind its downregulation by pro-inflammatory cytokines. Development of strategies to prevent MCL-1 loss in the early stages of T1D may enhance β-cell survival and thereby delay or prevent disease progression.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

GLP-1 analogs protect beta cells in models of Wolfram syndrome

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Pancreatic beta-cell tRNA hypomethylation and fragmentation link TRMT10A deficiency with diabetes

Transfer RNAs (tRNAs) are non-coding RNA molecules essential for protein synthesis. Post-transcriptionally they are heavily modified to improve their function, folding and stability. Intronic polymorphisms in CDKAL1, a tRNA methylthiotransferase, are associated with increased type 2 diabetes risk. Loss-of-function mutations in TRMT10A, a tRNA methyltransferase, are a monogenic cause of early onset diabetes and microcephaly. Here we confirm the role of TRMT10A as a guanosine 9 tRNA methyltransferase, and identify tRNA(Gln) and tRNA(iMeth) as two of its targets. Using RNA interference and induced pluripotent stem cell-derived pancreatic beta-like cells from healthy controls and TRMT10A-deficient patients we demonstrate that TRMT10A deficiency induces oxidative stress and triggers the intrinsic pathway of apoptosis in beta-cells. We show that tRNA guanosine 9 hypomethylation leads to tRNA(Gln) fragmentation and that 5'-tRNA(Gln) fragments mediate TRMT10A deficiency-induced beta-cell death. This study unmasks tRNA hypomethylation and fragmentation as a hitherto unknown mechanism of pancre-atic beta-cell demise relevant to monogenic and polygenic forms of diabetes.Peer reviewe

GLP-1 analogs protect beta cells and prevent diabetes in models of Wolfram syndrome.

info:eu-repo/semantics/nonPublishe