Adult β-cell dysfunction, a hallmark of type 2 diabetes, can be programmed by adverse fetal environment. We have shown that fetal glucocorticoids (GCs) participate in this programming through inhibition of β-cell development. Here we have investigated the molecular mechanisms underlying this regulation. We showed that GCs stimulate the expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a coregulator of the GCs receptor (GR), and that the overexpression of PGC-1α represses genes important for β-cell development and function. More precisely, PGC-1α inhibited the expression of the key β-cell transcription factor pancreatic duodenal homeobox 1 (Pdx1). This repression required the GR and was mediated through binding of a GR/PGC-1α complex to the Pdx1 promoter. To explore PGC-1α function, we generated mice with inducible β-cell PGC-1α overexpression. Mice overexpressing PGC-1α exhibited at adult age impaired glucose tolerance associated with reduced insulin secretion, decreased β-cell mass, and β-cell hypotrophy. Interestingly, PGC-1α expression in fetal life only was sufficient to impair adult β-cell function whereas β-cell PGC-1α overexpression from adult age had no consequence on β-cell function. Altogether, our results demonstrate that the GR and PGC-1α participate in the fetal programming of adult β-cell function through inhibition of Pdx1 expression.
Background. Accurate determination of islet purity and mass before transplantation is an essential part of quality control. The standard method is based on manual evaluation of these parameters and thus subjective and prone to errors. Therefore, we developed a computerized approach aimed at evaluating more objectively the number and purity of isolated human islets. Methods. Islets were isolated and purified from human pancreata according to a standard method. For each preparation, two samples were dithizone stained. One sample was analyzed manually by microscopy, following the standard procedure, and the other was digitally photographed for both digital manual and computerized analyses. Computerized analysis was performed using the MetaMorph and ImageJ softwares to automatically quantify purity and size of islets. Islet equivalent (IEQ) number was calculated using the Ricordi algorithm or considering the individual volume of each islet. Computerized analysis was validated using calibrated red glass microspheres. Results. When digital manual and computerized analyses were compared, mean values of total islet number, IEQ number calculated using the Ricordi algorithm, and purity were similar. Comparisons of individual values showed good correlations (r2≥0.89). By standard manual analysis, total islet number and purity were higher and IEQ number similar compared with digital manual and computerized analyses. IEQ number was 10% lower (P<0.0001) when calculated using individual sphere volumes compared with the Ricordi algorithm. Measurement of red glass microspheres showed identical values comparing standard manual and computerized analyses. Conclusions. Computer-assisted digital image analysis is an objective and a reliable method for analyzing pancreatic islets before transplantation.
Adult beta-cell dysfunction, a hallmark of type 2 diabetes, can be programmed by adverse fetal environment. We have shown that fetal glucocorticoids (GCs) participate in this programming through inhibition of beta-cell development. Here we have investigated the molecular mechanisms underlying this regulation. We showed that GCs stimulate the expression of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha), a coregulator of the GCs receptor (GR), and that the overexpression of PGC-1 alpha represses genes important for beta-cell development and function. More precisely, PGC-1 alpha inhibited the expression of the key beta-cell transcription factor pancreatic duodenal homeobox 1 (Pdx1). This repression required the GR and was mediated through binding of a GR/PGC-1 alpha complex to the Pdx1 promoter. To explore PGC-1 alpha function, we generated mice with inducible beta-cell PGC-1 alpha overexpression. Mice overexpressing PGC-1 alpha exhibited at adult age impaired glucose tolerance associated with reduced insulin secretion, decreased beta-cell mass, and beta-cell hypotrophy. Interestingly, PGC-1 alpha expression in fetal life only was sufficient to impair adult beta-cell function whereas beta-cell PGC-1 alpha overexpression from adult age had no consequence on beta-cell function. Altogether, our results demonstrate that the GR and PGC-1 alpha participate in the fetal programming of adult beta-cell function through inhibition of Pdx1 expression. Diabetes 62:1206-1216, 2013
Laminin-332 (LN-332) is a basement membrane component known to exert a beneficial effect on rat pancreatic beta cells in vitro. In this work, we analyzed the expression of LN-332 in human islets, its expression after inflammatory insults by cytokines, and the molecular mechanisms responsible for this effect. By Western blotting and RT-PCR, we showed that LN-332 was expressed in isolated human islets. By immunofluorescence on pancreas sections, we observed that labeling was confined to endocrine cells in islets. Confocal microscopy analysis on isolated islet cells revealed that labeling was granular but did not colocalize with hormone secretory granules. LN-332 was most abundant in cultured islets compared to freshly isolated islets and was found in culture medium, which suggests that it was secreted by islets. When islets were exposed to interleukin (IL)-1beta, expression and secretion of LN-332 increased as compared to control. No effect was observed with tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K) activity, inhibited culture- and IL-1beta-induced LN-332 expression in islets. These results show that LN-332, known to have some beneficial effect on beta cells in vitro, is produced and secreted by endocrine islet cells and is up-regulated by stressing conditions such as culture and IL-1beta-exposure.
