Abnormalities contributing to the pathogenesis of non-insulin-dependent diabetes mellitus include impaired ␤ cell function, peripheral insulin resistance, and increased hepatic glucose production. Glucocorticoids are diabetogenic hormones because they decrease glucose uptake and increase hepatic glucose production. In addition, they may directly inhibit insulin release. To evaluate that possible role of glucocorticoids in ␤ cell function independent of their other effects, transgenic mice with an increased glucocorticoid sensitivity restricted to their ␤ cells were generated by overexpressing the glucocorticoid receptor (GR) under the control of the insulin promoter. Intravenous glucose tolerance tests showed that the GR transgenic mice had normal fasting and postabsorptive blood glucose levels but exhibited a reduced glucose tolerance compared with their control littermates. Measurement of plasma insulin levels 5 min after intravenous glucose load demonstrated a dramatic decrease in acute insulin response in the GR transgenic mice. These results show that glucocorticoids directly inhibit insulin release in vivo and identify the pancreatic ␤ cell as an important target for the diabetogenic action of glucocorticoids. (

Islet transplantation offers improved glucose homeostasis in diabetic patients, but transplantation of islets is limited by the supply of donor pancreases. Undifferentiated precursors hold promise for cell therapy because they can expand before differentiation to produce a large supply of functional insulin-producing cells. Previously, we described proliferative populations of human islet-derived precursor cells (hIPCs) from adult islets. To show the differentiation potential of hIPCs, which do not express insulin mRNA after at least 1,000-fold expansion, we generated epithelial cell clusters (ECCs) during 4 days of differentiation in vitro. After transplantation into mice, 22 of 35 ECC preparations differentiated and matured into functional cells that secreted human C-peptide in response to glucose. Transcripts for insulin, glucagon, and somatostatin in recovered ECC grafts increased with time in vivo, reaching levels approximately 1% of those in adult islets. We show that hIPCs are mesenchymal stromal cells (MSCs) that adhere to plastic, express CD73, CD90, and CD105, and can differentiate in vitro into adipocytes, chondrocytes, and osteocytes. Moreover, we find a minor population of CD105 ؉ /CD73 ؉ /CD90 ؉ cells in adult human islets (prior to incubation in vitro) that express insulin mRNA at low levels. We conclude that hIPCs are a specific type of pancreas-derived MSC that are capable of differentiating into hormone-expressing cells. Their ability to mature into functional insulin-secreting cells in vivo identifies them as an important adult precursor or stem cell population that could offer a virtually unlimited supply of human islet-like cells for replacement therapy in type 1 diabetes. STEM CELLS 2007;25:3215-3222 Disclosure of potential conflicts of interest is found at the end of this article.

Metabolic transformation of glucocorticoid hormones constitutes a determinant of their cell-specific effects.The most important reaction for this class of steroids is the reversible C11 keto/␤-hydroxyl conversion between receptor-binding 11␤-OH steroids and the nonbinding 11-oxo compounds, carried out by 11␤-hydroxysteroid dehydrogenases (11␤-HSDs). In this study, we determined the role of glucocorticoid conversion by 11␤-HSD in pancreatic islets and its function in the regulation of insulin release. Pancreatic islets isolated from ob/ob mice display type 1 11␤-hydroxysteroid dehydrogenase activity, i.e. in intact cells the reductive reaction prevails, leading from dehydrocorticosterone to corticosterone. Expression of type 1 11␤-HSD mRNA was detected by reverse transcriptase-polymerase chain reaction in islets isolated from ob/ob mice and also from human tissue. Incubation of ␤-cells in the presence of 11-dehydrocorticosterone leads to a dose-dependent inhibition of insulin release, indicating cellular activation of 11-dehydrocorticosterone to the receptor ligand, further confirmed by reporter gene assays. Inhibition of 11␤-HSD activity by carbenoxolone reverses inhibition of insulin release. The presence of 11␤-HSD in islets supports the concept that reactivation of inert circulating hormone precursors in a cellspecific manner plays a major role in glucocorticoid physiology in rodents and man.

Glucocorticoids are diabetogenic hormones because they decrease glucose uptake, increase hepatic glucose production, and inhibit insulin release. To study the long-term effects of increased glucocorticoid sensitivity in ␤-cells, we studied transgenic mice overexpressing the rat glucocorticoid receptor targeted to the ␤-cells using the rat insulin I promoter. Here we report that these mice developed hyperglycemia both in the fed and the overnight-fasted states at 12-15 months of age. Progression from impaired glucose tolerance, previously observed in the same colony at the age of 3 months, to manifest diabetes was not associated with morphological changes or increased apoptosis in the ␤-cells. Instead, our current results suggest that the development of diabetes is due to augmented inhibition of insulin secretion through ␣ 2 -adrenergic receptors (␣ 2 -ARs). Thus, we found a significantly higher density of ␣ 2 -ARs in the islets of transgenic mice compared with controls, based on binding studies with the ␣ 2 -AR agonist UK 14304. Furthermore, incubation of islets with benextramine, a selective antagonist of the ␣ 2 -AR, restored insulin secretion in response to glucose in isolated islets from transgenic mice, whereas it had no effect on control islets. These results indicate that the chronic enhancement of glucocorticoid signaling in pancreatic ␤-cells results in hyperglycemia and impaired glucose tolerance. This effect may involve signaling pathways that participate in the regulation of insulin secretion via the ␣ 2 -AR. Diabetes 53 (Suppl. 1): S51-S59, 2004