Expression of 25-hydroxyvitamin D3-1α-hydroxylase in pancreatic islets

A number of studies have suggested that Vitamin D has a potential role in the development/treatment of diabetes. These effects may be mediated by circulating levels of I alpha,25(OH)(2)D-3, but local production of 1alpha,25(OH)2D3, catalysed by the enzyme 25-hydroxyvitamin D-3-1alpha-hydroxylase (1alpha-OHase), is also likely to be important. RT-PCR analyses demonstrated that both isolated rat islets and MIN6 cells (mouse insulin-secreting cell line, characteristic of P cells) expressed 1alpha-OHase mRNA. The transcript in both cell types was similar to that seen in HKC-8 cells (a renal cell line, which expresses 1alpha-OHase). Western blot analysis and immunolocalisation identified I alpha-OHase protein in MIN6 cells and human pancreatic tissue. In addition, suspensions of rat islets were able to convert [H-3]-25-hydroxyvitamin D-3 to [H-3]-1alpha,25(OH)(2)D-3, demonstrating 1alpha-OHase activity. Both cell systems expressed the Vitamin D receptor and 1alpha,25(OH)(2)D-3 (50 nM) evoked a rapid rise in [Ca2+], in MIN6 cells. This data clearly demonstrates islets are able to produce 1alpha,25(OH)(2)D-3 and respond rapidly to treatment with 1alpha,25(OH)(2)D-3. Therefore, we would postulate that local production of 1alpha,25(OH)(2)D-3 maybe an important autocrine link between Vitamin D status and pancreatic function. (C) 2004 Elsevier Ltd. All rights reserved.