Vitamin D metabolites influence expression of genes concerning cellular viability and function in insulin producing ß-cells (INS1E).

BACKGROUND: Studies have shown that vitamin D can enhance glucose-stimulated insulin secretion (GSIS) and change the expression of genes in pancreatic ß-cells. Still the mechanisms linking vitamin D and GSIS are unknown. MATERIAL AND METHODS: We used an established ß-cell line, INS1E. INS1E cells were pre-treated with 10 nM 1,25(OH)2vitamin D or 10 nM 25(OH)vitamin D for 72 h and stimulated with 22 mM glucose for 60 min. RNA was extracted for gene expression analysis. RESULTS: Expression of genes affecting viability, apoptosis and GSIS changed after pre-treatment with both 1,25(OH)2vitamin D and 25(OH)vitamin D in INS1E cells. Stimulation with glucose after pre-treatment of INS1E cells with 1,25(OH)2vitamin D resulted in 181 differentially expressed genes, whereas 526 genes were differentially expressed after pre-treatment with 25(OH)vitamin D. CONCLUSION: Vitamin D metabolites may affect pancreatic ß-cells and GSIS through changed gene expression for genes involved in ß-cell function and viability.

Discovery of novel vitamin D-regulated proteins in INS-1 cells: a proteomic approach.

BACKGROUND: Experimental evidence indicates that vitamin D may have a beneficial role in pancreatic ß-cell function. Global gene expression studies have shown that the active metabolite 1,25-dihydroxyvitamin D3 [1,25-(OH)2 D3 ] modulates genes involved in ion transport, lipid metabolism and insulin secretion. METHODS: We employed stable isotope labelling by amino acids in cell culture in combination with liquid chromatography-tandem mass spectrometry to quantitatively assess the impact of two vitamin D metabolites, 1,25-(OH)2 D3 and 25-hydroxyvitamin D3 [25-(OH)D3 ], on global protein expression on a model rat ß-cell line, insulinoma-derived INS-1 cells. RESULTS: Although treatment with 1,25-(OH)2 D3 resulted in 31 differentially expressed proteins, 25-(OH)D3 had no impact on protein expression. Of these 31 proteins, 29 were upregulated, whereas two showed a decrease in abundance. Proteins whose expression levels markedly increased in the presence of 1,25-(OH)2 D3 included Crat, Hmgn2, Protein Tmsbl1 and Gdap1. One of the most important findings in this study is upregulation of proteins implicated in insulin granule motility and insulin exocytosis, suggesting a positive effect on insulin secretion. Moreover, modulation of several membrane transport proteins suggests that 1,25-(OH)2 D3 has an impact on the homeostatic regulation of ions, which is critical for most functions in the ß-cell. CONCLUSIONS: In this study, we discovered a number of novel 1,25-(OH)2 D3 -regulated proteins, which may contribute to a better understanding of the reported beneficial effects of vitamin D on pancreatic ß-cells. All in all, our findings should pave the way for future studies providing insights into molecular mechanisms by which 1,25-(OH)2 D3 regulates protein expression in pancreatic ß-cells.