Gene Expression And Regulation Of Insulin And PDX-1 In Isolated Rat Islets

Objective To investigate the influence of nutrients, hormones, and cytokines on insulin and pancreas duodenum homeobox-1 (PDX-1) mRNA expression in isolated rat islets, elucidate the relationship between insulin and PDX-1 gene, and study the implications of these factors in the pathogenesis and treatment of type 2 diabetes mellitus.Methods The isolated rat islets were cultured and stimulated with glucose, glucagon-like peptide-1(GLP-1), leptin and transforming growth factor-β(TGF-β). Total cellular RNA was extracted, and the expression of insulin and PDX-1 gene was detected by semi-quantitative reverse transcription polymerase chain reaction ( RT-PCR).Results (1) Short-term exposure of isolated rat islets to supraphysiologic concentration of glucose increased insulin and PDX-1 gene expression, whereas chronic exposure exerts suppressive effect, indicating the glucose toxicity on β cells. Insulin and PDX-1 gene expression is reduced by underphysiologic glucose concentration as well. (2) At low and normal glucose concentrations, GLP-1 increased insulin and PDX-1 mRNA levels in a bell-shaped fashion; At high glucose concentration, dose-dependent increase in insulin and PDX-1 mRNA levels were observed, which were not bell-shaped. (3) At low glucose concentration, there was no change in insulin gene expression with different concentrations of leptin, though it could stimulate insulin gene expression in lower than normal concentrations with normal or high glucose levels, while insulin gene expression was suppressed by leptin in a dose-dependent manner in the medium with normal or high glucose. Nevertheless, leptin did not affect PDX-1 gene expression. (4) At lowglucose concentration, there was no change in insulin and PDX-1 gene expression with different concentrations of TGF-β, whereas a dose-dependent TGF-β stimulation of insulin and PDX-1 mRNA levels were observed at normal and high glucose concentrations.Conclusions (1) Chronic exposure of isolated rat islets to non-physiologic concentration of glucose decreased insulin and PDX-1 gene expression, suggesting that the normal glucose concentration plays an important role in the protection of islet (3 cell function for diabetic patients. (2) Insulin and PDX-1 mRNA levels were upregulated by GLP-1 in dose-dependent and glucose-dependent manners, indicating that GLP-1 is likely to be a new hypoglycemia agent for type 2 diabetes mellitus. (3) Different concentrations of leptin stimulated or suppressed insulin gene expression in a glucose-dependent manner, suggesting that the dysregulation of the adipoinsular axis may contribute to the pathogensis of adipogenic diabetes. (4) TGF-β increased insulin and PDX-1 mRNA levels in dose-dependent and glucose-dependent manners, indicating that TGF-β is a new theraeutic target for type 2 diabetes mellitus. (4) Glucose, GLP-1, TGF-β stimulated the transcription of insulin gene by means of transcription factor, PDX-1, though leptin exerts no such effect.