[Relationship between islet beta cell dysfunction and gene expression of uncoupling protein-2 and possible mechanism thereof].

OBJECTIVE

To study the effects of high fat diet on the functions of islet beta cells and the role of uncoupling protein-2 (UCP2) therein and possible mechanism.

METHODS

Forty SD rats were randomly divided into two equal groups: high-fat-(HF) diet group, fed with HF diet for 20 weeks, and normal diet control (NC) group, fed with normal diet. At the end of the twentieth week blood samples were collected from the heart to determine the serum fasting blood glucose (FBG) and fasting insulin (FINS), and plasma nitrotyrosine, malondialdehyde (MDA), and glutamylcysteinylglycine (GSH), indicators of oxidative stress. Glucose infusion rate (GIR) was measured using euglycemic hyperinsulinemic clamp test to evaluate the peripheral insulin resistance. Pancreatic islets were isolated and collected. Islet perfusion was conducted to evaluate the insulin secretion in the islet beta cells. Real-time PCR was used to detect the expression of insulin receptor substrate-1 (IRS-1), IRS-2, and uncoupling protein 2 (UCP2) genes in the islet. Immunohistochemistry was used to detect the protein expression of IRS-1 and IRS-2.

RESULTS

(1) The concentrations of plasma nitrotyrosine and MDA of the HF group were both significantly higher than those of the NC group (both P < 0.05). However, the plasma GSH of the HF group was significantly lower than that of the NC group (P < 0.01). (2) The blood glucose of both groups became stable since 60 min after the experiment and the GIR of the HF group was (5.25 +/- 1.2) mg x min(-1) x kg(-1), significantly lower r than that of the NC group [(13.6 +/- 1l.7) mg x min(-1) x kg(-1), P < 0.01). (3) The peak of glucose-stimulated insulin secretion (GSIS) of the HF group was significantly lower than that of the NC group; and the GSIS peak increase In comparison with the NC group. (4) In comparison with the NC group, the mRNA expression levels of IRS-1 and IRS-2 genes of the HF group were significantly lower, by 42.3% and 28.1% respectively (both P < 0.05), and the expression of UCP2 was significantly higher, by 32.5% (P < 0.05). (5) Compared with the NC group, the protein expression levels of IRS-1 and IRS-2 in the islets of the HF group were lower, by 26.3% and 11.2% respectively, however not significantly (both P > 0.05). (6) There was a significantly negative correlation between the UCP2 and IRS-1/IRS-2 gene expression in islet beta cells in the HF group (r = -0.621 and r = -0.436, both P < 0.05).

CONCLUSION

High-fat-diet impairs the expression of insulin signal transduction molecules and the function of islet beta cells that may be correlated with overexpression of UCP2. The basic insulin secretion of HF group was significantly higher than that of the NC group; but the glucose-stimulated insulin secretion (GSIS) peak decreased in comparison with the NC group. Compared with the NC group, the protein expression levels of IRS-1 and IRS-2 in the islets of the HF group were lower, by 26.3% (P < 0.05) and 11.2% (P > 0.05) respectively.