Uncoupling Protein 2 Promoter Polymorphism - 866G/A Affects Its Expression in β-Cells and Modulates Clinical Profiles of Japanese Type 2 Diabetic Patients

Abstract

Common uncoupling protein 2 (UCP2) promoter polymorphism -866G/A is reported to be associated with its expression in adipose tissue and the risk of obesity in Caucasians. On the other hand, several studies suggested that UCP2 expression in β-cells is an important determinant of insulin secretion. In the Japanese population, morbid obesity is very rare, and insulin secretion capacity is relatively low as compared with Caucasians. Because UCP2 would link to insulin secretion and obesity, it might explain this ethnic difference. Here, we report that the UCP2 promoter with the A allele. showed higher promoter activity in the INS-1 β-cell line. The frequency of the A allele is higher in our Japanese study than that in Caucasians. Type 2 diabetic patients with the A allele need insulin therapy earlier and showed higher frequency of insulin treatment. Moreover glucose-induced early insulin secretion is significantly lower in patients with the A allele. However, there was no difference in allele frequency between obese and lean type 2 diabetic patients. In conclusion, UCP2: promoter polymorphism -866G/A does not affect obesity in Japanese type 2 diabetic patients but affects its transcription in β-cells and modulates glucose-induced insulin secretion and eventually insulin requirement in Japanese type 2 diabetic patients. Higher A allele frequency in the Japanese population might partly explain the ethnic difference of insulin secretion capacity.