TOYONAGA Tetsushi Kumamoto University, School of medicine, Assistant Professor, 医学部, 助手 (60295128)
KISHIKAWA Hideki Kumamoto University, School of medicine, Lecturer, 医学部, 講師 (30161441)
|Budget Amount *help
¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1999 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1998 : ¥2,700,000 (Direct Cost : ¥2,700,000)
1. To examine if the natural IRS-1 gene variants contribute to the development of type 2 diabetes, we have studied the impact of four mutant IRS-1s (P170R, M209T, S809F and G971R) on insulin signaling. 32D-IR cells, stably overexpresing human IR and lack endo-genous IRS-1, were transfected with wild-type (WT) or four mutant IRS-1 cDNAs, and analyzed. Cells expressing P170R, M209T and G971R exhibited significant decrease in insulin actions as compared with WT, while S809F did not. These data suggested the contribution of IRS-1 variants to the development of type 2 diabetes.
2. To determine the molecular mechanism of bradykinin (BK) enhancement of the insulin signal, 32D cells were transfected with BK B2 receptor (BK2R) and/or insulin receptor and/or IRS-1 cDNA, and analyzed. In these cells, BK enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1 and increased IRS-1 associated PI 3-kinase activity. Furthermore, protein tyrosine phosphatase (PTPase) activity against insulin receptor in particulate factor of the cells was significantly reduced by BK, suggesting that effect of BK was in part mediated by inhibition of PTPase(s) localized in particulate fraction. Our results demonstrated that BK enhanced insulin signal cascade through the BK2R mediated signaling pathway.
3. To clarify the contribution of obesity in individuals with IRS-1 abnormality, we created obese IRS-1 (+/-) mice and characterized. Obese IRS-1 (+/-) mice showed twice higher plasma insulin than obese WT mice. Intraperitoneal glucose tolerance test showed higher blood glucose at 60 min in obese IRS-1(+/-) mice compared to obese WT mice, and intraperitoneal insulin toletance test showed higher insulin resistance in obese IRS-1 (+/-) mice compared to obese WT mice. These results suggest that gene abnormality, such as IRS-1 gene variants, which does not affect insulin resistance at normal body weight, could worsen insulin resistance in vivo when they complicated obesity.