Effects of angiotensin II on insulin signaling pathway in NIT-1 cells

Abstract

Objective To evaluate the effects of angiotensin Ⅱ on insulin signaling pathway in insulin-secreting NIT-1 cells in mice. Methods NIT-1 cells were cultured in the modified DMED, and then in the serum-free DMEM before assigned to the following 6 groups: angiotensin Ⅱ group (group A), insulin group (group B), angiotensin Ⅱ+ insulin group (group C), angiotensin Ⅱ+ insulin+ saralasin group (group D), angiotensin Ⅱ+ insulin+ Diphenyleneiodonium group (group E) and control group (group F). Expression of insulin receptor tyrosine phosphorylation (IR-β-Tyr), tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1-Tyr), serine phosphorylation of insulin receptor substrate-1 (IRS-1-Ser), and P47 phox were evaluated by Western blot. Level of H2O2 was detected by flow cytometry. Expression of insulin mRNA was evaluated by reverse transcript-polymerase chain reaction.One-way analysis of variance (ANOVA) and LSD test were used for data analysis. Results Expression of IRS-1-Ser was higher in the group A than group F. The levels of IR-β-Tyr (1.22±0.26 vs 1.95±0.19, LSD test, P<0.01) and IRS-1-Tyr (0.74±0.18 vs 1.25±0.23, P<0.01) in group C were lower than those in group B, whereas the level of IRS-Ser was higher (1.11±0.17 vs 0.62±0.10, P<0.01). The expressions of IR-β-Tyr and IRS-1-Tyr in groups D and E were significantly increased when compared with group C, and the level of IRS-1-Ser changed adversely. The levels of H2O2 and P47 phox in groups A and C were significantly increased when compared with group F, and those in groups D and E were lower in comparison with group C. The expression of insulin mRNA was significantly increased in groups D and E than group C (group D vs group C: 0.80±0.17 vs 0.62±0.19, P<0.05; group E vs group C: 0.82±0.19 vs 0.62±0.19, P<0.01). Conclusions Angiotensin Ⅱ could increase the expression of IRS-1-Ser and inhibit insulin-stimulated IR-β-Tyr and IRS-1-Tyr in NIT-1 cells. Oxidative stress induced by nicotinamide adenine dinucleotide phosphate oxidase may play an important role in the effect of angiotensin Ⅱ in NIT-1 cells. Key words: AngiotensinⅡ; Receptors, insulin; Oxidative stress