Objective: The beneficial effect of angiotensin(1-7) (Ang(1-7)), via the activation of its receptor, MAS-1, has been noted in diabetes treatment; however, how Ang(1-7) or MAS-1 affects insulin secretion remains elusive and whether the endogenous level of Ang(1-7) or MAS-1 is altered in diabetic individuals remains unexplored. We recently identified an important role of cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated Cl- channel, in the regulation of insulin secretion. Here, we tested the possible involvement of CFTR in mediating Ang(1-7)'s effect on insulin secretion and measured the level of Ang(1-7), MAS-1 as well as CFTR in the blood of individuals with or without type 2 diabetes.
Methods: Ang(1-7)/MAS-1/CFTR pathway was determined by specific inhibitors, gene manipulation, Western blotting as well as insulin ELISA in a pancreatic β-cell line, RINm5F. Human blood samples were collected from 333 individuals with (n = 197) and without (n = 136) type 2 diabetes. Ang(1-7), MAS-1 and CFTR levels in the human blood were determined by ELISA.
Results: In RINm5F cells, Ang(1-7) induced intracellular cAMP increase, cAMP-response element binding protein (CREB) activation, enhanced CFTR expression and potentiated glucose-stimulated insulin secretion, which were abolished by a selective CFTR inhibitor, RNAi-knockdown of CFTR, or inhibition of MAS-1. In human subjects, the blood levels of MAS-1 and CFTR, but not Ang(1-7), were significantly higher in individuals with type 2 diabetes as compared to those in non-diabetic healthy subjects. In addition, blood levels of MAS-1 and CFTR were in significant positive correlation in type-2 diabetic but not non-diabetic subjects.
Conclusion: These results suggested that MAS-1 and CFTR as key players in mediating Ang(1-7)-promoted insulin secretion in pancreatic β-cells; MAS-1 and CFTR are positively correlated and both upregulated in type 2 diabetes.
Keywords: CFTR; MAS-1; angiotensin(1–7); insulin; p-CREB; type 2 diabetes.