Nitric oxide (NO) is generally considered to play a protective role in blood vessels. However, others and we have obtained evidence that this may not always be the case but the mechanisms underlying diverse responses to NO are not known. The purpose of this proposal is to test an exciting new hypothesis on the capacity of chronically elevated insulin levels to switch the role of nitric oxide from protective to deleterious substance in blood vessels. We have found that the inhibitory effects of NO on both motility and proliferation are abrogated in vascular smooth muscle cells chronically treated with insulin. These findings support a new hypothesis on the role of insulin as a switcher of vascular smooth muscle cell phenotypic responses to NO. Our preliminary results indicate that the motility-stimulatory effect of NO, uncovered by chronic insulin treatment of cultured rat aortic smooth muscle cells, is associated with increased PI 3 kinase activity and requires the functional availability of angiotensin II, of the adapter protein Gab1 and the protein tyrosine phosphatase SHP2. Studies by others have found that Gab1 can be recruited to the plasma membrane via increased PIPS levels. However, the mechanistic linkage of chronic insulin treatment to Gab1 and SHP2 function has not been defined. Moreover, experiments to determine whether similar mechanisms may be applicable to abrogation of the antiproliferative effect of NO by chronic insulin treatment have not been performed. Finally, the pathophysiological significance of our results is unknown. We propose to implement the following specific aims:
Aim 1 : To determine whether increased angiotensin II function is necessary and/or sufficient to account for the effect of insulin on PI3K activity and NO-induced cell motility.
Aim 2 : To determine whether chronic insulin treatment recruits Gab1 to the cell membrane and whether insulin- independent recruitment of Gab1 or SHP2 to the cell membrane can mimic the motility-stimulatory effect of NO uncovered by chronic insulin treatment.
Aim 3 : To uncover mechanisms that describe how hyperinsulinemia attenuates the effect of NO as inhibitor of PDGF-induced DNA synthesis, in cultured rat aortic smooth muscle cells.
Aim 4 : To determine whether expression of inducible nitric oxide synthase in vascular injury enhances neointima formation in hyperinsulinemic mice, but has the opposite effect in normoinsulinemic mice or in hyperinsulinemic mice treated with an AT1 receptor antagonist. ? ? ?
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