Substantial experimental and clinical evidence suggests that the renin-angiotensin system (RAS), primarily via the angiotensin II (Angll)/AT1 receptor pathway, exerts pro-atherogenic and pro-thrombogenic effects, even in the absence of hypertension. Reports from the PI's laboratory, and from other groups, have demonstrated that AngII is a potent stimulator of plasminogen activator inhibitor-1(PAI-1) expression in cultured vascular cells and RAS inhibition reduces neointimal PAI-1 expression in vascular tissues in normotensive rats in vivo. Recently, we have also reported that the nitric oxide/cGMP pathway suppresses AngII-induced PAI-1 expression. In preliminary studies, we have found that cGMP inhibits AngII signaling through the SAPK/JNK pathway and have identified a 38 base pair region on the PAI-1 promoter, which is activated by this pathway and inhibited by both cGMP and MEK-1,2 inhibition. Mutational analysis of this region revealed that both AP-1 and Sp1 sites were required to support the MEKK-1 stimulation. Moreover, PAI-1 promoter activity was synergistically activated by combined over-expression of both c-Jun and Sp1. These results demonstrate a novel mechanism for MEKK-1/MEK1,2 activation of the PAI-1 promoter that is dependent on the cooperative effects of adjacent Sp1 and AP-1 elements. The hypothesis to be tested in this grant is that the AngII/ AT1 receptor signaling via MEKK-1/MEK,1,2/JNK pathways activate PAI-1 transcription and this response in suppressed by cGMP. To test this hypothesis, this proposal will examine the effects of expression of dominant negative components of these MAP kinase pathways on Ang II-signaling and its stimulation of endogenous PAI-1 mRNA expression. In addition, the effects of constitutively active components of these MAP kinase pathways on PAI-1 promoter activity will be examined. The effects of cGMP on these responses will be examined using novel constititively active guanylyl cyclases. The physiological relevance of AT1 receptor-induced PAI-1 expression will be investigated in both control and genetically induced diabetic mice. This proposal will examine the hypothesis that AngII/AT1 pathway increases vascular PAI-1 expression in type 1 diabetes. To examine this hypothesis, the regulation of angiotensin AT receptors and Ang II effects on PAI-1 expression will be examined in a novel transgenic model of spontaneous and specific type I diabetes developed in C57B1/6 mice (BDC2.51B6.g7g7 mice). The long-term objective is to identify novel targets and approaches to control the blood pressure independent effects of Ang II on PAI-1 expression.
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