Diabetes mellitus and hypertension are closely linked, and are major risk factors in the development of vascular disease. Growing experimental and clinical evidence has demonstrated that the renin-angiotensin system (RAS) contributes to the pathogenesis of these vascular complications. These studies have demonstrated that angiotensin-converting-enzyme (ACE) inhibitors reduce the progression of diabetic vascular complications by a mechanism which is, in part, independent of blood pressure control. Recently, while screening for novel actions of vasoactive hormones by differential mRNA display, I have discovered that angiotensin II (AII) is a potent stimulator of plasminogen activator inhibitor-2 (PAI-2) expression in rat microvessel endothelial (RME) cells and rat aortic smooth muscle cells (RASMC). These studies have been extended to show that PAI-1 expression is similarly induced in these vascular cells. Studies on the mechanism of AII-stimulated PAI-2 expression reveal that both PKC-dependent and PKC-independent signaling pathways contribute to the 44.8+/-12.5 (+/-S.E.M) fold increase in PAI-2 mRNA in RME cells. The PKC independent pathway which is coupled to AII-stimulated PAI-2 expression, is completely blocked with the tyrosine kinase inhibitor genistein. In contrast, AII stimulates a 12.4+/-1.6 fold increase in PAI-2 mRNA in RASMC, and this increase is entirely associated with PKC activation. We have initiated a search for a novel AII-stimulated tyrosine kinase-responsive transcriptional element with a series of 13 PAI-2/Chloramphenicol acetyltransferase (CAT) plasmids, including up to 3.3 Kb of the 5' flanking promoter sequence. Northern blot analysis of PAI-1 and PAI-2 mRNA levels in vascular tissues from control and diabetic rats demonstrated that the expression of these genes was elevated in the heart and aorta of diabetic animals. These elevated mRNA levels in diabetic rats are consistent with a number of recent clinical studies which have reported that PAI-1 is elevated in the plasma and in the tissues from diabetic individuals. The objective of this proposal is to examine the role of key, and possibly rate limiting, signal transduction elements in the AII- stimulated signaling pathway that regulate PAI-2 expression in RME cells. The role of these signaling pathways in PAI-2 transcription will be examined and we will use a series of PAI-2/CAT constructs to associate these signaling mechanisms with AII-responsive elements in the PAI-2 promoter. The striking AII-mediated induction of PAI-2 and PAI-1 in cultured vascular cells will also be used to examine the hypothesis that AII action contributes to alterations in gene expression in the diabetic vasculature, and a mechanism of ACE inhibitors action is to normalize this aberrant gene expression.
