MECHANISMS OF CARDIOVASCULAR DISEASE IN OBESITY

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Little information is available about the molecular mechanisms that promote the hypercoagulable state and increased risk for cardiovascular disease in human obesity. Although plasminogen activator inhibitor 1 (PAI-1) is consistently and significantly elevated in the plasma of obese humans and is a known risk factor for atherothrombolic disease, the origin and regulatory mechanism(s) that control its expression in obesity remain to be defined. Our studies of obese mice and cultured adipocytes suggest that elevated plasma PAI-1 results from increased synthesis by adipocytes in response to tumor necrosis factor-alpha and insulin, and that the adipocyte may play a central and previously unrecognized role in hemostatic gene expression in human obesity. The following observations provide additional novel insights into adipocytes and PAI-1 biosynthesis in obesity and form the basis of this application: (1) transforming growth factor beta (TGF-beta) mRNA is chronically elevated in adipose tissue of obese mice and is a powerful inducer of PAI-1 in adipocytes; (2) the adipocyte is the primary insulin-responsive cell in terms of PAI-1; and (3) insulin continues to induce PAI-1 in metabolically insulin-resistant adipocytes and mice. We hypothesize that the increased TGF-beta and hyperinsulinemia in obesity alters the biosynthetic activity of adipocytes and promotes the cardiovascular risk associated with this condition. In Aim 1, we will investigate the regulation and consequences of TGF-beta expression in obesity and during adipogenesis. The possibility that TGF-beta alters preadipocyte growth and differentiation as well as adipocyte gene expression, glucose homeostasis, and insulin-resistance will be explored in vivo and in vitro using specific inhibitors of TGF-beta. In Aim 2, we will examine additional models of murine obesity to determine the generality and tissue specificity of the effects of insulin on PAI-1. We will also employ inhibitors of insulin-signaling to define the pathways that control PAI-1 gene expression, and to test the hypothesis that in adipocytes, glucose homeostasis and PAI-1 gene expression are regulated by different pathways. These studies should provide novel information about TGF-beta and insulin and their respective roles in the regulation of PAI-1 in adipocytes in health and disease.