PROTEOLYSIS OF HMW FGF-2 BY THROMBIN AND ITS CARDIOVASCULAR IMPLICATIONS

New York University School Of Medicine, New York NY

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Abstract

DESCRIPTION (provided by applicant): Cardiovascular disease is the major contributor to morbidity and mortality in Western countries. It is characterized by structural and functional changes of blood vessel's wall that lead to reduced blood flow and eventually occlusion. The integrity of the vascular wall is maintained by homeostatic mechanisms controlled by the endothelium. Stress caused by age, oxidants, mechanical injury, and inflammation can result in endothelial dysfunction leading to remodeling of the vessel wall. We found that thrombin, a key protease of the coagulation cascade and inflammatory response, cleaves the high molecular weight (HMW) forms of basic fibroblast growth factor (FGF-2), a ubiquitous protein with trophic effects on vascular cells. The C-terminal fragment of FGF-2 generated by thrombin is similar to low molecular weight (LMW;18 kDa) FGF-2, and induces vascular cell activation of the mitogen-activated protein kinases ERK-1/2. The N-terminal fragment generated by thrombin cleavage of HMW FGF-2 contains a sequence rich in asymmetric-dimethyl-arginine (ADMA) residues. In free form ADMA inhibits key reactions for blood vessel homeostasis such as nitric oxide synthesis, and its serum levels, elevated in diabetes, renal failure, hypertension, and hypercholesterolemia, correlate with a poor prognosis in cardiovascular patients. We found that thrombin cleavage of HMW FGF-2 dramatically upregulates intracellular ADMA levels in cultured cells. Thus, the C-terminal cleavage product of HMW FGF-2 can activate intracellular signaling and control vascular cell functions, while the N- terminal fragment of FGF-2 generates ADMA, a powerful inhibitor of nitric oxide synthesis. Although degradation of methylarginine-rich proteins is recognized as the major source of free ADMA, the factors controlling this process are unknown. Therefore, we propose to investigate this novel role of FGF-2 in vitro and in vivo. The results of this project can provide relevant information of the pathogenetic mechanisms of vascular injury occurring in hypertension, diabetes, and dyslipidemia, conditions that are all characterized by elevated serum levels of ADMA. The elucidation of these mechanisms will foster the development of new pharmacological tools for the treatment of the cardiovascular disorders associated with these diseases.