Chronic venous insufficiency (CVI) is a common and costly disease characterized by excessive vein dilation and varicose veins. CVI commonly occurs in the lower extremity, suggesting a role of venous pressure and vein wall stretch. Also, the plasma and venous tissue levels of matrix metalloproteinases (MMPs) are elevated in CVI, suggesting a role for MMPs in vein dilation. We have found that prolonged stretch of rat veins is associated with decreased contraction and increased expression of MMP-2 and -9. Also, varix segments of varicose veins demonstrate reduced contraction as compared to control saphenous vein. These novel findings make it important to investigate the link between vein wall stretch and MMPs in the venous dilation associated with varicose veins, and to identify the upstream and downstream mechanisms involved. Our data suggest that prolonged vein stretch is associated with increased expression of hypoxia-inducible factors (HIF). Also, MMP- 2 and -9 induce relaxation of vein segments even in the absence of detectable extracellular matrix (ECM) degradation, suggesting inhibition of venous smooth muscle (VSM) contraction mechanisms. The objective of this proposal is to test the central hypothesis that increased venous pressure and prolonged vein wall stretch are associated with upregulation of a mechano-sensitive HIF-MMP pathway, which in turn causes downstream inhibition of VSM contraction mechanisms and increased degradation of ECM proteins, leading to excessive venous dilation. Consequently, downregulation of the HIF-MMP pathway should improve reactivity in veins subjected to prolonged stretch and in varicose veins. Mechanistic studies will be conducted in a rat model of increased femoral venous pressure, and on isolated iliac and femoral veins. Although the rat is a four-legged animal, the rat is a consistent breed that avoids the variability in age, sex and other confounding factors in humans. To enhance the translational aspects, experiments will be conducted on human varix veins as compared to adjacent proximal and distal veins, and control saphenous veins. The specific aims are to determine whether: 1) Increased venous pressure/vein wall stretch is associated with decreased vein contraction and upregulation of HIF/MMP pathway. 2) Increases in HIF/MMP activity promote venous dilation by downstream inhibition of the mechanisms of VSM contraction including [Ca2+]i, protein kinase C and Rho- kinase activity, and increased ECM degradation. 3) The increased venous dilation in varicose veins occurs as a result of upregulation of HIF/MMPs, and therefore downregulation of HIF or MMPs using HIF or MMP inhibitors and siRNA should improve contraction in varix segments to levels approaching those observed in the adjacent proximal or distal veins, or in control saphenous vein. These studies would elucidate the relation between increased venous pressure/vein wall stretch, HIF/MMP expression/activity, reduced mechanisms of VSM contraction, and excessive venous dilation. The results would highlight the benefits of specific inhibitors of HIF and MMPs as a new strategy to prevent the progression and recurrence of varicose veins.