Abstract 241: An Increased Response to Injury by Smooth Muscle Cells of Human Veins at Valve Sites

Abstract

Objective: Venous valves are prone to injury, thrombosis and fibrosis. We compared the behavior and gene expression of smooth muscle cells (SMCs) in the valve sinus vs non-valve sites to elucidate biological differences associated with vein valves. Methods: SMC migration was measured using 2.5 mm 2 explants of the intima/media of valve sinus segments (without valve leaflets) vs. non-valve segments of human saphenous veins. Proliferation and death of SMCs was determined by staining for Ki67 and TUNEL, respectively. Proliferation and migration of passaged valve vs non-valve SMCs was determined by cell counts and using microchemotaxis chambers. Global gene expression in valve vs non-valve intima/media was determined by RNA-Seq. Results: Valve SMCs demonstrated greater proliferation within tissue explants compared to non-valve SMCs (19.3±5.4% vs. 6.8±2.0% Ki67 positive nuclei at 4 days, respectively; mean ± SEM, 5 veins; P<.05). This was also true for migration (18.2±2.7 vs. 7.5±3.0 migrated SMCs/explant at 6 days, respectively; 24 veins, 15 explants/vein; P<.0001). Cell death was not different (39.6±16.1% vs. 41.5±16.0% TUNEL positive cells, respectively, at 4 days, 5 veins). Cultured valve SMCs also proliferated faster than non-valve SMCs in response to PDGF-BB (2.9±0.2 vs. 2.1±0.2 fold of control, respectively; P<.001; N=5 vein’s paired cells). This was also true for migration (6.5±1.2 vs. 4.4±0.8 fold of control, respectively; P<.001; N=7 vein’s paired cells). Blockade of FGF2 inhibited the increased responses of valve SMCs, but had no effect on non-valve SMCs. Exogenous FGF2 increased migration of valve, but not non-valve SMCs. Unexpectedly, blockade of FGF2 did not block migration of valve or non-valve SMCs from tissue explants. 37 genes were differentially expressed by valve compared to non-valve intimal/medial tissue (11 veins). Conclusions: Valve, compared to non-valve, SMCs have greater rates of migration and proliferation, which may in part explain the propensity for pathological lesion formation in valves. While FGF2 mediates these effects in cultured SMCs, the mediators of these stimulatory effects in valve wall tissue remain unidentified. Here, the newly identified differentially expressed genes may play a role.