Objective:Human saphenous vein (HSV) is widely used for coronary artery bypass grafting in patients with ischemic heart disease1,2. However, 30-50% of venous grafts fail within 10 years3. Vein graft failure involves intimal thickening as a result of endothelial cell (EC) damage and inflammation which promotes vascular smooth muscle cell (VSMC) de-differentiation, migration and proliferation. Proline Rich Homeodomain (PRH) protein is a transcription factor required for growth and differentiation4,5. We investigated whether adenovirus-mediated delivery of non-phosphorylated PRH (PRH-CC) protein attenuates VSMC proliferation without detrimental effects on EC. Approach and Results:PRH-CC overexpression in HSV-VSMCs significantly inhibited proliferation (27±0.1 vs. 36±0.2%), migration (27±9 vs. 356±33μm) and apoptosis (2.4±0.2 vs. 7.8±1.4%) compared to virus control. Western blotting and qPCR revealed that PRH-CC enhanced the expression of contractile markers (smoothelin and calponin) and enhanced collagen-gel contraction in HSV-VSMCs. Importantly, PRH-CC overexpression in HSV-ECs significantly reduced apoptosis (0.8±0.8 vs. 8±0.10%), without affecting proliferation (19±3 vs. 17±3%) and migration (154±57 vs. 190±86μm) compared to virus control. In HSV-ECs, PRH-CC significantly reduced TNF-α-induced VCAM-1 and ICAM-1 and monocyte adhesion (5.6±0.9 vs. 24±4 cells/field), and suppressed interleukin-6 (154±18 vs. 292±43pg/ml) and monocyte chemotactic factor-1 (111±48 vs. 1554±76pg/ml). Data were analysed with ANOVA, Student Newman Keuls post-hoc test, n=4, p<0.05. Conclusion:We observed that PRH-CC attenuated VSMC proliferation, migration and apoptosis and enhanced VSMC differentiation, whilst promoting the endothelial repair and anti-inflammatory properties. These novel findings highlight the potential for PRH-CC to preserve the endothelial function and suppress VSMC synthetic activity and thereby reduce vein graft failure.