Mechanical Loading Modulates the Differentiation State of Vascular Smooth Muscle Cells GUILLAUME GRENIER, Ph.D., 1,2 MURIELLE RE ´ MY-ZOLGHADRI, Ph.D., 1 FRANC ¸ OIS BERGERON, Ph.D., 1 RINA GUIGNARD, M.Sc., 1 KATHLEEN BAKER, M.Sc., 1 RAYMOND LABBE ´ , M.D., FRCS(C), 1 FRANC ¸ OIS A. AUGER, M.D., FRCP(C), 1 and LUCIE GERMAIN, Ph.D. 1 ABSTRACT The cause underlying the onset of stenosis after vascular reconstruction is not well understood. In the present study, we evaluated the effect of mechanical unloading on the differentiation state of human vascular smooth muscle cells (hVSMCs) using a tissue-engineered vascular media (TEVM). hVSMCs cultured in a mechanically loaded three-dimensional environment, known as a living tissue sheet, had a higher differentiated state than cells grown on plastic. When the living tissue sheet was detached from its support, the release of the residual stress resulted in a mechanical unloading and cells within the ex- tracellular matrix (ECM) dedifferentiated as shown by downregulation of differentiation markers. The relaxed living tissue sheet can be rolled onto a tubular mandrel to form a TEVM. The rolling procedure resulted in the reintroduction of a mechanical load leading to a cohesive compacted tissue. During this period, cells gradually redifferentiated and aligned circumferentially to the tubular support. Our results suggest that differentiation of hVSMCs can be driven by mechanical loading and may occur simulta- neously in the absence of other cell types. The extrapolation of our results to the clinical context suggests the hypothesis that hVSMCs may adopt a proliferative phenotype resulting from the mechanical un- loading of explanted blood vessels during vascular reconstruction. Therefore, we propose that this mech- anical unloading may play an important role in the onset of vascular graft stenosis. INTRODUCTION A THEROSCLEROSIS IS THE MAJOR CAUSE of morbidity and mortality in the industrialized world. 1,2 In the patho- genesis of atherosclerosis, stenosis leads to the obstruction of blood vessels and ultimately to poor nutrition of their downstream tissues. The main treatments remain angioplasty and vascular reconstruction. Angioplasty consists princi- pally of the insertion and inflation of a balloon and /or the expansion of a stent at the stenotic scar region to restore the patency of the obstructed blood vessel. On the other hand, vascular reconstruction uses native blood vessels, mainly saphenous vein and internal mammary artery, or a synthetic graft, to bypass surgically the obstructed area. Despite such treatments, stenosis may reoccur in up to 20–40% of pa- tients at treated sites and within the vascular graft. 3 One of the major events in the process of restenosis is the phenotypic modulation of human vascular smooth muscle cells (hVSMCs) within the affected vascular wall. 4 Dur- ing stenosis, hVSMCs undergo a transition in phenotype from a contractile (differentiated) to a synthetic (dedifferenti- ated) state. 4 Hence, quiescent hVSMCs undergo a complex 1 Laboratoire d’Organoge ´ne `se Expe ´rimentale (LOEX), Ho ˆpital du Saint-Sacrement du CHA, 1050, chemin Sainte-Foy, Que ´bec, Canada. 2 Current address: Research Centre on Aging, Faculty of Medicine, University of Sherbrooke, Department of Surgery, University of Sherbrooke, Que ´bec, Canada. TISSUE ENGINEERING Volume 12, Number 11, 2006 # Mary Ann Liebert, Inc. 1 (page numbers are temporary)