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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2007;27:540.)
© 2007 American Heart Association, Inc.

Vascular Biology

Stem Cell Factor Attenuates Vascular Smooth Muscle Apoptosis and Increases Intimal Hyperplasia After Vascular Injury

Chao-Hung Wang; Subodh Verma; I-Chang Hsieh; Agnes Hung; Ting-Tzu Cheng; Shin-Yi Wang; Yu-Chih Liu; William L. Stanford; Richard D. Weisel; Ren-Ke Li; Wen-Jin Cherng

From the Division of Cardiology, Department of Internal Medicine (C.-H.W., I.-C.H., A.H., T.-T.C., S.-Y.W., Y.-C.L., W.-J.C.), Chang Gung Memorial Hospital, Keelung; Chang Gung University College of Medicine, Taiwan; the Division of Cardiac Surgery (S.V.), St. Michael’s Hospital, Toronto, Canada; the Division of Cardiac Surgery (C.-H.W., S.V., R.D.W., R.-K.L.), Toronto General Hospital, Toronto, Canada; the Institute of Bioscience and Biotechnology (T.-T.C.), National Taiwan Ocean University; and the Institute of Biomaterials and Biomedical Engineering (W.L.S.), University of Toronto; Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Canada.

Correspondence to Chao-Hung Wang, MD, Division of Cardiology, Department of Internal Medicine, Chang Gung Memorial Hospital, 222 Mai Chin Road, Keelung, Taiwan. E-mail bearty{at}adm.cgmh.org.tw

Objective— Stem cell factor (SCF) through its cognate receptor, the tyrosine kinase c-kit, promotes survival and biological functions of hematopoietic stem cells and progenitors. However, whether SCF/c-kit interactions exacerbate intimal hyperplasia through attenuating VSMC apoptosis induced by vascular injury has not been thoroughly investigated.

Methods and Results— VSMCs were stimulated with serum deprivation and H₂O₂ to induce apoptosis. The transcription of c-kit mRNA and the expression of the c-kit protein by VSMCs were estimated by Q-polymerase chain reaction and Western blotting, respectively. The interactions of SCF and c-kit were investigated by in vitro and in vivo experiments. In vitro, H₂O₂ stimulation significantly induced apoptosis of VSMCs as evidenced by the 3- and 3.2-fold increases of cleaved caspase-3 compared with those in the control group by Western blot and flow cytometric analyses, respectively (P<0.01). Stimulation of apoptosis also caused 3.5- and 9-fold increases in c-kit mRNA transcription and protein expression, respectively, by VSMCs compared with those in the control group. Administration of SCF (10 to 1000 ng/mL) significantly lowered the amount of cleaved caspase-3 in H₂O₂-treated VSMCs (P<0.01). Specifically, SCF exerted this effect through activating Akt, followed by increasing Bcl-2 and then inhibiting the release of cytochrome-c from the mitochondria to the cytosol. In vivo, the mouse femoral artery was injured with a wire in SCF mutant (Sl/Sl^d), c-kit mutant (W/W^v), and colony control mice. In colony control mice, confocal microscopy demonstrated that the wire-injury generated a remarkable activation of caspase-3 on medial VSMCs, coinciding with upregulation of c-kit expression. The wire-injury also caused an increase in the expression of SCF on surviving medial VSMCs and cells in the adventitia. The upregulated c-kit expression in the vessel wall also facilitated homing by circulating SCF⁺ cells. Compared with colony control mice, vascular injury in SCF mutant and c-kit mutant mice caused a higher number of apoptotic VSMCs on day 14 and a lower number of proliferating cells, and resulted in significantly less neointimal formation (P<0.01) on day 28.

Conclusions— The interactions between SCF and the c-kit receptor play an important role in protecting VSMCs against apoptosis and in maintaining intimal hyperplasia after vascular injury.

Apoptotic stimulation of VSMCs upregulated c-kit mRNA transcription and c-kit protein expression, which attracted SCF-positive cells, thus contributing to neointimal formation. The SCF attenuated the apoptosis of VSMCs through the Akt–Bcl-2 pathway. This study demonstrated that the SCF/c-kit system protects VSMCs against apoptosis and maintained intimal hyperplasia after vascular injury.

Key Words: apoptosis • c-kit tyrosine kinase • intimal hyperplasia • restenosis • stem cell factor

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