Stem cell factor attenuates vascular smooth muscle apoptosis and increases intimal hyperplasia after vascular injury.
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.


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.
Wang
Chao-Hung
CH
Division of Cardiology, Department of Internal Medicine, Chang Gung Memorial Hospital, 222 Mai Chin Road, Keelung, Taiwan. bearty@adm.cgmh.org.tw
Verma
Subodh
S
Hsieh
I-Chang
IC
Hung
Agnes
A
Cheng
Ting-Tzu
TT
Wang
Shin-Yi
SY
Liu
Yu-Chih
YC
Stanford
William L
WL
Weisel
Richard D
RD
Li
Ren-Ke
RK
Cherng
Wen-Jin
WJ
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002465:Cell Movement; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005263:Femoral Artery / Q000166:cytology / Q000293:injuries; D005786:Gene Expression Regulation; D006965:Hyperplasia / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D019089:Stem Cell Factor / Q000378:metabolism* / Q000494:pharmacology; D017539:Tunica Intima / Q000473:pathology*
D012333:RNA, Messenger; D019089:Stem Cell Factor; D019009:Proto-Oncogene Proteins c-kit