Endothelial NO synthase deficiency promotes smooth muscle progenitor cells in association with upregulation of stromal cell-derived factor-1α in a mouse model of carotid artery ligation

Background-Endothelial NO deficiency (endothelial NO synthase [eNOS]-knockout [KO]) enhanced smooth muscle cell (SMC)-rich neointimal lesion formation in a mouse model of carotid artery ligation (CAL). Recent evidence indicated that stromal cell-derived factor-1 alpha (SDF-1 alpha)-mediated recruitment of circulating SMC progenitor cells substantially contributed to the SMC-rich neointimal hyperplasia induced by vascular injury. The goal of this study was to investigate the effects of eNOS deficiency on the expression of SDF-1 alpha and mobilization of circulating SMC progenitor cells in CAL model. Methods and Results-Two- to 3-month-old C57BL/6J wild-type (WT) and eNOS-KO mice were evaluated 1, 2, or 4 weeks after CAL. CAL-induced expression of SDF-1 alpha, as detected by immunohistochemical staining and further quantified by ELISA in the ligated carotid arteries, was moderate and transient with a peak at 1 week in WT mice. SDF-1 alpha expression was significantly higher at 1 week and persisted through 2 weeks in eNOS-KO mice. CAL was associated with increased circulating stem cell antigen-1+ (Sca-1(+))/c-Kit(-)/Lin(-) cells (interpreted as SMC progenitor cells), which peaked at 1 week in WT mice. This effect was also significantly greater and longer-lasting in eNOS-KO than WT mice. The number of circulating Sca-1(+)/c-Kit(-)/Lin(-) cells was positively correlated with the expression of SDF-1 alpha but not vascular endothelial growth factor in the ligated carotid arteries. Furthermore, immunostaining showed abundant Sca-1-positive cells in the adventitia of the 1-week ligated carotid arteries from eNOS-KO mice but not in WT mice. We also determined that eNOS deficiency enhanced CAL-induced intimal cell proliferation in the ligated arteries as detected by proliferating cell nuclear antigen staining but did not induce cell apoptosis as detected by staining for active caspase-3. Conclusion-Our results indicate that eNOS deficiency exacerbates CAL-induced expression of SDF-1 alpha and its receptor CXCR4. This is correlated with an increase in Sca-1 alpha cells in peripheral blood and adventitia, which may contribute to vascular remodeling and SMC-rich neointimal lesion formation. This suggests that constitutive eNOS inhibits SDF-1 alpha expression and provides an important vasculoprotective mechanism for intact endothelium to limit SMC proliferation and recruitment in response to vascular injury.