Abstract 1012: Notch Signaling Mediates Endothelial Progenitor Cell Fate in Injury-induced Arterial Remodeling under High Cholesterol Condition
Background: We have shown that activated EPCs accelerate re-endothelialization (ReEndo) in ApoE KO mice. However, the fate of EPCs in the injured artery has not been explored. We tested the hypothesis that Notch signaling may modulate EPC function and thereby play a significant role in vascular remodeling following arterial injury under high cholesterol (HC) conditions.
Methods and Results: Based on our previous observations, we evaluated cultured EPC functions under various HC concentrations. Interestingly, HC significantly increased EPC adhesion, migration, proliferation and anti-apoptotic activities at 150mg/dl, but decreased these activities at 500mg/dl. Apart from this biphasic effect of HC on EPC functions, real-time PCR analysis showed dose-dependent downregulation of Notch1 mRNA expression by HC in EPCs. We then evaluated EPC function with reduced Notch 1 expression using EPCs obtained from Tie2-Cre Notch1+/− mice (Notch1+/− EPCs) without HC vs. wild type (WT) EPCs treated with 150mg/dl HC resulting in a 50% reduction in Notch1 mRNA expression. Notch1+/− EPCs exhibited significantly increase cell functions similar to that in 150mg/dl HC-treated WT EPCs. Next, we evaluated in vivo Notch1+/− EPCs contribution to ReEndo using a bone marrow transplanted (BMT) mouse carotid injury model. The percent ReEndo was significantly higher in the Notch1+/− BMT mice than the WT BMT mice, suggesting that EPCs with reduced Notch 1 expression exert an effect that results in accelerated ReEndo. Conversely, when Notch1 mRNA expression in EPCs was reduced to 15% of basal levels by 500mg/dl, HC increased EPC apoptosis and decreased cell functions were noted. In vivo studies confirmed the increased EPC apoptosis detected by double immunostaining for TUNEL and β-gal in the injury-induced advanced atherosclerotic lesion in Tie2/LacZ transgenic BMT ApoE −/− mice fed with a Western diet.
Conclusion: HC exhibited concentration dependent repression of Notch 1 expression and biphasic effects on EPC function. These data suggest that Notch signaling mediates HC induced alterations in EPC activation/function. These findings may provide novel insights for better understanding the pathogenesis of atherosclerotic plaque including the contribution of BM derived cells.