Abstract 61: Hedgehog-Responsive Stem Cell Antigen 1 Positive Cells Contribute To Vascular Smooth Muscle Cell Accumulation Following Vascular Injury

Abstract

Background: Cardiovascular disease such as atherosclerosis is associated with the formation of an neointimal layer and medial hyperplasia as a result of the accumulation of vascular smooth muscle cells (vSMC) in the artery wall (i.e., intimal medial thickening, IMT). There is strong, albeit controversial, evidence indicating a putative role for stem cell antigen 1 positive (Sca1 + ) progenitor cell-derived vSMC in contributing to IMT. Interestingly, the Hedgehog (Hh) signaling receptor Patched 1 is present in the adventitial boundary and co-localizes with both Sca1 and Patched 1, the ligand for sonic hedgehog (SHh). The aim of our study was to determine the effect of Hh signaling on Sca1+ stem cells and their contribution to vSMC accumulation and IMT following vascular injury. Methods: Sca1 + stem cells were treated with differentiation inductive stimuli in the absence or presence of recombinant SHh (rSHh), with or without the Hh inhibitor cyclopamine, before the cells were examined for their stemness (telomerase activity), differentiation capacity (SMC differentiation) and epigenetic profile. In parallel, Sca1-eGFP transgenic mice were subjected to carotid injury (i.e., partial ligation), with or without cyclopamine, before IMT, Sca1 expression and SMC phenotype was assessed. Results: Sonic Hedgehog stimulated Sca1 + stem cell differentiation capacity, as demonstrated by enhanced expression of SMC differentiation markers in addition to their altered stemness, epigenetic profile (H3K4me2:H3K27me3) and proliferative status. In parallel studies, Hh signaling components were elevated in ligated carotids when compared to sham-operated controls, concomitant with increased Sca1 expression and SMC accumulation. Moreover, there was a significant attenuation of SMC accumulation and intimal medial thickening of injured carotids following Hh inhibition with cyclopamine. Conclusion: Sca1 + stem cells are Hh-responsive and they contribute to vSMC accumulation in the carotid following ligation injury.