Role of human smooth muscle cell progenitors in atherosclerotic plaque development and composition.

Aims: We analysed the possible protective role of human endothelial (EPCs) and smooth muscle (SPCs) progenitor cells on atherosclerosis development in apoE(-/-)RAG2(-/-) mice. We determined plasma levels of SPCs in coronary patients.
Methods and Results: ApoE(-/-)RAG2(-/-) mice received four intravenous injections of saline, 5 x 10(5) SPCs, or 5 x 10(5) EPCs every other week, one (preventive approach) or 12(curative approach) weeks after starting a high fat diet. Derived-SPC levels were quantified from blood mononuclear cells of patients with stable angina (n = 10) and acute coronary syndromes (ACS, n = 9). SPCs reduced atherosclerosis development by 42% (P < 0.001), but had no effect on lesion progression. In the SPC group, collagen and smooth muscle cell content were increased (+80%, P < 0.001, +46%, P < 0.05, respectively), and macrophage content was decreased (-41%, P < 0.05). In the curative approach, macrophage content decreased by 40.5% (P < 0.05) after SPC injection. EPC injection had no effect on atherosclerosis development or progression. Peripheral blood-derived SPC levels were reduced in patients with ACS compared with stable angina patients (P < 0.05).
Conclusion: We demonstrate that SPCs limit plaque development and promote changes in plaque composition towards a stable phenotype in mice. Our finding in patients suggests that reduced peripheral blood-derived SPC levels might represent a mechanism contributing to plaque destabilization.