Characterization of vascular smooth muscle progenitor cells in human peripheral blood

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Vascular smooth muscle cells (SMC) play an important role in human vascular diseases, including atherosclerosis, restenosis after angioplasty, transplant vasculopathy, and angiogenesis by producing extracellular matrix (ECM) proteins and proliferation. It has been believed that intimal SMC are migrated from media and they exhibit immature and inflammatory phenotype in human vascular lesions. Recently, we have demonstrated that circulating bone marrow-derived smooth muscle progenitor cells are involved in pathogenesis of neointimal hyperplasia in mouse aortic transplantation model, thus we gypothesized that vascular smooth muscle progenitor cells could exist in human peripheral circulation, contributing to human vascular fibroproliferative deseases. We cultured human peripheral blood mononuclear cells (PBMC) on ECM-coated plates in SMC-culture media and evaluated cellular phenotype by gene expression profiles. We first discovered expression of vascular smooth muscle α-actin (SM α-actin) … More , an essential vascular SMC marker, in circulating PBMC by RT-PCR, indicating the presence of "vascular smooth muscle progenitor cells" in human peripheral circulation. The SM α-actin positive cells were abundant in low-density PBMC faction (d<1.071 mg/mL) and the expression level of SM α-actin in PBMC varied substantially among donors. Large spindle-shaped, overlayered, SM α-actin-expressing cells ; "MC-like fibromuscular cells (FMC)" were cultured from the low-density PBMC. The SM-α-actin expression in PBMC-derived FMC increased during one month culture period. We confirmed expression of vascular SM α-actin in PBMC-dirived FMC by RT-PCR, Western blotting and immunostaining with a specific monoclonal antibody against SM α-actin (1A4). The PBMC-derived FMC had great ability of proliferation and express major SMC markers ; vimentin, SM22α, SM-1, and partially SM-2 during in vitro culture. Furthermore, they express ECM proteins, type-I and type-III collagen. These results provide a novel concept that "vascular smooth muscle progenitor cells" exist in human circulating peripheral blood and they could potentially contribute to pathogenesis of human vascular diseases and angiogenesis from luminal blood stream Less