Characteristics of coronary smooth muscle cells and adventitial fibroblasts

Recent findings suggesting the involvement of adventitial cells in coronary repair have raised questions regarding the phenotypic "plasticity" of medial smooth muscle cells (SMCs). Accordingly, the aims of the present study were to examine the characteristics of coronary medial and adventitial cells and to compare the responses of coronary and noncoronary SMCs to stimulation.

Enzymatically isolated coronary SMCs (human and porcine) were distinct from noncoronary SMCs, showing poor adhesion and spreading, as well as lower proliferation, collagen synthesis, and LDL degradation. Several extracellular matrix components (Matrigel, collagen I and IV, laminin, vitronectin, fibronectin) or growth factors (epidermal growth factor, platelet-derived growth factor-BB, insulin growth factor-1, interleukin-1alpha) failed to augment the adhesion or proliferation of coronary SMCs to the levels observed in noncoronary SMCs. Unlike coronary SMCs, coronary fibroblasts demonstrated high adhesion, proliferation, collagen synthesis, and avid LDL metabolism. Limited responses of coronary SMCs were associated with sustained expression of differentiation markers (alpha-smooth muscle actin, h-caldesmon, and smooth muscle myosin heavy chain), whereas noncoronary SMCs showed marked phenotypic heterogeneity.

Coronary SMCs appeared to maintain highly differentiated phenotype in response to stimulation, whereas coronary adventitial fibroblasts demonstrated several characteristics that are essential during vascular repair. Coronary SMCs, however, were distinct from noncoronary medial cells, which displayed greater phenotypic heterogeneity and versatility in culture. We postulate that the mechanism of vascular repair may differ among vascular beds, pointing to the importance of coronary artery-specific investigations in vascular biology.