Mechanisms of neointima formation and remodeling in the porcine coronary artery

Background-To characterize the cells responsible for neointima formation af ter porcine coronary artery wall injury, we studied the expression of smoot h muscle cell (SMC) differentiation markers in 2 models: (1) self-expanding stent implantation resulting in no or little interruption of internal elas tic lamina and (2) percutaneous transluminal coronary angioplasty (PTCA) re sulting in complete medial rupture and exposure of adventitia to blood comp onents. Methods and Results-The expression of alpha -smooth muscle (SM) actin, SM m yosin heavy chain isoforms 1 and 2, desmin, and smoothelin was investigated by means of immunohistochemistry and Western blots in tissues of the arter ial wall collected at different time points and in cell populations culture d from these tissues. The expression of smoothelin, a marker of late SMC di fferentiation, was used to discriminate between SMCs and myofibroblasts. Bo th stent- and PTCA-induced neointimal tissues and their cultured cell popul ations expressed all 4 markers. The adventitial tissue underlying PTCA-indu ced lesions temporarily expressed alpha -SM actin, desmin, and SM myosin he avy chain isoforms, but not smoothelin. When placed in culture, adventitial cells expressed only alpha -SM actin. Conclusions-Our results suggest that SMCs are the main components of corona ry artery neointima after both self-expanding stent implantation and PTCA. The adventitial reaction observed after PTCA evolves with a chronology inde pendent of that of neointima formation and probably corresponds to a myofib roblastic reaction.