Abstract 586: Smooth Muscle Cells Healing Atherosclerotic Plaque Disruptions are of Local, Not Blood, Origin in ApoE Knockout Mice
Background. Smooth muscle cell (SMC)-mediated healing of non-lethal plaque ruptures is considered a major mechanism in the formation of arterial stenoses, but the source of the healing SMCs is unknown. Recent studies have suggested that activated platelets on ruptured plaques may recruit SMCs from bone marrow-derived progenitor cells. In the present study, we analyzed the origin of healing SMCs after mechanical plaque disruption in apoE knockout (apoE−/−) mice.
Methods and Results. I. To investigate whether hematopoietic stem cells contribute to healing SMCs, old apoE−/− mice (n=15), 18 months of age, were lethally irradiated and reconstituted with bone marrow cells from enhanced green fluorescent (eGFP) transgenic apoE−/− mice. Four weeks later, mechanical plaque ruptures were produced in carotid plaques by repeated insertion of a microsurgical needle from the luminal side. In mice killed after 30 minutes (n=5), plaque disruption with superimposed, platelet-rich thrombosis was uniformly present. After one week (n=4), the luminal thrombi had resolved, and after four weeks (n=6), focal and distinct accumulations of SMCs indicative of healed disruption sites were found. No bone marrow-derived eGFP+ SMCs, identified by positive staining for smooth muscle α-actin (SMαA), were detected among 3560 SMCs analyzed in healed plaques. II. To investigate whether any circulating cell type contributes to healing SMCs, carotid bifurcations harboring advanced atherosclerotic plaques were cross-grafted between apoE−/− and eGFP+ apoE−/− mice followed by mechanical plaque disruption of the transplanted plaque. Healed plaques were analyzed after four weeks. In apoE−/− carotid plaques grafted into eGFP+apoE−/− mice (n=10), no eGFP+ SMCs were detected (among 7980 SMCs analyzed) except for very few near an anastomosis site. Consistently, in eGFP+apoE−/− carotid plaques grafted into apoE−/− mice (n=4), 97% of SMCs in healed plaques were eGFP+(2896 of 2982 SMCs analyzed), which was similar to that found in eGFP+apoE−/− positive controls (98%, n=2).
Conclusions. SMCs healing atherosclerotic plaque disruptions are derived entirely from the local arterial wall and not circulating progenitor cells in apoE−/− mice.