Cultured arterial smooth muscle cells maintain distinct phenotypes when implanted into carotid artery

Cultured arterial smooth muscle cells (SMCs) with distinct phenotypic featu res have been described by several laboratories; however, it is not present ly known whether this phenotypic heterogeneity can be maintained within an in vivo environment. To answer this question, we have seeded into the intim a of denuded rat carotid artery 2 SMC populations with well-established dis tinct biological features, ie, spindle-shaped, not growing in the absence o f serum, and well differentiated versus epithelioid, growing in the absence of serum, and relatively undifferentiated, derived from the aortic media o f newborn rats (aged 4 days) and old rats (aged > 18 months), respectively. We show that these 2 populations maintain their distinct biochemical featu res tie, expression of ct-smooth muscle actin, smooth muscle myosin heavy c hains, and cellular retinol binding protein-1) in the in vivo environment. The old rat media-derived SMCs continue to produce cellular retinol binding protein-1 but little alpha -smooth muscle actin and smooth muscle myosin h eavy chains, whereas the newborn rat media-derived SMCs continue to express cc-smooth muscle actin and smooth muscle myosin heavy chains but no cellul ar retinol binding protein-1. Our results reinforce the notion of arterial SMC phenotypic heterogeneity and suggest that in our model, heterogeneity i s controlled genetically and not by the local environment.