Phenotypic changes of human aortic smooth muscle cells during development and in the adult vessel.

To characterize phenotypic expression of human aortic smooth muscle cells (SMCs), we have studied the content of cytodifferentiation-related cytoskeletal proteins, and of fibronectin (FN) variants in the samples of media from the fetal, child, and adult aorta and in the subendothelial intima of the normal and atherosclerotic aorta. Mature SMCs from the adult aortic media contained high amounts of alpha-SM-actin, SM-myosin heavy chains, meta-vinculin, and 150 kDa caldesmon. Cytokeratin 8 and extra domain-containing variants of FN (A-FN and B-FN) were not found in these cells. The SMCs from the aortic media of 10-wk-old fetus contained low amounts of the SM markers, expressed cytokeratin 8, A-FN, and B-FN. In 25-wk-old fetus, as well as in 2- and 6-mo-old child, aortic medial SMCs expressed an intermediate phenotype, and only in 18-mo-old child were the cells found to be similar to those from adult media. SMCs from the normal adult subendothelial intima contained reduced amounts of meta-vinculin and of 150 kDa caldesmon, and they expressed A-FN. In addition, the SMCs from atherosclerotic fibrous plaque contained a decreased proportion of alpha-SM-actin and of SM-myosin heavy chains, whereas cytokeratin 8 was found. Therefore we conclude that the SMCs from intimal thickenings appear to express a less mature phenotype than that of the medial cells from adult aorta. Rather, these SMCs contain reduced amounts of the SM markers and express proteins typical of the fetal SMC phenotype, A-FN and cytokeratin 8.