Smooth muscle cells of the media in the dilatative pathology of ascending thoracic aorta: Morphology, immunoreactivity for osteopontin, matrix metalloproteinases, and their inhibitors

The etiopathogenesis of thoracic aortic aneurysms is currently an issue of debate. The present study investigated ultrastructural, morphometric, and i mmunohistochemical aspects of smooth muscle cells (SMCs) in chronic aneurys m of the thoracic aorta (aneurysm group), aortic dilatation associated with valvular disease (valvular group), and dissection of the thoracic aorta (d issection group). Fragments of the ascending aorta that had been taken from the patients during coronary bypass surgery were used as controls. No sign ificant difference was observed in the density of SMCs between the 3 pathol ogic, groups put together and the controls. Only separate analysis of SMC d ensity in each of the pathologic groups showed that the valvular group samp les had significantly smaller amounts of SMCs in the internal layer of the media than the dissection group samples and controls. Ultrastructural analy sis, in situ end labeling, propidium iodide assay, and DNA laddering did no t show apoptosis of SMCs in the samples investigated. Ultrastructure of SMC s characteristic of the synthetic phenotype, together with increased expres sion of osteopontin in the media of pathologic thoracic aortas indicated th e transition of SMCs from the contractile to the synthetic phenotype. Immun ohistochemical investigation showed that medial SMCs in the samples taken f rom aortas of all 3 pathologic groups expressed stronger immunoreactivity f or matrix metalloproteinase 1, 2, and 9 and tissue inhibitor of metalloprot einase 1 and 2 than the controls. The present study shows that during the f ormation of aneurysms, dissection of the thoracic aorta, or aortic dilatati on associated with valvular disease, loss of SMCs was not of great importan ce with respect to their transition from the contractile to the synthetic t ype in leading to increased production of matrix metalloproteinases.copyrig ht (C) 2001 by W.B. Saunders Company.