Regression of hypertrophied rat pulmonary arteries in organ culture is associated with suppression of proteolytic activity, inhibition of tenascin-C,and smooth muscle cell apoptosis

Increased elastase activity and deposition of the matrix glycoprotein tenas cin-C (TN), codistributing with proliferating smooth muscle cells (SMCs), a re features of pulmonary vascular disease. In pulmonary artery (PA) SMC cul tures, TN is regulated by matrix metalloproteinases (MMPs) and mechanical s tress. On attached collagen gels, MMPs upregulate TN, leading to SMC prolif eration, whereas on floating collagen, reduced MMPs suppress TN and induce SMC apoptosis, We now investigate the response of SMCs in the whole vessel by comparing attached and floating conditions using either normal PAs deriv ed from juvenile pigs or normal or hypertrophied rat PAs that were embedded in collagen gels for 8 days. Normal porcine PAs in attached collagen gels were characterized by increasing activity of MMP-2 and MMP-9 assessed by zy mography and TN deposition detected by Western immunoblotting and densitome tric analysis of immunoreactivity. PAs on floating collagen showed reduced activity of both MMPs and deposition of TN. Tenascin-rich foci were associa ted with proliferating cell nuclear antigen immunoreactivity, and TN-poor a reas with apoptosis, by terminal deoxynucleotidyl transferase-mediated nick end labeling assay, but no difference in wall thickness was observed. Alth ough normal rat PAs were similar to piglet vessels, hypertrophied rat PAs s howed an amplified response. Increased elastase, MMP-2, TN, and elastin dep osition, as well as SMC proliferating cell nuclear antigen positivity, corr elated with progressive medial thickening on attached collagen, whereas red uced MMP-2, elastase, TN, and induction of SMC apoptosis accompanied regres sion of the thickened media on floating collagen. In showing that hypertrop hied SMCs in the intact vessel can be made to apoptose and that resorption of extracellular matrix can be achieved by inhibition of elastase and MMPs, our study suggests novel strategies to reverse vascular disease.