Prostacyclin synthase expression is decreased in lungs front patients with severe pulmonary hypertension

Prostacyclin is a powerful vasodilator and inhibits platelet adhesion and cell growth. We hypothesized that a decrease in expression of the critical enzyme PGI(2) synthase (PGI(2)-S) in the lung may represent an important manifestation of pulmonary endothelial dysfunction in severe pulmonary hypertension (PH). Immunohistochemistry and Western blot analysis were used to assess lung PGI(2)-S protein expression, and in situ hybridization was used to assess PGI(2)-S mRNA expression. In the normal pulmonary circulation (n = 7), PGI(2)-S was expressed in 48% of small, 67% of medium, and 76% of large pulmonary arteries as assessed by immunohistochemistry. PPH (n = 12), cirrhosis-associated (n = 4) and HIV-associated PH (n = 2) lungs exhibited a marked reduction in PGI(2)-S expression, involving all size ranges of pulmonary arteries. Vessels with concentric lesions showed complete lack of PGI(2)-S expression. Congenital heart (n = 4) and CREST (n = 2) cases exhibited a more variable immunohistological pattern of PGI(2)-S expression. These results were complemented by in situ hybridization and Western blots of representative lung samples. We conclude that the different sizes of the pulmonary arteries express PGI(2)-S differently and that the loss of expression of PGI(2)-S represents one of the phenotypic alterations present in the pulmonary endothelial cells in severe PH.