Inhibition of matrix metalloproteinases by lung TIMP-1 gene transfer or doxycycline aggravates pulmonary hypertension in rats

Chronic hypoxic pulmonary hyper-tension (PH) results from persistent vasoco nstriction, excess muscularization, and extracellular matrix remodeling of pulmonary arteries. The matrix metalloproteinases (MMPs) are a family of pr oteinases implicated in extracellular matrix turnover and hence in smooth m uscle and endothelial cell migration and proliferation. Because MMP express ion and activity are increased in PH, we designed the present study to inve stigate whether inhibition of lung MMPs in rats subjected to chronic hypoxi a (CH) contributes to or protects against vascular remodeling and PH. To ac hieve lung MMP inhibition, rats exposed to 10% O-2 for 15 days were treated with either doxycycline (20 mg/kg per day by gavage starting 2 days before and continuing throughout the CI-I period) or a single dose of recombinant adenovirus (Ad) for the human tissue inhibitors of metalloproteinases-1 (h TIMP-1) gene (Ad,hTIMP-1, 10(8) plaque-forming units given intratracheally 2 days before CH initiation). Control groups either received no treatment o r were treated with an adenovirus containing no gene in the expression cass ette (Ad,Null), Efficacy of hTIMP-1 gene transfer was assessed both by ELIS A on bronchoalveolar lavages and by hTIMP-1 immunofluorescence on lung sect ions. MMP inhibition in lungs was evaluated by in situ zymography and gelat inolytic activity assessment using [H-3]gelatin. Rats treated with either d oxycycline or Ad.hTIMP-1 had higher pulmonary artery pressure and right hea rt ventricular hypertrophy more severe than their respective controls. Wors ening of PH was associated with increased muscularization and periadventiti al collagen accumulation in distal arteries. In conclusion, our study provi des compelling evidence that MMPs play a pivotal role in protecting against pulmonary artery remodeling.