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A7397 - MMP-8 Deficiency Promotes Vascular Remodeling and Exacerbates Hypoxia-Induced Pulmonary Hypertension
Author Block: P. B. Dieffenbach1, C. Mallarino1, A. Coronata1, F. Polverino1, S. H. Vitali2, C. A. Owen1, L. E. Fredenburgh1; 1Pulmonary / Critical Care Division, Brigham and Women's Hospital, Boston, MA, United States, 2Boston Children's Hospital, Westwood, MA, United States.
Rationale: Matrix metalloproteinase-8 (MMP-8) can regulate inflammatory and fibrotic responses to injury, and is associated with pulmonary fibrosis and vascular atherosclerosis. Several MMPs have been implicated in pulmonary arterial hypertension (PAH) pathogenesis; however, the role of MMP-8 has not been examined. Objective: To investigate the role of MMP-8 in vascular remodeling and development of PAH. Methods: MMP-8 levels were measured in plasma from PAH patients and controls by ELISA. Immunofluorescence staining for MMP-8 was performed on lung tissue from PAH patients and from rats exposed to monocrotaline (MCT) or sugen5416+hypoxia. MMP-8 mRNA expression was measured in lungs of rats exposed to MCT using qPCR. MMP-8-/- and wild-type (WT) C57BL/6J mice were exposed to hypoxia (10% O2) or normoxia for up to 8 weeks. Echocardiography measures of right ventricle (RV) performance at 8 weeks included tricuspid annulus excursion and RV dimensions. Invasive hemodynamics, Fulton’s index, and PA morphometry were performed to further assess pulmonary hypertension severity. Pulmonary artery smooth muscle cells (PASMCs) were isolated from MMP-8-/- and wildtype animals and were assayed for proliferation, gene expression (qPCR), and protein expression (Western blotting). Results: Circulating MMP-8 levels were found to be 18-fold increased in PAH patients compared to healthy controls (8.9±4.7ng/mL vs. 0.14±0.3ng/mL). MMP-8 expression was increased in pulmonary arteries (endothelial cells and PASMCs) from PAH patients, MCT-treated rats, and rats exposed to SU5416+hypoxia. Strikingly, MMP-8-/- mice showed increased mortality during exposure to hypoxia, with 50% survival at 8 weeks compared with 100% survival in WT mice (p=0.0008). MMP-8-/- mice developed significant elevation in right ventricular systolic pressure and right ventricular hypertrophy (RVH) at 8 weeks of hypoxia compared with MMP8+/+ mice and normoxic controls. Echocardiography demonstrated RV dysfunction, and histology revealed increased PA wall thickness. PASMCs isolated from MMP-8-/- mice had significantly enhanced proliferation compared with cells derived from MMP-8+/+ mice, accompanied by ~ 3-fold increased activity of the pro-proliferative transcriptional activators Yes-associated protein (YAP) and Transcriptional activator with PDZ-binding motif (TAZ). This downstream YAP-TAZ upregulation may be controlled by increased transforming growth factor beta (TGF-beta) activity. Conclusions: In summary, MMP-8 levels are increased in plasma and pulmonary arteries of PAH patients. Deficiency of MMP-8 in mice leads to increased mortality, RVH, and enhanced pulmonary vascular remodeling in response to hypoxia. This correlates with hyperproliferation of MMP-8-/- PASMCs and enhanced YAP/TAZ and TGF-beta transcriptional activity. MMP-8 may play a critical protective role in the pathobiology of PAH.