Increased extracellular superoxide and MMP9 attenuated COMP stabilization of BMPR2 potentially participate in pulmonary hypertension development

Abstract

The role of bone morphogenetic protein type 2 receptor (BMPR2) in the development of pulmonary hypertension was emphasized after identifying mutations of the gene encoding BMPR2 among patients with idiopathic pulmonary artery hypertension. Since then many studies were devoted to investigate restoring BMPR2 signaling as a therapeutic strategy. Also, roles for increased oxidant mechanisms have been identified in the lungs and right ventricle (RV) of several animal models of PH. However, it is unclear whether altered redox state plays a role in the regulation of the BMPR2 pathway in pulmonary vascular cells. Our current studies provide evidence for extracellular superoxide regulating BMPR2 expression via a Matrix Metallopeptidase 9 (MMP9)/cartilage oligomeric matrix protein (COMP) dependent pathway. Mice deficient of extracellular SOD (SOD3) show evidence of BMPR2 depletion both in the absence and presence of chronic hypoxia. Incubation of bovine pulmonary arteries under hypoxic conditions (1% O2 for 48h) increased MMP9 activity and expression which was associated with increased superoxide production and BMPR2 depletion. Moreover, adding exogenous superoxide dismutase (SOD) to the media inhibited MMP9 activation in response to acute hypoxia. In cultured human PASMC, 24 hours of hypoxia (1% O2) induced significant increase of MMP9 activity and reduced COMP expression. MMP9 contributes to COMP/BMPR2 depletion in chronic hypoxia based on MMP9 deficient mice showing a preserved expression of both COMP & BMPR2 in lung tissues. Moreover, MMP9 deficient mice exposed to chronic hypoxia or Sugen/hypoxia showed a marked reduction of the elevated RV systolic pressures and Fulton index measurements of right ventricular hypertrophy compared to wild type mice under the same experimental conditions. ECHO measurements of PAAT/ET ratio, which correlate inversely and linearly with mean pulmonary artery pressure, in hypoxia‐exposed MMP9 KO mice showed increased ratios compared to animals exposed to chronic hypoxia or Sugen/hypoxia. These data are consistent with depletion of MMP9 reducing the development of pulmonary hypertension. Thus, increased extracellular superoxide appears to promote pathological loop of MMP9 mediated depletion of COMP leading to destabilization of BMPR2 and loss of its pulmonary hypertensive protective actions.Support or Funding InformationSupported by NIH Grants HL115124 & HL129797