MMP9 and pulmonary arterial hypertension: Consistent with the pronounced matrix remodelling associated with many presentations of pulmonary hypertension, patients with high circulating levels of N-terminal propeptide of procollagen III (PIIINP), matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase I (TIMP-1) have a significantly worse survival than patients with lower (≤median) levels42,46,47.