Structural remodeling of pulmonary arteries through smooth muscle cell migration, proliferation, and oversecretion of extracellular matrix are the most notable pathological changes in PAH.39 The MMPs, particularly gelatinases MMP2 and MMP9, are involved in extracellular matrix turnover and hence, in smooth muscle cell migration and proliferation. Here, MMP9 is linked to pulmonary arterial hypertension.