In patients with PAH, MMP-1 expression was significantly increased in hypoxic M1 macrophages compared to that in hypoxic M0 macrophages, whereas the expression of MMP1 in M1 macrophages was significantly suppressed by p42/p44 MAPK, p38 MAPK, JNK-1/2, PI3K/AKT, and STAT3 inhibitors, but not by STAT1 inhibitor (Fig. 6B). This evidence concerns the gene MMP1 and pulmonary arterial hypertension.