The precise mechanisms that Fstl1 regulates ASM and VSM formation, if and how Fstl1 regulates some important signaling pathways, such as BMP, SHH, WNT and FGF, during lung SM development and SM-related lung diseases including pulmonary artery hypertension, are actively pursued in our laboratories. Here, FSTL1 is linked to pulmonary arterial hypertension.