Inhibition of Overactive Transforming Growth Factor-β Signaling by Prostacyclin Analogs in Pulmonary Arterial Hypertension

The heterozygous loss of function mutations in the Type II bone morphogenetic protein receptor (BMPR-II), a member of the transforming growth factor (TGF-beta) receptor family, underlies the majority of familial cases of pulmonary arterial hypertension (PAH). The TGF-beta 1 pathway is activated in PAH, and inhibitors of TGF-beta 1 signaling prevent the development and progression of PAH in experimental models. However, the effects of currently used therapies on the TGF-beta pathway remain unknown. Prostacyclin analogs comprise the first line of treatment for clinical PAH. We hypothesized that these agents effectively decrease the activity of the TGF-b1 pathway. Beraprost sodium (BPS), a prostacyclin analog, selectively inhibits proliferation in a dose-dependent manner in murine primary pulmonary arterial smooth muscle cells (PASMCs) harboring a pathogenic BMPR2 nonsense mutation in both the presence and absence of TGF-beta 1 stimulation. Our study demonstrates that this agent inhibits TGF-beta 1-induced SMAD-dependent and SMAD-independent signaling via a protein kinase A-dependent pathway by reducing the phosphorylation of SMADs 2 and 3 and p38 mitogen-activated protein kinase proteins. Finally, in a monocrotaline-induced rat model of PAH, which is associated with increased TGF-beta signaling, this study confirms that treprostinil, a stable prostacyclin analog, inhibits the TGF-beta pathway by reducing SMAD3 phosphorylation. Taken together, these data suggest that prostacyclin analogs inhibit dysregulated TGF-beta signaling in vitro and in vivo, and reduce BMPR-II-mediated proliferation defects in mutant mice PASMCs.