Regulation of TGF-β and BMP Signaling by Natural Triterpene Compounds in Pulmonary Arterial Hypertension (PAH)

Pulmonary arterial hypertension (PAH) is a devastating cardiovascular disorder caused by right heart failure leading to premature death. The TGFBR2 and BMPR-II receptors, which are members of the TGF-β receptor family, are considered promising targets for developing novel drugs in PAH. Lupeol and ψ-taraxasterol, naturally occurring triterpene molecules with proven anti-inflammatory, anti-cancer, and cardioprotective activities, hold considerable potential in the treatment of PAH. Hence, the present study aimed to evaluate the impacts of lupeol and ψ-taraxasterol isolated from Cirsium sintenisii Freyn on the TGF-β and BMP pathways, aiming to determine their therapeutic values in PAH. The effects of the compounds were extensively investigated using both in silico and wet lab experiments, including reporter assays, RT-PCR/QPCR, Western blots, and cell proliferations assays. Both lupeol and ψ-taraxasterol demonstrated interactions with the majority of components of these signaling pathways, including the TGFBR2 and BMPR-II receptors, suggesting that both compounds were capable of modulating the BMP and TGF-β pathways. Data derived from reporter assays, RT-PCR/QPCR, and Western blots demonstrated that lupeol and ψ-taraxasterol inhibited the TGF-β signaling pathway by reducing the phosphorylation of the SMAD3 protein and the expression of pai-1 transcripts. Additionally, ψ-taraxasterol enhanced BMP signaling via regulating the phosphorylation of SMAD1/5 proteins and upregulated the expression of id-1 transcripts. Finally, lupeol and ψ-taraxasterol inhibited abnormal proliferation of mutant-type (bmpr2^R899X+/-) PAMSCs stimulated with the TGF-β1 ligand with no discernible effects on wild-type cells. This is the first comprehensive report outlining the potential therapeutic effects of lupeol and ψ-taraxasterol in PAH, which may have immediate experimental and clinical applications not only in PAH but also other BMP- and TGF-β-associated disorders.