Abstract Background Increasing evidences support that endothelial dysfunction initiates and drives pulmonary vascular remodeling. Targeting endothelial dysfunction is a promising treatment strategy for pulmonary artery hypertension (PAH). Therefore, it is urgent to elucidate the pathological mechanism of endothelial dysfunction. Sine Oculis homeobox 1 (SIX1) is a critical transcription factor that regulates pulmonary vascular development. Lack of SIX1 impairs the differentiation of pulmonary vascular endothelial cells into smooth muscle cells. However, the role of SIX1 in endothelial dysfunction and PAH is unknown. Purpose To confirm the role of SIX1 in the endothelial dysfunction of PAH and to clarify the possibility of SIX1 serving as a therapeutic target for PAH. Results SIX1 was increased in lung tissues and endothelium of pulmonary arteries from PAH patients and PH rodent models. Silencing SIX1 inhibited hypoxia-induced proliferation, EndMT, and ET-1 release in vitro. Endothelial-specific SIX1 knock-out improved SU5416/hypoxia-induced PH and right ventricle (RV) failure. Endothelial-specific SIX1 overexpression induced moderate PH and RV hypertrophy. Mechanistically, MAST4 was the target of SIX1 regulating endothelial dysfunction. MAST4 accelerated MAPK1/3 activation by phosphorylating their threonine residues (Thr185/202). Structure-based virtual screening and surface plasmon resonance analysis revealed that Zafirlukast bound to SIX1, resulting in the inhibition of SIX1 transcriptional activity. Administration of Zafirlukast improved endothelial dysfunction and SU5416/hypoxia-induced PH. Methods The expression of SIX1 in lung tissues from PAH patients was detected. Tamoxifen-induced endothelial-specific SIX1 knock-out mice (SIX1fl/fl;Cdh5-CreERT2+) were treated with SU5416/hypoxia to induce pulmonary hypertension (PH). The indices of PH, including mean pulmonary artery pressure, pulmonary vascular remodeling, etc., were analyzed. Proliferation, endothelial-mesenchymal transition (EndMT), the release of ET-1 and NO, and inflammation were analyzed as the indices of endothelial dysfunction. Muti-omics profiling was used to investigate the underlying mechanisms. Structure-based virtual screening was conducted, and the efficacy of candidate drugs targeting SIX1 was assessed in SU5416/hypoxia-induced PH. Conclusions SIX1 promoted endothelial dysfunction by transcribing MAST4 and subsequently accelerating MAPK1/3 activation. Targeting SIX1 could be a promising strategy for future PAH treatment and drugs development.
Liu et al. (Sat,) studied this question.