Endothelial PHD2 deficiency induces apoptosis resistance and inflammation via AKT activation and AIP1 loss independent of HIF2α

Abstract

ABSTRACTBACKGROUNDIn hypoxic and pseudohypoxic rodent models of pulmonary arterial hypertension (PAH), hypoxia-inducible factor (HIF) inhibition reduces disease severity. However, HIF activation alone, due to genetic alterations or use of inhibitors of prolyl hydroxylase domain (PHD) enzymes, has not been definitively shown to cause PAH in humans, indicating the involvement of other mechanisms.METHODSPseudohypoxia was investigated in primary human lung endothelial cells by silencingPHD2,and inTie2-Cre/Phd2knockout mice, a rodent model of PAH. Lung vascular endothelial cells from PAH patients, and lung tissue from both SU5416/hypoxia PAH rats and PAH patients, were examined for validation.RESULTSPHD2silencing or inhibition, while activating HIF2α, induces apoptosis-resistance, hypo-proliferation, and IFN/STAT activation in endothelial cells, independent of HIF signaling. Mechanistically, PHD2 deficiency activates AKT and ERK, inhibits JNK, and reduces AIP1 (ASK1-interacting protein 1), all independent of HIF2α. Like PHD2,AIP1silencing affects these same kinase pathways and produces a similar dysfunctional endothelial cell phenotype, which can be partially reversed by AKT inhibition. These findings are corroborated in lung tissues of rodent PAH models and pulmonary vascular endothelial cells and tissues from PAH patients.CONCLUSIONSPHD2 deficiency in lung vascular endothelial cells induces an apoptosis-resistant, inflammatory, and hypo-proliferative phenotype. AKT activation and AIP1 loss, but not HIF signaling, drive these aberrant phenotypic changes. Our study suggests that HIF blockade alone may not suffice for PAH therapy; targeting PHD2, AKT, and AIP1 has the potential for developing more effective treatment.GRAPHIC ABSTRACTHighlightsPHD2silencing in human lung vascular endothelial cells suppresses apoptosis, inhibits proliferation, and activates STAT signaling, effects that persist despite HIF2α inhibition or knockdown.PHD2silencing activates AKT and ERK, inhibits JNK, and decreases AIP1, all independently of HIF2αLike PHD2,AIP1silencing led to similar alterations in kinase signaling and endothelial cell phenotypes, which are partially reversed by ATK inhibition.Thesein vitrofindings align with observations in lung vascular endothelial cells and tissues from rodent models of PAH as well as PAH patients.