Endothelial HIF-2α Contributes to Severe Pulmonary Hypertension by Inducing Endothelial-to-Mesenchymal Transition

Abstract

Pulmonary vascular remodeling characterized by concentric wall thickening and intraluminal obliteration is a major contributor to the elevated pulmonary vascular resistance in patients with idiopathic pulmonary arterial hypertension (IPAH). Here we report that increased hypoxia-inducible factor 2α (HIF-2α) in lung vascular endothelial cells (LVECs) under normoxic conditions is involved in the development of pulmonary hypertension (PH) by inducing endothelial-to-mesenchymal transition (EndMT), which subsequently results in vascular remodeling and occlusive lesions. We observed significant EndMT and markedly increased expression of SNAI, an inducer of EndMT, in LVECs from patients with IPAH and animals with experimental PH compared with normal controls. LVECs isolated from IPAH patients had a higher level of HIF-2α than that from normal subjects, whereas HIF-1α was upregulated in pulmonary arterial smooth muscle cells (PASMCs) from IPAH patients. The increased HIF-2α level, due to downregulated prolyl hydroxylase domain protein 2 (PHD2), a prolyl hydroxylase that promotes HIF-2α degradation, was involved in enhanced EndMT and upregulated SNAI1/2 in LVECs from patients with IPAH. Moreover, knockdown of HIF-2α (but not HIF-1α) with siRNA decreases both SNAI1 and SNAI2 expression in IPAH-LVECs. Mice with endothelial cell (EC)-specific knockout (KO) of the PHD2 gene, egln1 (egln1), developed severe PH under normoxic conditions, whereas Snai1/2 and EndMT were increased in LVECs of egln1 mice. EC-specific KO of the HIF-2α gene, hif2a, prevented mice from developing hypoxia-induced PH, whereas EC-specific deletion of the HIF-1α gene, hif1a, or smooth muscle cell (SMC)-specific deletion of hif2a, negligibly affected the development of PH. Also, exposure to hypoxia for 48-72 h increased protein level of HIF-1α in normal human PASMCs and HIF-2α in normal human LVECs. These data indicate that increased HIF-2α in LVECs plays a pathogenic role in the development of severe PH by upregulating SNAI1/2, inducing EndMT, and causing obliterative pulmonary vascular lesions and vascular remodeling.

Mechanisms contributing to persistently activated cell phenotypes in pulmonary hypertension

“…; Tang et al . ) or in pulmonary ECs (Cowburn et al . ) reduces or completely blocks the development of PH.…”

“…; Tang et al . ), or activating mutation of Hif2a (Tan et al . ) leads to PH development under normoxic conditions.…”

Endothelial-specific Loss of IFT88 Promotes Endothelial-to-Mesenchymal Transition and Exacerbates Bleomycin-induced Pulmonary Fibrosis

“…3C). In humans, endothelial cells undergoing EndMT demonstrate higher proliferation and migration 25,26 . To determine if the loss of Ift88-associated EndMT is also associated with increased proliferation and migration, we evaluated proliferation in scramble control-and siIft88-transfected HCAECs.…”

“…Recent data indicate that cardiac fibrosis is associated with the emergence of fibroblasts originating from ECs and that EndMT, an event that occurs during the formation of the atrioventricular cushion in the embryonic heart, may also play an important, albeit pathological role, in the post-natal state 18,19 . Furthermore, increased mesenchymal cell proliferation and migration is associated with EndMT and tissue fibrosis 25,46 . Transforming growth factor-β1 (Tgfβ1) induces ECs to undergo EndMT, whereas Bone Morphogenetic Protein 7 (BMP-7), which preserves the endothelial phenotype, significantly inhibits EndMT and the progression of cardiac fibrosis in mouse models of pressure overload 19 .…”

Endothelial cells and organ function: applications and implications of understanding unique and reciprocal remodelling

“…Furthermore, it is an important regulator of cytoskeleton structure and cell architecture, as well as intracellular signalling via initiation of transduction cascades, and it is thought to be determinant in the establishment of EC polarity . Even though HIF‐2α in EC is vital for vascular integrity, stability and recovery , it is also required for the onset and exacerbation of pulmonary hypertension , and deletion of lung EC HIF‐2α resulted in ameliorated hypertension phenotypes in mice . In general, HIF‐2α is seen as the gatekeeper of EC quiescence, but depending on the tissue or the combined parameters within certain conditions, stabilization of endothelial HIF‐2α is not advantageous.…”