Abstract

Pulmonary arterial hypertension (PAH) is a complex and progressive disorder, characterized by an increase in vascular remodeling, a rise in pulmonary arterial pressure and right heart failure. Recently, we and others showed that BMP antagonist Gremlin1 elicits pulmonary endothelial cell (EC) proliferation in response to hypoxia and that Gremlin1 haplodeficiency attenuates PAH. NADPH oxidase (Nox)-derived reactive oxygen species (ROS) seem to play a pivotal role in PAH. However, the mechanisms by which ROS propagates the disease are unclear. Transcription factor CREB, which is activated by hypoxia, ROS, and interaction with Ref-1 (redox factor 1), mediates gene transcription related to proliferation and vascular remodeling. We postulated that Nox1/Ref-1-mediated CREB activation leads to Gremlin1-induced EC proliferation. Human pulmonary arterial EC (HPAECs, Lonza) were subjected to 24 hr hypoxia (1% O 2 vs. normoxia - 21% O 2 ) to mimic the EC phenotype in PAH. Hypoxia upregulated Nox1 protein level (1.40±0.09-fold, p<0.05) and H 2 O 2 production level/mg protein (2.20±0.21-fold, p<0.0001) vs. normoxia. siNox1 (Nox1 gene silencing) abolished hypoxia-induced Nox1, and Nox1 inhibitor, NoxA1ds, decreased hypoxia-promoted H 2 O 2 . Moreover, siNox1 decreased hypoxia-induced pCREB (1.74±0.22-fold v. normoxia, vs. 1.07±0.08 siNox1+hypoxia, p<0.05), and siCREB decreased hypoxia-induced Gremlin1 (1.83±0.16 hypoxia vs. 0.35±0.01 siCREB+hypoxia, p<0.05). Further, hypoxia augmented nuclear pCREB/Ref-1 interaction (1.812±0.207-fold vs. normoxia, p<0.05) and pCREB association with its DNA binding motif. siRNA for Ref-1 impaired hypoxia-induced pCREB DNA binding (1.96±0.06 hypoxia vs. 0.815±0.219 siRef-1+hypoxia, p<0.01). Moreover, siCREB decreased hypoxia-induced EC proliferation (1.40±0.050 hypoxia vs. 0.96±0.04 siCREB+hypoxia). Finally, preliminary data show pCREB binding to the Gremlin1 promoter. Taken together, our data support a previously unidentified redox signaling pathway by which Nox1-derived ROS promote Gremlin1 expression and EC proliferation in PAH.

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