Activation of hypoxia-inducible factor-1 in pulmonary arterial smooth muscle cells by endothelin-1

Abstract

Pisarcik S, Maylor J, Lu W, Yun X, Undem C, Sylvester JT, Semenza GL, Shimoda LA. Activation of hypoxia-inducible factor-1 in pulmonary arterial smooth muscle cells by endothelin-1. Am J Physiol Lung Cell Mol Physiol 304: L549 -L561, 2013. First published February 15, 2013 doi:10.1152/ajplung.00081.2012.-Numerous cellular responses to hypoxia are mediated by the transcription factor hypoxia-inducible factor-1 (HIF-1). HIF-1 plays a central role in the pathogenesis of hypoxic pulmonary hypertension. Under certain conditions, HIF-1 may utilize feedforward mechanisms to amplify its activity. Since hypoxia increases endothelin-1 (ET-1) levels in the lung, we hypothesized that during moderate, prolonged hypoxia ET-1 might contribute to HIF-1 signaling in pulmonary arterial smooth muscle cells (PASMCs). Primary cultures of rat PASMCs were treated with ET-1 or exposed to moderate, prolonged hypoxia (4% O2 for 60 h). Levels of the oxygen-sensitive HIF-1␣ subunit and expression of HIF target genes were increased in both hypoxic cells and cells treated with ET-1. Both hypoxia and ET-1 also increased HIF-1␣ mRNA expression and decreased mRNA and protein expression of prolyl hydroxylase 2 (PHD2), which is the protein responsible for targeting HIF-1␣ for O2-dependent degradation. The induction of HIF-1␣ by moderate, prolonged hypoxia was blocked by BQ-123, an antagonist of ET-1 receptor subtype A. The effects of ET-1 were mediated by increased intracellular calcium, generation of reactive oxygen species, and ERK1/2 activation. Neither ET-1 nor moderate hypoxia induced the expression of HIF-1␣ or HIF target genes in aortic smooth muscle cells. These results suggest that ET-1 induces a PASMC-specific increase in HIF-1␣ levels by upregulation of HIF-1␣ synthesis and downregulation of PHD2-mediated degradation, thereby amplifying the induction of HIF-1␣ in PASMCs during moderate, prolonged hypoxia. calcium; prolyl hydroxylase; pulmonary hypertension IN A VARIETY OF CHRONIC lung diseases, the pulmonary circulation is exposed to prolonged periods of hypoxia, often resulting in the development of pulmonary hypertension. Numerous studies have described the structural and functional changes that occur in the pulmonary circulation in response to chronic hypoxia (60). Structural remodeling, characterized by pulmonary arterial smooth muscle cell (PASMC) proliferation, intimal thickening, and extension of muscle into previously nonmuscular arterioles, is commonly observed with pulmonary hypertension (23,40). Changes in the vascular wall are accompanied by active contraction of vessels, evidenced by acute reduction in pulmonary arterial pressure in response to vasodilatory agents (42, 44). These pulmonary vascular changes result, in large part, from altered expression of genes encoding ion channels and transporters that control PASMC ion homeostasis, including increased expression of Na ϩ /H ϩ exchanger isoform 1 (NHE1) and the canonical transient receptor potential (TRPC) family members TRPC1 and TRPC6, as well as reduced levels of mRNA...

Pulmonary Vascular and Ventricular Dysfunction in the Susceptible Patient (2015 Grover Conference Series)

“…In contrast, ET-1 failed to augment HIF-1α in aortic smooth muscle cells, suggesting a feature unique to PASMCs. 97 Since the primary source of ET-1 in vivo appears to be endothelial cells, these data, taken as a whole, suggest a possible model whereby enhanced HIF-2α expression in endothelial cells during CH produces ET-1, which then augments HIF-1α in PASMCs, initiating a feed-forward mechanism for upregulation of HIF-1 and, consequently, HIF target genes to promote the development of HPH.…”

Lung Circulation

“…In addition to regulating both Ca 2+ and pH homeostasis (566,666), HIFs also regulate other factors involved in the pathogenesis of PH, including ET-1 and VEGF [reviewed in (505)]. While hypoxia is an obvious stimulant for HIF activation, HIFs also can be upregulated under nonhypoxic conditions by a number of factors (505), including ET-1 (497). Moreover, HIF-1α protein is detectable in PASMCs from FHRs (72) and lungs of PAH patients (18,165), which is thought to be linked to mitochondrial dysfunction.…”

Endothelin-1-mediated vasoconstriction alters cerebral gene expression in iron homeostasis and eicosanoid metabolism

“…This establishes that transient vasoconstriction and the accompanying ischemic time frame is capable of inducing a potent inflammatory reaction. Furthermore, we observed induction of genes for oxidative stress linked proteins, such as Hif1a, Myc and Sod2/MnSOD at 24 h. Recent studies have demonstrated ET-1-dependent induction of Hif1a mRNA (Li et al, 2012;Pisarcik et al, 2013), with no documented effects on Sod2 and Myc. Intriguingly, statistically significant inductions of Ifnb, Tnf and Myc were also observed on the contralateral side of the brain, sampled at the same site, suggesting that a high degree of crosstalk exists between the injured hemisphere and its contralateral counterpart.…”