Hypoxia upregulates PGI-synthase and increases PGI2 release in human vascular cells exposed to inflammatory stimuli

Mercedes Camacho,Cristina Rodríguez,Anna Guadall,Sonia Alcolea,Mar Orriols,José-Román Escudero,José Martínez-González,Luis Vila

doi:10.1194/jlr.m011007

Abstract

Hypoxia affects vascular function and cell metabolism, survival, growth, and motility; these processes are partially regulated by prostanoids. We analyzed the effect of hypoxia and inflammation on key enzymes involved in prostanoid biosynthesis in human vascular cells. In human vascular smooth muscle cells (VSMC), hypoxia and interleukin (IL)-1β synergistically increased prostaglandin (PG)I₂ but not PGE₂ release, thereby increasing the PGI₂/PGE₂ ratio. Concomitantly, these stimuli upregulated cyclooxygenase-2 (COX-2) expression (mRNA and protein) and COX activity. Interestingly, hypoxia enhanced PGI-synthase (PGIS) expression and activity in VSMC and human endothelial cells. Hypoxia did not significantly modify the inducible microsomal-PGE-synthase (mPGES)-1. Hypoxia-inducible factor (HIF)-1α-silencing abrogated hypoxia-induced PGIS upregulation. PGIS transcriptional activity was enhanced by hypoxia; however, the minimal PGIS promoter responsive to hypoxia (-131 bp) did not contain any putative hypoxia response element (HRE), suggesting that HIF-1 does not directly drive PGIS transcription. Serial deletion and site-directed mutagenesis studies suggested several transcription factors participate cooperatively. Plasma levels of the stable metabolite of PGI₂ and PGIS expression in several tissues were also upregulated in mice exposed to hypoxia. These data suggest that PGIS upregulation is part of the adaptive response of vascular cells to hypoxic stress and could play a role in counteracting the deleterious effect of inflammatory stimuli.

Highlights

Hypoxia affects vascular function and cell metabolism, survival, growth, and motility; these processes are partially regulated by prostanoids
As the effect of hypoxia on the final synthases of the COX-pathway in vascular cells is as yet unknown, we aimed to investigate the effect of hypoxia on the prostanoid biosynthesis and mPGES-1 and PGIS expression in resting vascular cells and under exposure to a strong COX-2 inducer such as interleukin (IL)-1␤
Since the transcriptional response to hypoxia is primarily mediated by Hypoxia-inducible factor (HIF)-1␣, we explored the implication of HIF-1␣ in PGIS expression induced by hypoxia

Summary

Introduction

Hypoxia affects vascular function and cell metabolism, survival, growth, and motility; these processes are partially regulated by prostanoids. In human vascular smooth muscle cells (VSMC), hypoxia and interleukin (IL)-1␤ synergistically increased prostaglandin (PG)I2 but not PGE2 release, thereby increasing the PGI2/PGE2 ratio. These stimuli upregulated cyclooxygenase-2 (COX-2) expression (mRNA and protein) and COX activity. Plasma levels of the stable metabolite of PGI2 and PGIS expression in several tissues were upregulated in mice exposed to hypoxia These data suggest that PGIS upregulation is part of the adaptive response of vascular cells to hypoxic stress and could play a role in counteracting the deleterious effect of inflammatory stimuli.—Camacho, M., C. Hypoxia upregulates PGI-synthase and increases PGI2 release in human vascular cells exposed to inflammatory stimuli.

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