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Q. Song, C.A. Odonkor, G.W. McCollum, J.S. Penn; Peroxisome Proliferators Activated Receptor and Cycloxygenase Expression in Human Retinal Microvascular Endothelial Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5339.
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© ARVO (1962-2015); The Authors (2016-present)
Peroxisome proliferator activated receptors (PPARs) belong to a nuclear hormone receptor superfamily, and experimental evidence suggests that they either inhibit or promote retinal angiogenesis depending on the receptor subtype (PPARα, PPARß, PPAR γ). Some of the cyclooxygenase (COX)–derived eicosanoids are endogenous ligands for PPARs and may influence the angiogenic program by regulation of PPAR transcriptional activity. In this study, we have investigated the effect of VEGF and hypoxia on COX and PPAR expression in human retinal microvascular endothelial cells (HRMEC). Furthermore, we tested the effect of PPAR agonists on the transcription of a COX–2 promoter–luciferase reporter construct transfected into HRMEC.
HRMEC grown to 80% confluency were serum deprived (1% serum) for 24 hours and treated with VEGF or hypoxia for 0, 0.25, 0.5, 1, 2, 3, 4, 6 and 8 hours. COX and PPAR mRNA levels were assessed by RT–PCR. COX protein levels were measured by western blot analysis. HRMEC were transfected with a COX–2 promoter–luciferase reporter construct and, subsequently, were VEGF–treated or maintained in hypoxia. These cells were treated with 10µM WY–14643 (PPARα agonist), CPGI (PPARß agonist) or ciglitazone (PPAR γ agonist). Transcription initiated by the COX–2 promoter was assessed by luciferase activity.
VEGF–treatment or hypoxia increased COX–2 mRNA and protein levels in HRMEC; however, there was no effect on COX–1. PPARß and PPARγ mRNAs were detected in HRMEC but no PPARα mRNA expression was found. The mRNA levels of PPARß and PPARγ were increased to a maximum of approximately 5–fold each in hypoxia at 4 hours, but VEGF–treatment had no effect. Luciferase reporter analysis indicated COX–2 promoter activity was not regulated by PPAR ligands.
VEGF treatment upregulates COX–2 in HRMEC. COX–2, PPARß and PPARγ mRNAs are upregulated by hypoxia in HRMEC. Hypoxia–induced coordinated expression of COX and PPARs in HRMEC suggests a functional relationship; however, this relationship does not likely involve PPAR–agonist–induced transcription of the COX–2 gene.
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