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G.W. McCollum, R. Yang, J.S. Penn; Prostaglandin E2 Synthase mRNA Levels Are Increased in Response to Hypoxia in Rat Muller Cells . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2974.
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Purpose: There is evidence that prostaglandin–induced VEGF expression may stimulate tumor angiogenesis. VEGF has been implicated in the pathogenesis of proliferative retinopathies, and Müller cells (MC) are an important source of retinal VEGF under hypoxic conditions. In this work, the expression of prostaglandin receptors and synthases was surveyed in hypoxic and normoxic rat Müller cells and in non–treated and VEGF–treated human microvascular endothelial cells (HRMEC) by microarray analysis. Messenger RNA levels showing either a significant response to hypoxia or VEGF treatment or relatively high levels of expression were further investigated by quantitative real time RT–PCR. Methods: Rat Müller cells were grown to 70–80% confluency and subjected to hypoxic conditions (less than 2% oxygen) for 24 hr or were maintained in normoxia. Human microvascular endothelial cells (HRMEC) were grown to 70–80% confluency and either treated with 25 ng/ml VEGF for 24 hours or not treated. Total RNA was isolated from MC and HRMEC and analyzed using either the Affymetrix GeneChip Expression Set 230 containing full coverage of the transcribed rat genome or the Human Genome U133 2.0 array providing comprehensive coverage of the transcribed genome. Expression levels of some genes were further characterized by real time quantitiative RT–PCR. Results: Several prostaglandin receptors and synthases were expressed at various levels in MC and HRMEC. MC expressed prostaglandin E2 synthase at high levels with an approximate 50% increase in expression at 24 hours of hypoxia. The expression of prostaglandin receptors and synthases in HRMEC did not appear to be affected by VEGF treatment. However, the PGE2 receptor, EP4, was expressed at high levels in both treated and untreated cultures. Conclusions: Hypoxic MC are an in vivo source of retinal VEGF and VEGF is implicated in the pathogenesis of proliferative retinopathies. In this work, PGE2 synthase is up–regulated in response to hypoxia in MC and the EP4 receptor is expressed at high levels in HRMEC. These data suggest a possible link between hypoxia–induced retinal VEGF and PGE2 and/or a role for PGE2 in retinal angiogenesis.
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