Upregulation of stromal cell-derived factor 1 (SDF-1) expression in microvasculature endothelial cells in retinal ischemia-reperfusion injury

Stromal cell-derived factor 1 (SDF-1) is a potent chemotactic and angiogenic factor that has been proposed to play a role in the development of neovascularization. In this study, we explored the expression of SDF-1 in a rat model of retinal ischemia-reperfusion injury and investigated the possible role of retinal microvasculature endothelium cells in generation of this chemokine. Expression patterns of SDF-1 were studied in retina suffering ischemia-reperfusion insult in Sprague-Dawley rats by elevating the intraocular pressure to 110 mm for 60 minutes. The relative level of SDF-1 mRNA in retinas following 6, 12 and 24 hours reperfusion was determined by semi-quantitative RT-PCR. Immunohistochemical methods were used to detect specific lesions expressing SDF-1. The gene expression of SDF-1 in cultured human retinal microvasculature endothelial cells (HRMEC) under hypoxia conditions was assessed by semi-quantitative RT-PCR. The SDF-1 protein was analyzed by immunocytochemistry and fluorescence-activated cell sorting. Upregulation of SDF-1 mRNA (at 6, 12, and 24 hours of reperfusion) was observed, with the expression peak occurring at 12 hours. SDF-1 positive cells appeared initially around the retinal vessels,which diffused into the inner retinal layers. Hypoxia enhanced the expression of HIF-1 and SDF-1 mRNA in HRMEC. The production of SDF-1 protein by HRMEC was increased up to 320% after 6 hours of hypoxia, as demonstrated by fluorescence-activated cell sorting. The results of our study indicate that endogenous SDF-1 is up-regulated in retinal microvasculature suffering ischemia insult, and that microvasculature endothelial cells are potential contributors for generation of SDF-1 in ischemic retina.