Expression of hypoxia-inducible factor-1alpha and -2alpha in human choroidal neovascular membranes

Up-regulation of pro-angiogenic cytokine expression occurring secondary to hypoxia in physiologic and pathophysiologic conditions is mediated by the family of transcription regulators know as hypoxia inducible factors (HIF). The present study was undertaken to investigate the expression of HIF occurring in human choroidal neovascularization (CNV) and the posterior segment of young and old eyes.

Surgically excised CNV from patients with either age-related macular degeneration (AMD; n = 9), punctuate inner choroidopathy (PIC; n = 3) and young normal eyes were immunohistochemically probed with monoclonal antibodies against HIF-1alpha and -2alpha and compared to that for cell markers specific for vascular endothelial cells (CD34), macrophages (CD68), retinal pigment epithelial cells (RPE; panel cytokeratins/CK18) and VEGF. Following secondary antibody amplification, reactions were visualized with fast red chromogen.

Cellular immunoreactivity of membranes for HIF-2alpha was strong in eight out of nine AMD specimens but it was only weakly positive for HIF-1alpha in five specimens. In contrast, two out of three PIC specimens were weakly positive for HIF-1alpha but demonstrated no staining for HIF-2alpha. Immunohistochemical analysis revealed areas within the CNV membranes that were predominantly immunopositive for CD68 and cytokeratin indicating the presence of RPE and/or macrophages and that these cells strongly co-localized with the presence of HIF and VEGF. No immunochemical co-localization was observed with HIF and the endothelial cell marker CD34 in any membranes studied. Normal globes also demonstrated HIF-2 positivity to be predominantly localized to the central RPE rather than peripheral RPE irrespective of age of donor.

The localization of HIF expression supports the concept that hypoxia is a major stimulus for the development of submacular wound healing and within this context CNV is but one component of this process.