Abstract
Purpose: :
Age related macular degeneration (AMD) is the main cause of legal blindness in the elderly in developed countries. Severe vision loss is most frequently due to choroidal neovascularization (CNV).Therapy inhibiting vascular endothelial growth factor (VEGF) has yielded the best results in neovascular AMD, but little is known about the conditions leading to VEGF production. Hypoxia has been proposed as a key factor in AMD because of the critical dependence of the outer retina on high levels of choroidal oxygenation. Furthermore, lower choroidal circulatory parameters have been correlated with increased severity of AMD.The aim of this study was to determine whether the oxygen-regulated α-subunit of hypoxia inducible factor-1 (HIF-1α), the most important promoter of VEGF, could be localized in AMD-related CNV membranes.
Methods: :
Paraffin-embedded sections from 16 AMD-CNV membranes, surgically excised for therapeutic reasons, were immunostained for HIF-1α using the Ventana BenchMark fully automated machine. An ocular pathologist blinded to the clinical data graded the staining intensity for each of the following locations: retinal pigment epithelium (RPE), stromal cells and vascular endothelium (VE). Immunostains for CD68 were similarly performed to identify constitutive expression of HIF-1α by macrophages. Controls consisted of 7 enucleated eyes: 4 for choroidal melanoma, 1 for retinoblastoma and 2 normal eyes obtained 5 and 8 hours after death.
Results: :
In 9 of 14 membranes, the RPE showed positive staining for HIF-1α, 5 of them being strongly positive. RPE cells were not seen in 2 specimens.The VE was positive in 8 of 16 cases and stromal cells were considered positive for HIF-1α in 6 of 15 membranes. Strong positivity was seen in 4 and 2 cases for VE and stromal cells, respectively. One membrane was considered to have insufficient stromal cells for grading.In control eyes, focal areas of RPE, stromal cells and VE showed some mild staining for HIF-1α. Only the eye enucleated 8 hours after death had moderate staining. CD68 positive macrophages were present in 8 membranes. 3 of them were totally negative for HIF-1α. All the other 5 were positive for HIF-1α in the RPE and 3 of them in VE as well.
Conclusions: :
The high level of positivity for HIF-1α in CNV membranes, demonstrated mainly in RPE and VE, supports the hypothesis of hypoxia as a major contributing factor in the pathogenesis of neovascular AMD.
Keywords: choroid: neovascularization • hypoxia • pathology: human