Lipid Accumulation in Bruch’s Membrane Is Associated With an Increased Expression of Vascular Endothelial Growth Factor (VEGF) in the Choriocapillaries

Abstract

Abstract: : Purpose: To investigate the pathogenesis of neovascular age–related macular degeneration (AMD) in an established atherosclerotic mice model with low–density lipoprotein (LDL) receptor deficiency and increased accumulation of lipid in Bruch’s membrane. Methods: 8–months–old LDL–receptor–knock–out mice (C57BL/6 LDL–r(–/–)) and C57BL/6 controls were fed a standard rodent diet or a high fat diet western type for two months. Animals were sacrificed and serum total cholesterol (sTC) levels were determined. Eyes were examined by light microscopy (LM) and transmission electron microscopy (TEM). The amount of lipid vacuole accumulation in Bruch’s membrane was documented and graded. Immunohistochemical staining using a polyclonal antibody against vascular endothelial growth factor (VEGF)165 was performed. Results: Control animals did not exhibit any visible changes in the choriocapillaris by LM/TEM after standard diet (sTC 89.9+/–37.5mg/dl) or after high fat diet (sTC 150.6+/–43.9mg/dl). The choriocapillaris showed a regular structure with a thin basement membrane (bm) (0.03–0.06µm), strong fenestration of endothelium and a large capillary lumen. In contrast LDL–receptor–deficient mice after standard diet (sTC 189.0+/–37.5mg/dl) exhibit a thickened bm (0.07–0.1µm), reduced endothelial fenestration and a narrowed lumen. These changes were even more pronounced after high fat diet (sTC 498.3+/–134.3mg/dl). The bm thickness reached a maximum with 0.11–0.22µm. VEGF expression was detectable in the choriocapillaris of all mice. Control animals exhibit only a slight focal reaction, but with elevated sTC in LDL–receptor–deficient mice, VEGF was found more constantly. The overall intensity of staining was markedly increased. Most intensive VEGF expression was documented in knock–out mice following high fat diet with dense lipid deposits in Bruch’s membrane. Conclusions: VEGF is detectable as a physiological agent in the healthy choriocapillaris of control mice. Expression of VEGF is increased in LDL–receptor–deficient mice correlating with the amount of lipid accumulation in Bruch’s membrane. These findings may help to elucidate the pathogenesis of neovascular AMD.

Keywords: age-related macular degeneration • growth factors/growth factor receptors • transgenics/knock-outs