The Conditional Deletion of von Hippel-Lindau Gene in Adult Murine RPE Cells Induces a Rapid-onset In Vivo Phenotype That Strongly Resembles Advanced Human Age-related Macular Degeneration

Abstract

Purpose: : Numerous studies suggest that von Hippel-Lindau protein (pVHL) regulation of hypoxia-inducible factor-αs (HIF-1α and Hif-2α) during hypoxia, inflammation and aging is critical for normal RPE cell function and viability. RPE dysfunction or cell death can result in age-related macular degeneration, the leading cause of vision loss in the elderly. It is critical to better understand how these oxygen-sensing molecules function in adults but not in developmental stages, especially since age-related macular degeneration is not generally observed until after 55+ years. In this study we utilized inducible RPE-specific knockout technology to determine the precise in vivo function of VHL/HIF-α signaling during RPE homeostasis.

Methods: : Doxycycline injections in inducible VMD2-Cre mice activate Cre recombinase activity specifically in RPE cells in a mosaic pattern. VMD2-Cre mice were crossed with VHL^flox/flox, HIF-1α^flox/flox, or HIF-2α^flox/flox mice to inactivate different elements alone or in combination of the pVHL/HIF signaling pathway. The RPE and retinal phenotypes were examined using immunohistochemistry, confocal and electron microscopy, and confocal scanning laser ophthalmoscopy.

Results: : VHL;VMD2-Cre mice exhibit punctate autofluorescence patterns, accumulations of extracellular material resembling human drusen, expansion of the choriocapillaris layer, and photoreceptor degeneration within days of VHL gene inactivation. Nearly complete retinal degeneration occurs in VHL mutants after several months. Cumulatively, these phenotypes strongly resemble those observed in human AMD patients, and remarkably, can be rescued by gene inactivation of VHL, HIF-1α, and HIF-2α (VHL/HIF-1α/HIF-2α;VMD2-Cre KO).

Conclusions: : pVHL/HIF-αs signaling is critical for normal RPE cell function and survival. Dysregulation of VHL signaling in adult RPE cells induces a severe phenotype with a rapid-onset that strongly resembles human AMD. This discovery may be valuable for developing diagnostic tools and therapeutic strategies for finally treating AMD.

Keywords: age-related macular degeneration • retinal pigment epithelium • hypoxia