Oxidative DNA Damage in Microglia Exacerbates Retinal Inflammation and Degeneration through MUTYH-mediated Base Excision Repair in a Mouse Model of Retinitis Pigmentosa

Abstract

Purpose : Oxidative DNA damage contributes to the development of cancer and neurodegeneration. We previously demonstrated that oxidative DNA damage is substantially increased in the retina of animal models of retinitis pigmentosa (RP) and mediates photoreceptor cell death (Murakami Y, et al. Am J Pathol. 2012). In the present study, we further investigated the mechanisms by which oxidative DNA damage causes retinal degeneration in RP.

Methods : Rd10 mice, which have a missense mutation in the Pde6b gene, were crossed with mice deficient for Mutyh, a base excision repair enzyme against oxidative DNA damage, to generate rd10; Mutyh^-/- mice. Accumulation of 8-oxo-dG, a major oxidative base in DNA, were analyzed by immunohistochemistry. Immunofluoresence for Microglial markers (Iba-1 and F4/80) and single strand DNA breaks (SSBs) and TUNEL staining were performed in the retinal sections and whole mounts. Primary microglial cells were harvested from rd10 and rd10; Mutyh^-/- mice, and cocultured with 661W photoreceptor-like cells.

Results : In the early phase of retinal degeneration (p17), the retinas of rd10; Mutyh^-/- mice showed comparable punctate 8-oxo-dG staining, which was mostly co-localized at microglial cells, with rd10 mice; while they exhibited reduced SSBs formation. Consequently, at P21, the microglial activation was substantially suppressed in rd10; Mutyh^-/- mice, along with decreased 8-oxo-dG accumulation and attenuated photoreceptor cell death, suggesting that MUTYH-dependent base excision repair activates microglial cells and promotes retinal degeneration. Consistent with this idea, Mutyh deficiency in primary microglial cells suppressed TNF-α secretion and prevented cytotoxicity to 661W cells in response to oxidative damage.

Conclusions : Oxidative DNA damage in microglial cells triggers microglial activation and promotes photoreceptor cell death in RP, and MUTYH may be a novel therapeutic target to protect the retina against oxidative DNA injury.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.