Mitochondrial oxidative stress in the RPE and murine cytomegalovirus (MCMV) ocular latency synergize to enhance development of AMD-like pathology

Abstract

Purpose : Systemic neonatal MCMV infection of 129 mice spreads to the eye with subsequent establishment of ocular latency. Since oxidative stress-induced RPE damage is considered to be a key factor in AMD development, we wished to determine if oxidative stress in the RPE and MCMV ocular latency synergize to enhance development of AMD-like pathology.

Methods : MCMV (50 pfu per mouse), or medium as control, were injected intra-peritoneally (i.p.) into RPE-specific, SOD2-depleted (SOD2^flox/flox, Tyrosinase^Cre/ERT2+) or control mice at <3 days after birth. At 4 months p.i. when MCMV infection had become latent, tamoxifen was administered to induce the activity of Cre recombinase. At 4 months post-tamoxifen treatment, SD-OCT were performed. Eyes, RPE cells or choroid were collected for further examinations.

Results : At 4 months post-tamoxifen treatment, no replicating virus were detected in eyes of infected mice. MCMV DNA was present in 7 of 10 choroid samples from both infected RPE-specific, SOD2-depleted and control mice. Although MCMV DNA was detected in 4 of 10 RPE samples from infected control mice, it was present in 9 of 10 RPE samples from infected, RPE-specific, SOD2-depleted mice. OCT examinations showed that lesions were present in the majority of infected, RPE-specific, SOD2-depleted mice (16/28 eyes) but were observed only occasionally in infected, SOD2-sufficient control mice (3/20 eyes) or in uninfected, RPE-specific, SOD2-depleted mice (1/22 eyes) while no lesions were observed in uninfected, SOD2-sufficient control mice (0/18) with the majority of lesions being hyperreflective. The following pathological changes were observed only in eyes of infected, RPE-specific, SOD2-depleted mice: 1. Disorganized choroidal tissue. 2. Damaged or depleted RPE cells with undifferentiated fibroblast-like cells present in the RPE layer. 3. Deposits of cell-derived debris in the subretinal space. 4. Photoreceptor degeneration, including a depleted outer nuclear layer (ONL) and an apoptotic nuclear morphology, in some photoreceptors. 5. Migration of pigmented RPE cells to the photoreceptor inner segment layer (IS) and the inner and outer nuclear layers.

Conclusions : Mitochondrial oxidative stress in the RPE enhances spread of latent ocular MCMV infection, resulting in increased RPE degeneration and the development of a more severe AMD-like pathology.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.