Characterizing the effects of mitochondrial DNA mutations on retinal health in the Polg^D257A mouse.

Abstract

Purpose : Mitochondrial DNA (mtDNA) mutations that promote mitochondrial dysfunction have been implicated in age-related retinal diseases. This study used a novel pre-clinical model to test the hypothesis that impaired mitochondrial function due to mtDNA damage results in age-related retinal and retinal pigment epithelium (RPE) degeneration.

Methods : 3-, 6-, 9-, and 12-month-old Polg^D257A mutant and wild-type (WT) mice were imaged using optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy (cSLO)(N=4). In addition, photoreceptor and RPE functions were assessed using electroretinogram (ERG). Histological and immunohistological evaluation of the retinas of Polg^D257A mutant and control mice were also performed in cryosections. Cryosections (8 um) were incubated with commercially available antibodies specific to retinal cells and mitochondria. Sections were analyzed using a Leica TCS-SP8. A Student’s t-test was used for all statistical analyses.

Results : OCT image analysis revealed a decrease in the size of several retinal cell layers starting at 6 months of age. Most notably, the RPE and photoreceptor (PR) layers were significantly decreased compared to WT mice and accounted for nearly 57% of the total retinal degeneration observed. Analysis of SLO images detected a significant decrease in blue auto fluorescence at 6 months of age. ERG testing displayed a drastic reduction in a-wave, b-wave, and light-adapted response at 12 months of age. Finally, retinal tissue collected for immunofluorescence showed decreases in COX4 and Ezrin proteins compared to WT. Together, this data indicates that mtDNA mutations result in both degenerative and physiological effects in the mouse retina. The degeneration is associated with decreased total retina and RPE thickness, impaired electrophysiological activity from multiple neural retina cell types, and reduced essential proteins implicated in retinal metabolism and integrity.

Conclusions : Polg^D257A mutant mice that accumulate mtDNA mutations due to an error-prone exonuclease domain in Polymerase gamma, exhibit an age-related retinal pathology.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.