Photoreceptor Degeneration in Homozygous Male Per2(luc) Mice During Aging.

The Per2(luc) mouse model developed by Takahashi laboratory is one of the most powerful models to study circadian rhythms in real time. In this study, we report that photoreceptors degenerate in male Per2(luc) mice during aging. Young (2.5- to 5-month-old) and aged (11- to 13.5-month-old) homozygous male Per2(luc) mice and C57BL/6J mice were used for this study. Retina structure and function were investigated via spectral domain optical coherence tomography (SD-OCT), fundus imaging, and electroretinography (ERG). Zonula occludens-1 (ZO-1) immunofluorescence was used to analyze the retinal pigment epithelium (RPE) morphology. Fundus examination revealed no difference between young Per2(luc) and wild-type (WT) mice. However, the fundus of aged Per2(luc) mice showed white deposits, suggestive of age-related drusen-like formation or microglia, which were absent in age-matched WT mice. No differences in retinal structure and function were observed between young Per2(luc) and WT mice. However, with age, Per2(luc) mice showed a significant reduction in total retinal thickness with respect to C57BL/6J mice. The reduction was mostly confined to the photoreceptor layer. Consistent with these results, we observed a significant decrease in the amplitude of a- and b-waves of the ERG in aged Per2(luc) mice. Analysis of the RPE morphology revealed that in aged Per2(luc) mice there was an increase in compactness and eccentricity with a decrease in solidity with respect to the values observed in WT, pointing toward signs of aging in the RPE of Per2(luc) mice. Our data demonstrate that homozygous Per2(luc) mice show photoreceptor degeneration during aging and a premature aging of the RPE.