Neuroprotective Mechanisms of Dark Rearing on cGMP in rd10 mice

Abstract

Purpose : Dark-rearing (DR) rd10 mice has long been known to be neuroprotective, albeit poorly understood. We previously showed that DR slows the rate of retinal degeneration as expected, does not change whole retinal PDE6B expression levels, is associated with stronger mislocalized anti-PDE6B staining in the inner segments, and predominantly preserves rod photoreceptor function, but not cone receptor function. We hypothesize that DR-associated neuroprotection also fundamentally alters cGMP associated photoreceptor cytotoxicity.

Methods : Rd10 mice were DR from birth and compared to c57 and rd10 mice that were RR (12 hr light/12 hr dark cycle) from birth. At P15, 20, 27, and 35, whole retina homogenates were collected for cGMP mass spectrometry, and eye cups were harvested for cGMP IHC. ANOVA and Sidak were used for statistical analysis.

Results : For whole retinal cGMP, rd10 mice that were DR tended to have greater levels than RR rd10 mice at P15 and P27, with significance at P35 (5.16 ±0.84 vs. 3.12 ±0.55, p =0.026). For cGMP IHC, DR rd10 mice had significantly greater cGMP immunostaining of the photoreceptors than RR rd10 mice at P15 (1.73 ±0.40 vs 0.19 ±0.05, p=0.0361), but significantly lower cGMP staining than RR rd10 mice at P27 (2.27 ±0.37 vs 12.35 ±0.91, p<0.0001) and P35 (0.05 ±0.02 vs 6.14 ±0.59, p<0.0001). At P35, there was no difference in the negligible amount of cGMP immunostaining between c57 mice and rd10 DR mice (p>0.9999).

Conclusions : The neuroprotective mechanisms of DR in rd10 has opposing effects of increasing whole retinal cGMP levels, but reducing cGMP IHC immunostaining of the photoreceptors. These results suggest that cGMP-dependent photoreceptor pathophysiology is complex, and whole retinal cGMP levels and cGMP IHC immunostaining may be quantifying distinct processes associated with cGMP cytotoxicity.

This is a 2020 ARVO Annual Meeting abstract.