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Hope Titus, Kyle K. Weller, Jenny Li, Richard G Weleber, Mark E Pennesi, Paul Yang; Dark-rearing reduces degeneration and alters the characteristics of cGMP dysregulation in rd10 mice. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1001.
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© ARVO (1962-2015); The Authors (2016-present)
Elevated levels of cGMP have been thought to be involved in the mechanism of cell death in the rd10 mice. Whereas dark-rearing (DR) rd10 mice is neuroprotective, it is also paradoxical in that cGMP levels are thought to be elevated in the dark. In order to understand this mechanism in more detail, we assessed the retinal structure and presence of cGMP in DR rd10 mice.
Rd10 mice were DR from birth and compared to c57 and rd10 mice that were regularly reared in 12 hr light/12 hr dark cycle (RR) from postnatal day (P) 15 to 35. Optical coherence tomography (OCT) was used to assess outer retinal thickness (REC+). Whole retina tissue was collected for the quantification of cGMP levels using tandem liquid chromatography mass spectrometry (LC-MS). Eye cups were harvested for the assessment of photoreceptor morphology, Mueller cell activation, and cGMP positivity using IHC. ANOVA and Sidak were used statistical analysis.
With respect to REC+, DR rd10 mice degenerated linearly at a rate of 2 µm/day from P15-35 compared to RR rd10 mice which degenerated rapidly to similar levels by P16-19. Compared to RR rd10 mice, DR rd10 mice had significantly thicker REC+ at P27 (41.4±0.6 vs 102.8±0.7, p<0.0001) and P35 (31.6±0.9 vs 95.0±1.7, p<0.0001). However, DR rd10 mice had significantly thinner REC+ P27 (p<0.0001) and P35 (p<0.0001) compared to c57 mice which had stable REC+ at ~125 µm. Mueller cell activation gradually became more prominent from P20-35 in DR rd10 mice, yet the intensity of activation at P35 was still less than that of RR rd10 mice at P22. Cone arrestin staining showed that cone photoreceptor cell layer was still relatively well-defined with cone tips in DR rd10 mice at P35 compared with general disorganization and either lack or atypical cone tip morphology in RR rd10 mice at P22. Interestingly, cGMP positivity was negligible at P35 in DR rd10 mice, similar to that of RR rd10 mice at P13-15 and significantly lower than the high cGMP positivity found in RR rd10 mice P16-35. Whole retinal cGMP levels of DR rd10 mice (13.9±1.6 pmol/mL) were significantly greater than RR rd10 mice at P35 (5.5±0.5 pmol/mL, p=0.0170), and less than c57 mice at P35 (22.1±1.7, p=0.0461).
Dark-rearing rd10 mice not only slows the rate of retinal degeneration as expected, but it also fundamentally alters the characteristics of degeneration and cGMP dysregulation.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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