Abstract
Purpose :
Zebrafish regenerate damaged retinal neurons following acute injury but it is unclear whether regeneration occurs following inherited retinal degeneration. The zebrafish cep290-/- and bbs2-/- mutants are models of retinal ciliopathies that exhibit progressive photoreceptor degeneration as adults. Our goals were to determine if these zebrafish models retain the capacity for regeneration and if the diseased retina limits the potential for full regeneration.
Methods :
Immunohistochemistry was performed on retinal cryosections at various ages using antibodies to identify rods, cones, Muller glia, microglia and macrophages, and proliferating cells. Acute injury was generated by exposing animals to 30 min of UV light and 4 hrs of intense white light to cause photoreceptor loss in the dorsal retina, or by needle-poke injury. A minimum of 4 animals per group were tested. Data was quantified and analyzed using ANOVA with post hoc comparisons.
Results :
The zebrafish cep290-/- and bbs2-/- mutants exhibit progressive photoreceptor degeneration beginning at 3 months of age. Both cep290-/- and bbs2-/- mutants develop an immune response, with 4C4+ and L-plastin+ microglia accumulating in the outer nuclear layer (ONL) as well as the outer segment and RPE layers in the bbs2-/- mutants. Both mutants exhibit a significant increase in the number of PCNA+ cells in the ONL but only a 2-fold increase in proliferating Müller glia. At 4 days post injury with acute light damage, both wild-type and cep290-/- mutants were completely missing photoreceptors at the site of light damage and proliferating cells were observed in the INL. Following 1 month of recovery, however, the density of regenerated photoreceptors in cep290-/- mutants remained significantly lower than that of wild-type animals.
Conclusions :
Zebrafish cep290-/- and bbs2-/- mutants progressively lose cones beginning by 3 months of age. Loss of rods is mitigated by the proliferation of rod progenitors. Regeneration of lost cones occurs only following acute damage, suggesting that the mutants retain the ability to stimulate reprogramming and proliferation of Müller glia, but the necessary stimulus is insufficient. Finally our results suggest that the environment in the diseased retinas may not be permissive to a full regenerative response.
This is a 2020 ARVO Annual Meeting abstract.