Müller glia proliferation and cone regeneration is triggered by acute damage but not progressive photoreceptor degeneration in zebrafish cep290^-/- mutants

Abstract

Purpose : Zebrafish regenerate lost neurons following acute injury but little is known about whether regeneration occurs in genetic models of retinal degeneration. Here we examine the regenerative capacity of the zebrafish retina in animals with a slow retinal degeneration due to a nonsense mutation in cep290.

Methods : Transgenic lines and antibodies were used to identify rods and cones, and proliferating cells were labeled with antibodies against PCNA. EdU labeling was used to identify cells descended from retinal progenitors. Lesions were generated with an OCT-guided laser or with exposure to high intensity light.

Results : Mutation of zebrafish cep290 results in progressive photoreceptor degeneration. Larval cep290^fh297/fh297 zebrafish have normal retinal structure but have 18% fewer cones than wild-type siblings at 3 months of age, and 75% fewer cones by 12 months. Rhodopsin mislocalization was observed at 6 months. Compared to wild-type siblings, 6-month old cep290^-/- mutants had a 10-fold increase in the number of PCNA+ cells in the outer nuclear layer but only a 2-fold increase in proliferating Müller glia in the inner nuclear layer. The proliferating cells only differentiated into rods, suggesting regeneration of dying rod photoreceptors. Following acute injury by laser lesion or intense light exposure, both mutant and wild-type fish exhibited similar levels of Müller cell proliferation and regenerated both rods and cones. In cep290 mutants, however, areas with regenerated photoreceptors were indistinguishable from neighboring, non-lesioned, degenerating photoreceptors.

Conclusions : cep290^fh297/fh297 zebrafish slowly lose cones beginning at 3 months of age. While proliferation and production of rod progenitors is perpetually stimulated in these animals, regeneration of lost cones does not occur unless the retina sustains acute damage. This suggests that while the cep290 mutant retina retains the ability to regenerate both rods and cones, signals that stimulate reprogramming and proliferation of Müller glia into multipotent neural progenitors are lacking. Furthermore, the observation that newly regenerated cells within lesions fail to adopt the phenotype of non-degenerated retina indicates that the diseased retina limits the potential for complete restoration of photoreceptor density and architecture.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.