Retinitis Pigmentosa: over‐expression of anti‐ageing protein Klotho in degenerating photoreceptors

Abstract

Retinitis Pigmentosa involves a hereditary degeneration of photoreceptors by as yet unresolved mechanisms. The secretable protein α-Klotho has a function related to ageing processes, and α-Klotho-deficient mice have reduced lifespan and declining functions in several tissues. Here, we studied Klotho in connection with inherited photoreceptor degeneration. Increased nuclear immunostaining for α-Klotho protein was seen in degenerating photoreceptors in four different Retinitis Pigmentosa models (rd1, rd2 mice; P23H, S334ter rhodopsin mutant rats). Correspondingly, in rd1 retina α-Klotho mRNA expression was significantly up-regulated. Moreover, immunostaining for another Klotho family protein, β-Klotho, also co-localized with degenerating rd1 photoreceptors. The rd1 retina displayed reduced levels of fibroblast growth factor 15, a member of the fibroblast growth factor subfamily for which Klotho acts as a co-receptor. Exogenous α-Klotho protein added to retinal explant cultures did not affect cell death in rd1 retinae, but caused a severe layer disordering in wild-type retinae. Our study suggests Klotho as a novel player in the retina, with a clear connection to photoreceptor cell death as well as with an influence on retinal organization.