Abstract
Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We examined the retina of kcnj13 mutant zebrafish (obelixtd15, c.502T > C p.[Phe168Leu]) to provide new insights into the pathophysiology underlying these conditions. Detailed phenotyping of obelixtd15 fish revealed a late onset retinal degeneration at 12 months. Electron microscopy of the obelixtd15 retinal pigment epithelium (RPE) uncovered reduced phagosome clearance and increased mitochondrial number and size prior any signs of retinal degeneration. Melanosome distribution was also affected in dark-adapted 12-month obelixtd15 fish. At 6 and 12 months, ATP levels were found to be reduced along with increased expression of glial fibrillary acidic protein and heat shock protein 60. Quantitative RT-PCR of polg2, fis1, opa1, sod1/2 and bcl2a from isolated retina showed expression changes consistent with altered mitochondrial activity and retinal stress. We propose that the retinal disease in this model is primarily a failure of phagosome physiology with a secondary mitochondrial dysfunction. Our findings suggest that alterations in the RPE and photoreceptor cellular organelles may contribute to KCNJ13-related retinal degeneration and provide a therapeutic target.
Highlights
KCNJ13 (MIM #603208) is a three-exon gene located on chromosome 2q37 which encodes the 360-amino acid protein Kir7.1, a low-conductance inwardly rectifying potassium channel (Kir) that functions as a homotetramer[1,2,3,4]
We investigated www.nature.com/scientificreports mitochondrial function in the 6 mpf obetd[15] retina using Seahorse XF analysis, which revealed a decrease in baseline oxygen consumption rate (OCR) in the mutant, but did not reach statistical significance (n = 3, p = 0.0558)
The Kir7.1 protein is an inwardly rectifying potassium channel linked to two forms of retinal dystrophy, Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD)
Summary
KCNJ13 (MIM #603208) is a three-exon gene located on chromosome 2q37 which encodes the 360-amino acid protein Kir7.1, a low-conductance inwardly rectifying potassium channel (Kir) that functions as a homotetramer[1,2,3,4]. The retinal phenotype has been examined in Kcnj[13] mosaic mice[17] and most recently in conditional knockout mice generated using CRISPR/Cas[9], where loss of Kcnj[13] expression in the RPE caused severe and progressive thinning of the outer nuclear layer from 15 days post birth and a reduced response to light[18]. These findings highlight the essential role of RPE-based Kir7.1 in retinal photoreceptor function and survival. In view of these findings, we have characterized the retinal degeneration in the homozygous obetd[15] zebrafish, identifying alterations in melanosome function with phagosome and mitochondrial activity linked to retinal stress, furthering our understanding of the pathophysiology associated with KCNJ13 in the retina
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