A Splicing Mutation in Slc4a5 Results in Retinal Detachment and Retinal Pigment Epithelium Dysfunction

Fluid and solute transporters of the retinal pigment epithelium (RPE) are core components of the outer blood-retinal barrier. Characterizing these transporters and their role in retinal homeostasis may provide insights into ocular function and disease. Here, we describe RPE defects in mice, which exhibit hypopigmented patches in the central retina. Mapping and nucleotide sequencing of mice revealed a disrupted 5' splice donor sequence in , a sodium bicarbonate cotransporter gene. expression was reduced 19.7-fold in RPE relative to controls, and alternative splice variants were detected. SLC4A5 was localized to the Golgi apparatus of cultured human RPE cells and in apical and basal membranes. Fundus imaging, optical coherence tomography, microscopy, and electroretinography (ERG) of mice revealed retinal detachment, hypopigmented patches corresponding to neovascular lesions, and retinal folds. Detachment worsened and outer nuclear layer thickness decreased with age. ERG a- and b-wave response amplitudes were initially normal but declined in older mice. The direct current ERG fast oscillation and light peak were reduced in amplitude at all ages, whereas other RPE-associated responses were unaffected. These results link a new mutation to subretinal fluid accumulation and altered light-evoked RPE electrophysiological responses, suggesting that SLC4A5 functions at the outer blood-retinal barrier.