Abstract
Purpose :
The photocurrent is an ion gradient that retinal photoreceptors rely on for conversion of light into electrical impulses. This gradient is largely mediated by Na+/K+-ATPase pumps, which are localized in the photoreceptor inner segment, where they exist as a heterodimer (a catalytic α3 and a non-catalytic β2 subunits). Previous studies have shown that the mouse lacking ATP1B2 results in rapid photoreceptor degeneration, but the specific importance of ATP1B2 in cones remains unstudied. The goal of this study is to elucidate the role of ATP1B2 in the overall function and health of cone photoreceptors.
Methods :
Using CRISPR/Cas9, our lab generated a floxed Atp1b2 mouse model, which was then crossed with a cone-specific Cre to make a conditional knockout of Atp1b2 in cones. Visual function and retinal thickness were assessed using electroretinography (ERG) and optical coherence tomography. Morphology, protein localization, and protein expression were analyzed by immunohistochemistry and immunoblotting. Na+ concentrations were analyzed using CoroNa+ Green probes. Ultrastructural analysis was completed using transmission electron microscopy (TEM).
Results :
Mice with the conditional deletion of Atp1b2 in cones display progressive cone degeneration and severe loss of cone function compared to control littermates. A significant decrease and mislocalization of cone specific proteins, such as PDE6α’, and GNAT2, and accumulation of Na+ ions were observed in these mice. The ultrastructure of Atp1b2-/- cones at P60 showed a dysmorphic cone outer segment structure with abnormal swelling and holes. No major defects were observed in the cone IS, where the Na+/K+-ATPase is primarily localized. Interestingly, despite the normal expression of rod-specific proteins and only minor abnormalities to rod ultrastructure in cone Atpb2-/- retinas, a significant reduction of the scotopic ERG response was recorded in these mice at P60.
Conclusions :
Our data demonstrate that ATP1B2 is critical for cone photoreceptor function and survival. Loss of ATP1B2 from cones leads to accumulation of Na+ ions, which we hypothesize is likely the reason we observed abnormal ultrastructure of the cone OS and cone degeneration. Furthermore, our data suggest that alterations to the Na+ gradient in cones can also have a harmful effect on other retinal neurons such as rods, contributing to changes in overall retinal function and health.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.