# Atp1b2Atp1b1 Knock-In Mice Exhibit a Cone–Rod Dystrophy-Like Phenotype

## TL;DR

Mice with a genetic modification replacing the β2-subunit of the Na,K-ATPase with the β1-subunit develop a retinal disease similar to cone–rod dystrophy, with early cone loss followed by rod degeneration.

## Contribution

The study identifies a new mouse model for cone–rod dystrophy caused by Na,K-ATPase dysfunction.

## Key findings

- Atp1b2Atp1b1 knock-in mice show early and rapid loss of cone photoreceptor cells.
- Rod degeneration follows cone loss in the mutant mice, but other retinal cells remain unaffected.
- Expression of retinoschisin is reduced in mutant retinas due to lower β2-subunit levels.

## Abstract

The Na,K-ATPase is a heterodimeric ion pump consisting of various combinations of a catalytic α-subunit (α1, α2, α3, or α4, encoded by ATP1A1–ATP1A4) and a β-subunit (β1, β2, or β3, encoded by ATP1B1–ATP1B3). We have previously shown that Atp1b2 knock-out (ko) mice exhibit rapid photoreceptor cell degeneration, whereas Atp1b2Atp1b1 knock-in (ki) mice, which express the β1-subunit instead of the β2-subunit under regulatory elements of the Atp1b2 gene, exhibit slowly progressive retinal dystrophy. Here, we performed a detailed analysis of the retinal phenotype of the Atp1b2Atp1b1 ki mouse. We found that the number of cone photoreceptor cells in the mutant retinas was significantly reduced by postnatal day 28. The retinas of 4-month-old mice were almost devoid of cones. The early onset and rapid loss of cones was followed by a slowly progressive degeneration of rods. Other retinal cell types were unaffected. Nonradioactive in situ hybridization and immunohistochemistry revealed that wild-type photoreceptors expressed β3 and high levels of β2, while Atp1b2Atp1b1 ki photoreceptor cells expressed β3 and low levels of transgenic β1. Additionally, levels of retinoschisin, a secreted retina-specific protein that interacts directly with the β2-subunit, were greatly reduced in mutant retinas. The results demonstrate that the β1-subunit can functionally compensate, at least in part, for the absence of the β2-subunit. The results also show that cones are more susceptible to Na,K-ATPase dysfunction than rods. Taken together, the present study identifies the Atp1b2Atp1b1 ki mutant as a novel animal model of an early-onset and rapidly progressive cone–rod dystrophy.