# Müller Glial Kir4.1 Channel Dysfunction in APOE4‐KI Model of Alzheimer's Disease

## TL;DR

This study shows that APOE4 causes retinal issues in Alzheimer's by impairing Müller cells and their potassium channels, and MitoQ may help reverse these effects.

## Contribution

The study reveals a novel link between APOE4, mitochondrial dysfunction in Müller cells, and Kir4.1 channel impairment in Alzheimer's disease.

## Key findings

- APOE4 reduces Kir4.1 expression and potassium buffering in Müller cells.
- APOE4 causes mitochondrial damage and increased ROS in Müller cells.
- MitoQ treatment restores mitochondrial health and Kir4.1 expression in APOE4-expressing cells.

## Abstract

Alzheimer's disease (AD), particularly late‐onset AD (LOAD), affects millions worldwide, with the apolipoprotein ε4 (APOE4) allele being a significant genetic risk factor. Retinal abnormalities are a hallmark of LOAD, and our recent study demonstrated significant age‐related retinal impairments in APOE4‐knock‐in (KI) mice, highlighting that retinal impairments occur before the onset of cognitive decline in these mice. Müller cells (MCs), key retinal glia, are vital for retinal health, and their dysfunction may contribute to retinal impairments seen in AD. MCs maintain potassium balance via specialized inwardly rectifying K+ channels 4.1 (Kir4.1). This study posits that Kir4.1 channels will be impaired in APOE4‐KI, resulting in MC dysfunction. Additionally, we demonstrate that MC dysfunction in APOE4‐KI stems from alterations in mitochondrial dynamics and oxidative stress. Kir4.1 expression and function were studied using immunofluorescence and through the whole‐cell voltage clamp, respectively. In parallel, rat Müller cells (rMC‐1) were used to create an in vitro model for further mechanistic studies. MitoQ was used to evaluate its potential to mitigate APOE4‐induced deficits. APOE4 retinas and APOE4‐transfected rMC‐1 significantly reduced Kir4.1 expression, K+ buffering capacity, and increased mitochondrial damage. APOE4‐transfected rMC‐1 showed reduced mitochondrial membrane potential (ΔΨm) and increased mitochondrial reactive oxygen species (ROS). MitoQ treatment significantly reduced mitochondrial ROS and restored Kir4.1 expression in APOE4‐expressing cells. Our results demonstrate that APOE4 causes mitochondrial dysfunction and MC impairment, which may contribute to retinal pathology in AD. MitoQ restored mitochondrial health and Kir4.1 expression in APOE4‐expressing rMC‐1, suggesting targeting mitochondria may offer a promising therapeutic strategy for AD.

APOE4 impairs Müller cell health by reducing Kir4.1 expression and buffering.
APOE4 causes mitochondrial dysfunction with decreased ΔΨm and increased ROS.MitoQ restores Kir4.1 expression and reduces ROS in APOE4‐transfected cells.

APOE4 impairs Müller cell health by reducing Kir4.1 expression and buffering.

APOE4 causes mitochondrial dysfunction with decreased ΔΨm and increased ROS.

MitoQ restores Kir4.1 expression and reduces ROS in APOE4‐transfected cells.