Increased sensitivity to retinal light damage in aquaporin-4 knockout mice

Previous studies have shown that Müller cells respond to excessive light with mislocalization of inwardly rectifying potassium channel (Kir4.1) and aquaporin-4 (AQP4) proteins. We investigated whether the retina is protected against light-induced damage in AQP4 knockout (KO) mice. KO and wildtype (WT) CD1 mice were exposed to 12h of intense white light (16 000+/-2000 lux) for six successive days. Electroretinograms (ERGs) were mildly affected in WT mice three days after light exposure, but returned to baseline on the seventh day following light exposure. In comparison, ERGs of KO mice were severely and irreversibly impaired after light exposure. Consistent with the ERG findings, light exposure had no effect on retinal structure in WT mice but reduced the thickness of both the outer and inner nuclear layers in KO mice. These findings indicate that loss of AQP4 renders the retina more susceptible to light-induced retinal degeneration.