Prolonged Light Exposure Induces Circadian Impairment in Aquaporin-4-Knockout Mice.

Astrocytes are densely present in the suprachiasmatic nucleus (SCN), which is the master circadian oscillator in mammals, and are presumed to play a key role in circadian oscillation. However, specific astrocytic molecules that regulate the circadian clock are not yet well understood. In our study, we found that the water channel aquaporin-4 (AQP4) was abundantly expressed in SCN astrocytes, and we further examined its circadian role using AQP4-knockout mice. There was no prominent difference in circadian behavioral rhythms between and mice subjected to light-dark cycles and constant dark conditions. However, exposure to constant light induced a greater decrease in the mice rhythmicity. Although the damped rhythm in long-term constant light recovered after transfer to constant dark conditions in both genotypes, the period until the reappearance of original rhythmicity was severely prolonged in mice. In conclusion, AQP4 absence exacerbates the prolonged light-induced impairment of circadian oscillations and delays their recovery to normal rhythmicity.