Abstract
Purpose :
To determine whether the lens acts as a circadian clock that controls the rhythmic expression of genes involved in redox regulation
Methods :
Freshly dissected Wistar rat lenses (p21) were screened for the main orchestrators involved in the rhythmic expression of clock-controlled genes, BMAL1 and CLOCK by western blotting and immunohistochemistry. Rat lenses were cultured in isosmotic artifical aqueous humor under constant darkness and then fixed at 6-hr intervals over a 24-hr period. Lenses were cryosectioned in an equatorial plane and then labelled with antibodies against glutamate-cysteine ligase (GCL), the rate limiting enzyme involved in the synthesis of the antioxidant glutathione (GSH).
Results :
Western blotting revealed that BMAL1 and CLOCK are expressed in the rat lens and that BMAL1 was localised to the nucleated epithelium and cortical fibre cells, but not the anucleate mature fibre cells. As proof of concept that cyclic redox rhythms occur in the lens, changes in GCL expression were evident, with highest levels of GCL present during the day (0 and 24-hrs), and lower levels during the night (12-hrs), supporting the idea that the lens utilises circadian time keeping mechanisms to regulate GSH homeostasis.
Conclusions :
Collectively, these findings reveal that the lens contains some of the core molecular components of the circadian clock, and that oscillations in the expression of an enzyme required for GSH synthesis occurs during the day/night cycle. This implies that the lens may act as a circadian clock that controls the rhythmic expression of genes involved in GSH homeostasis to provide protection against UV insults. Since circadian rhythms are altered with advancing age, disruption of the circadian regulation of redox balance may be an initiating factor in age related lens cataract.
This is a 2020 ARVO Annual Meeting abstract.