Detection of the effects of circadian rhythm disruption due to chronic constant light on oocyte aging through MTOR signaling pathway

PER2 is one of the core circadian rhythm components and its expression has been demonstrated in ovarian cells. It has been also demonstrated that light exposure at night may cause attenuation in PER2 mRNA and protein levels. Circadian rhythm disruptions are thought to be associated with reproductive diseases. In female reproductive system, mTOR signaling pathway is thought to function in folliculogenesis and oocyte maturation in ovary. Also, it is associated with ovarian and oocyte aging. In a recent study, it has been demonstrated that there might be a relationship between PER2 and mTOR. We hypothesized that circadian rhythm disruption by constant light may alter PER2 protein levels in mouse ovary, and through possible relationship between PER2 and mTOR, circadian rhythm disruption by light may affect the ovarian morphology and function and may cause ovarian and oocyte aging. We aimed to show the effect of constant light on ovary and oocyte morphology. 6-8-week-old female Balb-c mice were used. We housed 12:12h L:L group in constant light and 12:12h L:D group in standard lightening conditions for one week. We performed food intake, body weight change analysis, open field test and vaginal smear. We evaluated ovarian morphology and follicle counting analysis of ovaries by hematoxylin&eosin staining and PAS staining. By immunofluorescence and immunohistochemistry, we evaluated oocyte aging markers. We also performed western blot for PER2, mTOR, p-mTOR and Caspase-3 protein levels. We demonstrated that circadian rhythm disruption caused alteration in their food intake and emotional behaviors and it caused decrease in primordial follicle numbers and increase in atretic follicles. It caused increase in oxidative stress and decrease in ZP3 expression in oocytes. We showed decreased protein levels of PER2, mTOR and p-mTOR. We demonstrated that circadian rhythm disruption by light may cause ovarian and oocyte aging-like consequences. Thus, circadian rhythm-based therapies may be useful for treatment of ovarian or oocyte-aging, at least to relieve their symptoms.