Female reproductive function changes during aging with the estrous cycle becoming more irregular during the transition to menopause. We found that intermittent shifts of the light-dark cycle disrupted regularity of estrous cycles in middle-aged female mice, whose estrous cycles were regular under unperturbed 24-hr light-dark cycles. Although female mice deficient in Cry1 or Cry2, the core components of the molecular circadian clock, exhibited regular estrous cycles during youth, they showed accelerated senescence characterized by irregular and unstable estrous cycles and resultant infertility in middle age. Notably, tuning the period length of the environmental light-dark cycles closely to the endogenous one inherent in the Cry-deficient females restored the regularity of the estrous cycles and, consequently, improved fertility in middle age. These results suggest that reproductive potential can be strongly influenced by age-related changes in the circadian system and normal reproductive functioning can be rescued by the manipulation of environmental timing signals. Takasu et al. show that weekly perturbation of the light-dark cycle disrupts estrous cycles in middle-aged female mice, and early infertility evident in female mice deficient in core circadian clock genes is improved by coordinating environmental and endogenous circadian rhythms. These findings suggest that an age-related decline in fertility may be rescued by control of environmental timing signals.
Takasu, N. N., Nakamura, T. J., Tokuda, I. T., Todo, T., Block, G. D., & Nakamura, W. (2015). Recovery from Age-Related Infertility under Environmental Light-Dark Cycles Adjusted to the Intrinsic Circadian Period. Cell Reports, 12(9), 1407–1413. https://doi.org/10.1016/j.celrep.2015.07.049