Cellular senescence and epigenomic remodeling in ovarian aging

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PROJECT SUMMARY/ABSTRACT Declines in ovarian function are closely associated with reductions in healthspan and longevity. Numerous studies have linked ovarian dysfunction to systemic organismal aging, although very little is known with regard to the basic, intrinsic mechanisms that initiate and perpetuate age-related ovarian functional declines. These knowledge gaps represent a critical barrier to developing treatments aimed at attenuating age-related ovarian failure. Ovarian aging is characterized by the progressive depletion of quiescent primordial follicles, which eventually leads to irregular patterns of ovulation and disruption of the ovarian endocrine milieu. This project will systemically explore how cell-type specific changes in cellular senescence and epigenetics/genomic organization contribute to age-related ovarian failure through the use of novel transgenic NuTRAP models that allow for the isolation of nucleic acids (DNA & RNA) specifically from oocytes, granulosa cells, or theca cells without the need for cell sorting. Successful completion of this project will determine: 1) what role cellular senescence and epigenetic modifications play in primordial follicle exhaustion, 2) if age-related cellular senescence and epigenetic modifications occur in a cell-type specific fashion along differing timelines, 3) if epigenetic changes precede or follow the emergence of cellular senescence, and 4) if the removal of senescent cells and/or the suppression of the SASP through senolytic drug treatment can extend reproductive lifespan. We hypothesize that granulosa cells encapsulating primordial follicles accumulate deleterious cellular and epigenetic alterations, undergo a senescence-like transition, and thereby accelerate primordial follicle growth and maturation, thereby leading to exhaustion. We will test this hypothesis through following aims. Specific Aim 1: Characterize cell type-specific changes in markers of cellular senescence in oocytes, granulosa, and theca cells from the aging ovary. We predict that senescence cell burden and inflammatory mediators will increase with advancing age and that granulosa cells are a major source of this phenotype. Specific Aim 2: Characterize cell type-specific changes in epigenetic alterations and transcriptional profiles within oocytes, granulosa, and theca cells from the aging ovary. We predict that the majority of age-related changes will be cell-specific and that `epigenetic clocks' of distinct cell types advance at different rates. We also anticipate that granulosa cells will display the greatest changes in epigenetic and transcriptional profiles and that this will correspond to declines in ovarian primordial follicle reserve. Aim 3: Determine if the clearance of senescent cells within the ovary restores ovarian function and prolongs reproductive fitness. We predict that senolytic treatment will increase the number of primordial follicles and that oocytes will accumulate less DNA damage with chronological aging. We also anticipate that this will result in a greater production of embryos with less DNA damage, thereby increasing the number of pregnancies, litters, and pups born to older female mice. The ultimate goal of this research is to develop clinical interventions that extend reproductive lifespan for systemic health benefits.