Reversal of Ovarian Aging in Mice Through AAV-mediated Oocyte Reprogramming in vivo

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Project Summary Aging is a complex multifactorial biological process shared by all living organisms. In the ovary, it manifests as a gradual decline of normal reproductive function which culminates in menopause when the number of oocytes falls below a threshold. Menopause is preceded, from the mid-30s onward, by a dramatically increased incidence of oocyte dysfunction due to aging which results in meiotic segregation errors, aneuploidy and poor embryo development. This cellular dysfunction clinically presents as infertility, failure of assisted reproduction technologies (ART), (recurrent) pregnancy loss and birth defects. There are currently no effective treatments to improve oocyte function in women with advanced reproductive age and novel methodological strategies are critically needed. Many factors involved in the meiotic machinery in oocytes have been implicated in age- related oocyte dysfunction. However, the underlying cause of ovarian aging and why the female germline undergoes accelerated aging relative to somatic cells remains unknown. Time-dependent accumulation of cellular damage is widely considered to underlie aging and there is evidence that the rate of aging is controlled, at least to some extent, by genetic pathways conserved in evolution. Recent studies indicate that in somatic cells an erosion of the epigenetic landscape (epigenomic drift) resulting cellular dysfunction may be primarily responsible for aging. Interestingly, these studies show that ‘partial reprogramming’ through ectopic expression of a limited set of pluripotency factors can restore youthful epigenetic patterns and reverse signs of aging in somatic cells. However, the effect of partial reprogramming on the cell identity of meiotic cells, which exhibit unique gene regulatory networks and maintain features of pluripotency, is unknown. This proposal examines the global mechanism of ovarian aging, challenges its irreversibility and develops a novel pathway for the future development of treatments to slow or reverse ovarian aging. We will employ a transgenic mouse model to examine the hypothesis that partial reprogramming of the cumulus cell-oocyte complex can reverse ovarian aging and restore reproductive function. We will use integrative multi-omics to define the role of the methylation clock and epigenetic drift in ovarian aging and whether non-oocyte cells of the ovary contribute to oocyte dysfunction due to aging. We will investigate whether partial reprogramming can reverse age-related transcriptional and epigenetic changes in the oocyte-cumulus-complex to more youthful patterns and restore fertility in vivo without altering the cellular identity of oocytes. We will then examine the translational potential of this approach using a novel AAV delivery system with the ability to cross the blood- follicle barrier and target oocytes and granulosa cells in vivo. This work will increase our understanding of the biology of ovarian aging and provide novel molecular targets for the development of epigenetic drugs that reverse the decline in human reproductive ovarian function and reduce the miscarriages, recurrent pregnancy loss and birth defects associated with advanced reproductive age.