The post-reproductive ovary shifts from a reproductive to an immune-like organ.

Reproductive aging in females is characterized by the irreversible depletion of ovarian follicles, yet the structure and function of the post-reproductive ovary remain poorly defined. Using paired histological and bulk transcriptomic analyses of ovaries from reproductively young (2 m), reproductively old (18 m), and post-reproductive (24 m) mice, we mapped how ovarian identity evolves beyond follicle exhaustion. As expected, follicle loss, stromal remodeling, and increased collagen deposition were observed in the reproductively old and post-reproductive cohorts. Transcriptomic analyses revealed a shift from reproductive functionality to an immune-dominant signature with age. Correspondingly, post-reproductive ovaries exhibited increased infiltration of T cells, macrophages, and multinucleated giant cells. Although old and post-reproductive ovaries diverged substantially from young ovaries, they also showed discrete transcriptomic differences, indicating that the ovary continues to undergo molecular changes after reproductive senescence. Lastly, age-dependent changes in ovarian factors that are predicted to be secreted suggest that the post-reproductive ovary could be a source of pro-inflammatory signaling mediators with the potential to modulate extra-ovarian tissues. These findings challenge the assumption that the post-reproductive ovary is inert, instead indicating that it acquires an immune identity with potential endocrine and paracrine influence on whole-body aging.