{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,31]],"date-time":"2026-08-31T05:22:52Z","timestamp":1788153772024,"version":"build-2803163510"},"reference-count":42,"publisher":"The Korean Society for Reproductive Medicine","issue":"3","license":[{"start":{"date-parts":[[2025,12,24]],"date-time":"2025-12-24T00:00:00Z","timestamp":1766534400000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["24K12551"],"award-info":[{"award-number":["24K12551"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["ecerm.org"],"crossmark-restriction":true},"short-container-title":["Clin Exp Reprod Med"],"published-print":{"date-parts":[[2026,9,1]]},"abstract":"<jats:p>Objective: Ovarian tissue cryopreservation is an essential fertility preservation technique. Two primary methods are used for ovarian tissue cryopreservation: slow freezing and vitrification. Recently, vitrification has been favored over slow freezing, and a closed system is recommended to prevent cross-contamination in liquid nitrogen. Follicular loss during freezing and thawing remains a major challenge. We investigated whether rapamycin, an inhibitor of the mechanistic target of rapamycin (mTOR) pathway, could mitigate primordial follicle loss during closed-system vitrification and thawing of mouse ovarian tissue.Methods: Mouse ovaries were vitrified and thawed with or without 750 nanomolar rapamycin, then immediately analyzed or cultured for 5 days. Activation of the mTOR pathway was assessed using phosphorylated S6 kinase immunostaining, and follicle survival and development were evaluated by histological analysis.Results: Closed-system vitrification did not induce apoptosis in primordial follicles. The median phosphorylated S6K-positive rate in primordial follicles was 7.1% in fresh controls, 87.9% in the rapamycin-free group, and 19.0% in the rapamycin-treated group (fresh-control vs. rapamycin-free and rapamycin-free vs. rapamycin-treated, both p&lt;0.001). Rapamycin treatment suppressed this activation, resulting in significantly higher primordial follicle counts after culture (605 vs. 289 follicles per ovary, p&lt;0.05) and a lower ratio of primary to primordial follicles, indicating reduced follicle activation.Conclusion: These findings demonstrate that rapamycin preserves the primordial follicle pool by preventing follicle activation during cryopreservation and thawing. Incorporating rapamycin into closed-system vitrification protocols may improve ovarian tissue cryopreservation outcomes and enhance fertility preservation for patients with cancer.<\/jats:p>","DOI":"10.5653\/cerm.2025.08165","type":"journal-article","created":{"date-parts":[[2025,12,24]],"date-time":"2025-12-24T05:08:22Z","timestamp":1766552902000},"page":"248-257","update-policy":"https:\/\/doi.org\/10.5653\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Rapamycin preserves primordial follicles during closed\u2011system vitrification of mouse ovarian 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