Transport Time Does Not Substantially Alter RNA Expression in Human Ovarian Tissue After Standardized Slow-Freezing for Fertility Preservation

Background: Fertility preservation aims to maintain reproductive potential in patients undergoing potentially gonadotoxic treatments, increasingly relying on centralized cryobanks requiring ovarian tissue transport. Ovarian tissue cryopreservation is a widely implemented, evidence-based procedure for young women (age 18–35) with a regular ovarian reserve. The ovaries of patients are typically transported overnight to a centralized cryobank for freezing and storage, using a certified hypothermic organ preservation solution such as histidine-tryptophan-ketoglutarate (HTK) at 4–8 °C. The molecular effects of transport on ovarian tissue remain unclear. Methods: In this prospective study of 36 breast cancer patients, we compared whole-transcriptome RNA (RNA-seq) expression in 18 frozen–thawed ovarian biopsies after overnight hypothermic transport followed by slow-freezing versus 18 direct slow-freezing within ≤2 h under FertiPROTEKT-standard conditions. Results: The RNA-seq analysis identified 6 significantly upregulated genes (Bonferroni < 0.05, fold change > 1.5), including histone H2B and mitochondrial NADH dehydrogenase subunit 6 (MT-ND6). The small number of differentially expressed genes suggests only limited transcriptional changes between the two transport conditions. H2B upregulation was confirmed by qPCR, while MT-ND6 showed only moderate levels in RNA-seq but remained stable in qPCR. Immunohistochemical analysis confirmed protein presence and localization in formalin-fixed tissue from four samples, constituting, to our knowledge, the first report of MT-ND6 protein expression in human ovarian tissue. Conclusions: Overall, these results are consistent with subtle changes in chromatin organization and mitochondrial energy metabolism. Since RNA-seq revealed only modest differences in gene expression, with no appreciable up- or downregulation of apoptosis- or damage-related genes after ≤24 h, this indicates tissue stability under the studied combined conditions (transport + cryopreservation). These findings are consistent with the feasibility of the workflow under the studied conditions of centralized ovarian tissue cryobanking combined with overnight transportation and hypothermic HTK solution.