Abstract: Objective To investigate the role of tacrolimus-binding protein 38 (FKBP38) in follicle development and the mechanism by which Fkbp38 gene deletion causes premature ovarian insufficiency (POI). Methods The Cre-loxp system was used to construct oocyte-specific Fkbp38 knockout transgenic mice. The genotype of the transgenic mice was identified using PCR, and the expression of FKBP38 in the oocytes was verified. The numbers of primordial follicles, primary follicles, secondary follicles and antral follicles in Fkbp38 knockout mice and non-transgenic littermate control mice were counted with HE staining under a microscope for analyzing the effect of Fkbp38 deletion on follicular development. The fertility and serum sex hormone levels of the mice were determined by reproduction experiments and ELISA to assess ovarian function. Ovarian granulosa cell apoptosis of the mice was assessed using TUNEL assay. The activity of the downstream target protein of phosphorylated ribosomal S6 (PS6) of mTOR signaling pathway was detected, and the expressions of BCL-2 and BAX proteins were determined using immunofluorescence assay for assessing oocyte development in the mice. Results The oocyte-specific Fkbp38 knockout transgenic mouse model was successfully constructed, which showed decreased fertility, disordered sex hormone levels, and significantly reduced primordial follicles, primary follicles and secondary follicles in the ovary (P<0.05), demonstrating POI-like changes. Compared with the control mice, oocyte- specific Fkbp38 knockout caused activation of the mTOR signaling pathway, significantly increased apoptosis of the granulosa cells, and obviously increased the BAX/BCL-2 ratio by increasing BAX expression and reducing BCL-2 expression in the oocytes (P<0.05). Conclusion FKBP38 plays an important role in follicle development, and Fkbp38 gene deletion in mice causes POI possibly by activating the mTOR signaling pathway and inducing granulosa cell apoptosis.

Key words: premature ovarian insufficiency; oocytes; Fkbp38; mTOR signaling pathway; apoptosis