BNIP3-mediated autophagy via the mTOR/ULK1 pathway induces primordial follicle loss after ovarian tissue transplantation

Purpose: To explore the underlying mechanism of primordial follicle loss in the early period following ovarian tissue transplantation (OTT).

Methods: BNIP3 was selected through bioinformatic protocols, as the hub gene related to Autophagy during OTT. BNIP3 and Autophagy in mice ovarian grafts and in hypoxia-mimicking KGN cells were detected using immunohistochemistry, transmission electron microscopy (TEM), western blotting, qPCR, and fluorescence staining. The regulatory role played by BNIP3 overexpression and the silencing of KGN cells in Autophagy via the mTOR/ULK1 pathway was investigated.

Results: Ultrastructure examination showed that autophagic vacuoles increased after mice ovarian auto-transplantation. The BNIP3 and autophagy-related proteins (Beclin-1, LC3B, and SQSTM1/p62) in mice ovarian granulosa cells of primordial follicle from ovarian grafts were altered compared with the control. Administration of an Autophagy Inhibitor in mice decreased the depletion of primordial follicles. In vitro experiments indicated that BNIP3 and Autophagy activity were upregulated in KGN cells treated with cobalt chloride (CoCl₂). The overexpression of BNIP3 activated Autophagy, whereas the silencing of BNIP3 suppressed it and reversed the Autophagy induced by CoCl₂ in KGN cells. Western blotting analysis showed the inhibition of mTOR and activation of ULK1 in KGN cells treated with CoCl₂ and in the overexpression of BNIP3, and the opposite results following BNIP3 silencing. The activation of mTOR reversed the Autophagy induced by BNIP3 overexpression.

Conclusions: BNIP3-induced Autophagy is crucial in primordial follicle loss during OTT procedure, and BNIP3 is a potential therapeutic target for primordial follicle loss after OTT.

Autophagy; BNIP3; Ovarian tissue transplantation; mTOR/ULK1 pathway.