Role of the PI3K and Hippo pathways in follicle activation after grafting of human ovarian tissue

Abstract

Purpose Our aim was to elucidate the mechanisms involved in follicle activation of the ovarian reserve after human ovarian tissue transplantation, with specific focus on the role of the effectors of the PI3K (mTOR and FOXO1) and Hippo (YAP) signaling pathways and whether they are somehow altered. Methods Frozen-thawed ovarian tissue was collected from six women (age 25-35 years) undergoing surgery for non-ovarian pathologies and divided into 4 fragments in each case: one for non-grafted controls and three for grafting to immunodeficient mice for 3, 7 and 21 days. The tissue was processed for hematoxylin and eosin staining, immunohistochemistry and immunofluorescence at different timepoints before and after grafting. Activation of the PI3K and Hippo signaling pathways was investigated by analysis of mTOR phosphorylation, FOXO1 cytoplasmic localization and YAP nuclear localization. Results No change in mTOR levels was observed in primordial follicles post-transplantation, but a significant upturn was recorded in growing follicles compared with primordial follicles, irrespective of grafting time. A higher percentage of primordial follicles was also found with FOXO1 in the cytoplasm after 3 days of transplantation than in non-grafted controls. Finally, a greater proportion of primordial follicles was detected with YAP in the nucleus at all timepoints after grafting. Conclusions This study supports the hypothesis that follicle activation may occur as an early event after transplantation, with follicle growth and death both contributing to the burnout phenomenon. This is the first time that the effectors of the PI3K and Hippo pathways have been investigated in grafted human ovarian tissue and their role in burnout documented.

In-vitro fragmentation of ovarian tissue activates primordial follicles through the Hippo pathway

“…This could indicate a rather limited role for the PI3K-Akt pathway in follicle development during tissue culture. Another hypothesis is the possible later involvement of the PI3K-Akt pathway in follicle development during tissue culture ( Masciangelo et al , 2020 ). This descriptive analysis is a valuable start for research.…”

Long-Term Advantages of Ovarian Reserve Maintenance and Follicle Development Using Adipose Tissue-Derived Stem Cells in Ovarian Tissue Transplantation

“…It is, therefore, vital to preserving the ovarian reserve at each clinical step, from surgical ovarian tissue retrieval to grafting of ovarian fragments. According to previous studies, two main events are responsible for the loss of around 50–90% of follicles after transplantation [ 15 , 34 ], namely follicle death due to hypoxia/ischemia [ 6 ] and massive follicle activation [ 11 , 35 ]. Indeed, not only do we witness a significant decrease in follicle density after human OTT due to hypoxia but also large-scale primordial follicle activation, with an increase in growing follicles as early as 3 days after grafting through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway [ 11 , 35 ].…”

In vitro Activation Prior to Transplantation of Human Ovarian Tissue: Is It Truly Effective?

“…We feel that ongoing research should aim to prevent follicle activation, possibly by exposing ovarian tissue to media containing factors that inhibit activation prior to grafting [a role for anti-Müllerian hormone? (44, 45)], or by manipulating the Akt-FoxO and mTOR pathways (46, 47). In any case, there is still work to be done before any firm conclusions can be drawn on the value of this IVA approach.…”