Role of the PI3K and Hippo pathways in follicle activation after grafting of human ovarian tissue
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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.
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.
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.
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.
KeywordsFollicle activation Ovarian tissue transplantation Burnout effect PI3K pathway Hippo pathway
The authors thank Mira Hryniuk, B.A., for reviewing the English language of the article, and Dolores Gonzalez and Olivier Van Kerk for their technical assistance.
Author contribution statement
R.M.: conception and design of the study, experimental procedures, analysis of results, statistical analysis and article preparation; C.H.: experimental procedures; M.C.C.: analysis of results and discussion contribution; D.D.M.: experimental procedures, analysis of results and discussion contribution; C.A.A.: discussion contribution; J.D.: data evaluation, discussion contribution and article revision; M.M.D.: conception of the study, data evaluation, discussion contribution and article revision.
This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS-PDR Convention T.0077.14, Télévie grant 7.4590.16 awarded to Rossella Masciangelo, EOS grant 30443682 to Maria Costanza Chiti, Télévie grant no. 7.6515.16 F to Diego Daniel Manavella and 5/4/150/5 grant to Marie-Madeleine Dolmans; CAA is an FSR-FNRS research associate), the Fonds Speciaux de Recherche, and the Foundation Against Cancer.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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