The Therapeutic Potential of Immature Oocytes from Fertility Preservation Procedures and their In-vitro Maturation at Different Ages

Pe'era Wasserzug Pash 2 Gilad Karavani 1 Eli Reich 2 Lital Zecharyahu 2 Talya Mordechai-Daniel 1,3 Tal Imbar 1,3 Michael Klutstein 2
1Department of Obstetrics and Gynecology,, Hadassah-Hebrew University Medical Center, Israel
2Institute of Dental Sciences, Faculty of Dental Medicine, The Hebrew University of Jerusalem, Israel
3Fertility Preservation Service, Hadassah-Hebrew University Medical Center, Israel

Objective:
Cryopreservation of ovarian cortical tissue (OTC) followed by auto-transplantation has emerged as a promising fertility preservation option . Immature oocyte can be found in the dissection medium and the ability to mature them in vitro and cryopreserve them, provides an additional option for fertility preservation. In this work we aim to evaluate the developmental potential and epigenetic function of these premature oocytes, in different age groups.


Results:
In both human and mouse, we saw a gradual increase in maturation rates with onset of puberty. Staining for heterochromatin markers showed that epigenetic alterations accompany this trend. Oocytes from pre-pubertal females presented lower rates of staining in both models. Oocytes from pre-pubertal females were then treated with FSH to resemble maturation. FSH treatment increased heterochromatin levels and maturation rates. Further experiments showed that pre-pubertal oocytes have higher rates of RNA processing. We hypothesize that this protects pre-pubertal oocytes from retrotransposon activation.

Discussion:
The ability to mature oocytes retrieved during OTC depends upon the patient`s age. Maturation potential is tightly correlated to heterochromatin state. Further experiments will test the effect of epigenetic modifying drugs, as an effective therapy enhancing in-vitro maturation of pre-pubertal oocytes.

Impact Statement:
Fertility preservation options in young pre-pubertal girls undergoing gonadotoxic treatments are limited to ovary cryopreservation, due to the low maturation ability of pre-pubertal oocytes. Here we examined and analyzed the quality and functionality of oocytes retrieved from this age group, in order to expand the range of treatments and increase success rates in pre-pubertal patients.