Ovarian Fragmentation and AKT Stimulation for Expansion of Fertile Lifespan

Abstract

Since the first baby was born after in vitro fertilization, the female infertility treatment has been well-developed, yielding successful outcomes. However, successful pregnancies for patients with premature ovarian insufficiency and diminished ovarian reserve are still difficult and diverse therapies have been suggested to improve the chances to have their genetically linked offspring. Recent studies demonstrated that the activation Akt pathway by using a phosphatase and tensin homolog enzyme inhibitor and a phosphatidylinositol-3 kinase stimulator can activate dormant primordial follicles in both mice and human ovaries. Subsequent researches suggested that the disruption of Hippo signaling pathway by ovarian fragmentation increased the expression of downstream growth factors and secondary follicle growth. Based on the combination of ovarian fragmentation and Akt stimulation, the in vitro activation (IVA) approach has resulted in successful follicle growth and live births in premature ovarian insufficiency patients. The approach with disruption of Hippo signaling only was also shown to be effective for treating poor ovarian responders with diminishing ovarian reserve, including advanced age women and cancer patients undergoing sterilizing treatments. This review aims to summarize the effectiveness of ovarian fragmentation and Akt stimulation on follicle growth and the potential of IVA in extending female fertile lifespan.

Keywords: Akt stimulation; diminished ovarian reserve; in vitro activation; ovarian fragmentation; premature ovarian insufficiency.

Figure 1

The PI3K/AKT/FOXO3 pathway in oocytes regulates primordial follicle activation. Mouse models were used to investigate the regulation of primordial follicle dormancy. The FOXO3 gene in primordial oocytes serves as a break to prevent the initiation of follicle growth. Activation of upstream RTKs by their cognate ligands (kit ligand, IGF-1, EGF, platelet-derived growth factor [PDGF], VEGF, etc) stimulates the autophosphorylation of intracellular regions of these receptors. Activated receptors then stimulate PI3K activity, leading to increases in PIP3 levels and AKT stimulation. Activated AKT then migrates to the cell nucleus and suppresses FOXO3 actions to promote primordial follicle growth.

Figure 2

Mechanical force disrupts ovarian Hippo signaling pathway and promotes follicle growth. Mechanical signals incurred by ovarian fragmentation, incision, drilling, or wedge resection lead to actin polymerization that disrupted ovarian Hippo signaling, resulting in nuclear translocation of Yes-associated protein (YAP). Nuclear YAP interacted with transcriptional enhanced associate domain (TEAD) transcriptional factors to increase the expression of downstream biochemical signals (cystein-rich 61, connective tissue growth factor, and nephroblastoma overexpressed [CCN] growth factors and BIRC apoptosis inhibitors), resulting in follicle growth. Ovarian damage–induced follicle growth started with mechanical stimulation but ended with local biochemical changes to promote follicle growth.

Figure 3

Ovarian fragmentation/AKT stimulation followed by autografting promotes follicle growth in POI patients to generate mature oocytes for IVF embryo transfer, pregnancy, and delivery. Under laparoscopic surgery, one or both ovaries from POI patients were removed and cut into strips before vitrification. After thawing, strips were fragmented into 1–2 mm² mm cubes, before incubation with AKT stimulators (a PTEN inhibitors and a PI3K stimulator). Two days later, cubes were autografted under laparoscopic surgery beneath the serosa of Fallopian tubes. Follicle growth was monitored weekly or biweekly via transvaginal ultrasound and based on serum estrogen levels. After detection of antral follicles, patients were treated with FSH followed by human chorionic gonadotropin when preovulatory follicles were found. Mature oocytes were then retrieved and fertilized with husbands' sperm in vitro before cyropreservation of 4-cell-stage embryos. Patients then received hormonal treatments to prepare the endometrium for implantation followed by transferring of thawed embryos.