Activation of dormant ovarian follicles to generate mature eggs

Abstract

Although multiple follicles are present in mammalian ovaries, most of them remain dormant for years or decades. During reproductive life, some follicles are activated for development. Genetically modified mouse models with oocyte-specific deletion of genes in the PTEN-PI3K-Akt-Foxo3 pathway exhibited premature activation of all dormant follicles. Using an inhibitor of the Phosphatase with TENsin homology deleted in chromosome 10 (PTEN) phosphatase and a PI3K activating peptide, we found that short-term treatment of neonatal mouse ovaries increased nuclear exclusion of Foxo3 in primordial oocytes. After transplantation under kidney capsules of ovariectomized hosts, treated follicles developed to the preovulatory stage with mature eggs displaying normal epigenetic changes of imprinted genes. After in vitro fertilization and embryo transfer, healthy progeny with proven fertility were delivered. Human ovarian cortical fragments from cancer patients were also treated with the PTEN inhibitor. After xeno-transplantation to immune-deficient mice for 6 months, primordial follicles developed to the preovulatory stage with oocytes capable of undergoing nuclear maturation. Major differences between male and female mammals are unlimited number of sperm and paucity of mature oocytes. Thus, short-term in vitro activation of dormant ovarian follicles after stimulation of the PI3K-Akt pathway allows the generation of a large supply of mature female germ cells for future treatment of infertile women with a diminishing ovarian reserve and for cancer patients with cryo-preserved ovaries. Generation of a large number of human oocytes also facilitates future derivation of embryonic stem cells for regenerative medicine.

Hippo signaling disruption and Akt stimulation of ovarian follicles for infertility treatment

“…Our earlier report demonstrated the ability of Akt stimulators to activate dormant primordial follicles (14). We now demonstrated additive increases in follicle growth when ovarian fragments containing secondary and smaller follicles were treated with Akt stimulators.…”

“…Similar to normal menstrual cycles, usually only one follicle emerged from the growing pool to reach the preovulatory stage. Although earlier data indicated that 6 mo are needed for the development of human primordial follicles to the preovulatory stage (14,19), all eight patients developed preovulatory follicles (∼2 cm) in less than 6 mo of grafting, with some of them (patients 1, 3, 5, and 7) developing preovulatory follicles within 3 wk, indicating rapid growth of secondary follicles. In contrast, preovulatory follicles developed after 6 mo of grafting were likely derived from primordial follicles.…”

“…In addition to the stimulatory role of Akt signaling in primordial follicle development (12,14), conditional deletion of the PTEN gene in granulosa cells of secondary follicles also promoted follicle growth (13). We isolated secondary follicles from juvenile mice and demonstrated the ability of Akt stimulating drugs (PTEN inhibitor and PI3K activator) to promote secondary follicle growth (Fig.…”

Alginate encapsulation supports the growth and differentiation of human primordial follicles within ovarian cortical tissue

“…For example, Akt pathway stimulation using pharmacological PTEN inhibitors has been shown to drive primordial follicle activation of human ovarian cortical tissue that was xenotransplanted into immunodeficient mice [77]. Moreover, a similar follicle activation protocol resulted in a human live birth in a patient with primary ovarian insufficiency [78].…”

Foxo3 negatively regulates the activation of mouse primordial oocytes

“…In mice, the oocyte-specific deletion of Pten (phosphatase and tensin homolog deleted on chromosome 10), which negatively regulates the action of PI3K, causes excessive activation of primordial follicles [19,20]. Li et al [21] treated human ovarian fragments and mouse ovaries with a PTEN inhibitor and transplanted them to SCID mice. After transplantation, increased numbers of antral follicles were obtained from inhibitor-treated groups than the control.…”