Targeted Disruption of Pten in Ovarian Granulosa Cells Enhances Ovulation and Extends the Life Span of Luteal Cells

Abstract

FSH activates the phosphatidylinositol-3 kinase (PI3K)/acute transforming retrovirus thymoma protein kinase pathway and thereby enhances granulosa cell differentiation in culture. To identify the physiological role of the PI3K pathway in vivo we disrupted the PI3K suppressor, Pten, in developing ovarian follicles. To selectively disrupt Pten expression in granulosa cells, Ptenfl/fl mice were mated with transgenic mice expressing cAMP response element recombinase driven by Cyp19 promoter (Cyp19-Cre). The resultant Pten mutant mice were fertile, ovulated more oocytes, and produced moderately more pups than control mice. These physiological differences in the Pten mutant mice were associated with hyperactivation of the PI3K/acute transforming retrovirus thymoma protein kinase pathway, decreased susceptibility to apoptosis, and increased proliferation of mutant granulosa cells. Strikingly, corpora lutea of the Pten mutant mice persisted longer than those of control mice. Although the follicular and luteal cell steroidogenesis in Ptenfl/fl;Cyp19-Cre mice was similar to controls, viable nonsteroidogenic luteal cells escaped structural luteolysis. These findings provide the novel evidence that Pten impacts the survival/life span of granulosa/luteal cells and that its loss not only results in the facilitated ovulation but also in the persistence of nonsteroidogenic luteal structures in the adult mouse ovary.

Activation of dormant ovarian follicles to generate mature eggs

“…No malignancy was found in mouse or human ovarian grafts or hosts during prolonged transplantation, indicating the present shortterm exposure to the PTEN inhibitor had minimal adverse effects despite the known function of PTEN as a tumor suppressor gene (29). These findings are consistent with a lack of tumorigenesis in mutant mice with PTEN deletion in oocyte or granulosa cells (3,30).…”

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

“…Conditional deletion of the PTEN gene in granulosa cells of secondary follicles in mice promoted follicle growth (13). We demonstrated additive increases in ovarian graft weights and follicle growth following Hippo signaling disruption (fragmentation) and Akt stimulation (treatment with PTEN inhibitors and PI3K activators).…”

“…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.…”

“…Studies using phosphatase and tensin homolog deleted from chromosome 10 (PTEN) deletion mice indicated the stimulatory roles of Akt signaling in the development of primordial (12) and secondary follicles (13). Our earlier report demonstrated the ability of Akt stimulators to activate dormant primordial follicles (14).…”

Cell-secreted vesicles containing microRNAs as regulators of gamete maturation

“…Based on results by Schauer and coworkers, these miRNAs are altered by LH induction in follicular fluid as well as in granulosa cells and are involved in cell survival and final differentiation. Predicted targets include PTEN and BMPR2 (miR-21; Qin et al 2009, Schauer et al 2013, involved in regulating granulosa cell proliferation (Fan et al 2008) and maturation of the cumulus-oocyte-complex (Assou et al 2006) and TJP1 (miR-212; Tang et al 2008) involved in cell-cell interactions and regulation of tight junctions in ovarian surface epithelial cells (Zhu et al 2004).…”