Ovulation Involves the Luteinizing Hormone-Dependent Activation of Gq/11 in Granulosa Cells

Abstract

The LH receptor (LHR) activates several families of heterotrimeric G proteins, but only the activation of Gs and subsequent generation of cAMP are universally accepted as important mediators of LH actions. To examine the involvement of the Gq/11 family on the actions of LH, we crossed Cyp19Cre and Gαq(f/f);Gα11(-/-) mice to generate mice with a granulosa cell-specific deletion of Gαq in the context of a global deletion of Gα11. Granulosa cells from Gαq(f/f);Gα11(-/-);Cre(+) mice have barely detectable levels of Gαq/11, have a normal complement of LHR, and respond to LHR activation with a transient increase in cAMP accumulation, but they fail to respond with increased inositol phosphate accumulation, an index of the activation of Gαq/11. The LHR-provoked resumption of meiosis, cumulus expansion, and luteinization are normal. However, the Gαq(f/f);Gα11(-/-);Cre(+) mice display severe subfertility because many of the oocytes destined for ovulation become entrapped in preovulatory follicles or corpora lutea. Because follicular rupture is known to be dependent on the expression of the progesterone receptor (Pgr), we examined the LHR-induced expression of Pgr and 4 of its target genes (Adamts-1, Ctsl1, Edn2, and Prkg2). These actions of the LHR were impaired in the ovaries of the Gαq(f/f);Gα11(-/-);Cre(+) mice. We conclude that the defect in follicular rupture is secondary to the failure of the LHR to fully induce the expression of the Pgr. This is the first conclusive evidence for the physiological importance of the activation of Gq/11 by the LHR and for the involvement of Gαq/11 in ovulation.

Dephosphorylation and inactivation of NPR2 guanylyl cyclase in granulosa cells contributes to the LH-induced decrease in cGMP that causes resumption of meiosis in rat oocytes

“…Among the PPP family, our findings using cantharidin argue against an important function for PPP3 (PP2B or calcineurin). Because PPP3 is activated by Ca 2+ , this conclusion is consistent with the finding that deletion of Gα q/11 in mouse granulosa cells, and the resulting prevention of LH-induced inositol phosphate accumulation, does not inhibit meiotic progression in response to LH (Breen et al, 2013). Taken together with our gene expression analysis, PPP1, PPP2 and/or PPP6 emerge as the most likely candidates for mediating the LH-induced dephosphorylation of NPR2.…”

Steroid signaling in mature follicles is important for Drosophila ovulation

“…However, our recent work demonstrated the involvement of follicle rupture and matrix metalloproteinase in Drosophila ovulation, reminiscent to mammalian ovulation (1,9,12). In addition, it seems that adrenergic regulation of calcium signaling is also conserved in regulating ovulation in both Drosophila and mammals (12,44,45). The steroid hormone progesterone and progesterone receptor signaling in preovulatory follicles is essential for mammalian ovulation (6).…”

Multiple Pathways Mediate Luteinizing Hormone Regulation of cGMP Signaling in the Mouse Ovarian Follicle1

“…Gonadotropin binding to the LH receptor causes activation of stimulatory G protein and adenylyl cyclase followed by an increase in cAMP [14], as well as activation of Gq11, which leads to activation of phospholipase C and Ca 2þ release [31][32][33]. The accumulation of these intracellular messengers in turn activates numerous downstream protein kinases, including PKA, MAPK, p38, AKT, and PKC, directly or indirectly, leading to complex branching pathways and altered gene expression by GCs [17,[34][35][36][37].…”