Ovulation has been likened to an inflammatory response since LH/hCG induces in preovulatory follicles genes such as prostaglandin synthase 2 (Ptgs2). However, our recent gene profiling experiments on cumulus celloocyte complexes (COCs) isolated from ovulatory follicles in vivo show that the repertoire of genes induced far exceeds that anticipated. Moreover, some are uniquely expressed in COCs compared to granulosa cells. Members of the EGF-like superfamily, amphiregulin (Areg), betacellulin (Btc) and epiregulin (Ereg) are among those induced most rapidly in COCs. Because both COC expansion and Areg expression are reduced by inhibition of p38MAPK (MAPK14) we hypothesize that p38MAPK mediates gonadotropin-induced expression of the Areg gene. AREG, in turn, activates ERK1/2 (MAPK3/1) to induce the expression of Ptgs2 and other genes in cultured COCs. Some of the genes induced in COCs by LH/hCG in vivo and by AREG in culture encode factors previously thought to be specific for immune cell-related surveillance functions; the pathogen recognition receptors (PPRs) that sense the environment and detect ?self from non-self or altered self?. COCs express the Toll-like receptors, a related cofactor Cd14, and the complement associated molecule C1q. Cd14, C1q and programmed cell death 1 (Pdcd1) are selectively expressed in ovulated COCs (compared to granulosa cells). These same genes are induced by either FSH, PGE or AREG in cultured COCs, but not granulosa cells. Although the specific physiological functions of TLRs receptors in ovarian cells are not yet known, we do know that the bacterial ligand LPS as well as fragments of hyaluronan can activate these receptors and induce the downstream target gene Il6. Preliminary data in Cd14 null mice also document that this pathway is functional in cumulus cells. Thus, we propose that the immune-like factors regulate cumulus cell fate and apoptosis and thereby impact oocyte quality. Based on these considerations we propose the following specific aims.
Specific Aim I : Determine the molecular mechanisms by which gonadotropins transactivate the Areg gene and by which AREG activates downstream signaling cascades and specific genes.
Specific Aim II : Determine the function of AREG target genes that are uniquely expressed at high levels in ovulated COCs (compared to granulosa cells) and that impact ovulation.
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