The ovulatory capacity and related genes are altered in transgenic mice hypersecreting human chorionic gonadotrophin hormone (hCG)
Laura Ratner1, Betina Gonzalez1, Matti Poutanen2, Ilpo Huhtaniemi3, Ricardo Calandra1 & Susana Rulli1
Hypersecretion of hCG in transgenic mice produces profound alterations in the ovary, thus triggering failures in ovulation and affecting fertility. The objective of this study was to analyze the response of immature female mice overexpressing moderated (hCGβ+; 0.1 IU/ml) and elevated (hCGαβ+; 7 IU/ml) levels of hCG to an ovulation induction protocol (PMSG 7.5 IU i.p.; after 48 h, hCG 7.5 IU i.p). Wild-type (WT) females subjected to the same protocol were used as controls. The ovulatory capacity was determined by the number of ovulated oocytes collected from the oviducts 18 h post-hCG: WT=21±3, hCGβ+=24±5; no oocytes were observed in the oviducts of hCGαβ+ females. The expression of genes involved in the ovulatory process, prostaglandin-endoperoxide synthase 2 (Ptgs2), progesterone receptor (Pgr), amphiregulin (Areg), epiregulin (Ereg), betacellulin (Btc) and estrogen sulfotransferase (Sult1e1) was determined by qRT-PCR. In WT and hCGβ+ females analyzed 4 h post-hCG showed a significant increase respect to the basal levels in all the genes studied (P< 0.05), whereas in hCGαβ+ females those changes were not observed. The cumulusoocyte complex (COC) expansion from WT and hCGαβ+ ovaries was studied in vivo by analyzing the histology 6 h post-hCG, and in vitro by incubating the COC with FSH for 20 h. An impairement of the COC expansion in hCGαβ+ females was observed both in vivo and in vitro, when compared with the correct expansion seen in WT mice. In conclusion, in hCGβ+ mice subjected to a protocol of ovulation induction, the ovulatory capacity was restablished and the induction of related genes were comparable with WT. In hCGαβ+ females, the mechanism of ovulation was significantly affected, indicating that elevated levels of hCG would be producing an alteration in the correct expression of factors involved in the intrafollicular signalling process, thus leading to anovulation.