Analysis of 17β-estradiol (E(2)) role in the regulation of corpus luteum function in pregnant rats: Involvement of IGFBP5 in the E(2)-mediated actions

BACKGROUND: In several species, considerably higher levels of estradiol-17 (E(2)) are synthesized in the CL. E(2) has been suggested to participate in the regulation of luteal steroidogenesis and luteal cell morphology. In pregnant rats, several experiments have been carried out to examine the effects of inhibition of luteal E(2) synthesis on CL structure and function. METHODS: During days 12–15 of pregnancy in rats, luteal E(2) was inhibited by way of daily oral administration of anastrozole (AI), a selective non-steroidal aromatase inhibitor, and experiments were also performed with E(2) replacement i.e. AI+ E(2) treatments. Luteal tissues from different treatment groups were subjected to microarray analysis and the differentially expressed genes in E(2) treated group were further examined for expression of specific E(2) responsive genes. Additional experiments were carried out employing recombinant growth hormone preparation and flutamide, an androgen receptor antagonist, to further address the specificity of E(2) effects on the luteal tissue. RESULTS: Microarray analysis of CL collected on day 16 of pregnancy post AI and AI+E(2) treatments showed significantly lowered cyp19a1 expression, E(2) levels and differential expression of a number of genes, and several of them were reversed in E(2) replacement studies. From the differentially expressed genes, a number of E(2) responsive genes were identified. In CL of AI pregnant rats, non-significant increase in expression of igf1, significant increase in igbp5, igf1r and decrease in expression of Erα were observed. In liver of AI treated rats, igf1 expression did not increase, but GH treatment significantly increased expression that was further increased with AI treatment. In CL of GH and AI+GH treated rats, expression of igfbp5 was higher. Administration of flutamide during days 12–15 of pregnancy resulted in non-significant increase in igfbp5 expression, however, combination of flutamide+AI treatments caused increased protein expression. Expression of few of the molecules in PI3K/Akt kinase pathway in different treatments was determined. CONCLUSIONS: The results suggest a role for E(2) in the regulation of luteal steroidogenesis, morphology and proliferation. igfbp5 was identified as one the E(2) responsive genes with important role in the mediation of E(2) actions such as E(2)-induced phosphorylation of PI3K/Akt kinase pathway. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12958-016-0153-1) contains supplementary material, which is available to authorized users.