126 EXPRESSION OF THE RECEPTOR FOR ADVANCED GLYCATION END PRODUCTS IN BOVINE OOCYTES AND EMBRYOS CULTURED IN LOW AND HIGH OXYGEN

Abstract

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily that binds a broad repertoire of advanced glycation end products ligands. It is constitutively expressed at a high level during embryonic development, but its levels decrease in adult tissues. The RAGE-ligand interaction induces a series of signal transduction cascades and leads to the activation of several inflammatory signalling pathways. This is why RAGE is frequently associated with pro-inflammatory responses and it is implicated as an underlying condition in immune disorders, cardiovascular diseases, diabetes, Alzheimer’s disease, and cancer. However, the physiological function of RAGE during embryogenesis and in aging is largely undefined. The aim of this work was to determine the basal levels on RAGE expression in bovine oocytes (germinal vesicle, GV, and in vitro-matured metaphase II) and in vitro-derived embryos developed in SOF medium, by qPCR (3 replicates each containing pooled RNA from 20 oocytes or embryos, t-test P < 0.05) and immunostaining. The expression of RAGE was similar in bovine oocytes, in cleaving embryos up to morula, and afterward declined at the blastocyst stage. However, a more detailed investigation, by the separation of the inner cell mass (ICM) from the trophoblast, indicated that expression decreased only in the trophoblast (over 5-fold) while it was maintained high in the isolated ICM. In the trophoblast, compared to the ICM, this finding coincided with an elevated expression of PSMA6 gene, which encodes for the 20S proteasome subunit, and ubiquitin (UBB) gene, suggesting a link between proteasome activity and RAGE expression. Then we investigated the expression of RAGE and the proteasome-ubiquitin system in embryos cultured under different oxygen concentrations [i.e. physiological (5%) or high (20%) O2 levels]. Preliminary results showed that RAGE expression was lower in embryos cultured in 20% O2 and conversely the expression of PSMA6 and UBB genes was higher. Thus, these results indicate that the activity of RAGE-mediated stress response pathway in pre-implantation bovine embryos is affected by O2 tension during in vitro culture. This work was funded by projects Epihealth FP7 n. 278418, EpiHealthNet FP7-PEOPLE-2012-ITN n. 317146, and Fecund FP7 n. 312097.