Expression of Akt Isoforms in the Rat Endometrium During Pregnancy and Pseudopregnancy.

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Rat gestation can be divided into various parts that would include fertilization, implantation, decidualization, decidual regression and parturition. However, little is known about the intracellular and molecular mechanisms involved in the endometrium regulating these different steps of pregnancy. Akt isoforms (Akt1, Akt2 and Akt3) are expressed and differentially regulated in normal tissues but their specific roles remain to be clarified in the endometrium. Our hypothesis is that the Akt signaling pathway and the three Akt isoforms are playing important and different roles in the rat endometrium during pregnancy. This pathway is critically involved in cell proliferation and survival but its regulation during pregnancy remains to be elucidated. It has been shown that X-linked Inhibitor of Apoptosis Protein (XIAP) might be involved in cell survival through regulation of Akt phosphorylation in different systems. XIAP is inhibited by second mitochondria-derived activator of caspase/Direct IAP Binding Protein with Low pI (Smac/DIABLO). Transcription factor NF-kappaB plays a pivotal role in inflammatory and immune responses. It can activate the transcription of many genes involved in the pregnancy process and is also known to be activated by Akt. Objective of the present study was to investigate the regulation of Akt pathway in the rat endometrium during pregnancy. Pseudopregnant rats were killed, from day 1 to 9, and during normal pregnancy, every two days from day 1 to 22. Uteri were removed to collect endometrial RNA, protein and tissues sections were prepared for immunochemistry. In the early stages of pregnancy, an increase of pAkt (active form) at day 5 was observed and only Akt3 was the active isoform. An increase of pAkt at day 3 was observed in pseudopregnant rats. It was possible to observe a translocation of NF-kappaB to the nuclus in pregnant but not in pseudopregnant rats. The difference observed between pregnancy and pseudopregnancy suggests that the presence of an embryo has an impact on the regulation of the Akt pathway. During the late state of pregnancy, we found that the active form of Akt was reduced during decidual regression and was increased at day 1 post-partum and that Akt3 was the active isoform. XIAP expression showed a peak on day 14 and then decreased thereafter. Smac/Diablo also showed a peak of expression at day 14. In vivo, PI3-K inhibitor wortmannin blocked Akt phosphorylation and reduced XIAP expression in the endometrium. In vitro, PI3-K inhibition decrease both pAkt and XIAP expression in decidual cells. These results suggest that Akt3 may be an important signalling protein in the rat endometrium to control cell survival.