Implantation, Pregnancy and Parturition
(M568) EXPRESSION OF Akt ISOFORMS AND THEIR INVOLVEMENT IN RAT DECIDUAL CELL SURVIVAL.
Frechette-Frigon, Guylaine1, Caron, Pierre-Luc1, Asselin, Eric1, 1 Universite du Quebec a Trois-Rivieres, Trois-Rivieres, Quebec, Canada
ABSTRACT- Prior to rat embryo implantation, endometrial cells proliferate and differenciate by a process called decidualization. Reaching the end of pregnancy (from day 14 to 20) apoptosis is observed in decidual cells allowing the regression of the decidua basalis (DB). However, little is known about the intracellular and intramolecular mechanisms involved in apoptosis regulation in the uterus during pregnancy. To date, three isoforms of the survival Akt protein have been identified: Akt1, Akt2, Akt3. Akt isoforms are expressed and regulated differently in normal tissues but their specific roles remain to be clarified. The aim of the present study was to characterize the regulation and expression of the Akt survival pathway and to determine the effect of Akt inhibition in vitro. Rats were killed at different days of pregnancy (day 2-20) and uteri were removed to collect endometrial protein and RNA extracts. A strong increase of apoptosis in the DB at days 14, 16 and 18 was observed. Active form of Akt (phospho-Akt) was strongly expressed throughout pregnancy but was low at the time of embryo implantation and reduced during DB regression. Using cultured decidual stromal cells obtained from ovariectomized rats treated with 17-estradiol and progesterone to induce decidualization, PI-3K/Akt inhibitors LY294002 and Wortmannin blocked Akt phosphorylation and induced apoptosis in a dose-dependent manner. Preliminary studies have demonstrated that Akt1, Akt2 and Akt3 are present in the endometrium throughout rat pregnancy and are regulated differently. In cultured decidual cells, the three isoforms are also present but their expression is not influenced by PI-3K inhibition. X-linked inhibitor of apoptosis protein (XIAP), a well known inhibitor of caspase activity, was significantly reduced in the presence of PI-3K inhibitors. Whether Akt isoforms are specifically involved in cell survival at the time of DB regression is currently under investigation. These results demonstrate that the survival PI-3K/Akt might be an important signalling pathway by which apoptosis and cell survival are regulated in the rat endometrium during the critical period of pregnancy. Supported by NSERC (238501-01).
KEY WORDS: decidua, pregnancy, Akt, XIAP