Expression of peroxisome proliferator-activated receptor isoforms in the rat uterus during early pregnancy

Peroxisome proliferator-activated receptors (PPARs) play an important role in different compartments of the female reproductive system in rodents and humans. However, expressional profiles and physiological functions of PPARs in the endometrium prior to the placentation are not well understood. In this study, we determined expressional profiles of the PPARs during early pregnancy. Immunocytochemistry revealed that both PPAR alpha and PPAR beta/delta were strongly detected in the endometrial stroma on days 4.5-6.5 of pregnancy, which is just a starting time of implantation. Delayed implantation animal model showed that the expressions of PPAR alpha and PPAR beta/delta occurred after the initiation of implantation in the endometrial stroma. Moreover, an in vitro decidualization model further revealed that the expression of PPAR alpha increased in the cultured rat endometrial stromal cells at 24 h after the decidualization treatment, but the expression of PPAR beta/delta was delayed and increased at 48 h after the treatment. PPAR gamma was expressed in the endometrial stroma and its expression decreased significantly at 2.5 days post-coitum and maintained a low level of expression during the period of implantation. These results indicate that PPAR alpha is expressed and induced by the initiation of implantation, prior to the expression of PPAR beta/delta in decidualized endometrium. Increasing expression of PPAR gamma during fertilization and its decline during the period of implantation further suggest that PPARs may play important roles during early pregnancy.