PARENT SESSION
TRAINEE RESEARCH COMPETITION
Haborside Foyer
7:30 AM-10:00 AM

(63) THE ROLE OF PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR (PPAR) IN THE PROCESS OF IMPLANTATION IN THE MINK (Mustela vison).

Desmarais, Joelle¹, Bennett, Richard¹, Gévry, Nicolas¹, Murphy, Bruce¹, ¹ Centre de Recherche en Reproduction Animale, St-Hyacinthe, CA

ABSTRACT- Peroxisome proliferator-activated receptor (PPAR) is a transcription factor of the orphan nuclear receptor family. A new role related to reproduction has been recently reported in the mouse where it was shown that prostacyclin (PGI₂, a product of the cyclo-oxygenase-2 (COX-2) pathway, mediates blastocyst implantation via PPAR. The aim of this study is to determine whether the PGI₂ signaling pathway and PPAR are involved in the implantation process that terminates diapause in a carnivore species, the mink. In situ hybridizations studies established the spatiotemporal expression pattern of PPAR mRNA, showing it is expressed in the uterine stroma associated with the early implanted blastocyst. Immunohistochemical data demonstrated that PPAR is localized to nuclei of the glandular epithelium in the region of embryo attachment. Mink embryos in diapause and embryos that had been activated with prolactin were co-cultured with mink uterine cell lines. It was observed that the activated embryos, in the presence of cells, produced PGI₂, as measured by the presence of its metabolite, 9-keto-PGF1 in the conditioned media. The cell lines alone, or incubated with embryos in diapause, did not increase the basal level of PGI₂. Moreover, in semi-quantitative RT-PCR experiments, we found that activated embryos induced PPAR expression in the uterine cell line, and no such expression was observed in cells alone or cells incubated with embryos in diapause. The uterine cell line was transfected with a luciferase reporter gene construct containing PPAR response elements (PPRE) and promoter assays were conducted in the presence of the ligand of PPAR and of its heterodimerization partner RXR, or conditioned media. Transcriptional activation of PPAR was confirmed in the presence of PGI₂ and 9-cis-retinoic acid (RXR ligand). These in vitro trials indicate that the activated embryo produces paracrine factors that induce PPAR ligands via the COX-2 pathway and PPAR expression and transcriptional activity in uterine glands in early gestation. Together, these results support the hypothesis that PPAR, when activated by PGI₂ plays a specific role in carnivore implantation, and that the activated embryo triggers the uterine prostaglandin synthesis. (Supported by NSERC to BDM)

KEY WORDS: embryonic diapause, implantation, PPAR , prostaglandins