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Reproduction (2006) 131 93-101
DOI: 10.1530/rep.1.00730
Copyright © 2006 Society for Reproduction and Fertility
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RESEARCH

Effects of luteinizing hormone on peroxisome proliferator-activated receptor {gamma} in the rat ovary before and after the gonadotropin surge

Jayeeta Banerjee and Carolyn M Komar

Department of Animal Science, Iowa State University, 2356 Kildee Hall, Ames, Iowa 50011-3150, USA

Correspondence should be addressed to Carolyn M Komar; Email: ckomar{at}iastate.edu

We have shown previously that mRNA for peroxisome proliferator-activated receptor {gamma} (PPAR{gamma}) is expressed in granulosa cells and downregulated by the luteinizing hormone (LH) surge. The current studies were undertaken to test the hypothesis that LH stimulates a decrease in the expression of PPAR{gamma}, as well as its activity, in granulosa cells. Ovaries were collected from immature rats 0 and 48 h after they received pregnant mares’ serum gonadotropin (PMSG), and 4 and 24 h after administration of human chorionic gonadotropin (hCG), and used for protein isolation or processed for immunolocalization of PPAR{gamma}. The amount of phosphorylated PPAR{gamma} was measured by immunoblot analysis to determine how LH affects the phosphorylation status, and therefore the activity, of PPAR{gamma}. Granulosa cells were also collected from immature rats 48 h after PMSG. Cells were cultured with LH in the absence and presence of H89 and cycloheximide to investigate the role of PKA and protein synthesis in the LH-mediated decline in mRNA for PPAR{gamma} respectively. Protein corresponding to PPAR{gamma} was localized to nuclei of granulosa cells 0 and 48 h after PMSG. Expression was greatly reduced by 4 h after hCG, with expression in mural granulosa cells lost before that in cumulus cells. The amount of phosphorylated PPAR{gamma} did not change during the periovulatory period. Blocking PKA activity had no effect on levels of mRNA for PPAR{gamma}. However, levels of mRNA for PPAR{gamma} were significantly increased in cells treated with cycloheximide (P < 0.05, ANOVA followed by Tukey’s HSD). These data suggest that PPAR{gamma} is tightly regulated in the ovary and that its expression is the primary mechanism by which LH influences the activity of PPAR{gamma}. In addition, protein synthesis may be involved in modulating levels of PPAR{gamma} in granulosa cells.




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P Froment, F Gizard, D Defever, B Staels, J Dupont, and P Monget
Peroxisome proliferator-activated receptors in reproductive tissues: from gametogenesis to parturition.
J. Endocrinol., May 1, 2006; 189(2): 199 - 209.
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