6th ESACP Congress, Heidelberg, April 7-11, 1999

A149
RELATIONSHIP BETWEEN PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR GAMMA (PPARG) AND CELL CYCLE IN LUTEIN CELLS
Viergutz T, Löhrke B, Pöhland R, Becker F, Kanitz W

Research Institute for the Biology of Farm Animals, Dummersdorf, Germany

Introduction Ovarian follicle cells differentiate to produce pregnancy- maintaining steroids ( progestins, i.e., progesterone and related steroids) after ovulation, generating the corpus luteum. The corpus luteum is regressed when fertilization of the released oocytes did not take place. The regulation of this process is not fully understood but may be associated with the expression of transcription factors activating gene products some which are involved in pathways of the cholesterol and lipid metabolism. As peroxisome proliferator-activated receptors (PPAR) may play a role for the differentiation of lutein cells, we were interested in the expression of PPARg and PPARg -mediated action on cell cycle progress , a PPAR form which is involved in the adipogenic differentiation. Methods The expression of PPARg in bovine lutein cells (day 12 of the ovarian cycle) was analyzed at the level of the mRNA and ectropic expression by imaging, flow cytometry, and blot analysis. Cell function was tested by progesterone secretion and by the response to the mitogenic drug aurintricarboxylic acid (ATA) and to 15-deoxy-D12,14 prostaglandin J2 (15-d PGJ2) an endogenous ligand of PPARg. Cell cycle was analyzed by flowcytometry, using propidium iodide staining after ethanol fixation and RNAse treatment. Results and Conclusions The cells (24 h culture) responded dose-dependently with increasing the progesterone secretion (up to 1.5 fold the basal level) to 15-d PGJ2. ATA was found to reduce the intracellular PPARg level and to promote the cell cycle progress, indicating ATA as tool for experimental changes of PPARg proteins in intact cells and for studying the physiological consequences. The ATA-mediated decrease of PPARg was accompanied with a reduced progesterone production and a progression of the cell cycle, indicative for a function of PPARg in both processes. The response to ATA was abrogated by a high dose (> 490 nM) of 15-dPGJ2, suggesting 15-dPGJ2 exerts its effect on steroidogenic activity via PPARg and a role of the 15-dPGJ2 -PPARg system for maintenance of a differentiated quiescent stage in lutein cells.