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6th ESACP Congress, Heidelberg, April 7-11, 1999 |
A149
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.
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