Detection and functional characterisation of the transcription factor peroxisome proliferator-activated receptor gamma in lutein cells.

A prominent functional change during diVerentiation of lutein cells from follicular thecal and granulosa cells is an enhanced production and secretion of progestins. The regulation of this process is not fully understood but may be associated with the expression of transcription factors which activate genes, products of which are involved in pathways of the cholesterol and lipid metabolism. As peroxisome proliferator-activated receptors (PPARs) play a role in both pathways, we were interested in the expression of PPARa, a PPAR form which is involved in adipogenic diVerentiation. First, we were able to show the expression of PPARa in bovine lutein cells (day 12 of the ovarian cycle) at the mRNA and protein level by imaging, flow cytometry and blot analysis, and secondly a role of PPARa in the secretion of progesterone. The cells (24 h culture) responded dose dependently by increasing progesterone secretion (up to 1·5-fold of the basal level) to an endogenous ligand of PPARa, 15-deoxy-˜ 12,14 prostaglandin J 2 (15-dPGJ 2 ) and to the thiazolidinedione ciglitizone. Aurintricarboxylic acid (ATA) was found to reduce the intracellular PPARa level and to promote cell cycle progress, indicating that ATA can be used as a tool for experimental changes of PPARa proteins in intact cells and for studying the physiological consequences. The ATA-mediated decrease of PPARa was accompanied by reduced progesterone production and a progression of the cell cycle, suggesting a function of PPARa in both processes. The response to ATA was abrogated by a high dose (>490 nM) of 15-dPGJ2, suggesting that 15-dPGJ2 exerts its eVect on steroidogenic activity via PPARa and that the 15-dPGJ2‐PPARa system plays a role in the maintenance of a diVerentiated quiescent stage in lutein cells.