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A prominent functional change during differentiation 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 PPAR , a PPAR form which is involved in adipogenic differentiation. First, we were able to show the expression of PPAR 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 PPAR 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 PPAR , 15-deoxy-12,14 prostaglandin J 2 (15-dPGJ 2 ) and to the thiazolidinedione ciglitizone. Aurintricarboxylic acid (ATA) was found to reduce the intracellular PPAR level and to promote cell cycle progress, indicating that ATA can be used as a tool for experimental changes of PPAR proteins in intact cells and for studying the physiological consequences. The ATA-mediated decrease of PPAR was accompanied by reduced progesterone production and a progression of the cell cycle, suggesting a function of PPAR in both processes. The response to ATA was abrogated by a high dose (>490 nM) of 15-dPGJ 2 , suggesting that 15-dPGJ 2 exerts its effect on steroidogenic activity via PPAR and that the 15-dPGJ 2 -PPAR system plays a role in the maintenance of a differentiated quiescent stage in lutein cells.

After parturition, one of the major problems related to nutritional management that is faced by the majority of dairy cows is negative energy balance (NEB). During NEB, excessive lipid mobilization takes place and hence the levels of free fatty acids, among them oleic acid, increase in the blood, but also in the follicular fluid. This accumulation can be associated with serious metabolic and reproductive disorders. In the present study, we analyzed the effects of physiological concentrations of oleic acid on cell morphology, apoptosis, necrosis, proliferation and steroid production, and on the abundance of selected transcripts in cultured bovine granulosa cells. Increasing oleic acid concentrations induced intracellular lipid droplet accumulation, thus resulting in a foam cell-like morphology, but had no effects on apoptosis, necrosis or proliferation. Oleic acid also significantly reduced the transcript abundance of the gonadotropin hormone receptors, FSHR and LHCGR, steroidogenic genes STAR, CYP11A1, HSD3B1 and CYP19A1, the cell cycle regulator CCND2, but not of the proliferation marker PCNA. In addition, treatment increased the transcript levels of the fatty acid transporters CD36 and SLC27A1, and decreased the production of 17-beta-estradiol and progesterone. From these data it can be concluded that oleic acid specifically affects morphological and physiological features and gene expression levels thus altering the functionality of granulosa cells. Suggestively, these effects might be partly due to the reduced expression of FSHR and thus the reduced responsiveness to FSH stimulation.

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