Relationship between different stages of the corpus luteum and the expression of the peroxisome proliferator-activated receptor gamma protein in bovine large lutein cells

Lutein cells produce progestins that support pregnancy. Steroidogenesis req uires coordination of the anabolic and catabolic pathways of lipid metaboli sm. Peroxisome proliferator-activated receptors (PPAR) are transcription fa ctors that are central in the regulation of lipid metabolism. Hence, they m ay play a role in regulation of the development and regression of the corpu s luteum. The present study investigated the expression of PPAR-gamma,n dur ing different stages of the corpus luteum. Lutein cells were isolated mecha nically from non-pregnant and pregnant heifers on days 5, 12 and 20 of the oestrous cycle (n = 3 for each day). PPAR-gamma in single cells was analyse d by flow cytometry. PPAR-gamma, and PPAR-gamma, isoforms were distinguishe d by immunoblotting. The cell cycle of the lutein cells was measured by the flow cytometric quantification of DNA in single cells, using propidium iod ide staining after ethanol fixation and RNAse treatment, and by the detecti on of the proliferating cell nuclear antigen (PCNA). The response of the ce lls to PPAR-gamma agonist 15-deoxy-Delta(12,14) prostaglandin J(2) (15dPGJ( 2), 200 and 490 nmol l(-1)) with and without changing the cell cycle by the anti-apoptogenic drug aurintricarboxylic acid (ATA, 10 mu mol l(-1)) was u sed as an in vitro model to study the relationship between the cell cycle a nd PPAR-gamma. The concentration of PPAR-gamma per cell from non-pregnant h eifers was significantly higher on day 5 (3.40 +/- 0.30 fmol) compared with that on day 12 (1.34 +/- 0.18 fmol, P < 0.05) and day 20 (0.55 +/- 0.2 fmo l, P < 0.05). In pregnant heifers, the concentration of PPAR-gamma was sign ificantly (P < 0.01) higher than in non-pregnant heifers. A decrease in the PPAR-gamma, isoform relative to PPAR-gamma(2) was observed in cells on day 12 of the oestrous cycle compared with day 5. The cell cycle (S phase port ion in cells on days 5, 12 and 20: 16 +/- 4%, 6 +/- 4% and 4 +/- 3%, respec tively) and the portion of cells with PCNA correlated with the amount of PP AR-gamma, in non-pregnant heifers. ATA promoted the S phase in cells of non -pregnant heifers (day 12) and the endogenous agonist of PPAR-gamma, 15dPGJ (2), inhibited the response to ATA in a dose-dependent manner, indicating t hat PPAR-gamma plays a role in the arrest of the cell cycle in lutein cells to maintain their differentiated state.