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

Abstract

Lutein cells produce progestins that support pregnancy. Steroidogenesis requires coordination of the anabolic and catabolic pathways of lipid metabolism. Peroxisome proliferator-activated receptors (PPAR) are transcription factors that are central in the regulation of lipid metabolism. Hence, they may play a role in regulation of the development and regression of the corpus luteum. The present study investigated the expression of PPAR-gamma, n during different stages of the corpus luteum. Lutein cells were isolated mechanically 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 analysed by flow cytometry. PPAR-gamma 1 and PPAR-gamma 2 isoforms were distinguished by immunoblotting. The cell cycle of the lutein cells was measured by the flow cytometric quantification of DNA in single cells, using propidium iodide staining after ethanol fixation and RNAse treatment, and by the detection of the proliferating cell nuclear antigen (PCNA). The response of the cells to PPAR-gamma agonist 15-deoxy-delta 12,14 prostaglandin J2 (15dPGJ2, 200 and 490 nmol l-1) with and without changing the cell cycle by the anti-apoptogenic drug aurintricarboxylic acid (ATA, 10 mumol l-1) was used as an in vitro model to study the relationship between the cell cycle and PPAR-gamma. The concentration of PPAR-gamma per cell from non-pregnant heifers 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 fmol, P < 0.05). In pregnant heifers, the concentration of PPAR-gamma was significantly (P < 0.01) higher than in non-pregnant heifers. A decrease in the PPAR-gamma 1 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 portion in cells on days 5, 12 and 20: 16 +/- 4%, 6 +/- 4% and 4 +/- 3%, respectively) and the portion of cells with PCNA correlated with the amount of PPAR-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, 15dPGJ2, inhibited the response to ATA in a dose-dependent manner, indicating that PPAR-gamma plays a role in the arrest of the cell cycle in lutein cells to maintain their differentiated state.

Peroxisome proliferator-activated receptors in the regulation of female reproductive functions

“…Many studies have shown that PPARs gene and/or protein expression varies depending on ovarian cell type, physiological status and the species [14,[22][23][24][25][26]. It has also been frequently reported that PPARs are engaged in the regulation of various ovarian functions.…”

Loss of the Peroxisome Proliferation-activated Receptor gamma (PPARγ) Does Not Affect Mammary Development and Propensity for Tumor Formation but Leads to Reduced Fertility

“…Loss of PPAR␥ in the Ovary Results in Reduced Fertility-PPAR␥ has been found in bovine (27)(28)(29), rat (30,31), and human (32) ovaries. Reverse transcription-PCR results confirmed that the PPAR␥ gene is also expressed in the mouse ovary (data not shown).…”

The effect of nutrition and metabolic status on the development of follicles, oocytes and embryos in ruminants

“…In cyclic ewes, the expression of PPARγ is mainly limited to the granulosa cells of antral follicles and corpora lutea (Froment et al, 2003). In cows, the concentration of PPARγ in the corpus luteum increased after ovulation, and then decreased during regression of the corpus luteum (Lohrke et al, 1998;Viergutz et al, 2000). Furthermore, in mice, the conditional inactivation of PPARγ in the ovary leads to reduced fertility (Cui et al, 2002).…”

“…This decrease is not because of an alteration in ovarian folliculogenesis, but a drop in the number of embryos implanted and probably because of decreased progesterone secretion by the corpora lutea (Cui et al, 2002). In bovine large lutein cells, PPARγ plays a role in the arrest of the cell cycle to maintain a differentiated state (Viergutz et al, 2000). Furthermore, synthetic ligands of PPARγ increased progesterone secretion by bovine lutein cells (Lohrke et al, 1998).…”