Peroxisome proliferator-activated receptor (PPAR) isoforms are differentially expressed in peri-implantation porcine conceptuses

Abstract

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family of ligand-dependent transcription factors. PPARs are critical regulators of glucose homeostasis and lipid metabolism, and affect cell proliferation and differentiation. In the current study, we examined (1) the profiles of PPARA, PPARD, and PPARG mRNA expression and DNA binding activity in porcine conceptuses collected on Days 10–11 (spherical and tubular conceptuses), 11–12 (filamentous conceptuses), 13–14, and 15–16 (elongated conceptuses) of pregnancy, (2) the presence of PPARA, PPARD, and PPARG proteins in Days 10, 12, and 15 conceptuses. Moreover, we analyzed the abundance of retinoid X receptor (RXR; PPARs heterodimer partner) transcripts as well as the correlation between PPARs mRNA expression and the expression of genes important for and/or associated with elongation of porcine conceptuses: aromatase (CYP19A1), prostaglandin endoperoxide synthase 2 (PTGS2), glucose transporter 1 (SLC2A1), and interleukin 1B (IL1B). PPARA mRNA expression in conceptuses did not change during Days 10–14 of gestation, but was greater on Days 15–16 compared to Days 10–11 (P < 0.05). A considerable increase in PPARD and PPARG mRNA expression was observed in filamentous conceptuses from Days 11–12 compared to spherical and tubular conceptuses from Days 10–11 (P < 0.01), followed by a decrease on Days 13–14 and 15–16 (P < 0.05). PPARA, PPARD, and PPARG proteins were present in conceptus tissue demonstrating nuclear localization clearly visible on Days 12 and 15 of pregnancy. DNA binding activity of the PPARD isoform was greater in filamentous conceptuses from Days 11–12 than in spherical and tubular conceptuses from Days 10–11 (P < 0.01). Moreover, concentrations of active PPARD and PPARG proteins in nuclear fractions of conceptus tissue were greater on Days 11–12 compared to Days 13–14 and 15–16 of pregnancy (P < 0.05). RXRA, RXRD, and RXRG mRNA expression in conceptuses increased on Days 11–12 compared to Days 10–11 (P < 0.05). PPARD and PPARG mRNA expression showed strong positive correlations with PTGS2 mRNA expression (P < 0.0001). Additionally, PPARD gene expression correlated with SLC2A1 and IL1B mRNA expression (P < 0.01). Collectively, these results indicate that among all three PPARs expressed in peri-implantation porcine conceptuses, PPARD and PPARG may be involved in conceptus elongation before implantation.