Expression of prostaglandin F _2α (PGF _2α) receptor and its isoforms in the bovine corpus luteum during the estrous cycle and PGF _2α-induced luteolysis

Prostaglandin F _2α (PGF _2α) induces luteolysis via a specific receptor, PTGFR. Although PTGFR mRNA expression in the bovine corpus luteum (CL) has been studied previously, changes in PTGFR protein and its localization are not fully understood during the life span of the CL. In addition to full-length PTGFR, several types of PTGFR isoforms, such as PTGFRα (type I) and PTGFRζ (type II), were reported in the bovine CL, suggesting isoform-specific luteal action. Full-length PTGFR mRNA in the bovine CL increased from the early to the mid-luteal phase and decreased during luteolysis, whereas PTGFR protein remained stable. PTGFR protein was localized to both luteal and endothelial cells and was expressed similarly during the life span of the CL. Like full-length PTGFR mRNA, PTGFRα and PTGFRζ mRNA also increased from the early to mid-luteal phases, and mRNA of PTGFRζ, but not PTGFRα, decreased in the regressing CL. During PGF _2α-induced luteolysis, the mRNAs of full-length PTGFR, PTGFR,α and PTGFRζ decreased rapidly (from 5 or 15 min after PGF _2α injection), but PTGFR protein decreased only 12 h later. Silencing full-length PTGFR using small interfering RNA prevented PGF _2α-stimulated cyclooxygenase-2 (PTGS2) mRNA induction. By contrast, PGF _2αcould stimulate vascular endothelial growth factor A (VEGFA) mRNA even when full-length PTGFR was knocked down, thus suggesting that PGF _2α may stimulate PTGS2 via full-length PTGFR, whereas VEGFA is stimulated via other PTGFR isoforms. Collectively, PTGFR protein was expressed continually in the bovine CL during the estrous cycle, implying that PGF _2αcould function throughout this period. Additionally, the bovine CL expresses different PTGFR isoforms, and thus PGF _2α may have different effects when acting via full-length PTGFR or via PTGFR isoforms.