Expression of Key Prostaglandin Synthases in Equine Endometrium During Late Diestrus and Early Pregnancy1

Abstract

Luteolysis in domestic species is mediated by the release of luteolytic pulses of prostaglandin (PG) F(2alpha) by the uterus at the end of diestrus, which must be suppressed by the conceptus to permit maternal recognition of pregnancy. In many species, including the horse, both the conceptus and the endometrium also synthesize PGE(2), which may antagonize PGF(2alpha) by playing a luteotropic and/or antiluteolytic role. While the release of PGE(2) and PGF(2alpha) by the equine endometrium in late diestrus and early pregnancy has been previously studied, the underlying prostaglandin synthase gene regulatory mechanisms remain poorly defined. To resolve this issue, cyclooxygenase-2 (COX-2), microsomal PGE(2) synthase (PGES), and PGF(2alpha) synthase (PGFS) expression were examined in a series of endometrial biopsies obtained from cycling mares on Days 10, 13, and 15 postovulation, as well as from pregnant mares on Day 15. Quantification of COX-2 expression revealed significant (P < 0.01) increases in both mRNA and protein levels at Day 15 in cycling endometrium relative to other timepoints. Importantly, the level of COX-2 expression in Day 15 pregnant endometrium was found to be comparable with that observed in Day 10 and Day 13 cycling animals, suggesting that the presence of the conceptus blocks the induction of COX-2. Immunohistochemistry demonstrated that the induction of COX-2 expression on Day 15 occurs specifically in surface epithelial cells in cycling animals only. As equine PGFS had not been previously characterized, a 1380-base pair (bp) cDNA transcript was cloned by a combination of reverse transcription-PCR techniques and found to be highly homologous to bovine liver-type PGFS. The pattern of expression observed for the terminal PG synthases was distinct from that of COX-2, as PGES and PGFS mRNA and protein levels were found to be invariant throughout the timecourse and unaffected by pregnancy. Similar to COX-2, however, the PGES and PGFS proteins were found to localize mainly to the surface epithelium. Thus, this study describes for the first time the regulation and spatial distribution of COX-2, PGES, and PGFS expression in equine endometrium in late diestrus, with a marked induction of COX-2 but not of PGES and PGFS expression in uterine epithelial cells at Day 15. Furthermore, the presence of the conceptus was shown to block the induction of COX-2 expression at Day 15, suggesting an important mechanism by which it may suppress uterine PGF(2alpha) release and prevent luteolysis during early pregnancy.

Membrane Prostaglandin E Synthase-1: A Novel Therapeutic Target

“…In a study of equine endometrium, expressions of mPGES-1 and PGFS were not found to change during late diestrus or in pregnant animals. This finding was interpreted to suggest that the equine conceptus may modulate endometrial prostaglandin synthesis mainly by regulating the expression of the COX-2 enzyme (Boerboom et al, 2004).…”

Expression Profiles of Interferon-Tau Stimulated Genes (ISGs) in Peripheral Blood Leucocytes (PBLs) and Milk Cells in Pregnant Dairy Cows

“…Primers for MX1, MX2, and ISG15 mRNAs were derived from Gifford et al [12] and Boerboom et al [15] . The primer pair sequences and product sizes are shown in Table 1.…”

“…All samples were evaluated in duplicate for each cDNA. Glyceraldehyde-3 phosphate dehydrogenase (GAPDH) mRNA primer was derived from Boerboom et al [15] and used as a housekeeping gene to normalize the expression of ISG15, MX1 and MX2. Mean threshold of cycle values from day of 0 was used as a reference point and Ct values for each days (day 0 and day 18) were used to calculate the fold change from this reference point using reference point Ct values according to 2 -∆∆ Ct method described by Livak and Schmittgen [16] .…”

Efeito da aplicação da hCG em diferentes dias do ciclo estral sobre a concentração sérica de progesterona e fluxo sanguíneo uterino e ovariano em éguas

“…Baseado nesses achados considera--se a expressão da COX--2 um evento chave na luteólise ou reconhecimento materno da gestação (BOERBOOM et al, 2004).…”

“…Durante o diestro, quando os níveis de progesterona aumentam, as dobras endometriais individualizadas não são discernidas (GINTHER, 1984;PIERSON, 1984;GINTHER, 1986;GINTHER, 1986;GRIFFIN;PYCOCK et al, 1995) SIROIS et al, 1992;RICHARDS, 1994;BOERBOOM;SIROIS, 2004;STOUT, 2011), prostaglandina endoperóxido sintase 2, entre outros (RICHARDS et al, 1998;ROBKER et al, 2000 Existem relatados na literatura dois tipos de evacuação folicular, a forma abrupta e a gradual (GINTHER, 1992;GINTHER, 1995;GASTAL, 2011;GINTHER, 2012), sendo a ocorrência de cada uma delas de 50%. Durante a abrupta, 15% do fluido folicular permanece no folículo, e sua duração é entre 5 a 90 segundos.…”