Evaluation of the contribution of cyclooxygenase 1 and cyclooxygenase 2 to the production of PGE2 and PGF2 alpha in epithelial cells from bovine endometrium

Abstract

In ruminants, the production of prostaglandins by the endometrium is critical for recognition of pregnancy. In the absence of an embryonic signal, luteolytic pulses of PGF 2␣ are released by the uterus. In contrast, the presence of a viable conceptus reduces the production of PGF 2␣ relative to PGE 2 and prevents luteolysis through the release of trophoblastic interferon (IFN-). Initially, it was thought that epithelial and stromal endometrial cells were specialized in the production of a single type of prostaglandin. However, purified cell populations of both types of cell can produce PGF 2␣ and PGE 2 ; therefore, selective production of PGF 2␣ and PGE 2 must be regulated within each type of cell. Two distinct prostaglandin synthases, cyclooxygenase 1 and cyclooxygenase 2, are involved in prostaglandin production and each may catalyse the production of a different prostaglandin. This possibility was investigated in cultured epithelial cells from bovine endometrium. Cells were treated with oxytocin or arachidonic acid, and expression of cyclooxygenase 1 and cyclooxygenase 2 proteins was monitored over time and correlated with prostaglandin accumulation. Cells were also treated with increasing doses of inhibitors of cyclooxygenase 1 or cyclooxygenase 2 (nonsteroidal anti-inflammatory drugs; NSAIDs) with or without arachidonic acid or oxytocin: flurbiprofen (0-50 mol l −1 ) was used as a non-selective inhibitor; valeryl salicylate (0-500 mol l −1 ) was used as a cyclooxygenase 1 inhibitor and NS-398 (0-1 mol l −1 ) was used as a cyclooxygenase 2 inhibitor. After stimulation with arachidonic acid or oxytocin, prostaglandin production and expression of cyclooxygenase 2 protein were increased. All inhibitors were able to block basal and stimulated prostaglandin production. These results indicate that in endometrium most, if not all, prostaglandin production is probably processed through cyclooxygenase 2.

Control of cyclic AMP concentration in bovine endometrial stromal cells by arachidonic acid

“…This is consistent with the induction of PDE by arachidonic acid and confirms that the effect on cAMP level was reflected in protein synthesis. The results also show that arachidonic acid has both stimulatory and inhibitory effects on COX-2, since it increases COX-2 levels in bovine endometrial epithelial cells when added alone (Parent et al 2003). These effects have different time courses, in that the action through PDE shown here is rapid (within 10 min), while the rise in COX-2 demonstrated by Parent et al (2003) peaks at 6 h. The explanation for these apparently contradictory responses may lie in the promiscuity of the COX-2 promoter, which is sensitive to many transcription factors.…”

“…Spatial separation arises because the epithelium expresses the OTR earlier than the stroma and is the principal source of PGF 2a , whereas the stroma does not express the OTR until oestrus, and produces principally PGE 2 (Asselin et al 1996, Robinson et al 1999. Expression of COX-2 in the epithelium is increased both by oxytocin in the non-pregnant animal (Parent et al 2003) and by IFN-t in pregnancy (Emond et al 2004). Interferons also activate phospholipase A 2 (Hannigan & Williams 1991), which would be expected to increase the availability of arachidonic acid to COX-2.…”

The effect of a diet supplemented with the n-6 polyunsaturated fatty acid linoleic acid on prostaglandin production in early- and late-pregnant ewes

“…However COX expression was not assessed following the explant culture period so it is possible that COX expression may have been further upregulated in vitro in tissues obtained from ewes on the high-LA diet. In support of this suggestion there is evidence that AA can itself upregulate COX-2 expression (Parent et al 2003). PG production by particular tissues can also be influenced by the extent to which either COX-1 or COX-2 colocalize with particular terminal PG synthases in different subcellular compartments and the fact that COX-1 requires a greater supply of AA than COX-2 to be functional (Murakami & Kudo 2004).…”

Role of Candidate Genes Regulating Uterine Prostaglandins Biosynthesis for Maternal Recognition of Pregnancy in Domestic Animals

“…There are two isoforms encoded by distinct genes [30]: the constitutive isoform, COX-1, is widely expressed in a variety of tissues and cells, whereas the inducible form, COX-2, is regulated by factors such as cytokines or tumor promoters [31]. COX-1 is constitutively expressed in most tissues and responsible for housekeeping functions and immediate response to levels of AA above 10 M. COX-2 is regulated by factors such as cytokines or tumour promoters and supports sustained production of PGs from relatively low levels of AA (below 2.5 M) [32]. PGH2 produced by COXs is the common precursor for generation of primary PGs including PGE2, PGF2 , by cell-specific isomerases and synthases (such as PGES for PGE2 and PGFS for PGF2 ).…”

“…The requirement of COX-2 for normal blastocyst implantation and decidualization in mice is due to the role of COX-2-derived PGs in regulation of vascular endothelial growth factor and angiopoietin signaling that influence uterine vascular permeability and angiogenesis [61,88,95]. Parent et al [32] have correlated the expression of PGES with that of COX-2, which is an important enzyme for the production of PGE2 in bovine endometrium. Increasing this production will modulate the PGE2/PGF2 ratio and contribute to establishment of pregnancy.…”