Immunohistochemical assessment of prostaglandin H-synthase in bovine endometrial biopsy samples collected throughout the oestrous cycle

Ultrastructural and Immunohistochemical Characterization of Maternal Myofibroblasts in the Bovine Placenta around Parturition

Myofibroblasts are contractile cells that exhibit features of both fibroblasts and smooth muscle cells. In the synepitheliochorial placenta of the cow myofibroblasts are found in the maternal stroma. However, a deeper understanding of the structure and function of the stromal myofibroblasts in the developed bovine placenta is still missing. Thus, immunohistochemical and ultrastructural analyses in bovine term placentomes, compared to non-pregnant caruncle samples, were conducted. To investigate functional aspects, contractility of placentomal caruncle slices was assessed in an in vitro contraction assay. Additionally, a three-dimensional reconstruction of a bovine placental myofibroblast was created. Immunofluorescent staining revealed a characteristic pattern, including cytoplasmic expression of α-smooth muscle actin, strong perinuclear signal for the intermediate filament vimentin and nuclear progesterone receptor staining. Ultrastructurally, stress fibers, extended cisternae of the rough endoplasmic reticulum and perinuclear intermediate filaments were observed. Moreover, in vitro stimulation with angiotensin-II, but not with prostaglandin F2α, induced contraction of placental caruncle tissue. Altogether, these results indicate that progesterone-responsive myofibroblasts represent a mesenchymal phenotype that is involved in the contractile properties of bovine placental stroma. Therefore, the present findings suggest a potential involvement of myofibroblasts in post-partum events of cattle, i.e., expulsion of fetal membranes and uterine involution.

Endometrial epidermal growth factor profile and its abnormalities in dairy cows

Normal cows have 2 peaks in endometrial epidermal growth factor (EGF) concentrations on Days 2–4 and 13–14, and the absence of peaks has been linked to reduced fertility in repeat breeder (RB) cows. However, the timing of the peaks (i.e., day of examinations) was estimated for a few cows per cycle day. Therefore, the present study characterized EGF peaks and examined if the absence of peaks in RB cows indicate either peak loss or changed timing. In Study 1, 20 Holstein cows were examined for EGF concentrations between Days 1 and 6 using repeated biopsy of the uterine endometrial tissues. Sixteen cows exhibited increased EGF concentrations for 2–3 days between Days 2 and 5. All 16 cows exhibited increased EGF concentrations on Day 3. In Study 2, 10 cows were examined for EGF concentrations between Days 11 and 16. Increased EGF concentrations for 2–3 days were found in 7 cows between Days 12 and 15. All 7 cows exhibited increased EGF concentrations on Days 13 and 14. In Study 3, 12 RB cows were examined for endometrial EGF concentrations between Days 1 and 6. Four cows exhibited an increase of EGF concentrations on Days 3 and 4, whereas 8 cows (66.7%) exhibited low EGF concentrations throughout the study period. In conclusion, Days 3 and 13–14 are suitable days to examine a cyclic change of endometrial EGF concentrations. Further, low EGF concentrations on Day 3 in RB cows indicated an absence, but not altered timing, of the EGF peak.

Peroxisome-proliferator-activated receptors and the control of levels of prostaglandin-endoperoxide synthase 2 by arachidonic acid in the bovine uterus

Arachidonic acid is a potential paracrine agent released by the uterine endometrial epithelium to induce PTGS2 [PG (prostaglandin)-endoperoxide synthase 2] in the stroma. In the present study, bovine endometrial stromal cells were used to determine whether PTGS2 is induced by arachidonic acid in stromal cells, and to investigate the potential role of PPARs (peroxisome-proliferator-activated receptors) in this effect. Arachidonic acid increased PTGS2 levels up to 7.5-fold within 6 h. The cells expressed PPARalpha and PPARdelta (also known as PPARbeta) (but not PPARgamma). PTGS2 protein level was increased by PPAR agonists, including polyunsaturated fatty acids, synthetic PPAR ligands, PGA1 and NSAIDs (non-steroidal anti-inflammatory drugs) with a time course resembling that of arachidonic acid. Use of agonists and antagonists indicated PPARalpha (but not PPARdelta or PPARgamma) was responsible for PTGS2 induction. PTGS2 induction by arachidonic acid did not require PG synthesis. PTGS2 levels were increased by the PKC (protein kinase C) activators 4beta-PMA and PGF(2alpha), and the effects of arachidonic acid, NSAIDs, synthetic PPAR ligands and 4beta-PMA were blocked by PKC inhibitors. This is consistent with PPAR phosphorylation by PKC. Induction of PTGS2 protein by 4beta-PMA in the absence of a PPAR ligand was decreased by the NF-kappaB (nuclear factor kappaB) inhibitors MG132 and parthenolide, suggesting that PKC acted through NF-kappaB in addition to PPAR phosphorylation. Use of NF-kappaB inhibitors allowed the action of arachidonic acid as a PPAR agonist to be dissociated from an effect through PKC. The results are consistent with the hypothesis that arachidonic acid acts via PPARalpha to increase PTGS2 levels in bovine endometrial stromal cells.

Pregnancy effects on distribution of progesterone receptors, oestrogen receptor α, glucocorticoid receptors, Ki-67 antigen and apoptosis in the bovine interplacentomal uterine wall and foetal membranes

Until recently, studies dealing with the uterus of the pregnant cow focus primarily on the placentome or on early and late pregnancy. Thus, there is a paucity of information about many aspects of the interplacentomal uterine wall including adherent foetal membranes. Corresponding tissue specimens were collected at the slaughterhouse and in animals undergoing premature caesarean section. Two specimens per month of pregnancy were assessed immunohistochemically for progesterone receptors, oestrogen receptor alpha and glucocorticoid receptors, Ki-67 protein and TUNEL procedure was performed. The latter two methods were employed in three animals each per months 1 and 2, 3 and 4, 7 and 8 and in six animals undergoing caesarean section at days 274 and 275 post insemination or during spontaneous labour. Results indicate that proliferation and apoptosis are of minor importance for tissue homeostasis since both can histochemically be detected only sporadically. Thus, at the sites investigated here, cellular hypertrophy plays an important role for tissue growth during pregnancy. Progesterone receptors, oestrogen receptor alpha and glucocorticoid receptors, however, exhibit cell type and pregnancy stage specific distribution patterns within the tissues assessed. Progesterone receptor immunoreactive scores remained fairly unchanged during pregnancy. Oestrogen receptor alpha scores, however, generally decreased and glucocorticoid receptors increased with ongoing gestation. Progesterone receptors and oestrogen receptor alpha were present in endometrial stroma and in myometrial smooth muscle cells during whole pregnancy. Oestrogen receptor alpha was detectable during whole pregnancy also in uterine glands. Progesterone receptors were, however, present at a very low level at the latter site only during months 1-3 and 6-9. Oestrogen receptor alpha and glucocorticoid receptors may also mediate uterine blood flow since they were present in the tunica media of uterine blood vessels. Results of the present study indicate, that progesterone and its receptor play an important role during whole gestation, mainly for uterine quiescence. Glucocorticoids and their receptors - possibly in cooperation with oestrogens and decreasing amounts of the oestrogen receptor alpha - should trigger processes initiating parturition, such as endometrial prostaglandin production. Further studies - including the periparturient period - should help to understand the exact role of the extraplacental compartment of the uterine wall for the initiation and progress of parturition.

Potential relationship between normalization of endometrial epidermal growth factor profile and restoration of fertility in repeat breeder cows

The present study characterized alterations of the endometrial epidermal growth factor (EGF) and examined potential relationships between normalization of the EGF and restoration of fertility in repeat breeder cows. In Experiment 1, endometrial tissues were obtained by biopsy on Days 3, 7 and 14 of the estrous cycle from 99 fertile dairy cows and normal ranges of uterine tissue EGF concentrations were determined. Then, eight fertile cows were examined for endometrial EGF concentrations on Days 3, 7 and 14 during the three consecutive estrous cycles. All eight cows had a normal EGF profile (EGF concentrations were within the normal ranges of all 3 days) in all three estrous cycles and endometrial EGF concentrations were similar among the three estrous cycles. In Experiment 2, 61 repeat breeder cows were examined EGF profile and 43 (70.5%) cows had altered EGF profiles compared with control profiles. A typical alteration was characterized by decreased concentrations on Days 3 and 14 and accounted for 86.0% of all alterations. When repeat breeder cows with altered EGF profiles (n=17) were left untreated, abnormality persisted in 14 (82.4%) cows at the second examination and only 3 animals became pregnant within the next two estrous cycles. Among 15 cows showing a typical alteration at the first examination, 11 (73.3%) cows had the same alteration until the third examination performed after two infertile inseminations following the second examination. When repeat breeder cows with altered EGF profiles (n=26) were given one of four therapeutic treatments, cows in which the EGF profile normalized after treatment had a greater pregnancy rate than those with altered profiles (11/14 animals versus 3/12 animals pregnant; P<0.05). In conclusion, suppressed endometrial EGF concentrations on Days 3 and 14 may be common alterations and persist between estrous cycles in repeat breeder cows. Potential relationship between normalization of the endometrial EGF profile and restoration of fertility was observed. Additional study to confirm results of the treatment is, however, necessary because the present study used a limited number of animals. Nevertheless, current data suggest that normalization of the EGF profile is one of the prerequisite factors to restore fertility.

Expression and Contribution of Three Different Isoforms of Prostaglandin E Synthase in the Bovine Endometrium1

Prostaglandins are involved in the regulation of several reproductive processes such as ovulation, luteolysis, and establishment of pregnancy. Prostaglandin E(2) (PGE(2)) appears to favor establishment of pregnancy in most mammals studied so far. The primary enzymes involved in the production of PGE(2) from arachidonic acid are cyclooxygenases and prostaglandin E synthases (PGES). Three PGES have been identified in humans, but in the bovine, microsomal PGES2 and cytosolic PGES genes have neither been cloned nor associated to any physiological processes. The present study was undertaken to clone bovine MPGES2 and CPGES and to report on their regulation in the endometrium during the estrous cycle. CPGES mRNA expression declines progressively during the cycle; its protein is not modulated according to a precise pattern. MPGES2 mRNA and protein expression decrease from the beginning of the cycle until Days 13-15 and then increase until ovulation. Immunohistochemical analysis reveals that both enzymes are located in luminal epithelial and glandular epithelial cells and at a lower level in stromal cells. In addition, using the bovine endometrial cell line BEND, where higher accumulation of PGE(2) is observed following treatment with phorbol 12-myristate 13-actetate (PMA) and tumor necrosis factor-alpha (TNF-alpha), we have found an associated increase of MPGES1 and COX2 but not CPGES or MPGES2 protein expression. Together, our results suggest that MPGES1 is not the only PGES present in the bovine endometrium but is the main enzyme associated with increased PGE(2) production in vitro.

Pregnancy and Bovine Somatotropin in Nonlactating Dairy Cows: II. Endometrial Gene Expression Related to Maintenance of Pregnancy

The objective was to evaluate the effects of pregnancy and bovine somatotropin (bST) on endometrial gene and protein expression related to maintenance of pregnancy in nonlactating dairy cows at d 17. In endometrial tissues, treatment with bST increased the steady state concentration of oxytocin receptor (OTR) mRNA; bST-treated cyclic (bST-C) cows had greater OTR mRNA than bST-treated pregnant (bST-P) cows. Estradiol receptor alpha (ERalpha) mRNA was reduced in bST-P cows compared with control P and C (no bST) cows. Western blotting revealed that pregnancy decreased the abundance of ERalpha protein, and bST stimulated an increase in ERalpha protein in C and P cows. Treatment with bST increased steady state concentrations of progesterone receptor (PR) mRNA. No differences were detected in steady state mRNA concentrations of prostaglandin H synthase-2 (PGHS-2), prostaglandin E synthase, and prostaglandin F synthase due to pregnancy or bST treatment. However, PGHS-2 protein was increased in response to pregnancy and bST treatment. Immunostaining indicated that P decreased ERalpha protein in luminal epithelium and increased PR protein in epithelial cells of the uterine glands. The PR protein response in the glands was less in bST-P cows than in P cows. In the stromal layer of the endometrium, bST decreased PR protein abundance in C and P cows. The PGHS-2 protein was localized exclusively in the luminal epithelium cells of endometrium and was increased in P cows. In conclusion, distinctly different mRNA and protein responses were detected between C and P cows related to prostaglandin biosynthesis, and bST-induced changes may potentially impact mechanisms associated with maintenance of pregnancy in nonlactating cows.