Binding of immunoglobulins to the major progesterone-induced proteins secreted by the sheep uterus

Proteomic analysis of amniotic and allantoic fluid from buffaloes during foetal development

The objective of this study was to describe the dynamic changes in protein composition and protein abundance in amniotic and allantoic fluids from buffaloes during gestation. Amniotic and allantoic fluids were collected during the first, second and third trimesters of gestation. The foetuses were measured and weighed. Fluid samples were centrifuged at 800 g for 10 min and then at 10,000 g for 60 min at 4°C. The supernatant was collected to determine the total protein concentration. Based on total protein concentration, an aliquot (50 μg) was used for in-solution tryptic digestion, and mass spectrometry analysis (nano-LC-MS/MS) was performed. A multivariate statistical analysis of the proteomic data was conducted. Across the different stages of buffalo gestation, fifty-one proteins were found in the amniotic fluid, and twenty-one were found in the allantoic fluid. A total of twelve proteins were common among the stages, and four presented significant differences (VIP score α > 1). Fibronectin and alpha-1-antiproteinase were more abundant in the amniotic fluid than in the allantoic fluid. Alpha-2-macroglobulin and alpha-2-HS-glycoprotein were more abundant in the allantoic fluid than in the amniotic fluid. Alpha-2-macroglobulin participates in remodelling and growth of the uterus at beginning of the gestation (first trimester), and these findings indicate that can serve as a potential tool for the early diagnosis of pregnancy in buffaloes.

Characterization of the cervical mucus plug in mares

The cervical mucus plug (CMP) is believed to play an integral role in the maintenance of pregnancy in the mare, primarily by inhibiting microbial entry. Unfortunately, very little is known about its composition or origin. To determine the proteomic composition of the CMP, we collected CMPs from mares (n = 4) at 9 months of gestation, and proteins were subsequently analyzed by nano-LC–MS/MS. Results were searched against EquCab2.0, and proteomic pathways were predicted by Ingenuity Pathway Analysis. Histologic sections of the CMP were stained with H&E and PAS. To identify the origin of highly abundant proteins in the CMP, we performed qPCR on endometrial and cervical mucosal mRNA from mares in estrus, diestrus as well as mares at 4 and 10 m gestation on transcripts for lactotransferrin, uterine serpin 14, uteroglobin, uteroferrin, deleted in malignant brain tumors 1 and mucins 4, 5b and 6. Overall, we demonstrated that the CMP is composed of a complex milieu of proteins during late gestation, many of which play an important role in immune function. Proteins traditionally considered to be endometrial proteins were found to be produced by the cervical mucosa suggesting that the primary source of the CMP is the cervical mucosa itself. In summary, composition of the equine CMP is specifically regulated not only during pregnancy but also throughout the estrous cycle. The structural and compositional changes serve to provide both a structural barrier as well as a physiological barrier during pregnancy to prevent infection of the fetus and fetal membranes.

Expression and Properties of Recombinant Ovine Uterine Serpin

Ovine uterine serpin (OvUS) is produced in the uterus of sheep under the influence of progesterone. It weakly inhibits pepsin and reduces proliferation of lymphocytes, tumor cell lines, and preimplantation embryos. When purified from uterine fluid, the concentration required for its antiproliferative effect in vitro is ~0.25–1 mg/ml. Here we show that recombinant (r) OvUS is a more potent regulator of cell proliferation than native (n) OvUS purified from uterine fluid. To produce rOvUS, RNA was extracted from endometrium from a pregnant ewe and cDNA was amplified by reverse transcription-polymerase chain reaction using gene-specific primers. The purified OvUS cDNA was inserted into the ampicillin-resistant plasmid vector pcDNA3.1/V5-His-TOPO. The plasmid was introduced into the TOP10 Escherichia coli strain, purified, and used for transfection of Freestyle 293-F cells. Digestion of rOvUS with protein N-glycosidase F confirmed that rOvUS was N-glycosylated. Both rOvUS and nOvUS inhibited proliferation of phytohemagglutin-activated sheep lymphocytes and the P388D1 mouse lymphoma and PC-3 prostate cell lines. Inhibition was greater for rOvUS than for nOvUS, and concentrations as low as 15 μg/ml rOvUS were effective at reducing lymphocyte proliferation. Addition of rOvUS to fertilized bovine embryos reduced the cleavage rate and the percentage of embryos that became blastocysts. Native OvUS did not affect cleavage rate and had a smaller effect on development to the blastocyst stage. Experiments demonstrate that OvUS is a more potent inhibitor of cell proliferation and embryonic development than previously believed and add credence to the putative role for the protein in regulating cell proliferation.

Crosstalk between uterine serpin (SERPINA14) and pregnancy-associated glycoproteins at the fetal-maternal interface in pregnant dairy heifers experimentally infected with Neospora caninum

Infection with Neospora caninum is the leading cause of abortion in cattle. In cows naturally infected with N caninum, plasma concentrations of pregnancy-associated glycoproteins (PAG) 1 and 2 indicate fetal-placental well-being, whereas an excess of progesterone in the second trimester of gestation has been related to high abortion rate. The immunosuppressive action of progesterone on the uterus during gestation has been attributed in part to the uterine serpins (SERPINA14). This study examines expression patterns of the genes SERPINA14, PAG, and PAG2 at the fetal-maternal interface in dairy heifers experimentally infected with N caninum during the second trimester of pregnancy, when most abortions takes place in natural conditions. Irrespective of infection, expression of SERPINA14 was higher, and expression of PAG1 and PAG2 lower, for intercaruncular endometrium than for caruncles or cotyledons. Cotyledonary tissues showed the highest expression of both PAG genes but lowest expression of SERPINA14. The expression of SERPINA14 was significantly higher in intercaruncular endometrium of control dams than for infected animals, pointing to potential disruption of modulation of maternal immune function during infection. Dramatically reduced SERPINA14 was particularly apparent in infected dams with aborted fetuses. There was also a negative association between N caninum antibody titers with SERPINA14 and PAG expression in infected animals, further suggesting that N caninum infection downregulates the uterine immunosuppressive function of SERPINA14.

Evolution and function of the uterine serpins (SERPINA14)

Uterine serpins (recently designated as SERPINA14) are hormonally induced proteins secreted in large quantities by the endometrial epithelium during pregnancy. The SERPINA14 proteins belong to the serine proteinase inhibitor (serpin) superfamily, but their apparent lack of inhibitory activity toward serine proteinases suggests that these proteins evolved a different function from the anti-proteinase activity typically found in most members of the serpin superfamily. The gene is present in a limited group of mammals in the Laurasiatheria superorder (ruminants, horses, pigs, dolphins and some carnivores) while being absent in primates, rodents, lagomorphs and marsupials. Thus, the gene is likely to have evolved by gene duplication after divergence of Laurasiatheria and to play an important role in pregnancy. That role may vary between species. In sheep, SERPINA14 probably serves an immunoregulatory role to prevent rejection of the fetal allograft. It is inhibitory to lymphocyte proliferation and natural killer cell function. In the pig, SERPINA14 is involved in iron transport to the fetus by binding to and stabilizing the iron-binding protein uteroferrin. It is possible that SERPINA14 has undergone divergence in function since the original emergence of the gene in a common ancestor of species possessing SERPINA14.

Antiproliferative Actions of Ovine Uterine Serpin

PROBLEM

Ovine uterine serpin (OvUS) is a member of the serine proteinase inhibitor superfamily and is the major protein produced by luminal and glandular epithelium of the sheep endometrium during mid to late pregnancy. The protein does not have prototypical proteinase inhibitory activity but can inhibit a wide variety of lymphocyte functions such as mitogen-induced proliferation and natural killer cell cytotoxicity.

METHOD OF STUDY

The antiproliferative actions of OvUS were studied.

RESULTS

It was demonstrated that, in addition to inhibiting lymphocyte proliferation, OvUS inhibits growth of two tumor cell lines (D17 and PC-3). The protein also interrupts development of pre-implantation embryos. Inhibition of cell proliferation is not universal, however, as OvUS did not inhibit growth of two non-tumorigenic cell lines (MDBK and BEND). The mechanism of action of inhibitory effects of OvUS is not known although experiments with inhibitors of protein kinase A indicate that the protein does not inhibit lymphocyte proliferation through this pathway. Moreover, the protein does not induce apoptosis.

CONCLUSIONS

The finding that OvUS has antiproliferative activity is demonstrative of the wide range of functions exerted by members of the serpin superfamily. The antiproliferative property of OvUS may reflect the role of the protein during pregnancy and may be exploitable for design of new antiproliferative drugs.

Binding of ovine uterine serpin to lymphocytes

PROBLEM

The endometrium of the sheep produces a progesterone-induced member of the serpin superfamily of serine proteinase inhibitors that can inhibit lymphocyte proliferation and reduce natural killer cell activity. Present results indicate that this molecule, called ovine uterine serpin (OvUS), can bind specifically to lymphocytes.

METHOD OF STUDY/RESULTS

Biotinylated OvUS bound to peripheral blood lymphocytes in a dose-dependent and saturable manner. Binding was inhibited by OvUS, but not by several other proteins, including serpin-enzyme complex (alpha 1-antitrypsin-trypsin). Heparin blocked binding when added to the binding reaction or when used to pretreat lymphocytes. Both lymphocytes and Madin-Darby bovine kidney (MDBK) cells also bound fluorescein isothiocyanate-labeled OvUS.

CONCLUSIONS

Results suggest that OvUS can interact with lymphocytes and other cells through binding to a cell surface molecule. Such binding may indicate that inhibition of lymphocyte activation by OvUS involves 1) binding of OvUS to a cell surface receptor or 2) competitive inhibition of binding between OvUS and a co-activation molecule required for lymphocyte activation.

Progesterone-regulated secretion of the serpin-like proteins of the ovine and bovine uterus

The uterine milk (UTM) proteins are the major progesterone-regulated proteins secreted by the sheep uterus during pregnancy. Recently, proteins related to the UTM proteins have been identified in uterine secretions of the pregnant cow and sow. The present objective was to determine the time course for induction of the UTM proteins in sheep and cattle. Twelve ovariectomized ewes received subcutaneous injections of either vehicle for 10 days or 100 mg/d of progesterone for 10 days or 30 days. The presence of UTM proteins was examined by Western blotting of uterine flushings and by immunoabsorption of radiolabeled UTM proteins from conditioned medium of endometrial explant cultures performed with [35S]methionine precursor. Uterine milk proteins were present in slight amounts in uterine flushings and endometrial-conditioned culture medium of some ewes in the control group, but amounts of proteins were greatly enhanced by progesterone after 10 or 30 days of treatment. Prolonged exposure to progesterone (30 days versus 10 days) increased amounts of UTM proteins. Immunohistochemical analysis of endometrium indicated that the major site of UTM proteins was the glandular epithelium. In the second experiment, nine ovariectomized cows were treated daily with vehicle for 12 days or 750 mg progesterone for 12 or 30 days. Uterine flushings and conditioned endometrial culture medium were examined for UTM proteins by Western blotting. Uterine milk proteins were present to some degree in cows treated with vehicle, and an enhancement in amounts of UTM proteins was not observed until after 30 days of progesterone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Uterine secretions of the cow contain proteins that are immunochemically related to the major progesterone-induced proteins of the sheep uterus

Proteins that cross-react with antiserum to the major progesterone-induced proteins found in the pregnant sheep uterus, the uterine milk proteins (UTM-proteins), were detected as radiolabelled secretory products of endometrium from pregnant cows. Cross-reactive proteins included a form at 57,000 molecular weight as well as other lower-molecular-weight variants found in lower amounts. Similar proteins were also detected in uterine fluid from a cow at day 270 of gestation. Using immunohistochemical procedures, proteins that cross-reacted with antiserum to sheep UTM-proteins could be localized to the epithelial cells of endometrial glands in the cow. Results indicate that UTM-protein-like molecules are secreted by the endometrium of the cow during pregnancy.

Secretion of the major progesterone-induced proteins of the sheep uterus by caruncular and intercaruncular endometrium of the pregnant ewe from days 20-140 of gestation

An experiment was performed to evaluate the types and quantity of proteins secreted by intercaruncular endometrium at days 20, 60, 100 and 140 of gestation and caruncular endometrium from days 100 and 140 of gestation. Tissues were obtained from ewes made unilaterally pregnant. Based on SDS polyacrylamide gel electrophoresis (SDS-PAGE), the major proteins present in uterine fluid at days 60-140 of gestation were the uterine milk proteins (UTM-proteins), a pair of structurally-related, progesterone-induced polypeptides with molecular weights of 55,000 and 57,000. These proteins were also present in uterine fluid at day 20, but the major protein at this time migrated coincident with albumin. Cultured explants of endometrium at all days of pregnancy produced UTM-proteins as their major radiolabelled product for both caruncular and intercaruncular endometrium. The amount of protein secretion in vitro was greater (P less than .04) for intercaruncular endometrium than for caruncular endometrium but was not significantly affected by stage of gestation or local presence of the conceptus. Immunohistochemical analysis revealed that UTM-proteins were present in glandular and luminal epithelium of intercaruncular endometrium and in both epithelial and stromal elements of caruncular endometrium. It was concluded that the UTM-proteins are produced earlier than previously described (i.e., day 20). In addition, caruncles contribute to the uterine secretory protein milieu through the secretion of proteins that are similar to that produced by the glandular intercaruncular epithelium.