Immunochemical detection, physicochemical characterization and levels of pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG) in seminal plasma of men

Endometrial protein PP14: a new test of endometrial function?

The human endometrium produces a number of proteins which are at least partly specific to that tissue. Two of these proteins have been the subject of much recent work. They were originally called ‘placental protein 12’ and ‘placental protein 14’ (PP12 and PP14) because they were isolated by Hans Bohn from extracts of whole placentae. However, it is now clear that they arise from the maternal endometrium (decidua) rather than the fetal trophoblast. Placental protein 12 has been shown to be identical to the insulin-like growth factor binding protein-1 (IGFBP-1). It is produced in many normal tissues and its measurement probably does not provide a specific index of endometrial function. By contrast, PP14 is detectable only in ‘reproductive’ tissues and, in theory, might be an excellent clinical test of endometrial function.

Roles of glycodelin in modulating sperm function

Glycodelin is a glycoprotein with three well-defined isoforms. They are named as glycodelin-S, glycodelin-A and glycodelin-F. The three isoforms have similar protein core but different carbohydrate moieties. Glycodelin-S is abundant in the human seminal plasma. It suppresses sperm capacitation and in doing so, it maintains the spermatozoa in an uncapacitated state before they enter into the uterine cavity. Glycodelin-A is abundant in the amniotic fluid. It is also secreted from endometrial glands into uterine fluid and is produced by the fallopian tube. Glycodelin-A is the first endogenous glycoprotein that was found to inhibit the binding of spermatozoa to the zona pellucida. The immunosuppressive properties of glycodelin-A suggest that the molecule may protect the spermatozoa from immune attack in the maternal reproductive tract. Glycodelin-F was first found in the follicular fluid, hence its name. It also inhibits spermatozoa-zona pellucida binding. In addition, glycodelin-F suppresses progesterone-induced acrosome reaction, and may serve to prevent premature acrosome reaction. Preliminary findings suggest possible presence of yet another glycodelin isoform in the extracellular matrix of cumulus oophorus. Unlike glycodelin-A and -F, it stimulates spermatozoa-zona pellucida binding. In summary, different isoforms of glycodelin have different biological roles on sperm function, and they act in succession to contribute to the success of fertilization.

Glycodelin: a major lipocalin protein of the reproductive axis with diverse actions in cell recognition and differentiation

Glycodelin is a glycoprotein that belongs to the lipocalin superfamily. Depending on glycosylation, glycodelin appears in various isoforms. In the uterus, glycodelin-A is the major progesterone-regulated glycoprotein secreted into uterine luminal cavity by secretory/decidualized endometrial glands. The other tissues expressing glycodelin include fallopian tubes, ovary, breast, seminal vesicle, bone marrow, and eccrine glands. Glycodelin-A potently and dose-dependently inhibits human sperm-egg binding, whereas differently glycosylated glycodelin-S from seminal plasma has no such effect. Absence of contraceptive glycodelin-A in the uterus during periovulatory midcycle is consistent with an open "fertile window." Glycodelin induced by local or systemic administration of progestogens may potentially reduce the fertilizing capacity of sperm in any phase of the menstrual cycle. Glycodelin also has immunosuppressive activity. Its high concentration at the fetomaternal interface may contribute to protection of the embryonic semiallograft. Besides being an epithelial differentiation marker, glycodelin appears to play a role in glandular morphogenesis, as transfection of glycodelin cDNA into a glycodelin-negative breast cancer cells resulted in formation of gland-like structures, restricted proliferation, and induction of other epithelial markers. These various properties, as well as the chemistry, biology, and clinical aspects of glycodelin, continue to be areas of active investigation reviewed in this communication.

Glycodelins

Glycodelin is a major glycoprotein that is synthesized in the endometrium in response to progesterone and relaxin exposure. Endometrium-derived glycodelin-A has contraceptive and immunosuppressive properties. Glycodelin is absent from the endometrium during the fertile periovulatory phase, but is synthesized in this tissue during the peri-implantation phase and is abundant during the last week of the luteal phase. Changes in local and/or circulating glycodelin concentrations have been observed in women with reproductive disorders. The chemical modification of glycodelins has resulted in compounds with antiviral activity.

Monoclonal antibodies to human secretory "pregnancy-associated endometrial alpha 1-globulin," an insulin-like growth factor binding protein: characterization and use in radioimmunoassay, Western blots, and immunohistochemistry

Monoclonal antibodies were raised against pregnancy-associated endometrial alpha 1-globulin (alpha 1-PEG), a 32 KD insulin-like growth factor binding protein (IGF-BP), which represents a major secretory product of the human decidualized endometrium during pregnancy. This class of IGF-BP has been implicated in the modulation of action, inhibitory and stimulatory, of insulin-like growth factors. Immunization with the protein purified from pregnancy endometrium resulted after myeloma fusion in the isolation of six hybridoma clones and the antibodies produced were characterized. The Ka of the antibodies ranged between 4.75 x 10(9) M-1 and 0.7 x 10(8) M-1. In Western blots all monoclonal antibodies reacted with purified protein of molecular weight 32 KD and specifically detected this IGF-BP species in culture medium and cytosolic extracts of pregnancy endometrium and amniotic fluid. The monoclonal antibodies appear to define three epitope-bearing regions as evidenced by their reactivity to polypeptide fragments of the protein. After synthesis and secretion by tissue explants in vitro the protein is susceptible to cleavage into fragments possessing different monoclonal antibody-defined reactivity. Employing immunohistochemical techniques the protein was principally localized to decidual cells in tissue sections of pregnancy endometrium and solely to these cells after enzymic digestion of the tissue. The implications of these results are discussed with respect to potential role of IGF-BP in the action of IGF upon the IGF-1 receptor-bearing populations, including lymphocytes and trophoblast cells, D in the decidua.

Secretory proteins of the endometrium--potential markers for endometrial dysfunction

In contrast to our detailed knowledge of endometrial structure, the study of endometrial function is still in its infancy. It seems likely that most of the changes that occur in the endometrium during the cycle are directed towards the promotion of implantation, and that the proteins secreted by the tissue have a role to play in the maintenance of pregnancy. One approach to the study of these proteins has been the incubation of endometrium in vitro with labelled amino acid precursors, and this method has revealed that in early pregnancy two proteins are quantitatively more important than the others synthesized and secreted by the endometrium. One of these proteins is a homologue of beta-lactoglobulin, also known as alpha 2-PEG, PP14 or PEP. It is synthesized by endometrial glands and no other source has been identified. Its synthesis is induced in the luteal phase of the menstrual cycle, rises to a peak in the early weeks of pregnancy and then rapidly declines as the decidua spongiosa is replaced by decidua compacta. The direction of its secretion appears to be into the amniotic fluid, and its function may be to transport a vitamin or other essential substance to the early conceptus: another possible function is immunosuppression. The protein can be measured in peripheral blood and may be useful as a marker of the effect of progesterone-or its lack of effect, as in the inadequate luteal phase. The other quantitatively important endometrial protein is IGF binding protein, which is produced mainly by stromal fibroblasts in the late luteal phase of the cycle. During the cycle the contribution of the endometrium to serum levels of IGF-BP is slight, but in pregnancy, as the amount of decidua compacta increases, levels in peripheral blood rise, with peaks at 18-24 weeks and at 36-40 weeks. The function of the protein may be to protect the mother by inhibiting IGF, or to enable IGF to stimulate the growth of endometrial stroma. Links between this protein and disorders of fetal growth have been suggested. The diversity of the possible functions of these proteins, and the continuing uncertainty over their roles, underline the complexity of endometrial functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Two fetal antigens (FA-1 and FA-2) and endometrial proteins (PP12 and PP14) isolated from amniotic fluid; preliminary observations in fetal and maternal tissues

Rabbit antihuman antibodies were derived by the injection of fractions of second trimester amniotic fluid known to contain proteins of endometrial/decidual origin. Using standard separation and absorption procedures, two antibody preparations were generated which demonstrated specificities against two and three proteins, respectively, in line immunoelectrophoresis and crossed immunoelectrophoresis. Analysis against proteins of fetal, maternal, endometrial and placental origin revealed that the bispecific antiserum reacted only with placental protein 14 (PP14; also known as progestagen-dependent endometrial protein, PEP) and one other hitherto undescribed antigen referred to as Fetal Antigen 1 (FA-1) molecular mass 60 kDa; electrophoretic mobility: slow; alpha 1-alpha 2; fast, albumin. The trispecific antiserum demonstrated specifities against placental protein 12 (PP12), alpha-fetoprotein (AFP) and another previously undescribed antigen referred to as Fetal Antigen 2 (FA-2) molecular mass 35 and 140 kDa; electrophoretic mobility: albumin. Following purification, monospecific antisera against each of these proteins (with the exception of AFP) were derived in new rabbits. Maternal and fetal blood, amniotic fluid and aqueous extracts from endometrial/decidual and placental tissues were analysed in rocket immunoelectrophoresis using these antisera to examine the distribution in these tissues. The analyses demonstrated a pattern of distribution typical for proteins of endometrial/decidual origin in these compartments in the case of PP12 and PP14, but suggested that the primary source of origin of FA-1 and FA-2 may be the fetus.

Detection and characterization of human secretory "pregnancy-associated endometrial alpha 2-globulin" in uterine luminal fluid

Pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG), the major secretory protein of the human endometrium as assessed by in vitro de novo synthesis and secretion, during the mid- to late-luteal phase of the menstrual cycle and early first trimester pregnancy, has now been detected immunochemically in uterine luminal flushings during the luteal phase of the menstrual cycle. Physicochemical characterization of this immunoreactive alpha 2-PEG demonstrated that it exhibited identical properties to the protein isolated from either the cytosol of pregnancy endometrium or medium from in vitro cultures of pregnancy endometrium, i.e. native Mr 56 K, subunit Mr 28 K, eluted from an anion exchange column at 0.11 M NaCl and bound to concanavalin A. These findings, together with other evidence, suggest that a major route of secretion of alpha 2-PEG during the luteal phase of the menstrual cycle in vivo is into the lumen of the uterus. These results are discussed with reference to the hypothesis that alpha 2-PEG, derived from the endometrial glandular epithelium, may represent the human functional analogue of uteroglobin and to the implications for the human of the hypothesized immunosuppressive role of uteroglobin and transglutaminase (Factor XIII) in masking Class I MHC antigens on gametes and the conceptus.