[Zona pellucida antigens in the human ovum: its importance in contraceptive strategies]

The zona pellucida (ZP) is the extracellular matrix surrounding the mammalian oocyte. This matrix consists of three families called ZP1, ZP2 and ZP3. These proteins suffer several posttraductional modifications to give them different immunological and functional properties. In mice has been demonstrated the important role of ZP3 as a receptor of sperm. In the past, research in this field was limited for the difficulty to get enough biological material from different mammalian species, especially from human sources. Recently, several laboratories have expressed ZP recombinant proteins, allowing the study of the proteins under physiologic and pathophysiological conditions, giving the possibility to utilize ZP as a contraceptive target.

[Vitamin D: implications for health and pregnancy]

Vitamin D gained importance since the discovery of its steroid structure. Vitamin D participates in mineral homeostasis, regulation of gene expression, and cell differentiation. Recent advances in the study of the enzyme involved in the conversion of 25-hydroxyvitamin D3 into 1,25-dihydroxyvitamin D3 (calcitriol), as well as the discovery of it's hormone mechanism of action, have led to a better knowledge and understanding of vitamin D endocrine system, as well as it's implication in health and pregnancy.

The ovary as an immune target

The ovary does not have a distinct morphologic barrier between the immune system and the developing gametes. This is in contrast to the testis in which the junctional complexes between the Sertoli cells form the blood-testis barrier. Whereas there are numerous factors, including genetic ones, associated with ovarian dysfunction, the immune factors have frequently been implicated in ovarian dysfunction. Much of our knowledge used to evaluate the immune system of the ovary has come from studies on the expression of the zona pellucida (ZP) proteins during ovarian development. Initial studies by Dunbar and colleagues demonstrated that immunization of rabbits with porcine ZP proteins (but not rabbit ZP proteins) would result in the generation of antibodies that inhibit sperm binding to the ZP and interfere with normal ovarian follicular development. In contrast to the rabbit and primate models, immunization of mice or rats with porcine ZP proteins does not have an effect on fertility or ovarian function although immunization of certain strains of mice with mouse ZP peptides and immune activator systems has been shown to result in ovarian pathology. Whereas immune inflammatory reactions have been observed in the mouse models, no such immune reactions have been observed in rabbit, guinea pig, or nonhuman primate models. Subsequent observations in nonhuman primates have shown that immunization of primates with ZP proteins expressed from cDNAs coding for the mouse and rabbit ZP2 (the mouse homologue has 60% amino acid identity with human ZP2) or the mouse ZP3 (the mouse protein has 67% amino acid identity with human ZP3) causes ovarian dysgenesis. In contrast, immunization of primates with recombinant rabbit ZP1 protein (the mouse homologue has 39% amino acid identity with human ZP1) does not affect nonhuman primate ovarian function or follicular development but will elicit antibodies that inhibit sperm binding to the primate ZP. These studies have collectively provided important information concerning the immunologic status of the ovary and demonstrate the species variations in immune responses to different ovarian immunogens.

Sex hormone-binding globulin stimulates chorionic gonadotrophin secretion from human cytotrophoblasts in culture

The effects of sex hormone-binding globulin (SHBG) on the secretion of human chorionic gonadotrophin (HCG) and cAMP by cultured human cytotrophoblasts were investigated. Cytotrophoblasts obtained from normal term placentae were cultured in serum-free medium with or without the addition of human SHBG. The presence of SHBG in the medium increased the release of HCG and the accumulation of cAMP. Ligand-free SHBG was able to raise both HCG and cAMP concentrations and the maximal response was observed with 1 nM of the steroid-binding globulin. Addition of either oestradiol or 5alpha-dihydro-testosterone (DHT) to cultures previously incubated with SHBG in a final molar ratio of 1:10 resulted in a further increase of HCG and cAMP concentrations. This effect was blocked when cultured placental cells were exposed to SHBG that was previously saturated with DHT or when incubated in the presence of steroids only. The results of the present study provide evidence for the in-vitro regulation of HCG secretion by SHBG and further support the concept that this steroid-binding protein may act as a mediator of steroid action at the cellular level. Finally, the increase in cAMP suggests that SHBG receptor located in the surface of syncytiotrophoblast membranes is coupled to adenylate cyclase as part of the G-protein receptor family. Our results may provide new insights into the biological implications of extracellular steroid-binding proteins as well as new perspectives on the endocrinology of pregnancy.

A bioactive 60-kilodalton prolactin species is preferentially secreted in cultures of mitogen-stimulated and nonstimulated peripheral blood mononuclear cells from subjects with systemic lupus erythematosus

We have evaluated the production of PRL by human peripheral mononuclear cells (PBMNC) from normal subjects and patients with systemic lupus erythematosus (SLE). Conditioned medium prepared from basal and Con-A-stimulated PBMNC was assessed for the presence of PRL-like by its ability to stimulate growth of PRL-responsive Nb2 rat lymphoma cells. In the presence or absence of Con-A, SLE PBMNC secrete significantly higher (P < 0.001) amounts of bioactive PRL-like species than normal cells. Growth of Nb2 cells by conditioned medium was inhibited with specific antiserum to human PRL. Western blotting using a polyclonal antibody to human PRL revealed a single 60-kDa PRL-like species in both normal and SLE PBMNC extracts, the immunoreactivity of which was preferentially found in SLE subjects. With the use of reverse transcription-PCR an expected 633-bp band was observed, and its similarity to pituitary PRL was further confirmed by Southern blot analysis with human PRL complementary DNA as a probe. We conclude that a high molecular mass PRL-like species is synthesized and secreted by PBMNC, and patients with SLE have an increased secretion of lymphocyte-derived PRL-like material.

Biologically active steroid and thyroid hormones stimulate secretion of sex hormone-binding globulin by human term placenta in culture

In this study, the influence of steroid and thyroid hormones and epidermal growth factor on the production of SHBG by placental tissue explants was investigated. Explants of trophoblastic tissue obtained from normal term placentas were cultured for 48 h in serum free culture medium, and then for an additional 24 h period in the presence or absence of various concentrations of either estradiol (0.25-5 nM), testosterone (0.5-500 nM), triiodothyronine (0.01-100 nM) or EGF (2-40 microM), respectively. Human SHBG concentration in culture media was estimated on each day by specific two-site time-resolved fluoroimmunometric assay and the results expressed as pmol/mg tissue protein. Binding characteristics and molecular structure of secreted SHBG were determined by [3H]5 alpha-DHT binding assays and Western blot analysis, respectively. Estradiol and triiodothyronine but not testosterone increased significantly (p < 0.05 vs. control) the secretion of SHBG into the culture media. Addition of EGF did not significantly change the production of SHBG at the various concentrations studied. [3H] 5 alpha-DHT binding assays and Western blot analysis of placental SHBG resulted in identical binding affinities (Kd 2.0 +/- 0.16 x 10(-9)M) and molecular structure to those obtained in serum from normal pregnant women. These findings support and extend previous observations by our laboratory indicating that SHBG gene is expressed in the placenta and provide further evidence on the hormonal regulatory characteristics of this steroid-binding protein in cultured placenta.

Genetic variations in human testosterone-estradiol binding globulin

The human testosterone-estradiol-binding globulin (hTeBG) is a plasma heterogeneous glycoprotein with high affinity for a number of circulating steroid hormones. The heterogeneity originates from differential glycosylation of a common protein precursor. Analysis of desialylated hTeBG by isoelectric focusing (IEF) has revealed that microheterogeneity could be partly attributed to variability in sialic acid content or rearrangement of amino acid composition. We have studied this possibility by the analysis of desialylated serum hTeBG by Western blotting of proteins previously separated on IEF-gels. Two distinct well-defined IEF patterns were identified. The most frequent consisted of two major IEF-bands of equal color intensity. The other pattern consisting of four IEF-bands was present in only 5.55% of the total serum samples analyzed. Family studies showed that these phenotypes were autosomally inherited with a simple Mendelian transmission and allele frequencies had an excellent agreement between the observed and expected phenotypes. Androgen affinity constants and serum concentrations of hTeBG variant were similar to those of normal hTeBG. Molecular analyses of each of the exons of hTeBG gene by denaturing gradient gel electrophoresis revealed the presence of a point mutation in exon 8. The studies presented herein confirm and extend previous reports on the existence of structural variants of hTeBG. In addition, the mutation reported in this study is probably the same as that recently identified within numerous ethnic groups throughout the world, thus further supporting the concept of a two allele gene worldwide concoding hTeBG.

Molecular characterization of a genetic variant of the steroid hormone-binding globulin gene in heterozygous subjects

Steroid hormone-binding globulin in human serum displays different isoelectric focusing (IEF) patterns among individuals, suggesting genetic variation in the gene for this extracellular steroid carrier protein. Analysis of allele frequencies and family studies suggested the existence of two codominant alleles of the gene. Subsequent determination of the molecular basis of a variant of the gene was carried out using DNA from homozygous individuals from a single Belgian family. It was of interest to characterize other variant individuals to determine whether all variants identified by IEF phenotyping were caused by the same mutation or whether other mutations occurred in the gene in different populations. Previous studies identified Mexican subjects who were heterozygous for the variant IEF phenotype. Denaturing gradient gel electrophoresis was used to localize the mutation in these subjects and to purify the variant allele for DNA sequence analysis. The results show that the mutation in this population is identical to that identified in the Belgian family, and no other mutations were detected in the gene. These data represent the first analysis of steroid hormone-binding globulin gene variation in heterozygous subjects and further support the conclusion of biallelism of the gene worldwide.

Evidence that human placenta is a site of sex hormone-binding globulin gene expression

The presence of an androgen-binding component in placenta was investigated in vitro using a tissue culture system of human placental explants. Explants of trophoblastic tissue from normal term placentas were kept in culture under appropriate conditions for at least 48 h in a serum-free medium. The existence of an androgen-binding protein was explored by binding assays, immunohistochemistry studies and Northern blot analyses of placental mRNA. Steady-state polyacrylamide gel electrophoresis and Scatchard plot analyses revealed the presence of a high affinity specific binding component for 5 alpha-dihydrotestosterone in cultured placenta. Immunohistochemical studies performed on intact placenta and on Percoll-gradient purified trophoblastic cells demonstrated the presence of specific immunoreactivity in the cytoplasm of syncytial cells. Northern blot analyses of placental mRNA showed a single hybridizable 32P-labeled human sex hormone-binding globulin (SHBG) cDNA band of approx. 1.6 kb which was identical in size to that obtained with liver mRNA. The results strongly suggest the placenta as an origin of SHBG and point out this tissue as an additional site of SHBG synthesis during pregnancy.

Prolactin size variants during pregnancy in women with ovulatory hyperprolactinemia: characterization by isoelectric focusing and lectin affinity chromatography

Previous studies from this laboratory have demonstrated the occurrence of important changes in PRL size heterogeneity in women with ovulatory hyperprolactinemia during gestation. A similar observation has been made, in normal women, for glycosylated PRL, which shows a progressive decrease as pregnancy progresses. In this study we decided to investigate the contribution of G-PRL on PRL heterogeneity throughout gestation in women with ovulatory hyperprolactinemia. Serum samples obtained throughout gestation were analysed by SDS-PAGE followed by immunoblotting and by isoelectric focusing of gels as well. The results indicated that, independent of the stage of pregnancy, the relative amounts of G-PRL as compared with the nonglycosylated form of the hormone remained quite constant. In addition, isoelectric focusing analyses of serum samples consistently resulted in an identical isoelectric point of PRL throughout all of the gestational period. These results suggested that changes in the relative proportions of PRL size species during pregnancy were not correlated with the degree of PRL glycosylation. Moreover, these observations further extended and supported the concept that the occurrence of PRL size heterogeneity depends mainly on thiol-disulfide interchange mechanisms, among PRL molecules, at the pituitary level.