Subcellular distribution of native estrogen receptor alpha and beta isoforms in rabbit uterus and ovary

The association of estrogen receptors with non-nuclear/cytoplasmic compartments in target tissues has been documented. However, limited information is available on the distribution of estrogen receptor isoforms, specially with regard to the newly described beta isotype. The subcellular localization of estrogen receptor alpha and beta isoforms was investigated in rabbit uterus and ovary. Native alpha and beta subtypes were immunodetected using specific antibodies after subjecting the tissue to fractionation by differential centrifugation. The ovary expressed alpha and beta estrogen receptors in predominant association to cytosolic components. However, in the uterus, a substantial proportion of the total estrogen binding capacity and coexpression of the two isoforms was detected in mitochondria and microsomes. The mitochondrial-enriched subfraction represented an important source of 17beta-estradiol binding, where the steroid was recognized in a stereospecific and high affinity manner. The existence of mitochondrial and membrane estrogen binding sites correlated with the presence of estrogen receptor alpha but mainly with estrogen receptor beta proteins. Using macromolecular 17beta-estradiol derivatives in Ligand Blot studies, we could confirm that both alpha and beta isoforms were expressed as the major estrogen binding proteins in the uterus, while estrogen receptor alpha was clearly the dominant isoform in the ovary. Other low molecular weight estrogen receptor alpha-like proteins were found to represent an independent subpopulation of uterine binding sites, expressed to a lesser extent. This differential cellular partitioning of estrogen receptor alpha and beta forms may contribute to the known diversity of 17beta-estradiol effects in target organs. Both estrogen receptor alpha and beta expression levels and cellular localization patterns among tissues, add complexity to the whole estrogen signaling system, in which membrane and mitochondrial events could also be implicated.     

Expression and cellular localization of naturally occurring beta estrogen receptors in uterine and mammary cell lines

The protein ER-alpha has been exhaustively characterized in estrogen-sensitive tissues and cell lines. However, little is known regarding the expression and cellular distribution of the newly identified ER-beta protein. We first quantified the specific estradiol binding site content in the estrogen-responsive cell lines MCF-7 (mammary) and SHM (myometrial). In the two cell types, these sites were associated to the expression of both ER-alpha and -beta isoforms. Native ER-beta was visualized to reside inside the nucleus by means of conventional indirect immunofluorescence. The cells expressed ER-beta as a tight approximately 50 kDa triplet when resolved by sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE) and blotted using antibodies mapping different domains of the cloned ER-beta version. When the cells were subjected to homogenization and differential centrifugation, a substantial proportion of ER-beta immunolabeling was localized at membrane subfractions. ER-beta expression and partitioning was confirmed by Ligand blotting assays using estrogen derivatives coupled to different macromolecular tags. However, ER-alpha was expressed as the major estrogen binding protein in both cell lines. Similar localization experiments were performed on HeLa cells (cervix). Though usually considered ER-negative, this cell line displayed basal significant estrogen binding capacity and co-expression of both ER isoforms. Taken as a whole, the results indicate that ER-beta could be expressed as functional estrogen binding proteins among a dominant population of ER-alpha sites in the cell lines under study.     

Steroid hormones acutely regulate expression of a Nudix protein-encoding gene in the endometrial epithelium of sheep

Steroid hormones regulate endometrial gene expression to meet the needs of developing embryos. Our hypothesis is that steroid hormones transiently induce expression of genes in the endometrial epithelium to make the uterine environment different between the earliest days of pregnancy. We identified one such gene product using differential display-polymerase chain reactions. The gene product that was strongly induced in ewes between day 3 and 6 of the estrous cycle was cloned and sequenced to identify it as encoding a member of the Nudix family of hydrolase enzymes. Northern blot analyses indicated that NUDT16 mRNA concentrations were elevated 10-fold in the endometrium of sheep from day 5 to 9 of the estrous cycle and returned to basal levels by day 11. In assays of RNA samples from 15 different tissues from an adult ewe, the concentrations of NUDT16 mRNA were greatest in endometrium. In situ hybridization localized NUDT16 mRNA exclusively to the endometrial epithelial cells of the glands and uterine lumen. In ovariectomized ewes, NUDT16 mRNA was induced by a regimen of alternating estrogen and progesterone therapy designed to mimic the hormonal experiences of a ewe at day 6 of the estrous cycle. The final estrogen treatment in the regimen was critical to the expression of NUDT16 as well as progesterone receptor and estrogen receptor-beta genes. Characterization of the NUDT16 gene identified putative steroid hormone response elements, which can now be investigated to understand its unique pattern of regulation in the earliest days of pregnancy.     

Peroxisome proliferator-activated receptor gamma agonists inhibit adipocyte expression of alpha1-acid glycoprotein

alpha1-Acid glycoprotein (alpha1-AGP) is an acute phase protein that can potentiate cytokine secretion by mononuclear cells and may induce thrombosis by stabilizing the inhibitory activity of plasminogen activator inhibitor-1. Thus, alpha1-AGP may promote pathobiologies associated with type 2 diabetes mellitus (T2DM) including insulin resistance and cardiovascular disease. Here, we demonstrate that antidiabetic peroxisome proliferator-activated receptor gamma (PPARgamma) agonists inhibited expression of 3T3-L1 adipocyte alpha1-AGP in a concentration- and time-dependent manner via an apparent PPARgamma-mediated mechanism. As a result, synthesis and secretion of the glycoprotein was reduced. While PPARgamma agonist regulation of genes with functional peroxisome proliferator response elements in their promoter such as phosphoenolpyruvate carboxykinase were unaffected when cellular protein synthesis was inhibited, downregulation of alpha1-AGP mRNA was ablated thereby supporting the proposition that PPARgamma activation inhibits alpha1-AGP expression indirectly. These results suggest a potential novel adipocytic mechanism by which PPARgamma agonists may ameliorate T2DM-associated insulin resistance and cardiovascular disease.     

Analysis in vitro of uterine estrogen receptor conformation of young and old rats

The conformation of estrogen receptor (ER) and its in vitro transformation by RNase, Urea and ATP were analysed using the uteri of young (16 weeks) and old (92 weeks) rats. Following the digestion of ER with proteolytic enzymes like trypsin and chymotrypsin and the analysis of cleaved fragments by SDS-PAGE, similar pattern is observed in both ages. In vitro transformation of ER by RNase, Urea and ATP shows that the degree of transformation is lower in old than young. Furthermore, the transformed ER from old is less capable of binding to DNA than that from young. Thus our results show that the conformation of ER probably does not change with age, but the degree of transformation and the ability of transformed receptor to bind to DNA decrease with age.     

Lymphocyte number and distribution in the rat uterine epithelium during estrous cycle and early pregnancy

Summary The number of intraepithelial lymphocytes (IEL) in the luminal and glandular epithelium of the uterus of virgin rats was analysed in diestrus, proestrus and estrus, and in nulliparous rats on days 5, 7 and 9 of pregnancy. IEL number was calculated either with respect to the number of epithelial cells or to the length of epithelium section. It was found that in diestrus, the number of IEL was, on average, 3.7 per 100 luminal epithelial cells or 6.7 per 1 mm of epithelium section, whereas in proestrus, it decreased to 0.9 and 1.2 IEL, respectively. On day 5 of pregnancy (before implantation) the number of IEL decreased further to 0.45 per 100 luminal epithelial cells or 0.9 per 1 mm of epithelium. On days 7 and 9 of pregnancy, IEL number further decreased in implantation sites, whereas in interimplantation sites it remained at the level calculated for day 5 of pregnancy. The population of uterine IEL consisted of small (82–99%) and large (1–18%) lymphocytes. In all stages of the estrous cycle, IEL occurred with a frequency of 68–87% in the basal region, 8–20% in the middle region and 4–12% in the apical region of the luminal epithelium width.     

Immunohistochemical detection of the retinoid acid receptors (RXR-alpha, -beta, -gamma) and Farnesoid X-activated receptor (FXR) in the marbled newt along the annual cycle

Retinoid acid receptors (RXR-alpha, -beta, -gamma) and Farnesoid X-activated receptor (FXR) expression in the testis of the marbled newt were investigated with special attention to the changes during the annual testicular cycle, using light microscopy immunohistochemistry and Western blot analysis. The annual testicular cycle of the marbled newt (Triturus marmoratus marmoratus) comprises three periods: (a) proliferative period (germ cell proliferation from primordial germ cells to round spermatids, April-June); (b) spermiogenesis period (July-September); and (c) quiescence period (interstitial and follicular cells form the glandular tissue, October-April). In the proliferative period, primordial germ cells and primary spermatogonia immunostained intensely to the three types of RXRs and also to FXR. In the other periods, immunostaining to these antibodies was weak or absent. Secondary spermatogonia stained weakly to the four antibodies in the proliferative period, and only to FXR, also weakly, in the spermiogenesis period. Immunoreactive primary spermatocytes were weakly labeled with the RXR antibodies in the proliferative period. Spermatids and spermatozoa did not stain to any antibody in any period. Follicular cells only immunostained to RXR-gamma and only in the quiescence period when they are forming the glandular tissue, together with the interstitial cells. As follicular cells, interstitial cells only immunostained in the quiescence period; however, they immunoreacted to the three types of RXRs. These findings suggest that in the newt, RXRs and FXR are involved in spermatogenesis control by regulating the proliferation of primordial germ cells and spermatogonia. In addition, RXR-gamma seems to be also involved in the development of the glandular (steroidogenic) tissue.     

内皮素-1对培养新生大鼠心肌细胞原癌基因c-fos表达的诱导

本实验用无血清的培养新生大鼠心肌细胞,探讨内皮素１（ＥＴ１）对原癌基因ｃｆｏｓ表达的作用。结果显示：ＥＴ１可显著诱导ｃｆｏｓ的表达,其表达的高峰在３０ｍｉｎ,２ｈ恢复到正常水平,并呈剂量依赖性反应和被ＥＴＡ的特异性受体拮抗剂ＢＱ１２３所阻断;蛋白激酶Ｃ（ＰＫＣ）激动剂ＰＭＡ可诱导ｃｆｏｓ表达,而ＰＫＣ抑制剂Ｓｔａｕｒｏｓｐｏｒｉｎｅ则可阻断ＥＴ１诱导的ｃｆｏｓ表达;钙通道阻断剂硝苯吡啶预处理心肌细胞对ＥＴ１诱导的心肌细胞的ｃｆｏｓ表达无明显的作用。这些结果提示,ＥＴ１诱导ｃｆｏｓ表达是通过ＥＴＡ受体介导的,ＰＫＣ在此过程中起重要作用。     

Modulation of c-myc and c-fos gene expression in regenerating rat liver by 2-mercaptopropionylglycine

Expression of the two proto-oncogenes, c- myc and c- fos, in proliferating liver, and the modulation of their expression by 2-mercaptopropionylglycine (MPG) has been investigated. A significant increase in the expression of both c-myc and c-fos was observed, attaining a peak at 30 min, followed by a gradual decline for 8h after partial hepatectomy. Treatment of partially hepatectomized animals with MPG resulted in a significant decrease in the expression of both genes, the decrease being more marked in c- myc mRNA levels. At later time points, there was a very small rise in the mRNA levels of these genes in MPG-treated animals but they still remained much lower than the peak levels observed in both genes 30 min after surgery. A decline in the recovery of liver weight in MPG-treated animals was also observed.     

Insulin gene expression pattern in rat pancreas during the estrous cycle.

Sex steroid hormones influence insulin homeostasis and glucose metabolism, estradiol (E2) and progesterone (P4) induce changes in both fasting and postprandial insulinemia in rodents, however, insulin gene expression during estrous cycle is unknown. The aim of the present study was to determine an insulin gene expression pattern during the estrous cycle in the rat. Groups of 6 adult rats in each day of the estrous cycle were used. Serum P4, E2, testosterone (T) and insulin concentrations were determined by radioimmunoassay (RIA). A Northern blot analysis was performed to assess insulin gene expression in pancreatic tissue. We found a marked variation in insulin gene expression during the estrous cycle. The highest insulin expression was observed during the proestrus day. Interestingly, E2 and P4 but not T levels were correlated with changes in insulin mRNA content. The variations in serum insulin during the cycle were correlated with its mRNA content in pancreas. The overall results showed variations in serum insulin and insulin gene expression during estrous cycle of the rat that correlated with circulating E2 and P4 levels.     

Regional alterations in brain amino acids during the estrous cycle of the rat

Concentrations of 11 amino acids, including the neurotransmitters GABA, glutamate, aspartate, glycine and taurine, were determined in 12 brain regions of female rats during different stages of the estrous cycle. In addition, amino acids and sex hormone levels were determined in plasma. All sample collections were done in the forenoon between 9 and 11 a.m. Most regional amino acid levels measured did not change signficantly during estrous cycle, but significant alterations were found for GABA and glutamate in hypothalamus. Both amino acids were slightly decreased in hypothalamus during proestrus, which might reflect an alteration of GABA turnover in response to the high estrogen levels during this stage. A decreased glutamate level during proestrus was also found in thalamus, while both glutamate and GABA did not vary throughout estrous cycle in any of the other examined regions, including substantia nigra, amygdala, striatum, cortex and hippocampus. When diestrus was subdivided according to progesterone levels, high levels of this hormone seemed to be associated with effects on metabolism of certain amino acids, including glycine in substantia nigra, alanine in thalamus and threonine in pons/medulla. However, the few changes in regional amino acid concentrations found during the estrous cycle were so small that the functional significance of these changes cannot be ascertained without further determination of the cellular or subcellular compartments of brain tissue involved.     

Effects of gonadal steroids during pubertal development on androgen and estrogen receptor‐α immunoreactivity in the hypothalamus and amygdala

Perinatal development is often viewed as the major window of time for organization of steroid‐sensitive neural circuits by steroid hormones. Behavioral and neuroendocrine responses to steroids are dramatically different before and after puberty, suggesting that puberty is another window of time during which gonadal steroids affect neural development. In the present study, we investigated whether the presence of gonadal hormones during pubertal development affects the number of androgen receptor and estrogen receptor α‐immunoreactive (AR‐ir and ERα‐ir, respectively) cells in limbic regions. Male Syrian hamsters were castrated either before or after pubertal development, and 4 weeks later they received a single injection of testosterone or oil vehicle 4 h prior to tissue collection. Immunocytochemistry for AR and ERα was performed on brain sections from testosterone‐treated and oil‐treated males, respectively. Adult males that had been castrated before puberty had a greater number of AR‐ir cells in the medial preoptic nucleus than adult males that had been castrated after puberty. There were no significant differences in ERα‐ir cell number in any of the brain regions examined. The demonstration that exposure to gonadal hormones during pubertal development is associated with reduced AR‐ir in the medial preoptic nucleus indicates that puberty is a period of neural development during which hormones shape steroid‐sensitive neural circuits. © 2000 John Wiley & Sons, Inc. J Neurobiol 44: 361–368, 2000     

Changes in the distribution of ZO-1, occludin,and claudins in the rat uterine epithelium during the estrous cycle

During the estrous cycle, the endometrium epithelium experiences marked cellular structural changes. For fertilization to proceed, maintenance of an adequate uterine environment by ovarian hormones is essential. Epithelial cells lining the uterine lumen are associated with each other by tight junctions (TJs), which regulate the passage of ions and molecules through the paracellular pathway. The aim of the present study was to assess by confocal immunofluorescence the distribution pattern of the TJ proteins ZO-1, occludin, and claudins 1–7 in the rat uterus during the estrous cycle. Our results reveal that on proestrus, the day when mating takes place, ZO-1, occludin, and claudins 1 and 5 are located in the TJs, while claudins 3 and 7 display a basolateral distribution. In contrast, on metestrus day, when no sexual mating occurs and the uterine lumen is devoid of secretions, none of these proteins were detected in the TJ region, and only a diffuse cytosolic staining was observed for some of the proteins. On estrus and diestrus days, an intermediate situation was encountered, since ZO-1 localized in the TJs, whereas occludin was no longer detectable in the TJs. The distribution of claudins during these stages varied from the lowermost portion of the basolateral membrane to its apex. In conclusion, the results show that the protein composition of TJs present in the luminal epithelial cells of the uterus changes during the different days of the estrous cycle, and suggest that the expression of TJ proteins participates in providing an adequate environment for a successful fertilization.This work was supported by grants PAPIIT (IN210902, IX228504) and PAIP (6190-08) from the National Autonomous University of Mexico (UNAM), and by grants G34511-M and 37846-N from the Mexican National Council on Science and Technology (CONACYT).     

Splice-isoform specific immunolocalization of neuronal nitric oxide synthase in mouse and rat brain reveals that the PDZ-complex-building nNOSalpha beta-finger is largely exposed to antibodies

Knock out mice deficient for the splice-isoform alphaalpha of neuronal nitric oxide synthase (nNOSalphaalpha) display residual nitric oxide synthase activity and immunosignal. To attribute this signal to the two minor neuronal nitric oxide synthase splice variants, betabeta and gammagamma, we generated isoform-specific anti-peptide antibodies against the nNOSalphaalpha specific betabeta-finger motif involved in PDZ domain scaffolding and the nNOSbetabeta specific N-terminus. The nNOSalphaalpha betabeta-finger-specific antibody clearly recognized the 160-kDa band of recombinant nNOSalphaalpha on Western blots. Using immunocytochemistry, this antibody displayed, in rats and wild-type mice, a labeling pattern similar to but not identical with that obtained using a commercial pan-nNOS antibody. This similarity indicates that the majority of immunocytochemically detectable nNOS is not likely to be complexed with PDZ-domain proteins via the betabeta-finger motif. This conclusion was confirmed by the inhibition of PSD-95/nNOS interaction by the nNOSalphaalpha betabeta-finger antibody in pull-down assays. By contrast, nNOSalphaalpha betabeta-finger labeling was clearly reduced in hippocampal and cortical neuropil areas enriched in NMDA receptor complex containing spine synapses. In nNOSalphaalpha knock out mice, nNOSalphaalpha was not detectable, whereas the pan-nNOS antibody showed a distinct labeling of cell bodies throughout the brain, most likely reflecting betabeta/gammagamma-isoforms in these cells. The nNOSbetabeta antibody clearly detected bacterial expressed nNOSbetabeta fusion protein and nNOSbetabeta in overexpressing HEK cells by Western blotting. Immunocytochemically, individual cell bodies in striatum, cerebral cortex, and in some brain stem nuclei were labeled in knock out but not in wild-type mice, indicating an upregulation of nNOSbetabeta in nNOSalphaalpha deficient animals.     

Beta 2-agonist treatment enhances uterine oxytocin receptor mRNA expression in pregnant rats

The objective of this study was to disclose an interaction between Beta(2)-adrenergic (Beta(2)-ARs) and oxytocin (OT) receptors (OTRs) in the late-pregnant rat uterus. We investigated the level of uterine OTR mRNA expression after the administration of Beta(2)-AR agonists fenoterol and hexoprenaline to rats from day 18 to 22 of pregnancy, and also tested the effect of fenoterol on uterine explants. Hexoprenaline induced a maximum 24% increase of OTR mRNA. Fenoterol in vivo elicited a maximum 125% increase of OTR mRNA, in vitro produced a maximum fourfold increase in OTR mRNA. In fenoterol-treated rats the maximal contractility increasing effect of OT on isolated uterine rings was significantly higher than in intact term pregnant rats, but the EC50 values were not statistically different. It was concluded that the enhanced expression of OTR mRNA induced by Beta(2)-agonists in the late-pregnant rat uterus may be a possible drawback to effective therapy of preterm uterine contractions with Beta(2)-agonists.