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D B Lubahn

Publications and source records attributed to D B Lubahn.

At least 73 records · Page 4Linked to original sources
PubMed1997

Estrogen up-regulates apolipoprotein E (ApoE) gene expression by increasing ApoE mRNA in the translating pool via the estrogen receptor alpha-mediated pathway.

The antiatherogenic property of estrogens is mediated via at least two mechanisms: first by affecting plasma lipoprotein profiles, and second by affecting the components of the vessel wall. Raising plasma apolipoprotein E (apoE) in mice protects them against diet-induced atherosclerosis (Shimano, H., Yamada, N., Katsuki, M., Gotoda, T., Harada, K., Murase, T., Fukuzawa, C., Takaku, F., and Yazaka, Y. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 1750-1754). It is possible that estrogen may be antiatherogenic at least in part by increasing plasma apoE levels. Therefore, we studied the regulation of apoE by estrogen. A survey of 15 inbred strains of mice showed that some mouse strains responded to injections or subcutaneously implanted pellets of estradiol by raising their apoB and apoE levels and some did not. We performed detailed studies in two "responder" strains, C57L and C57BL, and two "non-responder" strains, C3H and BALBc. Responders increased their plasma apoE levels 2.5-fold. Non-responders' levels were altered +/-10%. In the responders the distribution of apoE among the plasma lipoproteins shifted from high density lipoprotein toward the apoB-containing lipoprotein fractions. In nonresponders the shift was toward high density lipoprotein. Hepatic apoE mRNA levels and relative rates of apoE mRNA transcription were unchanged in all strains, suggesting that apoE regulation occurred at posttranscriptional loci. Therefore, we measured apoE synthesis in fresh liver slices and on isolated hepatic polysomes. Two-fold increases were noted but only in responders accompanied by selective 1.5-fold increases in polysomal apoE mRNA levels. Similar increases in apoE synthesis were also observed in castrated C57BL mice given either physiological or pharmacological replacement doses of estradiol, but not testosterone, suggesting that the effect of estradiol was specific on the distribution of apoE mRNA in the translationally active polysomal pool. Next, we examined whether the effects of estrogen on apoE translation were mediated by estrogen receptors (ER). ER-alpha knock-out mice and their wild-type littermates were administered estradiol. As expected, apoE levels and hepatic apoE synthesis increased more than 2-fold in the wild-type littermates, but only 20% increases in the plasma apoE and hepatic synthesis were observed in the ER knock-out mice. Hepatic apoE mRNA levels did not change in either the wild-type or the ER knock-out mice. Thus, estradiol up-regulates apoE gene expression by increasing levels of apoE mRNA in the polysomal translating pool. Furthermore, the increased polysomal recruitment of apoE mRNA is largely mediated by estrogen receptors.

Animals↗
PubMed1997

Estrogen receptor-dependent sexual differentiation of dopaminergic neurons in the preoptic region of the mouse.

Although it has been known for some time that estrogen exerts a profound influence on brain development a definitive demonstration of the role of the classical estrogen receptor (ERalpha) in sexual differentiation has remained elusive. In the present study we used a sexually dimorphic population of dopaminergic neurons in the anteroventral periventricular nucleus of the hypothalamus (AVPV) to test the dependence of sexual differentiation on a functional ERalpha by comparing the number of tyrosine hydroxylase (TH)-immunoreactive neurons in the AVPV of wild-type (WT) mice with that of mice in which the ERalpha had been disrupted by homologous recombination (ERKOalpha). Only a few ERalpha-immunoreactive neurons were detected in the AVPV of ERKOalpha mice, and the number of TH-immunoreactive neurons was three times that of WT mice, suggesting that disruption of the ERalpha gene feminized the number of TH-immunoreactive neurons. In contrast, the AVPV contains the same number of TH-immunoreactive neurons in testicular feminized male mice as in WT males, indicating that sexual differentiation of this population of neurons is not dependent on an intact androgen receptor. The number of TH-immunoreactive neurons in the AVPV of female ERKOalpha mice remained higher than that of WT males, but TH staining appeared to be lower than that of WT females. Thus, the sexual differentiation of dopamine neurons in the AVPV appears to be receptor specific and dependent on the perinatal steroid environment.

Animals↗
PubMed1997

A role for oestrogens in the male reproductive system.

Oestrogen is considered to be the 'female' hormone, whereas testosterone is considered the 'male' hormone. However, both hormones are present in both sexes. Thus sexual distinctions are not qualitative differences, but rather result from quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen, and as high as 250 pg ml(-1) in rete testis fluids, which is higher than serum oestradiol in the female. It is well known that male reproductive tissues express oestrogen receptors, but the role of oestrogen in male reproduction has remained unclear. Here we provide evidence of a physiological role for oestrogen in male reproductive organs. We show that oestrogen regulates the reabsorption of luminal fluid in the head of the epididymis. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. This finding raises further concern over the potential direct effects of environmental oestrogens on male reproduction and reported declines in human sperm counts.

Animals↗
PubMed1997

Estrogenic responses in estrogen receptor-alpha deficient mice reveal a distinct estrogen signaling pathway.

Estrogens are thought to regulate female reproductive functions by altering gene transcription in target organs primarily via the nuclear estrogen receptor-alpha (ER-alpha). By using ER-alpha "knock-out" (ERKO) mice, we demonstrate herein that a catecholestrogen, 4-hydroxyestradiol-17beta (4-OH-E2), and an environmental estrogen, chlordecone (kepone), up-regulate the uterine expression of an estrogen-responsive gene, lactoferrin (LF), independent of ER-alpha. A primary estrogen, estradiol-17beta (E2), did not induce this LF response. An estrogen receptor antagonist, ICI-182,780, or E2 failed to inhibit uterine LF gene expression induced by 4-OH-E2 or kepone in ERKO mice, which suggests that this estrogen signaling pathway is independent of both ER-alpha and the recently cloned ER-beta. 4-OH-E2, but not E2, also stimulated increases in uterine water imbibition and macromolecule uptake in ovariectomized ERKO mice. The results strongly imply the presence of a distinct estrogen-signaling pathway in the mouse uterus that mediates the effects of both physiological and environmental estrogens. This estrogen response pathway will have profound implications for our understanding of the physiology and pathophysiology of female sex steroid hormone actions in target organs.

Animals↗
PubMed1997

Responses in the brain of estrogen receptor alpha-disrupted mice.

These studies sought to determine if neurons in the estrogen receptor-alpha knockout (ERalphaKO) mouse brain concentrated 16alpha-[125I]iodo-11beta-methoxy-17beta-estradiol (125I-estrogen), and if so, whether estrogen binding augmented the expression of progesterone receptor (PR) mRNA. Mice were injected with 125I-estrogen and cryostat sections thaw mounted onto emulsion-coated slides. After 30-90 days of exposure, cells with a nuclear uptake and retention of 125I-estrogen were observed in a number of ERalphaKO mouse brain regions including the preoptic nucleus and arcuate nucleus of the hypothalamus, bed nucleus of the stria terminalis, and amygdala, although the number of labeled cells and intensity of nuclear concentration was markedly attenuated when compared with wild-type littermates. Competition studies with excess 17beta-estradiol, diethylstilbestrol, or moxestrol, but not with R5020 or dihydrotestosterone, prevented the nuclear concentration of 125I-estrogen. To determine if the low level of estrogen binding was capable of regulating gene expression, in situ hybridization was used to evaluate PR mRNA in the brain. ERalphaKO and wild-type mice were ovariectomized and treated with vehicle or 17beta-estradiol, and brains were sectioned and hybridized with a PR cRNA probe. Analysis of hybridization signal revealed a similar, low level of PR mRNA in ovariectomized wild-type and homozygous mice, and a marked increase in expression after treatment of ovariectomized animals with 17beta-estradiol, with the level of hybridization signal being significantly higher in wild-type animals when compared with ERalphaKO mice. The results demonstrate that estrogen binds in the ERalphaKO brain and is capable of modulating PR gene expression, thus supporting the presence and functionality of a nonclassical estrogen receptor.

Animals↗
PubMed1997

Stromal estrogen receptors mediate mitogenic effects of estradiol on uterine epithelium.

Estradiol-17beta (E2) acts through the estrogen receptor (ER) to regulate uterine growth and functional differentiation. To determine whether E2 elicits epithelial mitogenesis through epithelial ER versus indirectly via ER-positive stromal cells, uteri from adult ER-deficient ER knockout (ko) mice and neonatal ER-positive wild-type (wt) BALB/c mice were used to produce the following tissue recombinants containing ER in epithelium (E) and/or stroma (S), or lacking ER altogether: wt-S + wt-E, wt-S + ko-E, ko-S + ko-E, and ko-S + wt-E. Tissue recombinants were grown for 4 weeks as subrenal capsule grafts in intact female nude mice, then the hosts were treated with either E2 or oil a week after ovariectomy. Epithelial labeling index and ER expression were determined by [3H]thymidine autoradiography and immunohistochemistry, respectively. In tissue recombinants containing wt-S (wt-S + wt-E, wt-S + ko-E), E2 induced a similar large increase in epithelial labeling index compared with oil-treated controls in both types of tissue recombinants despite the absence of epithelial ER in wt-S + ko-E tissue recombinants. This proliferative effect was blocked by an ER antagonist, indicating it was mediated through ER. In contrast, in tissue recombinants prepared with ko-S (ko-S + ko-E and ko-S + wt-E), epithelial labeling index was low and not stimulated by E2 despite epithelial ER expression in ko-S + wt-E grafts. In conclusion, these data demonstrate that epithelial ER is neither necessary nor sufficient for E2-induced uterine epithelial proliferation. Instead, E2 induction of epithelial proliferation appears to be a paracrine event mediated by ER-positive stroma. These data in the uterus and similar studies in the prostate suggest that epithelial mitogenesis in both estrogen and androgen target organs are stromally mediated events.

Aging↗
PubMed1997

Vascular estrogen receptors and endothelium-derived nitric oxide production in the mouse aorta. Gender difference and effect of estrogen receptor gene disruption.

The present study was designed to test the hypothesis that estrogen receptors (ER) in the blood vessel wall play a role in the modulation of the release of endothelium-derived nitric oxide (EDNO). Both basal and stimulated release of EDNO were determined in aortic rings isolated from female and male wild-type and male homozygous estrogen receptor knock-out (ERKO) mice. 125I-17beta-estradiol binding in aortic tissue showed significantly more high affinity cytosolic- nuclear-binding sites in male compared with female wildtype mice. Estrogen receptor transcripts were present in the aorta of male wild-type mice, but they were absent in male ERKO animals. Basal release of EDNO (determined by endothelium-dependent contraction caused by NG-nitro-arginine) was significantly higher in aorta of wild-type male mice compared with wild-type female mice, and significantly lower in the aorta of male ERKO compared with male wild-type mice. Acetylcholine-induced endothelium-dependent relaxation was similar in all groups studied. No difference was observed in the activity of calcium-dependent nitric oxide synthase in homogenates of lungs and brain taken from male wild-type and ERKO mice. These studies show a significant association between the number of estrogen receptors and basal release of EDNO in the aorta of mice, and suggest that decreased vascular estrogen receptor number may represent a novel risk factor for cardiovascular diseases.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1997

Identification of DNA methylation markers for human breast carcinomas using the methylation-sensitive restriction fingerprinting technique.

We have developed a PCR-based method, called methylation-sensitive restriction fingerprinting (MSRF), to screen changes in DNA methylation in breast carcinomas. Two hypermethylation-containing fragments, HBC-1 (for "hypermethylation in breast cancer") and HBC-2, were identified in the amplified breast tumor DNA relative to the amplified normal breast DNA of a patient. Nucleotide sequence analysis revealed no significant matches between the sequence of HBC-1 and the known sequences in the GenBank database, whereas the sequence of HBC-2 matched the upstream region of an antisense WT1 (Wilms' tumor suppressor gene) promoter. The methylation status in the breast tumor DNA from this patient was confirmed by Southern hybridization using HBC-1 and HBC-2 as probes, respectively. Further analysis showed that HBC-1 was methylated aberrantly in 90% (17 of 19 patients) of the primary breast carcinomas examined. This study demonstrates that MSRF provides a useful means for screening aberrant changes in DNA methylation during tumorigenesis. The commonly methylated fragments identified by MSRF could potentially supplement pathological markers currently used for cancers and additionally lead to the discovery of novel methylated tumor suppressor genes.

Base Sequence↗
PubMed1997

Behavioral effects of estrogen receptor gene disruption in male mice.

Gonadal steroid hormones regulate sexually dimorphic development of brain functions and behaviors. Their nuclear receptors offer the opportunity to relate molecular events in neurons to simple instinctive mammalian behaviors. We have determined the role of estrogen receptor (ER) activation by endogenous estrogen in the development of male-typical behaviors by the use of transgenic estrogen-receptor-deficient (ERKO) mice. Surprisingly, in spite of the fact that they are infertile, ERKO mice showed normal motivation to mount females but they achieved less intromissions and virtually no ejaculations. Aggressive behaviors were dramatically reduced and male-typical offensive attacks were rarely displayed by ERKO males. Moreover, ER gene disruption demasculinized open-field behaviors. In the brain, despite the evident loss of functional ER protein, the androgen-dependent system appears to be normally present in ERKO mice. Together, these findings indicate that ER gene expression during development plays a major role in the organization of male-typical aggressive and emotional behaviors in addition to simple sexual behaviors.

Aggression↗
PubMed1997

Estrogen receptor function as revealed by knockout studies: neuroendocrine and behavioral aspects.

Estrogens are an important class of steroid hormones, involved in the development of brain, skeletal, and soft tissues. These hormones influence adult behaviors, endocrine state, and a host of other physiological functions. Given the recent cloning of a second estrogen receptor (ER) cDNA (the ER beta), work on alternate spliced forms of ER alpha, and the potential for membrane estrogen receptors, an animal with a null background for ER alpha function is invaluable for distinguishing biological responses of estrogens working via the ER alpha protein and those working via another ER protein. Data generated to date, and reviewed here, indicate that there are profound ramifications of the ER alpha disruption on behavior and neuroendocrine function. First, data on plasma levels of estradiol (E2), testosterone (T), and luteinizing hormone (LH) in wild-type (WT) versus ER alpha- mice confirm that ER alpha is essential in females for normal regulation of the hypothalamic-pituitary gonadal axis. Second, ovariectomized female ER alpha- mice do not display sexual receptivity when treated with a hormonal regime of estrogen and progesterone that induces receptivity in WT littermates. Finally, male sexual behaviors are disrupted in ER alpha- animals. Given decades of data on these topics our findings may seem self-evident. However, these data represent the most direct test currently possible of the specific role of the ER alpha protein on behavior and neuroendocrinology. The ER alpha- mouse can be used to ascertain the specific functions of ER alpha, to suggest functions for the other estrogen receptors, and to study indirect effects of ER alpha on behavior via actions on other receptors, neurotransmitters, and neuropeptides.

Animals↗
PubMed1997

Masculine sexual behavior is disrupted in male and female mice lacking a functional estrogen receptor alpha gene.

Masculine sexual behavior is regulated by testosterone (T). However, T can be metabolized to form estrogens or other androgens, which then activate their own receptors. We used knockout mice lacking a functional estrogen receptor alpha (ER alpha) gene to test the hypothesis that, following aromatization, T acts via the ER alpha to activate normal masculine sexual behavior. After gonadectomy and T replacement, wild-type (WT) male and female mice displayed masculine behavior. However, given the same T treatment, little masculine behavior was displayed by mice of either sex that lack a normal copy of the ER alpha gene. In particular, the latency to display masculine sex behavior and the number of mount attempts per trial were significantly reduced in the ER alpha- mice compared to WT littermates (P < 0.05). In addition, we found that in both sexes, ER alpha- mice have a smaller cluster of androgen receptor immunoreactivity in the bed nucleus of the stria terminalis. Using adult ER alpha- mice we were unable to determine whether these genotypic differences are due to organizational or activational effects. However, it is clear that the ER alpha plays a key role in the expression of masculine sexual behavior and in the regulation of androgen receptors in a neuronal cell population involved in the display of motivated behaviors.

Animals↗
PubMed1997

Elucidation of a role for stromal steroid hormone receptors in mammary gland growth and development using tissue recombinants.

The use of tissue recombinants in conjunction with steroid receptor deficient mice is described as a tool to dissect the complex paracrine pathways of sex-hormone-regulated epithelial growth and ductal morphogenesis in the mammary gland and other hormone target organs. The basic methodology involves the construction of the four possible tissue recombinants composed of epithelium (E) and stroma (S) from wild-type (wt) and knock-out (KO) mice: wt-S + wt-S, wt-S + KO-E, KO-S + KO-E, and KO-S + wt-E. All tissue recombinants are grown as subrenal capsule grafts in nude mice. Following appropriate hormonal challenge epithelial growth can be studied in the four types of tissue recombinants. Such studies using estrogen receptor, androgen receptor and progesterone receptor knockout mice demonstrate that epithelial steroid receptors are neither necessary nor sufficient for hormonal regulation of epithelial proliferation. Instead, hormonal regulation of epithelial proliferation is a paracrine event mediated by hormone-receptor-positive stromal cells.

Animals↗
PubMed1997

Estrogen inhibits the vascular injury response in estrogen receptor alpha-deficient mice.

The atheroprotective effects of estrogen in women are well recognized, but the underlying mechanisms responsible are not well understood. Blood vessel cells express the classic estrogen receptor, ER alpha (ref. 2-6), and are directly affected by estrogen, which inhibits the development of atherosclerotic and injury-induced vascular lesions. We have generated mice in which the ER alpha gene is disrupted and have used a mouse model of carotid arterial injury to compare the effects of estrogen on wild-type and estrogen receptor-deficient mice. Increases in vascular medial area and smooth muscle cell proliferation were quantified following vascular injury in ovariectomized mice treated with vehicle or with physiologic levels of 17 beta-estradiol. Surprisingly, in both wild-type and estrogen receptor-deficient mice, 17 beta-estradiol markedly inhibited to the same degree all measures of vascular injury. These data demonstrate that estrogen inhibits vascular by a novel mechanism that is independent of the classic estrogen receptor, ER alpha.

Animals↗
PubMed1997

Estrogen receptors are essential for female sexual receptivity.

One of the most important, robust and evolutionarily conserved functions for neural estrogen receptor (ER) is as a mediator of female sexual behavior. Using homozygotic ER knockout (ERKO) mice we tested the hypothesis that ER controls female receptivity. Females with either two normal copies of the ER gene (wild-types), or an insertational disruption (knockouts) of the ER were ovariectomized. Each female was treated with 17 beta-estradiol (EB) alone, and with EB in combination with progesterone, prior to tests for behavioral receptivity. Under both hormonal conditions female ERKO mice did not display sexual receptivity whereas wild-type litter-mates were receptive to males. Male behavior indicated that females of both genotypes were equally attractive. Brain tissues were examined with immunocytochemical methods showed that ERKOs had greatly reduced levels of ER immunoreactivity in hypothalamus. In sum, the data show that ER is required for the display of sexual receptivity, but is not essential for female attractivity.

Animals↗
PubMed1997

Role of estrogen receptor-alpha in the anterior pituitary gland.

Targeted insertional disruption of the mouse estrogen receptor-alpha (ER alpha) gene has provided a genetic model in which to test hypotheses that estrogens exert important effects in development and homeostatic functions of the anterior pituitary gland, particularly in the lactotroph and gonadotroph cell types. Analysis of ER alpha gene-disrupted mice reveals a marked reduction in PRL mRNA and a decrease in lactotroph cell number, but normal specification of lactotroph cell phenotype. Gonadotropin mRNA levels in ER alpha gene-disrupted female mice are elevated, consistent with previously described transcriptional suppression of gonadotropin subunit gene expression in response to sustained administration of estrogen in wild type mice. These results provide genetic evidence that ER alpha plays a critical role in PRL and gonadotropin gene transcription and is involved in lactotroph cell growth, but is not required for specification of lactotroph cell phenotype.

Animals↗
PubMed1996

Reversal of sex roles in genetic female mice by disruption of estrogen receptor gene.

Deficiency of normal estrogen receptor(ER) gene function led to behavioral change in female mice (ERKO females). Maternal behavior as measured by retrieving of pups was reduced. In some cases, pups were killed by the ERKO females, which was not seen in wild-type animals. Aggression toward other females was increased. Female-typical lordosis behavior was reduced for at least two reasons: less response to somatosensory stimuli on the hindquarters, as well as the fact that ERKO females were immediately treated as intruder males by resident 'stud' males and were thus attacked. In sum, disruption of the ER gene led to a pattern of hormonal and neural changes which caused the females to lose their normal female-typical behavior and to behave and be treated more like males.

Animals↗
PubMed1996

Targeted disruption of the estrogen receptor gene in male mice causes alteration of spermatogenesis and infertility.

The reproductive system of male mice homozygous for a mutation in the estrogen receptor (ER) gene (ER knock-out; ERKO) appears normal at the anatomical level. However, these males are infertile, indicating an essential role for ER-mediated processes in the regulation of male reproduction. Adult ERKO male mice have significantly fewer epididymal sperm than heterozygous or wild-type males. Although spermatogenesis is occurring in some seminiferous tubules of 3- to 5-month-old ERKO males, other tubules either have a dilated lumen and a disorganized seminiferous epithelium with few spermatogenic cells or lack a lumen and contain mainly Sertoli cells. There are no obvious differences in seminiferous tubules at 10 days of age between wild-type and ERKO mice, but the lumen in ERKO males is dilated in all seminiferous tubules by 20 days. However, spermatogenesis progresses and similar numbers of sperm are present in the cauda epididymis of ERKO and wild-type males until 10 weeks of age. Disruption of spermatogenesis and degeneration of the seminiferous tubules become apparent after 10 weeks in the caudal pole of the testis and progresses in a wave to the cranial pole by 6 months. However, the seminal vesicles, coagulating glands, prostate, and epididymis do not appear to be altered morphologically in ERKO mice. Serum testosterone levels are somewhat elevated, but LH and FSH levels are not significantly different from those in wild-type males. Sperm from 8- to 16-week-old mice have reduced motility and are ineffective at fertilizing eggs in vitro. In addition, ERKO males housed overnight with hormone-primed wild-type females produce significantly fewer copulatory plugs than do heterozygous or wild-type males. These results suggest that estrogen action is required for fertility in male mice and that the mutation of the ER in ERKO males leads to reduced mating frequency, low sperm numbers, and defective sperm function.

Animals↗