Deletion of estrogen receptors reveals a regulatory role for estrogen receptors-beta in bone remodeling in females but not in males

Modulation of Runx2 activity by estrogen receptor-alpha: implications for osteoporosis and breast cancer

The transcription factors Runx2 and estrogen receptor-alpha (ERalpha) are involved in numerous normal and disease processes, including postmenopausal osteoporosis and breast cancer. Using indirect immunofluorescence microscopy and pull-down techniques, we found them to colocalize and form complexes in a ligand-dependent manner. Estradiol-bound ERalpha strongly interacted with Runx2 directly through its DNA-binding domain and only indirectly through its N-terminal and ligand-binding domains. Runx2's amino acids 417-514, encompassing activation domain 3 and the nuclear matrix targeting sequence, were sufficient for interaction with ERalpha's DNA-binding domain. As a consequence of the interaction, Runx2's transcriptional activation activity was strongly repressed, as shown by reporter assays in COS7 cells, breast cancer cells, and late-stage MC3T3-E1 osteoblast cultures. Metaanalysis of gene expression in 779 breast cancer biopsies indicated negative correlation between the expression of ERalpha and Runx2 target genes. Selective ER modulators (SERM) induced ERalpha-Runx2 interactions but led to various functional outcomes. The regulation of Runx2 by ERalpha may play key roles in osteoblast and breast epithelial cell growth and differentiation; hence, modulation of Runx2 by native and synthetic ERalpha ligands offers new avenues in selective ER modulator evaluation and development.

Cardiotrophin-1 is an osteoclast-derived stimulus of bone formation required for normal bone remodeling

Cardiotrophin (CT-1) signals through gp130 and the LIF receptor (LIFR) and plays a major role in cardiac, neurological, and liver biology. We report here that CT-1 is also expressed within bone in osteoclasts and that CT-1 is capable of increasing osteoblast activity and mineralization both in vitro and in vivo. Furthermore, CT-1 stimulated CAAT/enhancer-binding protein-delta (C/EBP delta) expression and runt-related transcription factor 2 (runx2) activation. In neonate CT-1(-/-) mice, we detected low bone mass associated with reduced osteoblasts and many large osteoclasts, but increased cartilage remnants within the bone, suggesting impaired resorption. Cultured bone marrow (BM) from CT-1(-/-) mice generated many oversized osteoclasts and mineralized poorly compared with wildtype BM. As the CT-1(-/-) mice aged, the reduced osteoblast surface (ObS/BS) was no longer detected, but impaired bone resorption continued resulting in an osteopetrotic phenotype in adult bone. CT-1 may now be classed as an essential osteoclast-derived stimulus of both bone formation and resorption.

An advanced biosensor for the prediction of estrogenic effects of endocrine-disrupting chemicals on the estrogen receptor alpha

A label-free and time-resolved biosensor based on reflectometric interference spectroscopy (RIfS) has been developed to evaluate the agonistic or antagonistic effects of potential ligands with unknown behavior. The biosensor utilizes the specific interaction between the estrogen receptor alpha (ER alpha) and short specific peptides. The unique feature of these peptides allows the investigation of the behavior of ligands and the discrimination between the agonistic and antagonistic effects caused by conformational changes of the receptor. Thus, this developed biosensor allows not only the differentiation between ligands and nonligands of a receptor, but also the potential of these ligands to influence conformational changes in the receptor, leading to activation or inhibition of the receptor-dependent pathways. Owing to the robustness of the direct optical detection principle used, the biosensor is applicable to complex biological matrices, even crude cell extracts. Moreover, the reliability of the biosensor, including regeneration steps when performing subsequent measurements, has been verified.

Ginsenoside Rg1 promotes bone marrow stromal cells proliferation via the activation of the estrogen receptor-mediated signaling pathway

AIM

To investigate the possible mechanisms of ginsenoside Rg1 promoting bone marrow stromal cell (BMSC) proliferation.

METHODS

BMSC were isolated from bone marrow of Sprague-Dawley rats and maintained in vitro. After stimulation with 1 micromol/L ginsenoside Rg1 for the indicated time, the proliferation ability of BMSC were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide and [3H]-thymidine incorporation assays. The estrogen receptor (ER) binding activity of BMSC was determined by a specific ER antagonist and an ER binding assay. Furthermore, the influence of ginsenoside Rg1 on the expression of ERalpha was investigated by RT-PCR and Western blotting assays.

RESULTS

BMSC proliferation stimulated by 1 micromol/L ginsenoside Rg1 can be completely blocked by 1 micromol/L ER antagonist ICI 182, 780, or ERalpha- specific antagonist methylpiperidinopyrazole. Moreover, Rg1 failed to displace the specific binding of [3H]17beta-estradiol to BMSC cell lysates, suggesting that no direct interaction of Rg1 with the ER is needed for its estrogenic effects. In addition, 1 micromol/L Rg1 had no effects on the expression of ERalpha in either the mRNA or protein levels.

CONCLUSION

Our results indicate that ERalpha is essential for mediating the effects of Rg1 on stimulating BMSC proliferation, which might involve the ligand/receptor-independent activation of ERalpha.

Differential regulation of bone and body composition in male mice with combined inactivation of androgen and estrogen receptor-alpha

Osteoporosis and muscle frailty are important health problems in elderly men and may be partly related to biological androgen activity. This androgen action can be mediated directly through stimulation of the androgen receptor (AR) or indirectly through stimulation of estrogen receptor-alpha (ERalpha) following aromatization of androgens into estrogens. To assess the differential action of AR and ERalpha pathways on bone and body composition, AR-ERalpha double-knockout mice were generated and characterized. AR disruption decreased trabecular bone mass, whereas ERalpha disruption had no additional effect on the AR-dependent trabecular bone loss. In contrast, combined AR and ERalpha inactivation additionally reduced cortical bone and muscle mass compared with either AR or ERalpha disruption alone. ERalpha inactivation--in the presence or absence of AR--increased fat mass. We demonstrate that AR activation is solely responsible for the development and maintenance of male trabecular bone mass. Both AR and ERalpha activation, however, are needed to optimize the acquisition of cortical bone and muscle mass. ERalpha activation alone is sufficient for the regulation of fat mass. Our findings clearly define the relative importance of AR and ERalpha signaling on trabecular and cortical bone mass as well as body composition in male mice.

Osteoclast inhibitory lectin, an immune cell product that is required for normal bone physiology in vivo

Osteoclast inhibitory lectin (OCIL or clrb) is a member of the natural killer cell C-type lectins that have a described role mostly in autoimmune cell function. OCIL was originally identified as an osteoblast-derived inhibitor of osteoclast formation in vitro. To determine the physiological function(s) of OCIL, we generated ocil(-/-) mice. These mice appeared healthy and were fertile, with no apparent immune function defect, and phenotypic abnormalities were limited to bone. Histomorphometric analysis revealed a significantly lower tibial trabecular bone volume and trabecular number in the 10- and 16-week-old male ocil(-/-) mice compared with wild type mice. Furthermore, ocil(-/-) mice showed reduced bone formation rate in the 10-week-old females and 16-week-old males while Static markers of bone formation showed no significant changes in male or female ocil(-/-) mice. Examination of bone resorption markers in the long bones of ocil(-/-) mice indicated a transient increase in osteoclast number per unit bone perimeter. Enhanced osteoclast formation was also observed when either bone marrow or splenic cultures were generated in vitro from ocil(-/-) mice relative to wild type control cultures. Loss of ocil therefore resulted in osteopenia in adult mice primarily as a result of increased osteoclast formation and/or decreased bone formation. The enhanced osteoclastic activity led to elevated serum calcium levels, which resulted in the suppression of circulating parathyroid hormone in 10-week-old ocil(-/-) mice compared with wild type control mice. Collectively, our data suggest that OCIL is a physiological negative regulator of bone.

Estrogen and bone: insights from estrogen-resistant, aromatase-deficient, and normal men

Findings from estrogen-resistant and aromatase-deficient men have provided important insights into the role of estrogen in the male skeleton during growth. Importantly, as reported elsewhere in this issue, these data also suggested dose-response relationships between estrogen and bone turnover. In addition, studies in these unusual patients have stimulated research on defining the role of estrogen in regulating bone metabolism in normal adult and aging men, providing further insights into estrogen regulation of bone metabolism not only in men, but also in women.

Impact on bone of an estrogen receptor-alpha gene loss of function mutation

CONTEXT

The kindred described is the only known instance of a germ line loss of function mutation of estrogen receptor (ER)-alpha.

OBJECTIVE

Our objective was to assess the impact of a loss of function mutation in the ER-alpha gene on histomorphometry, bone volumetric density, bone geometry and skeletal growth, and ER-alpha heterozygosity on spine density and adult height in an extended pedigree.

DESIGN AND PARTICIPANTS

A longitudinal follow-up of the propositus with homozygous loss of function mutation of ER-alpha and single contact evaluation of the kindred were performed.

MAIN OUTCOME MEASURES

Iliac crest bone biopsy and peripheral quantitative computed tomography of propositus with serial measures of areal spine bone mineral density (aBMD) by dual-energy x-ray absorptiometry and bone age were performed. Members of pedigree were evaluated for ER-alpha mutation carrier status and spine aBMD.

RESULTS

Bone biopsy revealed marked osteopenia (cortex: 641 microm), low trabecular volume (10.6%), decreased thickness (76.2 microm), normal trabecular number, and low activation frequency (0.099/yr). Radial periosteal circumference was similar, endosteal circumference larger, and trabecular and cortical volumetric bone mineral density markedly lower (158 and 1092 mg/cm(3), respectively) than controls. Spine aBMD at age 28.5 yr (0.745 g/cm(2)) decreased to 0.684 g/cm(2) (Z score -3.85) in 3.5 yr. Bone age advanced from 15-17.5 yr. Kindred analysis revealed that gene carriers had spine aBMD Z scores less than zero (P = 0.003), but carriers and nonmutant members were similar (-0.84 +/- 0.26 vs. -0.64 +/- 0.16).

CONCLUSION

Homozygous ER-alpha disruption markedly affects bone growth, mineral content, and structure but not periosteal circumference. ER-alpha heterozygosity appears to not impair spine aBMD.

Overexpression of human hydroxysteroid (17beta) dehydrogenase 2 induces disturbance in skeletal development in young male mice

To understand the function of human hydroxysteroid (17beta) dehydrogenase 2 (HSD17B2) in the peripheral tissues in vivo, we studied the bone development in transgenic male mice ubiquitously expressing human HSD17B2. Bones of HSD17B2TG and WT males (26 days and 2 and 6 mo old) were analyzed by pQCT and histomorphometry, and data were correlated with serum testosterone (T), IGF-I, and osteocalcin concentrations. At the age of 26 days, the body weight of HSD17B2TG males was significantly lower, and the lengths of the tibia and femur of the HSD17B2TG males were significantly shorter. Histomorphometric and pQCT analyses showed lower trabecular and cortical BMD, a markedly smaller area of cortical bone at both of the diaphyses, and a smaller percentage of trabecular bone volume and thickness in the HSD17B2TG males. The data suggested slower osteoblast differentiation and a slower bone formation rate of femoral diaphysis on the periosteum but faster on the endocortical surface in HSD17B2TG males. The altered bone parameters were correlated with low serum T, IGF-I, and osteocalcin concentrations at the prepubertal age. Interestingly, after puberty, the bone parameters analyzed in the adult HSD17B2TG males were mostly normal, consistent with the normal body weight and normalized serum concentrations of IGF-I and T. In conclusion, HSD17B2TG males presented with growth retardation and a decreased bone formation rate at prepubertal age. These changes were associated with lower serum IGF-I, osteocalcin, and T concentrations. It is concluded that the enforced constitutive expression of HSD17B2 disturbs the coordinated action of IGF-I and sex steroids essential for pubertal bone growth.

Model-based comparative prediction of transcription-factor binding motifs in anabolic responses in bone

Understanding the regulatory mechanism that controls the alteration of global gene expression patterns continues to be a challenging task in computational biology. We previously developed an ant algorithm, a biologically-inspired computational technique for microarray data, and predicted putative transcription-factor binding motifs (TFBMs) through mimicking interactive behaviors of natural ants. Here we extended the algorithm into a set of web-based software, Ant Modeler, and applied it to investigate the transcriptional mechanism underlying bone formation. Mechanical loading and administration of bone morphogenic proteins (BMPs) are two known treatments to strengthen bone. We addressed a question: Is there any TFBM that stimulates both “anabolic responses of mechanical loading” and “BMP-mediated osteogenic signaling”? Although there is no significant overlap among genes in the two responses, a comparative model-based analysis suggests that the two independent osteogenic processes employ common TFBMs, such as a stress responsive element and a motif for peroxisome proliferator-activated receptor (PPAR). The post-modeling in vitro analysis using mouse osteoblast cells supported involvements of the predicted TFBMs such as PPAR, Ikaros 3, and LMO2 in response to mechanical loading. Taken together, the results would be useful to derive a set of testable hypotheses and examine the role of specific regulators in complex transcriptional control of bone formation.

TIEG-null mice display an osteopenic gender-specific phenotype

TGFbeta inducible early gene-1 (TIEG) was originally cloned from human osteoblasts (OB) and has been shown to play an important role in TGFbeta/Smad signaling, regulation of gene expression and OB growth and differentiation. To better understand the biological role of TIEG in the skeleton, we have generated congenic TIEG-null (TIEG(-/-)) mice in a pure C57BL/6 background. Through the use of DXA and pQCT analysis, we have demonstrated that the femurs and tibias of two-month-old female TIEG(-/-) mice display significant decreases in total bone mineral content, density, and area relative to wild-type (WT) littermates. However, no differences were observed for any of these bone parameters in male mice. Further characterization of the bone phenotype of female TIEG(-/-) mice involved mechanical 3-point bending tests, micro-CT, and histomorphometric analyses of bone. The 3-point bending tests revealed that the femurs of female TIEG(-/-) mice have reduced strength with increased flexibility compared to WT littermates. Micro-CT analysis of femurs of two-month-old female TIEG(-/-) mice revealed significant decreases in cortical bone parameters compared to WT littermates. Histomorphometric evaluation of the distal femur revealed that female TIEG(-/-) mice also display a 31% decrease in cancellous bone area, which is primarily due to a decrease in trabecular number. At the cellular level, female TIEG(-/-) mice exhibit a 42% reduction in bone formation rate which is almost entirely due to a reduction in double labeled perimeter. Differences in mineral apposition rate were not detected between WT and TIEG(-/-) mice. Taken together, these findings suggest that female TIEG(-/-) mice are osteopenic mainly due to a decrease in the total number of functional/mature OBs.

Estrogen receptor beta isoform-specific induction of transforming growth factor beta-inducible early gene-1 in human osteoblast cells: an essential role for the activation function 1 domain

The estrogen receptors (ER) alpha and beta are important ligand-mediated transcription factors known to play significant biological roles in numerous tissues including bone. Despite the high homology shared by these receptors, recent studies have suggested that their function is largely unique. Although these receptors have been studied in detail for more than a decade, little data exist concerning the mechanisms by which these two proteins regulate distinct sets of genes. Using the TGFbeta-inducible early gene-1 (TIEG) as a model, we demonstrate that TIEG is rapidly induced in response to estrogen in osteoblasts by ERbeta, but not ERalpha. We have identified the regulatory elements utilized by ERbeta and have demonstrated that ERbeta recruits steroid receptor coactivator (SRC)1 and SRC2 to this regulatory region. Additionally, deletion of the ERbeta-activation function 1 (AF1) domain drastically decreases the estrogen induction of TIEG. Through the use of chimeric receptors, we have demonstrated that the AF1 domain of ERbeta is responsible for recruiting SRC1 and SRC2 and inducing the expression of TIEG in osteoblasts. Finally, SRC1, but not SRC2, is essential for TIEG induction by ERbeta. Overall, these data demonstrate that the estrogen induction of TIEG is ERbeta specific and that the AF1 domain of ERbeta confers this specificity. Finally, a novel and important role for ERbeta's AF1 is implicated in the recruitment of specific coactivators, suggesting that the AF1 may play a significant role in conferring the differences in regulation of gene expression by these two receptors.

Expression of an estrogen receptor agonist in differentiating osteoblast cultures

Osteoblasts respond in direct and indirect ways to estrogens, and age-dependent changes in hormone levels and bone health can be limited by focused hormone replacement therapy. In this study, we report the release and isolation of an estrogen receptor agonist from osteoblast cultures. This entity reprises many aspects of estradiol activity in isolated osteoblasts, but differs from authentic estradiol by several biochemical and physical criteria. At levels that occur in conditioned medium from differentiating osteoblast cultures, the agonist directly drives gene expression through estrogen-sensitive response elements, activates the obligate osteoblast transcription factor Runx2, and potently enhances Smad-dependent gene expression in response to TGF-beta, but exhibits relatively lesser suppressive effects on gene expression through C/EBP and AP-1-binding protein transcription factors. Estrogen receptor agonist activity is resistant to heating at 100 degrees C and separable from the bulk of the remaining alcohol- and hexane-soluble molecules by C18 chromatography. MS and molecular fragmentation analyses predict a M(r) of 415.2 to 437.2. Therefore, in addition to earlier studies showing that osteoblasts readily respond to and metabolize various sex steroid-like substrates, we find that they also generate a potent estrogen receptor agonist during differentiation in vitro. Changes in the availability of a molecule like this within bone may relate to differences in skeletal integrity with aging or metabolic disease.

Estrogen-TGFbeta cross-talk in bone and other cell types: role of TIEG, Runx2, and other transcription factors

It is well established that E(2) and TGFbeta have major biological effects in multiple tissues, including bone. The signaling pathways through which these two factors elicit their effects are well documented. However, the interaction between these two pathways and the potential consequences of cross-talk between E(2) and TGFbeta continue to be elucidated. In this prospectus, we present known and potential roles of TIEG, Runx2, and other transcription factors as important mediators of signaling between these two pathways.

Oestrogen and the colon: potential mechanisms for cancer prevention

The role of oestrogen in oncogenesis has been examined extensively, especially in the context of breast cancer, and receptor modulators are an integral part of targeted treatment in this disease. The role of oestrogen signalling in colonic carcinoma is poorly understood. Men are more susceptible than women to colon cancer. Furthermore, hormone-replacement therapy affords an additive protective effect for postmenopausal women, and when these women do develop cancer, they typically have less aggressive disease. The discovery of a second oestrogen receptor (ERbeta) and its over expression in healthy human colon coupled with reduced expression in colon cancer suggests that this receptor might be involved. The underlying mechanism, however, remains largely unknown. In this Review, we discuss the various hypotheses presented in the published literature. We examine the cellular and molecular mechanisms through which oestrogen is purported to exert its protective influence, and we review the evidence available to support these claims.

Indirect androgen doping by oestrogen blockade in sports

Androgens can increase muscular mass and strength and remain the most frequently abused and widely available drugs used in sports doping. Banning the administration of natural or synthetic androgens has led to a variety of strategies to circumvent the ban of the most effective ergogenic agents for power sports. Among these, a variety of indirect androgen doping strategies aiming to produce a sustained rise in endogenous testosterone have been utilized. These include oestrogen blockade by drugs that act as oestrogen receptor antagonists (antioestrogen) or aromatase inhibitors. The physiological and pharmacological basis for the effects of oestrogen blockade in men, but not women, are reviewed.

The specific estrogen receptor antagonist ICI 182,780 masculinizes development of the zebra finch syrinx

In zebra finches, the vocal organ (syrinx) is larger in males compared to females. The exact mechanism responsible for this sex difference is not known, but it may be related to steroid hormones. Previous studies have demonstrated that treatment with estradiol feminizes the mass as well as fiber size of the two largest syrinx muscles (ventralis and dorsalis) in males. Treating females with the aromatase inhibitor fadrozole, however, does not induce masculinization. As an alternative approach to further clarify this paradoxical effect of estrogens on syrinx development, we administered the specific estrogen receptor antagonist ICI 182,780 during the first 25 days post-hatching. Daily injections of this drug significantly increased ventralis and dorsalis muscle fiber size in both sexes. Data also demonstrate that in males, the ventralis muscle makes an earlier contribution to the sex difference in syrinx mass by becoming dimorphic prior to dorsalis. Taken together, these data suggest that estrogens can influence development of the syrinx by feminizing morphology of this tissue. However, the lack of reported sex differences during development in steroid receptors, plasma steroid levels, and aromatase enzyme, indicate that hormones are not solely responsible for sex differences in this organ. Thus, similar to the neural forebrain regions that control song, complete sexual differentiation of the zebra finch syrinx likely involves additional factors.

The skeletal response to estrogen is impaired in female but not in male steroid receptor coactivator (SRC)-1 knock out mice

Estrogen (E) is critical for the maintenance of bone mass in both female and male mice and steroid receptor coactivator (SRC)-1 has been shown to be important for mediating E effects on bone, at least in female mice. In the present study, we defined the skeletal phenotype of male SRC-1 knock out (KO) mice and compared it with their female littermates. Further, to determine the role of SRC-1 in mediating effects of E on bone in male mice, we examined the skeletal effects of gonadectomy (gnx) with or without E replacement in male mice and placed these findings in the context of our previous studies in female SRC-1 KO mice. Analysis of a large group of male (WT, n=67; SRC-1 KO, n=56) and female (WT, n=66; SRC-1 KO, n=70) mice showed a significant decrease in trabecular volumetric bone mineral density (vBMD) in SRC-1 KO mice compared to their WT littermates in both genders (male SRC-1 KO, 275+/-3 vs. WT, 295+/-3 mg/cm(3), P<0.001; female SRC-1 KO, 210+/-2 vs. WT, 221+/-2 mg/cm(3), P<0.001). Following gnx and E replacement (10 microg/kg/day), we previously demonstrated that SRC-1 KO female mice have a defect in E action in trabecular, but not in cortical bone. In contrast, we now demonstrate that the same dose of E administered to gnx'd male SRC-1 KO mice was sufficient to prevent trabecular bone loss in these mice. For example, in WT female mice, gnx followed by E replacement maintained spine BMD (1.2+/-3.4% vs. baseline) as compared to gnx without E replacement (-12.7+/-2.6%, P<0.001 vs. sham); this effect of E was absent in SRC-1 KO female mice. By contrast, the identical dose of E was equally effective in maintaining spine BMD in E-treated gnx'd male WT (-5.2+/-5.1% vs. baseline) and male SRC-1 KO (-5.4+/-5.3%) mice, respectively, as compared to gnx'd mice without E treatment (WT, -17.6+/-2.5%, P=0.02; SRC-1 KO, -28.6+/-2.6%, P<0.001 vs. sham). E treatment was effective in suppressing cancellous bone turnover in both gnx'd WT and SRC-1 KO male mice as determined by significant reductions in osteoblast and osteoclast numbers; however, in female mice, E treatment only suppressed bone turnover in WT but not in SRC-1 KO mice. Collectively, these findings demonstrate that loss of SRC-1 results in trabecular osteopenia in male and female mice, but in contrast to female mice, this is not due to any detectable resistance to E action in trabecular bone in male SRC-1 KO mice.

The role of sex steroids in controlling pubertal growth

Longitudinal growth, which is primarily due to chondrocytic activity at the level of the epiphyseal growth plate, is influenced by many hormones and growth factors in an endocrine and paracrine manner. Their influence is even more complex during the accelerated growth period of puberty that accounts for about 20% of final adult height. Although abnormalities of growth during puberty are very common, the underlying mechanisms that govern the beginning and cessation of pubertal growth at the level of the growth plate are poorly understood. Sex steroids play a crucial role in pubertal growth both at the systemic level via the GH/IGF-1 axis and at the local level of the epiphyseal growth plate. In both sexes it is now accepted that oestrogen is the critical hormone in controlling growth plate acceleration and fusion. This paper reviews the mechanisms that influence pubertal growth and the problems that are associated with disorders of gonadal function.

Loss of ERE binding activity by estrogen receptor-α alters basal and estrogen-stimulated bone-related gene expression by osteoblastic cells

Estrogen receptor (ER)-alpha can signal either via estrogen response element (ERE)-mediated pathways or via alternate pathways involving protein-protein or membrane signaling. We previously demonstrated that, as compared to wild type (WT) controls, mice expressing a mutant ER-alpha lacking the ability to bind EREs (non-classical estrogen receptor knock-in (NERKI)) display significant impairments in the skeletal response to estrogen. To elucidate the mechanism(s) underlying these in vivo deficits, we generated U2OS cells stably expressing either WT ER-alpha or the NERKI receptor. Compared to cells transfected with the control vector, stable expression of ER-alpha, even in the absence of E2, resulted in an increase in mRNA levels for alkaline phosphatase (AP, by 400%, P < 0.01) and a decrease in mRNA levels for insulin growth factor-I (IGF-I) (by 65%, P < 0.001), with no effects on collagen I (col I) or osteocalcin (OCN) mRNA levels. By contrast, stable expression of the NERKI receptor resulted in the suppression of mRNA levels for AP, col I, OCN, and IGF-I (by 62, 89, 60, and 70%, P < 0.001). While E2 increased mRNA levels of AP, OCN, col I, and IGF-I in ER-alpha cells, E2 effects in the NERKI cells on AP and OCN mRNA levels were attenuated, with a trend for E2 to inhibit col I mRNA levels. In addition, E2 had no effects on IGF-I mRNA levels in NERKI cells. Collectively, these findings indicate that ERE signaling plays a significant role in mediating effects of estrogen on osteoblastic differentiation markers and on IGF-I mRNA levels.

Identification of target cells for the genomic effects of estrogens in bone

Estrogen has bone protective effects, but the exact mechanism behind these effects remains unclear. The aim of the present study was to identify the primary target cells in bone for the classical genomic effects of estrogens in vivo. For this purpose we have used reporter mice with a luciferase gene under the control of three estrogen-responsive elements (EREs), enabling detection of in vivo activation of gene transcription. Three-month-old ovariectomized mice were treated with a single dose (50 mug/kg) 17beta-estradiol (E2). Luciferase activity was analyzed in several tissues and in different bone marrow-derived lymphocyte enriched/depleted preparations using MacsMouse CD19 (for B lymphocytes) or CD90 (for T lymphocytes) MicroBeads (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany). Histological characterization of cells with high luciferase content was performed using immunohistochemistry. Both cortical bone and bone marrow displayed a rapid (within 1 h) and pronounced E2-induced increase in luciferase activity. The luciferase activity in total bone marrow and in bone marrow depleted of lymphocytes was increased six to eight times more than in either B-lymphocyte or T-lymphocyte enriched cell fractions 4 h after the E2 injection, demonstrating that mature lymphocytes are not major direct targets for the genomic effect of estrogens in bone. Immunohistochemistry identified clear luciferase staining in hypertrophic growth plate chondrocytes, megakaryocytes, osteoblasts, and lining cells, whereas no staining was seen in proliferative chondrocyte. Although most of the osteocytes did not display any detectable luciferase staining, a subpopulation of osteocytes both in cortical and trabecular bone stained positive for luciferase. In conclusion, hypertrophic growth plate chondrocytes, megakaryocytes, osteoblasts, lining cells, and a subpopulation of osteocytes were identified to respond to estrogen via the classical ERE-mediated genomic pathway in bone. Furthermore, our findings indicate that possible direct estrogenic effects on the majority of osteocytes, not staining positive for luciferase, on proliferative chondrocytes and on mature lymphocytes are mediated by non-ERE actions.

Estrogen and bone: osteoclasts take center stage

Loss of estrogen at menopause causes osteoporosis in many women, but estrogen's relevant cellular target in this process has remained unclear. In a recent study in Cell, Kato and colleagues (Nakamura et al., 2007) selectively ablate estrogen receptor alpha in osteoclasts and demonstrate that estrogen directly induces osteoclast apoptosis.

Ginkgo biloba extract EGb 761 attenuates hippocampal neuronal loss and cognitive dysfunction resulting from chronic restraint stress in ovariectomized rats

We have recently found that a combination of ovariectomy (OVX) and chronic restraint stress causes cognitive dysfunction and reduces hippocampal CA3 neurons in female rats and that estrogen replacement suppresses the OVX/stress-induced behavioral and morphological changes. In this study, we examined the effect of Ginkgo biloba extract (EGb 761), a popular herbal supplement, on the cognitive dysfunction and neuromorphological change in OVX/stress-subjected rats. Female Fisher 344 rats were randomly divided into three groups: vehicle-treated OVX, EGb 761 (50 mg/kg) -treated OVX and vehicle-treated sham-operated control groups. Two months after ovariectomy, all animals received restraint stress for 21 days (6 h/day), and were then subjected to a novel object recognition test followed by morphological examination by Nissl staining. EGb 761 was orally administered once daily until the behavioral analysis was done. Treatment with EGb 761 improved memory impairment and neuronal loss of hippocampus in the OVX/stress-subjected group in the same ways as 17beta-estradiol. On the other hand, EGb 761 did not affect the loss of bone mineral density and increase in body weight after OVX, although 17beta-estradiol attenuated them. These results have important implications for neuroprotective and cognition enhancing effects of EGb 761 in postmenopausal women and suggest that the effects are mediated by a different mechanism from estrogen.

Oestrogen receptors and linear bone growth

In this review we summarize available data regarding linear growth in oestrogen receptor alpha (ERalpha)- and oestrogen receptor beta (ERbeta)-deficient mice. We discuss these findings in relation to known oestrogenic effects in humans and the possibility of applying this knowledge for the therapeutic modulation of longitudinal bone growth employing selective oestrogen receptor modulators (SERMs). We conclude that SERMs potentially could offer new possibilities to modulate bone growth by specifically targeting different oestrogen receptors within the growth plate.

The skeletal responsiveness to mechanical loading is enhanced in mice with a null mutation in estrogen receptor-beta

Mechanical loading caused by physical activity can stimulate bone formation and strengthen the skeleton. Estrogen receptors (ERs) play some role in the signaling cascade that is initiated in bone cells after a mechanical load is applied. We hypothesized that one of the ERs, ER-beta, influences the responsiveness of bone to mechanical loads. To test our hypothesis, 16-wk-old male and female mice with null mutations in ER-beta (ER-beta(-/-)) had their right forelimbs subjected to short daily loading bouts. The loading technique used has been shown to increase bone formation in the ulna. Each loading bout consisted of 60 compressive loads within 30 s applied daily for 3 consecutive days. Bone formation was measured by first giving standard fluorochrome bone labels 1 and 6 days after loading and using quantitative histomorphometry to assess bone sections from the midshaft of the ulna. The left nonloaded ulna served as an internal control for the effects of loading. Mechanical loading increased bone formation rate at the periosteal bone surface of the mid-ulna in both ER-beta(-/-) and wild-type (WT) mice. The ulnar responsiveness to loading was similar in male ER-beta(-/-) vs. WT mice, but for female mice bone formation was stimulated more effectively in ER-beta(-/-) mice (P < 0.001). We conclude that estrogen signaling through ER-beta suppresses the mechanical loading response on the periosteal surface of long bones.

Genetic dissection of mouse distal chromosome 1 reveals three linked BMD QTLs with sex-dependent regulation of bone phenotypes

Genetic analyses with mouse congenic strains for distal Chr1 have identified three closely linked QTLs regulating femoral vBMD, mid-diaphyseal cortical thickness, and trabecular microstructure in a sex-dependent fashion. The homologous relationship between distal mouse Chr 1 and human 1q21-24 offers the possibility of finding common regulatory genes for cortical and trabecular bone.

INTRODUCTION

The distal third of mouse chromosome 1 (Chr 1) has been shown to carry a major quantitative trait locus (QTL) for BMD from several inbred mouse strain crosses. Genetic and functional analyses are essential to identify genes and cellular mechanisms for acquisition of peak bone mass.

MATERIALS AND METHODS

Nested congenic sublines of mice were developed with a C57BL/6J (B6) background carrying <1- to 9-Mbp-sized segments donated from C3H/HeJ (C3H). Isolated femurs from 16-wk-old female and male mice were measured by pQCT and microCT40 for volumetric (v)BMD, mid-diaphyseal cortical thickness, and distal trabecular phenotypes. Static and dynamic histomorphologic data were obtained on selected females and males at 16 wk.

RESULTS AND CONCLUSIONS

We found that the original BMD QTL, Bmd5, mapped to distal Chr 1 consists of three QTLs with different effects on vBMD and trabecular bone in both sexes. Compared with B6 controls, femoral vBMD, BMD, and cortical thickness (p < 0.0001) were significantly increased in congenic subline females, but not in males, carrying C3H alleles at QTL-1. Both females and males carrying C3H alleles at QTL-1 showed marked increases in BV/TV by microCT compared with B6 mice (p < 0.0001). Females increased BV/TV by increasing trabecular thickness, whereas males increased trabecular number. In addition, the microCT40 data showed two unique QTLs for male trabecular bone, QTL-2 and QTL-3, which may interact to regulate trabecular thickness and number. These QTLs are closely linked with and proximal to QTL-1. The histomorphometric data revealed sex-specific differences in cellular and bone formation parameters. Mice and humans share genetic homology between distal mouse Chr 1 and human Chr 1q20-24 that is associated with adult human skeletal regulation. Sex- and compartment-specific regulatory QTLs in the mouse suggest the need to partition human data by sex to improve accuracy of mapping and genetic loci identification.

Age-related changes in trabecular architecture differ in female and male C57BL/6J mice

We used microCT and histomorphometry to assess age-related changes in bone architecture in male and female C57BL/6J mice. Deterioration in vertebral and femoral trabecular microarchitecture begins early, continues throughout life, is more pronounced at the femoral metaphysis than in the vertebrae, and is greater in females than males.

INTRODUCTION

Despite widespread use of mice in the study of musculoskeletal disease, the age-related changes in murine bone structure and the relationship to whole body BMD changes are not well characterized. Thus, we assessed age-related changes in body composition, whole body BMD, and trabecular and cortical microarchitecture at axial and appendicular sites in mice.

MATERIALS AND METHODS

Peripheral DXA was used to assess body composition and whole body BMD in vivo, and microCT and histomorphometry were used to measure trabecular and cortical architecture in excised femora, tibia, and vertebrae in male and female C57BL/6J mice at eight time-points between 1 and 20 mo of age (n = 6-9/group).

RESULTS

Body weight and total body BMD increased with age in male and female, with a marked increase in body fat between 6 and 12 mo of age. In contrast, trabecular bone volume (BV/TV) was greatest at 6-8 wk of age and declined steadily thereafter, particularly in the metaphyseal region of long bones. Age-related declines in BV/TV were greater in female than male. Trabecular bone loss was characterized by a rapid decrease in trabecular number between 2 and 6 mo of age, and a more gradual decline thereafter, whereas trabecular thickness increased slowly over life. Cortical thickness increased markedly from 1 to 3 mo of age and was maintained or slightly decreased thereafter.

CONCLUSIONS

In C57BL/6J mice, despite increasing body weight and total body BMD, age-related declines in vertebral and distal femoral trabecular bone volume occur early and continue throughout life and are more pronounced in females than males. Awareness of these age-related changed in bone morphology are critical for interpreting the skeletal response to pharmacologic interventions or genetic manipulation in mice.

Skeletal remodeling in health and disease

The use of genetically manipulated mouse models, gene and protein discovery and the cataloguing of genetic mutations have each allowed us to obtain new insights into skeletal morphogenesis and remodeling. These techniques have made it possible to identify molecules that are obligatory for specific cellular functions, and to exploit these molecules for therapeutic purposes. New insights into the pathophysiology of diseases have also enabled us to understand molecular defects in a way that was not possible a decade ago. This review summarizes our current understanding of the carefully orchestrated cross-talk between cells of the bone marrow and between bone cells and the brain through which bone is constantly remodeled during adult life. It also highlights molecular aberrations that cause bone cells to become dysfunctional, as well as therapeutic options and opportunities to counteract skeletal loss.

Increased bone mass in male and female mice following tamoxifen administration

Tamoxifen is capable of preserving bone mass in gonadectomized rodents as well as intact female mice; however, a detailed 3D quantitative analysis of the structural changes produced in the growing skeleton of intact mice of both genders by this agent is lacking. Employing quantitative microcomputed tomography (muCT), we assessed the effects of 4-hydroxytamoxifen (OHT) on the femora of C57BL/6J mice administered this agent either for 12 (males and females) or 2 (females) weeks. In mice of either gender, but especially in females, 12 weeks of OHT exposure led to dramatic increases in both cortical and trabecular bone. Females exposed to OHT for either 2 or 12 weeks demonstrated significantly increased cortical wall thickness, trabecular bone volume, connectivity, and number, as well as decreased trabecular separation. Significant increases in several of these parameters were also evident in males after 12 weeks of OHT administration. In view of the expanding use of OHT to induce Cre-mediated recombination events, our findings suggest that care should be exercised when interpreting the skeletal phenotypes of mice exposed this agent, particularly in situations where the effects of OHT might synergize with the phenotypic outcome of a specific genetic alteration.

Loss of sex-specific difference in femoral bone parameters in male leptin knockout mice

Sex-dependent differences were identified in the femoral bone parameters of male and female ob/ob (leptin knockout) mice compared with their C57BL/6 wild-type background strain. Total fat, lean weight and body weight were not different between adult male and female leptin knockout mice. However, leptin knockout males exhibited lower lean weights than C57BL/6 males. Peripheral quantitative computerized tomographic measurements at the femoral midshaft revealed that the normal differences in the periosteal circumference, endosteal circumference, total bone mineral content, and polar moment of inertia normally observed between adult male and female wild-type mice were lost between adult male and female ob/ob mice. Significant reductions in these bone parameters were seen in male ob/ob mice compared to male wild-type mice but not in female ob/ob mice compared to female wild-type mice. In prepubertal mice, there were no differences in phenotype and femoral bone parameters between males and females within any strain, suggesting sex hormone functions. Serum free testosterone levels were 5.6-fold higher in adult male ob/ob mice than in adult male C57BL/6 wild-type mice, and serum estradiol levels were 1.8- and 1.3-fold greater in adult male and female ob/ob mice, respectively, than in their wild-type counterparts. Androgen receptor gene expression was not different in femur-derived bone cells of male ob/ob mice compared with wild-type mice. The loss of sex-related differences in these bone parameters in adult male ob/ob mice might result from deficient signaling in the androgen signaling pathway and the fact that leptin functions are permissive for androgen effects on bone development.

Altered ovarian function affects skeletal homeostasis independent of the action of follicle-stimulating hormone

Osteoporosis is a leading public health problem. Although a major cause in women is thought to be a decline in estrogen, it has recently been proposed that FSH or follitropin is required for osteoporotic bone loss. We examined the FSH receptor null mouse (FORKO mouse) to determine whether altered ovarian function could induce bone loss independent of FSH action. By 3 months of age, FORKO mice developed age-dependent declines in bone mineral density and trabecular bone volume of the lumbar spine and femur, which could be partly reversed by ovarian transplantation. Bilateral ovariectomy reduced elevated circulating testosterone levels in FORKO mice and decreased bone mass to levels indistinguishable from those in ovariectomized wild-type controls. Androgen receptor blockade and especially aromatase inhibition each produced bone volume reductions in the FORKO mouse. The results indicate that ovarian secretory products, notably estrogen, and peripheral conversion of ovarian androgen to estrogen can alter bone homeostasis independent of any bone resorptive action of FSH.

Estrogen receptors alpha and beta are inhibitory modifiers of Apc-dependent tumorigenesis in the proximal colon of Min/+ mice

Estrogen replacement therapy in postmenopausal women is associated with a reduction in colorectal cancer risk, potentially via interactions between 17beta-estradiol (E(2)) and the estrogen receptors (ER) alpha and beta. To study the role of E(2) in intestinal tumor inhibition, we separately crossed C57BL/6J-Min/+ (Min/+) mice with Eralpha(+/-) and Erbeta(+/-) mice to generate ER-deficient Min/+ progeny. We found an increased incidence of visible colon tumors and dysplastic microadenomas in ER-deficient Min/+ relative to Er(+/+)Min/+ controls. Small intestinal tumor numbers were unaffected. Invasive carcinomas were found only in Eralpha(+/-)Min/+ mice, suggesting that ERalpha plays additional non-cell autonomous roles that limit tumor progression. Histologic analyses of ER-deficient Min/+ colons, as well as colons from ovariectomized Min/+ mice (OvxMin/+) and E(2)-treated OvxMin/+ mice (OvxMin/+ +E(2)), revealed significant differences in crypt architecture, enterocyte proliferation, and goblet cell differentiation relative to Min/+ and Er(+/+)Apc(+/+) (wild-type) controls. The expression of ERalpha and ERbeta was regionally compartmentalized along the colonic crypt axis, suggesting functional antagonism. Our results indicate that ERalpha and ERbeta are inhibitory modifiers of Apc-dependent colon tumorigenesis. As a result, loss of E(2) and ER signaling in postmenopausal women may contribute to colorectal cancer development.

Effects of loss of classical estrogen response element signaling on bone in male mice

The role of estrogen signaling in the male skeleton via estrogen receptor (ER)-alpha is now well established. ERalpha can elicit responses through either classical estrogen response elements (ERE) pathways or nonclassical, non-ERE pathways. In the present study, we examined the effects of either the attenuation or loss of classical ERalpha signaling on the murine male skeleton. To accomplish this, we crossed male mice heterozygous for a knock-in mutation [nonclassical ERalpha knock-in (NERKI)], which abolishes the ERE-mediated pathway with female heterozygous ERalpha knockout mice (ERalpha+/-) and studied the F1 generation ERalpha+/+, ERalpha+/-, ERalpha+/NERKI, and ERalpha-/NERKI male progeny longitudinally using bone density and histomorphometry. The only ERalpha allele present in ERalpha-/NERKI mice is incapable of classical ERE-mediated signaling, whereas the heterozygous ERalpha+/NERKI mice have both one intact ERalpha and one NERKI allele. As compared with ERalpha+/+ littermates (n=10/genotype), male ERalpha+/NERKI and ERalpha-/NERKI mice displayed axial and appendicular skeletal osteopenia at 6, 12, 20, and 25 wk of age, as demonstrated by significant reductions in total bone mineral density (BMD) at representative sites (areal BMD by dual-energy x-ray absorptiometry at the lumbar vertebrae and femur and volumetric BMD by peripheral quantitative computed tomography at the tibia; P<0.05-0.001 vs. ERalpha+/+). The observed osteopenia in these mice was evident in both trabecular and cortical bone compartments. However, these decreases were more severe in mice lacking classical ERalpha signaling (ERalpha-/NERKI mice), compared with mice in which one wild-type ERalpha allele was present (ERalpha+/NERKI mice). Collectively, these data demonstrate that classical ERalpha signaling is crucial for the development of the murine male skeleton.

Estrogen receptor alpha genotype confers interindividual variability of response to estrogen and testosterone in mesenchymal-stem-cell-derived osteoblasts

Hormone replacement therapy is effectively used to prevent postmenopausal bone loss. Variation in response to the therapy is, however, frequently seen. In addition, the direct effects of sex steroids on isolated human bone marrow stromal cells have been reported to vary depending on the donor, but the biological mechanisms are not understood. The aim of this study was to investigate the effects of 17beta-estradiol (E2) and testosterone in human-bone-marrow-derived mesenchymal stem cell (MSC) cultures from both female and male donors of various ages. The osteoblast differentiation capacity and activity of the MSCs were quantified in vitro by measuring alkaline phosphatase activity and calcium deposition. We show here that also the osteoblast responses of MSCs to sex hormones vary widely depending on the donor. When the results from all donors were analyzed together, treatment with E2 increased calcium deposition significantly by MSCs of both sexes but ALP activity only in the male MSCs. Testosterone had no effect on ALP activity nor calcium deposition in either sex. To further characterize the individual variation, we investigated estrogen receptor alpha PvuII restriction site polymorphism with PCR. Restriction fragment-length polymorphism was assigned as P or non-P, P signifying the absence of the restriction site. Our results indicate that higher basal osteoblast differentiation capacity of MSCs is associated with the presence of the P allele in females, whereas higher response to sex steroids treatment is associated with the non-P allele. These results could help explain the contradictory effects of E2 on osteoblasts in vitro and might also provide new insights to understanding the differences in responses to hormone replacement therapy.

Bone protection by estrens occurs through non-tissue-selective activation of the androgen receptor

The use of estrogens and androgens to prevent bone loss is limited by their unwanted side effects, especially in reproductive organs and breast. Selective estrogen receptor modulators (SERMs) partially avoid such unwanted effects, but their efficacy on bone is only moderate compared with that of estradiol or androgens. Estrens have been suggested to not only prevent bone loss but also exert anabolic effects on bone while avoiding unwanted effects on reproductive organs. In this study, we compared the effects of a SERM (PSK3471) and 2 estrens (estren-alpha and estren-beta) on bone and reproductive organs to determine whether estrens are safe and act via the estrogen receptors and/or the androgen receptor (AR). Estrens and PSK3471 prevented gonadectomy-induced bone loss in male and female mice, but none showed true anabolic effects. Unlike SERMs, the estrens induced reproductive organ hypertrophy in both male and female mice and enhanced MCF-7 cell proliferation in vitro. Estrens directly activated transcription in several cell lines, albeit at much higher concentrations than estradiol or the SERM, and acted for the most part through the AR. We conclude that the estrens act mostly through the AR and, in mice, do not fulfill the preclinical efficacy or safety criteria required for the treatment or prevention of osteoporosis.

Antiremodeling agents influence osteoblast activity differently in modeling and remodeling sites of canine rib

Antiremodeling agents reduce bone loss in part through direct actions on osteoclasts. Their effects on osteoblasts and bone formation activity are less clear and may differ at sites undergoing modeling vs. remodeling. Skeletally mature intact beagles, 1-2 years old at the start of the study, were treated daily with clinically relevant doses of alendronate (0.10 or 0.20 mg/kg), risedronate (0.05 or 0.10 mg/kg), raloxifene (0.50 mg/kg), or vehicle (1 mL/kg). Dynamic bone formation parameters were histologically assessed on periosteal, endocortical/trabecular, and intracortical bone envelopes of the rib. Raloxifene significantly increased periosteal surface mineral apposition rate (MAR), a measure of osteoblast activity, compared to all other treatments (+108 to +175%, P < 0.02), while having no significant effect on MAR at either the endocortical/trabecular or intracortical envelope. Alendronate (both 0.10 and 0.20 doses) and risedronate (only the 0.10 dose) significantly (P < or = 0.05) suppressed MAR on the endocortical/trabecular envelope, while none of the bisphosphonate doses significantly altered MAR at either the periosteal or intracortical envelopes compared to vehicle. Based on these results, we conclude that (1) at clinically relevant doses the two classes of antiremodeling agents, bisphosphonates and selective estrogen receptor modulators, exert differential effects on osteoblast activity in the canine rib and (2) this effect depends on whether modeling or remodeling is the predominant mechanism of bone formation.

Effect of overexpression of estrogen receptors in osteoblasts

Our study focused on investigating the mechanism of action of estrogen in regulating p53 levels within osteoblasts. In the studies reported here, we attempted to understand the role of estrogen receptors, ER-alpha and ER-beta, in the regulation of p53 and osteoblast differentiation. We stably expressed ER-alpha and ER-beta in ROS 17/2.8 cells and isolated several single cell clones. These clones were initially characterized for expression of the exogenous receptors, and representative clones from each type were chosen for further analyses. Cell proliferation, alkaline phosphatase activity, and the viability of these clones in culture were tested. The cells expressing exogenous ER-alpha exhibited more differentiated characteristics than cells expressing ER-beta. Morphologically, ER-beta-overexpressing cells were more rounded than the ER-alpha-overexpressing cells, which were more elongated and fibroblastic in appearance. The ER-beta-expressing cells had a higher survival and growth rate when compared with ER-alpha cells. The ER-alpha clones were not as viable as ER-beta clones, and some of the ER-alpha cell lines showed signs of senescence, with an increase in senescence-associated (SA) galactosidase activity. The basal levels of p53 functional activity were higher in cells expressing ER-alpha as was protein expression of the p53-regulated gene p21. The significance of these receptors to osteoblast differentiation and p53 regulation is discussed.

[Pathophysiology and pathomorphology of osteoporosis]

Osteoporosis is a disease that leads to fragility fractures due to loss of bone mass and bone microstructure. This review presents an update on the fundamental pathophysiologic and pathomorphologic mechanisms of bone loss situations. Pathomorphologic characteristics such as perforations and microcallus formations are explained. The physiologic relevance of the remodeling process as well as its control by local-paracrine, systemic-endocrine and central-neural signaling pathways is discussed. Furthermore the role of hormones such as estrogen, FSH and leptin, of transcription-factors such as Runx2 and osterix and as well as that of the wnt signaling pathway for bone cell differentiation and function is presented. On the basis of current knowledge osteoporosis can be diagnosed, treated and fractures can be prevented. However, it is likely that new and even more effective diagnostic and therapeutic strategies will emerge as our understanding of the remodeling process that controls osteoblast and osteoclast function increases.

The mechanical phenotype of biglycan-deficient mice is bone- and gender-specific

Biglycan (bgn) is a small leucine-rich proteoglycan (SLRP) enriched in the extracellular matrix of skeletal tissues. While bgn is known to be involved in the growth and differentiation of osteoblast precursor cells and regulation of collagen fibril formation, it is unclear how these functions impact bone's geometric and mechanical properties, properties which are integral to the structural function of bone. Because the genetic control of bone structure and function is both local- and gender-specific and because there is evidence of gender-specific effects associated with genetic deficiencies, it was hypothesized that the engineered deletion of the gene encoding bgn would result in a cortical bone mechanical phenotype that was bone- and gender-specific. In 11-week-old C57BL6/129 mice, the cortical bone in the mid-diaphyses of the femora and tibiae of both genders was examined. Phenotypic changes in bgn-deficient mice relative to wild type controls were assayed by four-point bending tests to determine mechanical properties at the whole bone (structural) and tissue levels, as well as analyses of bone geometry and bone formation using histomorphometry. Of the bones examined, bgn deficiency most strongly affected the male tibiae, where enhanced cross-sectional geometric properties and bone mineral density were accompanied by decreased tissue-level yield strength and pre-yield structural deformation and energy dissipation. Because pre-yield properties alone were impacted, this implies that the gene deletion causes important alterations in mineral and/or the matrix/mineral ultrastructure and suggests a new understanding of the functional role of bgn in regulating bone mineralization in vivo.

Flavonoids derived from herbal Epimedium Brevicornum Maxim prevent OVX-induced osteoporosis in rats independent of its enhancement in intestinal calcium absorption

AIM

Factorial design was used to test our hypothesis whether a group of flavonoids (FE) derived from herbal Epimedium Brevicornum Maxim exerted its preventive effects on estrogen-deficiency-induced osteoporosis mainly through an enhancement in intestinal calcium absorption.

MATERIALS AND METHODS

Forty-five 12-month-old female Wistar rats were used and randomly assigned into sham-operated group and four ovariectomy (OVX) subgroups, i.e. OVX with vehicle (OVX group), OVX with FE (FE group), OVX with calcium supplement (CS group), and OVX with FE and CS (FE + CS group). Daily oral administration of FE (10 mg/kg/day) and/or CS (56 mg/kg/day) started on day 4 after OVX for 12 weeks. Before sacrificing the animals, urine and serum samples were collected for assaying indicators related to intestinal calcium absorption, regulator for calcium homeostasis, and markers of bone turnover. The left proximal femur was dissected for evaluation of the primary end-point (failure force), the second end-points (pQCT-quantified densitometry, geometry, and micro-CT-quantified 3-D trabecula micro-architecture), and pQCT-defined cross-sectional envelope.

RESULTS

FE was found to be able to prevent OVX-induced reduction in failure force as well as the above second end-points, without resulting in an increased uterus weight. CS had no preventive effect on OVX-induced reduction in failure force. Two-way factorial interaction analysis between FE and CS showed that the un-enhanced suppression of parathyroid hormone for calcium homeostasis did not provide link between the enhanced intestinal calcium absorption and the enhanced inhibition of bone resorption in the present study. Furthermore, the discrepancies between the enhanced intestinal calcium absorption and the un-enhanced end-point measures as well as anabolic effect were also revealed by the interaction analysis.

CONCLUSION

The present study suggested that FE inhibited bone resorption, stimulated bone formation, and accordingly prevented osteoporosis without hyperplastic effect on uterus in the OVX rat model, which was however independent of an enhancement in intestinal calcium absorption.

SOCS-3 negatively regulates innate and adaptive immune mechanisms in acute IL-1-dependent inflammatory arthritis

RA is an autoimmune disease characterized by sustained imbalance between pro- and antiinflammatory immune mechanisms. The SOCS proteins are negative regulators of cytokine signaling, but to date there has been little information on their function in disease. The generation of Socs3(-/Delta vav) mice, which lack SOCS-3 in the hematopoietic and endothelial cell compartment, allowed us to explore the role of endogenous SOCS-3 during acute inflammatory arthritis. Joint inflammation in Socs3(-/Delta vav) mice was particularly severe and was characterized by increased numbers of neutrophils in the inflamed synovium, bone marrow, peripheral blood, and spleen. These features were most likely due to increased production of and enhanced responsiveness to G-CSF and IL-6 during arthritis in these mice. Local osteoclast generation and bone destruction were also dramatically increased in the absence of SOCS-3, as was macrophage activation. Finally, SOCS-3 was found to negatively regulate CD4+ T lymphocyte activation, including production of the pleiotropic cytokine IL-17. The absence of SOCS-3 therefore had dramatic effects in this disease model, with a broader impact on cellular responses than SOCS-1 deficiency. These findings provide direct in vivo evidence that endogenous SOCS-3 is a critical negative regulator of multiple cell types orchestrating inflammatory joint disease.

FSH versus estrogen: who's guilty of breaking bones?

Bone loss after menopause or gonadectomy has been attributed to the drop in estrogen levels. A recent paper (Sun et al, 2006) challenges this view by showing that the pituitary hormone FSH, previously thought to target only the gonads, also acts on osteoclasts to activate bone resorption. In conjunction with genetic studies, these data raise the possibility that FSH, independent of estrogen, causes hypogonadal bone loss.

A new SNP in a negative regulatory region of the CYP19A1 gene is associated with lumbar spine BMD in postmenopausal women

Osteoporosis is a common disease of bone possessing a strong genetic component. Cytochrome P450 aromatase, which is encoded by the CYP19A1 gene, converts androgens to estradiol. Considerable evidence suggests that extragonadal estrogens play an important role in determining bone mineral density (BMD) in postmenopausal women, and, among them, those synthesized in bone cells may also be important for the determination of bone phenotype. Therefore, CYP19A1 is an excellent candidate gene for osteoporosis. Since a region upstream of exon I.3, including exon I.6, was identified as containing repressor elements of promoter pII, we conducted a search for SNPs in this region of CYP19A1. Two SNPs [Aro1(rs4775936) and Aro2] located in exon I.6 and promoter I.6, respectively, were identified and their association with BMD analyzed in a cohort of 256 Spanish postmenopausal women. Aro1(rs4775936), but not Aro2, was associated with lumbar spine BMD (P = 0.029). Homozygotes AA (16% of the women) exhibited significantly higher lumbar spine BMD, compared with GG or GA individuals. Therefore, this study describes the Aro1 polymorphism which lies within a regulatory region and which may be a functional polymorphism, partially responsible for the bone phenotype it is associated with.

Estrogen receptors and human disease

Estrogens influence many physiological processes in mammals, including but not limited to reproduction, cardiovascular health, bone integrity, cognition, and behavior. Given this widespread role for estrogen in human physiology, it is not surprising that estrogen is also implicated in the development or progression of numerous diseases, which include but are not limited to various types of cancer (breast, ovarian, colorectal, prostate, endometrial), osteoporosis, neurodegenerative diseases, cardiovascular disease, insulin resistance, lupus erythematosus, endometriosis, and obesity. In many of these diseases, estrogen mediates its effects through the estrogen receptor (ER), which serves as the basis for many therapeutic interventions. This Review will describe diseases in which estrogen, through the ER, plays a role in the development or severity of disease.

Isoflavones made simple - genistein's agonist activity for the beta-type estrogen receptor mediates their health benefits

Soy isoflavones, the focus of much research and controversy, are often referred to as "weak estrogens". In fact, genistein is a relatively potent agonist for the recently characterized beta isoform of the estrogen receptor (ERbeta). The low nanomolar serum concentrations of unconjugated free genistein achieved with high-nutritional intakes of soy isoflavones are near the binding affinity of genistein for this receptor, but are about an order of magnitude lower than genistein's affinity for the "classical" alpha isoform of the estrogen receptor (ERalpha). Moreover, these concentrations are far too low to inhibit tyrosine kinases or topoisomerase II, in vitro activities of genistein often cited as potential mediators of its physiological effects. The thesis that these physiological effects are in fact mediated by ERbeta activation provides a satisfying rationale for genistein's clinical activities. Hepatocytes do not express ERbeta; this explains why soy isoflavones, unlike oral estrogen, neither modify serum lipids nor provoke the prothrombotic effects associated with increased risk for thromboembolic disorders. The lack of uterotrophic activity of soy isoflavones reflects the fact that ERalpha is the exclusive mediator of estrogen's impact in this regard. Vascular endothelium expresses both ERalpha and ERbeta, each of which has the potential to induce and activate nitric oxide synthase; this may account for the favorable influence of soy isoflavones on endothelial function in postmenopausal women and ovariectomized rats. The ERbeta expressed in osteoblasts may mediate the reported beneficial impact of soy isoflavones on bone metabolism. Suggestive evidence that soy-rich diets decrease prostate cancer risk, accords well with the observation that ERbeta appears to play an antiproliferative role in healthy prostate. In the breast, ERalpha promotes epithelial proliferation, whereas ERbeta has a restraining influence in this regard - consistent with the emerging view that soy isoflavones do not increase breast cancer risk, and possibly may diminish it. Premenopausal women enjoy a relative protection from kidney failure; since ERbeta is an antagonist of TGF-beta signaling in mesangial cells, soy isoflavones may have nephroprotective potential. Estrogen also appears to protect women from left ventricular hypertrophy, and recent evidence suggests that this effect is mediated by ERbeta. In conjunction with reports that isoflavones may have a modestly beneficial impact on menopausal symptoms - perhaps reflecting the presence of ERbeta in the hypothalamus - these considerations suggest that soy isoflavone regimens of sufficient potency may represent a safe and moderately effective alternative to HRT in postmenopausal women. Further clinical research is required to characterize the impact of optimal genistein intakes on endothelial and bone function in men. Studies with ERbeta-knockout mice could be helpful for clarifying whether ERbeta does indeed mediate the chief physiological effects of low nanomolar genistein. S-equol, a bacterial metabolite of daidzein, has an affinity for ERbeta nearly as high as that of genistein; whether this compound contributes meaningfully to the physiological efficacy of soy isoflavones in some individuals is still unclear.

Estrogen in men: effects on bone accrual, maintenance and prevention of bone loss

Sex steroid hormones play an important role in the maintenance of bone mass in males as well as in females. Even though androgens represent the major sex steroid class in men, their primacy in regulating male skeletal remodeling has been questioned increasingly as direct and indirect evidence has emerged suggesting that estrogens also play a major role in male skeletal health. This review summarizes clinical and experimental evidence that estrogens are essential for bone accrual in the growing skeleton, maintenance of bone mass and prevention of bone loss in men.