Androgens and bone

Androgen receptor (AR) in osteocytes is important for the maintenance of male skeletal integrity: evidence from targeted AR disruption in mouse osteocytes

Androgens play a key role in the maintenance of male skeletal integrity. The regulation of this integrity by androgen receptor (AR) signaling has been mainly attributed to osteoblasts. Although osteocytes have emerged as key regulators of bone remodeling, the influence of sex steroids on these cells has been poorly studied. We aimed to investigate the role of AR signaling, specifically in osteocytes using the Cre/LoxP system in male mice (driven by dentin matrix protein 1 [ocy-ARKOs]). Osteocyte fractions of control (AR(ex2)/Y) and ocy-ARKO (ARflox(ex2)/Y; DMP1-cre) mice isolated through sequential collagenase digestion showed increasing AR expression toward the mature osteocyte fraction of control males compared with the more immature fractions, whereas this was reduced by >80% in ocy-ARKO osteocytes. The skeletal phenotype of mutant mice was further assessed by histomorphometry and quantitative micro-computed tomography at 12 and 32 weeks of age. Ocy-ARKOs had significantly lower trabecular bone volume and number in femora and tibias at 32 weeks as well as decreased trabecular number in the L(5) vertebra at 12 weeks. Biomechanical testing showed that ocy-ARKO femora were also stiffer and required a lower ultimate force to induce failure at 32 weeks. However, femoral cortical structure was not significantly different at any time point. The absence of AR in osteocyte also did not appear to affect trabecular bone formation nor its response to mechanical loading. In conclusion, selective inactivation of the AR in osteocytes of male mice accelerates age-related deterioration of skeletal integrity. These findings provide evidence for a direct role of androgens in the maintenance of trabecular bone through actions of the AR in osteocytes.

Determinants of bone microarchitecture and mechanical properties in obese men

CONTEXT

Recent studies have suggested that obesity in men is associated with increased fracture risk. Obesity in men is also associated with dysregulation of the GH/IGF-I and gonadal steroid axes, important regulators of bone homeostasis.

OBJECTIVE

The aim of the study was to investigate body composition and endocrine determinants of bone microarchitecture and mechanical properties in obese men.

DESIGN AND SETTING

We conducted a cross-sectional study at a clinical research center.

PARTICIPANTS

Thirty-five obese men (mean age, 33.8 ± 6.4 yr; mean body mass index, 36.5 ± 5.8 kg/m(2)) participated in the study.

OUTCOME MEASURES

Distal radius microarchitecture and mechanical properties were measured by three-dimensional high-resolution peripheral quantitative computed tomography and microfinite element analysis; body composition by computed tomography; bone marrow fat by proton magnetic resonance spectroscopy; total and free estradiol and testosterone; IGF-I; peak glucagon-stimulated GH; 25-hydroxyvitamin D.

RESULTS

Men with high visceral adipose tissue (VAT) had impaired mechanical properties compared to men with low VAT (P < 0.05), despite comparable body mass index. VAT was inversely associated and thigh muscle was positively associated with mechanical properties (P < 0.05). Bone marrow fat was inversely associated with cortical parameters (P ≤ 0.02). Free estradiol was positively associated with total density (P = 0.05). Free testosterone was positively associated with trabecular thickness and inversely with trabecular number (P ≤ 0.05). Peak stimulated GH was positively associated with trabecular thickness, as was IGF-I with cortical area (P ≤ 0.04).

CONCLUSION

VAT and bone marrow fat are negative predictors and muscle mass is a positive predictor of microarchitecture and mechanical properties in obese men. Testosterone, estradiol, and GH are positive determinants of trabecular microarchitecture, and IGF-I is a positive determinant of cortical microarchitecture. This supports the notion that VAT is detrimental to bone and that decreased GH and testosterone, characteristic of male obesity, may exert deleterious effects on microarchitecture, whereas higher estradiol may be protective.

Sex steroids and bone health status in men

Male osteoporosis is a health problem which deserves more attention as nearly 30% of osteoporotic fractures happen in men aged 50 years and above. Although men do not experience an accelerated bone loss phase and testosterone deficiency is not a universal characteristic for aged men, osteoporosis due to age-related testosterone deficiency does have a negative impact on bone health status of men. Observations from epidemiological studies indicate that elderly men with higher testosterone can preserve their BMD better and thus are less prone to fracture. Observations on men with estrogen resistance or aromatase deficiency indicate that estrogen is equally important in the maintenance of bone health status. This had been validated in several epidemiological studies which found that the relationships between estrogen and bone health indices are significant and sometimes stronger than testosterone. Studies on the relationship between quantitative ultrasound and bone remodeling markers suggest that testosterone and estrogen may have differential effects on bone, but further evidence was needed. In conclusion, both testosterone and estrogen are important in the maintenance of bone health in men.

Bone health and associated metabolic complications in neuromuscular diseases

This article reviews the recent literature regarding bone health as it relates to the patient living with neuromuscular disease (NMD). Studies defining the scope of bone-related disease in NMD are scant. The available evidence is discussed, focusing on abnormal calcium metabolism, increased fracture risk, and the prevalence of both scoliosis and hypovitaminosis D in Duchenne muscular dystrophy, amyotrophic lateral sclerosis, and spinal muscular atrophy. Future directions are discussed, including the urgent need for studies both to determine the nature and extent of poor bone health, and to evaluate the therapeutic effect of available osteoporosis treatments in patients with NMD.

17β-Hydroxyestra-4,9,11-trien-3-one (Trenbolone) preserves bone mineral density in skeletally mature orchiectomized rats without prostate enlargement

Testosterone enanthate (TE) administration attenuates bone loss in orchiectomized (ORX) rats. However, testosterone administration may increase risk for prostate/lower urinary tract related adverse events and polycythemia in humans. Trenbolone enanthate (TREN) is a synthetic testosterone analogue that preserves bone mineral density (BMD) and results in less prostate enlargement than testosterone in young ORX rodents. The purpose of this experiment was to determine if intramuscular TREN administration attenuates bone loss and maintains bone strength, without increasing prostate mass or hemoglobin concentrations in skeletally mature ORX rodents. Forty, 10 month old male F344/Brown Norway rats were randomized into SHAM, ORX, ORX+TE (7.0mg/week), and ORX+TREN (1.0mg/week) groups. Following surgery, animals recovered for 1 week and then received weekly: vehicle, TE, or TREN intramuscularly for 5 weeks. ORX reduced total and trabecular (t) BMD at the distal femoral metaphysis compared with SHAMs, while both TREN and TE completely prevented these reductions. TREN treatment also increased femoral neck strength by 28% compared with ORX animals (p<0.05), while TE did not alter femoral neck strength. In addition, TE nearly doubled prostate mass, compared with SHAMs (p<0.05). Conversely, TREN induced a non-significant 20% reduction in prostate mass compared with SHAMs, ultimately producing a prostate mass that was 64% below that found in ORX+TE animals (p<0.01). Hemoglobin concentrations and levator ani/bulbocavernosus (LABC) muscle mass were elevated in ORX+TE and ORX+TREN animals to a similar degree above both SHAM and ORX conditions (p<0.01). In skeletally mature rodents, both high-dose TE and low-dose TREN completely prevented the ORX-induced loss of tBMD at the distal femoral metaphysis and increased LABC mass. TREN also augmented femoral neck strength and maintained prostate mass at SHAM levels. These findings indicate that TREN may be an advantageous agent for future clinical trials evaluating agents capable of preventing bone loss resulting from androgen deficiency.

Androgen receptor antagonists: a patent review (2008-2011)

INTRODUCTION

Androgen receptor (AR) antagonists are predominantly used as chemical castration to treat prostate cancer (i.e., in conjunction with androgen deprivation therapy (ADT)). Unfortunately, castration-resistant prostate cancer (CRPC) typically develops that is refractory to targeted therapy. Insights into CRPC biology have led to the emergence of a promising clinical candidate MDV3100 (1) and a resurgence in this field. A pipeline of preclinical competitive (C-terminally directed) antagonists was discovered using a variety of innovative screening paradigms. Some inhibit nuclear translocation, selectively downregulate or degrade AR (SARD), antagonize wild-type and escape mutant AR (pan-antagonists) and/or antagonize AR target organs in vivo. Separately, the N-terminal domain has emerged as a promising novel target for noncompetitive antagonists.

AREAS COVERED

AR antagonists whose patents published between 2008 and 2011 are reviewed. Antagonists are organized based on the screening paradigm reported as discussed above.

EXPERT OPINION

Novel mechanisms provide a more informed basis for selecting a competitive antagonist; however, high potency and favorable in vivo properties remain paramount. Noncompetitive antagonists have theoretical advantages suggestive of improved clinical efficacy, but no clinical proof of concept as of yet.

Effects of Eurycoma longifolia on Testosterone Level and Bone Structure in an Aged Orchidectomised Rat Model

Testosterone replacement is the choice of treatment in androgen-deficient osteoporosis. However, long-term use of testosterone is potentially carcinogenic. Eurycoma longifolia (EL) has been reported to enhance testosterone level and prevent bone calcium loss but there is a paucity of research regarding its effect on the bone structural parameters. This study was conducted to explore the bone structural changes following EL treatment in normal and androgen-deficient osteoporosis rat model. Thirty-six male Sprague-Dawley rats aged 12 months were divided into normal control, normal rat supplemented with EL, sham-operated, orchidectomised-control, orchidectomised with testosterone replacement, and orchidectomised with EL supplementation groups. Testosterone serum was measured both before and after the completion of the treatment. After 6 weeks of the treatment, the femora were processed for bone histomorphometry. Testosterone replacement was able to raise the testosterone level and restore the bone volume of orchidectomised rats. EL supplementation failed to emulate both these testosterone actions. The inability of EL to do so may be related to the absence of testes in the androgen deficient osteoporosis model for EL to stimulate testosterone production.

Bone Micro-CT Assessments in an Orchidectomised Rat Model Supplemented with Eurycoma longifolia

Recent studies suggested that Eurycoma longifolia, a herbal plant, may have the potential to treat osteoporosis in elderly male. This study aimed to determine the effects of Eurycoma longifolia supplementation on the trabecular bone microarchitecture of orchidectomised rats (androgen-deficient osteoporosis model). Forty-eight-aged (10–12 months old) Sprague Dawley rats were divided into six groups of sham-operated (SHAM), orchidectomised control (ORX), orchidectomised + 7 mg/rat testosterone enanthate (TEN) and orchidectomised + Eurycoma longifolia 30 mg/kg (EL30), orchidectomised + Eurycoma longifolia 60 mg/kg (EL60), orchidectomised + Eurycoma longifolia 90 mg/kg (EL90). Rats were euthanized following six weeks of treatment. The left femora were used to measure the trabecular bone microarchitecture using micro-CT. Orchidectomy significantly decreased connectivity density, trabecular bone volume, and trabecular number compared to the SHAM group. Testosterone replacement reversed all the orchidectomy-induced changes in the micro-CT parameters. EL at 30 and 60 mg/kg rat worsened the trabecular bone connectivity density and trabecular separation parameters of orchidectomised rats. EL at 90 mg/kg rat preserved the bone volume. High dose of EL (90 mg/kg) may have potential in preserving the bone microarchitecture of orchidectomised rats, but lower doses may further worsen the osteoporotic changes.

Combined Effects of Eurycoma longifolia and Testosterone on Androgen-Deficient Osteoporosis in a Male Rat Model

Androgen-deficient osteoporosis in men is treated with testosterone therapy, which is associated with side effects. Eurycoma longifolia (EL) is known to possess androgenic properties and has been reported to protect bone from androgen-deficient osteoporosis in experimental animal models. The present study aimed to determine the effectiveness of combination therapy of EL and testosterone (T) in treating androgen-deficient osteoporosis. Forty male Sprague-Dawley rats were divided into: sham-operated (SHAM), orchidectomized-control (ORX), orchidectomized with testosterone (ORX + T), orchidectomized with EL (ORX + EL), and orchidectomized with combined T and EL therapy (ORX + T + EL). EL was administered via oral gavages daily at the dose of 15 mg/kg. T was injected intramuscularly at 8 mg/kg and 4 mg/kg for the ORX + T and ORX + T + EL groups, respectively. Following 6 weeks of treatment, the osteocalcin levels of ORX + T and ORX + T + EL groups were significantly lower than the SHAM group (P < 0.05). The posttreatment CTX levels of ORX + T and ORX + T + EL groups were significantly lower than their pretreatment levels (P < 0.05). Biomechanically, the strain parameter of the ORX + T + EL group was significantly higher than the ORX group (P < 0.05). Thus, the combination therapy of EL and low-dose T has potential for treatment of androgen-deficient osteoporosis. The lower T dose is beneficial in reducing the sideeffects of testosterone therapy.

Effect of host sex and sex hormones on muscle-derived stem cell-mediated bone formation and defect healing

Muscle-derived stem cells (MDSCs) are known to exhibit sexual dimorphism, by donor sex, of osteogenic, chondrogenic, and myogenic differentiation potential in vitro. Moreover, host sex differences in the myogenic capacity of MDSCs in vivo are also observed. This study investigated the role of host sex and host sex hormones in MDSC-mediated bone formation and healing. Using unaltered male, castrated male, unaltered female, and ovariectomized female mice, both MDSC-mediated ectopic bone formation and cranial defect healing were examined. Male hosts, whether unaltered or castrated, form significantly larger volumes of MDSC-mediated ectopic bone than female hosts (either unaltered or ovariectomized), and no differences in ectopic bone volume were found between hosts of the same sex. In a cranial defect healing model, similar results were found-unaltered and castrated male hosts display larger volumes of bone formed when compared with unaltered and ovariectomized female hosts. However, in this healing model, some volume differences were found between hosts of the same sex. In both models, these differences were attributed to varying rates of endochondral bone formation in male and female hosts.

Identification of gene pathways altered by deletion of the androgen receptor specifically in mineralizing osteoblasts and osteocytes in mice

Androgens play a key role in skeletal growth and maintenance in males and can mediate their actions, at least in part, via the androgen receptor (AR) in osteoblasts. To investigate the mechanisms by which androgens exert their effects via the AR in mineralizing osteoblasts and osteocytes, we identified gene targets/pathways regulated by the AR using targeted gene expression and microarray approaches on bone isolated from mice in which the AR is specifically deleted in mineralizing osteoblasts and osteocytes (mOBL-ARKOs). Gene ontology mining indicated a number of biological processes to be affected in the bones of mOBL-ARKOs including skeletal and muscular system development and carbohydrate metabolism. All genes identified to have altered expression in the bones of mOBL-ARKOs were confirmed by Q-PCR for their androgen responsiveness in an androgen deprivation and replacement mouse model. The osteoblast genes Col1a1 and Bglap and the osteoclast genes Ctsk and RANKL (Tnfs11) were upregulated in the bones of mOBL-ARKOs, consistent with the increased matrix synthesis, mineralization, and bone resorption observed previously in these mice. Of significant interest, we identified genes involved in carbohydrate metabolism (adiponectin and Dpp4) and in growth and development (GH, Tgfb (Tgfb2), Wnt4) as potential targets of androgen action via the AR in mineralizing osteoblasts.

Body composition, bone mineral density and fractures in late postmenopausal women with polycystic ovary syndrome - a long-term follow-up study

OBJECTIVE

Hyperandrogenism is one of the characteristic features of the polycystic ovary syndrome (PCOS). Androgens are important for bone mass. Studies on bone mineral density (BMD) and fractures in postmenopausal women with PCOS are lacking. The aim of this study was to investigate whether postmenopausal women with PCOS differ from controls regarding body composition, BMD and prevalence of fractures, and to compare women with PCOS with controls regarding correlations between total BMD and sex hormones.

DESIGN

A prospective 21-year follow-up study. Anthropometry, hormonal measurements and questionnaires were performed in 1987 and in 2008. Fractures were X-ray-verified. BMD measurements were taken in 1992, using single-photon absorptiometry (SPA), and in 2008, using dual-energy X-ray absorptiometry (DXA), to also enable measurements of body composition.

PATIENTS

Twenty-five women with PCOS (Rotterdam criteria), aged 61-78 years, and 68 randomly allocated age-matched controls.

MEASUREMENTS

Body composition, BMD, fractures and sex steroids.

RESULTS

At follow-up, the postmenopausal women with PCOS maintained a higher free androgen index (FAI), but had similar body fat, lean mass and BMD compared with controls. The hip circumference increased only in women with PCOS (P < 0·01), during follow-up. The fracture incidence was similar to that of controls (56% vs 41%, ns). In the controls, total BMD was positively correlated with oestradiol (R = 0·322, P < 0·01) and FAI (R = 0·307, P < 0·05) and negatively correlated with SHBG (R = -0·429, P < 0·001), but not in the women with PCOS.

CONCLUSIONS

Postmenopausal women with PCOS with persistently higher FAI had similar muscle mass, BMD and fracture incidence as controls during this long-term follow-up.

AST-induced bone loss in men with prostate cancer: exercise as a potential countermeasure

Androgen suppression treatment (AST) for men with prostate cancer is associated with a number of treatment-related side effects including an accelerated rate of bone loss. This loss of bone is greatest within the first year of AST and increases the risk for fracture. Pharmaceutical treatment in the form of bisphosphonates is currently used to counter the effects of hormone suppression on bone but is costly and associated with potential adverse effects. Recently, exercise has been shown to be an important adjuvant therapy to manage a range of treatment-related toxicities and enhance aspects of quality of life for men receiving AST. We propose that physical exercise may also have an important role in not only attenuating the bone loss associated with AST but in improving bone health and reducing fracture risk. In this review, the rationale underlying exercise as a countermeasure to AST-induced bone loss is provided.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

Regulation of adipose tissue energy availability through blood flow control in the metabolic syndrome

Maintenance of blood flow rate is a critical factor for tissue oxygen and substrate supply. The potentially large mass of adipose tissue deeply influences the body distribution of blood flow. This is due to increased peripheral resistance in obesity and the role of this tissue as the ultimate destination of unused excess of dietary energy. However, adipose tissue cannot grow indefinitely, and the tissue must defend itself against the avalanche of nutrients provoking inordinate growth and inflammation. In the obese, large adipose tissue masses show lower blood flow, limiting the access of excess circulating substrates. Blood flow restriction is achieved by vasoconstriction, despite increased production of nitric oxide, the vasodilatation effects of which are overridden by catecholamines (and probably also by angiotensin II and endothelin). Decreased blood flow reduces the availability of oxygen, provoking massive glycolysis (hyperglycemic conditions), which results in the production of lactate, exported to the liver for processing. However, this produces local acidosis, which elicits the rapid dissociation of oxyhemoglobin, freeing bursts of oxygen in localized zones of the tissue. The excess of oxygen (and of nitric oxide) induces the production of reactive oxygen species, which deeply affect the endothelial, blood, and adipose cells, inducing oxidative and nitrosative damage and eliciting an increased immune response, which translates into inflammation. The result of the defense mechanism for adipose tissue, localized vasoconstriction, may thus help develop a more generalized pathologic response within the metabolic syndrome parameters, extending its effects to the whole body.

The mutual dependence between bone and gonads

It has long been known that sex steroid hormones regulate bone mass accrual. This observation raises the testable hypothesis that bone may in turn regulate the synthesis and secretion of sex steroid hormones in one or both genders. This hypothesis is comprised within a more general hypothesis that bone mass, energy metabolism, and reproduction are regulated coordinately. The identification of osteocalcin as an osteoblast-specific secreted molecule allows us to address this question in molecular terms. This review details how the regulation of male fertility by osteocalcin was unraveled, and how osteocalcin signaling in Leydig cells of the testis occurs. It also discusses the implication of this novel mode of regulation of testosterone synthesis observed in males but not in females.

Characterization of steroid sulfatase in the MC3T3-E1 mouse pre-osteoblastic cell line

Regulation of bone density is partly dependent upon steroid hormones, with estrogens playing an important role. Inactive conjugated estrogens may serve as precursors to active estrogens, especially in post-menopausal women, via steroid sulfatase, which converts conjugated estrogens into unconjugated estrogens. The purpose of this study was to characterize steroid sulfatase in the MC3T3-E1 mouse pre-osteoblastic cell line. Enzyme conversion assays were performed on whole MC3T3-E1 cells in culture and on microsomes prepared by differential centrifugation. (3)H-E(1)S and (3)H-DHEAS were used as tracers, and radioinert E(1)S and DHEAS were used as substrate. Whole cells and microsomes exhibited steroid sulfatase activity, which was blocked by the specific inhibitor estrone-3-O-sulfamate (EMATE). The K(m) of steroid sulfatase in microsomes averaged 83 μM when using E(1)S as substrate and 64 μM when using DHEAS. Western blotting of MC3T3-E1 microsomes for steroid sulfatase was performed, after SDS-PAGE, using an antibody generated against a peptide based on a conserved region of steroid sulfatase. Western blotting revealed three bands of cross-reactivity, ranging from 50 to 79 kDa. Reverse transcriptase polymerase chain reaction (RT-PCR), using specific primers, resulted in a single cDNA band of the expected size (100 bp) and sequence, indicating the presence of steroid sulfatase mRNA. Growth assays revealed that the MC3T3-E1 cells were stimulated by estradiol-17β, and also by estrone sulfate and DHEAS, revealing that the cells can use steroid sulfatase to produce active estrogens. Furthermore, growth of these cells in the presence of estradiol, estrone and estrone sulfate was inhibited by the estrogen receptor blocker ICI 182,780, indicating that stimulation of cell growth is mediated by the estrogen receptor. In our studies, four lines of evidence (enzyme activity, immunoassay, RT-PCR and growth assays) demonstrated the presence of steroid sulfatase in mouse MC3T3-E1 bone cells. The existence of steroid sulfatase in these pre-osteoblastic cells, along with the ability of sulfated steroids to promote their growth, suggest the possibility that this enzyme is involved in regulation of bone density in mice.

Estrogen receptors α and β have different gender-dependent effects on the adaptive responses to load bearing in cancellous and cortical bone

To determine the effect of estrogen receptors (ER) α and β on bones' adaptive response to loading, we subjected the right tibiae of mice lacking ERα or ERβ activity to either axial loading or to disuse. Adaptive changes in architecture were assessed by comparing differences between the right (treated) and left (control) tibiae in these genotypes as assessed by microcomputed tomography. In female ERα(-/-) mice, the net-osteogenic response to loading was lower in cortical bone compared with their wild-type littermates (11.2 vs. 20.9% in ERα(+/+)), but it was higher in both cortical and cancellous bone of male ERα(-/-) mice (cortical 20.0 vs. 4.6% in ERα(+/+); cancellous 30.0 vs. 5.3% in ERα(+/+), P < 0.05). In ERβ(-/-) male and female mice, the net-osteogenic response to loading was higher in cortical bone (males 10.9 vs. 3.9% in ERβ(+/+); females 18.5 vs. 15.8% in ERβ(+/+), P < 0.05) but no different from controls in cancellous bone. The bone loss in response to disuse was less in cancellous bone of ERα(-/-) mice than in controls (-15.9 vs. -21.3%, respectively, P < 0.05) but no different at any other site or between any other groups. Our conclusion is that functional ERα enhances the net-osteogenic response to loading in cortical but not cancellous bone in female mice but reduces it in males. ERβ decreases the response to loading in cortical bone of males and females but has no effect in cancellous bone. Bone loss due to disuse in cortical bone is unaffected by ER status, but in cancellous bone, functional ERα contributes to greater disuse-related bone loss.

Androgens and estrogens prevent rosiglitazone-induced adipogenesis in human mesenchymal stem cells

Thiazolidinediones (TZD), a class of anti-diabetic drugs, determine bone loss and increase fractures particularly in post-menopausal women, thus suggesting a protective role of sex steroids. We have previously demonstrated that the TZD rosiglitazone (RGZ) negatively affects bone mass by inhibiting osteoblastogenesis, yet inducing adipogenesis, in bone marrow-derived human mesenchymal stem cells (hMSC). The aim of this study was to determine whether estrogens and androgens are able to revert the effects of RGZ on bone. hMSC express estrogen receptor α and β and the androgen receptor. We found that 17β-estradiol (10 nM), the phytoestrogen genistein (10 nM), testosterone (10 nM) and the non-aromatizable androgens dihydrotestosterone (10 nM) and methyltrienolone (10 nM) effectively counteracted the adipogenic effect of RGZ (1 μM) in hMSC induced to differentiate into adipocytes, as determined by evaluating the expression of the adipogenic marker peroxisome proliferator-activated receptor γ and the percentage of fat cells. Furthermore, when hMSC were induced to differentiate into osteoblasts, all the above-mentioned molecules and also quercetin, another phytoestrogen, significantly reverted the inhibitory effect of RGZ on the expression of the osteogenic marker osteocalcin and decreased the number of fat cells observed after RGZ exposure. Our study represents, to our knowledge, the first demonstration in hMSC that androgens, independently of their aromatization, and estrogens are able to counteract the negative effects of RGZ on bone. Our data, yet preliminary, suggest the possibility to try to prevent the negative effects of TZD on bone, using steroid receptor modulators, such as plant-derived phytoestrogens, which lack evident adverse effects.

The adiponectin paralog C1q/TNF-related protein 3 (CTRP3) stimulates testosterone production through the cAMP/PKA signaling pathway

CTRP3, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the new adipokine, CTRP3, in the reproductive system. CTRP3 was specifically expressed in interstitial Leydig cells, where testosterone is produced, in the adult mouse testis. CTRP3 increased testosterone production by TM3 mouse Leydig cells in a dose-dependent manner. The increased testosterone production was linked to upregulation of steroidogenic proteins expression, such as steroidogenic acute regulatory (StAR) protein and cholesterol side-chain cleavage cytochrome P450 (P450scc). Moreover, increases in intracellular cyclic AMP (cAMP) concentrations and the phosphorylation of cAMP-response element binding protein (CREB) in CTRP3-stimulated TM3 Leydig cells were observed. Inhibition of this signaling pathway by a specific protein kinase A (PKA) inhibitor, H89, blocked testosterone production in CTRP3-stimulated Leydig cells, suggesting that the stimulatory effect of CTRP3 on testosterone production is associated with activation of the cAMP/PKA signaling pathway. Thus, our results demonstrate a physiological role for CTRP3 in testicular steroidogenesis and provide novel insights in the intracellular mechanisms activated by this protein.

Estrogen, exercise, and the skeleton

Patterns of variation in bone size and shape provide crucial data for reconstructing hominin paleobiology, including ecogeographic adaptation, life history, and functional morphology. Measures of bone strength, including robusticity (diaphyseal thickness relative to length) and cross-sectional geometric properties such as moments of area, are particularly useful for inferring behavior because bone tissue adapts to its mechanical environment. Particularly during skeletal growth, exercise-induced strains can stimulate periosteal modeling so that, to some extent, bone thickness reflects individual behavior. Thus, patterns of skeletal robusticity have been used to identify gender-based activity differences, temporal shifts in mobility, and changing subsistence strategies. Although there is no doubt that mechanical loading leaves its mark on the skeleton, less is known about whether individuals differ in their skeletal responses to exercise. For example, the potential effects of hormones or growth factors on bone-strain interactions are largely unexplored. If the hormonal background can increase or decrease the effects of exercise on skeletal robusticity, then the same mechanical loads might cause different degrees of bone response in different individuals. Here I focus on the role of the hormone estrogen in modulating exercise-induced changes in human bone thickness.

Comparison of 7α-methyl-19-nortestosterone effectiveness alone or combined with progestins on androgen receptor mediated-transactivation

7α-methyl-19-nortestosterone (MENT) is an androgen with potent gonadotropin inhibitory activity and prostate-sparing effects. These attributes give MENT advantages over testosterone as a male contraceptive, but, as in the case of testosterone, a partial dose-dependent suppression of spermatogenesis has been observed. Combination of testosterone or MENT with synthetic progestins improves the rate of azoospermia; however, it is unknown whether these combinations affect hormone androgenicity or exert synergistic effects via progestational or androgenic interaction. Herein, using transactivation assays, we examined the ability of MENT alone or combined with several 19-nor-derived synthetic progestins to activate androgen receptor (AR)-dependent gene transcription. In addition, the capability of 7α-methyl-estradiol (7α-methyl-E2), an aromatized metabolite of MENT, to transactivate gene transcription via estrogen receptor α (ERα; ESR1) or ERβ (ESR2) was also investigated. As expected, MENT induced gene transactivation through either the progesterone receptor (PGR) or the AR. MENT was as efficient as progesterone in activating PGR-mediated reporter gene expression, but it was ten times more potent than testosterone and dihydrotestoterone in activating of AR-driven gene expression. The addition of increasing concentrations of other 19-nortestosterone derivatives (norethisterone or levonorgestrel) did not affect, in a significant manner, the ability of MENT to activate AR-dependent reporter gene transcription. The same results were obtained with different cell lines. 7α-Methyl-E2 resulted in potent estrogen activity via both ER subtypes with efficiency similar to natural E2. These results suggest that the addition of 19-nortestosterone-derived progestins, as a hormonal adjuvant in male fertility strategies for effective spermatogenic suppression, does not display any detrimental effect that would interfere with MENT androgenic transcriptional activity.

Sex steroids and bone health in men

The influence of sex steroids on bone in both men and women has long been recognized. In men, however, the relative contribution of androgens versus estrogens in the regulation of bone metabolism remains uncertain. Animal studies demonstrate that both estradiol (E2), via activation of estrogen receptor-α, and testosterone (T), via activation of the androgen receptor, regulate bone mass in male rodents. The main focus of this review is to summarize and discuss recent findings from the osteoporotic fractures in men (MrOS) cohorts regarding the impact of serum sex steroids on bone health in elderly men. Collectively, these data demonstrate that serum E2 is directly associated with bone mineral density (BMD) and that low serum E2 associates with higher rates of bone loss and fracture. In addition, they substantiate the concept of a threshold E2 level that determines fracture risk in elderly men. We propose that the effect of E2 on fracture risk is at least partly mediated by its effect on BMD, whereas the more modest effect of T on fracture risk mainly is mediated by effects on muscle strength and risk of falls. Findings from the MrOS cohorts also demonstrate that racial and genetic variations in aromatase activity influence serum E2 levels in men. In conclusion, there is compelling evidence that not only androgens, but also estrogens, are important regulators of bone health in men. Consequently, E2 should not exclusively be regarded as the 'female hormone' but as a sex steroid that is necessary for maintenance of bone health in men.

Estrogen receptor-α expression in neuronal cells affects bone mass

It has generally been assumed that bone mass is controlled by endocrine mechanisms and the local bone environment. Recent findings demonstrate that central pathways are involved in the regulation of bone mass. Estrogen is involved in the regulation of bone homeostasis and the CNS is also a target for estrogen actions. The aim of this study was to investigate in vivo the role of central estrogen receptor-α (ERα) expression for bone mass. Nestin-Cre mice were crossed with ERα(flox) mice to generate mice lacking ERα expression specifically in nervous tissue (nestin-ERα(-/-)). Bone mineral density was increased in both the trabecular and cortical bone compartments in nestin-ERα(-/-) mice compared with controls. Femoral bone strength was increased in nestin-ERα(-/-) mice, as demonstrated by increased stiffness and maximal load of failure. The high bone mass phenotype in nestin-ERα(-/-) mice was mainly caused by increased bone formation. Serum leptin levels were elevated as a result of increased leptin expression in white adipose tissue (WAT) and slightly increased amount of WAT in nestin-ERα(-/-) mice. Leptin receptor mRNA levels were reduced in the hypothalamus but not in bone. In conclusion, inactivation of central ERα signaling results in increased bone mass, demonstrating that the balance between peripheral stimulatory and central inhibitory ERα actions is important for the regulation of bone mass. We propose that the increased bone mass in nestin-ERα(-/-) mice is mediated via decreased central leptin sensitivity and thereby increased secretion of leptin from WAT, which, in turn, results in increased peripheral leptin-induced bone formation.

Tissue-selective regulation of androgen-responsive genes

INTRODUCTION

Androgens regulate a wide array of physiological processes, including male sexual development, bone and muscle growth, and behavior and cognition. Because androgens play a vital role in so many tissues, changes in androgen signaling are associated with a plethora of diseases. How such varied responses are achieved by a single stimulus is not well understood. Androgens act primarily through the androgen receptor (AR), a hormone nuclear receptor that is expressed in a select variety of tissues.

METHODS

In order to gain a better understanding of how the tissue-selective effects of androgens are achieved, we performed a comparison of microarray data, using previously published datasets and several of our own microarray datasets. These datasets were derived from clinically relevant, AR-expressing tissues dissected from rodents treated with the full androgen dihydrotestosterone (DHT).

RESULTS

We found that there is a diverse response to DHT, with very little overlap of androgen regulated genes in each tissue. Gene ontology analyses also indicated that, while several tissues regulate similar biological processes in response to DHT, most androgen regulated processes are specific to one or a few tissues. Thus, it appears that the disparate physiological effects mediated by androgens begin with widely varying effects on gene expression in different androgen-sensitive tissues.

CONCLUSION

The analysis completed in this study will lead to an improved understanding of how androgens mediate diverse, tissue-specific processes and better ways to assess the tissue-selective effects of AR modulators during drug development.

Tissue physiology and pathology of aromatase

Aromatase is expressed in multiple tissues, indicating a crucial role for locally produced oestrogens in the differentiation, regulation and normal function of several organs and processes. This review is an overview of the role of aromatase in different tissues under normal physiological conditions and its contribution to the development of some oestrogen-related pathologies.

Profiling insulin like factor 3 (INSL3) signaling in human osteoblasts

BACKGROUND

Young men with mutations in the gene for the INSL3 receptor (Relaxin family peptide 2, RXFP2) are at risk of reduced bone mass and osteoporosis. Consistent with the human phenotype, bone analyses of Rxfp2(-/-) mice showed decreased bone volume, alterations of the trabecular bone, reduced mineralizing surface, bone formation, and osteoclast surface. The aim of this study was to elucidate the INSL3/RXFP2 signaling pathways and targets in human osteoblasts.

METHODOLOGY/PRINCIPAL FINDINGS

Alkaline phosphatase (ALP) production, protein phosphorylation, intracellular calcium, gene expression, and mineralization studies have been performed. INSL3 induced a significant increase in ALP production, and Western blot and ELISA analyses of multiple intracellular signaling pathway molecules and their phosphorylation status revealed that the MAPK was the major pathway influenced by INSL3, whereas it does not modify intracellular calcium concentration. Quantitative Real Time PCR and Western blotting showed that INSL3 regulates the expression of different osteoblast markers. Alizarin red-S staining confirmed that INSL3-stimulated osteoblasts are fully differentiated and able to mineralize the extracellular matrix.

CONCLUSIONS/SIGNIFICANCE

Together with previous findings, this study demonstrates that the INSL3/RXFP2 system is involved in bone metabolism by acting on the MAPK cascade and stimulating transcription of important genes of osteoblast maturation/differentiation and osteoclastogenesis.

Towards a diagnostic and therapeutic consensus in male osteoporosis

The consensus views on osteoporosis in men are reported.

INTRODUCTION

A workshop was convened within a meeting on osteoporosis in men to identify areas of consensus amongst the panel (the authors) and the participants of the meeting.

METHODS

A public debate with an expert panel on preselected topics was conducted.

RESULTS AND CONCLUSIONS

Consensus views were reached on diagnostic criteria and several aspects on the pathophysiology and treatment of osteoporosis in men.

Castration-induced changes in mouse epididymal white adipose tissue

We analyzed the effects of castration on epididymal white adipose tissue (WAT) in C57BL/6J mice which were fed a regular or high-fat diet. Fourteen days following surgical castration profound effects on WAT tissue such as reductions in WAT wet weight and WAT/body weight ratio, induction of lipolysis and morphologic changes characterized by smaller adipocytes, and increased stromal cell compartment were documented in both dietary groups. Castrated animals had decreased serum leptin levels independent of diet but diet-dependent decreases in serum adiponectin and resistin. The castrated high-fat group had dramatically lower serum triglyceride levels. Immunohistochemical analysis revealed higher staining for smooth muscle actin, macrophage marker Mac-3, and Cxcl5 in the castrated than in the control mice in both dietary groups. We also detected increased fatty-acid synthase expression in the stromal compartment of WAT in the regular-diet group. Castration also reduces the expression of androgen receptor in WAT in the regular-diet group. We conclude that castration reduces tissue mass and affects biologic function of WAT in mice.

Triazole ring-opening leads to the discovery of potent nonsteroidal 17β-hydroxysteroid dehydrogenase type 2 inhibitors

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) catalyzes the oxidation of the highly potent steroids: the estrogen estradiol (E2) and the androgen testosterone (T) to the less active estrone and androstenedione, respectively. Inhibition of this enzyme may help maintain the local E2 level in bone tissue when the circulating E2 level drops and is therefore a novel and promising approach for the treatment of osteoporosis. In this work, a series of new nonsteroidal and achiral 17β-HSD2 inhibitors, namely N-benzyl-diphenyl-3(or 4)-carboxamide and N-benzyl-5-phenyl-thiophene-2-carboxamide was designed and the compounds were synthesized in a two to three steps reaction. A small library was built applying parallel synthesis. Highly potent 17β-HSD2 inhibitors could be identified in the thiophene-2-carboxamide class with IC(50) in the low nanomolar range. These compounds also showed a good selectivity profile toward 17β-HSD1 and toward the estrogen receptors α and β. The most interesting 17β-HSD2 inhibitor identified in this study is the 5-(2-fluoro-3-methoxyphenyl)-N-(3-hydroxybenzyl)-N-methylthiophene-2-carboxamide 6w displaying an IC(50) of 61 nM and a selectivity factor of 73 toward 17β-HSD1.

Coordinated tether formation in anatomically distinct mice growth centers is dependent on a functional vitamin D receptor and is tightly linked to three-dimensional tissue morphology

Bone bridges linking the epiphysis and metaphysis termed "tethers" have been found in the femoral growth plates of C57Bl/6 mice and are disrupted when the vitamin D receptor (VDR) is ablated. It is unknown if tethers are found in other growth centers, if they are regulated in a comparable manner, or if they have a functional role in skeletal development or stability. To address this, distal femoral growth plates (GPs) and spheno-occipital synchondroses (SOSs) of wild-type C57Bl/6 mice from 2 to 15 weeks of age were analyzed using μCT scans. The GPs and SOSs of VDR+/+ and VDR-/- mice fed regular or rescue diets to restore mineral homeostasis until 10 weeks of age were also scanned. Tethers in GPs and SOSs both thickened and accumulated in number as these growth centers decreased in size. Ablating the VDR made GPs and SOSs rachitic and nearly eliminated tether formation. Rescue diets restored the volume of both growth centers but only partially restored growth center thickness and tether formation, suggesting that lα,25-dihydroxy vitamin D(3) partially regulates tether formation in these growth centers via its receptor. In VDR+/+ mice 2-15 weeks in age, growth center thickness was inversely correlated to animal weight whereas tether phenotype (tether volume/growth center volume, tether number/mm, tether width, tether spacing) was significantly related to animal weight. In both 2-15 week old VDR+/+ and 10 week old VDR+/+ and VDR-/- mice on normal and rescue diets, tether phenotype (tether number/mm, tether spacing) had strikingly similar relationships to growth center thickness. These results show that tethers are present in growth centers in different anatomic and undergo developmental changes in a comparable manner; in both sites, VDR-regulated tether formation is strongly linked to growth center morphology; and tether formation is associated with body weight, suggesting a role in maintaining growth plate stability during growth.

Concerted actions of insulin-like growth factor 1, testosterone, and estradiol on peripubertal bone growth: a 7-year longitudinal study

A better understanding of how bone growth is regulated during peripuberty is important for optimizing the attainment of peak bone mass and for the prevention of osteoporosis in later life. In this report we used hierarchical models to evaluate the associations of insulin-like growth factor 1 (IGF-1), estradiol (E(2) ), and testosterone (T) with peripubertal bone growth in a 7-year longitudinal study. Two-hundred and fifty-eight healthy girls were assessed at baseline (mean age 11.2 years) and at 1, 2, 3.5, and 7 years. Serum concentrations of IGF-1, E(2) , and T were determined. Musculoskeletal properties in the left lower leg were measured using peripheral quantitative computed tomography (pQCT). Serum levels of IGF-1, E(2) , and T increased dramatically before menarche, whereas they decreased, plateaued, or increased at a lower rate, respectively, after menarche. IGF-1 level was positively associated with periosteal circumference (PC) and total bone mineral content (tBMC) throughout peripuberty but not after adjustment for muscle cross-sectional area (mCSA). On the other hand, IGF-1 was associated with tibial length (TL) independently of mCSA before menarche. T was positively associated with TL, PC, tBMC, and cortical volumetric bone mineral density, independent of mCSA, before menarche but not after. E(2) was associated with TL positively before menarche but negatively after menarche. These findings suggest that during puberty, circulating IGF-1 promotes bone periosteal apposition and mass accrual indirectly, probably through stimulating muscle growth, whereas the effects of sex steroids on bone growth differ before and after menarche, presenting a biphasic pattern. Hence the concerted actions of these hormones are essential for optimal bone development in peripuberty.

Understanding extranuclear (nongenomic) androgen signaling: what a frog oocyte can tell us about human biology

Steroids are key factors in a myriad of mammalian biological systems, including the brain, kidney, heart, bones, and gonads. While alternative potential steroid receptors have been described, the majority of biologically relevant steroid responses appear to be mediated by classical steroid receptors that are located in all parts of the cell, from the plasma membrane to the nucleus. Interestingly, these classical steroid receptors modulate different signals depending upon their location. For example, receptors in the plasma membrane interact with membrane signaling molecules, including G proteins and kinases. In contrast, receptors in the nucleus interact with nuclear signaling molecules, including transcriptional co-regulators. These extranuclear and intranuclear signals function together in an integrated fashion to regulate important biological functions. While most studies on extranuclear steroid signaling have focused on estrogens, recent work has demonstrated that nongenomic androgen signaling is equally important and that these two steroids modulate similar signaling pathways. In fact, by taking advantage of a simple model system whereby a physiologically relevant androgen-mediated process is regulated completely independent of transcription (Xenopus laevis oocyte maturation), many novel and conserved concepts in nongenomic steroid signaling have been uncovered and characterized.

Diseases affecting bone quality: beyond osteoporosis

BACKGROUND

Bone quantity, quality, and turnover contribute to whole bone strength. Although bone mineral density, or bone quantity, is associated with increased fracture risk, less is known about bone quality. Various conditions, including disorders of mineral homeostasis, disorders in bone remodeling, collagen disorders, and drugs, affect bone quality.

QUESTIONS/PURPOSES

The objectives of this review are to (1) identify the conditions and diseases that could adversely affect bone quality besides osteoporosis, and (2) evaluate how these conditions influence bone quality.

METHODS

We searched PubMed using the keywords "causes" combined with "secondary osteoporosis" or "fragility fracture." After identifying 20 disorders/conditions, we subsequently searched each condition to evaluate its effect on bone quality.

RESULTS

Many disorders or conditions have an effect on bone metabolism, leading to fragility fractures. These disorders include abnormalities that disrupt mineral homeostasis, lead to an alteration of the mineralization process, and ultimately reduce bone strength. The balance between bone formation and resorption is also essential to prevent microdamage accumulation and maintain proper material and structural integrity of the bone. As a result, diseases that alter the bone turnover process lead to a reduction of bone strength. Because Type I collagen is the most abundant protein found in bone, defects in Type I collagen can result in alterations of material property, ultimately leading to fragility fractures. Additionally, some medications can adversely affect bone.

CONCLUSIONS

Recognizing these conditions and diseases and understanding their etiology and pathogenesis is crucial for patient care and maintaining overall bone health.

7α-methyl-19-nortestosterone vs. testosterone implants for hypogonadal osteoporosis: a preclinical study in the aged male orchidectomized rat model

Overt male hypogonadism induces not only osteoporosis but also unfavourable changes in body composition, which can be prevented by testosterone (T) replacement. In this preclinical study, the potential of synthetic androgen 7α-methyl-19-nortestosterone (MENT) as alternative treatment for male hypogonadism was evaluated in comparison with T. Eleven-month-old male rats were orchidectomized (orch) and left untreated for 2-months. Subsequently, the effects of 4-month MENT (12 μg/day) and T (72 μg/day) treatment on bone, muscle and fat were analysed using microcomputed tomography, dual-energy X-ray absorptiometry, dynamic bone histomorphometry and muscle fibre typing. At the onset of treatment, orch rats were clearly hypogonadal. This was evidenced by significant reductions of androgen-sensitive organ weight, lean mass, cortical thickness and trabecular bone volume compared with sham-operated aged-matched controls (sham). MENT and T restored weight of androgen-sensitive organs to a similar extent, with a superior anabolic action of MENT on levator ani muscle. Both androgens not only fully rescued hypogonadal loss of lean mass but also restored muscle fibre type composition and trabecular bone volume. Cortical bone loss was similarly prevented by MENT and T, but without full recovery to sham. Both androgens stimulated periosteal bone formation, but with a stronger effect of T. By contrast, MENT more strongly suppressed endocortical bone formation and bone turnover rate and reduced fat mass and serum leptin to a greater extent than T. MENT and T are both effective replacement therapies to stimulate bone and muscle in hypogonadal rats, with stronger lipolytic action of MENT.

The ESR1 (6q25) locus is associated with calcaneal ultrasound parameters and radial volumetric bone mineral density in European men

Purpose

Genome-wide association studies (GWAS) have identified 6q25, which incorporates the oestrogen receptor α gene (ESR1), as a quantitative trait locus for areal bone mineral density (BMD_a) of the hip and lumbar spine. The aim of this study was to determine the influence of this locus on other bone health outcomes; calcaneal ultrasound (QUS) parameters, radial peripheral quantitative computed tomography (pQCT) parameters and markers of bone turnover in a population sample of European men.

Methods

Eight single nucleotide polymorphisms (SNP) in the 6q25 locus were genotyped in men aged 40–79 years from 7 European countries, participating in the European Male Ageing Study (EMAS). The associations between SNPs and measured bone parameters were tested under an additive genetic model adjusting for centre using linear regression.

Results

2468 men, mean (SD) aged 59.9 (11.1) years had QUS measurements performed and bone turnover marker levels measured. A subset of 628 men had DXA and pQCT measurements. Multiple independent SNPs showed significant associations with BMD using all three measurement techniques. Most notably, rs1999805 was associated with a 0.10 SD (95%CI 0.05, 0.16; p = 0.0001) lower estimated BMD at the calcaneus, a 0.14 SD (95%CI 0.05, 0.24; p = 0.004) lower total hip BMD_a, a 0.12 SD (95%CI 0.02, 0.23; p = 0.026) lower lumbar spine BMD_a and a 0.18 SD (95%CI 0.06, 0.29; p = 0.003) lower trabecular BMD at the distal radius for each copy of the minor allele. There was no association with serum levels of bone turnover markers and a single SNP which was associated with cortical density was also associated with cortical BMC and thickness.

Conclusions

Our data replicate previous associations found between SNPs in the 6q25 locus and BMD_a at the hip and extend these data to include associations with calcaneal ultrasound parameters and radial volumetric BMD.

Association between ER-α polymorphisms and bone mineral density in patients with Turner syndrome subjected to estroprogestagen treatment--a pilot study

Reduced bone mineral density (BMD) is present in many women with Turner syndrome (TS), and hypo-estrogenism is known to play a vital role in bone mineralization disturbances. It has been suggested that genetic factors play an important role in the regulation of BMD. The aim of this study was to analyze the association between Pvu II and XbaI ER-α polymorphisms and BMD in TS patients subjected to estroprogestagen (EP) treatment. Thirty-two TS patients aged 17-38 (mean age 22.7 ± 8.2) along with 82 healthy controls were the subjects for this study. Baseline values of hormonal parameters, BMD and bone density markers were measured in the subjects. Subsequently, TS patients underwent 4 years of EP therapy. The results of laboratory parameters and BMD were analyzed in regard to PvuII and XbaI polymorphic variants of the ER-α gene. The increase in BMD of TS subjects was the highest in the 1st (7.5%, p = 0.013) and 2nd (6.6%, p = 0.008) years of treatment. Four years of EP therapy was reflected by a significant increase in BMD z-scores in patients with xx and Xx genotypes of the XbaI gene and in those with with the pp and Pp genotypes of PvuII. In patients with haplotypes other than XXPP, BMD z-scores were significantly higher compared to their baseline after 2 (p = 0.002), 3 (p < 0.001) and 4 (p < 0.001) years of treatment. In conclusion, genotypes xx and pp were shown to be prognostic markers of a good response to EP treatment, whereas the XXPP haplotype carriers were revealed to have the risk factors for insufficient responsiveness against EP treatment in BMD control.

The reduced trabecular bone mass of adult ARKO male mice results from the decreased osteogenic differentiation of bone marrow stroma cells

Male mice with androgen receptor knock-out (ARKO) show significant bone loss at a young age. However, the lasting effect of AR inactivation on bone in aging male mice remains unclear. We designed this study to evaluate the effect of AR on bone quality in aging male mice and to find the possible causes of AR inactivation contributing to the bone loss. The mice were grouped according to their ages and AR status and their trabecular bones were examined by micro-CT analysis at 6, 12, 18, and 30 weeks old. We found that bone mass consistently decreased and the bone microarchitectures continuously deteriorated in male ARKO mice at designated time points. To determine the cause of the bone loss in ARKO mice, we further examined the role of AR in bone cell fate decision and differentiation and we conducted experiments on bone marrow stromal cells (BMSC) obtained from wild type (WT) and AR knockout (KO) mice. We found that ARKO mice had higher numbers of colony formation unit-fibroblast (CFU-F), and CD44 and CD34 positive cells in bone marrow than WT mice. Our Q-RT-PCR results showed lower expression of genes linked to osteogenesis in BMSCs isolated from ARKO mice. In conclusion, AR nullification disrupted bone microarchitecture and caused trabecular bone mass loss in male ARKO mice. And the fate of BMSCs was impacted by the loss of AR. Therefore, these findings suggest that AR may accelerate the use of progenitor cells and direct them into osteogenic differentiation to affect bone metabolism.

Reduced bone mass and muscle strength in male 5α-reductase type 1 inactivated mice

Androgens are important regulators of bone mass but the relative importance of testosterone (T) versus dihydrotestosterone (DHT) for the activation of the androgen receptor (AR) in bone is unknown. 5α-reductase is responsible for the irreversible conversion of T to the more potent AR activator DHT. There are two well established isoenzymes of 5α-reductase (type 1 and type 2), encoded by separate genes (Srd5a1 and Srd5a2). 5α-reductase type 2 is predominantly expressed in male reproductive tissues whereas 5α-reductase type 1 is highly expressed in liver and moderately expressed in several other tissues including bone. The aim of the present study was to investigate the role of 5α-reductase type 1 for bone mass using Srd5a1^−/− mice. Four-month-old male Srd5a1^−/− mice had reduced trabecular bone mineral density (−36%, p<0.05) and cortical bone mineral content (−15%, p<0.05) but unchanged serum androgen levels compared with wild type (WT) mice. The cortical bone dimensions were reduced in the male Srd5a1^−/− mice as a result of a reduced cortical periosteal circumference compared with WT mice. T treatment increased the cortical periosteal circumference (p<0.05) in orchidectomized WT mice but not in orchidectomized Srd5a1^−/− mice. Male Srd5a1^−/− mice demonstrated a reduced forelimb muscle grip strength compared with WT mice (p<0.05). Female Srd5a1^−/− mice had slightly increased cortical bone mass associated with elevated circulating levels of androgens. In conclusion, 5α-reductase type 1 inactivated male mice have reduced bone mass and forelimb muscle grip strength and we propose that these effects are due to lack of 5α-reductase type 1 expression in bone and muscle. In contrast, the increased cortical bone mass in female Srd5a1^−/− mice, is an indirect effect mediated by elevated circulating androgen levels.

CCI-779 inhibits cell-cycle G2-M progression and invasion of castration-resistant prostate cancer via attenuation of UBE2C transcription and mRNA stability

The cell-cycle G(2)-M phase gene UBE2C is overexpressed in various solid tumors including castration-resistant prostate cancer (CRPC). Our recent studies found UBE2C to be a CRPC-specific androgen receptor (AR) target gene that is necessary for CRPC growth, providing a potential novel target for therapeutic intervention. In this study, we showed that the G(1)-S cell-cycle inhibitor-779 (CCI-779), an mTOR inhibitor, inhibited UBE2C mRNA and protein expression in AR-positive CRPC cell models abl and C4-2B. Treatment with CCI-779 significantly decreased abl cell proliferation in vitro and in vivo through inhibition of cell-cycle progression of both G(2)-M and G(1)-S phases. In addition, exposure of abl and C4-2B cells to CCI-779 also decreased UBE2C-dependent cell invasion. The molecular mechanisms for CCI-779 inhibition of UBE2C gene expression involved a decreased binding of AR coactivators SRC1, SRC3, p300, and MED1 to the UBE2C enhancers, leading to a reduction in RNA polymerase II loading to the UBE2C promoter, and attenuation of UBE2C mRNA stability. Our data suggest that, in addition to its ability to block cell-cycle G(1) to S-phase transition, CCI-779 causes a cell-cycle G(2)-M accumulation and an inhibition of cell invasion through a novel UBE2C-dependent mechanism, which contributes to antitumor activities of CCI-779 in UBE2C overexpressed AR-positive CRPC.

GATA4 regulates estrogen receptor-alpha-mediated osteoblast transcription

Estrogens regulate osteoblast differentiation and mineralization. We identified GATA4 as a transcription factor expressed in osteoblasts and directly regulated by 17β-estradiol in this cell type but not in breast cancer cells, another estrogen-responsive tissue. Chromatin immunoprecipitation sequencing (chromatin immunoprecipitation sequencing) reveals that estrogen receptor α (ERα) binds to chromatin near GATA4 at five different enhancers. GATA4 and ERα are both recruited to ERα binding sites near genes that are specifically expressed in osteoblasts and control osteoblast differentiation. Maximal binding of GATA4 precedes ERα binding, and GATA4 is necessary for histone 3 lysine 4 dimethylation at ERα binding sites, suggesting that GATA4 is a pioneer factor for ERα. As such, knockdown of GATA4 reduced recruitment of ERα to DNA. Our study illustrates that GATA4 is a pioneer factor for ERα recruitment to osteoblast-specific enhancers.

Direct transcriptional targets of sex steroid hormones in bone

The sex steroid hormones, androgens and estrogens, via their respective nuclear receptors, regulate bone mineral density in humans and mice. Very little is known about the direct targets of the androgen and estrogen receptors in bone cells. First, models of hormone and receptor deficiency in mouse and human bone are discussed. This review then focuses on the direct targets of the receptors in osteoblasts and osteoclasts. A direct target of a NR is defined here as a gene that is regulated by NR binding to the DNA (either through DNA binding or association with a DNA binding protein) at an enhancer or promoter of that gene. The experimental evidence that illustrates androgen and estrogen gene regulation in osteoblasts and osteoclasts will be summarized and compared with the phenotype of the hormones in vivo.