Function of androgen receptor in gene regulations

Most of the androgen actions are considered to be mediated by the androgen receptor (AR) of the target genes. The AR is composed of a fairly large molecule because of the long A/B domains of its N-terminal. However, the independent roles of the AR as well as those of the estrogen receptors largely remained unknown mainly due to the lack of the AR knockout (ARKO) mice line. We have succeeded in generating the ARKO mouse by means of a conditional targeting using the Cre/loxP system. The ARKO males grew healthily although they showed a typical feature of the testicular feminization mutation (Tfm) and the hormonal assay revealed significantly lower serum androgen and higher LH levels in comparison with those of the wild type (WT) males. The serum estrogen levels were, however, comparable between both the ARKO and the WT. Another hallmark of the ARKO males was a state of high bone turnover osteopenia, in which the acceleration in the bone resorption clearly exceeded the bone formation. Male-typical behaviors were disrupted in male ARKO mice. Aiming at a quick differentiation of an androgen-dependent polyQ disease such as Kennedy's disease, the authors also developed the Drosophila fly-eye model in which the wild type and the polyQ-expanded human AR (hAR) was induced in the eyes of Drosophila. When androgen was administered to the flies induced with the polyQ-expanded hAR, their optical nerves were devastated.     

CARM1 deficiency inhibits osteoblastic differentiation of bone marrow mesenchymal stem cells and delays osteogenesis in mice

Bone repair remains a clinical challenge due to low osteogenic capacity. Coactivator associated arginine methyltransferase 1 (CARM1) is a protein arginine methyltransferase that mediates arginine methylation and endochondral ossification. However, the roles of CARM1 in osteoblastic differentiation and bone remodeling have not been explored. In our study, heterozygous CARM1-knockout (KO) mice were generated using the CRISPR-Cas9 system and a model of femoral defect was created. At day 7 postsurgery, CARM1-KO mice exhibited obvious bone loss compared with wild type (WT) mice, as evidenced by reduced bone mineral density (BMD), bone volume/total volume (BV/TV), trabecular thickness (Tb.Th), and trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). Deletion of CARM1 in mice lowered synthesis and accumulation of collagen at the injury sites. The alkaline phosphatase (ALP) activity and osteogenic-related gene expression were declined in CARM1-KO mice. To further understand the role of CARM1 in osteoblastic differentiation, bone marrow mesenchymal stem cells (BMSCs) were isolated from the tibia and femur of WT or CARM1-KO mice. CARM1 deletion decreased histone arginine methylation and inhibited osteoblastic differentiation and mineralization. The mRNA sequencing of CARM1-KO BMSCs revealed the possible regulatory molecules by CARM1, which could deepen our understanding of CARM1 regulatory mechanisms. These data could be of interest to basic researchers and provide the direction for future research into bone-related disorders.     

Critical role of filamin-binding LIM protein 1 (FBLP-1)/migfilin in regulation of bone remodeling

Bone remodeling is a complex process that must be precisely controlled to maintain a healthy life. We show here that filamin-binding LIM protein 1 (FBLP-1, also known as migfilin), a kindlin- and filamin-binding focal adhesion protein, is essential for proper control of bone remodeling. Genetic inactivation of FBLIM1 (the gene encoding FBLP-1) in mice resulted in a severe osteopenic phenotype. Primary FBLP-1 null bone marrow stromal cells (BMSCs) exhibited significantly reduced extracellular matrix adhesion and migration compared with wild type BMSCs. Loss of FBLP-1 significantly impaired the growth and survival of BMSCs in vitro and decreased the number of osteoblast (OB) progenitors in bone marrow and OB differentiation in vivo. Furthermore, the loss of FBLP-1 caused a dramatic increase of osteoclast (OCL) differentiation in vivo. The level of receptor activator of nuclear factor κB ligand (RANKL), a key regulator of OCL differentiation, was markedly increased in FBLP-1 null BMSCs. The capacity of FBLP-1 null bone marrow monocytes (BMMs) to differentiate into multinucleated OCLs in response to exogenously supplied RANKL, however, was not different from that of WT BMMs. Finally, we show that a loss of FBLP-1 promotes activating phosphorylation of ERK1/2. Inhibition of ERK1/2 activation substantially suppressed the increase of RANKL induced by the loss of FBLP-1. Our results identify FBLP-1 as a key regulator of bone homeostasis and suggest that FBLP-1 functions in this process through modulating both the intrinsic properties of OB/BMSCs (i.e., BMSC-extracellular matrix adhesion and migration, cell growth, survival, and differentiation) and the communication between OB/BMSCs and BMMs (i.e., RANKL expression) that controls osteoclastogenesis.     

Alkbh1‐mediated DNA N6‐methyladenine modification regulates bone marrow mesenchymal stem cell fate during skeletal aging

ObjectivesDNA N6‐methyladenine (N6‐mA) demethylase Alkbh1 participates in regulating osteogenic differentiation of mesenchymal stem cell (MSCs) and vascular calcification. However, the role of Alkbh1 in bone metabolism remains unclear.Materials and MethodsBone marrow mesenchymal stem cells (BMSCs)‐specific Alkbh1 knockout mice were used to investigate the role of Alkbh1 in bone metabolism. Western blot, qRT‐PCR, and immunofluorescent staining were used to evaluate the expression of Alkbh1 or optineurin (optn). Micro‐CT, histomorphometric analysis, and calcein double‐labeling assay were used to evaluate bone phenotypes. Cell staining and qRT‐PCR were used to evaluate the osteogenic or adipogenic differentiation of BMSCs. Dot blotting was used to detect the level of N6‐mA in genomic DNA. Chromatin immunoprecipitation (Chip) assays were used to identify critical targets of Alkbh1. Alkbh1 adeno‐associated virus was used to overexpress Alkbh1 in aged mice.ResultsAlkbh1 expression in BMSCs declined during aging. Knockout of Alkbh1 promoted adipogenic differentiation of BMSCs while inhibited osteogenic differentiation. BMSC‐specific Alkbh1 knockout mice exhibited reduced bone mass and increased marrow adiposity. Mechanistically, we identified optn as the downstream target through which Alkbh1‐mediated DNA m6A modification regulated BMSCs fate. Overexpression of Alkbh1 attenuated bone loss and marrow fat accumulation in aged mice.ConclusionsOur findings demonstrated that Alkbh1 regulated BMSCs fate and bone‐fat balance during skeletal aging and provided a potential target for the treatment of osteoporosis.     

The role of estrogen receptor-beta, in the early age-related bone gain and later age-related bone loss in female mice

The molecular and cellular mechanism of estrogen action in skeletal tissue remains unclear. The purpose of this study was to understand the role of estrogen receptor-beta, (ERbeta) on cortical and cancellous bone during growth and aging by comparing the bone phenotype of 6- and 13-month-old female mice with or without ERbeta. Groups of 11-14 wild-type (WT) controls and ERbeta knockout (BERKO) female mice were necropsied at 6 and 13 months of age. At both ages, BERKO mice did not differ significantly from WT controls in uterine weight and uterine epithelial thickness, indicating that ERbeta does not regulate the growth of uterine tissue. Femoral length increased significantly by 5.5% at 6 months of age in BERKO mice compared with WT controls. At 6 months of age, peripheral quantitative computerized tomography (pQCT) analysis of the distal femoral metaphysis (DFM) and femoral shafts showed that BERKO mice had significantly higher cortical bone content and periosteal circumference as compared with WT controls at both sites. In contrast to the findings in cortical bone, at 6 months of age, there was no difference between BERKO and WT mice in trabecular density, trabecular bone volume (TBV), or formation and resorption indices at the DFM. In 13-month-old WT mice, TBV (-41%), trabecular density (-27%) and cortical thickness decreased significantly. while marrow cavity and endocortical circumference increased significantly compared with 6-month-old WT mice. These age-related decreases in cancellous and endocortical bone did not occur in BERKO mice. At 13 months of age, BERKO mice had significantly higher total, trabecular and cortical bone, while having significantly lower bone resorption, bone formation and bone turnover in DFM compared with WT mice. These results indicate that deleting ERbeta protected against age-related bone loss in both the cancellous and endocortical compartments by decreasing bone resorption and bone turnover in aged female mice. These data demonstrate that in female mice, ERbeta plays a role in inhibiting periosteal bone formation, longitudinal and radial bone growth during the growth period, while it plays a role in stimulating bone resorption, bone turnover and bone loss on cancellous and endocortical bone surfaces during the aging process.     

Heparanase is expressed in osteoblastic cells and stimulates bone formation and bone mass

Heparan sulfate proteoglycans (HSPGs) are ubiquitous macromolecules. In bone, they are associated with cell surfaces and the extracellular matrix (ECM). The heparan sulfate (HS) chains of HSPGs bind a multitude of bioactive molecules, thereby controlling normal and pathologic processes. The HS-degrading endoglycosidase, heparanase, has been implicated in processes such as inflammation, vascularization associated with wound healing and malignancies, and cancer metastasis. Here we show progressive mRNA expression of the hpa gene (encoding heparanase) in murine bone marrow stromal cells undergoing osteoblastic (bone forming) differentiation and in primary calvarial osteoblasts. Bone marrow stromal cells derived from transgenic mice expressing recombinant human heparanase (rh-heparanase) and MC3T3 E1 osteoblastic cells exposed to soluble rh-heparanase spontaneously undergo osteogenic differentiation. In addition, the transgenic bone marrow stromal cells degrade HS chains. In wild-type (WT) and hpa-transgenic (hpa-tg) mice, heparanase is weakly expressed throughout the bone marrow with a substantial increase in osteoblasts and osteocytes, especially in the hpa-tg mice. Heparanase expression was absent in osteoclasts. Micro-computed tomographic and histomorphometric skeletal analyses in male and female hpa-tg versus WT mice show markedly increased trabecular bone mass, cortical thickness, and bone formation rate, but no difference in osteoclast number. Collectively, our data suggest that proteoglycans tonically suppress osteoblast function and that this inhibition is alleviated by HS degradation with heparanase.     

Age-related skeletal dynamics and decrease in bone strength in DNA repair deficient male trichothiodystrophy mice

Accumulation of DNA damage caused by oxidative stress is thought to be one of the main contributors of human tissue aging. Trichothiodystrophy (TTD) mice have a mutation in the Ercc2 DNA repair gene, resulting in accumulation of DNA damage and several features of segmental accelerated aging. We used male TTD mice to study the impact of DNA repair on bone metabolism with age. Analysis of bone parameters, measured by micro-computed tomography, displayed an earlier decrease in trabecular and cortical bone as well as a loss of periosteal apposition and a reduction in bone strength in TTD mice with age compared to wild type mice. Ex vivo analysis of bone marrow differentiation potential showed an accelerated reduction in the number of osteogenic and osteoprogenitor cells with unaltered differentiation capacity. Adipocyte differentiation was normal. Early in life, osteoclast number tended to be increased while at 78 weeks it was significantly lower in TTD mice. Our findings reveal the importance of genome stability and proper DNA repair for skeletal homeostasis with age and support the idea that accumulation of damage interferes with normal skeletal maintenance, causing reduction in the number of osteoblast precursors that are required for normal bone remodeling leading to a loss of bone structure and strength.     

Androgen receptor gene knockout male mice exhibit impaired cardiac growth and exacerbation of angiotensin II-induced cardiac fibrosis

Androgen has anabolic effects on cardiac myocytes and has been shown to enhance left ventricular enlargement and function. However, the physiological and patho-physiological roles of androgen in cardiac growth and cardiac stress-induced remodeling remains unclear. We aimed to clarify whether the androgen-nuclear androgen receptor (AR) system contributes to the cardiac growth and angiotensin II (Ang II)-stimulated cardiac remodeling by using systemic AR-null male mice. AR knock-out (ARKO) male mice, at 25 weeks of age, and age-matched wild-type (WT) male mice were treated with or without Ang II stimulation (2.0 mg/kg/day) for 2 weeks. ARKO mice with or without Ang II stimulation showed a significant reduction in the heart-to-body weight ratio compared with those of WT mice. In addition, echocardiographic analysis demonstrated impairments of both the concentric hypertrophic response and left ventricular function in Ang II-stimulated ARKO mice. Western blot analysis of the myocardium revealed that activation of extracellular signal-regulated kinases (ERK) 1/2 and ERK5 by Ang II stimulation were lower in ARKO mice than those of WT mice. Ang II stimulation caused more prominent cardiac fibrosis in ARKO mice than in WT mice with enhanced expression of types I and III collagen and transforming growth factor-beta1 genes and with increased Smad2 activation. These results suggest that, in male mice, the androgen-AR system participates in normal cardiac growth and modulates cardiac adaptive hypertrophy and fibrosis during the process of cardiac remodeling under hypertrophic stress.     

Icariin promotes osteogenic differentiation of bone marrow stromal cells and prevents bone loss in OVX mice via activating autophagy

Osteoporosis (OP) results from the impaired function of endogenous bone marrow mesenchymal stem cells (BMSCs). Icariin (ICA) has shown potential osteoprotective effects. However, the molecular mechanism for the anabolic action of ICA remains largely unknown. The objective of the present study is to investigate whether ICA prevents bone loss by acting on BMSCs via affecting the level of autophagy after ovariectomy (OVX). The BMSCs were extracted from BALB/c mice treated with ICA, chloroquine (CQ, an autophagy inhibitor) or ICA + CQ. The OVX mice were injected with ICA, CQ, or ICA + CQ for 1 month. We performed Alizarin Red staining and alkaline phosphatase staining to detect osteogenic differentiation of BMSCs. Micro-CT, hematoxylin and eosin staining, Oil Red O staining, and tartrate-resistant acid phosphatase staining were used to assess the bone mass, lipid droplets and osteoclasts in femurs. Autophagy activity in BMSCs from different groups was evaluated by Western blot analysis. The osteogenic differentiation of BMSCs from OVX-induced OP mice was decreased. Treatment with ICA reduced bone loss and formation of osteoclasts and increased osteogenic differentiation of BMSCs in vitro and vivo. In addition, autophagy was enhanced in BMSCs of OVX mice treated with ICA. Our results indicate that ICA prevents OVX-induced bone loss possibly by strengthening the osteogenic differentiation of BMSCs via increasing autophagic activity.     

RANKL from bone marrow adipose lineage cells promotes osteoclast formation and bone loss

Receptor activator of NF‐κB ligand (RANKL) is essential for osteoclast formation and bone remodeling. Nevertheless, the cellular source of RANKL for osteoclastogenesis has not been fully uncovered. Different from peripheral adipose tissue, bone marrow (BM) adipose lineage cells originate from bone marrow mesenchymal stromal cells (BMSCs). Here, we demonstrate that adiponectin promoter‐driven Cre expression (Adipoq^Cre ) can target bone marrow adipose lineage cells. We cross the Adipoq^Cre mice with rankl^fl/fl mice to conditionally delete RANKL from BM adipose lineage cells. Conditional deletion of RANKL increases cancellous bone mass of long bones in mice by reducing the formation of trabecular osteoclasts and inhibiting bone resorption but does not affect cortical bone thickness or resorption of calcified cartilage. Adipoq^Cre; rankl^fl/fl mice exhibit resistance to estrogen deficiency and rosiglitazone (ROS)‐induced trabecular bone loss but show bone loss induced by unloading. BM adipose lineage cells therefore represent an essential source of RANKL for the formation of trabecula osteoclasts and resorption of cancellous bone during remodeling under physiological and pathological conditions. Targeting bone marrow adiposity is a promising way of preventing pathological bone loss.     

Modulation of unloading-induced bone loss in mice with altered ERK signaling

Genetic variations mediate skeletal responsiveness to mechanical unloading, with individual space travelers exhibiting large variations in the extent of bone loss. We previously identified genomic regions harboring several hundred genes that can modulate the magnitude of skeletal adaptation to mechanical unloading. Here, bioinformatic filters aided in shortlisting 30 genes with bone-related and mechanoregulatory roles. The genes CD44, FGF2, NOD2, and Fas, all associated with ERK signaling, were then functionally tested in hindlimb-unloaded (HLU) knockout (KO) mice. Compared to their respective normally ambulating wildtype (WT) controls, all KO strains, except Fas mice, had lower trabecular bone volume, bone volume fraction, and/or trabecular number. For cortical bone and compared to ambulatory WT mice, CD44^?/? had impaired properties while FGF2^?/? showed enhanced indices. NOD2^?/? and Fas^?/? did not have a cortical phenotype. In all KO and WT groups, HLU resulted in impaired trabecular and cortical indices, primarily due to trabecular tissue loss and mitigation of cortical bone growth. The difference in trabecular separation between HLU and ambulatory controls was significantly greater in CD44^?/? and NOD2^?/? mice than in WT mice. In cortical bone, differences in cortical thickness, total pore volume, and cortical porosity between HLU and controls were aggravated in CD44^?/? mice. In contrast, deletion of NOD2 and Fas genes mitigated the differences in Po.V between HLU and control mice. Together, we narrowed a previous list of QTL-derived candidate genes from over 300 to 30, and showed that CD44, NOD2, and Fas have distinct functions in regulating changes in trabecular and cortical bone indices during unloading.     

Role of growth hormone receptor signaling in osteogenesis from murine bone marrow progenitor cells

Growth hormone (GH) regulates many of the factors responsible for controlling the development of bone marrow progenitor cells (BMPCs). The aim of this study was to elucidate the role of GH in osteogenic differentiation of BMPCs using GH receptor null mice (GHRKO). BMPCs from GHRKO and their wild-type (WT) littermates were quantified by flow cytometry and their osteogenic differentiation in vitro was determined by cell morphology, real-time RT-PCR, and biochemical analyses. We found that freshly harvested GHRKO marrow contains 3% CD34 (hematopoietic lineage), 43.5% CD45 (monocyte/macrophage lineage), and 2.5% CD106 positive (CFU-F/BMPC) cells compared to 11.2%, 45%, and 3.4% positive cells for (WT) marrow cells, respectively. When cultured for 14 days under conditions suitable for CFU-F expansion, GHRKO marrow cells lost CD34 positivity, and were markedly reduced for CD45, but 3- to 4-fold higher for CD106. While WT marrow cells also lost CD34 expression, they maintained CD45 and increased CD106 levels by 16-fold. When BMPCs from GHRKO mice were cultured under osteogenic conditions, they failed to elongate, in contrast to WT cells. Furthermore, GHRKO cultures expressed less alkaline phosphatase, contained less mineralized calcium, and displayed lower osteocalcin expression than WT cells. However, GHRKO cells displayed similar or higher expression of cbfa-1, collagen I, and osteopontin mRNA compared to WT. In conclusion, we show that GH has an effect on the proportions of hematopoietic and mesenchymal progenitor cells in the bone marrow, and that GH is essential for both the induction and later progression of osteogenesis.     

MicroRNA‐31a‐5p from aging BMSCs links bone formation and resorption in the aged bone marrow microenvironment

The alteration of age‐related molecules in the bone marrow microenvironment is one of the driving forces in osteoporosis. These molecules inhibit bone formation and promote bone resorption by regulating osteoblastic and osteoclastic activity, contributing to age‐related bone loss. Here, we observed that the level of microRNA‐31a‐5p (miR‐31a‐5p) was significantly increased in bone marrow stromal cells (BMSCs) from aged rats, and these BMSCs demonstrated increased adipogenesis and aging phenotypes as well as decreased osteogenesis and stemness. We used the gain‐of‐function and knockdown approach to delineate the roles of miR‐31a‐5p in osteogenic differentiation by assessing the decrease of special AT‐rich sequence‐binding protein 2 (SATB2) levels and the aging of BMSCs by regulating the decline of E2F2 and recruiting senescence‐associated heterochromatin foci (SAHF). Notably, expression of miR‐31a‐5p, which promotes osteoclastogenesis and bone resorption, was markedly higher in BMSCs‐derived exosomes from aged rats compared to those from young rats, and suppression of exosomal miR‐31a‐5p inhibited the differentiation and function of osteoclasts, as shown by elevated RhoA activity. Moreover, using antagomiR‐31a‐5p, we observed that, in the bone marrow microenvironment, inhibition of miR‐31a‐5p prevented bone loss and decreased the osteoclastic activity of aged rats. Collectively, our results reveal that miR‐31a‐5p acts as a key modulator in the age‐related bone marrow microenvironment by influencing osteoblastic and osteoclastic differentiation and that it may be a potential therapeutic target for age‐related osteoporosis.     

Matrix remodeling associated 7 promotes differentiation of bone marrow mesenchymal stem cells toward osteoblasts

The matrix remodeling associated 7 (MXRA7) gene had been ill-studied and its biology remained to be discovered. Inspired by our previous findings and public datasets concerning MXRA7, we hypothesized that the MXRA7 gene might be involved in bone marrow mesenchymal stem cells (BMSCs) functions related to bone formation, which was checked by utilizing in vivo or in vitro methodologies. Micro-computed tomography of MXRA7-deficient mice demonstrated retarded osteogenesis, which was reflected by shorter femurs, lower bone mass in both trabecular and cortical bones compared with wild-type (WT) mice. Histology confirmed the osteopenia-like feature including thinner growth plates in MXRA7-deficient femurs. Immunofluorescence revealed less osteoblasts in MXRA7-deficient femurs. Polymerase chain reaction or western blot analysis showed that when WT BMSCs were induced to differentiate toward osteoblasts or adipocytes in culture, MXRA7 messenger RNA or protein levels were significantly increased alongside osteoblasts induction, but decreased upon adipocytes induction. Cultured MXRA7-deficient BMSCs showed decreased osteogenesis upon osteogenic differentiation induction as reflected by decreased calcium deposition or lower expression of genes responsible for osteogenesis. When recombinant MXRA7 proteins were supplemented in a culture of MXRA7-deficient BMSCs, osteogenesis or gene expression was fully restored. Upon osteoblast induction, the level of active β-catenin or phospho-extracellular signal-regulated kinase in MXRA7-deficient BMSCs was decreased compared with that in WT BMSCs, and these impairments could be rescued by recombinant MXRA7 proteins. In adipogenesis induction settings, the potency of MXRA7-deficient BMSCs to differentiate into adipocytes was increased over the WT ones. In conclusion, this study demonstrated that MXRA7 influences bone formation via regulating the balance between osteogenesis and adipogenesis in BMSCs.     

Human CD133-derived bone marrow stromal cells establish ectopic hematopoietic microenvironments in immunodeficient mice

Cultured adherent bone marrow stromal cells (BMSCs) are capable of forming ectopic hematopoietic microenvironments (HMEs) in immunodeficient mice. However, the cell surface phenotype of the native bone marrow stem/progenitor cell that gives rise to BMSCs that support hematopoiesis remains poorly defined. We recently reported the derivation of human BMSC-like cells (CD133BMSCs) by magnetic cell sorting against Prominin-1 (CD133), an epitope expressed by embryonic, fetal, and adult stem cells. Here we demonstrate that CD133BMSCs are capable of forming ectopic HMEs. Cultured adherent CD133BMSCs derived from sorted CD133-positive cells lacked CD133 expression, but were uniformly positive for CD146, an epitope recently described to identify self-renewing osteoprogenitor cells that could transfer the HME. CD133BMSCs were genetically-tagged by lentivirus, expanded, and seeded into HA/TCP/fibrin constructs that were implanted subcutaneously. After 60 days, CD133BMSCs produced human osteocytes, osteoblasts, adipocytes, and reticular cells that supported murine hematopoiesis. CD133BMSCs that were not transduced with lentivirus also formed HMEs. Control constructs seeded with human dermal fibroblasts formed connective tissue, but failed to form HMEs. Our data indicate that CD133 expression identifies a native human bone marrow stem/progenitor cell that gives rise to BMSCs capable of forming the HME.     

IL-23 is critical for induction of arthritis, osteoclast formation, and maintenance of bone mass

The role of IL-23 in the development of arthritis and bone metabolism was studied using systemic IL-23 exposure in adult mice via hydrodynamic delivery of IL-23 minicircle DNA in vivo and in mice genetically deficient in IL-23. Systemic IL-23 exposure induced chronic arthritis, severe bone loss, and myelopoiesis in the bone marrow and spleen, which resulted in increased osteoclast differentiation and systemic bone loss. The effect of IL-23 was partly dependent on CD4(+) T cells, IL-17A, and TNF, but could not be reproduced by overexpression of IL-17A in vivo. A key role in the IL-23-induced arthritis was made by the expansion and activity of myeloid cells. Bone marrow macrophages derived from IL-23p19(-/-) mice showed a slower maturation into osteoclasts with reduced tartrate-resistant acid phosphatase-positive cells and dentine resorption capacity in in vitro osteoclastogenesis assays. This correlated with fewer multinucleated osteoclast-like cells and more trabecular bone volume and number in 26-wk-old male IL-23p19(-/-) mice compared with control animals. Collectively, our data suggest that systemic IL-23 exposure induces the expansion of a myeloid lineage osteoclast precursor, and targeting IL-23 pathway may combat inflammation-driven bone destruction as observed in rheumatoid arthritis and other autoimmune arthritides.     

Propranolol attenuates calorie restriction- and high calorie diet-induced bone marrow adiposity

We investigated the effects of β-adrenergic activation on bone marrow adiposity and on adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). C57BL/6 mice were subjected to a control (CON), high calorie (HIGH) or low calorie (LOW) diet for 12 weeks. In each group, mice were treated with vehicle (VEH) or propranolol. The number of adipocytes per area bone marrow was increased in LOWVEH and HIGHVEH mice compared with CONVEH mice, which was attenuated by propranolol. Isoproterenol increased lipid droplet accumulation and adipogenic marker gene expression in 3T3-L1 preadipocytes and mouse BMSCs, which were blocked by propranolol. Conditioned medium obtained from MC3T3-E1 osteoblasts suppressed adipogenic differentiation of 3T3-L1 cells, which was significantly attenuated by treatment of MC3T3-E1 cells with isoproterenol. These data suggest that β-adrenergic activation enhances bone marrow adipogenesis via direct stimulation of BMSCs adipogenesis and indirect inhibition of osteoblast anti-adipogenic potential. [BMB Reports 2014; 47(10): 587-592]     

Testosterone prevents orchidectomy-induced bone loss in estrogen receptor-alpha knockout mice.

To examine the role of the estrogen receptor-alpha (ERalpha) during male skeletal development, bone density and structure of aged ERalphaKO mice and wild-type (WT) littermates were analyzed and skeletal changes in response to sex steroid deficiency and replacement were also studied. In comparison to WT, ERalphaKO mice had smaller and thinner bones, arguing for a direct role of ERalpha to obtain full skeletal size in male mice. However, male ERalphaKO mice had significantly more trabecular bone as assessed both by pQCT and histomorphometry, indicating that ERalpha is not essential to maintain cancellous bone mass. Six weeks following orchidectomy (ORX), both WT and ERalphaKO mice showed high-turnover osteoporosis as revealed by increases in serum osteocalcin and decreases in trabecular (-38% and -58% in WT and ERalphaKO, respectively) and cortical bone density (-5% and -4% in WT and ERalphaKO, respectively). Administration of testosterone propionate (T, 5 mg/kg/day) completely prevented bone loss both in ERalphaKO and in WT mice. As expected, estradiol (E2, 60 microg/kg/day) replacement did not prevent cancellous bone loss in ORX ERalphaKO mice. However, E2 stimulated bone formation at the endocortical surface in ORX ERalphaKO, suggesting that osteoblasts may respond to nonERalpha-mediated estrogen action. In conclusion, although functional ERalpha may play a significant role during male skeletal development, this receptor does not seem essential for androgen-mediated skeletal maintenance in older male mice.