Bone anti-resorptive effects of coumarins on RANKL downstream cellular signaling: a systematic review of the literature.

BACKGROUND: Members of the botanical families Apiaceae/Umbelliferae, Asteraceae, Fabaceae/Leguminosae, and Thymelaeaceae are rich in coumarins and have traditionally been used as ethnomedicines in many regions including Europe, Asia, and South America. Coumarins are a class of secondary metabolites that are widely present in plants, fungi, and bacteria and exhibit several pharmacological, biochemical, and therapeutic effects. Recently, many plants rich in coumarins and their derivatives were found to affect bone metabolism. OBJECTIVE: To review scientific literature describing the mechanisms of action of coumarins in osteoclastogenesis and bone resorption. MATERIALS AND METHODS: For this systematic review, the PubMed, Scopus, and Periodical Capes databases and portals were searched. We included in vitro research articles published between 2010 and 2020 that evaluated coumarins using osteoclastogenic markers. RESULTS: Coumarins have been reported to downregulate RANKL-RANK signaling and various downstream signaling pathways required for osteoclast development, such as NF-κB, MAPK, Akt, and Ca2+ signaling, as well as pathways downstream of the nuclear factor of activated T-cells (NFATc1), including tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), and matrix metalloproteinase 9 (MMP-9). CONCLUSIONS: Coumarins primarily inhibit osteoclast differentiation and activation by modulating different intracellular signaling pathways; therefore, they could serve as potential candidates for controlled randomized clinical trials aimed at improving human bone health.

Recent genetic advances in innate immunity of psoriatic arthritis.

Psoriatic arthritis (PsA) is a heterogeneous disease that affects multiple organ systems including the peripheral and axial joints, entheses and nails. PsA is associated with significant comorbidities including cardiovascular, metabolic, and psychiatric diseases. The pathogenesis of PsA is complex and involves genetic, immunologic and environmental factors. Recent evidence suggests the heritability for PsA to be stronger and distinct from that of PsC. Prominent genes identified via GWAS for PsA include HLA-B/C, HLAB, IL12B, IL23R, TNP1, TRAF3IP3, and REL. We review the genetics of psoriatic arthritis and discuss the role of the innate immune system as important in the pathogenesis of PsA by focusing on key signaling pathways and cellular makeup. Understanding the candidate genes identified in PsA highlights pathways of critical importance to the pathogenesis of psoriatic disease including the key role of the innate immune response, mediated through IL-23/IL-17 axis, RANK and NFκB signaling pathways.

[Progress of research on the relationship between calcitonin gene-related peptide and RANK/RANKL/OPG system in the bone reconstruction].

OBJECTIVE: To summarize the research progress on the calcitonin gene-related peptide (CGRP) and receptor activator of nuclear factor κB (RANK)/receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin (OPG) system during bone reconstruction to provide theoretical basis for further research on the prevention and treatment of bone-related diseases. METHODS: The relevant research results at home and abroad in recent years were analyzed and summarized. RESULTS: CGRP and RANK/RANKL/OPG system play important regulatory roles in the bone reconstruction. CONCLUSION: At present, the research on the mechanism of CGRP and RANK/RANKL/OPG system in bone reconstruction is insufficient. Therefore, it is necessary to study further on the process and interrelation of CGRP and RANK/RANKL/OPG system in bone reconstruction to confirm their mechanism, which will bring new ideas and methods for the treatment of bone related diseases in clinic.

Soluble RANKL is physiologically dispensable but accelerates tumour metastasis to bone.

Receptor activator of NF-κB ligand (RANKL) is a multifunctional cytokine known to affect immune and skeletal systems, as well as oncogenesis and metastasis1-4. RANKL is synthesized as a membrane-bound molecule, and cleaved into its soluble form by proteases5-7. As the soluble form of RANKL does not contribute greatly to bone remodelling or ovariectomy-induced bone loss8, whether soluble RANKL has a role in pathological settings remains unclear. Here we show that soluble RANKL promotes the formation of tumour metastases in bone. Mice that selectively lack soluble RANKL (Tnfsf11ΔS/ΔS)5-7,9 have normal bone homoeostasis and develop a normal immune system but display markedly reduced numbers of bone metastases after intracardiac injection of RANK-expressing melanoma and breast cancer cells. Deletion of soluble RANKL does not affect osteoclast numbers in metastatic lesions or tumour metastasis to non-skeletal tissues. Therefore, soluble RANKL is dispensable for physiological regulation of bone and immune systems, but has a distinct and pivotal role in the promotion of bone metastases.

Dynamics of Bone Cell Interactions and Differential Responses to PTH and Antibody-Based Therapies.

We propose a mathematical model describing the dynamics of osteoblasts and osteoclasts in bone remodeling. The goal of this work is to develop an integrated modeling framework for bone remodeling and bone cell signaling dynamics that could be used to explore qualitatively combination treatments for osteoporosis in humans. The model has been calibrated using 57 checks from the literature. Specific global optimization methods based on qualitative objectives have been developed to perform the model calibration. We also added pharmacokinetics representations of three drugs to the model, which are teriparatide (PTH(1-34)), denosumab (a RANKL antibody) and romosozumab (a sclerostin antibody), achieving excellent goodness-of-fit of human clinical data. The model reproduces the paradoxical effects of PTH on the bone mass, where continuous administration of PTH results in bone loss but intermittent administration of PTH leads to bone gain, thus proposing an explanation of this phenomenon. We used the model to simulate different categories of osteoporosis. The main attributes of each disease are qualitatively well captured by the model, for example changes in bone turnover in the disease states. We explored dosing regimens for each disease based on the combination of denosumab and romosozumab, identifying adequate ratios and doses of both drugs for subpopulations of patients in function of categories of osteoporosis and the degree of severity of the disease.

Circulating Receptor Activator of Nuclear Factor-κB (RANK), RANK ligand (RANKL), and Mammographic Density in Premenopausal Women.

The receptor activator of nuclear factor-κB (RANK) pathway plays essential roles in breast development. Mammographic density is a strong risk factor for breast cancer, especially in premenopausal women. We, therefore, investigated the associations of circulating RANK and soluble RANK ligand (sRANKL) with mammographic density in premenopausal women. Mammographic density was measured as volumetric percent density in 365 cancer-free premenopausal women (mean age, 47.5 years) attending screening mammogram at the Washington University School of Medicine (St. Louis, MO). We used linear regression models adjusted for confounders, to compare the least-square means of volumetric percent density across tertiles of circulating RANK and sRANKL. Furthermore, because RANKL levels in mammary tissue are modulated by progesterone, we stratified analyses by progesterone levels. The mean volumetric percent density increased across tertiles of circulating RANK from 8.6% in tertile 1, to 8.8% in tertile 2, and 9.5% in tertile 3 (P trend = 0.02). For sRANKL, the mean volumetric percent density was 8.5% in tertile 1, 9.4% in tertile 2, and 9.0% in tertile 3 (P trend = 0.30). However, when restricted to women with higher progesterone levels, the mean volumetric percent density increased from 9.1% in sRANKL tertile 1 to 9.5% in tertile 2, and 10.1% in tertile 3 (P trend = 0.01). Circulating RANK was positively associated with volumetric percent density, while circulating sRANKL was positively associated with volumetric percent density among women with higher progesterone levels. These findings support the inhibition of RANKL signaling as a pathway to reduce mammographic density and possibly breast cancer incidence in high-risk women with dense breasts.

The Role of Osteoprotegerin as a Cardioprotective Versus Reactive Inflammatory Marker: the Chicken or the Egg Paradox

Cardiovascular disease is one of the most frequent causes of mortality and morbidity worldwide. Several variables have been identified as risk factors for cardiovascular disease. Recently, the role of receptor activator of nuclear factor kappa B, receptor activator of nuclear factor kappa B ligand, and the osteoprotegerin system has been recognized as more important in the pathogenesis of cardiovascular disease. Besides their roles in the regulation of bone resorption, these molecules have been reported to be associated with the pathophysiology of cardiovascular disease. There are conflicting data regarding the impact of osteoprotegerin, a glycoprotein with a regulatory role in the cardiovascular system. The aim of this review is to discuss the current knowledge and the role of osteoprotegerin in cardiovascular disease.

The Effect of Lunasin on Receptor Activator of Nuclear Factor Kappa-B Ligand-mediated Osteoclast Formation from RAW 264.7 Cells.

INTRODUCTION: To date, no study has investigated the antiresorptive property of lunasin. Hence, the present study aimed to assess the ability of lunasin to inhibit the osteoclast formation using RAW 264.7 cells. We hypothesized that lunasin is able to inhibit osteoclast formation. METHODS: In the present study, the murine monocytic cell line RAW 264.7 was induced to differentiate into mature osteoclasts in the presence of recombinant receptor activator of nuclear factor kappa-B ligand. Tartrate-resistant acid phosphatase, a marker of osteoclasts, was used to identify osteoclasts. Cell lines were divided into different groups and exposed to different concentrations of 50 µmol/L, 75 µmol/L, and 100 µmol/L active and inactive lunasin. The control group was RAW 264.7 cells with receptor activator of nuclear factor kappa-B ligand. Tartrate-resistant acid phosphatase-positive cells of 3 or more nuclei, indicative of mature osteoclasts, were counted by 3 observers. The mean number of the data collected was analyzed using 1-way analysis of variance and the multiple comparison post hoc Bonferroni correction. RESULTS: There was a significant difference in the reduction of osteoclast formation in all the active lunasin groups (P < .001) compared with the control group and the inactive lunasin group (P < .001). CONCLUSIONS: Considering the suppressive effect of lunasin on osteoclastogenesis, the use of lunasin as a potential antiresorptive agent can be evaluated in future studies.

Mechanisms involved in bone resorption regulated by vitamin D.

Active forms of vitamin D enhance osteoclastogenesis in vitro and in vivo through the vitamin D receptor (VDR) in osteoblast-lineage cells consisting of osteoblasts and osteocytes. This pro-resorptive activity was evident basically with higher concentrations of active vitamin D than those expected in physiological conditions. Nevertheless, vitamin D compounds have been used in Japan for treating osteoporosis to increase bone mineral density (BMD). Of note, the increase in BMD by long-term treatment with pharmacological (=near-physiological) doses of vitamin D compounds was caused by the suppression of bone resorption. Therefore, whether vitamin D expresses pro-resorptive or anti-resorptive properties seems to be dependent on the treatment protocols. We established osteoblast lineage-specific and osteoclast-specific VDR conditional knockout (cKO) mice using Osterix-Cre transgenic mice and Cathepsin K-Cre knock-in mice, respectively. According to our observation using these cKO mouse lines, neither VDR in osteoblast-lineage cells nor that in osteoclasts played important roles for osteoclastogenesis and bone resorption at homeostasis. However, using our cKO lines, we observed that VDR in osteoblast-lineage cells, but not osteoclasts, was involved in the anti-resorptive properties of pharmacological doses of vitamin D compounds in vivo. Two different osteoblast-lineage VDR cKO mouse lines were reported. One is a VDR cKO mouse line using alpha 1, type I collagen (Col1a1)-Cre transgenic mice (here we call Col1a1-VDR-cKO mice) and the other is that using dentin matrix protein 1 (Dmp1)-Cre transgenic mice (Dmp1-VDR-cKO mice). Col1a1-VDR-cKO mice exhibited slightly increased bone mass due to lowered bone resorption. In contrast, Dmp1-VDR-cKO mice exhibited no difference in BMD in agreement with our results regarding Ob-VDR-cKO mice. Here we discuss contradictory results and multiple modes of actions of vitamin D in bone resorption in detail. (279 words).

Acute ketamine administration corrects abnormal inflammatory bone markers in major depressive disorder.

Patients with major depressive disorder (MDD) have clinically relevant, significant decreases in bone mineral density (BMD). We sought to determine if predictive markers of bone inflammation-the osteoprotegerin (OPG)-RANK-RANKL system or osteopontin (OPN)-play a role in the bone abnormalities associated with MDD and, if so, whether ketamine treatment corrected the abnormalities. The OPG-RANK-RANKL system plays the principal role in determining the balance between bone resorption and bone formation. RANKL is the osteoclast differentiating factor and diminishes BMD. OPG is a decoy receptor for RANKL, thereby increasing BMD. OPN is the bone glue that acts as a scaffold between bone tissues matrix composition to bind them together and is an important component of bone strength and fracture resistance. Twenty-eight medication-free inpatients with treatment-resistant MDD and 16 healthy controls (HCs) participated in the study. Peripheral bone marker levels and their responses to IV ketamine infusion in MDD patients and HCs were measured at four time points: at baseline, and post-infusion at 230 min, Day 1, and Day 3. Patients with MDD had significant decreases in baseline OPG/RANKL ratio and in plasma OPN levels. Ketamine significantly increased both the OPG/RANKL ratio and plasma OPN levels, and significantly decreased RANKL levels. Bone marker levels in HCs remained unaltered. We conclude that the OPG-RANK-RANKL system and the OPN system play important roles in the serious bone abnormalities associated with MDD. These data suggest that, in addition to its antidepressant effects, ketamine also has a salutary effect on a major medical complication of depressive illness.

RANK rewires energy homeostasis in lung cancer cells and drives primary lung cancer.

Lung cancer is the leading cause of cancer deaths. Besides smoking, epidemiological studies have linked female sex hormones to lung cancer in women; however, the underlying mechanisms remain unclear. Here we report that the receptor activator of nuclear factor-kB (RANK), the key regulator of osteoclastogenesis, is frequently expressed in primary lung tumors, an active RANK pathway correlates with decreased survival, and pharmacologic RANK inhibition reduces tumor growth in patient-derived lung cancer xenografts. Clonal genetic inactivation of KRasG12D in mouse lung epithelial cells markedly impairs the progression of KRasG12D -driven lung cancer, resulting in a significant survival advantage. Mechanistically, RANK rewires energy homeostasis in human and murine lung cancer cells and promotes expansion of lung cancer stem-like cells, which is blocked by inhibiting mitochondrial respiration. Our data also indicate survival differences in KRasG12D -driven lung cancer between male and female mice, and we show that female sex hormones can promote lung cancer progression via the RANK pathway. These data uncover a direct role for RANK in lung cancer and may explain why female sex hormones accelerate lung cancer development. Inhibition of RANK using the approved drug denosumab may be a therapeutic drug candidate for primary lung cancer.

Mathematical Model of Bone Remodeling Captures the Antiresorptive and Anabolic Actions of Various Therapies.

A better understanding of the molecular pathways regulating the bone remodeling process should help in the development of new antiresorptive regulators and anabolic regulators, that is, regulators of bone resorption and of bone formation. Understanding the mechanisms by which parathyroid hormone (PTH) influences bone formation and how it switches from anabolic to catabolic action is important for treating osteoporosis (Poole and Reeve in Curr Opin Pharmacol 5:612-617, 2005). In this paper we describe a mathematical model of bone remodeling that incorporates, extends, and integrates several models of particular aspects of this biochemical system (Cabal et al. in J Bone Miner Res 28(8):1830-1836, 2013; Lemaire et al. in J Theor Biol 229:293-309, 2004; Peterson and Riggs in Bone 46:49-63, 2010; Raposo et al. in J Clin Endocrinol Metab 87(9):4330-4340, 2002; Ross et al. in J Disc Cont Dyn Sys Series B 17(6):2185-2200, 2012). We plan to use this model as a bone homeostasis platform to develop anabolic and antiresorptive compounds. The model will allow us to test hypotheses about the dynamics of compounds and to test the potential benefits of combination therapies. At the core of the model is the idealized account of osteoclast and osteoblast signaling given by Lemaire et al. (J Theor Biol 229:293-309, 2004). We have relaxed some of their assumptions about the roles of osteoprotegerin, transforming growth factor [Formula: see text], and receptor activator of nuclear factor [Formula: see text]B ligand; we have devised more detailed models of the interactions of these species. We have incorporated a model of the effect of calcium sensing receptor antagonists on remodeling (Cabal et al. in J Bone Miner Res 28(8):1830-1836, 2013). We have also incorporated a basic model of the effects of vitamin D on calcium homeostasis. We have included a simple model of the mechanism proposed by Bellido et al. (2003), Ross et al. (J Disc Cont Dyn Sys Series B 17(6):2185-2200, 2012), of the influence of PTH on osteoblast apoptosis, a mechanism that accounts for the anabolic response to pulsatile PTH administration. Finally, we have devised a simple model of the administration and effects of bisphosphonates. The biomarkers in the model are procollagen type 1 amino-terminal propeptide and C-terminal telopeptide. Bone mineral density is the model's principal endpoint.

RANK Signaling Blockade Reduces Breast Cancer Recurrence by Inducing Tumor Cell Differentiation.

RANK expression is associated with poor prognosis in breast cancer even though its therapeutic potential remains unknown. RANKL and its receptor RANK are downstream effectors of the progesterone signaling pathway. However, RANK expression is enriched in hormone receptor negative adenocarcinomas, suggesting additional roles for RANK signaling beyond its hormone-dependent function. Here, to explore the role of RANK signaling once tumors have developed, we use the mouse mammary tumor virus-Polyoma Middle T (MMTV-PyMT), which mimics RANK and RANKL expression patterns seen in human breast adenocarcinomas. Complementary genetic and pharmacologic approaches demonstrate that therapeutic inhibition of RANK signaling drastically reduces the cancer stem cell pool, decreases tumor and metastasis initiation, and enhances sensitivity to chemotherapy. Mechanistically, genome-wide expression analyses show that anti-RANKL therapy promotes lactogenic differentiation of tumor cells. Moreover, RANK signaling in tumor cells negatively regulates the expression of Ap2 transcription factors, and enhances the Wnt agonist Rspo1 and the Sca1-population, enriched in tumor-initiating cells. In addition, we found that expression of TFAP2B and the RANK inhibitor, OPG, in human breast cancer correlate and are associated with relapse-free tumors. These results support the use of RANKL inhibitors to reduce recurrence and metastasis in breast cancer patients based on its ability to induce tumor cell differentiation. Cancer Res; 76(19); 5857-69. ©2016 AACR.

Switching on the Aire conditioner.

Aire has been cloned as the gene responsible for a hereditary type of organ-specific autoimmune disease. Aire controls the expression of a wide array of tissue-restricted Ags by medullary thymic epithelial cells (mTECs), thereby leading to clonal deletion and Treg-cell production, and ultimately to the establishment of self-tolerance. However, relatively little is known about the mechanism responsible for the control of Aire expression itself. In this issue of the European Journal of Immunology, Haljasorg et al. [Eur. J. Immunol. 2015. 45: 3246-3256] have reported the presence of an enhancer element for Aire that binds with NF-κB components downstream of the TNF receptor family member, RANK (receptor activator of NF-κB). The results suggest that RANK has a dual mode of action in Aire expression: one involving the promotion of mTEC differentiation and the other involving activation of the molecular switch for Aire within mature mTECs.

A highly conserved NF-κB-responsive enhancer is critical for thymic expression of Aire in mice.

Autoimmune regulator (Aire) has a unique expression pattern in thymic medullary epithelial cells (mTECs), in which it plays a critical role in the activation of tissue-specific antigens. The expression of Aire in mTECs is activated by receptor activator of nuclear factor κB (RANK) signaling; however, the molecular mechanism behind this activation is unknown. Here, we characterize a conserved noncoding sequence 1 (CNS1) containing two NF-κB binding sites upstream of the Aire coding region. We show that CNS1-deficient mice lack thymic expression of Aire and share several features of Aire-knockout mice, including downregulation of Aire-dependent genes, impaired terminal differentiation of the mTEC population, and reduced production of thymic Treg cells. In addition, we show that CNS1 is indispensable for RANK-induced Aire expression and that CNS1 is activated by NF-κB pathway complexes containing RelA. Together, our results indicate that CNS1 is a critical link between RANK signaling, NF-κB activation, and thymic expression of Aire.

[Vascular Calcification - Pathological Mechanism and Clinical Application - . Vascular calcification as a clinical manifestation of bone-vascular axis].

Several clinical studies has been shown the close relationship between osteoporosis and arteriosclerosis, and basic researches confirmed the reasonability of this association by the findings that organized molecular mechanism of bone formation in bone tissue was also observed in the lesion of vascular calcification, RANK/RANKL/OPG axis is one of potent and explainable molecular mechanism for bone-vascular association. However, one recent clinical intervetion study using RANKL antibody for post menopauisal women with primary osteoporosis could not validate that relationship. Further examinations are needed to improve understanding of the precise mechanism in this area.

Telmisartan decreases inflammation by modulating TNF-α, IL-10, and RANK/RANKL in a rat model of ulcerative colitis.

BACKGROUND: Telmisartan is an antihypertensive angiotensin II receptor blocker. This antihypertensive shows antiinflammatory activity. PURPOSE: In this study, the antiinflammatory activity of telmisartan was tested in an acetic acid (10%) model of ulcerative colitis (UC) in rats. METHODS: Rats were given 1, 3, and 5mg/kg/day of telmisartan orally for 3 days before induction of UC. The same doses were also administered 2 and 24h after induction. Rats from the non-colitis and non-treated colitis groups were administered vehicle (saline, 5 ml/kg) orally and another group received sulfasalazine (50mg/kg/day). Colons tissue was analyzed by macroscopic, by histopathology, by the immunohistochemical examination of RANKL/RANK pathway; by ELISA analysis of the levels of IL-10, TNF-α, myeloperoxidase (MPO) and malonaldehyde (MDA). RESULTS: Telmisartan at 5mg/kg reduced levels of MPO, MDA, TNF-α and increased of IL-10 (p<0.05). Additionally, telmisartan reduced macroscopic damage, number of ulcers, and inflammatory and histopathological processes such as neutrophil infiltration, changes in cytoarchitecture, and necrosis. Immunohistochemistry revealed down-regulation of nuclear factor-kappaB receptor/nuclear factor-kappaB ligand (RANK/RANKL) in groups treated with sulfasalazine or telmisartan. CONCLUSION: Telmisartan exerts beneficial effects in an acetic acid model of colitis in rats. These effects may be due to accelerated termination of the acute inflammatory phase, indicated by decreased TNF-α and increased production of IL-10 and low expression of RANKL and RANK.

RANKL/OPG; Critical role in bone physiology.

After it was proposed that the osteoblast lineage controlled the formation of osteoclasts, cell culture methods were developed that established this to be the case. Evidence was obtained that cytokines and hormones that promote osteoclast formation act first on osteoblast lineage cells to promote the production of a membrane-bound regulator of osteoclastogenesis. This proved to be receptor activator of NF-kB ligand (RANKL) a member of the tumor necrosis factor ligand family that acts upon its receptor RANK in the hematopoietic lineage, with interaction restricted by a decoy soluble receptor osteoprotegerin (OPG), also a product of the osteoblast lineage. The physiological roles of these factors were established through genetic and pharmacological studies, have led to a new physiology of bone, with complete revision of older ideas over the last 15 years, ultimately leading to the development of new pharmaceutical agents for bone disease.

Role of periodontal ligament fibroblasts in osteoclastogenesis: a review.

During the last decade it has become clear that periodontal ligament fibroblasts may contribute to the in vitro differentiation of osteoclasts. We surveyed the current findings regarding their osteoclastogenesis potential. Periodontal ligament fibroblasts have the capacity to select and attract osteoclast precursors and subsequently to retract and enable migration of osteoclast precursors to the bone surface. There, fusion of precursors takes place, giving rise to osteoclasts. The RANKL-RANK-osteoprotegerin (OPG) axis is considered crucial in this process. Periodontal ligament fibroblasts produce primarily OPG, an osteoclastogenesis-inhibitory molecule. However, they may be influenced in vivo by direct or indirect interactions with bacteria or by mechanical loading. Incubation of periodontal ligament fibroblasts with bacteria or bacterial components causes an increased expression of RANKL and other osteoclastogenesis-stimulating molecules, such as tumor necrosis factor-α and macrophage-colony stimulating factor. Similar results are observed after the application of mechanical loading to these fibroblasts. Periodontal ligament fibroblasts may be considered to play an important role in the remodelling of alveolar bone. In vitro experiments have demonstrated that periodontal ligament fibroblasts adapt to bacterial and mechanical stimuli by synthesizing higher levels of osteoclastogenesis-stimulating molecules. Therefore, they probably contribute to the enhanced osteoclast formation observed during periodontitis and to orthodontic tooth movement.

[Pathophysiology of osteoporosis]. / Patofiziologija osteoporoze.

The balance of degradation and bone formation is important for the normal process of remodeling and maintenance of bone mass. Genetic, hormonal, immunological and other factors affect bone remodeling throughout life. Disorder of bone turnover plays key role in the pathophysiology of osteoporosis and presents a complex process which involves bone cells, cytokines and their receptors. Nowadays, important role of RANK/RANKL/OPG system in the pathophysiology of osteoporosis is well known, but it is still important to investigate the intracellular signaling pathways in the development of osteoporosis and other metabolic bone diseases.