Regulation of bone remodeling by the central and peripheral nervous system

Etiology and Measurement of Peri-Implant Crestal Bone Loss (CBL)

The etiology of peri-implant crestal bone loss is today better understood and certain factors proposed in the past have turned out to not be of concern. Regardless, the incidence of crestal bone loss remains higher than necessary and this paper reviews current theory on the etiology with a special emphasis on traditional and innovative methods to assess the level of crestal bone around dental implants that will enable greater sensitivity and specificity and significantly reduce variability in bone loss measurement.

Impact of the Autonomic Nervous System on the Skeleton

It is from the discovery of leptin and the central nervous system as a regulator of bone remodeling that the presence of autonomic nerves within the skeleton transitioned from a mere histological observation to the mechanism whereby neurons of the central nervous system communicate with cells of the bone microenvironment and regulate bone homeostasis. This shift in paradigm sparked new preclinical and clinical investigations aimed at defining the contribution of sympathetic, parasympathetic, and sensory nerves to the process of bone development, bone mass accrual, bone remodeling, and cancer metastasis. The aim of this article is to review the data that led to the current understanding of the interactions between the autonomic and skeletal systems and to present a critical appraisal of the literature, bringing forth a schema that can put into physiological and clinical context the main genetic and pharmacological observations pointing to the existence of an autonomic control of skeletal homeostasis. The different types of nerves found in the skeleton, their functional interactions with bone cells, their impact on bone development, bone mass accrual and remodeling, and the possible clinical or pathophysiological relevance of these findings are discussed.

Bone loss in MPTP mouse model of Parkinson's disease is triggered by decreased osteoblastogenesis and increased osteoclastogenesis

Bone loss is a non-motor symptom of Parkinson's disease (PD). It is unclear whether a patient's immobility or the endocrine changes in the body causes bone deterioration. To address this issue, we used an animal model of the disease where Swiss albino mice were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on day 1 and were left untreated for eight weeks. Behavioral phenotypes of PD, and striatal acetylcholinesterase and dopamine levels were measured. Cortical and trabecular bones were assessed by μ-CT and histology. Gene expression studies were done through quantitative real-time PCR. Effect of MPP+ and MPTP-treated mice serum on MC3T3E-1, SH-SY5Y, and primary osteoclast cells were also studied. Our results demonstrated that MPTP treatment leads to PD like symptoms. It shows a loss of trabecular bone mass and quality by decreasing osteoblast and increased osteoclast number and activity. This effect was accompanied by reduced osteogenic and elevated osteoclastogenic genes expression. While MPP+ had a cytotoxic effect on dopaminergic neurons, it did not affect bone cells. However, ex-vivo treatment of the serum from MPTP-treated mice decreased osteoblastogenesis and increased osteoclastogenesis in cell culture. In conclusion, our study suggests that MPTP-induced parkinsonian features in mice leads to trabecular bone loss by decreased bone formation and increased bone resorption due to changes in the serum circulating factors. This study characterizes the microarchitectural and cellular changes in the skeleton of a mouse model of PD that can be further utilized to investigate therapeutic avenues to treat bone loss in PD patients.

Central adiponectin induces trabecular bone mass partly through epigenetic downregulation of cannabinoid receptor CB1

Central adiponectin (APN) in either the globular (gAPN) or full-length forms decreases sympathetic tone and increases trabecular bone mass in mice through the hypothalamus. It is known that cannabinoid type-1 (CB1) receptors are expressed in the hypothalamic ventromedial nucleus and participate in energy metabolism by controlling sympathetic activity. However, whether central APN could influence endocannabinoid signaling through CB1 receptor to regulate bone metabolism has not been characterized. Here we demonstrate that gAPN downregulated CB1 expression in embryonic mouse hypothalamus N1 cells in vitro. gAPN intracerebroventricular (icv) infusions also decreased hypothalamic CB1 expression and bone formation parameters in APN-knockout (APN-KO) and wild-type mice. Most importantly, mice pretreated with icv infusions with the CB1 receptor agonist arachidonyl-2'-chloroethylamine or antagonist rimonabant attenuated or enhanced respectively central APN induction of bone formation. We then investigated whether epigenetic signaling mechanisms were involved in the downregulation of hypothalamic CB1 expression by gAPN. We found gAPN enhanced expression levels of various histone deacetylases (HDACs), especially HDAC5. Furthermore, chromatin immunoprecipitation assays revealed HDAC5 bound to the transcriptional start site transcription start site 2 region of the CB1 promoter. In summary, our study identified a possible novel central APN-HDAC5-CB1 signaling mechanism that promotes peripheral bone formation through epigenetic regulation of hypothalamic CB1 expression.

Selective serotonin re-uptake inhibitor sertraline inhibits bone healing in a calvarial defect model

Bone wound healing is a highly dynamic and precisely controlled process through which damaged bone undergoes repair and complete regeneration. External factors can alter this process, leading to delayed or failed bone wound healing. The findings of recent studies suggest that the use of selective serotonin reuptake inhibitors (SSRIs) can reduce bone mass, precipitate osteoporotic fractures and increase the rate of dental implant failure. With 10% of Americans prescribed antidepressants, the potential of SSRIs to impair bone healing may adversely affect millions of patients' ability to heal after sustaining trauma. Here, we investigate the effect of the SSRI sertraline on bone healing through pre-treatment with (10 mg·kg-1 sertraline in drinking water, n = 26) or without (control, n = 30) SSRI followed by the creation of a 5-mm calvarial defect. Animals were randomized into three surgical groups: (a) empty/sham, (b) implanted with a DermaMatrix scaffold soak-loaded with sterile PBS or (c) DermaMatrix soak-loaded with 542.5 ng BMP2. SSRI exposure continued until sacrifice in the exposed groups at 4 weeks after surgery. Sertraline exposure resulted in decreased bone healing with significant decreases in trabecular thickness, trabecular number and osteoclast dysfunction while significantly increasing mature collagen fiber formation. These findings indicate that sertraline exposure can impair bone wound healing through disruption of bone repair and regeneration while promoting or defaulting to scar formation within the defect site.

Effects of Ultra-early Hyperbaric Oxygen Therapy on Femoral Calcitonin Gene-Related Peptide and Bone Metabolism of Rats With Complete Spinal Transection

STUDY DESIGN

Seventy-five Sprague-Dawley rats were randomly divided into sham, complete spinal cord transection (CSCT) and hyperbaric oxygen (HBO) groups. Among them, rats in HBO group were further divided into 3 hours group (HBO1) and 12 hours group (HBO2).

OBJECTIVE

To study the effects of ultra-early HBO therapy on femoral calcitonin gene-related peptide (CGRP) and bone metabolism of rats with CSCT.

SUMMARY OF BACKGROUND DATA

Complete spinal cord injury (SCI) is still an unresolved problem in clinical practice. Studies on changes in (calcitonin gene-related peptide) CGRP and bone metabolism and osteoporosis prevention after SCI have important clinical significance.

METHODS

Rats in the sham group underwent laminectomy alone, whereas rats in the other three groups underwent laminectomy and CSCT at the level of the 10th thoracic vertebra. Six weeks after operation, rat blood samples and femoral samples from CSCT area were taken and prepared for immunohistochemical staining of CGRP, quantitative polymerase chain reaction (qPCR) of CGRP mRNA, enzyme-linked immunosorbent assay (ELISA) for the levels of serum bone-specific alkaline phosphatase (sBAP), serum osteocalcin (sOC), serum type-I collagen amino-terminal peptide (sNTX), and urinary deoxypyridinoline (uDPD). These data were statistically analyzed using paired LSD or Tamhane.

RESULTS

The number of CGRP-positive cells and expression of CGRP mRNA in femur were significantly reduced, and the levels of sBAP, sOC, sNTX, and uDPD were significantly increased in CSCT, HBO1, and HBO2 groups than in the sham group, (P < 0.05-0.01). In addition, the number of CGRP-positive cells, expression of CGRP mRNA in femur, and the levels of sBAP and sOC were significantly enhanced, but the levels of sNTX and uDPD were significantly lowered in HBO1 group than in HBO2 and CSCT groups (P < 0.05).

CONCLUSION

Ultra-early HBO therapy could improve bone turnover, promote bone formation, and prohibit bone resorption by enhancing CGRP synthesis in the sensory neurons in posterior horn of spinal cord.

LEVEL OF EVIDENCE

N/A.

Exosomes: novel regulators of bone remodelling and potential therapeutic agents for orthodontics

Recent studies suggest that exosomes are involved in intercellular communication required for the maintenance of healthy bone. Exosomes are small (30-150 nm in diameter) extracellular vesicles that are formed in multivesicular bodies and are released from cells as the multivesicular bodies fuse with the plasma membrane. Regulatory exosomes have the capacity to exert profound control over target cells. They can stimulate plasma membrane receptors and are also internalized by the target cell delivering proteins, lipids, small molecules and functional RNAs from the cell of origin. We and others have recently reported on regulatory exosomes from osteoclasts and osteoblasts. Key candidate molecules identified in exosome-based regulation of bone remodelling include receptor activator of nuclear factor kappa B (RANK), RANK-ligand (RANKL), ephrinA2, semaphorin 4D, microRNA-146a and microRNA- 214-3p. Exosomes will likely prove to be crucial elements in the communication networks integrating bone cells (osteoclasts, osteoblasts, osteocytes) and linking bone to other tissue. Exosomes collected from bone cells grown in culture may prove useful to augment bone remodelling associated with orthodontic force application or required for the repair of craniofacial bone. Various technologies allow exosomes to be engineered to improve their targeting and efficacy for therapeutic purposes. In summary, exosomes have emerged as important elements of the machinery for intercellular communication between bone cells. They hold great promise as therapeutic targets, biomarkers and therapeutic agents for orthodontists.

Osteolytic cancer cells induce vascular/axon guidance processes in the bone/bone marrow stroma

Prostate and breast cancers frequently metastasize to bone. The physiological bone homeostasis is perturbed once cancer cells proliferate at the bone metastatic site. Tumors are complex structures consisting of cancer cells and numerous stroma cells.

In this study, we show that osteolytic cancer cells (PC-3 and MDA-MB231) induce transcriptome changes in the bone/bone marrow microenvironment (stroma). This stroma transcriptome differs from the previously reported stroma transcriptome of osteoinductive cancer cells (VCaP). While the biological process “angiogenesis/vasculogenesis” is enriched in both transcriptomes, the “vascular/axon guidance” process is a unique process that characterizes the osteolytic stroma. In osteolytic bone metastasis, angiogenesis is denoted by vessel morphology and marker expression specific for arteries/arterioles. Interestingly, intra-tumoral neurite-like structures were in proximity to arteries. Additionally, we found that increased numbers of mesenchymal stem cells and vascular smooth muscle cells, expressing osteolytic cytokines and inhibitors of bone formation, contribute to the osteolytic bone phenotype.

Osteoinductive and osteolytic cancer cells induce different types of vessels, representing functionally different hematopoietic stem cell niches. This finding suggests different growth requirements of osteolytic and osteoinductive cancer cells and the need for a differential anti-angiogenic strategy to inhibit tumor growth in osteolytic and osteoblastic bone metastasis.

Elucidating the Mechanism(s) Underlying Antipsychotic and Antidepressant-Mediated Fractures

Mood spectrum disorders and medications used to treat these disorders, such as atypical antipsychotic drugs (AA), are associated with metabolic and endocrine side effects including obesity, dyslipidemia, hyperglycemia and increased risk of fractures. Antidepressant medications, including selective serotonin reuptake inhibitors (SSRI), have also been reported to increase fracture risk in some patients. The pharmacology underlying the increased risk of fractures is currently unknown. Possible mechanisms include alternations in dopaminergic and/or serotonergic signaling pathways. As these medications distribute to the bone marrow as well as to the brain, it is possible that drug-induced fractures are due to both centrally mediated effects as well as direct effects on bone turnover. Given the growing patient population that is prescribed these medications for both on- and off-label indications, understanding the level of risk and the mechanisms underlying drug-induced fractures is important for informing both prescribing and patient monitoring practices.

Preliminary Evidence of an Association Between ADHD Medications and Diminished Bone Health in Children and Adolescents

BACKGROUND

The US Centers for Disease Control and Prevention estimate that 3.5 million children use psychotropic drugs for attention-deficit hyperactivity disorder (ADHD). With an increase in use of these types of drugs, thorough understanding of their potential side effects on the growing skeleton is needed. The purpose of this study was to determine whether there is an association between use of ADHD medication and diminished bone health.

METHODS

Three waves of the National Health and Nutrition Examination Survey public-use data set, collected from 2005 through 2010, were compiled for this study (N=5315). Bone health was measured using dual-energy x-ray absorptiometry scans, which were performed for participants aged 8 to 17 years to determine bone mineral density (BMD) for 3 regions: (1) total femur; (2) femoral neck; and (3) lumbar. Use of ADHD medications was determined by self-reported responses to questions regarding prescription drug use, which were answered by either the respondent or the respondent's parent or guardian. Multiple statistical techniques were used to produce estimates of association between ADHD medication use and z score age and sex standardized BMD measures, including survey adjusted univariate, survey adjusted multiple linear regression, and generalized estimating equations with a propensity-matched subsample (N=1967). Multivariate models adjusted for covariates including time period, age, sex, race/ethnicity, family income to poverty ratio, and total number of prescription medications.

RESULTS

Conservative estimates of the difference in standardized BMD measures between the ADHD medication group and the nonmedicated group range from -0.4855 (±0.27; P<0.001) for total femoral, -0.4671 (±0.27; P<0.001) for femoral neck, and -0.3947 (±0.29; P<0.01) for lumbar. Significantly more children on ADHD medications versus match subjects on no medication had BMDs with in osteopenic range (38.3% vs. 21.6%, P<0.01).

DISCUSSION

The findings suggest that there are real and nontrivial differences in BMD for children and adolescents taking ADHD medications, as compared with similar children not taking any prescription medications. Prescribing physicians and parents should be aware of potential bone health risks associated with these medications.

LEVEL OF EVIDENCE

Level III-case-control study.

In vivo and In vitro Identification of Endocannabinoid Signaling in Periodontal Tissues and Their Potential Role in Local Pathophysiology

The endocannabinoid system (ECS) with its binding receptors CB1 and CB2 impacts multiple pathophysiologies not only limited to neuronal psychoactivity. CB1 is assigned to cerebral neuron action, whereas CB2 is mainly expressed in different non-neuronal tissues and associated with immunosuppressive effects. Based on these tissue-selective CB receptor roles, it was the aim of this study to analyze potential expression in periodontal tissues under physiological conditions and inflammatory states. In vivo, CB receptor expression was investigated on human periodontal biopsies with or without bacterial inflammation and on rat maxillae with or without sterile inflammation. In vitro analyses were performed on human periodontal ligament (PDL) cells at rest or under mechanical strain via qRT-PCR, Western blot, and immunocytochemistry. P < 0.05 was set statistical significant. In vivo, CB1 expression was significantly higher in healthy PDL structures compared to CB2 (13.5% ± 1.3 of PDL tissues positively stained; 7.1% ± 0.9). Bacterial inflammation effected decrease in CB1 (9.7% ± 2.4), but increase in CB2 (14.7% ± 2.5). In contrast, sterile inflammation caused extensive CB1 (40% ± 1.9) and CB2 (41.7% ± 2.2) accumulations evenly distributed in the tooth surrounding PDL. In vitro, CB2 was ubiquitously expressed on gene and protein level. CB1 was constitutively expressed on transcriptional level (0.41% ± 0.09), even higher than CB2 (0.29% ± 0.06), but undetectable on protein level. Analyses further revealed expression changes of both receptors in mechanically loaded PDL cells. CB1 and CB2 are varyingly expressed in periodontal tissues, both adjusted by different entities of periodontal inflammation and by mechanical stress. This indicates potential ECS function as regulatory tool in controlling of periodontal pathophysiology.

Muscle-Bone Crosstalk: Emerging Opportunities for Novel Therapeutic Approaches to Treat Musculoskeletal Pathologies

Osteoporosis and sarcopenia are age-related musculoskeletal pathologies that often develop in parallel. Osteoporosis is characterized by a reduced bone mass and an increased fracture risk. Sarcopenia describes muscle wasting with an increasing risk of injuries due to falls. The medical treatment of both diseases costs billions in health care per year. With the impact on public health and economy, and considering the increasing life expectancy of populations, more efficient treatment regimens are sought. The biomechanical interaction between both tissues with muscle acting on bone is well established. Recently, both tissues were also determined as secretory endocrine organs affecting the function of one another. New exciting discoveries on this front are made each year, with novel signaling molecules being discovered and potential controversies being described. While this review does not claim completeness, it will summarize the current knowledge on both the biomechanical and the biochemical link between muscle and bone. The review will highlight the known secreted molecules by both tissues affecting the other and finish with an outlook on novel therapeutics that could emerge from these discoveries.

Targeted Pth4-expressing cell ablation impairs skeletal mineralization in zebrafish

Skeletal development and mineralization are essential processes driven by the coordinated action of neural signals, circulating molecules and local factors. Our previous studies revealed that the novel neuropeptide Pth4, synthesized by hypothalamic cells, was involved in bone metabolism via phosphate regulation in adult zebrafish. Here, we investigate the role of pth4 during skeletal development using single-cell resolution, two-photon laser ablation of Pth4:eGFP-expressing cells and confocal imaging in vivo. Using a stable transgenic Pth4:eGFP zebrafish line, we identify Pth4:eGFP-expressing cells as post-mitotic neurons. After targeted ablation of eGFP-expressing cells in the hypothalamus, the experimental larvae exhibited impaired mineralization of the craniofacial bones whereas cartilage development was normal. In addition to a decrease in pth4 transcript levels, we noted altered expression of phex and entpd5, genes associated with phosphate homeostasis and mineralization, as well as a delay in the expression of osteoblast differentiation markers such as sp7 and sparc. Taken together, these results suggest that Pth4-expressing hypothalamic neurons participate in the regulation of bone metabolism, possibly through regulating phosphate balance during zebrafish development.

Osteoimmunology: The Conceptual Framework Unifying the Immune and Skeletal Systems

The immune and skeletal systems share a variety of molecules, including cytokines, chemokines, hormones, receptors, and transcription factors. Bone cells interact with immune cells under physiological and pathological conditions. Osteoimmunology was created as a new interdisciplinary field in large part to highlight the shared molecules and reciprocal interactions between the two systems in both heath and disease. Receptor activator of NF-κB ligand (RANKL) plays an essential role not only in the development of immune organs and bones, but also in autoimmune diseases affecting bone, thus effectively comprising the molecule that links the two systems. Here we review the function, gene regulation, and signal transduction of osteoimmune molecules, including RANKL, in the context of osteoclastogenesis as well as multiple other regulatory functions. Osteoimmunology has become indispensable for understanding the pathogenesis of a number of diseases such as rheumatoid arthritis (RA). We review the various osteoimmune pathologies, including the bone destruction in RA, in which pathogenic helper T cell subsets [such as IL-17-expressing helper T (Th17) cells] induce bone erosion through aberrant RANKL expression. We also focus on cellular interactions and the identification of the communication factors in the bone marrow, discussing the contribution of bone cells to the maintenance and regulation of hematopoietic stem and progenitors cells. Thus the time has come for a basic reappraisal of the framework for understanding both the immune and bone systems. The concept of a unified osteoimmune system will be absolutely indispensable for basic and translational approaches to diseases related to bone and/or the immune system.

Stem cells applications in bone and tooth repair and regeneration: New insights, tools, and hopes

The exploration of stem and progenitor cells holds promise for advancing our understanding of the biology of tissue repair and regeneration mechanisms after injury. This will also help in the future use of stem cell therapy for the development of regenerative medicine approaches for the treatment of different tissue-species defects or disorders such as bone, cartilages, and tooth defects or disorders. Bone is a specialized connective tissue, with mineralized extracellular components that provide bones with both strength and rigidity, and thus enable bones to function in body mechanical supports and necessary locomotion process. New insights have been added to the use of different types of stem cells in bone and tooth defects over the last few years. In this concise review, we briefly describe bone structure as well as summarize recent research progress and accumulated information regarding the osteogenic differentiation of stem cells, as well as stem cell contributions to bone repair/regeneration, bone defects or disorders, and both restoration and regeneration of bones and cartilages. We also discuss advances in the osteogenic differentiation and bone regeneration of dental and periodontal stem cells as well as in stem cell contributions to dentine regeneration and tooth engineering.

CRMP4 Inhibits Bone Formation by Negatively Regulating BMP and RhoA Signaling

We identified the neuroprotein collapsing response mediator protein-4 (CRMP4) as a noncanonical osteogenic factor that regulates the differentiation of mouse bone marrow skeletal stem cells (bone marrow stromal stem cells [mBMSCs]) into osteoblastic cells. CRMP4 is the only member of the CRMP1-CRMP5 family to be expressed by mBMSCs and in osteoprogenitors of both adult mouse and human bones. In vitro gain-of-function and loss-of-function of CRMP4 in murine stromal cells revealed its inhibitory effect on osteoblast differentiation. In addition, Crmp4-deficient mice (Crmp4^-/- ) displayed a 40% increase in bone mass, increased mineral apposition rate, and bone formation rate, compared to wild-type controls. Increased bone mass in Crmp4^-/- mice was associated with enhanced BMP2 signaling and BMP2-induced osteoblast differentiation in Crmp4^-/- osteoblasts (OBs). Furthermore, Crmp4^-/- OBs exhibited enhanced activation of RhoA/focal adhesion kinase (FAK) signaling that led to cytoskeletal changes with increased cell spreading. In addition, Crmp4^-/- OBs exhibited increased cell proliferation that was mediated via inhibiting cyclin-dependent kinase inhibitor 1B, p27^Kip1 and upregulating cyclin D1 expression which are targets of RhoA signaling pathway. Our findings identify CRMP4 as a novel negative regulator of osteoblast differentiation. © 2016 American Society for Bone and Mineral Research.

Mechanical mandible competence in rats with nutritional growth retardation

OBJECTIVE

In order to provide a better understanding of the sympathetic nervous system as a negative regulator of bone status, the aim of the study was to establish the biomechanical mandible response to different doses of a β-adrenergic antagonist such as propranolol (P) in a stress-induced food restriction model of growth retardation.

METHODS

Rats were assigned to eight groups: Control (C), C+P3.5 (CP3.5), C+P7 (CP7), C+P14 (CP14), NGR, NGR+P3.5 (NGRP3.5), NGR+P7 (NGRP7) and NGR+P14 (NGRP14). C, CP3.5, CP7 and CP14 rats were freely fed with the standard diet. NGR, NGRP3.5, NGRP7 and NGRP14 rats received, for 4 weeks (W4), 80% of the amount of controls food consumed. Propranolol 3.5, 7 and 14mg/kg/day was injected ip 5days per week in CP3.5 and NGRP3.5, CP7 and NGRP7, CP14 and NGRP14, respectively. At W4, zoometry, mandible morphometry, static histomorphometric and biomechanical competence were performed.

RESULTS

A dose of Propranolol 7mg/kg/day induced interradicular bone volume accretion reaching a mandible stiffness according to chronological age.

CONCLUSION

These findings evidenced that sympathetic nervous system activity is a negative regulator of mandible mechanical competence in the nutritional growth retardation model. Propranolol 7mg/kg/day, under the regimen usage, seems to be appropriate to blockade SNS activity on mandible mechanical performance in NGR rats, probably associated to an effect on bone mechanostat system ability to detect disuse mode as an error.

Emerging therapeutic targets in cancer induced bone disease: A focus on the peripheral type 2 cannabinoid receptor

Skeletal complications are a common cause of morbidity in patients with primary bone cancer and bone metastases. The type 2 cannabinoid (Cnr2) receptor is implicated in cancer, bone metabolism and pain perception. Emerging data have uncovered the role of Cnr2 in the regulation of tumour-bone cell interactions and suggest that agents that target Cnr2 in the skeleton have potential efficacy in the reduction of skeletal complications associated with cancer. This review aims to provide an overview of findings relating to the role of Cnr2 receptor in the regulation of skeletal tumour growth, osteolysis and bone pain, and highlights the many unanswered questions and unmet needs. This review argues that development and testing of peripherally-acting, tumour-, Cnr2-selective ligands in preclinical models of metastatic cancer will pave the way for future research that will advance our knowledge about the basic mechanism(s) by which the endocannabinoid system regulate cancer metastasis, stimulate the development of a safer cannabis-based therapy for the treatment of cancer and provide policy makers with powerful tools to assess the science and therapeutic potential of cannabinoid-based therapy. Thus, offering the prospect of identifying selective Cnr2 ligands, as novel, alternative to cannabis herbal extracts for the treatment of advanced cancer patients.

Exercise-induced irisin in bone and systemic irisin administration reveal new regulatory mechanisms of bone metabolism

Irisin is a polypeptide hormone derived from the proteolytic cleavage of fibronectin-type III domain-containing 5 (FNDC5) protein. Once released to circulation upon exercise or cold exposure, irisin stimulates browning of white adipose tissue (WAT) and uncoupling protein 1 (UCP1) expression, leading to an increase in total body energy expenditure by augmented UCP1-mediated thermogenesis. It is currently unknown whether irisin is secreted by bone upon exercise or whether it regulates bone metabolism in vivo. In this study, we found that 2 weeks of voluntary wheel-running exercise induced high levels of FNDC5 messenger RNA as well as FNDC5/irisin protein expression in murine bone tissues. Increased immunoreactivity due to exercise-induced FNDC5/irisin expression was detected in different regions of exercised femoral bones, including growth plate, trabecular bone, cortical bone, articular cartilage, and bone–tendon interface. Exercise also increased expression of osteogenic markers in bone and that of UCP1 in WAT, and led to bodyweight loss. Irisin intraperitoneal (IP) administration resulted in increased trabecular and cortical bone thickness and osteoblasts numbers, and concurrently induced UCP1 expression in subcutaneous WAT. Lentiviral FNDC5 IP administration increased cortical bone thickness. In vitro studies in bone cells revealed irisin increases osteoblastogenesis and mineralization, and inhibits receptor activator of nuclear factor-kB ligand (RANKL)-induced osteoclastogenesis. Taken together, our findings show that voluntary exercise increases irisin production in bone, and that an increase in circulating irisin levels enhances osteogenesis in mice.

Pth4, an ancient parathyroid hormone lost in eutherian mammals, reveals a new brain-to-bone signaling pathway

Regulation of bone development, growth, and remodeling traditionally has been thought to depend on endocrine and autocrine/paracrine modulators. Recently, however, brain-derived signals have emerged as key regulators of bone metabolism, although their mechanisms of action have been poorly understood. We reveal the existence of an ancient parathyroid hormone (Pth)4 in zebrafish that was secondarily lost in the eutherian mammals' lineage, including humans, and that is specifically expressed in neurons of the hypothalamus and appears to be a central neural regulator of bone development and mineral homeostasis. Transgenic fish lines enabled mapping of axonal projections leading from the hypothalamus to the brainstem and spinal cord. Targeted laser ablation demonstrated an essential role for of pth4-expressing neurons in larval bone mineralization. Moreover, we show that Runx2 is a direct regulator of pth4 expression and that Pth4 can activate cAMP signaling mediated by Pth receptors. Finally, gain-of-function experiments show that Pth4 can alter calcium/phosphorus levels and affect expression of genes involved in phosphate homeostasis. Based on our discovery and characterization of Pth4, we propose a model for evolution of bone homeostasis in the context of the vertebrate transition from an aquatic to a terrestrial lifestyle.-Suarez-Bregua, P., Torres-Nuñez, E., Saxena, A., Guerreiro, P., Braasch, I., Prober, D. A., Moran, P., Cerda-Reverter, J. M., Du, S. J., Adrio, F., Power, D. M., Canario, A. V. M., Postlethwait, J. H., Bronner, M E., Cañestro, C., Rotllant, J. Pth4, an ancient parathyroid hormone lost in eutherian mammals, reveals a new brain-to-bone signaling pathway.

Ablation of Y1 receptor impairs osteoclast bone-resorbing activity

Y₁ receptor (Y₁R)-signalling pathway plays a pivotal role in the regulation of bone metabolism. The lack of Y₁R-signalling stimulates bone mass accretion that has been mainly attributed to Y₁R disruption from bone-forming cells. Still, the involvement of Y₁R-signalling in the control of bone-resorbing cells remained to be explored. Therefore, in this study we assessed the role of Y₁R deficiency in osteoclast formation and resorption activity. Here we demonstrate that Y₁R germline deletion (Y₁R^−/−) led to increased formation of highly multinucleated (n > 8) osteoclasts and enhanced surface area, possibly due to monocyte chemoattractant protein-1 (MCP-1) overexpression regulated by RANKL-signalling. Interestingly, functional studies revealed that these giant Y₁R^−/− multinucleated cells produce poorly demineralized eroded pits, which were associated to reduce expression of osteoclast matrix degradation markers, such as tartrate-resistant acid phosphatase-5b (TRAcP5b), matrix metalloproteinase-9 (MMP-9) and cathepsin-K (CTSK). Tridimensional (3D) morphologic analyses of resorption pits, using an in-house developed quantitative computational tool (BonePit), showed that Y₁R^−/− resorption pits displayed a marked reduction in surface area, volume and depth. Together, these data demonstrates that the lack of Y₁Rs stimulates the formation of larger multinucleated osteoclasts in vitro with reduced bone-resorbing activity, unveiling a novel therapeutic option for osteoclastic bone diseases based on Y₁R-signalling ablation.

Chronic Psychosocial Stress Impairs Bone Homeostasis: A Study in the Social Isolation Reared Rat

Chronic psychosocial stress is a key player in the onset and aggravation of mental diseases, including psychosis. Although a strong association between this psychiatric condition and other medical co-morbidities has been recently demonstrated, few data on the link between psychosis and bone homeostasis are actually available. The aim of this study was to investigate whether chronic psychosocial stress induced by 4 or 7 weeks of social isolation in drug-naïve male Wistar rats could alter bone homeostasis in terms of bone thickness, mineral density and content, as well as markers of bone formation and resorption (sclerostin, cathepsin K, and CTX-I). We found that bone mineral density was increased in rats exposed to 7 weeks of social isolation, while no differences were detected in bone mineral content and area. Moreover, 7 weeks of social isolation lead to increase of femur thickness with respect to controls, suggesting the development of a hyperostosis condition. Isolated rats showed no changes in sclerostin levels, a marker of bone formation, compared to grouped animals. Conversely, bone resorption markers were significantly altered after 7 weeks of social isolation in terms of decrease in cathepsin K and increase of CTX-I. No alterations were found after 4 weeks of isolation rearing. Our observations suggest that chronic psychosocial stress might affect bone homeostasis, more likely independently from drug treatment. Thus, the social isolation model might help to identify possible new therapeutic targets to treat the burden of chronic psychosocial stress and to attempt alternative therapy choices.

PTH regulates β2-adrenergic receptor expression in osteoblast-like MC3T3-E1 cells

As the aged population is soaring, prevalence of osteoporosis is increasing. However, the molecular basis underlying the regulation of bone mass is still incompletely understood. Sympathetic tone acts via beta2 adrenergic receptors in bone and regulates the mass of bone which is the target organ of parathyroid hormone (PTH). However, whether beta2 adrenergic receptor is regulated by PTH in bone cells is not known. We therefore investigated the effects of PTH on beta2 adrenergic receptor gene expression in osteoblast-like MC3T3-E1 cells. PTH treatment immediately suppressed the expression levels of beta2 adrenergic receptor mRNA. This PTH effect was dose-dependent starting as low as 1 nM. PTH action on beta2 adrenergic receptor gene expression was inhibited by a transcriptional inhibitor, DRB, but not by a protein synthesis inhibitor, cycloheximide suggesting direct transcription control. Knockdown of beta2 adrenergic receptor promoted PTH-induced expression of c-fos, an immediate early response gene. With respect to molecular basis for this phenomenon, knockdown of beta2 adrenergic receptor enhanced PTH-induced transcriptional activity of cyclic AMP response element-luciferase construct in osteoblasts. Knockdown of beta2 adrenergic receptors also enhanced forskolin-induced luciferase expression, revealing that adenylate cyclase activity is influenced by beta2 adrenergic receptor. As for phosphorylation of transcription factor, knockdown of beta2 adrenergic receptor enhanced PTH-induced phosphorylation of cyclic AMP response element binding protein (CREB). These data reveal that beta2 adrenergic receptor is one of the targets of PTH and acts as a suppressor of PTH action in osteoblasts.

Fat and Sucrose Intake Induces Obesity-Related Bone Metabolism Disturbances: Kinetic and Reversibility Studies in Growing and Adult Rats

Metabolic and bone effects were investigated in growing (G, n = 45) and mature (M, n = 45) rats fed a high-fat/high-sucrose diet (HFS) isocaloric to the chow diet of controls (C, n = 30 per group). At week 19, a subset of 15 rats in each group (HFS or C, at both ages) was analyzed. Then one-half of the remaining 30 HFS rats in each groups continued HFS and one-half were shifted to C until week 27. Although no serum or bone marrow inflammation was seen, HFS increased visceral fat, serum leptin and insulin at week 19 and induced further alterations in lipid profile, serum adiponectin, and TGFβ1, TIMP1, MMP2, and MMP9, suggesting a prediabetic phenotype and cardiovascular dysfunction at week 27 more pronounced in M than G. These events were associated with dramatic reduction of osteoclastic and osteoid surfaces with accelerated mineralizing surfaces in both HFS age groups. Mineral metabolism and its major regulators were disturbed, leading to hyperphosphatemia and hypocalcemia. These changes were associated with bone alterations in the weight-bearing tibia, not in the non-weight-bearing vertebra. Indeed in fat rats, tibia trabecular bone accrual increased in G whereas loss of trabecular bone in M was alleviated. At diaphysis cortical porosity increased in G and even more in M at week 27. After the diet switch, metabolic and bone cellular disturbances fully reversed in G, but not in M. Trabecular benefit of the obese was preserved in both age groups and in M the age-related bone loss was even lighter after the diet switch than in prolonged HFS. At the diaphysis, cortical porosity normalized in G but not in M. Hypocalcemia in G and M was irreversible. Thus, the mild metabolic syndrome induced by isocaloric HFS is able to alter bone cellular activities and mineral metabolism, reinforce trabecular bone, and affect cortical bone porosity in an irreversible manner in older rats.

Skeletal integration of energy homeostasis: Translational implications

New evidence has recently emerged defining a close relationship between fat and bone metabolism. Adipose tissue is one of the largest organs in the body but its functions vary by location and origin. Adipocytes can act in an autocrine manner to regulate energy balance by sequestering triglycerides and then, depending on demand, releasing fatty acids through lipolysis for energy utilization, and in some cases through uncoupling protein 1 for generating heat. Adipose tissue can also act in an endocrine or paracrine manner by releasing adipokines that modulate the function of other organs. Bone is one of those target tissues, although recent evidence has emerged that the skeleton reciprocates by releasing its own factors that modulate adipose tissue and beta cells in the pancreas. Therefore, it is not surprising that these energy-modulating tissues are controlled by a central regulatory mechanism, primarily the sympathetic nervous system. Disruption in this complex regulatory circuit and its downstream tissues is manifested in a wide range of metabolic disorders, for which the most prevalent is type 2 diabetes mellitus. The aim of this review is to summarize our knowledge of common determinants in the bone and adipose function and the translational implications of recent work in this emerging field.

Inhibition of titanium-particle-induced inflammatory osteolysis after local administration of dopamine and suppression of osteoclastogenesis via D2-like receptor signaling pathway

Chronic inflammation and extensive osteoclast formation play critical roles in wear-debris-induced peri-implant osteolysis. We investigated the potential impact of dopamine on titanium-particle-induced inflammatory osteolysis in vivo and in vitro. Twenty-eight C57BL/6J mice were randomly assigned to four groups: sham control (PBS treatment), titanium (titanium/PBS treatment), low- (titanium/2 μg kg(-1) day(-1) dopamine) and high-dopamine (titanium/10 μg kg(-1) day(-1) dopamine). After 2 weeks, mouse calvariae were collected for micro-computed tomography (micro-CT) and histomorphometry analysis. Bone-marrow-derived macrophages (BMMs) were isolated to assess osteoclast differentiation. Dopamine significantly reduced titanium-particle-induced osteolysis compared with the titanium group as confirmed by micro-CT and histomorphometric data. Osteoclast numbers were 34.9% and 59.7% (both p < 0.01) lower in the low- and high-dopamine-treatment groups, respectively, than in the titanium group. Additionally, low RANKL, tumor necrosis factor-α, interleukin-1β and interleukin-6 immunochemistry staining were noted in dopamine-treatment groups. Dopamine markedly inhibited osteoclast formation, osteoclastogenesis-related gene expression and pro-inflammatory cytokine expression in BMMs in a dose-dependent manner. Moreover, the resorption area was decreased with 10(-9) M and 10(-8) M dopamine to 40.0% and 14.5% (both p < 0.01), respectively. Furthermore, the inhibitory effect of dopamine was reversed by the D2-like-receptor antagonist haloperidol but not by the D1-like-receptor antagonist SCH23390. These results suggest that dopamine therapy could be developed into an effective and safe method for osteolysis-related disease caused by chronic inflammation and excessive osteoclast formation.

Bone remodeling in the context of cellular and systemic regulation: the role of osteocytes and the nervous system

Bone is a dynamic tissue that undergoes constant remodeling. The appropriate course of this process determines development and regeneration of the skeleton. Tight molecular control of bone remodeling is vital for the maintenance of appropriate physiology and microarchitecture of the bone, providing homeostasis, also at the systemic level. The process of remodeling is regulated by a rich innervation of the skeleton, being the source of various growth factors, neurotransmitters, and hormones regulating function of the bone. Although the course of bone remodeling at the cellular level is mainly associated with the activity of osteoclasts and osteoblasts, recently also osteocytes have gained a growing interest as the principal regulators of bone turnover. Osteocytes play a significant role in the regulation of osteogenesis, releasing sclerostin (SOST), an inhibitor of bone formation. The process of bone turnover, especially osteogenesis, is also modulated by extra-skeletal molecules. Proliferation and differentiation of osteoblasts are promoted by the brain-derived serotonin and hypothetically inhibited by its intestinal equivalent. The activity of SOST and serotonin is either directly or indirectly associated with the canonical Wnt/β-catenin signaling pathway, the main regulatory pathway of osteoblasts function. The impairment of bone remodeling may lead to many skeletal diseases, such as high bone mass syndrome or osteoporosis. In this paper, we review the most recent data on the cellular and molecular mechanisms of bone remodeling control, with particular emphasis on the role of osteocytes and the nervous system in this process.

Energy Excess, Glucose Utilization, and Skeletal Remodeling: New Insights

Skeletal complications have recently been recognized as another of the several comorbidities associated with diabetes. Clinical studies suggest that disordered glucose and lipid metabolism have a profound effect on bone. Diabetes-related changes in skeletal homeostasis result in a significant increased risk of fractures, although the pathophysiology may differ from postmenopausal osteoporosis. Efforts to understand the underlying mechanisms of diabetic bone disease have focused on the direct interaction of adipose tissue with skeletal remodeling and the potential influence of glucose utilization and energy uptake on these processes. One aspect that has emerged recently is the major role of the central nervous system in whole-body metabolism, bone turnover, adipose tissue remodeling, and beta cell secretion of insulin. Importantly, the skeleton contributes to the metabolic balance inherent in physiologic states. New animal models have provided the insights necessary to begin to dissect the effects of obesity and insulin resistance on the acquisition and maintenance of bone mass. In this Perspective, we focus on potential mechanisms that underlie the complex interactions between adipose tissue and skeletal turnover by focusing on the clinical evidence and on preclinical studies indicating that glucose intolerance may have a significant impact on the skeleton. In addition, we raise fundamental questions that need to be addressed in future studies to resolve the conundrum associated with glucose intolerance, obesity, and osteoporosis.

Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells

Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

Inner Ear Vestibular Signals Regulate Bone Remodeling via the Sympathetic Nervous System

The inner ear vestibular system has numerous projections on central brain centers that regulate sympathetic outflow, and skeletal sympathetic projections affect bone remodeling by inhibiting bone formation by osteoblasts and promoting bone resorption by osteoclasts. In this study, we show that bilateral vestibular lesions in mice cause a low bone mass phenotype associated with decreased bone formation and increased bone resorption. This reduction in bone mass is most pronounced in lower limbs, is not associated with reduced locomotor activity or chronic inflammation, and could be prevented by the administration of the β-blocker propranolol and by genetic deletion of the β2-adrenergic receptor, globally or specifically in osteoblasts. These results provide novel experimental evidence supporting a functional autonomic link between central proprioceptive vestibular structures and the skeleton. Because vestibular dysfunction often affects the elderly, these results also suggest that age-related bone loss might have a vestibular component and that patients with inner ear pathologies might be at risk for fracture. Lastly, these data might have relevance to the bone loss observed in microgravity, as vestibular function is altered in this condition as well. © 2015 American Society for Bone and Mineral Research.

Integrating new discoveries into the "vicious cycle" paradigm of prostate to bone metastases

In prostate to bone metastases, the "vicious cycle" paradigm has been traditionally used to illustrate how metastases manipulate the bone forming osteoblasts and resorbing osteoclasts in order to yield factors that facilitate growth and establishment. However, recent advances have illustrated that the cycle is far more complex than this simple interpretation. In this review, we will discuss the role of exosomes and hematopoietic/mesenchymal stem/stromal cells (MSC) that facilitate the establishment and activation of prostate metastases and how cells including myeloid-derived suppressor cells, macrophages, T cells, and nerve cells contribute to the momentum of the vicious cycle. The increased complexity of the tumor-bone microenvironment requires a system level approach. The evolution of computational models to interrogate the tumor-bone microenvironment is also discussed, and the application of this integrated approach should allow for the development of effective therapies to treat and cure prostate to bone metastases.

Endocrinology of bone/brain crosstalk

Bone metabolism is regulated by the action of two skeletal cells: osteoblasts and osteoclasts. This process is controlled by many genetic, hormonal and lifestyle factors, but today more and more studies have allowed us to identify a neuronal regulation system termed 'bone-brain crosstalk', which highlights a direct relationship between bone tissue and the nervous system. The first documentation of an anatomic relationship between nerves and bone was made via a wood cut by Charles Estienne in Paris in 1545. His diagram demonstrated nerves entering and leaving the bones of a skeleton. Later, several studies were conducted on bone innervation and, as of today, many observations on the regulation of bone remodeling by neurons and neuropeptides that reside in the CNS have created a new research field, that is, neuroskeletal research.

Small vessel disease/white matter disease of the brain and its association with osteoporosis

BACKGROUND

Evidence now suggests the role of neural effect on bone mass control. The effect of small vessel disease of the brain on osteoporosis has not been studied. The aim of this study was to investigate the association of white matter disease (WMD) of the brain with osteoporosis in the elderly.

METHODS

In this retrospective cross-sectional study, 780 consecutive patient charts between 2010 and 2011 were reviewed in the Senior's Outpatient Clinic at the University of Alberta Hospital. Subjects with brain computerized tomography (CT) were included in the study. Subjects with incomplete information, intracranial hemorrhage, acute stroke, cerebral edema, and/or normal pressure hydrocephalus on the CT were excluded. WMD was quantified on CT using Wahlund's scoring protocol. Osteoporosis information was obtained from the chart, which has been diagnosed based on bone mineral density (BMD) information. Logistic regression analysis was done to determine the association of WMD severity with osteoporosis after controlling for confounding vascular risk factors.

RESULTS

Of the 505 subjects who were included in the study, 188 (37%) had osteoporosis and 171 (91%) of these osteoporotic subjects were females. The mean age was 79.8 ± 7.04 years. The prevalence of WMD in osteoporosis subjects was 73%. In the unadjusted logistic regression analysis, there was a significant association between WMD severity and osteoporosis (odds ratio (OR): 1.10; 95% confidence interval (CI): 1.05 - 1.14; P < 0.001) and the significance remained in the adjusted model, after correcting for age, sex and all vascular risk factors (OR: 1.11; 95% CI: 1.05 - 1.18; P < 0.001).

CONCLUSION

WMD severity of the brain was associated with osteoporosis in the elderly.

Adult bone strength of children from single-parent families: the Midlife in the United States Study

Bone health may be negatively impacted by childhood socio-environmental circumstances. We examined the independent associations of single-parent childhood and parental death or divorce in childhood with adult bone strength indices. Longer exposure to a single-parent household in childhood was associated with lower bone strength in adulthood.

INTRODUCTION

Because peak bone mass is acquired during childhood, bone health may be negatively impacted by childhood socio-environmental disadvantage. The goal of this study was to determine whether being raised in a single-parent household is associated with lower bone strength in adulthood.

METHODS

Using dual-energy X-ray absorptiometry data from 708 participants (mean age 57 years) in the Midlife in the United States Biomarker Project, we examined the independent associations of composite indices of femoral neck bone strength relative to load (in three failure modes: compression, bending, and impact) in adulthood with the experience of single-parent childhood and parental death or divorce in childhood.

RESULTS

After adjustment for gender, race, menopause transition stage, age, and body mass index, each additional year of single-parent childhood was associated with 0.02 to 0.03 SD lower indices of adult femoral neck strength. In those with 9-16 years of single-parent childhood, the compression strength index was 0.41 SD lower, bending strength index was 0.31 SD lower, and impact strength index was 0.25 SD lower (all p values < 0.05). In contrast, parental death or divorce during childhood was not by itself independently associated with adult bone strength indices. The magnitudes of these associations were unaltered by additional adjustment for lifestyle factors and socioeconomic status in childhood and adulthood.

CONCLUSIONS

Independent of parental death or divorce, growing up in a single-parent household is associated with lower femoral neck bone strength in adulthood, and this association is not entirely explained by childhood or adult socioeconomic conditions or lifestyle choices.

A four-season molecule: osteocalcin. Updates in its physiological roles

Osteocalcin (OC) is the main non-collagenous hydroxyapatite-binding protein synthesized by osteoblasts, odontoblasts, and hypertrophic chondrocytes. It has a regulatory role in mineralization and it is considered a marker of bone cell metabolism. Recent findings evidenced new extra-skeletal roles for OC, depicting it as a real hormone. OC shares many functional features with the common hormones, such as tissue-specific expression, circadian rhythm, and synthesis as a pre-pro-molecule. However, it has some peculiar features making it a unique molecule: OC exists in different forms based on the degree of carboxylation. Indeed, OC has three glutamic acid residues, in position 17, 21, and 24, which are subject to γ-carboxylation, through the action of a vitamin K-dependent γ-glutamyl carboxytransferase. The degree of carboxylation, and thus the negative charge density, determines the affinity for the calcium ions deposited in the extracellular matrix of the bone. The modulation of the carboxylation could, thus, represent the mechanism by which the body controls the circulating levels, and hence the hormonal function, of OC. There are evidences linking OC, and the bone metabolism, with a series of endocrine (glucose metabolism, energy metabolism, fertility) physiological (muscle activity) and pathological functions (ectopic calcification). Aim of this review is to give a full overview of the physiological roles of OC by collecting the newest experimental findings on this intriguing molecule.

Biomechanical aspects of the muscle-bone interaction

There is growing interest in the interaction between skeletal muscle and bone, particularly at the genetic and molecular levels. However, the genetic and molecular linkages between muscle and bone are achieved only within the context of the essential mechanical coupling of the tissues. This biomechanical and physiological linkage is readily evident as muscles attach to bone and induce exposure to varied mechanical stimuli via functional activity. The responsiveness of bone cells to mechanical stimuli, or their absence, is well established. However, questions remain regarding how muscle forces applied to bone serve to modulate bone homeostasis and adaptation. Similarly, the contributions of varied, but unique, stimuli generated by muscle to bone (such as low-magnitude, high-frequency stimuli) remains to be established. The current article focuses upon the mechanical relationship between muscle and bone. In doing so, we explore the stimuli that muscle imparts upon bone, models that enable investigation of this relationship, and recent data generated by these models.

Inflammatory and bone turnover markers in a cross-sectional and prospective study of acute Charcot osteoarthropathy

AIMS

To assess markers of inflammation and bone turnover at presentation and at resolution of Charcot osteoarthropathy.

METHODS

We measured serum inflammatory and bone turnover markers in a cross-sectional study of 35 people with Charcot osteoarthropathy, together with 34 people with diabetes and 12 people without diabetes. In addition, a prospective study of the subjects with Charcot osteoarthropathy was conducted until clinical resolution.

RESULTS

At presentation, C-reactive protein (P = 0.007), tumour necrosis factor-α (P = 0.010) and interleukin-6 (P = 0.002), but not interleukin-1β, (P = 0.254) were significantly higher in people with Charcot osteoarthropathy than in people with and without diabetes. Serum C-terminal telopeptide (P = 0.004), bone alkaline phosphatase (P = 0.006) and osteoprotegerin (P < 0.001), but not tartrate-resistant acid phosphatase (P = 0.126) and soluble receptor activator of nuclear factor-κβ ligand (P = 0.915), were significantly higher in people with Charcot osteoarthropathy than in people with and without diabetes. At follow-up it was found that tumour necrosis factor-α (P = 0.012) and interleukin-6 (P = 0.003), but not C-reactive protein (P = 0.101), interleukin-1β (P = 0.457), C-terminal telopeptide (P = 0.743), bone alkaline phosphatase (P = 0.193), tartrate-resistant acid phosphatase (P = 0.856), osteoprotegerin (P = 0.372) or soluble receptor activator of nuclear factor-kβ ligand (P = 0.889), had significantly decreased between presentation and the 3 months of casting therapy time point, and all analytes remained unchanged from 3 months of casting therapy until resolution. In people with Charcot osteoarthropathy, there was a positive correlation between interleukin-6 and C-terminal telopeptide (P = 0.028) and tumour necrosis factor-α and C-terminal telopeptide (P = 0.013) only at presentation.

CONCLUSIONS

At the onset of acute Charcot foot, serum concentrations of tumour necrosis factor-α and interleukin-6 were elevated; however, there was a significant reduction in these markers at resolution and these markers may be useful in the assessment of disease activity.

A novel specialized staging system for cancellous fracture healing, distinct from traditional healing pattern of diaphysis corticalfracture?

Metaphysis cancellous bone fracture is one of the most common fracture types in clinical orthopedic practice. The specialized healing process of cancellous bone fracture has long been ignored by the academic society. Comparing with diaphyseal cortical bone healing, cancellous bone healing showed less bone tissue necrosis, barely any hematoma formation, limited inflammation events and no external callus formation. Based on our clinical practice and preliminary study, we hypothesize that the healing process of metaphysis cancellous fracture is a distinct process which could be concluded into five overlapping stages with distinguished histological features of each other. Different from the traditional theory defining diaphyseal cortical fracture, our novel staging theory is specialized in cancellous bone tissue fully considering its unique histological features. This novel staging system may help clinical orthopedists gain specialized understanding concerning cancellous healing process and aid in their clinical evaluation and treatment to metaphysis cancellous bone fracture.

Bone mass and hormone analysis in patients with spinal cord injury: evidence for a gonadal axis disruption

CONTEXT

Bone loss is a constant finding in patients with spinal cord injury (SCI).

OBJECTIVE

We sought to evaluate potential modifiable factors that could lead to bone loss in complete motor paraplegia by examining gonadal axis hormones, vitamin D status, and bone markers.

DESIGN

This is a cross sectional.

SETTING

It includes SCI Outpatient.

PATIENTS AND OTHER PARTICIPANTS

Twenty-nine chronic male patients with SCI were compared with 17 age-matched, able-bodied men.

MAIN OUTCOME MEASURE

The bone mineral density (BMD) of lower limbs and lumbar spine were measured using dual x-ray absorptiometry. Parathormone, 25-hydroxyvitamin D [25(OH)D], collagen type I C-terminal telopeptide (CTX), and sexual hormone were measured.

RESULTS

Patients with SCI had lower BMD at the inferior limbs sites. CTX showed an inverse relationship with the time since injury. Patients had lower free T levels (SCI, 12.00 ± 2.91 vs controls, 19.51 ± 5.72; P ≤ .001), and the majority (72%) had normal/low levels of gonadotropins. Low T, however, was not related to low bone mass in patients with SCI. In the controls, the 25(OH)D level was positively correlated with the T and with the lumbar spine BMD, but these correlations were not observed in the SCI.

CONCLUSIONS

Impairment of testicular function after SCI was indicated by the low levels of T and the loss of correlation between T and 25(OH)D levels; this correlation was present in the able-bodied controls. Inappropriate levels of gonadotropins were identified in most patients, featuring a hypogonadotropic hypogonadism and suggesting a disruption of the pituitary-gonadal axis. T concentrations might not be an effective target for bone loss therapy.

Osteoporosis in the at-risk asthmatic

The effect of inhaled glucocorticosteroids (ICS) on bone metabolism and subsequent osteoporosis is controversial. Explanations for this controversy include various study designs, duration of use, outcome measures, and population demographics of research studies with intranasal or inhalational ICS. Patients with poorly controlled asthma are at greatest risk of osteoporosis because they are commonly treated with intermittent or continuous systemic corticosteroids (SCS) or high-dose ICS. A 45-year-old Caucasian woman presents with moderate-to-severe asthma with frequent albuterol use and nighttime awakenings at least once weekly. She is on fluticasone/salmeterol 500/50 μg one inhalation twice daily and montelukast 10 mg/day. She requires prednisone 15 mg three times per day for 5 days up to three times a year. Is this patient at greater risk of osteopenia, characterized by a T-score between -1.0 and -2.5, and subsequent osteoporosis and an increased risk of fractures? If she has osteopenia, should she be treated with a bisphosphonate? The risk of osteoporosis and fracture increases significantly with frequent administration of SCS, and patients on such medications should undergo preventative measures and treatment. This study discuses factors that contribute to an increased risk of osteoporosis/osteopenia in patients with asthma and suggests recommendations based on the current literature.

A review of osteocyte function and the emerging importance of sclerostin

➤ Osteocytes, derived from osteoblasts, reside within bone and communicate extensively with other bone cell populations to regulate bone metabolism. The mature osteocyte expresses the protein sclerostin, a negative regulator of bone mass.➤ In normal physiologic states, the protein sclerostin acts on osteoblasts at the surface of bone and is differentially expressed in response to mechanical loading, inflammatory molecules such as prostaglandin E2, and hormones such as parathyroid hormone and estrogen.➤ Pathologically, sclerostin dysregulation has been observed in osteoporosis-related fractures, failure of implant osseous integration, metastatic bone disease, and select genetic diseases of bone mass.➤ An antibody that targets sclerostin, decreasing endogenous levels of sclerostin while increasing bone mineral density, is currently in phase-III clinical trials.➤ The osteocyte has emerged as a versatile, indispensable bone cell. Its location within bone, extensive dendritic network, and close communication with systemic circulation and other bone cells produce many opportunities to treat a variety of orthopaedic conditions.

Neuropeptide y attenuates stress-induced bone loss through suppression of noradrenaline circuits

Chronic stress and depression have adverse consequences on many organ systems, including the skeleton, but the mechanisms underlying stress-induced bone loss remain unclear. Here we demonstrate that neuropeptide Y (NPY), centrally and peripherally, plays a critical role in protecting against stress-induced bone loss. Mice lacking the anxiolytic factor NPY exhibit more anxious behavior and elevated corticosterone levels. Additionally, following a 6-week restraint, or cold-stress protocol, Npy-null mice exhibit three-fold greater bone loss compared to wild-type mice, owing to suppression of osteoblast activity. This stress-protective NPY pathway acts specifically through Y2 receptors. Centrally, Y2 receptors suppress corticotropin-releasing factor expression and inhibit activation of noradrenergic neurons in the paraventricular nucleus. In the periphery, they act to control noradrenaline release from sympathetic neurons. Specific deletion of arcuate Y2 receptors recapitulates the Npy-null stress response, coincident with elevated serum noradrenaline. Importantly, specific reintroduction of NPY solely in noradrenergic neurons of otherwise Npy-null mice blocks the increase in circulating noradrenaline and the stress-induced bone loss. Thus, NPY protects against excessive stress-induced bone loss, through Y2 receptor-mediated modulation of central and peripheral noradrenergic neurons.

Pulsed focused ultrasound treatment of muscle mitigates paralysis-induced bone loss in the adjacent bone: a study in a mouse model

Bone loss can result from bed rest, space flight, spinal cord injury or age-related hormonal changes. Current bone loss mitigation techniques include pharmaceutical interventions, exercise, pulsed ultrasound targeted to bone and whole body vibration. In this study, we attempted to mitigate paralysis-induced bone loss by applying focused ultrasound to the midbelly of a paralyzed muscle. We employed a mouse model of disuse that uses onabotulinumtoxinA-induced paralysis, which causes rapid bone loss in 5 d. A focused 2 MHz transducer applied pulsed exposures with pulse repetition frequency mimicking that of motor neuron firing during walking (80 Hz), standing (20 Hz), or the standard pulsed ultrasound frequency used in fracture healing (1 kHz). Exposures were applied daily to calf muscle for 4 consecutive d. Trabecular bone changes were characterized using micro-computed tomography. Our results indicated that application of certain focused pulsed ultrasound parameters was able to mitigate some of the paralysis-induced bone loss.

The role of catecholamines in mesenchymal stem cell fate

Mesenchymal stem cells (MSCs) are multipotent stem cells found in many adult tissues, especially bone marrow (BM) and are capable of differentiation into various lineage cells such as osteoblasts, adipocytes, chondrocytes and myocytes. Moreover, MSCs can be mobilized from connective tissue into circulation and from there to damaged sites to contribute to regeneration processes. MSCs commitment and differentiation are controlled by complex activities involving signal transduction through cytokines and catecholamines. There has been an increasing interest in recent years in the neural system, functioning in the support of stem cells like MSCs. Recent efforts have indicated that the catecholamine released from neural and not neural cells could be affected characteristics of MSCs. However, there have not been review studies of most aspects involved in catecholamines-mediated functions of MSCs. Thus, in this review paper, we will try to describe the current state of catecholamines in MSCs destination and discuss strategies being used for catecholamines for migration of these cells to damaged tissues. Then, the role of the nervous system in the induction of osteogenesis, adipogenesis, chondrogenesis and myogenesis from MSCs is discussed. Recent progress in studies of signaling transduction of catecholamines in determination of the final fate of MSCs is highlighted. Hence, the knowledge of interaction between MSCs with the neural system could be applied towards the development of new diagnostic and treatment alternatives for human diseases.

Do effects of propranolol on the skeletal system depend on the estrogen status?

BACKGROUND

Propranolol, a nonselective β-adrenergic receptor antagonist, was reported to favorably affect the skeletal system in different animal models. The aim of the study was to investigate whether the effects of propranolol on the skeletal system depend on the estrogen status.

METHODS

The in vivo experiments were carried out on the following groups of mature female Wistar rats: sham-operated control rats, sham-operated rats receiving propranolol, ovariectomized (OVX) control rats, OVX rats receiving propranolol, OVX rats receiving estradiol, OVX rats receiving estradiol and propranolol. Propranolol hydrochloride (10 mg/kg po) and/or estradiol (0.1 mg/kg po) were administered daily for 4 weeks. Bone mass, mineral and calcium content, macrometric and histomorphometric parameters, and mechanical properties were examined. In vitro, effects of estradiol and propranolol on the formation of mouse osteoclasts and on the mRNA expression of genes related to osteoclastogenesis, bone formation and mineralization, as well as adrenergic and estrogen signalling in mouse osteoblasts were investigated.

RESULTS AND CONCLUSION

Propranolol exerted some favorable effects on the rat skeletal system in vivo, independently of the estrogen status. However, in vitro studies indicated a possibility of some antagonistic relations between the estradiol and propranolol effects.

Sympathetic denervation-induced MSC mobilization in distraction osteogenesis associates with inhibition of MSC migration and osteogenesis by norepinephrine/adrb3

The sympathetic nervous system regulates bone formation and resorption under physiological conditions. However, it is still unclear how the sympathetic nerves affect stem cell migration and differentiation in bone regeneration. Distraction osteogenesis is an ideal model of bone regeneration due to its special nature as a self-engineering tissue. In this study, a rat model of mandibular distraction osteogenesis with transection of cervical sympathetic trunk was used to demonstrate that sympathetic denervation can deplete norepinephrine (NE) in distraction-induced bone callus, down-regulate β3-adrenergic receptor (adrb3) in bone marrow mesenchymal stem cells (MSCs), and promote MSC migration from perivascular regions to bone-forming units. An invitro Transwell assay was here used to demonstrate that NE can inhibit stroma-derived factor-1 (SDF-1)-induced MSC migration and expression of the migration-related gene matrix metalloproteinase-2 (MMP-2) and downregulate that of the anti-migration gene tissue inhibitor of metalloproteinase-3 (TIMP-3). Knockdown of adrb3 using siRNA abolishes inhibition of MSC migration. An in vitro osteogenic assay was used to show that NE can inhibit the formation of MSC bone nodules and expression of the osteogenic marker genes alkaline phosphatase (ALP), osteocalcin (OCN), and runt-related transcription factor-2 (RUNX2), but knockdown of adrb3 by siRNA can abolish such inhibition of the osteogenic differentiation of MSCs. It is here concluded that sympathetic denervation-induced MSC mobilization in rat mandibular distraction osteogenesis is associated with inhibition of MSC migration and osteogenic differentiation by NE/adrb3 in vitro. These findings may facilitate understanding of the relationship of MSC mobilization and sympathetic nervous system across a wide spectrum of tissue regeneration processes.