The role of neuropilin in bone/cartilage diseases

Bone remodeling is the balance between osteoblasts and osteoclasts. Bone diseases such as osteoporosis and osteoarthritis are associated with imbalanced bone remodeling. Skeletal injury leads to limited motor function and pain. Neurophilin was initially identified in axons, and its various ligands and roles in bone remodeling, angiogenesis, neuropathic pain and immune regulation were later discovered. Neurophilin promotes osteoblast mineralization and inhibits osteoclast differentiation and its function. Neuropolin-1 provides channels for immune cell chemotaxis and cytokine diffusion and leads to pain. Neuropolin-1 regulates the proportion of T helper type 17 (Th17) and regulatory T cells (Treg cells), and affects bone immunity. Vascular endothelial growth factors (VEGF) combine with neuropilin and promote angiogenesis. Class 3 semaphorins (Sema3a) compete with VEGF to bind neuropilin, which reduces angiogenesis and rejects sympathetic nerves. This review elaborates on the structure and general physiological functions of neuropilin and summarizes the role of neuropilin and its ligands in bone and cartilage diseases. Finally, treatment strategies and future research directions based on neuropilin are proposed.

Lipid metabolism within the bone micro-environment is closely associated with bone metabolism in physiological and pathophysiological stages

Recent advances in society have resulted in the emergence of both hyperlipidemia and obesity as life-threatening conditions in people with implications for various types of diseases, such as cardiovascular diseases and cancer. This is further complicated by a global rise in the aging population, especially menopausal women, who mostly suffer from overweight and bone loss simultaneously. Interestingly, clinical observations in these women suggest that osteoarthritis may be linked to a higher body mass index (BMI), which has led many to believe that there may be some degree of bone dysfunction associated with conditions such as obesity. It is also common practice in many outpatient settings to encourage patients to control their BMI and lose weight in an attempt to mitigate mechanical stress and thus reduce bone pain and joint dysfunction. Together, studies show that bone is not only a mechanical organ but also a critical component of metabolism, and various endocrine functions, such as calcium metabolism. Numerous studies have demonstrated a relationship between metabolic dysfunction in bone and abnormal lipid metabolism. Previous studies have also regarded obesity as a metabolic disorder. However, the relationship between lipid metabolism and bone metabolism has not been fully elucidated. In this narrative review, the data describing the close relationship between bone and lipid metabolism was summarized and the impact on both the normal physiology and pathophysiology of these tissues was discussed at both the molecular and cellular levels.

Control of osteocyte dendrite formation by Sp7 and its target gene osteocrin

Some osteoblasts embed within bone matrix, change shape, and become dendrite-bearing osteocytes. The circuitry that drives dendrite formation during "osteocytogenesis" is poorly understood. Here we show that deletion of Sp7 in osteoblasts and osteocytes causes defects in osteocyte dendrites. Profiling of Sp7 target genes and binding sites reveals unexpected repurposing of this transcription factor to drive dendrite formation. Osteocrin is a Sp7 target gene that promotes osteocyte dendrite formation and rescues defects in Sp7-deficient mice. Single-cell RNA-sequencing demonstrates defects in osteocyte maturation in the absence of Sp7. Sp7-dependent osteocyte gene networks are associated with human skeletal diseases. Moreover, humans with a SP7R316C mutation show defective osteocyte morphology. Sp7-dependent genes that mark osteocytes are enriched in neurons, highlighting shared features between osteocytic and neuronal connectivity. These findings reveal a role for Sp7 and its target gene Osteocrin in osteocytogenesis, revealing that pathways that control osteocyte development influence human bone diseases.

Progression of vertebral bone disease in mucopolysaccharidosis VII dogs from birth to skeletal maturity

Mucopolysaccharidosis (MPS) VII is a lysosomal storage disorder characterized by deficient β-glucuronidase activity, leading to accumulation of incompletely degraded heparan, dermatan and chondroitin sulfate glycosaminoglycans. Patients with MPS VII exhibit progressive spinal deformity, which decreases quality of life. Previously, we demonstrated that MPS VII dogs exhibit impaired initiation of secondary ossification in the vertebrae and long bones. The objective of this study was to build on these findings and comprehensively characterize how vertebral bone disease manifests progressively in MPS VII dogs throughout postnatal growth. Vertebrae were collected postmortem from MPS VII and healthy control dogs at seven ages ranging from 9 to 365 days. Microcomputed tomography and histology were used to characterize bone properties in primary and secondary ossification centers. Serum was analyzed for bone turnover biomarkers. Results demonstrated that not only was secondary ossification delayed in MPS VII vertebrae, but that it progressed aberrantly and was markedly diminished even at 365 days-of-age. Within primary ossification centers, bone volume fraction and bone mineral density were significantly lower in MPS VII at 180 and 365 days-of-age. MPS VII growth plates exhibited significantly lower proliferative and hypertrophic zone cellularity at 90 days-of-age, while serum bone-specific alkaline phosphatase (BAP) was significantly lower in MPS VII dogs at 180 days-of-age. Overall, these findings establish that vertebral bone formation is significantly diminished in MPS VII dogs in both primary and secondary ossification centers during postnatal growth.

Human model of IRX5 mutations reveals key role for this transcription factor in ventricular conduction

AIMS

Several inherited arrhythmic diseases have been linked to single gene mutations in cardiac ion channels and interacting proteins. However, the mechanisms underlying most arrhythmias, are thought to involve altered regulation of the expression of multiple effectors. In this study, we aimed to examine the role of a transcription factor (TF) belonging to the Iroquois homeobox family, IRX5, in cardiac electrical function.

METHODS AND RESULTS

Using human cardiac tissues, transcriptomic correlative analyses between IRX5 and genes involved in cardiac electrical activity showed that in human ventricular compartment, IRX5 expression strongly correlated to the expression of major actors of cardiac conduction, including the sodium channel, Nav1.5, and Connexin 40 (Cx40). We then generated human-induced pluripotent stem cells (hiPSCs) derived from two Hamamy syndrome-affected patients carrying distinct homozygous loss-of-function mutations in IRX5 gene. Cardiomyocytes derived from these hiPSCs showed impaired cardiac gene expression programme, including misregulation in the control of Nav1.5 and Cx40 expression. In accordance with the prolonged QRS interval observed in Hamamy syndrome patients, a slower ventricular action potential depolarization due to sodium current reduction was observed on electrophysiological analyses performed on patient-derived cardiomyocytes, confirming the functional role of IRX5 in electrical conduction. Finally, a cardiac TF complex was newly identified, composed by IRX5 and GATA4, in which IRX5 potentiated GATA4-induction of SCN5A expression.

CONCLUSION

Altogether, this work unveils a key role for IRX5 in the regulation of human ventricular depolarization and cardiac electrical conduction, providing therefore new insights into our understanding of cardiac diseases.

TRPM8 modulates temperature regulation in a sex-dependent manner without affecting cold-induced bone loss

Trpm8 (transient receptor potential cation channel, subfamily M, member 8) is expressed by sensory neurons and is involved in the detection of environmental cold temperatures. TRPM8 activity triggers an increase in uncoupling protein 1 (Ucp1)-dependent brown adipose tissue (BAT) thermogenesis. Bone density and marrow adipose tissue are both influenced by rodent housing temperature and brown adipose tissue, but it is unknown if TRPM8 is involved in the co-regulation of thermogenesis and bone homeostasis. To address this, we examined the bone phenotypes of one-year-old Trpm8 knockout mice (Trpm8-KO) after a 4-week cold temperature challenge. Male Trpm8-KO mice had lower bone mineral density than WT, with smaller bone size (femur length and cross-sectional area) being the most striking finding, and exhibited a delayed cold acclimation with increased BAT expression of Dio2 and Cidea compared to WT. In contrast to males, female Trpm8-KO mice had low vertebral bone microarchitectural parameters, but no genotype-specific alterations in body temperature. Interestingly, Trpm8 was not required for cold-induced trabecular bone loss in either sex, but bone marrow adipose tissue in females was significantly suppressed by Trpm8 deletion. In summary, we identified sex differences in the role of TRPM8 in maintaining body temperature, bone microarchitecture and marrow adipose tissue. Identifying mechanisms through which cold temperature and BAT influence bone could help to ameliorate potential bone side effects of obesity treatments designed to stimulate thermogenesis.

Current Analysis of Skeletal Phenotypes in Down Syndrome

PURPOSE

Down syndrome (DS) is caused by trisomy 21 (Ts21) and results in skeletal deficits including shortened stature, low bone mineral density, and a predisposition to early onset osteoporosis. Ts21 causes significant alterations in skeletal development, morphology of the appendicular skeleton, bone homeostasis, age-related bone loss, and bone strength. However, the genetic or cellular origins of DS skeletal phenotypes remain unclear.

RECENT FINDINGS

New studies reveal a sexual dimorphism in characteristics and onset of skeletal deficits that differ between DS and typically developing individuals. Age-related bone loss occurs earlier in the DS as compared to general population. Perturbations of DS skeletal quality arise from alterations in cellular and molecular pathways affected by the overexpression of trisomic genes. Sex-specific alterations occur in critical developmental pathways that disrupt bone accrual, remodeling, and homeostasis and are compounded by aging, resulting in increased risks for osteopenia, osteoporosis, and fracture in individuals with DS.

Crosstalk between Bone and Nerves within Bone

For the past two decades, the function of intrabony nerves on bone has been a subject of intense research, while the function of bone on intrabony nerves is still hidden in the corner. In the present review, the possible crosstalk between bone and intrabony peripheral nerves will be comprehensively analyzed. Peripheral nerves participate in bone development and repair via a host of signals generated through the secretion of neurotransmitters, neuropeptides, axon guidance factors and neurotrophins, with additional contribution from nerve-resident cells. In return, bone contributes to this microenvironmental rendezvous by housing the nerves within its internal milieu to provide mechanical support and a protective shelf. A large ensemble of chemical, mechanical, and electrical cues works in harmony with bone marrow stromal cells in the regulation of intrabony nerves. The crosstalk between bone and nerves is not limited to the physiological state, but also involved in various bone diseases including osteoporosis, osteoarthritis, heterotopic ossification, psychological stress-related bone abnormalities, and bone related tumors. This crosstalk may be harnessed in the design of tissue engineering scaffolds for repair of bone defects or be targeted for treatment of diseases related to bone and peripheral nerves.

Metabolic regulation of skeletal cell fate and function in physiology and disease

The skeleton is diverse in its functions, which include mechanical support, movement, blood cell production, mineral storage and endocrine regulation. This multifaceted role is achieved through an interplay of osteoblasts, chondrocytes, bone marrow adipocytes and stromal cells, all generated from skeletal stem cells. Emerging evidence shows the importance of cellular metabolism in the molecular control of the skeletal system. The different skeletal cell types not only have distinct metabolic demands relating to their particular functions but also are affected by microenvironmental constraints. Specific metabolites control skeletal stem cell maintenance, direct lineage allocation and mediate cellular communication. Here, we discuss recent findings on the roles of cellular metabolism in determining skeletal stem cell fate, coordinating osteoblast and chondrocyte function, and organizing stromal support of haematopoiesis. We also consider metabolic dysregulation in skeletal ageing and degenerative diseases, and provide an outlook on how the field may evolve in the coming years.

Craniofacial and Long Bone Development in the Context of Distraction Osteogenesis

BACKGROUND

Bone retains regenerative potential into adulthood, and surgeons harness this plasticity during distraction osteogenesis. The underlying biology governing bone development, repair, and regeneration is divergent between the craniofacial and appendicular skeleton. Each type of bone formation is characterized by unique molecular signaling and cellular behavior. Recent discoveries have elucidated the cellular and genetic processes underlying skeletal development and regeneration, providing an opportunity to couple biological and clinical knowledge to improve patient care.

METHODS

A comprehensive literature review of basic and clinical literature regarding craniofacial and long bone development, regeneration, and distraction osteogenesis was performed.

RESULTS

The current understanding in craniofacial and long bone development and regeneration is discussed, and clinical considerations for the respective distraction osteogenesis procedures are presented.

CONCLUSIONS

Distraction osteogenesis is a powerful tool to regenerate bone and thus address a number of craniofacial and appendicular skeletal deficiencies. The molecular mechanisms underlying bone regeneration, however, remain elusive. Recent work has determined that embryologic morphogen gradients constitute important signals during regeneration. In addition, striking discoveries have illuminated the cellular processes underlying mandibular regeneration during distraction osteogenesis, showing that skeletal stem cells reactivate embryologic neural crest transcriptomic processes to carry out bone formation during regeneration. Furthermore, innovative adjuvant therapies to complement distraction osteogenesis use biological processes active in embryogenesis and regeneration. Additional research is needed to further characterize the underlying cellular mechanisms responsible for improved bone formation through adjuvant therapies and the role skeletal stem cells play during regeneration.

Failures of Endochondral Ossification in the Mucopolysaccharidoses

PURPOSE OF REVIEW

The mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders characterized by abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. MPS patients frequently exhibit failures of endochondral ossification during postnatal growth leading to skeletal deformity and short stature. In this review, we outline the current understanding of the cellular and molecular mechanisms underlying failures of endochondral ossification in MPS and discuss associated treatment challenges and opportunities.

RECENT FINDINGS

Studies in MPS patients and animal models have demonstrated that skeletal cells and tissues exhibit significantly elevated GAG storage from early in postnatal life and that this is associated with impaired cartilage-to-bone conversion in primary and secondary ossification centers, and growth plate dysfunction. Recent studies have begun to elucidate the underlying cellular and molecular mechanisms, including impaired chondrocyte proliferation and hypertrophy, diminished growth factor signaling, disrupted cell cycle progression, impaired autophagy, and increased cell stress and apoptosis. Current treatments such as hematopoietic stem cell transplantation and enzyme replacement therapy fail to normalize endochondral ossification in MPS. Emerging treatments including gene therapy and small molecule-based approaches hold significant promise in this regard. Failures of endochondral ossification contribute to skeletal deformity and short stature in MPS patients, increasing mortality and reducing quality of life. Early intervention is crucial for effective treatment, and there is a critical need for new approaches that normalize endochondral ossification by directly targeting affected cells and signaling pathways.

Understanding Bone Disease in Patients with Diabetic Kidney Disease: a Narrative Review

PURPOSE OF REVIEW

Both diabetes and kidney disease associate with the development of bone disease and an increased risk of fragility fractures. The etiologies of bone disease in patients with diabetic kidney disease (DKD) are multiple and complex. This review explores the association between DKD and bone disease and discusses how the presence of both diabetes and kidney disease may impair bone quality and increase fracture risk. Diagnostic tools as well as future research areas are also discussed.

RECENT FINDINGS

Patients with DKD have an increased risk of fragility fracture, most pronounced in patients with type 1 diabetes, and in DKD a high prevalence of adynamic bone disease is found. Recent studies have demonstrated disturbances in the interplay between bone regulating factors in DKD, such as relative hypoparathyroidism and alterations of bone-derived hormones including fibroblast growth factor-23 (FGF-23), sclerostin and klotho, which lead to bone disease. This review examines the current knowledge on bone disease in patients with DKD, clinical considerations for patient care, as well as subjects for future research.

Dual-Peptide-Functionalized Nanofibrous Scaffolds Recruit Host Endothelial Progenitor Cells for Vasculogenesis to Repair Calvarial Defects

Vasculogenesis (de novo formation of vessels) induced by endothelial progenitor cells (EPCs) is requisite for vascularized bone regeneration. However, there exist few available options for promoting vasculogenesis within artificial bone grafts except for exogenous EPC transplantation, which suffers from the source of EPC, safety, cost, and time concerns in clinical applications. This study aimed at endogenous EPC recruitment for vascularized bone regeneration by using a bioinspired EPC-induced graft. The EPC-induced graft was created by immobilizing two bioactive peptides, WKYMVm and YIGSR, on the surface of poly(ε-caprolactone) (PCL)/poliglecaprone (PGC) nanofibrous scaffolds via a polyglycolic acid (PGA)-binding peptide sequence. Remarkable immobilization efficacy of WKYMVm and YIGSR peptides and their sustained release (over 14 days) from scaffolds were observed. In vivo and in vitro studies showed robust recruitment of EPCs, which subsequently contributed to early vasculogenesis and ultimate bone regeneration. The dual-peptide-functionalized nanofibrous scaffolds proposed in this study provide a promising therapeutic strategy for vasculogenesis in bone defect repair.

Integrin-specific hydrogels modulate transplanted human bone marrow-derived mesenchymal stem cell survival, engraftment, and reparative activities

Stem cell therapies are limited by poor cell survival and engraftment. A hurdle to the use of materials for cell delivery is the lack of understanding of material properties that govern transplanted stem cell functionality. Here, we show that synthetic hydrogels presenting integrin-specific peptides enhance the survival, persistence, and osteo-reparative functions of human bone marrow-derived mesenchymal stem cells (hMSCs) transplanted in murine bone defects. Integrin-specific hydrogels regulate hMSC adhesion, paracrine signaling, and osteoblastic differentiation in vitro. Hydrogels presenting GFOGER, a peptide targeting α2β1 integrin, prolong hMSC survival and engraftment in a segmental bone defect and result in improved bone repair compared to other peptides. Integrin-specific hydrogels have diverse pleiotropic effects on hMSC reparative activities, modulating in vitro cytokine secretion and in vivo gene expression for effectors associated with inflammation, vascularization, and bone formation. These results demonstrate that integrin-specific hydrogels improve tissue healing by directing hMSC survival, engraftment, and reparative activities.

Human Fibroblasts as a Model for the Study of Bone Disorders

Bone tissue degeneration is an urgent clinical issue, making it a subject of intensive research. Chronic skeletal disease forms can be prevalent, such as the age-related osteoporosis, or rare, in the form of monogenetic bone disorders. A barrier in the understanding of the underlying pathological process is the lack of accessibility to relevant material. For this reason, cells of non-bone tissue are emerging as a suitable alternative for models of bone biology. Fibroblasts are highly suitable for this application; they populate accessible anatomical locations, such as the skin tissue. Reports suggesting their utility in preclinical models for the study of skeletal diseases are increasingly becoming available. The majority of these are based on the generation of an intermediate stem cell type, the induced pluripotent stem cells, which are subsequently directed to the osteogenic cell lineage. This intermediate stage is circumvented in transdifferentiation, the process regulating the direct conversion of fibroblasts to osteogenic cells, which is currently not well-explored. With this mini review, we aimed to give an overview of existing osteogenic transdifferentiation models and to inform about their applications in bone biology models.

The Role of NF-κB in Physiological Bone Development and Inflammatory Bone Diseases: Is NF-κB Inhibition "Killing Two Birds with One Stone"?

Nuclear factor-κB (NF-κB) is a transcription factor that regulates the expression of various genes involved in inflammation and the immune response. The activation of NF-κB occurs via two pathways: inflammatory cytokines, such as TNF-α and IL-1β, activate the "classical pathway", and cytokines involved in lymph node formation, such as CD40L, activate the "alternative pathway". NF-κB1 (p50) and NF-κB2 (p52) double-knockout mice exhibited severe osteopetrosis due to the total lack of osteoclasts, suggesting that NF-κB activation is required for osteoclast differentiation. These results indicate that NF-κB may be a therapeutic target for inflammatory bone diseases, such as rheumatoid arthritis and periodontal disease. On the other hand, mice that express the dominant negative form of IκB kinase (IKK)-β specifically in osteoblasts exhibited increased bone mass, but there was no change in osteoclast numbers. Therefore, inhibition of NF-κB is thought to promote bone formation. Taken together, the inhibition of NF-κB leads to "killing two birds with one stone": it suppresses bone resorption and promotes bone formation. This review describes the role of NF-κB in physiological bone metabolism, pathologic bone destruction, and bone regeneration.

Pisidium coreanum Inhibits Multinucleated Osteoclast Formation and Prevents Estrogen-Deficient Osteoporosis

Mollusks have served as important sources of human food and medicine for a long time. Raw Pisidium coreanum, a freshwater bivalve of the phylum Mollusca, is used in traditional therapies in parts of Asia. However, the therapeutic effects of Pisidium coreanum on bone diseases are not known. We investigated the functional roles of Pisidium coreanum in osteoporotic bone diseases. Pisidium coreanum inhibited the differentiation of bone marrow-derived monocytic cells into mature osteoclasts in vitro. The ovariectomized mice that received oral administration of Pisidium coreanum showed improvements in both trabecular and cortical bones. This preventive activity of Pisidium coreanum against bone loss was due to limited osteoclast maturation with reduced osteoclast surface extent in trabecular bone tissue. The formation of large multinucleated osteoclasts in vitro was significantly decreased in response to Pisidium coreanum, consistent with the reduced expression levels of osteoclast markers and fusion-related genes, such as NFATc1, p65, integrinαvβ3, DC-STAMP, OC-STAMP, Atp6v0d2, FAK, CD44, and MFR. These data suggest that Pisidium coreanum inhibits osteoclast differentiation by negatively regulating the fusion of mononuclear osteoclast precursors. Thus, our data demonstrate the ability of Pisidium coreanum to effectively prevent estrogen-deficient osteoporosis through inhibition of multinucleated osteoclast formation.

Role of Citrate in Pathophysiology and Medical Management of Bone Diseases

Citrate is an intermediate in the “Tricarboxylic Acid Cycle” and is used by all aerobic organisms to produce usable chemical energy. It is a derivative of citric acid, a weak organic acid which can be introduced with diet since it naturally exists in a variety of fruits and vegetables, and can be consumed as a dietary supplement. The close association between this compound and bone was pointed out for the first time by Dickens in 1941, who showed that approximately 90% of the citrate bulk of the human body resides in mineralised tissues. Since then, the number of published articles has increased exponentially, and considerable progress in understanding how citrate is involved in bone metabolism has been made. This review summarises current knowledge regarding the role of citrate in the pathophysiology and medical management of bone disorders.

Zoledronate and Raloxifene combination therapy enhances material and mechanical properties of diseased mouse bone

Current interventions to reduce skeletal fragility are insufficient at enhancing both the quantity and quality of bone when attempting to improve overall mechanical integrity. Bisphosphonates, such as Zoledronate (ZOL), are used to treat a variety of bone disorders by increasing bone mass to decrease fracture risk, but long-term use has been shown in some settings to compromise bone quality. Alternatively, Raloxifene (RAL) has recently been demonstrated to improve tissue quality and overall mechanical properties in a cell-independent manner by binding to collagen and increasing tissue hydration. We hypothesized that a combination of RAL and ZOL would improve mechanical and material properties of bone more than either monotherapy alone by enhancing both quantity and quality. In this study, wildtype (WT) and heterozygous (OIM+/-) male mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL, ZOL, or both from 8 weeks to 16 weeks of age. Using the OIM model allows for investigation of therapeutic effects on a quality-based bone disease. Combination treatment resulted in higher trabecular architecture, cortical mechanical properties, and cortical fracture toughness in diseased mouse bone. Two fracture toughness properties, which are direct measures of the tissue's ability to resist the initiation and propagation of a crack, were significantly improved with combination treatment in OIM+/- compared to control. There was no significant effect on fracture toughness with either monotherapy alone in either genotype. Following the mass-based effects of ZOL, trabecular bone volume fraction was significantly higher with combination treatment in both genotypes. Combination treatment resulted in higher ultimate stress in both genotypes. RAL and combination treatment in OIM+/- also increased resilience compared to the control. In conclusion, this study demonstrates the beneficial effects of using combination drug treatments to increase bone mass while simultaneously improving tissue quality, especially to enhance the mechanical integrity of diseased bone. Combination therapies could be a potential method to improve bone health and combat skeletal fragility on both the microscopic and macroscopic levels.

Peripheral Neuropathy as a Component of Skeletal Disease in Diabetes

PURPOSE OF REVIEW

The goal of this review is to explore clinical associations between peripheral neuropathy and diabetic bone disease and to discuss how nerve dysfunction may contribute to dysregulation of bone metabolism, reduced bone quality, and fracture risk.

RECENT FINDINGS

Diabetic neuropathy can decrease peripheral sensation (sensory neuropathy), impair motor coordination (motor neuropathy), and increase postural hypotension (autonomic neuropathy). Together, this can impair overall balance and increase the risk for falls and fractures. In addition, the peripheral nervous system has the potential to regulate bone metabolism directly through the action of local neurotransmitters on bone cells and indirectly through neuroregulation of the skeletal vascular supply. This review critically evaluates existing evidence for diabetic peripheral neuropathy as a risk factor or direct actor on bone disease. In addition, we address therapeutic and experimental considerations to guide patient care and future research evaluating the emerging relationship between diabetic neuropathy and bone health.

Mendelian bone fragility disorders

Mendelian bone fragility disorders are caused by genetic variants that can be inherited in an autosomal dominant, autosomal recessive or X-linked manner and have a large detrimental effect on bone strength. As a rule, the more damaging the genetic defect is, the earlier the first fracture will occur, typically during bone development. This review focusses on conditions where bone fragility is the most conspicuous characteristic, of which osteogenesis imperfecta (OI) is the best-known disorder. The large majority of individuals with an OI phenotype have disease-causing dominant variants in COL1A1 or COL1A2, the genes coding for collagen type I. Interestingly, large sequencing databases indicate that there are about 10 times more carriers of COL1A1/COL1A2 variants that should lead to OI than there are individuals with a diagnosis of OI. It is possible that at least some of these variants lead to incomplete OI phenotypes and are diagnosed as osteoporosis during adulthood. Apart from mutations affecting collagen type I production, biallelic mutations in LRP5 and WNT1 can cause very rare and severe bone fragility disorders. Heterozygous pathogenic variants in these genes are much more common and can cause the clinical picture of primary osteoporosis. As sequencing studies are more widely performed in adults with bone fragility disorders, evidence is emerging that what appears as primary osteoporosis in fact can be due to mutations in bona fide OI genes. The distinction between OI and primary osteoporosis is therefore likely to blur in future.

RANKL is a therapeutic target of bone destruction in rheumatoid arthritis

Although remarkable advances have been made in the treatment of rheumatoid arthritis (RA), novel therapeutic options with different mechanisms of action and fewer side effects have been expected. Recent studies have demonstrated that bone-resorbing osteoclasts are critically involved in the bone destruction associated with RA. Denosumab, a human antibody against receptor activator of nuclear factor-kappa B ligand (RANKL), efficiently suppressed the progression of bone erosion in patients with RA by suppressing osteoclast differentiation and activation in several clinical studies, although it had no effect on inflammation or cartilage destruction. Denosumab, in combination with anti-rheumatic drugs, is considered a pivotal therapeutic option for the prevention of bone destruction in RA.

Congenital disorders of bone and blood

Bone and marrow are the two facets of the same organ, in which bone and hematopoietic cells coexist and interact. Marrow and skeletal tissue influence each-other and a variety of genetic disorders directly targets both of them, which may result in combined hematopoietic failure and skeletal malformations. Other conditions primarily affect one organ with secondary influences on the other. For instance, various forms of congenital anemias reduce bone mass and induce osteoporosis, while osteoclast failure in osteopetrosis prevents marrow development reducing medullary cavities and causing anemia and pancytopenia. Understanding the pathophysiology of these conditions may facilitate diagnosis and management, although many disorders are presently incurable. This article describes several congenital bone diseases and their relationship to hematopoietic tissue.

[The prevention and treatment of vascular calcification.]

We had called the various bone disorder in chronic kidney disease(CKD)as a "ROD:renal osteodystrophy" until last decade. However the concept of ROD have changed into the chronic kidney disease-mineral and bone disease(CKD-MBD)within this decade. This concept is containing systemic disorder affected mortality. Vascular calcification is an independent risk factor for the development of cardiovascular disease and mortality. The best strategy to prevent and treat vascular calcification would consist of the CKD-MBD management. It is expected that the treatment of preventing directly vascular calcification to appear by finding the detailed mechanism in the future.

Multi-Scale Approach for the Evaluation of Bone Mineralization in Strontium Ranelate-Treated Diabetic Rats

Long-term diabetes mellitus can induce osteopenia and osteoporosis, an increase in the incidence of low-stress fractures, and/or delayed fracture healing. Strontium ranelate (SrR) is a dual-action anti-osteoporotic agent whose use in individuals with diabetic osteopathy has not been adequately evaluated. In this study, we studied the effects of an oral treatment with SrR and/or experimental diabetes on bone composition and biomechanics. Young male Wistar rats (half non-diabetic, half with streptozotocin/nicotinamide-induced diabetes) were either untreated or orally administered 625 mg/kg/day of SrR for 6 weeks. After sacrifice, femora from all animals were evaluated by a multi-scale approach (X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma optical-emission spectrometry, static histomorphometry, pQCT, and mechanical testing) to determine chemical, crystalline, and biomechanical properties. Untreated diabetic animals (versus untreated non-diabetic) showed a decrease in femoral mineral carbonate content, in cortical thickness and BMC, in trabecular osteocyte density, in maximum load supported at rupture and at yield point, and in overall toughness at mid-shaft. Treatment of diabetic animals with SrR further affected several parameters of bone (some already impaired by diabetes): crystallinity index (indicating less mature apatite crystals); trabecular area, BMC, and vBMD; maximum load at yield point; and structural elastic rigidity. However, SrR was also able to prevent the diabetes-induced decreases in trabecular osteocyte density (completely) and in bone ultimate strength at rupture (partially). Our results indicate that SrR treatment can partially but significantly prevent some bone structural mechanical properties as previously affected by diabetes, but not others (which may even be worsened).

Notch in skeletal physiology and disease

Notch (Notch1 through 4) are transmembrane receptors that play a fundamental role in cell differentiation and function. Notch receptors are activated following interactions with their ligands in neighboring cells. There are five classic ligands termed Jagged (Jag)1 and Jag2 and Delta-like (Dll)1, Dll3, and Dll4. Recent work has established Notch as a signaling pathway that plays a critical role in the differentiation and function of cells of the osteoblast and osteoclast lineages and in skeletal development and bone remodeling. The effects of Notch are cell-context dependent, and the four Notch receptors carry out specific functions in the skeleton. Gain- and loss-of-function mutations of components of the Notch signaling pathway result in a variety of congenital disorders with significant craniofacial and skeletal manifestations. The Notch ligand Jag1 is a determinant of bone mineral density, and Notch plays a role in the early phases of fracture healing. Alterations in Notch signaling are associated with osteosarcoma and with the metastatic potential of carcinoma of the breast and of the prostate. Controlling Notch signaling could prove useful in diseases of Notch gain-of-function and in selected skeletal disorders. However, clinical data on agents that modify Notch signaling are not available. In conclusion, Notch signaling is a novel pathway that regulates skeletal homeostasis in health and disease.

ACR Appropriateness Criteria® Acutely Limping Child Up To Age 5

Imaging plays in important role in the evaluation of the acutely limping child. The decision-making process about initial imaging must consider the level of suspicion for infection and whether symptoms can be localized. The appropriateness of specific imaging examinations in the acutely limping child to age 5 years is discussed with attention in each clinical scenario to the role of radiography, ultrasound, nuclear medicine, computed tomography, and magnetic resonance imaging. Common causes of limping such as toddler's fracture, septic arthritis, transient synovitis, and osteomyelitis are discussed. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Relationship between symptomatic osteochondral lesions of the talus and quality of life, body mass index, age, size and anatomic location

INTRODUCTION

The aim of the study was to assess the relationship between symptomatic osteochondral lesions of the talus (OLTs) and age, body mass index (BMI), quality of life (QOL), size and anatomic location.

METHODS

Fifty-two patients with chronic OLTs were analyzed including BMI, Visual Analogue Scale (VAS), American Orthopaedic Foot and Ankle Society (AOFAS), Short-Form Health Survey (SF-12 divided into Mental (MCS) and Physical (PCS) score) and the 12-Item General Health Questionnaire (GHQ-12). Every patient underwent magnetic resonance imaging (MRI) and computed tomography (CT) examinations. We carried out a sub-analysis by dividing the talus into 6 areas, 3 vertical (medial, central and lateral group) and 3 horizontal (anterior, middle and posterior group).

RESULTS

There were 31 (60%) male and 21 (40%) female patients. Mean MCS and PCS resulted respectively 43.9 and 35.2. OLTs were located as follows: medial 20 (38.50%); central 13 (24.0%); and lateral 19 (36.50%); anterior 24 (46.15%); middle 16 (30.77%); and posterior 12 (23.08%). No significant differences were found among different groups with the exception of the anterior and posterior group for MCS (p=0.021). In the central group we identified a negative correlation (R=-0.672) between aging and AOFAS and a positive correlation between BMI and lesion size. We found a positive correlation between CT and MRI in each group.

CONCLUSIONS

OLTs impact patients' quality of life particularly in the physical component. Additionally, in patients with central lesions we found a positive linear correlation between lesion size and BMI and a worsening of the ankle with increasing age.

Multiple Myeloma and Bone: The Fatal Interaction

Multiple myeloma (MM) is the second-most-common hematologic malignancy and the most frequent cancer to involve bone. MM bone disease (MMBD) has devastating consequences for patients, including dramatic bone loss, severe bone pain, and pathological fractures that markedly decrease the quality of life and impact survival of MM patients. MMBD results from excessive osteoclastic bone resorption and persistent suppressed osteoblastic bone formation, causing lytic lesions that do not heal, even when patients are in complete and prolonged remission. This review discusses the cellular and molecular mechanisms that regulate the uncoupling of bone remodeling in MM, the effects of MMBD on tumor growth, and potential therapeutic approaches that may prevent severe bone loss and repair damaged bone in MM patients.

Bone Mechanical Properties in Healthy and Diseased States

The mechanical properties of bone are fundamental to the ability of our skeletons to support movement and to provide protection to our vital organs. As such, deterioration in mechanical behavior with aging and/or diseases such as osteoporosis and diabetes can have profound consequences for individuals' quality of life. This article reviews current knowledge of the basic mechanical behavior of bone at length scales ranging from hundreds of nanometers to tens of centimeters. We present the basic tenets of bone mechanics and connect them to some of the arcs of research that have brought the field to recent advances. We also discuss cortical bone, trabecular bone, and whole bones, as well as multiple aspects of material behavior, including elasticity, yield, fracture, fatigue, and damage. We describe the roles of bone quantity (e.g., density, porosity) and bone quality (e.g., cross-linking, protein composition), along with several avenues of future research.

How should we diagnose disease in palaeopathology? Some epistemological considerations

This paper analyses some of the epistemological frameworks that underpin diagnosis in palaeopathology. Currently, the dominant approach is comparative: relationships between skeletal lesions and disease in a reference group in which there is independent evidence of the diseases present in individuals are used to identify disease in unknown archaeological skeletons on the basis of the lesions present. This is essentially a reference sample - target sample approach, analogous to that used to develop methodology in other areas of biological anthropology (e.g. age estimation in palaeodemography). As well as considerable strengths, this approach also has significant weaknesses. Many of these arise from the nature of the reference material (mainly pathology museum and other skeletal collections, and published collations of medical imaging data) used to develop diagnostic criteria. There may also be a tendency toward over-emphasis on pattern-matching between reference and target material, and an under-emphasis on developing our understanding of the biology of bone lesions. Despite its shortcomings, the comparative approach is likely to remain the foundation of most palaeopathological work, but we should increasingly augment it with other diagnostic approaches, especially those grounded in the pathophysiology of bony responses to disease.

Biology and treatment of myeloma related bone disease

Myeloma bone disease (MBD) is the most common complication of multiple myeloma (MM), resulting in skeleton-related events (SREs) such as severe bone pain, pathologic fractures, vertebral collapse, hypercalcemia, and spinal cord compression that cause significant morbidity and mortality. It is due to an increased activity of osteoclasts coupled to the suppressed bone formation by osteoblasts. Novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition have recently been described, including the receptor activator of nuclear factor-kB ligand/osteoprotegerin pathway, activin-A and the wingless-type signaling inhibitors, dickkopf-1 (DKK-1) and sclerostin. These molecules interfere with tumor growth and survival, providing possible targets for the development of novel drugs for the management of lytic disease in myeloma but also for the treatment of MM itself. Currently, bisphosphonates are the mainstay of the treatment of myeloma bone disease although several novel agents such as denosumab and sotatercept appear promising. This review focuses on recent advances in MBD pathophysiology and treatment, in addition to the established therapeutic guidelines.

The Proteasome and Myeloma-Associated Bone Disease

Bone disease is the hallmark of multiple myeloma (MM), a hematological malignancy characterized by osteolytic lesions due to a severe uncoupled and unbalanced bone remodeling with pronounced osteoblast suppression. Bone metastasis is also a frequent complication of solid tumors including advanced breast or prostate cancer. In the past years, the ubiquitin-proteasome pathway has been proved critical in regulating the balance between bone formation and bone resorption. Proteasome inhibitors (PIs) are a new class of drugs, currently used in the treatment of MM, that affect both tumor cells and bone microenvironment. Particularly, PIs stimulate osteoblast differentiation by human mesenchymal stromal cells and increase bone regeneration in mice. Interestingly, in vitro data indicate that PIs block MM-induced osteoblast and osteocyte cell death by targeting both apoptosis and autophagy. The preclinical data are supported by the following effects observed in MM patients treated with PIs: increase of bone alkaline phosphatase levels, normalization of the markers of bone turnover, and reduction of the skeletal-related events. Moreover, the histomorphometric data indicate that the treatment with bortezomib stimulates osteoblast formation and maintains osteocyte viability in MM patients. This review updates the evidence on the effects of PIs on bone remodeling and on cancer-induced bone disease while focusing on MM bone disease.

New agents in the Treatment of Myeloma Bone Disease

Patients with multiple myeloma develop a devastating bone disease driven by the uncoupling of bone remodelling, excess osteoclastic bone resorption and diminished osteoblastic bone formation. The bone phenotype is typified by focal osteolytic lesions leading to pathological fractures, hypercalcaemia and other catastrophic bone events such as spinal cord compression. This causes bone pain, impaired functional status, decreased quality of life and increased mortality. Early in the disease, malignant plasma cells occupy a niche environment that encompasses their interaction with other key cellular components of the bone marrow microenvironment. Through these interactions, osteoclast-activating factors and osteoblast inhibitory factors are produced, which together uncouple the dynamic process of bone remodelling, leading to net bone loss and focal osteolytic lesions. Current management includes antiresorptive therapies, i.e. bisphosphonates, palliative support and orthopaedic interventions. Bisphosphonates are the mainstay of treatment for myeloma bone disease (MBD), but are only partially effective and do have some significant disadvantages; for example, they do not lead to the repair of existing bone destruction. Thus, newer agents to prevent bone destruction and also promote bone formation and repair existing lesions are warranted. This review summarises novel ways that MBD is being therapeutically targeted.

[Prevalence and determinants of bone remodelancy disorders in patients with diabetes.]

The article presents the results of structural change and functional state of bone in patients with diabetes mellitus. Total of 235 patients aged 40 to 70 years, of these, 98 (41 men, 57 women) type 1 and 137 (52 men, 85 women) type 2 diabetes patients were included in the study. DM1 duration 16,6±0,6 years, BMI: 26,1±0,2 kg/m2 and DM2: 8,1±0,7 years, BMI: 30±0,4 kg/m2. Investigated the level of 25(OH)D, PTH, serum bone remodeling markers (ALP, PINP, b-CTx) and DXA. The results of the study demonstrated that the content of serum bone remodeling markers in patients with DM1 and DM2, in comparison to the control group, indicate pathological processes in bone remodeling with decrease bone formation marker PINP in patients with DM1 by 16%, with DM2 by 12% in comparison with the control and an increase bone resorption marker b-CTx by 32% with DM1 and in 25% patients with DM2, of whom of women were 1,5 times more than men. Patients with DM2 had lower b-CTx values and a relatively higher level of P1NP, which reflects a less pronounced change in bone turnover compared to patients with DM1, regardless of age and duration of disease. T-score BMD of L1-L4 area was reduced in 64 and 44% of patients with DM1 and DM2; T-score BMD of femoral neck area - in 41 and 36% of patients. These results suggest that bone disorders and related fractures, is a clinically significant and commonly underestimated problem in diabetes.

Dental Manifestations of Pediatric Bone Disorders

PURPOSE OF REVIEW

Several bone disorders affecting the skeleton often are manifest in the maxillofacial region. This review presents the most common bone disorders in children and their dental-oral manifestations: fibrous dysplasia, Paget's disease, osteogenesis imperfecta, renal osteodystrophy, hypophosphatasia, and osteoporosis. The specific intraoral characteristics will reviewed in detail.

RECENT FINDINGS

Recent studies confirmed the close relationship between the mandible and the maxilla with the most prevalent systemic bone disorders in children. This review will help practitioners to integrate the oral health into the systemic health and improve the multidisciplinary approach of pediatric patients between medicine and dentistry.

Effect of lanthanum carbonate on coronary artery calcification and bone mineral density in maintenance hemodialysis patients with diabetes complicated with adynamic bone disease: A prospective pilot study

BACKGROUND

The incidence of adynamic bone disease (ABD) is increasing. Coronary artery calcification (CAC) may be severe in patients with ABD on maintenance hemodialysis (MHD). The aim of this study was to evaluate the effect of lanthanum carbonate (LC) on CAC and bone mineral density (BMD) in MHD patients with diabetes complicated with ABD.

METHODS

A total of 92 MHD cases were divided into the calcium carbonate (CC) and LC groups. Primary outcome measure was the changes in the degree of CAC score (CACS) and BMD in forearm from baseline to 12 months. Secondary outcomes included changes in serum markers of CKD-MBD and side-effects.

RESULTS

After 12 months, serum levels of calcium, phosphate, FGF23, and MGP were decreased significantly, while iPTH, b-ALP, PINP and β-CTX, and CACS and BMD were increased in LC group compared with those at baseline (P < .05). After 12 months treatment, serum levels of calcium, phosphate, FGF23, and CACS were lowered, while MGP, b-ALP, PINP, β-CTX, BMD, and iPTH were higher in LC group than in CC group. Pearson correlation analyses revealed that BMD in forearm was positively correlated with iPTH and MGP, while negatively with CACS. CACS was positively correlated with serum calcium, phosphate and FGF23, while negatively with serum MGP. Multivariate linear regression revealed changes of BMD in forearm and femoral neck and changes of serum FGF23 were independent influential factors for changes of CACS (P < .05).

CONCLUSIONS

In MHD patients with diabetes complicated with ABD, lanthanum carbonate could delay CAC progress, and improve bone transport and bone density.

Bone disease in diabetes: another manifestation of microvascular disease?

Type 1 and type 2 diabetes are generally accepted to be associated with increased bone fracture risk. However, the pathophysiological mechanisms of diabetic bone disease are poorly understood, and whether the associated increased skeletal fragility is a comorbidity or a complication of diabetes remains under debate. Although there is some indication of a direct deleterious effect of microangiopathy on bone, the evidence is open to question, and whether diabetic osteopathy can be classified as a chronic, microvascular complication of diabetes remains uncertain. Here, we review the current knowledge of potential contributory factors to diabetic bone disease, particularly the association between diabetic microangiopathy and bone mineral density, bone structure, and bone turnover. Additionally, we discuss and propose a pathophysiological model of the effects of diabetic microvascular disease on bone, and examine the progression of bone disease alongside the evolution of diabetes.

Serum 25-Hydroxyvitamin D Insufficiency in Search of a Bone Disease

CONTEXT

Vitamin D "insufficiency" and "deficiency" are defined as serum 25-hydroxyvitamin D [25(OH)D] levels <75 and <30 nmol/L, respectively. We aimed to determine whether these values signal hypocalcemia and hypophosphatemia, secondary hyperparathyroidism, high bone remodeling, low areal bone mineral density (aBMD), microstructural deterioration, or reduced matrix mineralization density (MMD) and so suggest whether bone fragility is present.

METHODS

Concentrations of 25(OH)D, calcium, phosphate, creatinine, and parathyroid hormone (PTH) were measured in 11,855 participants. Serum C-terminal telopeptide of type 1 collagen, procollagen type 1 N-terminal propeptide (P1NP), aBMD, and distal radius microstructure and MMD were measured in a second subset of 150 participants.

RESULTS

A breakpoint for calcium, PTH, and alkaline phosphatase was identified at a threshold 25(OH)D level <30 nmol/L. There was no plateau beyond 75 nmol/L. In the subgroup with measurements of bone morphology, no associations were detectable between serum 25(OH)D concentration, aBMD, trabecular density, cortical porosity, or MMD. Among 1439 participants with serum 25(OH)D <30 nmol/L, 6.1% had low serum calcium, 3.4% had low serum phosphate, 6.1% had high alkaline phosphatase, and 34.2% had elevated PTH. Most participants did not have any abnormalities.

CONCLUSION

At a 25(OH)D threshold of ≤30 nmol/L, abnormalities in biochemical features support the notion of a "deficiency" state predisposing to bone disease. However, no deleterious effects were found in participants within an insufficiency threshold of a 25(OH)D level of 30 to 75 nmol/L, which challenges the rationale justifying vitamin D supplementation in these individuals.

Bone Mineralization and Fracture Risk Assessment in the Pediatric Population

Identifying children most susceptible to clinically significant fragility fractures (low trauma fractures or vertebral compression fractures) or recurrent fractures is an important issue facing general pediatricians and subspecialists alike. Over the last decade, several imaging technologies, including dual-energy X-ray absorptiometry and peripheral quantitative computed tomography, have become useful to identify abnormal bone mineralization in children and in adolescents. This review aimed to summarize the latest literature on the utility of these modalities as they pertain to use in pediatrics. In addition, we review several disease states associated with poor bone health and increased fracture risk in children, and discuss the implications of low bone mineral density in these patients. Finally, we will highlight the gaps in knowledge with regard to pediatric bone health and make recommendations for future areas of research.

Bone Pain and Muscle Weakness in Cancer Patients

PURPOSE OF REVIEW

In this article, we will discuss the current understanding of bone pain and muscle weakness in cancer patients. We will describe the underlying physiology and mechanisms of cancer-induced bone pain (CIBP) and cancer-induced muscle wasting (CIMW), as well as current methods of diagnosis and treatment. We will discuss future therapies and research directions to help patients with these problems.

RECENT FINDINGS

There are several pharmacologic therapies that are currently in preclinical and clinical testing that appear to be promising adjuncts to current CIBP and CIMW therapies. Such therapies include resiniferitoxin, which is a targeted inhibitor of noceciptive nerve fibers, and selective androgen receptor modulators, which show promise in increasing lean mass. CIBP and CIMW are significant causes of morbidity in affected patients. Current management is mostly palliative; however, targeted therapies are poised to revolutionize how these problems are treated.

Functional Diversity of Ciliary Proteins in Bone Development and Disease

PURPOSE OF REVIEW

The primary cilium is a non-motile microtubule-based organelle that senses a diverse range of extracellular signals. While recent studies highlight the importance of ciliary-dependent developmental signals, including Hedgehog, Wnt, and platelet-derived growth factor, it is not well understood whether and how bone morphogenetic protein (BMP) signaling, a key regulator of skeletogenesis, is involved in cilia-related bone developmental aspects and in the etiology of skeletal disorders.

RECENT FINDINGS

Increasing evidence suggests that osteoblast- or osteocyte-specific deletion of ciliary proteins leads to diverse skeletal malformations, reinforcing the idea that primary cilia are indispensable for regulating bone development and maintenance. Furthermore, it became evident that ciliary proteins not only contribute to ciliogenesis but also orchestrate cellular trafficking. This review summarizes the current understanding of ciliary proteins in bone development and discusses the potential role of BMP signaling in primary cilia, enabling us to unravel the potential pathogenesis of skeletal ciliopathies.

Retrospective Review of Atypical Femoral Fracture in Metastatic Bone Disease Patients Receiving Denosumab Therapy

BACKGROUND

Denosumab therapy is used to reduce skeletal-related events in metastatic bone disease (MBD). There have been reports of atypical femoral fracture (AFF) in osteoporotic patients treated with denosumab but none in the context of higher dose and more frequent denosumab therapy for MBD. The goal of this study was to assess the incidence of AFF in MBD.

PATIENTS AND METHODS

We conducted a retrospective review of 253 patients who received a minimum of 12 doses of denosumab at 120 mg each for MBD. To identify patients with asymptomatic atypical stress reactions in the lateral subtrochanteric femur (which precede fractures), we reviewed the skeletal images of 66 patients who had received at least 21 doses of denosumab for AFF features.

RESULTS

These patients received a median of 17 doses, with a median treatment duration of 23 months. There was 1 case of undiagnosed clinical AFF detected after chart review and 2 cases of subclinical atypical femoral stress reaction observed on imaging review after 23 doses of denosumab over 33 months, 28 doses over 27 months, and 21 doses over 21 months, respectively. Scout computed tomography films showed diffuse cortical thickening of diaphysis with localized periosteal reaction of lateral femoral cortex. Bone scan and magnetic resonance imaging scan of 2 patients with stress reactions confirmed the diagnosis.

CONCLUSION

The incidence of clinical AFF in this context is 0.4% (1/253; 95% confidence interval [CI] 0.1%-2.2%), and the incidence of atypical femoral stress reaction based on imaging review is 4.5% (3/66; 95% CI 1.6%-12.5%). Clinicians should be aware of the clinical prodrome (which may or may not be present) and antecedent imaging changes associated with AFF. The Oncologist 2017;22:438-444Implications for Practice: Among patients with metastatic bone disease treated with denosumab, cases of clinical and subclinical atypical femoral fracture (AFF) are rare. The one detected case of clinical fracture went unrecognized despite prodromic symptoms. Clinicians should be aware of (a) the potential prodrome of anterior thigh/groin pain and (b) subclinical imaging changes in the lateral femur, both of which may precede clinical AFF.

The Role of the Osteocyte in Bone and Nonbone Disease

When normal physiologic functions go awry, disorders and disease occur. This is universal; even for the osteocyte, a cell embedded within the mineralized matrix of bone. It was once thought that this cell was simply a placeholder in bone. Within the last decade, the number of studies of osteocytes has increased dramatically, leading to the discovery of novel functions of these cells. With the discovery of novel physiologic functions came the discoveries of how these cells can also be responsible for not only bone diseases and disorders, but also those of the kidney, heart, and potentially muscle.

Application of anti-Sclerostin therapy in non-osteoporosis disease models

Sclerostin, a known inhibitor of the low density lipoprotein related protein 5 and 6 (LRP5 and LRP6) cell surface signaling receptors, is integral in the maintenance of normal bone mass and strength. Patients with loss of function mutations in SOST or missense mutations in LRP5 that prevent Sclerostin from binding and inhibiting the receptor, have significantly increased bone mass. This observation leads to the development of Sclerostin neutralizing therapies to increase bone mass and strength. Anti-Sclerostin therapy has been shown to be effective at increasing bone density and strength in animal models and patients with osteoporosis. Loss of function of Sost or treatment with a Sclerostin neutralizing antibody improves bone properties in animal models of Osteoporosis Pseudoglioma syndrome (OPPG), likely due to action through the LRP6 receptor, which suggests patients may benefit from these therapies. Sclerostin antibody is effective at improving bone properties in mouse models of Osteogenesis Imperfecta, a genetic disorder of low bone mass and fragility due to type I collagen mutations, in as little as two weeks after initiation of therapy. However, these improvements are due to increases in bone quantity as the quality (brittleness) of bone remains unaffected. Similarly, Sclerostin antibody treatment improves bone density in animal models of other diseases. Sclerostin neutralizing therapies are likely to benefit many patients with genetic disorders of bone, as well as other forms of metabolic bone disease.

[Immobilization and bone remodeling disorder.]

Mechanical stress is essential for us to maintain bone volume and structure. Immobilization and unloading, such as motor paralysis, long-term bedrest and casting of fractured area, cause rapidly remarkable bone loss. The bone remodeling disorder following immobilization demonstrates the acceleration of bone resorption and the suppression of bone formation, and molecular mechanism of the bone remodeling disorder has been gradually revealed recently. It is very difficult for us to improve the bone loss due to disuse completely. Thus, prevention of disuse osteoporosis is important. We should choose suitable treatment after considering the pathophysiology of disuse osteoporosis, and attempt early intervention as soon as possible.

Probiotics in Gut-Bone Signaling

The intestinal environment is linked to an array of conditions and diseases, including osteoporosis. Human and animal studies indicate that probiotics can benefit intestinal health and may provide a useful therapeutic to prevent and/or treat bone loss. Probiotics are defined as live microorganisms that when administered in adequate amounts will confer a health benefit on the host. In this review, we will focus on (1) probiotics (definition, history, nomenclature, types), (2) the effects of probiotics on bone health, and (3) mechanisms of probiotic prevention of bone pathologies.

The adult zebrafish as polyhedric model for skeletal studies

In the last decade, several examples have been produced by scientific literature about zebrafish as a model to study human bone diseases. In fish, bone turnover, reparation and remodeling of the adult bone tissue cannot be studied in embryonic or juvenile stages. In addition, fins and scales represent unique anatomical features useful to study adult bone metabolism and diseases. For these reasons, the adult zebrafish represents an innovative and readily available resource for studying the bone metabolism at cellular and molecular level. Although the adult fish is less used than the embryo, several applications have been found in the last years with the production of innovative pathological models in adult zebrafish, helpful to understand the mechanisms of bone physiopathology. The use of mutants, regenerating organs, transgenic fish and scales have increased the power of this model in the last years.

Rapid phenotyping of knockout mice to identify genetic determinants of bone strength

The genetic determinants of osteoporosis remain poorly understood, and there is a large unmet need for new treatments in our ageing society. Thus, new approaches for gene discovery in skeletal disease are required to complement the current genome-wide association studies in human populations. The International Knockout Mouse Consortium (IKMC) and the International Mouse Phenotyping Consortium (IMPC) provide such an opportunity. The IKMC generates knockout mice representing each of the known protein-coding genes in C57BL/6 mice and, as part of the IMPC initiative, the Origins of Bone and Cartilage Disease project identifies mutants with significant outlier skeletal phenotypes. This initiative will add value to data from large human cohorts and provide a new understanding of bone and cartilage pathophysiology, ultimately leading to the identification of novel drug targets for the treatment of skeletal disease.