Sequence analysis of measles virus nucleocapsid transcripts in patients with Paget's disease

Paget's Disease or Densifying Metastasis: How to Sort It Out

Although the prevalence of Paget's disease has decreased over the past 20 years, incidental discovery on imaging is not unusual. The challenge is to establish the diagnosis, especially in unusual forms that may be mistaken for metastases. This review describes the typical imaging features of Paget's disease and some rare presentations that may be more difficult to recognize.

Updates on Paget's Disease of Bone

Paget's disease of the bone is a prevalent bone disease characterized by disorganized bone remodeling; however, it is comparatively uncommon in East Asian countries, including China, Japan, and Korea. The exact cause still remains unknown. In genetically susceptible individuals, environmental triggers such as paramyxoviral infections are likely to cause the disease. Increased osteoclast activity results in increased bone resorption, which attracts osteoblasts and generates new bone matrix. Fast bone resorption and formation lead to the development of disorganized bone tissue. Increasing serum alkaline phosphatase or unique radiographic lesions may serve as the diagnostic indicators. Common symptoms include bone pain, bowing of the long bones, an enlarged skull, and hearing loss. The diagnosis is frequently confirmed by radiographic and nuclear scintigraphy of the bone. Further, bisphosphonates such as zoledronic acid and pamidronate are effective for its treatment. Moreover, biochemical monitoring is superior to the symptoms as a recurrence indicator. This article discusses the updates of Paget's disease of bone with a clinical case.

Update on the pathogenesis and genetics of Paget’s disease of bone

Studies over the past two decades have led to major advances in the pathogenesis of Paget’s disease of bone (PDB) and particularly on the role of genetic factors. Germline mutations of different genes have been identified, as a possible cause of this disorder, and most of the underlying pathways are implicated in the regulation of osteoclast differentiation and function, whereas other are involved in cell autophagy mechanisms. In particular, about 30 different germline mutations of the Sequestosome 1 gene (SQSTM1) have been described in a significant proportion of familial and sporadic PDB cases. The majority of SQSTM1 mutations affect the ubiquitin-binding domain of the protein and are associated to a more severe clinical expression of the disease. Also, germline mutations in the ZNF687 and PFN1 genes have been associated to severe, early onset, polyostotic PDB with increased susceptibly to neoplastic degeneration, particularly giant cell tumor. Mutations in the VCP (Valosin Containing Protein) gene cause the autosomal dominant syndrome “Inclusion Body Myopathy, PDB, Fronto-temporal Dementia,” characterized by pagetic manifestations, associated with myopathy, amyotrophic lateral sclerosis and fronto-temporal dementia. Moreover, germline mutations in the TNFRSF11A gene, which encodes for RANK, were associated with rare syndromes showing some histopathological, radiological, and clinical overlap with PDB and in two cases of early onset PDB-like disease. Likewise, genome wide association studies performed in unrelated PDB cases identified other potential predisposition genes and/or susceptibility loci. Thus, it is likely that polygenic factors are involved in the PDB pathogenesis in many individuals and that modifying genes may contribute in refining the clinical phenotype. Moreover, the contribution of somatic mutations of SQSTM1 gene and/or epigenetic mechanisms in the pathogenesis of skeletal pagetic abnormalities and eventually neoplastic degeneration, cannot be excluded. Indeed, clinical and experimental observations indicate that genetic susceptibility might not be a sufficient condition for the clinical development of PDB without the concomitant intervention of viral infection, in primis paramixoviruses, and/or other environmental factors (e.g., pesticides, heavy metals or tobacco exposure), at least in a subset of cases. This review summarizes the most important advances that have been made in the field of cellular and molecular biology PDB over the past decades.

The evaluation and treatment of Paget's disease of bone

Paget's disease of bone is a localized skeletal disorder, which is more common in England and in countries to which the English migrated. In recent decades, the prevalence in most countries has decreased. A family history of the disorder is present in approximately 15% of patients. Patients may be asymptomatic and may be diagnosed accidently as a consequence of an elevated serum alkaline phosphatase level or a finding on an x-ray or nuclear bone scan. The diagnosis is made by x-ray but nuclear bone scans define the extent of the disease. Salmon calcitonin and bisphosphonate drugs have proven effective, but by far, the most effective therapy is a single 5 mg intravenous infusion of zoledronic acid. This can normalize alkaline phosphatase levels for up to 6.5 years. A variety of gene mutations may predispose individuals to develop the disease but environmental factors such as measles virus likely play an important role.

The osteoclast, a target cell for microorganisms

Bone is a highly adaptive tissue with regenerative properties that is subject to numerous diseases. Infection is one of the causes of altered bone homeostasis. Bone infection happens subsequently to bone surgery or to systemic spreading of microorganisms. In addition to osteoblasts, osteoclasts (OCs) also constitute cell targets for pathogens. OCs are multinucleated cells that have the exclusive ability to resorb bone mineral tissue. However, the OC is much more than a bone eater. Beyond its role in the control of bone turnover, the OC is an immune cell that produces and senses inflammatory cytokines, ingests microorganisms and presents antigens. Today, increasing evidence shows that several pathogens use OC as a host cell to grow, generating debilitating bone defects. In this review, we exhaustively inventory the bacteria and viruses that infect OC and report the present knowledge in this topic. We point out that most of the microorganisms enhance the bone resorption activity of OC. We notice that pathogen interactions with the OC require further investigation, in particular to validate the OC as a host cell in vivo and to identify the cellular mechanisms involved in altered bone resorption. Thus, we conclude that the OC is a new cell target for pathogens; this new research area paves the way for new therapeutic strategies in the infections causing bone defects.

Fusion and hemagglutinin proteins of canine distemper virus promote osteoclast formation through NF-κB dependent and independent mechanisms

Paget's disease (PD) features abnormal osteoclasts (OC) which sharply increase in number and size and then intensely induce bone resorption. The purpose of this study was to determine the direct effects of canine distemper virus (CDV) and its fusion protein and hemagglutinin protein (F + H) on receptor activator of nuclear factor kappa-B ligand (RANKL) induced OC formation in vitro. Immunofluorescence assay, OC morphological and functional detection, intracellular signaling pathway detection, Real-time PCR analysis and ELISA were applied in this study. Immunofluorescence assay provided the conclusive proof that CDV can infect and replicate in RAW264.7 mouse monocyte cell line, primary human peripheral blood mononuclear cells (PBMC) and their further fused OC. Both CDV and F + H significantly promoted OC formation and bone resorption ability induced by RANKL. Meanwhile, intracellular signaling transduction analysis revealed CDV and F + H specifically upregulated the phosphorylation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) induced by RANKL, respectively. Furthermore, without RANKL stimulation, both CDV and F + H slightly induced OC-like cells formation in RAW264.7 cell line even in the presence of NF-κB inhibitor. F + H upregulate OC differentiation and activity through modulation of NF-κB signaling pathway, and induce OC precursor cells merging dependent on the function of glycoproteins themselves. These results meant that F and H proteins play a pivotal role in CDV supporting OC formation. Moreover, this work further provide a new research direction that F and H proteins in CDV should be considered as a trigger during the pathogenesis of PD.

NFAM1 signaling enhances osteoclast formation and bone resorption activity in Paget's disease of bone

Paget's disease of bone (PDB) is marked by the focal activity of abnormal osteoclasts (OCLs) with excess bone resorption. We previously detected measles virus nucleocapsid protein (MVNP) transcripts in OCLs from patients with PDB. Also, MVNP stimulates pagetic OCL formation in vitro and in vivo. However, the mechanism by which MVNP induces excess OCLs/bone resorption activity in PDB is unclear. Microarray analysis identified MVNP induction of NFAM1 (NFAT activating protein with ITAM motif 1) expression. Therefore, we hypothesize that MVNP induction of NFAM1 enhances OCL differentiation and bone resorption in PDB. MVNP transduced normal human PBMC showed an increased NFAM1 mRNA expression without RANKL treatment. Further, bone marrow cells from patients with PDB demonstrated elevated levels of NFAM1 mRNA expression. Interestingly, shRNA suppression of NFAM1 inhibits MVNP induced OCL differentiation and bone resorption activity in mouse bone marrow cultures. Live cell widefield fluorescence microscopy analysis revealed that MVNP induced intracellular Ca²⁺ oscillations and levels were significantly reduced in NFAM1 suppressed preosteoclasts. Further, western blot analysis demonstrates that shRNA against NFAM1 inhibits MVNP stimulated PLCγ, calcineurin, and Syk activation in preosteoclast cells. Furthermore, NFAM1 expression controls NFATc1, a critical transcription factor expression and nuclear translocation in MVNP transuded preosteoclast cells. Thus, our results suggest that MVNP modulation of the NFAM1 signaling axis plays an essential role in pagetic OCL formation and bone resorption activity.

Management of Paget's Disease of the Calcaneum

The calcaneum is not the most common site for Paget's disease of bone, with only a few reports of monostotic involvement. We present 2 cases of Paget's disease of bone affecting the calcaneus, present an overview of the published data, and describe our management of these interesting cases.

Measles virus nucleocapsid protein modulates the Signal Regulatory Protein-β1 (SIRPβ1) to enhance osteoclast differentiation in Paget's disease of bone

Paget's disease of bone (PDB) is a chronic localized bone disorder in an elderly population. Environmental factors such as paramyxovirus are implicated in PDB and measles virus nucleocapsid protein (MVNP) has been shown to induce pagetic osteoclasts (OCLs). However, the molecular mechanisms underlying MVNP stimulation of OCL differentiation in the PDB are unclear. We therefore determined the MVNP regulated gene expression profiling during OCL differentiation. Agilent microarray analysis of gene expression identified high levels of SIRPβ1 (353-fold) expression in MVNP transduced human bone marrow mononuclear cells stimulated with RANKL. Real-time PCR analysis further confirmed that MVNP alone upregulates SIRPβ1 mRNA expression in these cells. Also, bone marrow mononuclear cells derived from patients with PDB showed high levels of SIRPβ1 mRNA expression compared to normal subjects. We further show that MVNP increases SIRPβ1 interaction with DAP12 adaptor protein in the presence and absence of RANKL stimulation. shRNA knockdown of SIRPβ1 expression in normal human bone marrow monocytes decreased the levels of MVNP enhanced p-Syk and c-Fos expression. In addition, SIRPβ1 knockdown significantly decreased MVNP stimulated dendritic cell-specific transmembrane protein (DC-STAMP) and connective tissue growth factor (CTGF) mRNA expression during OCL differentiation. Furthermore, we demonstrated the contribution of SIRPβ1 in MVNP induced OCL formation and bone resorption. Thus, our results suggest that MVNP modulation of SIRPβ1 provides new insights into the molecular mechanisms which control high bone turnover in PDB.

Case report of early aseptic loosening of total hip arthroplasty in monostotic paget disease, a diagnostic challenge

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Paget disease of bone can lead with severe bone destruction.

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Altered bone metabolism in patients with arthroplasties has a difficult diagnosis.

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We propose laboratory studies when severe boen destruction is seen in radiological images from hip implants.

Paget’s disease of bone is a localised chronic osteopathy which produces bone deformities, bone hypervascularity, structural weakness and altered joint biomechanics. Although radiological diagnosis of Paget's disease of bone is usually straightforward, monostotic cases may potentially raise specific problems which require invasive and expensive procedures such as bone biopsies. The pelvis and upper femur are frequently affected, resulting in disabling hip disease that may require total hip arthroplasty. We report a case of Paget disease of bone in an 84-year-old woman, which was initially identified as avascular necrosis of the hip, reason for which she underwent total hip arthroplasty. During follow up, the patient complained about hip pain and in a few months she was not able to walk because of an early loosening with bone destruction. Radiological and laboratory exams were carried out with normal results except for alkaline phosphatase (AP). After treatment with biphosphonates hip pain relieved but hip reconstruction was not possible. In this paper we present an early aseptic loosening of hip arthroplasty due to monostotic Paget’s disease of bone, a rare ethiology of loosening which poses particular diagnostic difficulties prompting an excessive use of excisional biopsies.

Genetics of Paget's disease of bone

Paget's disease of bone (PDB) is a common metabolic bone disease characterised by focal areas of increased bone turnover, which primarily affects people over the age of 55 years. Genetic factors have a fundamental role in the pathogenesis of PDB and are probably the main predisposing factor for the disease. The genetic contribution to PDB susceptibility ranges from rare pathogenic mutations in the single gene SQSTM1 to more common, small effect variants in at least seven genetic loci that predispose to the disease. These loci have additive effects on disease susceptibility and interact with SQSTM1 mutations to affect disease severity, making them a potentially useful tool in predicting disease risk and complication and in managing treatments. Many of these loci harbour genes that have important function in osteoclast differentiation such as CSF1, DCSTAMP and TNFRSF11A. Other susceptibility loci have highlighted new molecular pathways that have not been previously implicated in regulation of bone metabolism such as OPTN, which was recently found to negatively regulate osteoclast differentiation. PDB-susceptibility variants exert their effect either by affecting the protein coding sequence such as variants found in SQSTM1 and RIN3 or by influencing gene expression such as those found in OPTN and DCSTAMP. Epidemiological studies indicate that environmental triggers also have a key role in PDB and interact with genetic factors to influence manifestation and severity of the disease; however, further studies are needed to identify these triggers.

Paget's disease of bone-genetic and environmental factors

Paget's disease of bone is generally diagnosed in individuals aged >50 years, usually manifests in one or several bones and is initiated by osteoclast-induced osteolytic lesions. Subsequently, over a period of many years, osteoblastic activity can result in sclerosis and deformation of bone. The prevalence of Paget's disease is highest in the UK and in countries where a large number of residents have ancestors from the UK. Currently, in many countries, the prevalence of the disorder has decreased. A considerable number of affected patients have a family history of Paget's disease and the disorder has an autosomal dominant pattern of inheritance but with incomplete penetrance. A large number of mutations in SQSTM1 (which encodes sequestosome-1; also known as ubiquitin-binding protein p62) seem to account for the susceptibility to develop Paget's disease in some families; the involvement of other genes is currently under investigation. In addition to a genetic cause, environmental factors have been proposed to have a role in the pathogenesis of Paget's disease. Although most evidence has been presented for measles virus as an aetiologic factor, some studies have not confirmed its involvement. The decreasing incidence of Paget's disease, which could be attributed to measles vaccination along with the measles virus nucleocapsid protein induction of Paget's disease lesions in transgenic mice, supports an aetiologic role of the virus.

Paget Disease of Bone

The current understanding of Paget disease of bone (PDB) has vastly changed since Paget described the first case in 1877. Medical management of this condition remains the mainstay of treatment. Surgical intervention is usually only used in fractures through pagetic bone, need for realignment to correct deformity in major long bones, prophylactic treatment of impending fractures, joint arthroplasty in severe arthritis, or spinal decompression in cases of bony compression of neural elements. Advances in surgical technique have allowed early return to function and mobilization. Despite medical and surgical intervention, a small subset of patients with PDB develops Paget sarcoma.

New insights into the role of sequestosome 1/p62 mutant proteins in the pathogenesis of Paget's disease of bone

Paget's disease of bone (PDB) is characterized by focal areas of aberrant and excessive bone turnover, specifically increased bone resorption and disorganized bone formation. Germline mutations in the sequestosome 1/p62 (SQSTM1/p62) gene are common in PDB patients, with most mutations affecting the ubiquitin-associated domain of the protein. In vitro, osteoclast precursor cells expressing PDB-mutant SQSTM1/p62 protein are associated with increases in nuclear factor κB activation, osteoclast differentiation, and bone resorption. Although the precise mechanisms by which SQSTM1/p62 mutations contribute to disease pathogenesis and progression are not well defined, it is apparent that as well as affecting nuclear factor κB signaling, SQSTM1/p62 is a master regulator of ubiquitinated protein turnover via autophagy and the ubiquitin-proteasome system. Additional roles for SQSTM1/p62 in the oxidative stress-induced Keap1/Nrf2 pathway and in caspase-mediated apoptosis that were recently reported are potentially relevant to the pathogenesis of PDB. Thus, SQSTM1/p62 may serve as a molecular link or switch between autophagy, apoptosis, and cell survival signaling. The purpose of this review is to outline recent advances in understanding of the multiple pathophysiological roles of SQSTM1/p62 protein, with particular emphasis on their relationship to PDB, including challenges associated with translating SQSTM1/p62 research into clinical diagnosis and treatment.

Paget's Disease of Bone: A Review of Epidemiology, Pathophysiology and Management

Paget's disease of bone is a common disorder which may affect one or many bones. Although many patients are asymptomatic, a variety of symptoms and complications may occur. Fortunately, effective pharmacologic therapy, primarily with potent bisphosphonates, is now available to treat patients with complications or symptoms. This review of Paget's disease of bone will include epidemiology and pathophysiology, complications and clinical findings, indications for treatment, and the drugs currently available to treat this condition.

Pathogenesis of Paget disease of bone

Paget disease of bone (PDB) is a common disease characterized by focal areas of increased and disorganized bone turnover. Some patients are asymptomatic, whereas others develop complications such as pain, osteoarthritis, fracture, deformity, deafness, and nerve compression syndromes. PDB is primarily caused by dysregulation of osteoclast differentiation and function, and there is increasing evidence that this is due, in part, to genetic factors. One of the most important predisposing genes is SQSTM1, which harbors mutations that cause osteoclast activation in 5-20 % of PDB patients. Seven additional susceptibility loci for PDB have been identified by genomewide association studies on chromosomes 1p13, 7q33, 8q22, 10p13, 14q32, 15q24, and 18q21. Although the causal variants remain to be discovered, three of these loci contain CSF1, TNFRSF11A, and TM7SF4, genes that are known to play a critical role in osteoclast differentiation and function. Environmental factors are also important in the pathogenesis of PDB, as reflected by the fact that in many countries the disease has become less common and less severe over recent years. The most widely studied environmental trigger is paramyxovirus infection, but attempts to detect viral transcripts in tissues from patients with PDB have yielded mixed results. Although our understanding of the pathophysiology of PDB has advanced tremendously over the past 10 years, many questions remain unanswered, such as the mechanisms responsible for the focal nature of the disease and the recent changes in prevalence and severity.

Measles virus, immune control, and persistence

Measles remains one of the most important causes of child morbidity and mortality worldwide with the greatest burden in the youngest children. Most acute measles deaths are owing to secondary infections that result from a poorly understood measles-induced suppression of immune responses. Young children are also vulnerable to late development of subacute sclerosing panencephalitis, a progressive, uniformly fatal neurologic disease caused by persistent measles virus (MeV) infection. During acute infection, the rash marks the appearance of the adaptive immune response and CD8(+) T cell-mediated clearance of infectious virus. However, after clearance of infectious virus, MeV RNA persists and can be detected in blood, respiratory secretions, urine, and lymphoid tissue for many weeks to months. This prolonged period of virus clearance may help to explain measles immunosuppression and the development of lifelong immunity to re-infection, as well as occasional infection of the nervous system. Once MeV infects neurons, the virus can spread trans-synaptically and the envelope proteins needed to form infectious virus are unnecessary, accumulate mutations, and can establish persistent infection. Identification of the immune mechanisms required for the clearance of MeV RNA from multiple sites will enlighten our understanding of the development of disease owing to persistent infection.

No evidence for an association between persistent measles virus infection and otosclerosis among patients with otosclerosis in Japan

Otosclerosis, which is characterized by disordered bone remodeling, occurs exclusively in the human temporal bone. The etiology of the disease is unknown, but a popular hypothesis is that it is caused by persistent measles virus (MV) infection. Paramyxovirus-like filamentous structures were found in otosclerotic lesions of stapes footplates from patients with otosclerosis. Although MV RNAs have been detected in otosclerotic samples by using reverse transcription-PCR, no complete MV mRNA sequence has been reported, nor has infectious virus been isolated from clinical samples. Furthermore, one study failed to obtain evidence of MV infection in otosclerotic bone samples. In this study, we tested, by three different protocols, for the presence of MV in clinical samples from patients with otosclerosis in Japan. We used a highly sensitive reverse transcription-quantitative PCR method which is able to detect viral mRNA in cells infected with MV at around one infectious unit per well. We obtained no evidence of MV infection in bone samples, primary cell cultures derived from stapes bones, or MV-susceptible cell lines (Vero/hSLAM and II-18 cells) cocultured with bone samples or primary cell cultures derived from them. Thus, our results do not support the hypothesis that persistent MV infection is involved in the pathoetiology of otosclerosis.

Mutant p62P392L stimulation of osteoclast differentiation in Paget's disease of bone

Paget's disease of the bone (PDB) is an autosomal dominant trait with genetic heterogeneity, characterized by abnormal osteoclastogenesis. Sequestosome 1 (p62) is a scaffold protein that plays an important role in receptor activator of nuclear factor κB (RANK) signaling essential for osteoclast (OCL) differentiation. p62P392L mutation in the ubiquitin-associated (UBA) domain is widely associated with PDB; however, the mechanisms by which p62P392L stimulate OCL differentiation in PDB are not completely understood. Deubiquitinating enzyme cylindromatosis (CYLD) has been shown to negatively regulate RANK ligand-RANK signaling essential for OCL differentiation. Here, we report that CYLD binds with the p62 wild-type (p62WT), non-UBA mutant (p62A381V) but not with the UBA mutant (p62P392L) in OCL progenitor cells. Also, p62P392L induces expression of c-Fos (2.8-fold) and nuclear factor of activated T cells c1 (6.0-fold) transcription factors critical for OCL differentiation. Furthermore, p62P392L expression results in accumulation of polyubiquitinated TNF receptor-associated factor (TRAF)6 and elevated levels of phospho-IκB during OCL differentiation. Retroviral transduction of p62P392L/CYLD short hairpin RNA significantly increased TRAP positive multinucleated OCL formation/bone resorption activity in mouse bone marrow cultures. Thus, the p62P392L mutation abolished CYLD interaction and enhanced OCL development/bone resorption activity in PDB.

Emerging strategies and therapies for treatment of Paget's disease of bone

Paget's disease of bone (PDB) is a progressive monostotic or polyostotic metabolic bone disease characterized by focal abnormal bone remodeling, with increased bone resorption and excessive, disorganized, new bone formation. PDB rarely occurs before middle age, and it is the second most frequent metabolic bone disorder after osteoporosis, affecting up to 3% of adults over 55 years of age. One of the most striking and intriguing clinical features is the focal nature of the disorder, in that once the disease is established within a bone, there is only local spread within that bone and no systemic dissemination. Despite many years of intense research, the etiology of PDB has still to be conclusively determined. Based on a detailed review of genetic and viral factors incriminated in PDB, we propose a unifying hypothesis from which we can suggest emerging strategies and therapies. PDB results in weakened bone strength and abnormal bone architecture, leading to pain, deformity or, depending on the bone involved, fracture in the affected bone. The diagnostic assessment includes serum total alkaline phosphatase, total body bone scintigraphy, skull and enlarged view pelvis x-rays, and if needed, additional x-rays. The ideal therapeutic option would eliminate bone pain, normalize serum total alkaline phosphatase with prolonged remission, heal radiographic osteolytic lesions, restore normal lamellar bone, and prevent recurrence and complications. With the development of increasingly potent bisphosphonates, culminating in the introduction of a single intravenous infusion of zoledronic acid 5 mg, these goals of treatment are close to being achieved, together with long-term remission in almost all patients. Based on the recent pathophysiological findings, emerging strategies and therapies are reviewed: ie, pulse treatment with zoledronic acid; denosumab, a fully human monoclonal antibody directed against RANK ligand; tocilizumab, an interleukin-6 receptor inhibitor; odanacatib, a cathepsin K inhibitor; and proteasome and Dickkopf-1 inhibitors.

Genetic variation in the TNFRSF11A gene encoding RANK is associated with susceptibility to Paget's disease of bone

RANK (receptor activator of nuclear factor-κB), encoded by TNFRSF11A, is a key protein in osteoclastogenesis. TNFRSF11A mutations cause Paget's disease of bone (PDB)-like diseases (ie, familial expansile osteolysis, expansile skeletal hyperphosphatasia, and early-onset PDB) and an osteoclast-poor form of osteopetrosis. However, no TNFRSF11A mutations have been found in classic PDB, neither in familial nor in isolated cases. To investigate the possible relationship between TNFRSF11A polymorphisms and sporadic PDB, we conducted an association study including 32 single-nucleotide polymorphisms (SNPs) in 196 Belgian sporadic PDB patients and 212 control individuals. Thirteen SNPs and 3 multimarker tests (MMTs) turned out to have a p value of between .036 and 3.17 × 10(-4) , with the major effect coming from females. Moreover, 6 SNPs and 1 MMT withstood the Bonferroni correction (p < .002). Replication studies were performed for 2 nonsynonymous SNPs (rs35211496 and rs1805034) in a Dutch and a British cohort. Interestingly, both SNPs resulted in p values ranging from .013 to 8.38 × 10(-5) in both populations. Meta-analysis over three populations resulted in p = .002 for rs35211496 and p = 1.27 × 10(-8) for rs1805034, again mainly coming from the female subgroups. In an attempt to identify the underlying causative SNP, we performed functional studies for the coding SNPs as well as resequencing efforts of a 31-kb region harboring a risk haplotype within the Belgian females. However, neither approach resulted in significant evidence for the causality of any of the tested genetic variants. Therefore, further studies are needed to identify the real cause of the increased risk to develop PDB shown to be present within TNFRSF11A.

Genetic aspects of the Paget's disease of bone: concerns on the introduction of DNA-based tests in the clinical practice. Advantages and disadvantages of its application

BACKGROUND

A large amount of genetic studies have clearly demonstrated the existence of a genetic susceptibility to Paget's disease of bone (PDB). Although the disease is genetically heterogeneous, the SQSTM1/p62 gene, encoding a protein with a pathophysiological role in both osteoclast differentiation and activity, has been found worldwide to harbour germline mutations in most of the PDB patients from geographically distant populations originating from different areas of Europe, both in sporadic and familial cases.

MATERIALS AND METHODS

Thus, SQSTM1/p62 gene mutations may confer an increased lifetime risk of developing PDB.

RESULTS

Several different genotype-phenotype analyses have shown a high penetrance for such mutations. These results suggest the opportunity to perform genetic testing in affected individuals and then, after the identification of a SQSTM1/p62 gene germline mutation, in their relatives as a real and concrete strategy to increase the diagnostic sensitivity in most of the asymptomatic mutant carriers. However, it is of note to underlie that an incomplete penetrance for SQSTM1/p62 gene mutations has also been reported.

CONCLUSIONS

In light of all these contradictory evidences, a review on whether, when and why apply the DNA test to those subjects, its interpretation and clinical application is necessary. In fact, a growing number of preventive care options are now available to affected patients and families and the process of systematically assessing risk is becoming increasingly important for both patients and physicians.

Paget's disease of bone

Paget's disease of bone is a focal bone disorder that is common among older people of Western European descent. It is an unusual disorder, for although we now have safe and highly effective treatment, there are many aspects of its pathogenesis and natural history that we do not yet understand. Recent years have seen significant advances in the understanding of its epidemiology, genetics and molecular biology, but an integrated view that incorporates all these aspects remains elusive. In this review we examine some of the outstanding problems, the solutions to which seem likely to change our understanding of bone cell biology.

Absence of somatic SQSTM1 mutations in Paget's disease of bone

BACKGROUND

Paget's disease is a common focal bone disorder that appears to be caused by a combination of genetic and environmental factors. Mutations in the SQSTM1 gene are found in about one third of families with Paget's disease and 8% of sporadic cases. Other potential loci linked to the disease have also been identified, and a number of environmental factors have been suggested to be involved in the disease. However, the focal nature of Paget's is still unexplained. Therefore, we examined the possibility that somatic mutations in the SQSTM1 gene are present in the local lesions, using RNA collected from primary osteoblast and bone marrow cell cultures of patients with this condition.

METHODS

SQSTM1 was sequenced, and allelic discrimination for the common P392L mutation was performed in cDNA samples from 14 osteoblast cultures and from 14 cultures of bone marrow cells.

RESULTS

In these 28 samples drawn from 23 patients, the wild-type sequence of SQSTM1 was found in all but one marrow sample, which was heterozygous for the P392L mutation. DNA from peripheral blood in this subject had an identical sequence of SQSTM1, indicating that this was a germline mutation.

CONCLUSION

We conclude that somatic mutations for SQSTM1 are not commonly present in Paget's disease.

Pathogenesis of Paget's disease of bone

Paget's disease of bone is a common condition characterised by increased and disorganised bone turnover which can affect one or several bones throughout the skeleton. These abnormalities disrupt normal bone architecture and lead to various complications such as bone pain osteoarthritis, pathological fracture, bone deformity, deafness, and nerve compression syndromes. Genetic factors play an important role in PDB and mutations or polymorphisms have been identified in four genes that cause classical Paget's disease and related syndromes. These include TNFRSF11A, which encodes RANK, TNFRSF11B which encodes osteoprotegerin, VCP which encodes p97, and SQSTM1 which encodes p62. All of these genes play a role in the RANK-NFkappaB signalling pathway and it is likely that the mutations predispose to PDB by disrupting normal signalling, leading to osteoclast activation. Although Paget's has traditionally be considered a disease of the osteoclast there is evidence that stromal cell function and osteoblast function are also abnormal, which might account for the fact that the disease is associated with increased bone formation as well as resorption. Environmental factors also contribute to Paget's disease. Most research has focused on paramyxovirus infection as a possible environmental trigger but evidence in favour of the involvement of viruses in the disease remains conflicting. Other factors which have been implicated as possible disease triggers include mechanical loading, dietary calcium and environmental toxins. Further work will be required to identify additional genetic variants that predispose to Paget's disease and to determine how the causal mutations and predisposing polymorphisms interact with environmental factors to influence bone cell function and cause the focal bone lesions that are characteristic of the disease.

A SQSTM1/p62 mutation linked to Paget's disease increases the osteoclastogenic potential of the bone microenvironment

Paget's disease of bone (PDB) is the second most common bone disease and is characterized by focal bone lesions which contain large numbers of abnormal osteoclasts (OCLs) and very active normal osteoblasts in a highly osteoclastogenic marrow microenvironment. The etiology of PDB is not well understood and both environmental and genetic causes have been implicated in its pathogenesis. Mutations in the SQSTM1/p62 gene have been identified in up to 30% of Paget's patients. To determine if p62 mutation is sufficient to induce PDB, we generated mice harboring a mutation causing a P-to-L (proline-to-leucine) substitution at residue 394 (the murine equivalent of human p62(P392L), the most common PDB-associated mutation). Bone marrow cultures from p62(P394L) mice formed increased numbers of OCLs in response to receptor activator of NF-kappaB ligand (RANKL), tumor necrosis factor alpha (TNF-alpha) or 1alpha,25-(OH)(2)D(3), similar to PDB patients. However, purified p62(P394L) OCL precursors depleted of stromal cells were no longer hyper-responsive to 1alpha,25-(OH)(2)D(3), suggesting effects of the p62(P394L) mutation on the marrow microenvironment in addition to direct effects on OCLs. Co-cultures of purified p62(P394L) stromal cells with either wild-type (WT) or p62(P394L) OCL precursors formed more OCLs than co-cultures containing WT stromal cells due to increased RANKL production by the mutant stromal cells. However, despite the enhanced osteoclastogenic potential of both OCL precursors and marrow stromal cells, the p62(P394L) mice had histologically normal bones. These results indicate that this PDB-associated p62 mutation is not sufficient to induce PDB and suggest that additional factors acting together with p62 mutation are necessary for the development of PDB in vivo.

Paget disease of bone

Despite significant advances in management, Paget disease remains an enigmatic disorder. There are no animal models, and while its end result --a focal disorder of accelerated bone turnover--is easily recognized, the causes and evolution of the disorder remain uncertain. Recent evidence strongly implicates both genetic and environmental factors in its etiology. The authors consider some of the unresolved questions surrounding Paget disease, including the attenuating prevalence and severity of the disease; how these observations might be reconciled with an apparently highly penetrant genetic susceptibility; what the putative environmental triggers of Paget disease might be; and what relapse after treatment tells us. Most observations seem to fit best with the idea that Paget disease behaves as a multifocal benign neoplasm.

Failure to detect measles virus ribonucleic acid in bone cells from patients with Paget's disease

BACKGROUND

Paget's disease is a condition of focal accelerated bone turnover. Electron-microscopy investigations of osteoclasts from pagetic lesions have identified nuclear inclusion bodies that have a similar appearance to viral nucleocapsid particles. Subsequently, RNA from several paramyxoviruses has been detected in pagetic tissue, and it was suggested that these viruses, in particular measles, might play a role in the etiology of Paget's disease. We have tested for measles virus sequences in osteoblasts and bone marrow cells collected from pagetic lesions and healthy bone.

METHODS

Bone and bone marrow samples were taken from Paget's patients and control subjects, and cells were cultured from each of these tissues. RNA was extracted from 13 osteoblast cultures and 13 cultures of bone marrow cells derived from pagetic lesions, and from 26 and 23 control osteoblast and bone marrow cultures, respectively. These samples were sourced from 22 patients with Paget's disease and 31 controls. RT-PCR-nested PCR amplification was used for the detection of the genes for the measles nucleocapsid and matrix proteins.

RESULTS

Measles virus sequences were not detected in any of the pagetic or control samples. However, measles virus sequences were identified in samples of a measles virus culture isolate included as a positive control, and in a brain sample from a patient with subacute sclerosing panencephalitis, a condition associated with chronic measles infection.

CONCLUSION

The results of the study do not support the hypothesis that measles virus plays a role in the pathogenesis of Paget's disease.

Interferons and viruses: an interplay between induction, signalling, antiviral responses and virus countermeasures

The interferon (IFN) system is an extremely powerful antiviral response that is capable of controlling most, if not all, virus infections in the absence of adaptive immunity. However, viruses can still replicate and cause disease in vivo, because they have some strategy for at least partially circumventing the IFN response. We reviewed this topic in 2000 [Goodbourn, S., Didcock, L. & Randall, R. E. (2000). J Gen Virol 81, 2341-2364] but, since then, a great deal has been discovered about the molecular mechanisms of the IFN response and how different viruses circumvent it. This information is of fundamental interest, but may also have practical application in the design and manufacture of attenuated virus vaccines and the development of novel antiviral drugs. In the first part of this review, we describe how viruses activate the IFN system, how IFNs induce transcription of their target genes and the mechanism of action of IFN-induced proteins with antiviral action. In the second part, we describe how viruses circumvent the IFN response. Here, we reflect upon possible consequences for both the virus and host of the different strategies that viruses have evolved and discuss whether certain viruses have exploited the IFN response to modulate their life cycle (e.g. to establish and maintain persistent/latent infections), whether perturbation of the IFN response by persistent infections can lead to chronic disease, and the importance of the IFN system as a species barrier to virus infections. Lastly, we briefly describe applied aspects that arise from an increase in our knowledge in this area, including vaccine design and manufacture, the development of novel antiviral drugs and the use of IFN-sensitive oncolytic viruses in the treatment of cancer.

Atypical Paget's Disease With Quantitative Assessment of Tracer Kinetics

INTRODUCTION

Paget's disease of bone is characterized by alterations in skeletal metabolism, affecting a single or multiple bones. Paget's is usually confined to an individual bone and typically does not spread or extend across joints. A patient with an unusual pattern of disease is presented together with quantitative assessment of the tracer kinetics pre- and posttreatment.

MATERIAL AND METHODS

A 75-year-old lady patient presented to her general practitioner in May 2002 with a history of lethargy. Clinical examination was unremarkable and further investigations such as blood tests (alkaline phosphatase levels), Tc-99m MDP bone scan, biopsy, and CT scan were carried out.

RESULTS

Alkaline phosphatase levels were greater than 2000 IU/L (Normal: 31-116 IU/L). The Tc-99m MDP bone scan showed strikingly increased uptake in the central skeleton involving the thoracic vertebrae and the adjoining ribs. The bone biopsy was inconclusive. CT scan revealed symmetrical expansion of the ribs with bridging osteophytes across the ribs and spine. The patient was treated with risedronate and quantitative analysis of the pre- and posttherapy bone scans showed reduced plasma clearance in the pagetic bones.

CONCLUSIONS

This case illustrates an unusual distribution of bone lesions in Paget's disease, which we think could be due to the result of degenerative disease leading to bridging and allowing direct extension of disease from one bone to another.

The molecular pathogenesis of Paget disease of bone

Paget disease of bone (PDB) is a condition characterised by increased bone remodelling at discrete lesions throughout the skeleton. The primary cellular abnormality in PDB involves a net increase in the activity of bone-resorbing osteoclasts, with a secondary increase in bone-forming osteoblast activity. Genetic factors are known to play an important role, with mutations affecting different components of the RANK–NF-κB signalling pathway having been identified in patients with PDB and related disorders. Whilst the disease mechanism in these cases is likely to involve aberrant RANK-mediated osteoclast NF-κB signalling, the precise relationship between other potential contributors, such as viruses and environmental factors, and the molecular pathogenesis of PDB is less clear. This review considers the roles of these different factors in PDB, and concludes that a fuller understanding of their contributions to disease aetiology is likely to be central to future advances in the clinical management of this debilitating skeletal disorder.

Multicenter blinded analysis of RT-PCR detection methods for paramyxoviruses in relation to Paget's disease of bone

Conflicting results have been reported on the detection of paramyxovirus transcripts in Paget's disease, and a possible explanation is differences in the sensitivity of RT-PCR methods for detecting virus. In a blinded study, we found no evidence to suggest that laboratories that failed to detect viral transcripts had less sensitive RT-PCR assays, and we did not detect measles or distemper transcripts in Paget's samples using the most sensitive assays evaluated.

INTRODUCTION

There is conflicting evidence on the possible role of persistent paramyxovirus infection in Paget's disease of bone (PDB). Some workers have detected measles virus (MV) or canine distemper virus (CDV) transcripts in cells and tissues from patients with PDB, but others have failed to confirm this finding. A possible explanation might be differences in the sensitivity of RT-PCR methods for detecting virus. Here we performed a blinded comparison of the sensitivity of different RT-PCR-based techniques for MV and CDV detection in different laboratories and used the most sensitive assays to screen for evidence of viral transcripts in bone and blood samples derived from patients with PDB.

MATERIALS AND METHODS

Participating laboratories analyzed samples spiked with known amounts of MV and CDV transcripts and control samples that did not contain viral nucleic acids. All analyses were performed on a blinded basis.

RESULTS

The limit of detection for CDV was 1000 viral transcripts in three laboratories (Aberdeen, Belfast, and Liverpool) and 10,000 transcripts in another laboratory (Manchester). The limit of detection for MV was 16 transcripts in one laboratory (NIBSC), 1000 transcripts in two laboratories (Aberdeen and Belfast), and 10,000 transcripts in two laboratories (Liverpool and Manchester). An assay previously used by a U.S.-based group to detect MV transcripts in PDB had a sensitivity of 1000 transcripts. One laboratory (Manchester) detected CDV transcripts in a negative control and in two samples that had been spiked with MV. None of the other laboratories had false-positive results for MV or CDV, and no evidence of viral transcripts was found on analysis of 12 PDB samples using the most sensitive RT-PCR assays for MV and CDV.

CONCLUSIONS

We found that RT-PCR assays used by different laboratories differed in their sensitivity to detect CDV and MV transcripts but found no evidence to suggest that laboratories that previously failed to detect viral transcripts had less sensitive RT-PCR assays than those that detected viral transcripts. False-positive results were observed with one laboratory, and we failed to detect paramyxovirus transcripts in PDB samples using the most sensitive assays evaluated. Our results show that failure of some laboratories to detect viral transcripts is unlikely to be caused by problems with assay sensitivity and highlight the fact that contamination can be an issue when searching for pathogens by sensitive RT-PCR-based techniques.

Differential gene expression in cultured osteoblasts and bone marrow stromal cells from patients with Paget's disease of bone

Paget's disease is a focal condition of bone. To study changes in cells within pagetic lesions, we cultured osteoblasts and stromal cells from 22 patients and compared gene expression in these cells to cells from healthy bone. We identified several differentially regulated genes, and we suggest that these changes could lead to the formation of the lesions.

INTRODUCTION

Paget's disease is a focal condition of bone of unknown cause. Although it is regarded as primarily an osteoclast disorder, the tight coupling of the activity of osteoclasts and osteoblasts suggests that the osteoblast could play a key role in its pathogenesis. The aim of the study was to identify possible changes in pagetic osteoblasts and stromal cells that might contribute to the development of pagetic lesions.

MATERIALS AND METHODS

Candidate genes were identified based on known bone cell regulators, supplemented with microarray analysis. Gene expression was determined by real-time PCR in primary cultures of osteoblasts and bone marrow stromal cells from pagetic patients and control subjects. Concentrations of secreted proteins were determined by ELISA.

RESULTS

Dickkopf1 mRNA and protein levels were increased in both pagetic osteoblast and stromal cell cultures, and interleukin (IL)-1 and IL-6 were overexpressed in pagetic osteoblasts. These changes parallel recent findings in myeloma bone disease, which shares some clinical similarities with Paget's disease. Alkaline phosphatase was overexpressed, and bone sialoprotein and osteocalcin were underexpressed in pagetic osteoblasts, consistent with their circulating levels in pagetic patients. It is hypothesized that overexpression of Dickkopf1, IL-1, and IL-6 would result in stimulation of osteoclast proliferation and inhibition of osteoblast growth, leading to the development of the characteristic lytic bone lesions. By stimulating osteoblast differentiation, Dickkopf1 and IL-6 may also promote mineralization, leading to the conversion of lytic lesions to sclerotic.

CONCLUSIONS

These findings suggest that dysregulated gene expression in pagetic osteoblasts could cause the changes in bone cell number and function characteristic of Paget's disease.

[Treatment of Paget's disease of bone: importance of the zoledronic acid]

Paget's disease is a localised monostotic or polyostotic bone disease of unknown origin. It may be caused by a slow viral infection and/or genetic factors. It is characterised by increased bone remodelling and an initially excessive osteoclastic bone resorption, followed by a secondary increase in osteoblastic activity, leading to replacement of the normal bone by a disorganized, enlarged, and weakened osseous structure prone to deformities and fractures. The disease may be diagnosed by radiography, scintigraphy and biochemical tests. The primary aim of treatment is to reduce pain and risk of developing long-term complications. Potent antiresorptive drugs are now available, which control the increased bone remodelling and have led to a dramatic improvement in treatment. Zoledronic acid, a new generation of bisphosphonates, has the advantage of great potency and long duration of remission and a short infusion time.

Experimental models of Paget's disease

We targeted the MVNP gene to the OCL lineage in transgenic mice. These mice developed abnormal OCLs and bone lesions similar to those found in Paget's patients. These results show that persistent expression of MVNP in OCLs can induce pagetic-like bone lesions in vivo.

INTRODUCTION

Paget's disease (PD) is one of the most exaggerated examples of abnormal bone remodeling, with increased bone resorption and excessive new bone formation. However, its etiology is unclear. A viral etiology for PD has been suggested based on the presence of paramyxoviral-like nuclear inclusions, detection of measles virus nucleocapsid (MVNP) mRNA or protein in osteoclasts (OCLs) from PD lesions, and in vitro studies showing that transfection of normal OCL precursors with the MVNP gene results in formation of OCLs that express a pagetic phenotype (increased numbers of OCLs; increased responsivity to 1,25(OH)(2)D(3), RANKL, and TNF-alpha; increased expression of the TAF(II)-17 gene, and increased bone resorption capacity).

MATERIALS AND METHODS

We targeted MVNP to cells in the OCL lineage in transgenic mice using the TRACP promoter.

RESULTS

Histomorphometric analysis showed that there was a 64% increase in OCL perimeter (p = 6.0002) and 37% increase in osteoblast (OBL) perimeter in MVNP mice. In a mouse that was 14 months of age, there was a 225% increase in OBL perimeter and 149% in OBL perimeter. This was accompanied by increased cancellous bone volume (83%) and trabecular width (47%) and number (25%), with a marked increase in the amount of woven bone. In contrast, cancellous bone volume decreased between 3 and 12 months in wildtype (WT) mice, whereas cancellous bone volume in MVNP mice increased over the same time period. Ex vivo studies showed that the numbers of OCLs formed in marrow cultures from MVNP mice were increased, and the OCLs were hyper-responsive to 1,25(OH)(2)D(3) and had an increased bone resorbing capacity compared with WT cultures.

CONCLUSION

These results show that expression of MVNP in OCL in vivo results in a bone phenotype that is characteristic of PD.

Identification and molecular characterization of a novel splice-site mutation (G1205C) in the SQSTM1 gene causing Paget's disease of bone in an extended American family

Paget's disease of bone (PDB) is a common late-onset bone disorder characterized by focal areas of abnormal bone remodeling. Positional cloning efforts resulted in the identification of seven genetic loci (PDB1-7) with putative involvement in the pathogenesis of PDB. Meanwhile, the PDB-causing gene from the PDB3 region on chromosome 5q35 has been identified as the SQSTM1 gene. All mutations identified in this gene so far are located in or close to the ubiquitin-associated (UBA) domain of the protein. In 2001, we reported genotyping results of genetic markers located in the PDB3 region in an extended American family, indicating the involvement of the PDB3 locus. Here, we report the identification of a novel mutation (G1205C) in the SQSTM1 gene in this family. The G1205C mutation is located in the splice donor site of intron 7 and reverse-transcription polymerase chain reaction experiments showed that the presence of the C allele results in the production of two abnormal mRNA transcripts. Translation of the first transcript would result in a protein that lacks amino acids 351-388, including 26 amino acids of the second PEST domain in addition to two amino acids of the UBA domain. The second mutant mRNA transcript could result in a truncated protein (390X) that lacks almost the complete UBA domain. PDB mutations that disrupt the function of the PEST domain of SQSTM1 have not been reported before, so probably the pathogenic effect of both transcripts resides in the disruption of the ubiquitin-binding properties of the protein.

Canine distemper virus induces human osteoclastogenesis through NF-kappaB and sequestosome 1/P62 activation

Previous studies have implicated CDV in the pathogenesis of Paget's disease; however, there has been no direct evidence that CDV can infect human cells. We studied the effects of CDV on osteoclastogenesis in vitro and showed that CDV had a dose-dependent effect on osteoclastogenesis, through a possible mechanism involving activation of NF-kappaB and sequestosome 1/p62.

INTRODUCTION

Paget's disease is characterized by a dramatic increase in size and number of osteoclasts. The etiology of the disorder is still unclear; however, evidence points to either a viral infection or a genetic susceptibility or a combination of both. Previously, we have shown that canine distemper virus (CDV) RNA is present in Pagetic bone. However, the effects of CDV on human osteoclast formation in vitro have not been studied previously.

MATERIALS AND METHODS

Replicate cultures (n = 5) of purified human osteoclast precursors were infected with increasing doses of CDV and cultured on dentine slices for 14 days. Osteoclasts were stained for TRACP, and the dentine slices were examined for evidence of resorption. Control cells were incubated in the absence of virus. In each case, 10 high-power microscopy fields were analyzed. Immunocytochemical analyses were performed for p65, Gab2, sequestosome 1/p62, and ubiquitin.

RESULTS

CDV dose-dependently increased osteoclast number and size (p < 0.0001, ANOVA), and there was a concomitant increase in resorption (p < 0.0001, ANOVA). CDV infection induced nuclear translocation of p65 and led to a dramatic increase in sequestosome 1/p62 and ubiquitin expression.

CONCLUSIONS

These results provide the first conclusive proof that CDV can infect and replicate in human osteoclast precursors, raising possible zoonotic implications for CDV. The increased osteoclastogenesis is accompanied by NF-kappaB and sequestosome 1/p62 activation. This study provides further evidence for the possible role of paramyxoviruses in the pathogenesis of Paget's disease.

Molecular detection of measles virus in primary cell cultures of otosclerotic tissue

CONCLUSION

Primary cell cultures were established from otosclerotic/otospongiotic footplate bone particles. Although this procedure is time-consuming, the quality and quantity of RNA isolated from these cells were much higher in comparison with the direct isolation of RNA from footplate bone samples and the preparation was more suitable for the detection of measles virus (MeV) RNA.

OBJECTIVE

Morphological and biochemical investigations suggest that persistent MeV infection participates in the development of otosclerotic foci. However, this hypothesis is controversial because the detection of MeV in otosclerotic foci is inconsistent since the results are dependent on the presence and stage of foci in the investigated bone particles. Unfortunately, this cannot be confirmed before investigation. To study the presence of the MeV by different techniques in otosclerotic foci, stapes footplate fragments were collected during stapedectomy from patients suffering from clinical otosclerosis.

MATERIALS AND METHODS

MeV-specific RT-PCR was performed on total RNA isolated directly from four fresh frozen footplate bone fragments and from the cells of 16 primary cultures of otosclerotic tissue samples. In order to rescue persisting MeV, the primary footplate cells were cocultured with MeV permissive B95a cells.

RESULTS

MeV was not detected in RNA from fresh frozen otosclerotic materials, but analysis of the RNA from 5 of the 16 primary cell cultures showed MeV-positive results. Nucleotide sequencing of a 317 bp MeV-specific RT-PCR fragment confirmed the presence of the MeV RNA genome. Here, we report the first determination of MeV sequences in total RNA isolated from primary cells cultured from otosclerotic tissue. Persisting MeV in primary footplate cells could not be recovered by coculturing with B95a cells.

Paget's disease of bone

Paget's disease of bone is a focal disorder of bone remodeling accompanied initially by an increase in bone resorption, followed by a disorganized and excessive formation of bone, leading to pain, fractures and deformities. It exhibits a marked geographical variation in its prevalence. In Brazil it predominantly affects persons of European descent. The majority of the reported cases of the disease in Brazil are from Recife, owing to its peculiar mixed European colonization over approximately four centuries. The etiology is complex and involves both genetic and environmental factors. The disease is often asymptomatic and diagnosis is usually based on biochemical markers of bone turnover, radionuclide bone scan and radiological examination. Bisphosphonates, in particular zoledronic acid, are regarded as the treatment of choice for Paget's disease of bone.

Expression of measles virus nucleocapsid protein in osteoclasts induces Paget's disease-like bone lesions in mice

We targeted the MVNP gene to the OCL lineage in transgenic mice. These mice developed abnormal OCLs and bone lesions similar to those found in Paget's patients. These results show that persistent expression of MVNP in OCLs can induce pagetic-like bone lesions in vivo.

INTRODUCTION

Paget's disease (PD) of bone is the second most common bone disease. Both genetic and viral factors have been implicated in its pathogenesis, but their exact roles in vivo are unclear. We previously reported that transfection of normal human osteoclast (OCL) precursors with the measles virus nucleocapsid (MVNP) or measles virus (MV) infection of bone marrow cells from transgenic mice expressing a MV receptor results in formation of pagetic-like OCLs.

MATERIALS AND METHODS

Based on these in vitro studies, we determined if the MVNP gene from either an Edmonston-related strain of MV or a MVNP gene sequence derived from a patient with PD (P-MVNP), when targeted to cells in the OCL lineage of transgenic mice with the TRACP promoter (TRACP/MVNP mice), induced changes in bone similar to those found in PD.

RESULTS

Bone marrow culture studies and histomorphometric analysis of bones from these mice showed that their OCLs displayed many of the features of pagetic OCLs and that they developed bone lesions that were similar to those in patients with PD. Furthermore, IL-6 seemed to be required for the development of the pagetic phenotype in OCLs from TRACP/MVNP mice.

CONCLUSIONS

These results show that persistent expression of the MVNP gene in cells of the OCL lineage can induce pagetic-like bone lesions in vivo.

Role of RANKL in physiological and pathological bone resorption and therapeutics targeting the RANKL-RANK signaling system

Osteoclasts are primary cells for physiological and pathological bone resorption, and receptor activator of nuclear factor-kappaB ligand (RANKL) is critically involved in the differentiation, activation, and survival of these cells. Recently, therapeutics for pathological bone destruction targeting RANKL pathways has attracted a great deal of attention. Herein, we review the recent advances in the research on osteoclast biology and discuss the advantages and disadvantages of anti-RANKL therapies.

The role of immune cells and inflammatory cytokines in Paget's disease and multiple myeloma

The osteoclast (OCL) is the primary cell involved in the pathogenesis of Paget's disease (PD) and the destructive bone process in multiple myeloma (MM). Both of these diseases are characterized by increased numbers of OCLs actively resorbing bone, but they differ in that bone formation is greatly increased in PD and is suppressed in MM. The marrow microenvironment plays a critical role in both disease processes, through the increased expression of inflammatory cytokines that enhance osteoclastogenesis and, in the case of MM, also suppress osteoblast (OBL) activity. In addition, the OCLs in PD are intrinsically abnormal, are markedly increased in number and size, and are hyper-responsive to inflammatory cytokines and 1,25-(OH)2D3. This article discusses the role of immune cells and inflammatory cytokines and chemokines in the increased OCL activity in PD and MM bone disease, as well as the potential role of interleukin-3 in the suppression of OBL activity in MM.