A negative search for a paramyxoviral etiology of Paget's disease of bone: molecular, immunological, and ultrastructural studies in UK patients

Progressive Cheek Swelling in an Older Woman

An 87-year-old woman presents with sudden-onset worsening right facial swelling and pain and generalized maxillary alveolar hyperplasia. What is your diagnosis?

Osteocytes and Paget's Disease of Bone

PURPOSE OF REVIEW

To describe the contributions of osteocytes to the lesions in Paget's disease, which are characterized by locally overactive bone resorption and formation.

RECENT FINDINGS

Osteocytes, the most abundant cells in bone, are altered in Paget's disease lesions, displaying increased size, decreased canalicular length, incomplete differentiation, and less sclerostin expression compared to controls in both patients and mouse models. Pagetic lesions show increased senescent osteocytes that express RANK ligand, which drives osteoclastic bone resorption. Abnormal osteoclasts in Paget's disease secrete abundant IGF1, which enhances osteocyte senescence, contributing to lesion formation. Recent data suggest that osteocytes contribute to lesion formation in Paget's disease by responding to high local IGF1 released from abnormal osteoclasts. Here we describe the characteristics of osteocytes in Paget's disease and their role in bone lesion formation based on recent results with mouse models and supported by patient data.

[Paget's disease of bone: 1877-2023. Etiology, and management of a disease on epidemiologic transition]

Paget's disease of bone is characterized by the alteration, in one or several bone locations, of the equilibrium between bone formation and bone resorption. This imbalance results in a disorganized, widened bone, in many cases with increased bone density, although more fragile. A genetic predisposition for Paget's disease of bone could explain between 5% and 40% of the cases. Different environmental factors should explain the rest of the cases. Paget's disease of bone was classically considered the second most common metabolic bone disease. However, in recent decades there has been a marked decrease in both incidence and clinical severity. These changes have led to believe that the influence of some environmental factor may have diminished or even disappeared. This decrease in incidence should not be an excuse for abandoning Paget's disease of bone research, but rather it should be the reason to remain searching to try to understand better its pathogenesis.

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.

A Panel-Based Sequencing Analysis of Patients with Paget's Disease of Bone Suggests Enrichment of Rare Genetic Variation in regulators of NF-κB Signaling and Supports the Importance of the 7q33 Locus

Paget's disease of bone (PDB) is a common bone disorder characterized by focal lesions caused by increased bone turnover. Monogenic forms of PDB and PDB-related phenotypes as well as genome-wide association studies strongly support the involvement of genetic variation in components of the NF-κB signaling pathway in the pathogenesis of PDB. In this study, we performed a panel-based mutation screening of 52 genes. Single variant association testing and a series of gene-based association tests were performed. The former revealed a novel association with NFKBIA and further supports an involvement of variation in NR4A1, VCP, TNFRSF11A, and NUP205. The latter indicated a trend for enrichment of rare genetic variation in GAB2 and PRKCI. Both single variant tests and gene-based tests highlighted two genes, NR4A1 and NUP205. In conclusion, our findings support the involvement of genetic variation in modulators of NF-κB signaling in PDB and confirm the association of previously associated genes with the pathogenesis of PDB.

Paget's Disease of Bone: Osteoimmunology and Osteoclast Pathology

PURPOSE OF REVIEW

The purpose of this review is to recognize clinical features of Paget's disease of bone and to describe how the osteoclast, a myeloid-derived cell responsible for bone resorption, contributes to the disease.

RECENT FINDINGS

Recent studies have identified several variants in SQSTM1, OPTN, and other genes that may predispose individuals to Paget's disease of bone; studies of these genes and their protein products have elucidated new roles for these proteins in bone physiology. Understanding the pathologic mechanisms in the Pagetic osteoclast may lead to the identification of future treatment targets for other inflammatory and autoimmune diseases characterized by abnormal bone erosion and/or osteoclast activation.

Bisphosphonates in the management of Paget's disease

The first clinical use of bisphosphonates was in Paget's disease of bone (PDB) when disodium etidronate was found to be effective at suppressing metabolic activity of the disease. Subsequently, PDB became a testing ground for many bisphosphonates using changes in alkaline phosphatase (ALP) as the primary outcome measure in clinical trials. Bisphosphonates are now considered to be the treatment of choice for PDB since they are highly effective at suppressing the elevations in bone turnover that are characteristic of the disease. Short term studies have shown that treatment with alendronate and risedronate can promote formation of lamellar bone in affected sites and improve x-ray appearances in some patients. Bisphosphonates have also been shown to improve bone pain in PDB and within the bisphosphonates, zoledronic acid (ZA) is most likely to give a favourable pain response. Many patients with PDB do not have pain however, even when there is increased metabolic activity and more research is needed to find out why this is the case. The effects of bisphosphonates on complications of PDB such as deformity, pathological fractures and deafness have not been adequately studied since most clinical trials have been short term and have not collected information on these important outcomes. The PRISM and PRISM-EZ studies investigated the long-term effects of bisphosphonates in patients with established PDB using a treat-to-target approach and showed that intensive bisphosphonate therapy aimed at normalising ALP was no more effective than symptom directed treatment with bisphosphonates at preventing complications of PDB. The Zoledronate in the Prevention of Paget's Disease (ZiPP) trial, which is currently in progress, seeks to determine whether early intervention with this potent bisphosphonate might be effective in preventing disease progression. Should the ZiPP study yield positive results, genetic testing coupled to prophylactic bisphosphonate therapy might represent a new indication for these highly effective inhibitors of bone resorption in future years.

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.

A mutation in p62 protein (p. R321C), associated to Paget's disease of bone, causes a blockade of autophagy and an activation of NF-kB pathway

Paget's disease of bone (PDB) is a bone disorder characterized by an increase in bone turnover in a disorganized way with a large increase in bone resorption followed by bone formation. The most important known genetic factor predisposing to PDB is mutation in Sequestosome1 (SQSTM1) gene. We have studied the prevalence of SQSTM1 mutations and examined genotype-phenotype correlations in a Spanish cohort of PDB patients. Also, we have characterized three PDB patients that carry the c.961C>T SQSTM1 gene mutation that it is localized in exon 6 of SQSTM1 gene and it causes the p. R321C mutation. This mutation has been reported in patients with amyotrophic lateral sclerosis and frontotemporal dementia but in our knowledge this is the first time that p62 p. R321C mutation is associated to PDB. We show that p62 p.R321C mutation could induce blockage of autophagy and cell proliferation through NF-kB pathway. These results reinforce the hypothesis of autophagy involvement in Paget's disease of bone.

A Clinical Perspective on Advanced Developments in Bone Biopsy Assessment in Rare Bone Disorders

Introduction: Bone biopsies have been obtained for many centuries and are one of the oldest known medical procedures in history. Despite the introduction of new noninvasive radiographic imaging techniques and genetic analyses, bone biopsies are still valuable in the diagnosis of bone diseases. Advanced techniques for the assessment of bone quality in bone biopsies, which have emerged during the last decades, allows in-depth tissue analyses beyond structural changes visible in bone histology. In this review, we give an overview of the application and advantages of the advanced techniques for the analysis of bone biopsies in the clinical setting of various rare metabolic bone diseases. Method: A systematic literature search on rare metabolic bone diseases and analyzing techniques of bone biopsies was performed in PubMed up to 2019 week 34. Results: Advanced techniques for the analysis of bone biopsies were described for rare metabolic bone disorders including Paget's disease of bone, osteogenesis imperfecta, fibrous dysplasia, Fibrodysplasia ossificans progressiva, PLS3 X-linked osteoporosis, Loeys-Diets syndrome, osteopetrosis, Erdheim-Chester disease, and Cherubism. A variety of advanced available analytical techniques were identified that may help to provide additional detail on cellular, structural, and compositional characteristics in rare bone diseases complementing classical histopathology. Discussion: To date, these techniques have only been used in research and not in daily clinical practice. Clinical application of bone quality assessment techniques depends upon several aspects such as availability of the technique in hospitals, the existence of reference data, and a cooperative network of researchers and clinicians. The evaluation of rare metabolic bone disorders requires a repertoire of different methods, owing to their distinct bone tissue characteristics. The broader use of bone material obtained from biopsies could provide much more information about pathophysiology or treatment options and establish bone biopsies as a valuable tool in rare metabolic bone diseases.

Diagnosis and Management of Paget's Disease of Bone in Adults: A Clinical Guideline

An evidence-based clinical guideline for the diagnosis and management of Paget's disease of bone (PDB) was developed using GRADE methodology, by a Guideline Development Group (GDG) led by the Paget's Association (UK). A systematic review of diagnostic tests and pharmacological and nonpharmacological treatment options was conducted that sought to address several key questions of clinical relevance. Twelve recommendations and five conditional recommendations were made, but there was insufficient evidence to address eight of the questions posed. The following recommendations were identified as the most important: 1) Radionuclide bone scans, in addition to targeted radiographs, are recommended as a means of fully and accurately defining the extent of metabolically active disease in patients with PDB. 2) Serum total alkaline phosphatase (ALP) is recommended as a first-line biochemical screening test in combination with liver function tests in screening for the presence of metabolically active PDB. 3) Bisphosphonates are recommended for the treatment of bone pain associated with PDB. Zoledronic acid is recommended as the bisphosphonate most likely to give a favorable pain response. 4) Treatment aimed at improving symptoms is recommended over a treat-to-target strategy aimed at normalizing total ALP in PDB. 5) Total hip or knee replacements are recommended for patients with PDB who develop osteoarthritis in whom medical treatment is inadequate. There is insufficient information to recommend one type of surgical approach over another. The guideline was endorsed by the European Calcified Tissues Society, the International Osteoporosis Foundation, the American Society of Bone and Mineral Research, the Bone Research Society (UK), and the British Geriatric Society. The GDG noted that there had been a lack of research on patient-focused clinical outcomes in PDB and identified several areas where further research was needed. © 2019 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Antibody Response to Paramyxoviruses in Paget's Disease of Bone

Paget's disease of bone (PDB) is a common skeletal disorder characterised by focal abnormalities of increased and disorganised bone turnover. Genetic factors play a central role in the pathogenesis of PDB but environmental factors also contribute. Measles virus (MV), respiratory syncytial virus (RSV) and canine distemper virus (CDV) have all been implicated as potential disease triggers but the data are conflicting. Since chronic paramyxovirus infection with measles is known to be accompanied by increased production of antiviral antibodies, we have analysed circulating concentrations of antibodies to MV, CDV, and RSV as well as mumps, rubella and varicella zoster virus (VZV) in 463 patients with PDB and 220 aged and gender-matched controls. We also studied the relation between viral antibody concentrations and various markers of disease severity and extent in 460 PDB patients. A high proportion of cases and controls tested positive for antiviral antibodies but there was no significant difference in circulating antibody concentrations between PDB cases and controls for MV, CDV, RSV, rubella or VZV. However, mumps virus antibody levels were significantly higher in the PDB cases (mean ± SD = 3.1 ± 0.84 vs. 2.62 ± 0.86. p < 0.001). There was no association between disease severity and circulating antibody concentrations to any of the viruses. In conclusion, we found no evidence to suggest that PDB is associated with abnormalities of immune response to measles or other paramyxoviruses, although there was evidence of a greater antibody response to mumps. The results do not support that hypothesis that PDB is associated with a persistent infection with measles or other paramyxoviruses.

Epidemiology and pathology of Paget's disease of bone - a review

Paget's disease of bone (PDB) is a noninflammatory, metabolic, skeletal disorder characterized by localized excessive osteoclastic bone resorption that is followed by compensatory increased osteoblastic activity leading to unstructured, fibroblastic, and biomechanically unstable bone. As a result, there is deformity and enlargement of the bone with a defective and disorganized pattern. Here, we review the epidemiology, etiology, pathology, macrostructure, histology, and quantitative histomorphometry findings of PDB. Hyperosteoclastosis and poor definition of the boundary between cortical and medullary bone are the main histological findings in PDB. Additionally, Pagetic bone is also characterized by hypertrophy and alteration of trabecular parameters.

Clinical and Genetic Advances in Paget's Disease of Bone: a Review

Paget’s disease of bone (PDB) is the second most common metabolic bone disorder, after osteoporosis. It is characterised by focal areas of increased and disorganised bone turnover, coupled with increased bone formation. This disease usually appears in the late stages of life, being slightly more frequent in men than in women. It has been reported worldwide, but primarily affects individuals of British descent. Majority of PDB patients are asymptomatic, but clinical manifestations include pain, bone deformity and complications, like pathological fractures and deafness. The causes of the disease are poorly understood and it is considered as a complex trait, combining genetic predisposition with environmental factors. Linkage analysis identified SQSTM1, at chromosome 5q35, as directly related to the disease. A number of mutations in this gene have been reported, pP392L being the most common variant among different populations. Most of these variants affect the ubiquitin-associated (UBA) domain of the protein, which is involved in autophagy processes. Genome-wide association studies enlarged the number of loci associated with PDB, and further fine-mapping studies, combined with functional analysis, identified OPTN and RIN3 as causal genes for Paget’s disease. A combination of risk alleles identified by genome-wide association studies led to the development of a score to predict disease severity, which could improve the management of the disease. Further studies need to be conducted to elucidate other important aspects of the trait, such as its focal nature and the epidemiological changes found in some populations. In this review, we summarize the clinical characteristics of the disease and the latest genetic advances to identify susceptibility genes. We also list current available treatments and prospective options.

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.

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.

Polymorphisms in autophagy genes are associated with paget disease of bone

Paget disease of bone (PDB) is a focal bone disorder affecting the skeleton segmentally. The main alteration resides in osteoclasts that increase in size, number and activity. Many osteoclasts have cytoplasmic inclusions that have been associated with protein aggregates, increasing the evidences of a possible deregulation of autophagy in the development of the PDB. Autophagy starts with encapsulation of the target into a double-membrane-bound structure called an “autophagosome.” It has been reported that at least 18 ATG genes (autophagy-related genes) are involved in autophagosome formation. We have studied the distribution of genotypes of the ATG2B rs3759601, ATG16L1 rs2241880, ATG10 rs1864183 and ATG5 rs2245214 polymorphisms in a Spanish cohort of subjects with PDB and compared with healthy subjects. Our results show that being a carrier of the C allele of the ATG16L1 rs2241880 and the G allele of ATG5 rs2245214 polymorphisms were associated with an increased risk of developing PDB, whereas being a carrier of the T allele of ATG10 rs1864183 polymorphism decreased the risk of suffering the disease in our series. This is the first report that shows an association between autophagy and Paget Disease of Bone and requires further confirmation in other series.

Paget's Disease of Bone among Various Ethnic Groups

Paget's disease of bone (PDB) is a relatively benign disease common among many European populations, including those in the UK, Italy and Spain. However, it appears to be rare among Scandinavians and non-European immigrants living in Europe. The prevalence among Asian populations may be underestimated because a large number of reported cases were discovered incidentally. There is a need for surveys addressing the prevalence rate and consequences of PDB to be carried out in various parts of the world, particularly Asia.

Current perspectives on bisphosphonate treatment in Paget's disease of bone

Paget's disease of bone is a chronic metabolic bone disease with focal increase in bone turnover. The exact etiology of the disease is uncertain, although genetic and environmental factors are believed to be important. Bisphosphonate is the main class of medication being used to control disease activity via its antiresorptive effect. This review discusses the controversies concerning the use of bisphosphonates in the treatment of Paget's disease of bone, the efficacy of different bisphosphonates in controlling disease activity, and the possible rare side effects of bisphosphonates. Symptoms are the main indication for treatment in Paget's disease of bone. As treatment benefits in asymptomatic individuals remain controversial and nonevidence based, the decision to treat these patients should be individualized to their risk and benefit profiles. There are several trials conducted to evaluate and compare the efficacy of different regimes of bisphosphonates for treating Paget's disease of bone. Most trials used biochemical markers rather than clinical symptoms or outcomes as parameters for comparison. Zoledronate is an attractive option as it can achieve high rates of biochemical remission and sustain long duration of suppression by a single dose. Atypical femoral fracture and osteonecrosis of the jaw are two rare and severe side effects reported, possibly related to the use of bisphosphonates in patients with osteoporosis and malignancy-induced hypercalcemia. As the regimes of bisphosphonates used for treating Paget's disease of bone are different from those two diseases, the risks of developing these two possible side effects are expected to be very low, although this remains unknown. Vitamin D and calcium supplement should be given to patients at risk of vitamin D insufficiency when given zoledronate, as symptomatic hypocalcemia may develop. For those intolerant of bisphosphonates, subcutaneous calcitonin can be used for a limited period due to its associated risk of malignancy.

Genetics of Paget's disease of bone

Paget's disease of bone (PDB) is a common condition, which is characterised by focal areas of increased and disorganized bone remodeling. Genetic factors play an important role in the disease. In some cases, Paget's disease is inherited in an autosomal dominant manner and the most common cause for this is a mutation in the SQSTM1 gene. Other familial cases have been linked to the OPTN locus on Chromosome 10p13 and still other variants have been identified by genome wide association studies that lie within or close to genes that play roles in osteoclast differentiation and function. Mutations in TNFRSF11A, TNFRSF11B and VCP have been identified in rare syndromes with PDB-like features. These advances have improved understanding of bone biology and the causes of PDB. The identification of genetic markers for PDB also raises the prospect that genetic profiling could identify patients at high risk of developing complications, permitting enhanced surveillance and early therapeutic intervention.

Republished: Paget's disease of bone: clinical review and update

Paget's disease (PD) is a focal disorder of bone remodelling that occurs commonly in older people. In this article, we review clinical aspects of PD with an emphasis on recent findings. The epidemiology of PD appears to be changing rapidly, with several groups in different parts of the world reporting a marked reduction in the prevalence and incidence of PD, as well as in the severity of disease seen by clinicians. These findings seem most likely to be caused by changes in exposure to unknown environmental factors that have a role in the development of PD. However, genetic factors are also important. Mutations in SQSTM1 occur in 25-50% of familial PD. Genotype-phenotype relationships are present, as PD develops at an earlier age and is more extensive and severe in those with SQSTM1 mutations, and these findings are more pronounced in those with truncating mutations. However, the prevalence of PD in adults with SQSTM1 mutations is uncertain, and it is not known how such mutations might cause PD. Ultimately, if the cause of PD is determined, it seems likely that it will include both genetic and environmental factors. Lastly, clinical trials have shown that potent bisphosphonates are highly effective treatments for active PD, and reduce pain, improve quality of life, normalise bone turnover and heal lytic lesions on radiographs. They can also induce sustained remission that persists for many years.

SOCS-1/3 participation in FGF-2 signaling to modulate RANK ligand expression in paget's disease of bone

Paget's disease of bone (PDB) is a chronic focal skeletal disorder characterized by excessive bone resorption followed by disorganized new bone formation. Measles virus nucleocapsid (MVNP) is implicated in pathogenesis of PDB. RANK ligand (RANKL), a critical osteoclastogenic factor expressed on bone marrow stromal/preosteoblast cells is upregulated in PDB. We recently demonstrated that fibroblast growth factor-2 (FGF-2) which induces RANKL expression is elevated in PDB. In this study, we hypothesized that FGF-2 modulates suppressors of cytokine signaling (SOCS) to induce RANKL expression in PDB. We identified increased levels of SOCS-1/3 mRNA expression in bone marrow mononuclear cells derived from patients with PDB compared to normal subjects. Interestingly, conditioned media obtained from MVNP transduced osteoclast progenitor cells significantly increased SOCS-1/3 mRNA expression in stromal/preosteoblast cells. We next examined if SOCS participates in FGF-2 signaling to modulate RANKL gene expression. We showed that FGF-2 stimulation significantly increased SOCS-1/3 expression in human bone marrow stromal/preosteoblast cells. In addition, co-expression of SOCS-1/3 with hRANKL gene promoter-luciferase reporter plasmid in marrow stromal cells demonstrated a significant increase in promoter activity without FGF-2 stimulation. Furthermore, siRNA inhibition of STAT-1 suppresses FGF-2 increased SOCS-1/3 expression in these cells. Thus, our results suggest that SOCS participates in FGF-2 modulation of RANKL expression in PDB.

Paget's disease of bone: clinical review and update

Paget's disease (PD) is a focal disorder of bone remodelling that occurs commonly in older people. In this article, we review clinical aspects of PD with an emphasis on recent findings. The epidemiology of PD appears to be changing rapidly, with several groups in different parts of the world reporting a marked reduction in the prevalence and incidence of PD, as well as in the severity of disease seen by clinicians. These findings seem most likely to be caused by changes in exposure to unknown environmental factors that have a role in the development of PD. However, genetic factors are also important. Mutations in SQSTM1 occur in 25-50% of familial PD. Genotype-phenotype relationships are present, as PD develops at an earlier age and is more extensive and severe in those with SQSTM1 mutations, and these findings are more pronounced in those with truncating mutations. However, the prevalence of PD in adults with SQSTM1 mutations is uncertain, and it is not known how such mutations might cause PD. Ultimately, if the cause of PD is determined, it seems likely that it will include both genetic and environmental factors. Lastly, clinical trials have shown that potent bisphosphonates are highly effective treatments for active PD, and reduce pain, improve quality of life, normalise bone turnover and heal lytic lesions on radiographs. They can also induce sustained remission that persists for many years.

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.

Morbillivirus cross-species infection: is there a risk for humans?

The WHO has set regional elimination goals for measles eradication to be achieved by 2020 or earlier. A major question is whether an opportunity for veterinary virus infection of humans may arise when measles is eradicated and if vaccination is discontinued. Lessons have been learned from animal to human virus transmission i.e., HIV and more recently from severe acute respiratory syndrome and avian influenza virus infections. We are therefore alerted to the risk of zoonosis from the veterinary morbilliviruses. In this review the evidence from viral genomics, animal studies and cell culture experiments will be explored to evaluate the possibility of cross-infection of humans with these viruses.

Genotype-phenotype correlation in juvenile Paget disease: role of molecular alterations of the TNFRSF11B gene

Juvenile Paget disease (JPD) {MIM 239000} is a rare inherited bone disease that affects children. The patients affected with JPD present an altered bone turnover, therefore, show a phenotype characterized by progressive bone deformities, fractures, and short stature. Deletions or missense mutations of the TNFRSN11B gene are common in these children. This gene encodes a soluble protein, the osteoprotegerin, which leads to uncontrolled osteoclastogenesis when mutated. JPD is characterized by a strong genotype-phenotype correlation, so depending on the alteration of the TNFRSN11B gene, the phenotype is variable. This review describes the different clinical features which are characteristic of JPD and the correspondence with the different molecular alterations of the TNFRSN11B gene.

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.

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.

Paget’s disease: clinical update

Paget’s disease is a chronic disorder of bone remodeling, characterized by an abnormal increase of osteoclast and, hence, osteoblast activity. The imbalance of bone turnover results in the formation of unhealthy and fragile bone. It also leads to impairment of adjacent joints and to a risk of various complications. Current research focuses on the elucidation of the etiologic role viral infection and predisposing genetic factors. Paget’s disease is commonly discovered by chance; its suspicion is raised either by high level of alkaline phosphatase or by the X-ray of the pathological bone. Bisphosphonates have proven to be effective in controlling disease activity because they inhibit osteoclast function. Their use is recommended when bone-derived serum alkaline phosphatase is high and/or when disease localizations are highly suspected for the development of complications. Orv. Hetil., 2011, 152, 1337–1346.

A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause a Paget's disease-like disorder in mice

Mutations of SQSTM1 occur in about10% of patients with Paget's disease of bone (PDB), but it is unclear whether they play a causal role or regulate susceptibility to an environmental trigger. Here we show that mice with a proline to leucine mutation at codon 394 of mouse sqstm1 (P394L), equivalent to the P392L SQSTM1 mutation in humans, develop a bone disorder with remarkable similarity to PDB. The P394L mutant mice developed focal bone lesions with increasing age and by 12 months, 14/18 (77%) heterozygotes and 20/21 (95%) homozygotes had lesions, compared with 0/18 (0%) wild-type littermates (P< 0.001). Lesions predominantly affected the lower limbs in an asymmetric manner and were characterized by focal increases in bone turnover, with increased bone resorption and formation, disruption of the normal bone architecture and accumulation of woven bone. Osteoclasts within lesions were larger and more nucleated than normal and some contained nuclear inclusions similar to those observed in human PDB. Osteoclast precursors from P394L mutant mice had increased sensitivity to RANKL in vitro resulting in the generation of osteoclasts that were larger and more nucleated than those generated from wild-type littermates. There was increased expression of sqstm1, autophagy-related gene 5 (atg5) and light chain 3 gene (lc3) in osteoclast precursors and increased LC3-II protein levels in Bafilomycin-treated osteoclasts from P394L mutant mice compared with wild-type suggesting dysregulation of autophagy and enhanced autophagosome formation. These studies demonstrate that SQSTM1 mutations can cause a PDB-like skeletal disorder in the absence of an additional trigger and provide a new disease model for PDB.

The etiology of Paget's disease of bone: viral and genetic interactions

Studies of the etiology of Paget's disease have focused separately on the viral and genetic components of the disease. In this issue of Cell Metabolism, Kurihara et al. (2011) join these components, reporting that sequestosome 1 mutation in patients and mice activates osteoclasts, while measles virus induces the phenotype of Paget's disease.

New knowledge on critical osteoclast formation and activation pathways from study of rare genetic diseases of osteoclasts: focus on the RANK/RANKL axis

Functional, biochemical and genetic studies have over the past decade identified many causative genes in the osteoclast diseases osteopetrosis and Paget's disease of bone. Here, we outline all osteoclast diseases and their genetic associations and then focus specifically on those diseases caused by mutations in the critical osteoclast molecule Receptor Activator of Nuclear factor Kappa B (RANK). Both loss and gain-of-function mutations have been found in humans leading to osteopetrosis and high bone turnover phenotypes, respectively. Osteopetrosis-associated RANK mutations are widely distributed over the RANK molecule. It is likely that some negatively affect ligand binding, whereas others preclude appropriate association of RANK with downstream signalling molecules. In the Paget-like disorders, familial expansile osteolysis, early onset Paget's disease and expansile skeletal hyperphosphatasia, heterozygous insertion mutations are found in the RANK signal peptide. These prevent signal peptide cleavage, trapping the protein translated from the mutated allele in the endoplasmic reticulum. Whole animal studies replicate the hyperactive osteoclast phenotype associated with these disorders and present only with heterozygous expression of the mutation, suggesting an as yet unexplained effect of the mutant allele on normal RANK function. We discuss the cell biological studies and animal models that help us to understand the nature of these different RANK defects and describe how careful dissection of these conditions can help understand critical pathways in osteoclast development and function. We highlight areas that require further study, particularly in light of the pharmacological interest in targeting the RANK signalling pathway to treat diseases caused by excessive bone resorption.

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.

RANKL-RANK signaling regulates expression of xenotropic and polytropic virus receptor (XPR1) in osteoclasts

Formation of multinucleated bone-resorbing osteoclasts results from activation of the receptor activated NF-kappaB ligand (RANKL)-receptor activated NF-kappaB (RANK) signaling pathway in primary bone marrow macrophages and a macrophage cell line (RAW 264.7). Osteoclasts, through bone remodeling, are key participants in the homeostatic regulation of calcium and phosphate levels within the body. Microarray analysis using Gene Expression Dynamic Inspector (GEDI) clustering software indicated that osteoclast differentiation is correlated with an increase in xenotropic and polytropic virus receptor 1 (XPR1) mRNA transcripts. XPR1 is a receptor of the xenotropic and polytropic murine leukemia virus and homolog of yeast Syg1 and plant Pi transporter PHO1. Quantitative PCR was used to validate the up-regulation of XPR1 message following RANKL stimulation in both primary bone marrow cells and a macrophage cell line. Immunostaining for the XPR1 protein showed that there is translocation of XPR1 to the membranes of the sealing zone in mature osteoclasts. This study is the first to demonstrate that the expression of retro-viral receptor, XPR1, is regulated by RANKL-RANK signaling.

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.

FGF-2 stimulation of RANK ligand expression in Paget's disease of bone

Receptor activator for nuclear factor-kappaB ligand (RANKL), a critical osteoclastogenic factor expressed in marrow stromal/preosteoblast cells is up-regulated in Paget's disease of bone (PDB). We previously demonstrated that heat-shock factor-2 (HSF-2) is a downstream target of fibroblast growth factor-2 (FGF-2) signaling to induce RANKL expression in bone marrow stromal/preosteoblast cells. In this study, we identified a 2.5-fold increase in serum FGF-2 levels in patients (n = 8) with PDB compared with normal subjects (n = 10). We showed that HSF-2 co-immunoprecipitates with heat-shock protein-27 (HSP-27) and that FGF-2 stimulation significantly increased phospho-HSP-27 levels in marrow stromal cells. Confocal microscopy revealed HSF-2 colocalization with HSP-27 in unstimulated cells and HSF-2 nuclear translocation upon FGF-2 stimulation. We further show that FGF-2 stimulation significantly increased the levels of phosphorylated signal transducers and activators of the transcription (p-STAT-1) in these cells. Western blot analysis confirmed that small interfering RNA suppression of STAT-1 significantly decreased (3.2-fold) RANKL expression and promoter activity in FGF-2-stimulated cells. Chromatin immunoprecipitation assay revealed STAT-1 binding to a putative motif located far upstream (-8 kb) in the hRANKL gene promoter region. These results suggest STAT-1 is a downstream effector of FGF-2 signaling and that elevated levels of FGF-2 stimulates RANKL expression in PDB.

Paget's disease: epidemiology and pathophysiology

Paget's disease of bone is a focal disorder of aging bone. The classic late-onset Paget's disease is often caused by a P392L mutation in the gene SQSTM1, which disturbs signaling pathways in osteoclasts on cell activation. This prevalent mutation is neither necessary nor sufficient to cause Paget's disease. Its identification, along with the elucidation of other mutations underlying early-onset Paget's and Paget's disease seen in association with inclusion body myopathy and frontotemporal dementia, have redefined our understanding of genetic disorders of bone remodeling by emphasizing the importance of environmental determinants in their pathophysiology.

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.

Pathogenesis and immunopathology of systemic and nervous canine distemper

Canine distemper is a worldwide occurring infectious disease of dogs, caused by a morbillivirus, closely related to measles and rinderpest virus. The natural host range comprises predominantly carnivores. Canine distemper virus (CDV), an enveloped, negative-sense RNA virus, infects different cell types, including epithelial, mesenchymal, neuroendocrine and hematopoietic cells of various organs and tissues. CDV infection of dogs is characterized by a systemic and/or nervous clinical course and viral persistence in selected organs including the central nervous system (CNS) and lymphoid tissue. Main manifestations include respiratory and gastrointestinal signs, immunosuppression and demyelinating leukoencephalomyelitis (DL). Impaired immune function, associated with depletion of lymphoid organs, consists of a viremia-associated loss of lymphocytes, especially of CD4+ T cells, due to lymphoid cell apoptosis in the early phase. After clearance of the virus from the peripheral blood an assumed diminished antigen presentation and altered lymphocyte maturation cause an ongoing immunosuppression despite repopulation of lymphoid organs. The early phase of DL is a sequel of a direct virus-mediated damage and infiltrating CD8+ cytotoxic T cells associated with an up-regulation of pro-inflammatory cytokines such as interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-alpha and IL-12 and a lacking response of immunomodulatory cytokines such as IL-10 and transforming growth factor (TGF)-beta. A CD4+-mediated delayed type hypersensitivity and cytotoxic CD8+ T cells contribute to myelin loss in the chronic phase. Additionally, up-regulation of interferon-gamma and IL-1 may occur in advanced lesions. Moreover, an altered balance between matrix metalloproteinases and their inhibitors seems to play a pivotal role for the pathogenesis of DL. Summarized, DL represents a biphasic disease process consisting of an initial direct virus-mediated process and immune-mediated plaque progression. Immunosuppression is due to early virus-mediated lymphocytolysis followed by still poorly understood mechanisms affecting antigen presentation and lymphocyte maturation.