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.

Ubiquitin- and ATP-dependent unfoldase activity of P97/VCP•NPLOC4•UFD1L is enhanced by a mutation that causes multisystem proteinopathy.

p97 is a "segregase" that plays a key role in numerous ubiquitin (Ub)-dependent pathways such as ER-associated degradation. It has been hypothesized that p97 extracts proteins from membranes or macromolecular complexes to enable their proteasomal degradation; however, the complex nature of p97 substrates has made it difficult to directly observe the fundamental basis for this activity. To address this issue, we developed a soluble p97 substrate-Ub-GFP modified with K48-linked ubiquitin chains-for in vitro p97 activity assays. We demonstrate that WT p97 can unfold proteins and that this activity is dependent on the p97 adaptor NPLOC4-UFD1L, ATP hydrolysis, and substrate ubiquitination, with branched chains providing maximal stimulation. Furthermore, we show that a p97 mutant that causes inclusion body myopathy, Paget's disease of bone, and frontotemporal dementia in humans unfolds substrate faster, suggesting that excess activity may underlie pathogenesis. This work overcomes a significant barrier in the study of p97 and will allow the future dissection of p97 mechanism at a level of detail previously unattainable.

Biology and Treatment of Paget's Disease of Bone.

Paget's disease of bone (PDB) is a common skeletal disorder characterized by increased and disorganized bone remodeling affecting one or more skeletal sites. Although some patients are asymptomatic others develop complications such as bone pain, deformity, nerve compression syndromes, and fragility fractures. Genetic factors play an important role in the pathogenesis of PDB and there is strong evidence that susceptibility is determined by variants within or close to genes that regulate osteoclast function. Environmental factors also play a key role but the nature of the environmental triggers is less clear. Bisphosphonates are a highly effective treatment for the elevations in bone turnover that are characteristic of PDB but it is unclear at present if they alter the natural history of the disease. Here, we review the epidemiology, clinical, cellular, and molecular abnormalities in PDB as well as environmental and genetic triggers, and current available treatment options.

Paget's Disease of Bone: Progress Towards Remission and Prevention.

Paget's disease of bone is a focal disorder of bone remodelling leading to areas of enlarged weakened bone manifesting with chronic pain, bone deformity, and fracture. Predominantly a disease of older adults, its prevalence is strongly linked to European ancestry. Pre-disposing factors include exposure to viruses such as measles and mutations in the SQSTM1 gene. PDB is diagnosed on plain radiograph, the extent of disease is delineated by radionuclide bone imaging, the degree of activity is quantified biochemically, and it is treated with a nitrogen-containing bisphosphonate, most effectively by a single intravenous infusion of zoledronate 5mg. Lifelong specialist follow-up is advocated because some patients require repeated infusions. Current clinical research is focusing on genetic factors in order to identify patients suitable for prevention.

Paget's disease.

Paget's disease of bone is the most common metabolic bone disease after osteoporosis and affects 2-4% of adults over 55 years of age. Its etiology is only partly understood and includes both genetic and environmental factors. The disease may be asymptomatic and can be uncovered incidentally on x-ray or in biochemical tests performed for another condition. It can also manifest itself with bone pain, deformity, fracture or other complications. Paget's disease is diagnosed by x-rays and in general has very typical radiological features, but occasionally the clinical picture may be unusual and a differential diagnosis of sclerotic or lytic metastases needs to be considered. Plasma total alkaline phosphatase activity is the most clinically useful indicator of disease activity. It is elevated in most untreated patients, but may be within the normal range in patients with monostotic or limited disease. Bisphosphonate therapy is indicated for patients with symptoms and should also be considered in patients with disease sites that suggest a risk of complications, such as long bones, vertebrae or base of the skull. Orthopedic surgery in Paget's disease patients includes almost exclusively the correction of fractures and arthroplasty.

[Paget's disease of bone: new therapeutic strategies]. / La malattia di Paget: a proposito di nuove strategie terapeutiche.

Paget's disease of bone is a chronic disorder of unknown etiology that can result in enlarged and misshapen bones. The excessive breakdown and formation of bone tissue cause affected bones to weaken, resulting in pain, misshapen bones, fractures, and arthritis in the joints. In most cases the diagnosis is achieved casually, as only 5% of patients develop burning pain at the level of affected bones. As regards therapy, the use of anti-reabsorbing drugs, such as bisphosphonates and calcitonin, appears reasonable. Given the disease pathogenesis, the administration of denosumab and tocilizumab may be a valuable alternative to inhibit RANK expression, and thus osteoclast formation, and interleukin-6 production.

[Paget's disease of bone: 1877-2023. Etiology, and management of a disease on epidemiologic transition]. / Enfermedad ósea de Paget: 1877-2023. Etiología y abordaje de una enfermedad en transición epidemiológica.

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.

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.

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.

[Paget's disease: clinical update]. / A Paget-kór aktuális kérdései.

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.

A case of Paget's disease in hemodialysis.

Paget's disease is the second most common bone disease after osteoporosis and causes an excessive bone turnover. Moreover, chronic kidney failure causes an impairment of bone mineral metabolism and electrolytes and PTH homeostasis. As far as we know, this is the first reported case of Paget's disease in a hemodialysis patient: the patient was also affected by secondary hyperparathyroidism and was successfully treated with clodronate, cinacalcet and paracalcitol. The safety and efficacy of this combined therapy was periodically revised in a 12-month follow-up considering the common markers of bone turnover as well as the dosage of OPG, RANKL, IL-6 and MCSF, involved in the pathophysiology of Paget's disease.

Pathogenesis and management of Paget's disease of bone.

Paget's disease of bone is a common disease characterised by focal areas of increased bone turnover, affecting one or several bones throughout the skeleton. Paget's disease is often asymptomatic but can be associated with bone pain and other complications such as osteoarthritis, pathological fracture, bone deformity, deafness, and nerve compression syndromes. Genetic factors have an important role in this disease, and mutations have been identified in four genes that cause Paget's disease and related syndromes. The most important of these is Sequestosome 1 (SQSTM1), which is a scaffold protein in the nuclear factor kappaB (NFkappaB) signalling pathway. Patients with SQSTM1 mutations have severe Paget's disease of bone and a high degree of penetrance with increasing age. Environmental factors also contribute. Most research has focused on paramyxovirus infection as a possible trigger, but evidence for this notion is conflicting. Other potential triggers include deficiency of dietary calcium and repetitive mechanical loading of the skeleton. Medical management of Paget's disease of bone is based on giving inhibitors of osteoclastic bone resorption, and bisphosphonates are the treatment of first choice. Bisphosphonate therapy is primarily indicated for patients who have bone pain arising from increased metabolic activity in affected bones. Bisphosphonate therapy is highly effective at reducing bone turnover, and it has been shown to heal radiological lesions and restore normal histology; however, the long-term effects of bisphosphonates on disease progression have not been adequately studied. No firm evidence as yet exists to show that bisphosphonates can prevent the development of complications of Paget's disease of bone, and further work is needed to address the effects of treatment on long-term clinical outcome.

Paget's disease 1: epidemiology, causes and clinical features.

The first in this two-part unit on Paget's disease outlines the epidemiology, pathophysiology, causes and clinical features of this long-term bone condition.

Paget disease of bone in an elderly patient with chronic renal disease and weight loss: A case report.

RATIONALE: Asymptomatic Paget disease of bone (PDB) is mostly diagnosed by accidental finding of osteolytic lesion on the plain film. However, in elderly patient with chronic renal insufficiency and weight loss, it is crucial to differentiate PDB from metabolic and metastatic bone diseases for further treatment and better outcome. PATIENT CONCERNS: An 80-year-old man with chronic kidney disease presented to our emergency department due to fever with chillness for a day, while the abdominal fullness, anorexia, and weight loss had been noted for 3 months. Mixed osteoblastic and lytic changes in the pelvic bone were accidentally found on the abdominal plain film. DIAGNOSIS: The patient was diagnosed as asymptomatic PDB and urinary tract infection of Pseudomonas aeruginosa. INTERVENTIONS AND OUTCOME: The patient received 7 days intravenous and followed by 7 days oral antibiotic treatment, which lead to clinical improvement of his urinary tract infection. No pharmacological treatment was initiated for the asymptomatic and localized PDB. The patient was discharged under stable condition afterward. LESSONS: In patients with mixed osteolytic and blastic lesions, the differential diagnoses include metabolic and metastatic bone disease. Thorough understanding of the morphology of the bone lesions in high risk patient, not only helps to make differential diagnosis, but it also leads to precise treatment and better outcome.

Gene-environment interactions in Paget's disease of bone.

OBJECTIVES: This study explored the role of outdoor and indoor air pollutants in Paget's disease of bone (PDB). METHODS: We performed a survey in 140 French-Canadian patients with PDB, including 39 carriers of p.Pro392Leu mutation (SQSTM1 gene) and 113 healthy not mutated controls. The survey covered outdoor air pollution near the residence and indoor air pollutants by focusing on heating fuels and exposure to tobacco smoke. In a subgroup of patients, urinary concentrations of 17 heavy metals and 11 polycyclic aromatic hydrocarbons were measured by mass spectrometry. In light of what we learned from the survey and urinary assays, we explored the in vitro effects of certain toxics on osteoclasts in PDB. We conducted in vitro monocytes differentiation from peripheral blood of more than 40 participants, whose osteoclasts were treated with or without the toxic. The morphology of osteoclasts, their bone resorption abilities, gene and protein expression levels, and cellular oxidative stress levels were assayed. RESULTS: An inhibitory effect of cigarette smoke condensate and heavy metals was observed on morphology and bone resorption activity of patients' osteoclasts. SQSTM1 gene expression was upregulated in osteoclasts from patients with PDB versus healthy controls in presence of cadmium, and SQSTM1 protein expression was upregulated in presence of bismuth and tobacco smoke condensates, in particular in osteoclasts from carriers of the SQSTM1 mutation. Furthermore, high levels of oxidative stress in patients' osteoclasts were observed. CONCLUSIONS: Our in vitro experiments suggest an interaction between SQSTM1 gene and exposure to cadmium and tobacco smoke condensates.

Paget disease of bone.

Paget disease of bone (PD) is characterized by excessive bone resorption in focal areas followed by abundant new bone formation, with eventual replacement of the normal bone marrow by vascular and fibrous tissue. The etiology of PD is not well understood, but one PD-linked gene and several other susceptibility loci have been identified, and paramyxoviral gene products have been detected in pagetic osteoclasts. In this review, the pathophysiology of PD and evidence for both a genetic and a viral etiology for PD will be discussed.

Paget's disease of bone.

Paget's disease of bone is a focal disorder of bone remodelling that progresses slowly and leads to changes in the shape and size of affected bones and to skeletal, articular and vascular complications. In some parts of the world it is the second most common bone disorder after osteoporosis though in recent years its prevalence and severity appear to decrease. The disease is easily diagnosed and effectively treated but its pathogenesis remains incompletely understood.

Molecular effect of an OPTN common variant associated to Paget's disease of bone.

Paget's disease of bone (PDB) is a chronic bone disorder and although genetic factors appear to play an important role in its pathogenesis, to date PDB causing mutations were identified only in the Sequestosome 1 (SQSTM1) gene at the PDB3 locus. PDB6 locus, also previously linked to PDB, contains several candidate genes for metabolic bone diseases. We focused our analysis in the most significantly associated variant with PDB, within the Optineurin (OPTN) gene, i.e. the common variant rs1561570. Although it was previously shown to be strongly associated with PDB in several populations, its contribution to PDB pathogenesis remains unclear. In this study we have shown that rs1561570 may contribute to PDB since its T allele results in the loss of a methylation site in patients' DNA, leading to higher levels of OPTN gene expression and a corresponding increase in protein levels in patients' osteoclasts. This increase in OPTN expression leads to higher levels of NF-κB translocation into the nucleus and increasing expression of its target genes, which may contribute to the overactivity of osteoclasts observed in PDB. We also reported a tendency for a more severe clinical phenotype in the presence of a haplotype containing the rs1561570 T allele, which appear to be re-enforced with the presence of the SQSTM1/P392L mutation. In conclusion, our work provides novel insight towards understanding the functional effects of this variant, located in OPTN intron 7, and its implication in the contribution to PDB pathogenesis.

Pathophysiology and genetics of metabolic bone disorders characterized by increased bone turnover.

Bone is the most important supportive tissue in the human body, and in order to maintain its integrity, it is continuously renewed by a process called "remodeling". Paget's disease of bone (PDB), familial expansile osteolysis (FEO), expansile skeletal hyperphosphatasia (ESH), early-onset Paget's disease of bone (EOPDB), and juvenile Paget's disease (JPD) are all metabolic bone disorders characterized by accelerated bone remodeling. Histological studies have shown that bone-resorbing osteoclasts are the primary disease-causing cells in these disorders. In this review, we provide an overview of the clinical differences between diseases with increased bone turnover. Our main focus is on Paget's disease because this is, by far, the most common form of this type of disease. Molecular genetic studies of these disorders have revealed key players in bone remodeling and have provided further insights in signal transduction in osteoclasts. Moreover, a syndromal form of PDB has been characterized in which PDB is associated with inclusion body myopathy and frontotemporal dementia, pointing toward similar biological pathways in osteoclasts, muscle, and brain cells. However, several additional genes underlying conditions with increased bone turnover remain to be identified.

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-kappaB 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-kappaB 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.