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 Disease of Bone Harboring Bone Metastatic Neuroendocrine Cancer: A Case Report.

In this case report, we describe an uncommon case of neuroendocrine cancer of unknown origin began with cauda equina syndrome in a patient affected by Paget disease of bone (PDB). A 76-year-old man with diagnosis of PDB, without history of pain or bone deformity, developed sudden severe low back pain. Bone alkaline phosphatase was increased and MRI and whole-body scintigraphy confirmed the localization of the disease at the third vertebra of the lumbar spine. Treatment with Neridronic Acid was started, but after only 2 weeks of therapy anuria and bowel occlusion occurred together with lower limb weakness and walking impairment. Cauda equina syndrome consequent to spinal stenosis at the level of L2-L3 was diagnosed after admission to Emergency Department and the patient underwent neurosurgery for spinal medulla decompression. The histologic results showed a complete subversion of bone structure in neoplastic tissue, consistent with metastatic neuroendocrine carcinoma of unknown origin. In conclusion, low back pain in the elderly may require deep investigation to individuate rare diseases. In asymptomatic patients with apparently stable PDB, the sudden appearance of pain or neurologic symptoms may alert the clinician for the possibility of other superimposing diseases, like bone metastases.

Adolescent-onset multisystem proteinopathy due to a novel VCP variant.

Valosin-containing protein (VCP) pathogenic variants are the most common cause of multisystem proteinopathy presenting with inclusion body myopathy, amyotrophic lateral sclerosis/frontotemporal dementia, and Paget disease of bone in isolation or in combination. We report a patient manifesting with adolescent-onset myopathy caused by a novel heterozygous VCP variant (c.467G > T, p.Gly156Val). The myopathy manifested asymmetrically in lower limbs and extended to proximal, axial, and upper limb muscles, with loss of ambulation at age 35. Creatine kinase value was normal. Alkaline phosphatase was elevated. Electromyography detected mixed low amplitude, short duration and high amplitude, long duration motor unit potentials. Muscle biopsy showed features of inclusion body myopathy, which in combination with newly diagnosed Paget disease of bone, supported the VCP variant pathogenicity. In conclusion, VCP-multisystem proteinopathy is not only a disease of adulthood but can have a pediatric onset and should be considered in differential diagnosis of neuromuscular weakness in the pediatric population.

Genetic Screening of ZNF687 and PFN1 in a Paget's Disease of Bone Cohort Indicates an Important Role for the Nuclear Localization Signal of ZNF687.

Paget's disease of bone (PDB) is a common, late-onset bone disorder, characterized by focal increases of bone turnover that can result in bone lesions. Heterozygous pathogenic variants in the Sequestosome 1 (SQSTM1) gene are found to be the main genetic cause of PDB. More recently, PFN1 and ZNF687 have been identified as causal genes in patients with a severe, early-onset, polyostotic form of PDB, and an increased likelihood to develop giant cell tumors. In our study, we screened the coding regions of PFN1 and ZNF687 in a Belgian PDB cohort (n = 188). In the PFN1 gene, no variants could be identified, supporting the observation that variants in this gene are extremely rare in PDB. However, we identified 3 non-synonymous coding variants in ZNF687. Interestingly, two of these rare variants (p.Pro937His and p.Arg939Cys) were clustering in the nuclear localization signal of the encoded ZNF687 protein, also harboring the p.Pro937Arg variant, a previously reported disease-causing variant. In conclusion, our findings support the involvement of genetic variation in ZNF687 in the pathogenesis of classical PDB, thereby expanding its mutational spectrum.

Novel Variants in the VCP Gene Causing Multisystem Proteinopathy 1.

Valosin-containing protein (VCP) gene mutations have been associated with a rare autosomal dominant, adult-onset progressive disease known as multisystem proteinopathy 1 (MSP1), or inclusion body myopathy (IBM), Paget's disease of bone (PDB), frontotemporal dementia (FTD), (IBMPFD), and amyotrophic lateral sclerosis (ALS). We report the clinical and genetic analysis findings in five patients, three from the same family, with novel VCP gene variants: NM_007126.5 c.1106T>C (p.I369T), c.478G>A (p.A160T), and c.760A>T (p.I254F), associated with cardinal MSP1 manifestations including myopathy, PDB, and FTD. Our report adds to the spectrum of heterozygous pathogenic variants found in the VCP gene and the high degree of clinical heterogeneity. This case series prompts increased awareness and early consideration of MSP1 in the differential diagnosis of myopathies and/or PDB, dementia, or ALS to improve the diagnosis and early management of clinical symptoms.

The potential for over diagnosis of Paget's disease of bone using macroscopic analysis.

OBJECTIVE: This study explores the validity of Paget's disease of bone (PDB) reported in unpublished skeletal reports, based on macroscopic analysis alone. MATERIALS: The high prevalence of 'suspected' Paget's disease (10.7%) in an early modern sample from St John's the Evangelist Church in Redhill, Surrey is reassessed. METHODS: Signs of PDB were examined in 53 well-preserved adults aged 35 + years using macroscopic, radiographic and histological techniques. RESULTS: Macroscopic features of PDB were identified in 8 individuals (15%), with 5 individuals later rejected using radiography. Two individuals showed classic radiographic features of PDB, with a third presenting possible features in radiography (5.7%). These three cases were confirmed by histological analysis. CONCLUSIONS: PDB should not be suggested as a single diagnosis in cases of bone hypertrophy without confirmation using radiography. SIGNIFICANCE: The growing popularity of 'big data' projects and limited collections access means that unpublished cases of PDB are often included in large scale analyses, impacting our understanding of the evolution of this disease. Using macroscopic analysis alone leads to overdiagnosis. Histological analysis is unnecessary when radiographic features are present, but provides a useful diagnostic step in long bones in advanced cases of PBD. LIMITATIONS: The radiographic sample in this study was limited to three individuals. SUGGESTIONS FOR FURTHER RESEARCH: The conclusion that radiography alone can be used to identify PDB in archaeological cases merits further research on a larger number of cases.

Multisystem Proteinopathy Due to VCP Mutations: A Review of Clinical Heterogeneity and Genetic Diagnosis.

In this work, we review clinical features and genetic diagnosis of diseases caused by mutations in the gene encoding valosin-containing protein (VCP/p97), the functionally diverse AAA-ATPase. VCP is crucial to a multitude of cellular functions including protein quality control, stress granule formation and clearance, and genomic integrity functions, among others. Pathogenic mutations in VCP cause multisystem proteinopathy (VCP-MSP), an autosomal dominant, adult-onset disorder causing dysfunction in several tissue types. It can result in complex neurodegenerative conditions including inclusion body myopathy, frontotemporal dementia, amyotrophic lateral sclerosis, or combinations of these. There is also an association with other neurodegenerative phenotypes such as Alzheimer-type dementia and Parkinsonism. Non-neurological presentations include Paget disease of bone and may also include cardiac dysfunction. We provide a detailed discussion of genotype-phenotype correlations, recommendations for genetic diagnosis, and genetic counselling implications of VCP-MSP.

Imaging of Paget's Disease of Bone.

Paget's disease is a metabolic bone disorder affecting the elderly and characterized by bone resorption followed by compensatory bone formation. Radiography is the imaging modality of choice for the diagnosis whereas bone scintigraphy helps stage the extent of the disease and assess response to treatment. MRI and CT are important imaging methods in the assessment of complications and surgical planning. Osteolytic lesions of Paget's first phase present with well-defined margins on radiographs, most commonly in the femur, pelvis, and skull. Cortical thickening, trabecular coarsening, bone marrow sclerosis, and deformities of long bones are present in the mixed- and late-sclerotic phases.

A case of Paget's disease of bone associated with hypomyopathic dermatomyositis.

Dermatomyositis is associated with malignancies and is known to have systemic involvement. However, associations with bone diseases have not been well described in the current literature. This article describes the second reported case of the co-existence of dermatomyositis and Paget's disease of bone (PDB), but this is the first report to describe such co-existence in a specific subtype of dermatomyositis-hypomyopathic dermatomyositis. Our patient was a 51 year old woman who presented with prolonged fever, myalgia, morning stiffness, and rashes pathognomonic of dermatomyositis. There was no muscle weakness clinically, although muscle enzymes were increased and electromyogram revealed myopathic changes. Further imaging showed the incidental finding of a T11 vertebral bone lesion, of which biopsy confirmed the diagnosis of PDB. Our report illustrates the diagnostic approach to bone lesions in patients with dermatomyositis and takes a closer look at the pathophysiology and management implications of the co-occurrence of these two rare diseases.

The role of autophagy in bone homeostasis.

Autophagy is an evolutionarily conserved intracellular process and is considered one of the main catabolism pathways. In the process of autophagy, cells are digested nonselectively or selectively to recover nutrients and energy, so it is regarded as an antiaging process. In addition to the essential role of autophagy in cellular homeostasis, autophagy is a stress response mechanism for cell survival. Here, we review recent literature describing the pathway of autophagy and its role in different bone cell types, including osteoblasts, osteoclasts, and osteocytes. Also discussed is the mechanism of autophagy in bone diseases associated with bone homeostasis, including osteoporosis and Paget's disease. Finally, we discuss the application of autophagy regulators in bone diseases. This review aims to introduce autophagy, summarize the understanding of its relevance in bone physiology, and discuss its role and therapeutic potential in the pathogenesis of bone diseases such as osteoporosis.

'Bone within bone appearance' in a pathological fracture.

A 60-year-old man presented to our hospital with complaints of pain and deformity on his right thigh for the past 2 days following a history of accidental slip and fall. Radiological investigations suggested a pathological type 2 Seinsheimer subtrochanteric fracture of the right femur with a 'bone within bone' appearance, which posed a diagnostic dilemma as this radiological appearance is seen in a spectrum of conditions. Radiographic skeletal survey failed to identify a similar appearance elsewhere in the body. Laboratory investigations pointed in favour of bone mineral disease, and histopathological examination of the bone narrowed it down to Paget's disease. The fracture was fixed with a contralateral distal femur locking compression plate. The fracture site failed to show signs of union until 6 months postsurgery and hence the patient was advised for grafting procedure. The patient deferred surgery and remains without major complications until 18 months of follow-up.

Ostm1 from Mouse to Human: Insights into Osteoclast Maturation.

The maintenance of bone mass is a dynamic process that requires a strict balance between bone formation and resorption. Bone formation is controlled by osteoblasts, while osteoclasts are responsible for resorption of the bone matrix. The opposite functions of these cell types have to be tightly regulated not only during normal bone development, but also during adult life, to maintain serum calcium homeostasis and sustain bone integrity to prevent bone fractures. Disruption of the control of bone synthesis or resorption can lead to an over accumulation of bone tissue in osteopetrosis or conversely to a net depletion of the bone mass in osteoporosis. Moreover, high levels of bone resorption with focal bone formation can cause Paget's disease. Here, we summarize the steps toward isolation and characterization of the osteopetrosis associated trans-membrane protein 1 (Ostm1) gene and protein, essential for proper osteoclast maturation, and responsible when mutated for the most severe form of osteopetrosis in mice and humans.

Osteoclast signaling-targeting miR-146a-3p and miR-155-5p are downregulated in Paget's disease of bone.

MicroRNA (miRs) are small, non-coding RNA that post-transcriptionally regulate DNA expression. We hypothesized that specific miR profiles may be a feature of overactive osteoclasts in Paget's disease of bone (PDB), a disorder characterized by an increased and disorganized bone remodeling that typically begins with excessive bone resorption. We compared the expression profile of 13 miRs in human osteoclasts differentiated in vitro from peripheral blood mononuclear cells (PBMCs) of patients with PDB (n = 10) or age- and sex- matched healthy subjects (n = 10). We selected 13 miRs for testing, on the basis of their previously reported roles either in human osteoclast differentiation, in bone diseases, or in osteoclast important signaling pathways. From those expression results, 3 miRNAs were further selected for in-vitro studies aiming at modulating miR expression in human cord blood monocyte derived osteoclasts: 2 miRs (miR-146a-3p and miR-155-5p) whose expression was significantly reduced in pagetic osteoclasts, as well as miRNA-133a-3p, stable in PDB relative to controls, but with known regulatory importance within osteoclasts. We demonstrated a positive (miR-133a-3p) or negative (miR-155-5p, miR-146a-3p) impact of those miRs on the formation of osteoclasts and/or their bone resorption capacity in this human model. Signaling pathways were significantly affected, including p38 MAP-kinase (miR-133a-3p), RANKL-induced TRAF6/NFκB signaling (miR-146a-3p), and MITF expression (miR-155-5p). Osteoclast miRNA profiles might have an important value to yield significant new insights into the osteoclast phenotype in PDB and in other bone diseases with hyperactive osteoclasts.

The two faces of giant cell tumor of bone.

Giant cell tumor (GCT) is a bone-destructive benign neoplasm characterized by distinctive multinucleated osteoclast-like giant cells with osteolytic properties distributed among neoplastic stromal cells. GCT is locally aggressive with progressive invasion of adjacent tissues and occasionally displays malignant characteristics including lung metastasis. GCT is characterized genetically by highly recurrent somatic mutations at the G34 position of the H3F3A gene, encoding the histone variant H3.3, in stromal cells. This leads to deregulated gene expression and increased proliferation of mutation-bearing cells. However, when GCT complicates Paget disease of bone (GCT/PDB) it behaves differently, showing a more malignant phenotype with 5-year survival less than 50%. GCT/PDB is caused by a germline mutation in the ZNF687 gene, which encodes a transcription factor involved in the repression of genes surrounding DNA double-strand breaks to promote repair by homologous recombination. Identification of these driver mutations led to novel diagnostic tools for distinguishing between these two tumors and other osteoclast-rich neoplasms. Herein, we review the clinical, histological, and molecular features of GCT in different contexts focusing also on pharmacological treatments.

Osteoclast-derived IGF1 is required for pagetic lesion formation in vivo.

We report that transgenic mice expressing measles virus nucleocapsid protein (MVNP) in osteoclasts (OCLs) (MVNP mice) are Paget's disease (PD) models and that OCLs from patients with PD and MVNP mice express high levels of OCL-derived IGF1 (OCL-IGF1). To determine OCL-IGF1's role in PD and normal bone remodeling, we generated WT and MVNP mice with targeted deletion of Igf1 in OCLs (Igf1-cKO) and MVNP/Igf1-cKO mice, and we assessed OCL-IGF1's effects on bone mass, bone formation rate, EphB2/EphB4 expression on OCLs and osteoblasts (OBs), and pagetic bone lesions (PDLs). A total of 40% of MVNP mice, but no MVNP/Igf1-cKO mice, had PDLs. Bone volume/tissue volume (BV/TV) was decreased by 60% in lumbar vertebrae and femurs of MVNP/Igf1-cKO versus MVNP mice with PDLs and by 45% versus all MVNP mice tested. Bone formation rates were decreased 50% in Igf1-cKO and MVNP/Igf1-cKO mice versus WT and MVNP mice. MVNP mice had increased EphB2 and EphB4 levels in OCLs/OBs versus WT and MVNP/Igf1-cKO, with none detectable in OCLs/OBs of Igf1-cKO mice. Mechanistically, IL-6 induced the increased OCL-IGF1 in MVNP mice. These results suggest that high OCL-IGF1 levels increase bone formation and PDLs in PD by enhancing EphB2/EphB4 expression in vivo and suggest OCL-IGF1 may contribute to normal bone remodeling.

Global deletion of Optineurin results in altered type I IFN signaling and abnormal bone remodeling in a model of Paget's disease.

Genome-wide association studies (GWAS) have identified Optineurin (OPTN) as genetically linked to Paget's disease of the bone (PDB), a chronic debilitating bone remodeling disorder characterized by localized areas of increased bone resorption and abnormal bone remodeling. However, only ~10% of mouse models with a mutation in Optn develop PDB, thus hindering the mechanistic understanding of the OPTN-PDB axis. Here, we reveal that 100% of aged Optn global knockout (Optn-/-) mice recapitulate the key clinical features observed in PDB patients, including polyostotic osteolytic lesions, mixed-phase lesions, and increased serum levels of alkaline phosphatase (ALP). Differentiation of primary osteoclasts ex vivo revealed that the absence of Optn resulted in an increased osteoclastogenesis. Mechanistically, Optn-deficient osteoclasts displayed a significantly decreased type I interferon (IFN) signature, resulting from both defective production of IFNß and impaired signaling via the IFNα/ßR, which acts as a negative feedback loop for osteoclastogenesis and survival. These data highlight the dual roles of OPTN in the type I IFN response to restrain osteoclast activation and bone resorption, offering a novel therapeutic target for PDB. Therefore, our study describes a novel and essential mouse model for PDB and define a key role for OPTN in osteoclast differentiation.

Enterococcus faecalis causes osteitis deformans in aGolden Lancehead snake (Bothrops insularis): a case report / Enterococcus faecalis causa osteíte deformante em uma serpente Jararaca-ilhoa (Bothrops insularis): relato de caso

Osteitis deformans (Paget's disease) is a chronic bone disorder characterized by excessive osteoclast-mediated bone resorption followed by new bone formation. The present paper reports this condition in an 18-year-old captive golden lancehead (Bothrops insularis) from Brazil. This patient initially exhibited anorexia and swelling in the middle third of the spine associated with locomotor disability. For diagnosis, radiography, ultrasound, computed tomography, cytology, and microbiological culture were performed. Diagnostic imaging showed bone changes, vertebral fusion, and bone proliferation. Cytology revealed blood cells how toxic heterophiles, reactive monocytes, young red blood cells, and polychromasia compatible with an infectious process. A bacterial culture identified an ampicillin-susceptible strain of Enterococcus faecalis. Antibiotic treatment was promptly started, but the snake died 25 days later. Histopathologically, the bone tissue showed a generalized thickening of the vertebral trabeculae. For the first time, the presence of E. faecalisassociated with the development of osteitis deformans in snakes was presented.(AU)

Osteíte deformante (Doença de Paget) é um distúrbio ósseo crônico caracterizado por reabsorção óssea excessiva mediada por osteoclastos, seguida por nova formação óssea. O presente trabalho relata essa condição em uma serpente jararaca-ilhoa (Bothrops insularis) do Brasil de 18 anos. O paciente apresentou inicialmente anorexia e um inchaço no primeiro terço médio da coluna associado com a incapacidade locomotora. O diagnóstico foi estabelecido com o apoio de radiografia, ultrassonografia, tomografia computadorizada, citologia e cultura microbiológica. O diagnóstico por imagem mostrou alterações ósseas, fusão de vértebras e proliferação óssea. A citologia mostrou células sanguíneas como heterófílos tóxicos, monócitos reativos, células sanguíneas jovens e policromasia compatíveis com um processo infeccioso. A cultura bacteriana identificou uma cepa de Enterococcus faecalis suscetível à ampicilina. O tratamento com antibióticos foi iniciado imediatamente, mas a serpente morreu 25 dias depois. Histopatologicamente, o tecido ósseo mostrou um espessamento generalizado das trabéculas vertebrais. Portanto, foi demonstrado pela primeira vez a presença de E. faecalis associada ao desenvolvimento de osteíte deformante em uma serpente.(AU)