Nicholas A. Athanasou

Cellular biology of bone-resorbing cells.

Resorption of bone occurs continuously throughout life, first as part of skeletal growth and modeling and, later, in the process of bone-remodeling in the adult skeleton. Since the 1970s, considerable progress has been made in unraveling the basic cellular mechanisms that regulate the formation and activity of the osteoclast, the main cellular agent of bone resorption. These recent advances have resulted mainly from the introduction of new methods of isolation and culture of osteoclasts and evaluation of resorptive activity; techniques have also been developed for the generation of osteoclasts in long-term culture of precursor cells found in hematopoietic tissues and peripheral blood. Although reports have suggested that other cells (such as tumor cells or macrophages) are capable of degrading bone matrix48,104,152 and releasing local factors that contribute to resorption of bone45,102,105,113, the osteoclast is the only cell specialized for this function.nnThe purpose of this review is to integrate new knowledge regarding the formation of osteoclasts and the regulation of their activity within a general view of the cellular biology of normal and pathological bone resorption. After a review of the criteria by which osteoclastic cells are defined, the origin and formation of osteoclasts will be considered, along with mechanisms governing their recruitment, activation, and function. The manner in which these mechanisms contribute to osteoclastic bone resorption under various pathological conditions as well as the possible roles of other cells (both skeletal and extraskeletal in origin) in this process will be discussed.nnStudies on the biology of bone-resorbing cells can be properly evaluated only if the criteria for the recognition of osteoclasts are clearly defined. On histological sections, osteoclasts are readily identified as large multinucleated cells that lie in apposition to a bone surface undergoing lacunar resorption …

Multiple Symmetrical Lipomatosis — A mitochondrial disorder of brown fat

Multiple Symmetrical Lipomatosis (MSL) is an unusual disorder characterized by the development of axial lipomas in adulthood. The pathoetiology of lipoma tissue in MSL remains unresolved. Seven patients with MSL were followed for a mean period of 12 years (8-20 years). All patients had cervical lipomas ranging from subtle lesions to disfiguring masses; six patients had peripheral neuropathy and five had proximal myopathy. Myoclonus, cerebellar ataxia and additional lipomas were variably present. All patients showed clinical progression. Muscle histopathology was consistent with mitochondrial disease. Five patients were positive for mtDNA point mutation m.8344A>G, three of whom underwent lipoma resection--all samples were positive for uncoupling protein-1 mRNA (unique to brown fat). Lipoma from one case stained positive for adipocyte fatty-acid protein-2 (unique to brown fat and immature adipocytes). This long-term study hallmarks the phenotypic heterogeneity of MSLs associated clinical features. The clinical, genetic and molecular findings substantiate the hypothesis that lipomas in MSL are due to a mitochondrial disorder of brown fat.

Giant cells in pigmented villo nodular synovitis express an osteoclast phenotype

AIM: To determine the cytochemical and functional phenotype of multinucleated giant cells in pigmented villo nodular synovitis (PVNS). METHODS: Giant cells isolated from a patient with PVNS of the knee were assessed for a number of markers used to distinguish osteoclasts from macrophages/ macrophage polykaryons: evidence of tartrate resistant acid phosphatase (TRAP) activity; expression of CD11b, CD14, CD51, and calcitonin receptors; and the ability of the giant cells to carry out lacunar resorption. RESULTS: Isolated giant cells expressed an osteoclast antigenic phenotype (positive for CD51, negative for CD11b and CD14) and were TRAP and calcitonin receptor positive. They also showed functional evidence of osteoclast differentiation, producing numerous lacunar bone resorption pits on bone slices in short term culture. CONCLUSIONS: The giant cells in this case of PVNS express all the phenotypical features of osteoclasts including the ability to carry out lacunar resorption. This may account for the bone destruction associated with this aggressive synovial lesion.

Osteoclast precursors circulate in avian blood.

SummaryThe osteoclast is known to be derived from a marrow-residing precursor that is a member of the mononuclear phagocyte family, but the means by which this cell moves from marrow to bone is unknown. We herein demonstrate that mononuclear progenitors capable of differentiating, in vitro, into cells exhibiting the osteoclast phenotype circulate in chickens. The mononuclear fraction was isolated on a density gradient from blood drawn from calcium-deprived laying hens and the plastic-adherent population was obtained. These cells are members of the mononuclear phagocyte family, as demonstrated by nonspecific esterase and tartrate-resistant acid phosphatase (TRAP) activities, expression of the macrophage-specific mannose receptor, and their ability to phagocytose latex particles. When cultured in the presence of devitalized bone, these cells undergo progressive multinucleation and ultimately become essentially indistinguishable from isolated osteoclasts and those generated from bone marrow precursors. Specifically, the blood-derived polykaryons are TRAP-positive, exhibit characteristic ruffled membranes, and express the osteoclast antigens 121F and 23C6. When placed on bone slices, these cells from typical resorptive “pits.” Moreover, when cultured with 3H-proline-labeled bone, the blood monocytegenerated osteoclasts mobilize matrix as effectively as those derived from marrow. Thus, osteoclast precursors circulate in the blood of laying hens and can be induced to differentiate in vitro.

Potent and Selective KDM5 Inhibitor Stops Cellular Demethylation of H3K4me3 at Transcription Start Sites and Proliferation of MM1S Myeloma Cells.

Summary Methylation of lysine residues on histone tail is a dynamic epigenetic modification that plays a key role in chromatin structure and gene regulation. Members of the KDM5 (also known as JARID1) sub-family are 2-oxoglutarate (2-OG) and Fe2+-dependent oxygenases acting as histone 3 lysine 4 trimethyl (H3K4me3) demethylases, regulating proliferation, stem cell self-renewal, and differentiation. Here we present the characterization of KDOAM-25, an inhibitor of KDM5 enzymes. KDOAM-25 shows biochemical half maximal inhibitory concentration values of <100 nM for KDM5A-D in vitro, high selectivity toward other 2-OG oxygenases sub-families, and no off-target activity on a panel of 55 receptors and enzymes. In human cell assay systems, KDOAM-25 has a half maximal effective concentration of ∼50 μM and good selectivity toward other demethylases. KDM5B is overexpressed in multiple myeloma and negatively correlated with the overall survival. Multiple myeloma MM1S cells treated with KDOAM-25 show increased global H3K4 methylation at transcriptional start sites and impaired proliferation.

Hypoxia-inducible factor 1-alpha does not regulate osteoclastogenesis but enhances bone resorption activity via prolyl-4-hydroxylase 2.

Osteogenic–angiogenic coupling is promoted by the hypoxia‐inducible factor 1‐alpha (HIF‐1α) transcription factor, provoking interest in HIF activation as a therapeutic strategy to improve osteoblast mineralization and treat pathological osteolysis. However, HIF also enhances the bone‐resorbing activity of mature osteoclasts. It is therefore essential to determine the full effect(s) of HIF on both the formation and the bone‐resorbing function of osteoclasts in order to understand how they might respond to such a strategy. Expression of HIF‐1α mRNA and protein increased during osteoclast differentiation from CD14+ monocytic precursors, additionally inducing expression of the HIF‐regulated glycolytic enzymes. However, HIF‐1α siRNA only moderately affected osteoclast differentiation, accelerating fusion of precursor cells. HIF induction by inhibition of the regulatory prolyl‐4‐hydroxylase (PHD) enzymes reduced osteoclastogenesis, but was confirmed to enhance bone resorption by mature osteoclasts. Phd2+/− murine osteoclasts also exhibited enhanced bone resorption, associated with increased expression of resorption‐associated Acp5, in comparison with wild‐type cells from littermate controls. Phd3−/− bone marrow precursors displayed accelerated early fusion, mirroring results with HIF‐1α siRNA. In vivo, Phd2+/− and Phd3−/− mice exhibited reduced trabecular bone mass, associated with reduced mineralization by Phd2+/− osteoblasts. These data indicate that HIF predominantly functions as a regulator of osteoclast‐mediated bone resorption, with little effect on osteoclast differentiation. Inhibition of HIF might therefore represent an alternative strategy to treat diseases characterized by pathological levels of osteolysis.

Fracture-related infection: A consensus on definition from an international expert group

Fracture-related infection (FRI) is a common and serious complication in trauma surgery. Accurately estimating the impact of this complication has been hampered by the lack of a clear definition. The absence of a working definition of FRI renders existing studies difficult to evaluate or compare. In order to address this issue, an expert group comprised of a number of scientific and medical organizations has been convened, with the support of the AO Foundation, in order to develop a consensus definition. The process that led to this proposed definition started with a systematic literature review, which revealed that the majority of randomized controlled trials in fracture care do not use a standardized definition of FRI. In response to this conclusion, an international survey on the need for and key components of a definition of FRI was distributed amongst all registered AOTrauma users. Approximately 90% of the more than 2000 surgeons who responded suggested that a definition of FRI is required. As a final step, a consensus meeting was held with an expert panel. The outcome of this process led to a consensus definition of FRI. Two levels of certainty around diagnostic features were defined. Criteria could be confirmatory (infection definitely present) or suggestive. Four confirmatory criteria were defined: Fistula, sinus or wound breakdown; Purulent drainage from the wound or presence of pus during surgery; Phenotypically indistinguishable pathogens identified by culture from at least two separate deep tissue/implant specimens; Presence of microorganisms in deep tissue taken during an operative intervention, as confirmed by histopathological examination. Furthermore, a list of suggestive criteria was defined. These require further investigations in order to look for confirmatory criteria. In the current paper, an overview is provided of the proposed definition and a rationale for each component and decision. The intention of establishing this definition of FRI was to offer clinicians the opportunity to standardize clinical reports and improve the quality of published literature. It is important to note that the proposed definition was not designed to guide treatment of FRI and should be validated by prospective data collection in the future.

Giant cell tumour of the hyoid--first reported case.

Giant cell tumours of bone are most commonly found in the epiphyses of weight-bearing long bones. They are rarely found in the head and neck and only 17 cases involving the laryngeal framework have been reported. To date, there have been no reports of a giant cell tumour arising from the hyoid bone. We present such a case which presented as a lump overlying the greater cornu of the hyoid, review the literature and discuss the management of this locally aggressive tumour.

Correlation of serum metal ion levels with pathological changes of ARMD in failed metal-on-metal-hip-resurfacing arthroplasties

BackgroundMetal-on-metal-hip-resurfacing arthroplasties (MoMHRAs) have been associated with an increased failure rates due to an adverse-response-to-metal-debris (ARMD) associated with a spectrum of pathological features. Serum levels of cobalt (Co) and chromium (Cr) are used to assess MoMHRAs, with regard to ARMD, but it is not certain whether ion levels correlate with pathological changes in periprosthetic tissues.MethodsSerum Co and Cr levels were correlated with histological findings in 38 revised MoMHRAs (29 pseudotumour cases and 9 non-pseudotumour cases revised for pain). The extent of necrosis and macrophage infiltrate as well as the aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) response was assessed semi-quantitatively; the prosthesis linear wear rate (PLWR) was also determined in ten cases.ResultsCr levels were elevated in 82% and Co levels elevated in 53% of cases; the PLWR correlated with Cr level (rhoxa0=xa00.8, pxa0=xa00.006). Tissue necrosis and macrophage infiltration were noted in all, most of which also exhibited significant ALVAL. Although a discrete correlation was not seen between Co and/or Cr ion levels and the extent of necrosis, degree of macrophage infiltration, or ALVAL score, it was noted that cases with acceptable metal ions levels had high ALVAL score.ConclusionHistological features of both innate and adaptive immune response to metal wear are seen in periprosthetic tissues in cases with both elevated and non-elevated metal ion levels. MoMHRA failures with acceptable ion levels exhibited a pronounced ALVAL response. Although metal ion levels are elevated in most cases of MoMHRA failure due to ARMD, the finding of a normal metal ion level does not exclude this diagnosis.

Pleomorphic liposarcoma of bone: a rare primary malignant bone tumour.

BackgroundLiposarcoma is an extremely rare primary bone sarcoma.Case presentationWe report a case of primary pleomorphic liposarcoma that arose in an 18xa0year old male in the metaphysis of the left tibia. Plain radiographs showed a partly sclerotic lesion and MR imaging a heterogeneous tumour predominantly isointense on T1- and high-signal on T2-weighted sequences with focal areas of increased T1 signal that suppressed with fat saturation. PET/CT showed marked FDG uptake (SUVxa0=xa017.1) in the primary tumour as well as a metastasis in the right distal femur and multiple small pulmonary metastases. Histologically, the tumour was a pleomorphic liposarcoma containing large tumour cells with vacuolated cytoplasm and hyperchromatic pleomorphic nuclei as well as numerous lipoblasts and scattered brown fat-like cells. Tumour cells strongly expressed FABP4/aP2, a marker of adipocyte differentiation, and UCP1, a marker of brown fat, but not S100. The case was treated with neoadjuvant MAP chemotherapy, resulting in extensive (>xa095%) necrosis in the primary tumour and almost complete resolution of the femoral and pulmonary metastases.ConclusionsPleomorphic liposarcoma can present as a sclerotic primary malignant bone tumour; markers of adipose differentiation are useful in histological diagnosis and neoadjuvant MAP chemotherapy results in significant tumor necrosis.