Pronounced femur malunion after pathological bone fracture due to a simple bone cyst in the shaft of the femur, treated using Ilizarov fixation: a case report.

BACKGROUND: Although a simple bone cyst carries the risk of pathological fractures, it rarely causes severe deformity. Here we report a case of severe femoral deformity after multiple pathological fractures due to simple bone cysts, and consider the reason for the progression of malunion despite multiple previous treatments. Finally, we propose a treatment option for malunion correction. CASE PRESENTATION: A 9-year, 7-month-old Japanese girl was referred to our facility with obvious deformity of her right femur, caused by multiple simple bone cyst-related pathological fractures. The deformity included bowing of approximately 90° and an internal rotation of 60° in the middle third of the femoral shaft. To correct this deformity, we excised the lesion, thus shortening the femur, then corrected the alignment and applied an Ilizarov fixator to extend the bone. At present, 3 years after surgery, the deformity has not recurred and our patient is living without any limitations in daily activities or regular exercise. CONCLUSIONS: When a long bone is in a prolonged state of deformation, the deformity not only progresses as the bone grows, but the soft tissues remain unbalanced and treatment becomes increasingly difficult. To prevent increasing bone deformity and fragility, the deformity should be corrected as quickly as possible using intramedullary nailing or other fixation techniques. We believe that our shortening-distraction method is effective for the treatment of severe deformity with unbalanced soft tissues.

NANS-mediated synthesis of sialic acid is required for brain and skeletal development.

We identified biallelic mutations in NANS, the gene encoding the synthase for N-acetylneuraminic acid (NeuNAc; sialic acid), in nine individuals with infantile-onset severe developmental delay and skeletal dysplasia. Patient body fluids showed an elevation in N-acetyl-D-mannosamine levels, and patient-derived fibroblasts had reduced NANS activity and were unable to incorporate sialic acid precursors into sialylated glycoproteins. Knockdown of nansa in zebrafish embryos resulted in abnormal skeletal development, and exogenously added sialic acid partially rescued the skeletal phenotype. Thus, NANS-mediated synthesis of sialic acid is required for early brain development and skeletal growth. Normal sialylation of plasma proteins was observed in spite of NANS deficiency. Exploration of endogenous synthesis, nutritional absorption, and rescue pathways for sialic acid in different tissues and developmental phases is warranted to design therapeutic strategies to counteract NANS deficiency and to shed light on sialic acid metabolism and its implications for human nutrition.

ADAM17 regulates IL-1 signaling by selectively releasing IL-1 receptor type 2 from the cell surface.

Interleukin (IL)-1 is one of the most evolutionarily conserved cytokines and plays an essential role in the regulation of innate immunity. IL-1 binds to two different receptors, IL-1R1 and IL-1R2, which share approximately 28% amino acid homology. IL-1R1 contains a cytoplasmic domain and is capable of transducing cellular signals; by contrast, IL-1R2 lacks a functional cytoplasmic domain and serves as a decoy receptor for IL-1. Interestingly, IL-1R2 is proteolytically cleaved and also functions as a soluble receptor that blocks IL-1 activity. In the present study, we examined the shedding properties of IL-1R2 and demonstrate that ADAM17 is de facto the major sheddase for IL-1R2 and that introducing a mutation into the juxta-membrane domain of IL-1R2 significantly desensitizes IL-1R2 to proteolytic cleavage. IL-1R1 was almost insensitive to ADAM17-dependent cleavage; however, the replacement of the juxta-membrane domain of IL-R1 with that of IL-1R2 significantly increased the sensitivity of IL-1R1 to shedding. Furthermore, we demonstrate that ADAM17 indirectly enhances IL-1 signaling in a cell-autonomous manner by selectively cleaving IL-1R2. Taken together, the data collected in the present study indicate that ADAM17 affects sensitivity to IL-1 by changing the balance between IL-1R1 and the decoy receptor IL-1R2.

Arthroscopic treatment of femoral nerve paresthesia caused by an acetabular paralabral cyst.

This report describes a rare case of femoral nerve paresthesia caused by an acetabular paralabral cyst of the hip joint. A 68-year-old woman presented with a 6-month history of right hip pain and paresthesia along the anterior thigh and radiating down to the anterior aspect of the knee. Radiography showed osteoarthritis with a narrowed joint space in the right hip joint. Magnetic resonance imaging showed a cyst with low T1- and high T2-weighted signal intensity arising from a labral tear at the anterior aspect of the acetabulum. The cyst was connected to the joint space and displaced the femoral nerve to the anteromedial side. The lesion was diagnosed as an acetabular paralabral cyst causing femoral neuropathy. Because the main symptom was femoral nerve paresthesia and the patient desired a less invasive procedure, arthroscopic labral repair was performed to stop synovial fluid flow to the paralabral cyst that was causing the femoral nerve paresthesia. After surgery, the cyst and femoral nerve paresthesia disappeared. At the 18-month follow-up, the patient had no recurrence. There have been several reports of neurovascular compression caused by the cyst around the hip joint. To the authors' knowledge, only 3 cases of acetabular paralabral cysts causing sciatica have been reported. The current patient appears to represent a rare case of an acetabular paralabral cyst causing femoral nerve paresthesia. The authors suggest that arthroscopic labral repair for an acetabular paralabral cyst causing neuropathy can be an option for patients who desire a less invasive procedure.

Fracture of an osteochondroma of the femoral neck caused by impingement against the ischium.

This article describes 2 cases of osteochondroma emanating from the posterior aspect of the femoral neck with a fracture at the base of its stalk caused by impingement between the tumor and the ischium. A 44-year-old man and a 57-year-old man presented with left hip pain. Radiographs revealed a mass at the posterior aspect of the femoral neck. Computed tomography and magnetic resonance imaging revealed that the mass was fractured at the stalk. The relationship between the tumor and the ischium was examined with an image intensifier. The tumor impinged on the ischium with slight flexion and external rotation of the hip joint. In both patients, the tumor was excised, and the pathological report was osteochondroma. At follow-up, the patients had full hip joint range of motion, and lateral radiographs of the left hip joint showed complete resection of the tumor without recurrence. To the authors' knowledge, the current cases are the first reports of fracture of an osteochondroma with confirmed impingement using an image intensifier pre- and intraoperatively. Both patients had histories of restricted hip range of motion and a sudden onset of pain. After excision, the patients recovered to activities of daily living with no complications. An osteochondroma at the posterior aspect of the femoral neck can impinge on the ischium and fracture at its base with a sudden onset of pain. Awareness of this mechanism of impingement may lead to a better understanding of patient symptoms caused by osteochondroma of the femoral neck.

The transient appearance of zipper-like actin superstructures during the fusion of osteoclasts.

Multinucleated osteoclasts are responsible for bone resorption. Hypermultinucleated osteoclasts are often observed in some bone-related diseases such as Paget's disease and cherubism. The cellular mechanics controlling the size of osteoclasts is poorly understood. We introduced EGFP-actin into RAW 264.7 cells to monitor actin dynamics during osteoclast differentiation. Before their terminal differentiation into osteoclasts, syncytia displayed two main types of actin assembly, podosome clusters and clusters of zipper-like structures. The zipper-like structures morphologically resembled the adhesion zippers found at the initial stage of cell-cell adhesion in keratinocytes. In the zipper-like structure, Arp3 and cortactin overlapped with the distribution of dense F-actin, whereas integrin ß3, paxillin and vinculin were localized to the periphery of the structure. The structure was negative for WGA-lectin staining and biotin labeling. The zipper-like structure broke down and transformed into a large actin ring, called a podosome belt. Syncytia containing clusters of zipper-like structures had more nuclei than those with podosome clusters. Differentiated osteoclasts with a podosome belt also formed the zipper-like structure at the cell contact site during cell fusion. The breakdown of the cell contact site resulted in the fusion of the podosome belts following plasma membrane fusion. Additionally, osteoclasts in mouse calvariae formed the zipper-like structure in the sealing zone. Therefore, we propose that the zipper-like actin superstructures might be involved in cell-cell interaction to achieve efficient multinucleation of osteoclasts. Understanding of the zipper-like structure might lead to selective therapeutics for bone diseases caused by hypermultinucleated osteoclasts.

Dual functions of cell-autonomous and non-cell-autonomous ADAM10 activity in granulopoiesis.

Previous studies have revealed various extrinsic stimuli and factors involved in the regulation of hematopoiesis. Among these, Notch-mediated signaling has been suggested to be critically involved in this process. Herein, we show that conditional inactivation of ADAM10, a membrane-bound protease with a crucial role in Notch signaling (S2 cleavage), results in myeloproliferative disorder (MPD) highlighted by severe splenomegaly and increased populations of myeloid cells and hematopoietic stem cells. Reciprocal transfer of bone marrow cells between wild-type and ADAM10 mutant mice revealed that ADAM10 activity in both hematopoietic and nonhematopoietic cells is involved in the development of MPD. Notably, we found that MPD caused by lack of ADAM10 in nonhematopoietic cells was mediated by G-CSF, whereas MPD caused by ADAM10-deficient hematopoietic cells was not. Taken together, the present findings reveal previously undescribed nonredundant roles of cell-autonomous and non-cell-autonomous ADAM10 activity in the maintenance of hematopoiesis.

The IRE1α-XBP1 pathway is essential for osteoblast differentiation through promoting transcription of Osterix.

During skeletal development, osteoblasts produce large amounts of extracellular matrix proteins and must therefore increase their secretory machinery to handle the deposition. The accumulation of unfolded protein in the endoplasmic reticulum induces an adoptive mechanism called the unfolded protein response (UPR). We show that one of the most crucial UPR mediators, inositol-requiring protein 1α (IRE1α), and its target transcription factor X-box binding protein 1 (XBP1), are essential for bone morphogenic protein 2-induced osteoblast differentiation. Furthermore, we identify Osterix (Osx, a transcription factor that is indispensible for bone formation) as a target gene of XBP1. The promoter region of the Osx gene encodes two potential binding motifs for XBP1, and we show that XBP1 binds to these regions. Thus, the IRE1α-XBP1 pathway is involved in osteoblast differentiation through promoting Osx transcription.

Receptor activator of NF-kappaB (RANK) ligand induces ectodomain shedding of RANK in murine RAW264.7 macrophages.

Osteoclastogenesis is a highly sophisticated process that involves a variety of membrane-bound proteins expressed in osteoblasts and osteoclast precursors. Over the past several years, proteolytic cleavage and release of the ectodomain of membrane-bound proteins, also referred to as ectodomain shedding, has emerged as an important posttranslational regulatory mechanism for modifying the function of cell surface proteins. In line with this notion, several membrane-bound molecules involved in osteoclastogenesis, including CSF-1R and receptor activator of NF-kappaB ligand (RANKL), are proteolytically cleaved and released from the cell surface. In this study, we investigated whether receptor activator of NF-kappaB (RANK), one of the most essential molecules in osteoclastogenesis, undergoes ectodomain shedding. The results showed that RANK is released in the form of a soluble monomeric protein and that TNF-alpha-converting enzyme is involved in this activity. We also identified potential cleavage sites in the juxtamembrane domain of RANK and found that rRANKL induces RANK shedding in a macrophage-like cell line RAW264.7 via TNFR-associated factor 6 and MAPK pathways. Furthermore, we found that RANKL-induced osteoclastogenesis is accelerated in TNF-alpha-converting enzyme-deficient osteoclast precursors. These observations suggest the potential involvement of ectodomain shedding in the regulation of RANK functions and may provide novel insights into the mechanisms of osteoclastogenesis.

IL-27 abrogates receptor activator of NF-kappa B ligand-mediated osteoclastogenesis of human granulocyte-macrophage colony-forming unit cells through STAT1-dependent inhibition of c-Fos.

IL-27 was first discovered as a factor supporting initial Th1 immune responses. Subsequent studies revealed that this cytokine has pleiotropic effects, including inhibition of certain immune cells, a regulatory role in hemopoietic stem cell differentiation, and antitumor activities. However, the role of human IL (hIL)-27 in human osteoclast precursors and inflammatory bone disease is unclear. Here, we examined the direct effect of hIL-27 on human osteoclastogenesis. Human bone marrow cells cultured in MethoCult medium containing human (h) GM-CSF, human stem cell factor, and hIL-3 expressed Mac-1, c-kit, and c-Fms. These cells, called hCFU-GMs, also expressed the IL-27 receptor, an IL-27Ralpha (WSX-1)/gp130 heterodimer. Cultivation in hM-CSF and human receptor activator of NF-kappaB ligand induced the differentiation of tartrate-resistant acid phosphatase-positive multinucleated cells (osteoclasts) from hCFU-GMs, and hIL-27 inhibited this osteoclastogenesis in a dose-dependent manner. hIL-27 also repressed bone resorption by osteoclasts on a dentine slice. hIL-27 caused a remarkable increase in STAT1 phosphorylation and enhanced the STAT1 protein level. It also inhibited the expression of receptor activator of NF-kappaB ligand-induced c-Fos and cytoplasmic, calcineurin-dependent 1 NFAT (NFATc1), which are indispensable transcription factors for osteoclastogenesis. Fludarabine, a STAT1 inhibitor, and STAT1 small interfering RNA partially rescued the inhibition of osteoclastogenesis by IL-27. A WSX-1 deficiency caused severe inflammatory bone destruction primed by Escherichia coli cell wall lysate in vivo. Therefore, hIL-27 may act as an anti-inflammatory cytokine in human bone destruction, by inhibiting osteoclastogenesis from hCFU-GMs via STAT1-dependent down-regulation of the transcription factor c-Fos. Our results suggest that hIL-27 may prove useful as a therapeutic target for inflammatory bone destruction.

PIAS3 negatively regulates RANKL-mediated osteoclastogenesis directly in osteoclast precursors and indirectly via osteoblasts.

Cytokine signaling via various transcription factors regulates receptor activator of nuclear factor (NF)-kappaB ligand (RANKL)-mediated osteoclast differentiation from monocyte/macrophage lineage cells involved in propagation and resolution of inflammatory bone destruction. Protein inhibitor of activated STAT3 (PIAS3) was initially identified as a molecule that inhibits DNA binding of STAT3 and regulates many transcription factors through distinct mechanisms. To analyze PIAS3 function in osteoclasts in vivo, we have generated transgenic mice in which PIAS3 is specifically expressed in the osteoclast lineage using the tartrate-resistant acid phosphatase (TRAP) gene promoter. PIAS3 transgenic mice showed an osteopetrotic phenotype due to impairment of osteoclast differentiation. Overexpression of PIAS3 in RAW264.7 cells suppressed RANKL-induced osteoclastogenesis by inhibiting the expression of c-Fos and NFATc1. Interestingly, PIAS3 inhibits the transcriptional activity of microphthalmia-associated transcription factor (MITF) independent of sumoylation. Down-regulation of PIAS3 markedly enhances RANKL-mediated osteoclastogenesis in RAW264.7 cells. Furthermore, overexpression of PIAS3 in mouse primary osteoblast (POB), down-regulates RANKL expression induced by interleukin-6 (IL-6) cytokine family, and inhibits osteoclast formation from bone marrow macrophages (BMMs) in vitro coculture system. Down-regulation of PIAS3 leads to the accelerated expression of RANKL in POB stimulated with IL-6 and soluble IL-6 receptor (sIL-6R). Taken together, our results clearly indicate that PIAS3 negatively regulates RANKL-mediated osteoclastogenesis directly in osteoclast precursors and indirectly via osteoblasts.