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Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly.
Krauss JL, Roper PM, Ballard A, Shih CC, Fitzpatrick JAJ, Cassat JE, Ng PY, Pavlos NJ, Veis DJ
(2019) mBio 10:
MeSH Terms: Animals, Bacterial Proteins, Cell Differentiation, Cells, Cultured, Female, Macrophages, Male, Mice, Osteoblasts, Osteoclasts, Osteomyelitis, Phagosomes, RANK Ligand, Staphylococcus aureus
Show Abstract · Added March 25, 2020
Osteomyelitis (OM), or inflammation of bone tissue, occurs most frequently as a result of bacterial infection and severely perturbs bone structure. OM is predominantly caused by , and even with proper treatment, OM has a high rate of recurrence and chronicity. While has been shown to infect osteoblasts, it remains unclear whether osteoclasts (OCs) are also a target of intracellular infection. Here, we demonstrate the ability of to intracellularly infect and divide within OCs. OCs were differentiated from bone marrow macrophages (BMMs) by exposure to receptor activator of nuclear factor kappa-B ligand (RANKL). By utilizing an intracellular survival assay and flow cytometry, we found that at 18 h postinfection the intracellular burden of increased dramatically in cells with at least 2 days of RANKL exposure, while the bacterial burden decreased in BMMs. To further explore the signals downstream of RANKL, we manipulated factors controlling OC differentiation, NFATc1 and alternative NF-κB, and found that intracellular bacterial growth correlates with NFATc1 levels in RANKL-treated cells. Confocal and time-lapse microscopy in mature OCs showed a range of intracellular infection that correlated inversely with -phagolysosome colocalization. The propensity of OCs to become infected, paired with their diminished bactericidal capacity compared to BMMs, could promote OM progression by allowing to evade initial immune regulation and proliferate at the periphery of lesions where OCs are most abundant. The inflammation of bone tissue is called osteomyelitis, and most cases are caused by an infection with the bacterium To date, the bone-building cells, osteoblasts, have been implicated in the progression of these infections, but not much is known about how the bone-resorbing cells, osteoclasts, participate. In this study, we show that can infect osteoclasts and proliferate inside these cells, whereas bone-residing macrophages, immune cells related to osteoclasts, destroy the bacteria. These findings elucidate a unique role for osteoclasts to harbor bacteria during infection, providing a possible mechanism by which bacteria could evade destruction by the immune system.
Copyright © 2019 Krauss et al.
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14 MeSH Terms
The proto-oncogene function of Mdm2 in bone.
Olivos DJ, Perrien DS, Hooker A, Cheng YH, Fuchs RK, Hong JM, Bruzzaniti A, Chun K, Eischen CM, Kacena MA, Mayo LD
(2018) J Cell Biochem 119: 8830-8840
MeSH Terms: Analysis of Variance, Animals, Bone Density, Bone Remodeling, Calcification, Physiologic, Cancellous Bone, Cell Line, Tumor, Female, Humans, Male, Mice, Mice, Inbred C57BL, Mice, Inbred DBA, Osteoblasts, Osteoclasts, Osteogenesis, Osteosarcoma, Proto-Oncogene Proteins c-mdm2, Proto-Oncogenes
Show Abstract · Added April 1, 2019
Mouse double minute 2 (Mdm2) is a multifaceted oncoprotein that is highly regulated with distinct domains capable of cellular transformation. Loss of Mdm2 is embryonically lethal, making it difficult to study in a mouse model without additional genetic alterations. Global overexpression through increased Mdm2 gene copy number (Mdm2 ) results in the development of hematopoietic neoplasms and sarcomas in adult animals. In these mice, we found an increase in osteoblastogenesis, differentiation, and a high bone mass phenotype. Since it was difficult to discern the cell lineage that generated this phenotype, we generated osteoblast-specific Mdm2 overexpressing (Mdm2 ) mice in 2 different strains, C57BL/6 and DBA. These mice did not develop malignancies; however, these animals and the MG63 human osteosarcoma cell line with high levels of Mdm2 showed an increase in bone mineralization. Importantly, overexpression of Mdm2 corrected age-related bone loss in mice, providing a role for the proto-oncogenic activity of Mdm2 in bone health of adult animals.
© 2018 Wiley Periodicals, Inc.
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19 MeSH Terms
Hallmarks of Bone Metastasis.
Johnson RW, Suva LJ
(2018) Calcif Tissue Int 102: 141-151
MeSH Terms: Animals, Bone Marrow Cells, Bone Neoplasms, Bone and Bones, Breast Neoplasms, Female, Humans, Mice, Osteoblasts, Osteoclasts, Osteolysis
Show Abstract · Added March 26, 2019
Breast cancer bone metastasis develops as the result of a series of complex interactions between tumor cells, bone marrow cells, and resident bone cells. The net effect of these interactions are the disruption of normal bone homeostasis, often with significantly increased osteoclast and osteoblast activity, which has provided a rational target for controlling tumor progression, with little or no emphasis on tumor eradication. Indeed, the clinical course of metastatic breast cancer is relatively long, with patients likely to experience sequential skeletal-related events (SREs), often over lengthy periods of time, even up to decades. These SREs include bone pain, fractures, and spinal cord compression, all of which may profoundly impair a patient's quality-of-life. Our understanding of the contributions of the host bone and bone marrow cells to the control of tumor progression has grown over the years, yet the focus of virtually all available treatments remains on the control of resident bone cells, primarily osteoclasts. In this perspective, our focus is to move away from the current emphasis on the control of bone cells and focus our attention on the hallmarks of bone metastatic tumor cells and how these differ from primary tumor cells and normal host cells. In our opinion, there remains a largely unmet medical need to develop and utilize therapies that impede metastatic tumor cells while sparing normal host bone and bone marrow cells. This perspective examines the impact of metastatic tumor cells on the bone microenvironment and proposes potential new directions for uncovering the important mechanisms driving metastatic progression in bone based on the hallmarks of bone metastasis.
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MeSH Terms
UNC-45a promotes myosin folding and stress fiber assembly.
Lehtimäki JI, Fenix AM, Kotila TM, Balistreri G, Paavolainen L, Varjosalo M, Burnette DT, Lappalainen P
(2017) J Cell Biol 216: 4053-4072
MeSH Terms: Actomyosin, Cell Adhesion, Cell Line, Tumor, Cell Movement, Cell Polarity, Gene Expression, Humans, Intracellular Signaling Peptides and Proteins, Myosin Type II, Osteoblasts, Proteasome Endopeptidase Complex, Protein Folding, Protein Isoforms, Stress Fibers, Tetratricopeptide Repeat
Show Abstract · Added March 14, 2018
Contractile actomyosin bundles, stress fibers, are crucial for adhesion, morphogenesis, and mechanosensing in nonmuscle cells. However, the mechanisms by which nonmuscle myosin II (NM-II) is recruited to those structures and assembled into functional bipolar filaments have remained elusive. We report that UNC-45a is a dynamic component of actin stress fibers and functions as a myosin chaperone in vivo. UNC-45a knockout cells display severe defects in stress fiber assembly and consequent abnormalities in cell morphogenesis, polarity, and migration. Experiments combining structured-illumination microscopy, gradient centrifugation, and proteasome inhibition approaches revealed that a large fraction of NM-II and myosin-1c molecules fail to fold in the absence of UNC-45a. The remaining properly folded NM-II molecules display defects in forming functional bipolar filaments. The C-terminal UNC-45/Cro1/She4p domain of UNC-45a is critical for NM-II folding, whereas the N-terminal tetratricopeptide repeat domain contributes to the assembly of functional stress fibers. Thus, UNC-45a promotes generation of contractile actomyosin bundles through synchronized NM-II folding and filament-assembly activities.
© 2017 Lehtimäki et al.
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15 MeSH Terms
Skeletal Colonization by Breast Cancer Cells Is Stimulated by an Osteoblast and β2AR-Dependent Neo-Angiogenic Switch.
Mulcrone PL, Campbell JP, Clément-Demange L, Anbinder AL, Merkel AR, Brekken RA, Sterling JA, Elefteriou F
(2017) J Bone Miner Res 32: 1442-1454
MeSH Terms: Animals, Bone and Bones, Breast Neoplasms, Cell Line, Tumor, Coculture Techniques, Female, Humans, Mice, Mice, Knockout, Neoplasm Metastasis, Neoplasm Proteins, Neovascularization, Pathologic, Osteoblasts, Receptors, Adrenergic, beta-2, Vascular Endothelial Growth Factor A
Show Abstract · Added April 26, 2017
The skeleton is a common site for breast cancer metastasis. Although significant progress has been made to manage osteolytic bone lesions, the mechanisms driving the early steps of the bone metastatic process are still not sufficiently understood to design efficacious strategies needed to inhibit this process and offer preventative therapeutic options. Progression and recurrence of breast cancer, as well as reduced survival of patients with breast cancer, are associated with chronic stress, a condition known to stimulate sympathetic nerve outflow. In this study, we show that stimulation of the beta 2-adrenergic receptor (β2AR) by isoproterenol, used as a pharmacological surrogate of sympathetic nerve activation, led to increased blood vessel density and Vegf-a expression in bone. It also raised levels of secreted Vegf-a in osteoblast cultures, and accordingly, the conditioned media from isoproterenol-treated osteoblast cultures promoted new vessel formation in two ex vivo models of angiogenesis. Blocking the interaction between Vegf-a and its receptor, Vegfr2, blunted the increase in vessel density induced by isoproterenol. Genetic loss of the β2AR globally, or specifically in type 1 collagen-expressing osteoblasts, diminished the increase in Vegf-positive osteoblast number and bone vessel density induced by isoproterenol, and reduced the higher incidence of bone metastatic lesions induced by isoproterenol after intracardiac injection of an osteotropic variant of MDA-MB-231 breast cancer cells. Inhibition of the interaction between Vegf-a and Vegfr2 with the blocking antibody mcr84 also prevented the increase in bone vascular density and bone metastasis triggered by isoproterenol. Together, these results indicate that stimulation of the β2AR in osteoblasts triggers a Vegf-dependent neo-angiogenic switch that promotes bone vascular density and the colonization of the bone microenvironment by metastatic breast cancer cells. © 2017 American Society for Bone and Mineral Research.
© 2017 American Society for Bone and Mineral Research.
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15 MeSH Terms
Hematopoietic Stem Cell Mobilization Is Necessary but Not Sufficient for Tolerance in Islet Transplantation.
Stocks BT, Thomas AB, Elizer SK, Zhu Y, Marshall AF, Wilson CS, Moore DJ
(2017) Diabetes 66: 127-133
MeSH Terms: Allografts, Animals, Female, Flow Cytometry, Hematopoietic Stem Cell Mobilization, Hematopoietic Stem Cell Transplantation, Islets of Langerhans Transplantation, Leukocyte Common Antigens, Mice, Mice, Inbred NOD, Osteoblasts
Show Abstract · Added November 1, 2016
Overcoming the immune response to establish durable immune tolerance in type 1 diabetes remains a substantial challenge. The ongoing effector immune response involves numerous immune cell types but is ultimately orchestrated and sustained by the hematopoietic stem cell (HSC) niche. We therefore hypothesized that tolerance induction also requires these pluripotent precursors. In this study, we determined that the tolerance-inducing agent anti-CD45RB induces HSC mobilization in nonautoimmune B6 mice but not in diabetes-prone NOD mice. Ablation of HSCs impaired tolerance to allogeneic islet transplants in B6 recipients. Mobilization of HSCs resulted in part from decreasing osteoblast expression of HSC retention factors. Furthermore, HSC mobilization required a functioning sympathetic nervous system; sympathectomy prevented HSC mobilization and completely abrogated tolerance induction. NOD HSCs were held in their niche by excess expression of CXCR4, which, when blocked, led to HSC mobilization and prolonged islet allograft survival. Overall, these findings indicate that the HSC compartment plays an underrecognized role in the establishment and maintenance of immune tolerance, and this role is disrupted in diabetes-prone NOD mice. Understanding the stem cell response to immune therapies in ongoing human clinical studies may help identify and maximize the effect of immune interventions for type 1 diabetes.
© 2017 by the American Diabetes Association.
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11 MeSH Terms
Novel Genetic Variants Associated With Increased Vertebral Volumetric BMD, Reduced Vertebral Fracture Risk, and Increased Expression of SLC1A3 and EPHB2.
Nielson CM, Liu CT, Smith AV, Ackert-Bicknell CL, Reppe S, Jakobsdottir J, Wassel C, Register TC, Oei L, Alonso N, Oei EH, Parimi N, Samelson EJ, Nalls MA, Zmuda J, Lang T, Bouxsein M, Latourelle J, Claussnitzer M, Siggeirsdottir K, Srikanth P, Lorentzen E, Vandenput L, Langefeld C, Raffield L, Terry G, Cox AJ, Allison MA, Criqui MH, Bowden D, Ikram MA, Mellström D, Karlsson MK, Carr J, Budoff M, Phillips C, Cupples LA, Chou WC, Myers RH, Ralston SH, Gautvik KM, Cawthon PM, Cummings S, Karasik D, Rivadeneira F, Gudnason V, Orwoll ES, Harris TB, Ohlsson C, Kiel DP, Hsu YH
(2016) J Bone Miner Res 31: 2085-2097
MeSH Terms: Animals, Biopsy, Bone Density, Cancellous Bone, Excitatory Amino Acid Transporter 1, Gene Expression Regulation, Genetic Association Studies, Genetic Predisposition to Disease, Humans, Linkage Disequilibrium, Lumbar Vertebrae, Mice, Molecular Sequence Annotation, Organ Size, Osteoblasts, Polymorphism, Single Nucleotide, Quantitative Trait Loci, Receptor, EphB2, Risk Factors, Spinal Fractures, Spine
Show Abstract · Added March 27, 2018
Genome-wide association studies (GWASs) have revealed numerous loci for areal bone mineral density (aBMD). We completed the first GWAS meta-analysis (n = 15,275) of lumbar spine volumetric BMD (vBMD) measured by quantitative computed tomography (QCT), allowing for examination of the trabecular bone compartment. SNPs that were significantly associated with vBMD were also examined in two GWAS meta-analyses to determine associations with morphometric vertebral fracture (n = 21,701) and clinical vertebral fracture (n = 5893). Expression quantitative trait locus (eQTL) analyses of iliac crest biopsies were performed in 84 postmenopausal women, and murine osteoblast expression of genes implicated by eQTL or by proximity to vBMD-associated SNPs was examined. We identified significant vBMD associations with five loci, including: 1p36.12, containing WNT4 and ZBTB40; 8q24, containing TNFRSF11B; and 13q14, containing AKAP11 and TNFSF11. Two loci (5p13 and 1p36.12) also contained associations with radiographic and clinical vertebral fracture, respectively. In 5p13, rs2468531 (minor allele frequency [MAF] = 3%) was associated with higher vBMD (β = 0.22, p = 1.9 × 10 ) and decreased risk of radiographic vertebral fracture (odds ratio [OR] = 0.75; false discovery rate [FDR] p = 0.01). In 1p36.12, rs12742784 (MAF = 21%) was associated with higher vBMD (β = 0.09, p = 1.2 × 10 ) and decreased risk of clinical vertebral fracture (OR = 0.82; FDR p = 7.4 × 10 ). Both SNPs are noncoding and were associated with increased mRNA expression levels in human bone biopsies: rs2468531 with SLC1A3 (β = 0.28, FDR p = 0.01, involved in glutamate signaling and osteogenic response to mechanical loading) and rs12742784 with EPHB2 (β = 0.12, FDR p = 1.7 × 10 , functions in bone-related ephrin signaling). Both genes are expressed in murine osteoblasts. This is the first study to link SLC1A3 and EPHB2 to clinically relevant vertebral osteoporosis phenotypes. These results may help elucidate vertebral bone biology and novel approaches to reducing vertebral fracture incidence. © 2016 American Society for Bone and Mineral Research.
© 2016 American Society for Bone and Mineral Research.
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MeSH Terms
Combined treatment with a transforming growth factor beta inhibitor (1D11) and bortezomib improves bone architecture in a mouse model of myeloma-induced bone disease.
Nyman JS, Merkel AR, Uppuganti S, Nayak B, Rowland B, Makowski AJ, Oyajobi BO, Sterling JA
(2016) Bone 91: 81-91
MeSH Terms: Animals, Bone Diseases, Bone and Bones, Bortezomib, Cancellous Bone, Cell Count, Cell Line, Tumor, Disease Models, Animal, Drug Therapy, Combination, Mice, Inbred C57BL, Multiple Myeloma, Osteoblasts, Receptors, Transforming Growth Factor beta, Signal Transduction, Transforming Growth Factor beta, Tumor Burden
Show Abstract · Added July 18, 2016
Multiple myeloma (MM) patients frequently develop tumor-induced bone destruction, yet no therapy completely eliminates the tumor or fully reverses bone loss. Transforming growth factor-β (TGF-β) activity often contributes to tumor-induced bone disease, and pre-clinical studies have indicated that TGF-β inhibition improves bone volume and reduces tumor growth in bone metastatic breast cancer. We hypothesized that inhibition of TGF-β signaling also reduces tumor growth, increases bone volume, and improves vertebral body strength in MM-bearing mice. We treated myeloma tumor-bearing (immunocompetent KaLwRij and immunocompromised Rag2-/-) mice with a TGF-β inhibitory (1D11) or control (13C4) antibody, with or without the anti-myeloma drug bortezomib, for 4weeks after inoculation of murine 5TGM1 MM cells. TGF-β inhibition increased trabecular bone volume, improved trabecular architecture, increased tissue mineral density of the trabeculae as assessed by ex vivo micro-computed tomography, and was associated with significantly greater vertebral body strength in biomechanical compression tests. Serum monoclonal paraprotein titers and spleen weights showed that 1D11 monotherapy did not reduce overall MM tumor burden. Combination therapy with 1D11 and bortezomib increased vertebral body strength, reduced tumor burden, and reduced cortical lesions in the femoral metaphysis, although it did not significantly improve cortical bone strength in three-point bending tests of the mid-shaft femur. Overall, our data provides rationale for evaluating inhibition of TGF-β signaling in combination with existing anti-myeloma agents as a potential therapeutic strategy to improve outcomes in patients with myeloma bone disease.
Published by Elsevier Inc.
2 Communities
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16 MeSH Terms
Impact of sarA and Phenol-Soluble Modulins on the Pathogenesis of Osteomyelitis in Diverse Clinical Isolates of Staphylococcus aureus.
Loughran AJ, Gaddy D, Beenken KE, Meeker DG, Morello R, Zhao H, Byrum SD, Tackett AJ, Cassat JE, Smeltzer MS
(2016) Infect Immun 84: 2586-94
MeSH Terms: Animals, Bacterial Proteins, Gene Expression Regulation, Bacterial, Mice, Mice, Inbred C57BL, Mutation, Operon, Osteoblasts, Osteoclasts, Osteomyelitis, Proteomics, Staphylococcal Infections, Staphylococcus aureus, Virulence, Virulence Factors
Show Abstract · Added April 3, 2018
We used a murine model of acute, posttraumatic osteomyelitis to evaluate the virulence of two divergent Staphylococcus aureus clinical isolates (the USA300 strain LAC and the USA200 strain UAMS-1) and their isogenic sarA mutants. The results confirmed that both strains caused comparable degrees of osteolysis and reactive new bone formation in the acute phase of osteomyelitis. Conditioned medium (CM) from stationary-phase cultures of both strains was cytotoxic to cells of established cell lines (MC3TC-E1 and RAW 264.7 cells), primary murine calvarial osteoblasts, and bone marrow-derived osteoclasts. Both the cytotoxicity of CM and the reactive changes in bone were significantly reduced in the isogenic sarA mutants. These results confirm that sarA is required for the production and/or accumulation of extracellular virulence factors that limit osteoblast and osteoclast viability and that thereby promote bone destruction and reactive bone formation during the acute phase of S. aureus osteomyelitis. Proteomic analysis confirmed the reduced accumulation of multiple extracellular proteins in the LAC and UAMS-1 sarA mutants. Included among these were the alpha class of phenol-soluble modulins (PSMs), which were previously implicated as important determinants of osteoblast cytotoxicity and bone destruction and repair processes in osteomyelitis. Mutation of the corresponding operon reduced the cytotoxicity of CM from both UAMS-1 and LAC cultures for osteoblasts and osteoclasts. It also significantly reduced both reactive bone formation and cortical bone destruction by CM from LAC cultures. However, this was not true for CM from cultures of a UAMS-1 psmα mutant, thereby suggesting the involvement of additional virulence factors in such strains that remain to be identified.
Copyright © 2016, American Society for Microbiology. All Rights Reserved.
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Repurposing the Nonsteroidal Anti-inflammatory Drug Diflunisal as an Osteoprotective, Antivirulence Therapy for Staphylococcus aureus Osteomyelitis.
Hendrix AS, Spoonmore TJ, Wilde AD, Putnam NE, Hammer ND, Snyder DJ, Guelcher SA, Skaar EP, Cassat JE
(2016) Antimicrob Agents Chemother 60: 5322-30
MeSH Terms: Animals, Anti-Bacterial Agents, Anti-Inflammatory Agents, Non-Steroidal, Bacterial Proteins, Bone Density Conservation Agents, Cell Survival, Delayed-Action Preparations, Diflunisal, Drug Repositioning, Female, Gene Expression, Humans, Mice, Mice, Inbred C57BL, Osteoblasts, Osteomyelitis, Primary Cell Culture, Staphylococcal Infections, Staphylococcus aureus, Trans-Activators, Treatment Outcome
Show Abstract · Added April 8, 2017
Staphylococcus aureus osteomyelitis is a common and debilitating invasive infection of bone. Treatment of osteomyelitis is confounded by widespread antimicrobial resistance and the propensity of bacteria to trigger pathological changes in bone remodeling that limit antimicrobial penetration to the infectious focus. Adjunctive therapies that limit pathogen-induced bone destruction could therefore limit morbidity and enhance traditional antimicrobial therapies. In this study, we evaluate the efficacy of the U.S. Food and Drug Administration-approved, nonsteroidal anti-inflammatory (NSAID) compound diflunisal in limiting S. aureus cytotoxicity toward skeletal cells and in preventing bone destruction during staphylococcal osteomyelitis. Diflunisal is known to inhibit S. aureus virulence factor production by the accessory gene regulator (agr) locus, and we have previously demonstrated that the Agr system plays a substantial role in pathological bone remodeling during staphylococcal osteomyelitis. Consistent with these observations, we find that diflunisal potently inhibits osteoblast cytotoxicity caused by S. aureus secreted toxins independently of effects on bacterial growth. Compared to commonly used NSAIDs, diflunisal is uniquely potent in the inhibition of skeletal cell death in vitro Moreover, local delivery of diflunisal by means of a drug-eluting, bioresorbable foam significantly limits bone destruction during S. aureus osteomyelitis in vivo Collectively, these data demonstrate that diflunisal potently inhibits skeletal cell death and bone destruction associated with S. aureus infection and may therefore be a useful adjunctive therapy for osteomyelitis.
Copyright © 2016, American Society for Microbiology. All Rights Reserved.
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21 MeSH Terms