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Brendan F Boyce

Publications and source records attributed to Brendan F Boyce.

At least 19 recordsLinked to original sources
PubMed2006

CRTAP is required for prolyl 3- hydroxylation and mutations cause recessive osteogenesis imperfecta.

Prolyl hydroxylation is a critical posttranslational modification that affects structure, function, and turnover of target proteins. Prolyl 3-hydroxylation occurs at only one position in the triple-helical domain of fibrillar collagen chains, and its biological significance is unknown. CRTAP shares homology with a family of putative prolyl 3-hydroxylases (P3Hs), but it does not contain their common dioxygenase domain. Loss of Crtap in mice causes an osteochondrodysplasia characterized by severe osteoporosis and decreased osteoid production. CRTAP can form a complex with P3H1 and cyclophilin B (CYPB), and Crtap-/- bone and cartilage collagens show decreased prolyl 3-hydroxylation. Moreover, mutant collagen shows evidence of overmodification, and collagen fibrils in mutant skin have increased diameter consistent with altered fibrillogenesis. In humans, CRTAP mutations are associated with the clinical spectrum of recessive osteogenesis imperfecta, including the type II and VII forms. Hence, dysregulation of prolyl 3-hydroxylation is a mechanism for connective tissue disease.

Amino Acid Sequence↗
PubMed2006

SRC inhibitors in metastatic bone disease.

Src tyrosine kinase was the first gene product shown to have an essential function in bone using recombinant DNA technology after its expression was knocked out in mice approximately 15 years ago. Since then, our understanding of the regulation of bone catabolism has advanced significantly with the identification of other key enzymes that regulate osteoclast formation, activation, and survival after their knockout in mice or recognition of mutations in them in humans. This led to the discovery or development of specific inhibitors of some of these key enzymes, including Src, as proof-of-concept lead compounds or potential clinical candidates for the prevention of diseases associated with increased bone resorption, such as osteoporosis and metastatic bone disease. Although bisphosphonates have been prescribed with proven and improving efficacy for the prevention of bone loss for >30 years, adverse effects, such as upper gastrointestinal tract symptoms, and the requirement to take them at least 2 hours before food have limited patient compliance. Thus, with growing knowledge of the pathways regulating osteoclast function and the appreciation that some of these are active also in tumor cells, drug companies have made efforts to identify small-molecular lead compounds for development into new therapeutic agents for the prevention of bone loss with efficacy that matches or supersedes that of bisphosphonates. In this article, we review our current understanding of the signaling pathways that regulate osteoclast formation, activation, and survival with specific reference to the role of Src tyrosine kinase and downstream signaling and highlight in a variety of models of increased bone resorption the effects of Src kinase inhibitors that have been targeted to bone to limit potential adverse effects on other cells.

Animals↗
PubMed2006

Advances in treating metastatic bone cancer: summary statement for the First Cambridge Conference.

The First Cambridge Conference on Advances in Treating Metastatic Bone Cancer, a symposium held in Cambridge, Massachusetts, October 28 to 29, 2005, was convened to discuss recent advances and research related to the natural history of bone metastases and skeletal complications, bone cancer biology, treatment of myeloma and other solid tumors, and treatment-induced bone loss. The conference format combined brief presentations with extended periods of discussion. The conclusions reached during the 2-day meeting are summarized in this article and presented in more detail in the individual articles and accompanying discussion sessions that comprise the conference proceedings.

Bone Neoplasms↗
PubMed2006

Tumor necrosis factor-alpha increases circulating osteoclast precursor numbers by promoting their proliferation and differentiation in the bone marrow through up-regulation of c-Fms expression.

Osteoclasts are essential cells for bone erosion in inflammatory arthritis and are derived from cells in the myeloid lineage. Recently, we reported that tumor necrosis factor-alpha (TNFalpha) increases the blood osteoclast precursor (OCP) numbers in arthritic patients and animals, which are reduced by anti-TNF therapy, implying that circulating OCPs may have an important role in the pathogenesis of erosive arthritis. The aim of this study is to investigate the mechanism by which TNFalpha induces this increase in OCP frequency. We found that TNFalpha stimulated cell division and conversion of CD11b+/Gr-1-/lo/c-Fms- to CD11b+/Gr-1-/lo/c-Fms+ cells, which was not blocked by neutralizing macrophage colony-stimulating factor (M-CSF) antibody. Ex vivo analysis of monocytes demonstrated the following: (i) blood CD11b+/Gr-1-/lo but not CD11b-/Gr-1- cells give rise to osteoclasts when they were cultured with receptor activator NF-kappaB ligand and M-CSF; and (ii) TNF-transgenic mice have a significant increase in blood CD11b+/Gr-1-/lo cells and bone marrow proliferating CD11b+/Gr-1-/lo cells. Administration of TNFalpha to wild type mice induced bone marrow CD11b+/Gr-1-/lo cell proliferation, which was associated with an increase in CD11b+/Gr-1-/lo OCPs in the circulation. Thus, TNFalpha directly stimulates bone marrow OCP genesis by enhancing c-Fms expression. This results in progenitor cell proliferation and differentiation in response to M-CSF, leading to an enlargement of the marrow OCP pool. Increased marrow OCPs subsequently egress to the circulation, forming a basis for elevated OCP frequency. Therefore, the first step of TNF-induced osteoclastogenesis is at the level of OCP genesis in the bone marrow, which represents another layer of regulation to control erosive disease.

Animals↗
PubMed2006

Osteoclast precursors: cytokine-stimulated immunomodulators of inflammatory bone disease.

PURPOSE OF REVIEW: Proinflammatory cytokines produced in inflamed joints promote the generation and release from the bone marrow of osteoclast precursors (OCPs). These OCPs are recruited to inflamed joints where, in response to proinflammatory cytokines, they differentiate into osteoclasts and behave as immunomodulatory cells. We review the regulation of OCP formation and differentiation, and propose that they are not only sources of bone-resorbing osteoclasts, but also of immune cells that influence the progression of inflammatory bone diseases. RECENT FINDINGS: OCP numbers are increased in the blood of humans and animals with tumor necrosis factor (TNF)-mediated arthritis and they correlate with serum TNF levels, which can be lowered by anti-TNF therapy. TNF stimulates bone marrow OCP generation in part by increasing their expression of c-Fms. These precursors then leave the bone marrow and circulate in the blood stream. Receptor activator NF-kappaB ligand (RANKL) and TNF, which are elevated in inflamed joints, mediate OCP differentiation into osteoclasts and other cell types, including dendritic cells. They also stimulate OCPs to produce proinflammatory cytokines and chemokines. RANKL inhibition prevents joint inflammation in TNF-mediated arthritis. SUMMARY: OCPs are effector immunomodulatory cells in inflammatory bone diseases. They respond to and secrete cytokines, and are therefore targets for anti-inflammatory therapy.

Bone Diseases↗
PubMed2006

Autoimmunity and bone.

Focal erosions of cartilage and bone, which occur in the joints of patients with autoimmune inflammatory arthritis (i.e., rheumatoid arthritis (RA) and psoriatic arthritis [PsA]), represent the most debilitating and irreversible components of the disease. Over the last decade, seminal breakthroughs in our understanding of the cells and signal transduction pathways central to this process have been elucidated. From this information an established paradigm has been developed to explain focal erosions in which osteoclasts responsible for erosions are derived from bone marrow-derived myeloid precursors. Using the tumor necrosis factor (TNF) transgenic mouse model of erosive arthritis and anti-TNF clinical trials with PsA patients, we have demonstrated that systemic TNF induces the migration of CD11b+ osteoclast precursors (OCP) from the bone marrow into peripheral blood. These OCP can then enter the joints in blood vessels, translocate across the receptor activator of NF-kappaB ligand (RANKL) rich inflamed synovium, and differentiate into active osteoclasts. In direct contrast to this, systemic lupus erythematosus (SLE) patients appear to have an innate resistance to bone resorption. Our hypothesis to explain this phenomenon is that systemic interferon-alpha (IFN-alpha) diverts the bone marrow-derived myeloid precursors away from the osteoclast lineage and stimulates their differentiation into dendritic cells (DC). In support of this model, several labs have used microarray analyses to define the IFN-induced transcriptome in peripheral blood mononuclear cells (PBMC) from SLE patients. Here we propose the hypothesis that systemic TNF induces osteoclastic differentiation of PBMC in PsA patients that correlates with their erosive disease, and that the innate immune TNF/IFN axis in patients with autoimmune disease dictates their erosive phenotype. To demonstrate this, we injected wild-type C57B/6 and TNF-Tg mice with poly I:C, which is known to induce systemic IFN responses, and show its dominant effects on increasing the number of circulating CD11b+/CD11c+ precursor dendritic cells (pDC), concomitant with a dramatic reduction in CD11b+/CD11c- OCP. Thus, systemic factors produced by autoimmunity have a dramatic impact on active myelopoiesis and bone homeostasis.

Animals↗
PubMed2006

Future anti-catabolic therapeutic targets in bone disease.

Understanding of the regulation of bone catabolism has advanced significantly over the past two decades with the identification of key enzymes that regulate osteoclast formation, activation, and survival following their knockout in mice or recognition of mutations in humans. This led to the discovery of specific inhibitors of some of these key enzymes as proof-of-concept lead compounds or potential clinical candidates for the prevention of osteoporosis and other diseases associated with increased bone resorption. Bisphosphonates have been the major therapeutic agents prescribed for the prevention of bone loss in a variety of pathologic conditions for over 30 years. More potent amino bisphosphonates have increased efficacy than earlier drugs, but side effects such as upper gastrointestinal symptoms and the requirement to take them at least 2 h before food have limited patient compliance. This, coupled with the growing knowledge of the pathways regulating osteoclast function, has driven efforts to identify small molecular lead compounds that could be developed into new therapeutic agents with efficacy that matches or supersedes that of bisphosphonates for the prevention of bone loss. In this article, we review briefly the effects of specific inhibitors of bone resorption that have been developed to date and highlight in a variety of models of increased bone resorption the effects of Src kinase inhibitors that have been targeted to bone to limit potential unwanted side effects on other cells.

Bone Diseases↗
PubMed2005

Tumor necrosis factor promotes Runx2 degradation through up-regulation of Smurf1 and Smurf2 in osteoblasts.

Tumor necrosis factor (TNF) plays an important role in the pathogenesis of inflammatory bone loss through stimulation of osteoclastic bone resorption and inhibition of osteoblastic bone formation. Compared with the well established role of TNF in osteoclastogenesis, mechanisms by which TNF inhibits osteoblast function have not been fully determined. Runx2 is an osteoblast-specific transcription factor whose steady-state protein levels are regulated by proteasomal degradation, mediated by the E3 ubiquitin ligases, Smurf1 and Smurf2. We hypothesized that TNF inhibits osteoblast function through Smurf-mediated Runx2 degradation. We treated C2C12 and 2T3 osteoblast precursor cell lines and primary osteoblasts with TNF and found that TNF, but not interleukin-1, significantly increased Smurf1 and Smurf2 expression. TNF increased the degradation of endogenous or transfected Runx2 protein, which was blocked by treating cells with a proteasomal inhibitor or by infecting cells with small interfering (si)RNA against Smurf1 or Smurf2. TNF inhibited the expression of bone morphogenetic protein and transforming growth factor-beta signaling reporter constructs, and the inhibition of each was blocked by Smurf1 siRNA and Smurf2 siRNA, respectively. Overexpression of Smurf1 and/or Smurf2 siRNAs prevented the inhibitory effect of TNF on Runx2 reporter. Consistent with these in vitro findings, bones from TNF transgenic mice or TNF-injected wild type mice had increased Smurf1 and decreased Runx2 protein levels. We propose that one of the mechanisms by which TNF inhibits bone formation in inflammatory bone disorders is by promoting Runx2 proteasomal degradation through up-regulation of Smurf1 and Smurf2 expression.

Animals↗
PubMed2005

Regulation of apoptosis in osteoclasts and osteoblastic cells.

In postnatal life, the skeleton undergoes continuous remodeling in which osteoclasts resorb aged or damaged bone, leaving space for osteoblasts to make new bone. The balance of proliferation, differentiation, and apoptosis of bone cells determines the size of osteoclast or osteoblast populations at any given time. Bone cells constantly receive signals from adjacent cells, hormones, and bone matrix that regulate their proliferation, activity, and survival. Thus, the amount of bone and its microarchitecture before and after the menopause or following therapeutic intervention with drugs, such as sex hormones, glucocorticoids, parathyroid hormone, and bisphosphonates, is determined in part by effects of these on survival of osteoclasts, osteoblasts, and osteocytes. Understanding the mechanisms and regulation of bone cell apoptosis will enhance our knowledge of bone cell function and help us to develop better therapeutics for the management of osteoporosis and other bone diseases.

Adaptation, Physiological↗
PubMed2005

Remodeling of cortical bone allografts mediated by adherent rAAV-RANKL and VEGF gene therapy.

Structural allograft healing is limited because of a lack of vascularization and remodeling. To study this we developed a mouse model that recapitulates the clinical aspects of live autograft and processed allograft healing. Gene expression analyses showed that there is a substantial decrease in the genes encoding RANKL and VEGF during allograft healing. Loss-of-function studies showed that both factors are required for autograft healing. To determine whether addition of these signals could stimulate allograft vascularization and remodeling, we developed a new approach in which rAAV can be freeze-dried onto the cortical surface without losing infectivity. We show that combination rAAV-RANKL- and rAAV-VEGF-coated allografts show marked remodeling and vascularization, which leads to a new bone collar around the graft. In conclusion, we find that RANKL and VEGF are necessary and sufficient for efficient autograft remodeling and can be transferred using rAAV to revitalize structural allografts.

Animals↗
PubMed2005

Roles for NF-kappaB and c-Fos in osteoclasts.

NF-kappaB and c-Fos are transcription factors that are activated in immune cells and in most other cell types following stimulation by a variety of factors, including cytokines, growth factors, and hormones. They regulate the expression of a large number of genes, and both are activated in osteoclast precursors after RANKL, IL-1, or TNF bind to their respective receptors. However, of these cytokines, only RANKL is required for the induction of osteoclast formation in vivo. Nevertheless, it is likely that IL-1, TNF, and other cytokines participate in the upregulation of osteoclast formation seen in a variety of conditions that affect the skeleton in which cytokine production is increased, including estrogen deficiency and inflammatory bone diseases. In this review, the RANKL/ OPG/RANK system and roles for NF-kappaB and c-Fos in osteoclasts are reviewed along with our current understanding of how this system may be disrupted in common bone diseases, such as postmenopausal osteoporosis, inflammatory arthritis, and Paget's disease.

Animals↗
PubMed2005

Osteoclast precursors, RANKL/RANK, and immunology.

Rapid progress has been made in recent years in our understanding of the mechanisms regulating the formation, activation, and survival of osteoclasts, which are derived from precursor cells in the myeloid lineage. In contrast, study of the regulation of osteoclast precursors (OCPs) has been relatively slow, in part because it has been hard to accurately identify them. However, following the discovery of cell-surface markers that facilitated purification of OCPs, recent studies have demonstrated that peripheral blood OCP numbers are increased in tumor necrosis factor (TNF)-mediated arthritis, both in animals and humans, and these numbers correlate with serum TNF levels. The increase can be reversed by anti-TNF therapy. Furthermore, the precursor cells that give rise to osteoclasts can also differentiate into other cell types, including dendritic cells. Receptor activator nuclear factor-kappaB ligand (RANKL) stimulates OCPs to produce pro-inflammatory cytokines and chemokines, and RANKL blockade prevents joint inflammation in a murine model of inflammatory arthritis. These findings suggest that OCPs may serve as a source for both osteoclasts and other effector cells and participate actively in the pathogenesis of diseases. Here, we review our current understanding of the regulation of OCP formation and differentiation and provide a model of a vicious cycle in which pro-inflammatory cytokines produced in inflamed joints feedback on the bone marrow to promote the generation and release of OCPs. The OCPs then home to the inflamed joints to differentiate into mature osteoclasts or to produce more inflammatory factors in the presence of RANKL. Disruption of this cycle could provide a new strategy for the development of drugs to treat inflammatory arthritis and other disorders associated with elevated OCP/myeloid progenitors.

Animals↗
PubMed2005

Lead exposure inhibits fracture healing and is associated with increased chondrogenesis, delay in cartilage mineralization, and a decrease in osteoprogenitor frequency.

Lead exposure continues to be a significant public health problem. In addition to acute toxicity, Pb has an extremely long half-life in bone. Individuals with past exposure develop increased blood Pb levels during periods of high bone turnover or resorption. Pb is known to affect osteoblasts, osteoclasts, and chondrocytes and has been associated with osteoporosis. However, its effects on skeletal repair have not been studied. We exposed C57/B6 mice to various concentrations of Pb acetate in their drinking water to achieve environmentally relevant blood Pb levels, measured by atomic absorption. After exposure for 6 weeks, each mouse underwent closed tibia fracture. Radiographs were followed and histologic analysis was performed at 7, 14, and 21 days. In mice exposed to low Pb concentrations, fracture healing was characterized by a delay in bridging cartilage formation, decreased collagen type II and type X expression at 7 days, a 5-fold increase in cartilage formation at day 14 associated with delayed maturation and calcification, and a persistence of cartilage at day 21. Fibrous nonunions at 21 days were prevalent in mice receiving very high Pb exposures. Pb significantly inhibited ex vivo bone nodule formation but had no effect on osteoclasts isolated from Pb-exposed animals. No significant effects on osteoclast number or activity were observed. We conclude that Pb delays fracture healing at environmentally relevant doses and induces fibrous nonunions at higher doses by inhibiting the progression of endochondral ossification.

Animals↗
PubMed2005

TNF-alpha and pathologic bone resorption.

Chronic inflammatory bone diseases, such as rheumatoid arthritis, periodontal disease and aseptic periprosthetic osteolysis, are characterized by bone loss around affected joints and teeth caused by increased osteoclastic bone resorption. This resorption is mediated largely by the increased local production of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNFa). These cytokines may induce resorption indirectly by affecting the production of the essential osteoclast differentiation factor, receptor activator of NF-kB ligand, and/or its soluble decoy receptor, osteoprotegerin, by osteoblast/stromal cells or directly by enhancing proliferation and/or activity of cells in the osteoclast lineage. The importance of TNFa in the pathogenesis of various forms of bone loss is supported by both experimental and clinical evidence. However, TNFa is not absolutely required for osteoclastogenesis, erosive arthritis, or osteolysis, as all these events could occur in the absence of TNFa and whether TNFa promotes osteoclast formation independently of RANK signaling is still a topic of debate. Here we review our current understanding of the mechanisms whereby TNFa increases osteoclastogenesis in vitro and in vivo.

Animals↗
PubMed2004

Malignant autosomal recessive osteopetrosis caused by spontaneous mutation of murine Rank.

UNLABELLED: We report the first case of lethal autosomal recessive osteopetrosis in mice caused by a spontaneous 8-bp deletion in exon 2 of the Rank gene. The phenotype, including a block in RANKL-dependent osteoclast differentiation and lymph node agenesis, copies that of Rank(-/-) mice, which have been produced by targeted recombination. INTRODUCTION: Commitment of osteoclast progenitors to the osteoclast lineage requires RANKL/RANK-mediated intercellular signals. Gene-targeted defects in this signaling pathway resulted in osteoclast deficiency and severe osteopetrosis in mice, but to date, there have been no reports of spontaneous mutations in Rankl or Rank resulting in osteopetrosis. MATERIALS AND METHODS: Mice with malignant osteopetrosis and absent lymph nodes appeared spontaneously in a highly inbred colony. Appropriate crosses were analyzed to establish the pattern of inheritance. Tissues from affected pups and littermates were evaluated grossly, histopathologically, and radiographically. Osteoclast development from splenocytes was tested in vitro under a variety of conditions, including after infection with RANK-encoding retrovirus. Rank mutational analysis was performed by direct sequencing of RT-PCR products and genomic DNA. RESULTS: The inheritance pattern was consistent with autosomal recessive inheritance, and the phenotype resembled that of either Rankl or Rank knockout mice with the exception of as yet unexplained death of most mice 2-3 weeks after weaning. Osteoclast precursors from the spleens of affected pups failed to form osteoclasts in vitro when stimulated with macrophage-colony stimulating factor (M-CSF) and RANKL, unless they were forced to express wildtype Rank cDNA. Molecular genetic studies identified an 8-bp deletion in exon 2 of the Rank gene. The resulting allele, termed Rank(del8), encodes only a small portion of the RANK extracellular domain, which is probably nonfunctional. CONCLUSIONS: The phenotypic similarities between Rank(del8) and mice previously described with a combined insertion and deletion in Rank confirm the role of this receptor in osteoclastogenesis and lymph node development and suggest that some forms of malignant osteopetrosis in humans could result from a similar defect.

Animals↗
PubMed2004

Systemic tumor necrosis factor alpha mediates an increase in peripheral CD11bhigh osteoclast precursors in tumor necrosis factor alpha-transgenic mice.

OBJECTIVE: To investigate the mechanisms whereby tumor necrosis factor alpha (TNFalpha) increases osteoclastogenesis in vivo. METHODS: TNFalpha-transgenic (TNF-Tg) and wild-type mice injected with TNFalpha were studied. In vitro osteoclastogenesis assays, monocyte colony-forming assays, and fluorescence-activated cell sorting were performed using splenocytes, peripheral blood mononuclear cells (PBMCs), and bone marrow cells to quantify and characterize osteoclast precursors (OCPs). Etanercept, a TNFalpha antagonist, was used to block TNFalpha activity in vivo. The effects of TNFalpha on proliferation, apoptosis, and differentiation of OCPs were assessed using 5-bromo-2'-deoxyuridine labeling, annexin V staining, and reverse transcriptase-polymerase chain reaction. RESULTS: OCP numbers were increased 4-7-fold in PBMCs and spleen, but not in bone marrow of TNF-Tg mice. The OCPs in spleen were in the CD11b(high) population and contained both c-Fms- and c-Fms+ cells. The increased number of OCPs correlated with the initiation of detectable TNFalpha in serum and the onset of inflammatory arthritis in TNF-Tg mice. Etanercept eliminated the increase in peripheral OCPs. TNFalpha did not affect proliferation, survival, or differentiation of CD11b(high) splenocytes in vivo or in vitro, but caused a rapid increase in CD11b+ cells in blood within 4 hours of a single injection and an accumulation of CD11b(high) OCPs in spleen after 3 days of multiple injections. CONCLUSION: Systemic TNFalpha induces a marked increase in circulating OCPs that is reversible by anti-TNF therapy and may result from their mobilization from bone marrow. Our findings provide a new mechanism whereby TNFalpha stimulates osteoclastogenesis in patients with inflammatory arthritis, suggesting that CD11b+ PBMCs could be used to evaluate a patient's potential for erosive disease and the efficacy of anti-TNF therapy.

Animals↗