HIV and Bone Disease: A Perspective of the Role of microRNAs in Bone Biology upon HIV Infection

Increased life expectancy and the need for long-term antiretroviral therapy have brought new challenges to the clinical management of HIV-infected individuals. The prevalence of osteoporosis and fractures is increased in HIV-infected patients; thus optimal strategies for risk management and treatment in this group of patients need to be defined. Prevention of bone loss is an important component of HIV care as the HIV population grows older. Understanding the mechanisms by which HIV infection affects bone biology leading to osteoporosis is crucial to delineate potential adjuvant treatments. This review focuses on HIV-induced osteoporosis within the context of microRNAs (miRNAs) by reviewing first basic concepts of bone biology as well as current knowledge of the role of miRNAs in bone development. Evidence that HIV-associated osteoporosis is in part independent of therapies employed to treat HIV (HAART) is supported by cross-sectional and longitudinal studies and is the focus of this review.

Macrophage-specific TLR2 signaling mediates pathogen-induced TNF-dependent inflammatory oral bone loss

Porphyromonas gingivalis is a primary etiological agent of chronic periodontal disease, an infection-driven chronic inflammatory disease that leads to the resorption of tooth-supporting alveolar bone. We previously reported that TLR2 is required for P. gingivalis-induced alveolar bone loss in vivo, and our in vitro work implicated TNF as a key downstream mediator. In this study, we show that TNF-deficient (Tnf(-/-)) mice are resistant to alveolar bone loss following oral infection with P. gingivalis, and thus establish a central role for TNF in experimental periodontal disease. Using bone marrow-derived macrophages (BMDM) from wild-type and gene-specific knockout mice, we demonstrate that the initial inflammatory response to P. gingivalis in naive macrophages is MyD88 dependent and requires cooperative signaling of TLR2 and TLR4. The ability of P. gingivalis to activate cells via TLR2 or TLR4 was confirmed in TLR2- or TLR4-transformed human embryonic kidney cells. Additional studies using bacterial mutants demonstrated a role for fimbriae in the modulation of TLR-mediated activation of NF-κB. Whereas both TLR2 and TLR4 contributed to TNF production in naive macrophages, P. gingivalis preferentially exploited TLR2 in endotoxin-tolerant BMDM to trigger excessive TNF production. We found that TNF induced surface TLR2 expression and augmented TLR-induced cytokine production in P. gingivalis-stimulated BMDM, establishing a previously unidentified TNF-dependent feedback loop. Adoptive transfer of TLR2-expressing macrophages to TLR2-deficient mice restored the ability of P. gingivalis to induce alveolar bone loss in vivo. Collectively, our results identify a TLR2- and TNF-dependent macrophage-specific mechanism underlying pathogen-induced inflammatory bone loss in vivo.

IL-17 mediates estrogen-deficient osteoporosis in an Act1-dependent manner

Estrogen-deficient osteoporosis may be an inflammatory disorder and we therefore asked if IL-17 participates in its pathogenesis. Deletion of the principal IL-17 receptor (IL-17RA) protects mice from ovariectomy (OVX)-induced bone loss. Further supporting a central role of IL-17 in its pathogenesis, OVX-induced osteoporosis is prevented by a blocking antibody targeting the cytokine. IL-17 promotes osteoclastogenesis by stimulating RANK ligand (RANKL) expression by osteoblastic cells, mediated by the IL-17RA SEFIR/TILL domain. Estrogen deprivation, however does not enhance IL-17RA mRNA expression by osteoblasts or in bone, but augments that of Act1, an IL-17RA-interacting protein and signaling mediator. Similar to IL-17RA(-/-) mice, those lacking Act1 are protected from OVX-induced bone loss. Also mirroring IL-17RA-deficiency, absence of Act1 in osteoblasts, but not osteoclasts, impairs osteoclastogenesis via dampened RANKL expression. Transduction of WT Act1 into Act1(-/-) osteoblasts substantially rescues their osteoclastogenic capacity. The same construct, however, lacking its E3 ligase U-box or its SEFIR domain, which interacts with its counterpart in IL-17RA, fails to do so. Estrogen deprivation, therefore, promotes RANKL expression and bone resorption in association with upregulation of the IL-17 effector, Act1, supporting the concept that post-menopausal osteoporosis is a disorder of innate immunity.

Brucella abortus-infected macrophages modulate T lymphocytes to promote osteoclastogenesis via IL-17

The pathogenic mechanisms of bone loss caused by Brucella species have not been completely deciphered. Although T lymphocytes (LTs) are considered important to control infection, the mechanism of Brucella-induced T-cell responses to immunopathological features is not known. We present in vitro and in vivo evidence showing that Brucella abortus-induced inflammatory response leads to the activation of LTs, which further promote osteoclastogenesis. Pre-activated murine LTs treated with culture supernatant from macrophages infected with B. abortus induced bone marrow-derived monocytes (BMMs) to undergo osteoclastogenesis. Furthermore, osteoclastogenesis was mediated by CD4(+) T cells. Although B. abortus-activated T cells actively secreted the pro-osteoclastogenic cytokines RANKL and IL-17, osteoclastogenesis depended on IL-17, because osteoclast generation induced by Brucella-activated T cells was completely abrogated when these cells were cultured with BMMs from IL-17 receptor knockout mice. Neutralization experiments indicated that IL-6, generated by Brucella infection, induced the production of pro-osteoclastogenic IL-17 from LTs. By using BMMs from tumor necrosis factor receptor p55 knockout mice, we also demonstrated that IL-17 indirectly induced osteoclastogenesis through the induction of tumor necrosis factor-α from osteoclast precursors. Finally, extensive and widespread osteoclastogenesis was observed in the knee joints of mice injected with Brucella-activated T cells. Our results indicate that activated T cells, elicited by B. abortus-infected macrophages and influenced by the inflammatory milieu, promote the generation of osteoclasts, leading to bone loss.

Fluid pressure induces osteoclast differentiation comparably to titanium particles but through a molecular pathway only partly involving TNFα

In contrast to the well-understood inflammatory pathway driven by TNFα, by which implant-derived particles induce bone resorption, little is known about the process in which loosening is generated as a result of force-induced mechanical stimulus at the bone-implant interface. Specifically, there is no knowledge as to what cells or signaling pathways couple mechanical stimuli to bone resorption in context of loosening. We hypothesized that different stimuli, i.e., fluid flow versus wear particles, act through different cytokine networks for activation and localization of osteoclasts. By using an animal model in which osteoclasts and bone resorption were induced by fluid pressure or particles, we were able to detect distinct differences in osteoclast localization and inflammatory gene expression between fluid pressure and titanium particles. Fluid pressure recruits and activates osteoclasts with bone marrow contact away from the fluid pressure exposure zone, whereas titanium particles recruit and activate osteoclasts in areas in direct contact to particles. Fluid pressure induced weaker expression of the selected inflammatory related genes, although the eventual degree of osteoclast induction was similar in both models. Using TNFαRa (4 mg/kg) (Enbrel) and dexamethasone (2 mg/kg) as specific and more general suppressors of inflammation we showed that the TNFαRa failed to generate statistically impaired osteoclast generation while dexamethasone was much more potent. These results demonstrate that fluid pressure induces osteoclasts at a different localization than titanium particles by a molecular pathway less associated with TNFα and the innate system, which open up for other pathways controlling pressure induced osteoclastogenesis.

IL-4 inhibits TNF-α-mediated osteoclast formation by inhibition of RANKL expression in TNF-α-activated stromal cells and direct inhibition of TNF-α-activated osteoclast precursors via a T-cell-independent mechanism in vivo

It has been reported that osteoclastogenesis is induced by tumor necrosis factor (TNF)-α. Interleukin (IL)-4 is the most important cytokine involved in humoral immunity. However, no studies have investigated the effect of IL-4 on TNF-α-mediated osteoclast formation in vivo. In this study, we investigated the effect of IL-4 on TNF-α-mediated osteoclast formation in vivo. TNF-α was administered with and without IL-4 into the supracalvariae of mice. The number of osteoclasts and the levels of mRNA for cathepsin K and tartrate-resistant acid phosphate, both osteoclast markers, in mice administered TNF-α and IL-4 were lower than those in mice administered TNF-α alone. The level of tartrate-resistant acid phosphatase form 5b (TRACP5b) as a marker of bone resorption in mice administered both TNF-α and IL-4 was also lower. We showed that IL-4 inhibited TNF-α-mediated osteoclast formation in osteoclast precursors in vitro. Expression of receptor activator of NF-κB ligand (RANKL) in TNF-α-activated stromal cells was also inhibited. Furthermore, we investigated whether IL-4 had effects on both stromal cells and osteoclast precursors in TNF-α-mediated osteoclast formation in vivo. Using mice whose stromal cells and osteoclast precursors were chimeric for the presence of TNF receptors, IL-4 inhibited TNF-α-mediated osteoclast formation in the presence of TNF-α-responsive stromal cells, and TNF-α-responsive osteoclast precursors in vivo. IL-4 also inhibited TNF-α-induced RANKL expression in the presence of TNF-α-responsive stromal cells in vivo. This event is dependent on p38 inhibition in vitro. Additionally, IL-4 inhibited TNF-α-mediated osteoclast formation in T cell-depleted mice. In summary, we conclude that IL-4 inhibited TNF-α-mediated osteoclast formation by inhibiting expression of RANKL in TNF-α-activated stromal cells, and directly inhibited TNF-α-activated osteoclast precursors in vivo via a T cell-independent mechanism.

IL1 gene polymorphisms in relation to external apical root resorption concurrent with orthodontia

OBJECTIVE

External apical root resorption (EARR) is permanent shortening of the end of the tooth root. It is a common clinical complication of orthodontic treatment. Polymorphisms in the interleukin 1 (IL1) gene cluster have been related to an increased EARR risk. The aim of this study was to analyze possible associations of IL1 gene variants with EARR in Czech population.

SUBJECTS AND METHODS

In this case-control study, 32 patients with EARR (age 15.0 ± 4.1 years) and 74 controls (age 15.2 ± 5.3 years) were genotyped using PCR-based methods for IL1A (-889C/T), IL1B (+3953C/T), and IL1RN [IL1 receptor antagonist, variable number tandem repeat (VNTR)] gene polymorphisms.

RESULTS

While no statistical significant differences in the IL1A and IL1B genotype, allele and reconstructed IL1 haplotype frequencies between patients with EARR and controls were found, marginally significant differences were observed in the frequencies of IL1RN variant (P = 0.05 for *22 genotype and P = 0.06 for a short (2) allele). In addition, significant associations between IL1RN*12, *22 genotypes and the short (2) allele and EARR were identified in the subgroup of girls (P = 0.04 and P = 0.02, P = 0.02).

CONCLUSIONS

Although no significant role of IL1A (-889C/T) and IL1B (+3953C/T) variants in EARR was confirmed, IL1RN VNTR may be associated with EARR, especially in girls.

Bach1 regulates osteoclastogenesis in a mouse model via both heme oxygenase 1-dependent and heme oxygenase 1-independent pathways

OBJECTIVE

Reducing inflammation and osteoclastogenesis by heme oxygenase 1 (HO-1) induction could be beneficial in the treatment of rheumatoid arthritis (RA). However, the function of HO-1 in bone metabolism remains unclear. This study was undertaken to clarify the effects of HO-1 and its repressor Bach1 in osteoclastogenesis.

METHODS

In vitro osteoclastogenesis was compared in Bach1-deficient and wild-type mice. Osteoclasts (OCs) were generated from bone marrow-derived macrophages by stimulation with macrophage colony-stimulating factor and RANKL. Osteoclastogenesis was assessed by tartrate-resistant acid phosphatase staining and expression of OC-related genes. Intracellular signal pathways in OC precursors were also assessed. HO-1 short hairpin RNA (shRNA) was transduced into Bach1(-/-) mouse bone marrow-derived macrophages to examine the role of HO-1 in osteoclastogenesis. In vivo inflammatory bone loss was evaluated by local injection of tumor necrosis factor α (TNFα) into calvaria.

RESULTS

Transcription of HO-1 was down-regulated by stimulation with RANKL in the early stage of OC differentiation. Bach1(-/-) mouse bone marrow-derived macrophages were partially resistant to the RANKL-dependent HO-1 reduction and showed impaired osteoclastogenesis, which was associated with reduced expression of RANK and components of the downstream TNF receptor-associated factor 6/c-Fos/NF-ATc1 pathway as well as reduced expression of Blimp1. Treatment with HO-1 shRNA increased the number of OCs and expression of OC-related genes except for the Blimp1 gene during in vitro osteoclastogenesis from Bach1(-/-) mouse bone marrow-derived macrophages. TNFα-induced bone destruction was reduced in Bach1(-/-) mice in vivo.

CONCLUSION

The present findings demonstrate that Bach1 regulates osteoclastogenesis under inflammatory conditions, via both HO-1-dependent and HO-1-independent mechanisms. Bach1 may be worthy of consideration as a target for treatment of inflammatory bone loss in diseases including RA.

Mitigation of inflammation with foods

Constant overproduction of pro-inflammatory molecules leads to chronic inflammation. Unlike acute inflammation, which is essential for healing, chronic inflammation can delay healing and, if left unchecked, contribute to a host of diseases. There is growing evidence that some dietary factors can play important roles in maintaining health and even reversing the progression of chronic diseases, with anti-inflammatory effects as important underlying mechanism. Such findings add to the body of evidence that certain dietary components, including polyphenols and other types of compounds, found in various dietary factors including fruits, berries, vegetables, nuts, whole grains, and foods of marine origin, can play an important role in attenuating and mitigating chronic pro-inflammatory processes associated with chronic diseases.

The gut microbiota regulates bone mass in mice

The gut microbiota modulates host metabolism and development of immune status. Here we show that the gut microbiota is also a major regulator of bone mass in mice. Germ-free (GF) mice exhibit increased bone mass associated with reduced number of osteoclasts per bone surface compared with conventionally raised (CONV-R) mice. Colonization of GF mice with a normal gut microbiota normalizes bone mass. Furthermore, GF mice have decreased frequency of CD4(+) T cells and CD11b(+) /GR 1 osteoclast precursor cells in bone marrow, which could be normalized by colonization. GF mice exhibited reduced expression of inflammatory cytokines in bone and bone marrow compared with CONV-R mice. In summary, the gut microbiota regulates bone mass in mice, and we provide evidence for a mechanism involving altered immune status in bone and thereby affected osteoclast-mediated bone resorption. Further studies are required to evaluate the gut microbiota as a novel therapeutic target for osteoporosis.

Methotrexate chemotherapy promotes osteoclast formation in the long bone of rats via increased pro-inflammatory cytokines and enhanced NF-κB activation

Cancer chemotherapy with methotrexate (MTX) is known to cause bone loss. However, the underlying mechanisms remain unclear. This study investigated the potential role of MTX-induced pro-inflammatory cytokines and activation of NF-κB in the associated osteoclastogenesis in rats. MTX (0.75 mg/kg per day) was administered for 5 days, and bone and bone marrow specimens were collected on days 6, 9, and 14. Compared with a normal control, MTX increased the density of osteoclasts within the metaphyseal bone and the osteoclast formation potential of marrow cells on day 9. RT-PCR analysis of mRNA expression for pro-osteoclastogenic cytokines in the metaphysis indicated that, although the receptor activator of NF-κB ligand/osteoprotegerin axis was unaffected, expression of tumor necrosis factor (TNF)-α, IL-1, and IL-6 increased on day 9. Enzyme-linked immunosorbent assay analysis of plasma showed increased levels of TNF-α on day 6 and of IL-6 on day 14. Plasma from treated rats induced osteoclast formation from normal bone marrow cells, which was attenuated by a TNF-α-neutralizing antibody. Indicative of a role for NF-κB signaling, plasma on day 6 increased NF-κB activation in RAW(264.7) cells, and plasma-induced osteoclastogenesis was abolished in the presence of the NF-κB inhibitor, parthenolide. Our results demonstrate mechanisms for MTX-induced osteoclastogenesis and show that MTX induces osteoclast differentiation by generating a pro-osteoclastogenic environment in both bone and the circulation, specifically with increased TNF-α levels and activation of NF-κB.

MicroRNA-181b regulates NF-κB-mediated vascular inflammation

EC activation and dysfunction have been linked to a variety of vascular inflammatory disease states. The function of microRNAs (miRNAs) in vascular EC activation and inflammation remains poorly understood. Herein, we report that microRNA-181b (miR-181b) serves as a potent regulator of downstream NF-κB signaling in the vascular endothelium by targeting importin-α3, a protein that is required for nuclear translocation of NF-κB. Overexpression of miR-181b inhibited importin-α3 expression and an enriched set of NF-κB-responsive genes such as adhesion molecules VCAM-1 and E-selectin in ECs in vitro and in vivo. In addition, treatment of mice with proinflammatory stimuli reduced miR-181b expression. Rescue of miR-181b levels by systemic administration of miR-181b "mimics" reduced downstream NF-κB signaling and leukocyte influx in the vascular endothelium and decreased lung injury and mortality in endotoxemic mice. In contrast, miR-181b inhibition exacerbated endotoxin-induced NF-κB activity, leukocyte influx, and lung injury. Finally, we observed that critically ill patients with sepsis had reduced levels of miR-181b compared with control intensive care unit (ICU) subjects. Collectively, these findings demonstrate that miR-181b regulates NF-κB-mediated EC activation and vascular inflammation in response to proinflammatory stimuli and that rescue of miR-181b expression could provide a new target for antiinflammatory therapy and critical illness.

HIV: inflammation and bone

HIV infection and antiretroviral therapy (ART) are now established independent risk factors for osteoporosis. With a spate of recent studies reporting significant elevations in fracture prevalence in HIV patients, and a rapidly aging demographic, defining the mechanisms underlying HIV/ART-induced skeletal decline has become imperative. The recent emergence of the field of "osteoimmunology" has provided a conceptual framework to explain how the immune and skeletal systems interact. Furthermore, it is becoming clear that inflammatory states leading to perturbations in the immuno-skeletal interface, a convergence of common cells and cytokine mediators that regulate both immune and skeletal systems, conspire to imbalance bone turnover and induce osteoporosis. In this review we examine the role of inflammation in the bone loss associated with diverse inflammatory conditions and new concepts into how the underlying mechanisms by which inflammation and immune dysregulation impact bone turnover may be pertinent to the mechanisms involved in HIV/ART-induced bone loss.

Constitutive activation of p38 MAPK in tumor cells contributes to osteolytic bone lesions in multiple myeloma

Bone destruction is a hallmark of multiple myeloma and affects more than 80% of patients. However, current therapy is unable to completely cure and/or prevent bone lesions. Although it is accepted that myeloma cells mediate bone destruction by inhibition of osteoblasts and activation of osteoclasts, the underlying mechanism is still poorly understood. This study demonstrates that constitutive activation of p38 mitogen-activated protein kinase in myeloma cells is responsible for myeloma-induced osteolysis. Our results show that p38 is constitutively activated in most myeloma cell lines and primary myeloma cells from patients. Myeloma cells with high/detectable p38 activity, but not those with low/undetectable p38 activity, injected into SCID or SCID-hu mice caused bone destruction. Inhibition or knockdown of p38 in human myeloma reduced or prevented myeloma-induced osteolytic bone lesions without affecting tumor growth, survival, or homing to bone. Mechanistic studies showed that myeloma cell p38 activity inhibited osteoblastogenesis and bone formation and activated osteoclastogenesis and bone resorption in myeloma-bearing SCID mice. This study elucidates a novel molecular mechanism—sactivation of p38 signaling in myeloma cells—by which myeloma cells induce osteolytic bone lesions and indicates that targeting myeloma cell p38 may be a viable approach to treating or preventing myeloma bone disease.

The Anti-Inflammatory, Phytoestrogenic, and Antioxidative Role of Labisia pumila in Prevention of Postmenopausal Osteoporosis

Osteoporosis is characterized by skeletal degeneration with low bone mass and destruction of microarchitecture of bone tissue which is attributed to various factors including inflammation. Women are more likely to develop osteoporosis than men due to reduction in estrogen during menopause which leads to decline in bone-formation and increase in bone-resorption activity. Estrogen is able to suppress production of proinflammatory cytokines such as IL-1, IL-6, IL-7, and TNF-α. This is why these cytokines are elevated in postmenopausal women. Studies have shown that estrogen reduction is able to stimulate focal inflammation in bone. Labisia pumila (LP) which is known to exert phytoestrogenic effect can be used as an alternative to ERT which can produce positive effects on bone without causing side effects. LP contains antioxidant as well as exerting anti-inflammatory effect which can act as free radical scavenger, thus inhibiting TNF-α production and COX-2 expression which leads to decline in RANKL expression, resulting in reduction in osteoclast activity which consequently reduces bone loss. Hence, it is the phytoestrogenic, anti-inflammatory, and antioxidative properties that make LP an effective agent against osteoporosis.

Molecular basis of requirement of receptor activator of nuclear factor κB signaling for interleukin 1-mediated osteoclastogenesis

IL-1, a proinflammatory cytokine, is implicated in bone loss in various pathological conditions by promoting osteoclast formation, survival, and function. Although IL-1 alone can sufficiently prolong osteoclast survival and activate osteoclast function, IL-1-mediated osteoclastogenesis requires the receptor activator of NF-κB (RANK) ligand (RANKL). However, the molecular basis of the dependence of IL-1-mediated osteoclastogenesis on RANKL is not fully understood. Here we show that although IL-1 cannot activate the expression of the osteoclast genes encoding matrix metalloproteinase 9, cathepsin K, tartrate-resistant acid phosphatase, and carbonic anhydrase II in bone marrow macrophages (BMMs), RANKL renders these osteoclast genes responsive to IL-1. We further demonstrate that IL-1 alone fails to induce the expression of nuclear factor of activated T cell cytoplasmic 1 (NFATc1), a master transcriptional regulator of osteoclastogenesis), in BMMs but can up-regulate its expression in the presence of permissive levels of RANKL or with RANKL pretreatment. The RANK IVVY motif, which has been previously shown to commit BMMs to the osteoclast lineage in RANKL- and TNF α-mediated osteoclastogenesis, also plays a crucial role in IL-1-mediated osteoclastogenesis by changing the four osteoclast marker and NFATc1 genes to an IL-1-inducible state. Finally, we show that MyD88, a known critical component of the IL-1 receptor I signaling pathway, plays a crucial role in IL-1-mediated osteoclastogenesis from RANKL-primed BMMs by up-regulating the expression of the osteoclast marker and NFATc1 genes. This study reveals a novel mechanism of IL-1-mediated osteoclastogenesis and supports the promising potential of the IVVY motif to serve as a therapeutic target for inflammatory bone loss.

Interleukin-4 inhibits RANKL-induced NFATc1 expression via STAT6: a novel mechanism mediating its blockade of osteoclastogenesis

Interleukin-4 (IL-4) is an important immune regulatory protein that possesses potent anti-osteoclastogenic properties, and does so via the transcription factor STAT6. Previous studies have shown that IL-4 selectively blocks RANKL-induced activation of NF-κB and mitogen-activated protein kinase (MAPK) pathway molecules, suggesting that the cytokine arrests osteoclastogenesis by blockade of these signaling cascades. However, the fact that the inhibitory effect on these pathways requires prolonged IL-4 pretreatment, and that the cytokine fails to exert an anti-osteoclastogenic effect after short-term pre-exposure of RANKL to osteoclast precursors, suggests that an additional, more immediate mechanism may also be involved. In this study, we found that simultaneous exposure of IL-4 did not alter RANKL-dependent activation of NF-κB or MAPKs, whereas the cytokine did block RANKL-induced nuclear factor activated T cells c1 (NFATc1), a master osteoclastogenic transcription factor. This inhibitory effect of IL-4 required STAT6, consistent with its functional role in osteoclastogenesis. In addition, the cytokine also partially impaired RANKL-stimulated bone resorption. Furthermore, IL-4 suppressed expression of RANKL-induced osteoclast specific genes in a STAT6-dependent manner, but failed to do so when osteoclast precursors were pre-exposed to RANKL. Thus, we provide the first evidence that IL-4 inhibits osteoclast formation by inhibiting RANKL induction of NFATc1 via STAT6 as an early event, in addition to its suppression of other signaling pathways. The inhibitory effect is ultimately regulated at the gene expression transcriptional level.

Bisphosphonates: effects on osteoblast

PURPOSE

Bisphosphonates are synthetic analogues of pyrophosphate usually used in treating bone disorders such as osteoporosis, Paget's disease, fibrous dysplasia, hypercalcemia of malignancy, and inflammation-related bone loss. Though therapeutic effects of bisphosphonates depend primarily on their inhibitory effect on osteoclasts, increasing attention is being given to other effector cells, such as osteoblasts. This review focuses on the presumed effect of bisphosphonates on osteoblasts.

METHODS

A review of the literature was conducted to evaluate the pharmacodynamic effects of bisphosphonates including inhibition of osteoclasts and apoptosis of osteocytes and osteoblasts as well as their potential stimulatory effects on the proliferation of osteoblasts.

RESULTS

Studies have demonstrated that bisphosphonates may stimulate proliferation of osteoblasts and inhibit apoptosis of osteocytes and osteoblasts.

CONCLUSION

Considering that osteoblasts may be involved in bone disorders, such as osteoporosis, osteopetrosis, osteogenesis imperfecta, and Paget's disease, and that bisphosphonates may stimulate proliferation of osteoblasts and inhibit apoptosis of osteocytes and osteoblasts, it is conceivable that a role for bisphosphonates exists in these diseases beyond merely the osteoclast influence.

Why TNF-α inhibition is not sufficient to avoid juxta-articular erosions in chronic arthritis?

There is an emerging interest in the role of anti-TNF-α therapy in reducing bone damage in chronic arthritis with special regard to rheumatoid arthritis. Accumulation of osteoclasts in rheumatoid synovial tissues, and their activation due to osteoclastogenic cytokines and chemokines at cartilage erosion sites suggest that they may advantageously be considered as therapeutic targets. Given that the primary role of TNF-α in osteoclastogenesis, the inhibition of TNF-α represents an important strategy for reducing bone damage in rheumatoid arthritis. In point of fact, there is evidence that treatment with anti-TNF-α agents may avoid or reduce bone damage in rheumatoid arthritis, even if further studies are required to provide a biological explanation and a link for the observation of the advantageous effects of TNF-α inhibitors on the progression of bone damage in chronic arthritis. The existence of factors involved in osteoclast activation, including IL-1, IL-6, IL-7, IL-11, IL-17, M-CSF, TGF-β, MIP-1α, MIP-1β, IP-10, MIG, and OSCAR, indicates that TNF-α is only a single player in the great molecular cauldron of osteoclastogenesis. The presence of mediators behind the TNF-α and RANK-RANKL complex that may be independent in inducing osteoclastogenesis, such as NFATc1, suggests that the anti-TNF-α therapy will not provide a complete reduction of bone damage in chronic arthritis.

Nitric oxide mediates low magnesium inhibition of osteoblast-like cell proliferation

An adequate intake of magnesium (Mg) is important for bone cell activity and contributes to the prevention of osteoporosis. Because (a) Mg is mitogenic for osteoblasts and (b) reduction of osteoblast proliferation is detected in osteoporosis, we investigated the influence of different concentrations of extracellular Mg on osteoblast-like SaOS-2 cell behavior. We found that low Mg inhibited SaOS-2 cell proliferation by increasing the release of nitric oxide through the up-regulation of inducible nitric oxide synthase (iNOS). Indeed, both pharmacological inhibition with the iNOS inhibitor l-N(6)-(iminoethyl)-lysine-HCl and genetic silencing of iNOS by small interfering RNA restored the normal proliferation rate of the cells. Because a moderate induction of nitric oxide is sufficient to potentiate bone resorption and a relative deficiency in osteoblast proliferation can result in their inadequate activity, we conclude that maintaining Mg homeostasis is relevant to ensure osteoblast function and, therefore, to prevent osteoporosis.

Anti IL-17A therapy inhibits bone loss in TNF-α-mediated murine arthritis by modulation of the T-cell balance

Tumour necrosis factor alpha (TNF-α) is a major inducer for inflammation and bone loss. Here, we investigated whether interleukin (IL)-17 plays a role in TNF-α-mediated inflammation and bone resorption. Human TNF-α transgenic (hTNFtg) mice were treated with a neutralizing anti-IL-17A antibody and assessed for inflammation, cartilage and bone damage. T-cell transcription factors and lymphokine patterns were measured in the LNs. IL-17A inhibition in the absence of IL-1 was also evaluated by treating hTNFtg/IL-1(-/-) mice with an IL-17A neutralizing antibody. IL-17A neutralization had only minor effects on TNF-α-induced inflammation but effectively reduced local and systemic bone loss by blocking osteoclast differentiation in vivo. Effects were based on a shift to bone-protective T-cell responses such as enhanced Th2 differentiation, IL-4 and IL-12 expression and Treg cell numbers. Whereas inflammation in hTNFtg/IL-1(-/-) mice was highly sensitive to IL-17A blockade, no shift in the T-cell lineages and no additional benefit on bone mass were observed in response to IL-17A neutralization. We thus conclude that IL-17A is a key mediator of TNF-α-induced bone loss by closely interacting with IL-1 in blocking bone protective T-cell responses.

Effects of inflammatory and anti-inflammatory cytokines on the bone

BACKGROUND

Inflammatory diseases are linked to enhanced bone loss. The effect of inflammation on bone is mediated by proinflammatory cytokines, which regulate bone formation as well as bone resorption thereby altering bone homeostasis.

MATERIALS AND METHODS

In this article we summarize the key insights in cytokine regulation of bone. We describe the major pro- and anti-inflammatory mediators, which are involved in the regulation of bone and describe the mechanisms by which these cytokines alter bone balance.

RESULTS

We describe the effects of tumor necrosis factor (TNF), interleukin (IL)- 1 family members, IL-6, IL-17 and interferons (IFN) on bone and discuss the mechanisms by which these individual cytokines affect the bone resorbing and the bone forming cells.

CONCLUSIONS

Several proinflammatory cytokines (such as TNFa, IL-1 and IL-17) are major triggers for osteoclast activation explaining the enhanced bone loss during inflammation. Other such as IL-12, IL-18, IL-33 and IFN are strong suppressors of osteoclast differentiation and inhibit bone loss. Thus the cytokine composition of an inflammatory tissue is decisive whether inflammation triggers bone loss or not.

Macrophage-elicited osteoclastogenesis in response to Brucella abortus infection requires TLR2/MyD88-dependent TNF-α production

Osteoarticular complications are common in human brucellosis, but the pathogenic mechanisms involved are largely unknown. In this manuscript, we described an immune mechanism for inflammatory bone loss in response to infection by Brucella abortus. We established a requirement for MyD88 and TLR2 in TNF-α-elicited osteoclastogenesis in response to B. abortus infection. CS from macrophages infected with B. abortus induced BMM to undergo osteoclastogenesis. Although B. abortus-infected macrophages actively secreted IL-1β, IL-6, and TNF-α, osteoclastogenesis depended on TNF-α, as CS from B. abortus-infected macrophages failed to induce osteoclastogenesis in BMM from TNFRp55⁻/⁻ mice. CS from B. abortus-stimulated MyD88⁻/⁻ and TLR2⁻/⁻ macrophages failed to express TNF-α, and these CS induced no osteoclast formation compared with that of the WT or TLR4⁻/⁻ macrophages. Omp19, a B. abortus lipoprotein model, recapitulated the cytokine production and subsequent osteoclastogenesis induced by the whole bacterium. All phenomena were corroborated using human monocytes, indicating that this mechanism could play a role in human osteoarticular brucellosis. Our results indicate that B. abortus, through its lipoproteins, may be involved in bone resorption through the pathological induction of osteoclastogenesis.

Feedback inhibition of osteoclastogenesis during inflammation by IL-10, M-CSF receptor shedding, and induction of IRF8

Inflammation plays a key role in excessive bone loss in conditions such as rheumatoid arthritis and periodontitis. An important paradigm in immunology is that inflammatory factors activate feedback inhibition mechanisms to restrain inflammation and limit associated tissue damage. We hypothesized that inflammatory factors would activate similar feedback mechanisms to restrain bone loss in inflammatory settings. We have identified three mechanisms that inhibit osteoclastogenesis and are induced by inflammatory factors such as toll-like receptor ligands and cytokines; downregulation of expression of costimulatory molecules such as TREM-2; induction of shedding, and thereby inactivation of the M-CSF receptor c-Fms, leading to decreased RANK transcription; and induction of transcriptional repressors such as interferon regulatory factor 8. It is likely that these mechanisms work in a complementary and cooperative manner to fine tune the extent of osteoclastogenesis in inflammatory settings, and their augmentation may represent an alternative therapeutic approach to suppress bone resorption.

Increased expression of interleukin-22 by synovial Th17 cells during late stages of murine experimental arthritis is controlled by interleukin-1 and enhances bone degradation

OBJECTIVE

Interleukin-22 (IL-22) is a mediator in antimicrobial responses and inflammatory autoimmune diseases. Although IL-22 and its receptor, IL-22R, have been identified in the synovium of rheumatoid arthritis patients, the source of IL-22 and its contribution to disease pathogenicity remain to be established. This study was undertaken to investigate the regulation of IL-22 by Th17 cells in vitro and to evaluate the potential for IL-22 depletion in an experimental arthritis model using mice deficient in the IL-1 receptor antagonist (IL-1Ra-/-).

METHODS

Naive murine T cells were cultured under conditions leading to polarization of the cells into subsets of Th1, Th2, induced Treg, and Th17. Cytokines were measured in the culture supernatants, and the cells were analyzed by fluorescence-activated cell sorting. Tissue samples from the inflamed ankle synovium of IL-1Ra-/- mice were isolated, and messenger RNA levels of marker genes were quantified. IL-1Ra-/- mice were treated with neutralizing anti-IL-22 antibodies. Synovial cells were isolated from the inflamed tissue and sorted into fractions for analysis of cytokine production.

RESULTS

In vitro tests showed that Th17 cells produced high levels of IL-22 after stimulation with IL-1 or IL-23. Interestingly, a synergistic increase in the production of IL-22 was observed after combining IL-1 and IL-23. In vivo, IL-1Ra-/- mice displayed a progressive erosive arthritis, characterized by up-regulation of IL-17 in mildly and severely inflamed tissue, whereas the levels of IL-22 and IL-22R were increased only in severely inflamed synovia. Anti-IL-22 treatment of IL-1Ra-/- mice significantly reduced the inflammation and bone erosion. Analysis of isolated single cells from the inflamed synovia revealed that IL-22 was mainly produced by IL-17-expressing T cells.

CONCLUSION

These findings suggest that IL-22 plays an important role in IL-1-driven chronic joint destruction.

Genetic responses to nanostructured calcium-phosphate-coated implants

Nanostructured calcium phosphate (CaP) has been histologically and biomechanically proven to enhance osseointegration of implants; however, conventional techniques were not sufficiently sensitive to capture its biological effects fully. Here, we compared the conventional removal torque (RTQ) evaluation and gene expression in tissues around nanostructured CaP-coated implants, using real-time RT-PCR, with those of uncoated implants, in a rabbit model. At 2 wks, RTQ values were significantly higher, alkaline phosphatase (ALP) expression was significantly higher, and runt-related transcription factor 2 and tumor necrosis factor-α expressions were significantly lower in the coated than in the uncoated implants. This indicates that inflammatory responses were suppressed and osteoprogenitor activity increased around the CaP-coated surface. At 4 wks, although RTQ values did not significantly differ between the 2 groups, ALP and osteocalcin (OCN) were significantly up-regulated in the coated group, indicating progressive mineralization of the bone around the implant. Moreover, an osteoclast marker, adenosine triphosphatase, which indicates acidification of the resorption lacunae, was significantly higher for the coated implants, suggesting gradual resorption of the CaP coating. This study reveals detailed genetic responses to nanostructured CaP-coated implants and provides evidence that the effect of nanotopography is significant during the osseointegration cascade.

The aqueous extract of Angelica sinensis, a popular Chinese herb, inhibits wear debris-induced inflammatory osteolysis in mice

BACKGROUND

More and more studies have shown Angelica sinensis' (AS) therapeutic action on chronic inflammatory diseases in recent years. We investigated effects of aqueous extract of AS on inflammatory cytokines release and wear debris particles-induced osteolysis.

MATERIALS AND METHODS

Ultra high molecular weight polyethylene (UHMWPE) particles were used to induce inflammation in RAW264.7 cell and C57BL/J6 mice. AS extract was obtained through a series of purification steps, and divided into high dose group and low dose group during the research of cell culture, tissue culture, and animal treatment. After 72 h culture with optimal particles, supernatants were collected for cytokine analysis. Calvaria were harvested from the mice model after 10 d treatment with the AS extract. Six calvaria of each group were cultured into medium for 72 h for analyzing cytokine generated in vivo. Histologic analyses and micro-computed tomography (micro-CT) scan were used to determine osteoclastogenesis and inflammatory bone resorption.

RESULTS

Concentration of tumor necrosis-alpha (TNF-α) and interleukin-1beta (IL-1β) was significantly attenuated by AS extract both in vitro and in vivo. The osteolysis area and the osteoclast numbers were decreased from 0.406 ± 0.0799 to 0.117 ± 0.0103 mm(2), and from 22.7 ± 5.0 to 11.3 ± 1.8, respectively (P < 0.01). Compared with the control group, the protection effects of AS extract was further confirmed with data of the more accurate 3-dimension micro-CT reconstruction.

CONCLUSIONS

This study suggests a potential resolution of inhibiting wear debris particles-induced inflammatory bone resorption, as well as a possible way of inhibiting aseptic loosening after joint replacement surgery.

Osteoimmunology at the nexus of arthritis, osteoporosis, cancer, and infection

Over the past decade and a half, the biomedical community has uncovered a previously unappreciated reciprocal relationship between cells of the immune and skeletal systems. Work in this field, which has been termed "osteoimmunology," has resulted in the development of clinical therapeutics for seemingly disparate diseases linked by the common themes of inflammation and bone remodeling. Here, the important concepts and discoveries in osteoimmunology are discussed in the context of the diseases bridging these two organ systems, including arthritis, osteoporosis, cancer, and infection, and the targeted treatments used by clinicians to combat them.

Osteoporosis, the risk of vertebral fracture, and periodontal disease in an elderly group in Mexico City

OBJECTIVES

The aims of this study were to identify the possible association of osteoporosis, fracture risk and periodontitis, and consider the role of pharmacological treatment of osteoporosis and the periodontal condition.

METHODS

Patients aged 60 and older from the Mexican National Medical Science and Nutrition Institute Salvador Zubirán participated in the study. DXA was used to assess osteoporosis and risk of vertebral fracture. A modified version of the extent and severity index (ESI) was applied to evaluate periodontitis (cut-off point for attachment loss ≥ 4 mm) and all teeth were examined.

RESULTS

One hundred and sixty-six patients were examined, 88.6% were females, 47.0% had osteoporosis and 38.6% showed a high risk of fracture. The modified ESI was 5.13 mm (SD 1.4), 57.8% (SD 29.7). The model for periodontitis severity showed an association with oral hygiene (OR = 1.85) and use of osteoporosis medication (OR = 0.43). The model for the extent of periodontitis identified an association with smoking (OR = 2.37), osteoporosis (OR = 1.82) and osteoporosis medication (OR = 0.36). The model for tooth loss detected an association with fracture risk (OR = 3.02) and osteoporosis medication (OR = 0.33).

CONCLUSION

Periodontitis extent was associated with osteoporosis, and tooth loss with fracture risk.

Interleukin-33: a novel player in osteonecrosis of the femoral head?

Osteonecrosis of the femoral head (ONFH) is a disabling disease affecting young adults, which usually leads to the destruction of the hip joint. It is mainly due to an inadequate blood supply that causes the death of osteocytes and bone marrow cells. Joint salvaging procedures are numerous but relatively inefficient, justifying the need for new therapeutic strategies. In this regard, the recently discovered interleukin (IL)-33 alarmin appears as a possible target. Indeed, IL-33 seems to be specifically released by necrotic cells, and interestingly, is constitutively expressed in human bone, in particular by osteocytes, osteoblasts and marrow adipocytes. Moreover, recent reports suggesting that IL-33 modulates angiogenesis, vascular permeability, osteoclastogenesis and bone resorption, indicate that IL-33 may play a role in ONFH.

Impact of sirolimus, tacrolimus and mycophenolate mofetil on osteoclastogenesis--implications for post-transplantation bone disease

BACKGROUND

Post-transplantation bone disease is associated with a high degree of morbidity including pain and fractures. Glucocorticoid-induced osteoporosis on top of pre-existing renal osteodystrophy is considered the major pathogenic factor, while the role of non-glucocorticoid immunosuppressants is less well defined.

METHODS

In this study, we investigated the influence of sirolimus (SRL) versus calcineurin inhibitor (CI)-based immunosuppressive regimens on biomarkers of bone resorption in renal transplant patients. In addition, the impact of SRL, tacrolimus and mycophenolate mofetil (MMF) on osteoclast activation and function was assessed in cell culture systems.

RESULTS

Using this approach, we demonstrated reduced serum levels of bone resorption markers in patients treated with SRL after kidney transplantation compared to a CI-based regimen. In line with this observation, we detected profoundly reduced osteoclast differentiation and subsequently diminished hydroxyapatite resorption in the presence of SRL compared to MMF and tacrolimus in vitro. Moreover, SRL significantly reduced osteoclast precursor proliferation in vitro compared to tacrolimus and led to augmented apoptosis in osteoclast precursors.

CONCLUSIONS

Taken together, SRL was shown to inhibit osteoclast formation in vivo and in vitro. SRL thus may have the potential to balance osteoclast promoting effects of glucocorticoids and CI, thereby counteracting the development of accelerated osteoporosis in renal transplant recipients.

IL-33 shifts the balance from osteoclast to alternatively activated macrophage differentiation and protects from TNF-alpha-mediated bone loss

IL-33 is a new member of the IL-1 family, which plays a crucial role in inflammatory response, enhancing the differentiation of dendritic cells and alternatively activated macrophages (AAM). Based on the evidence of IL-33 expression in bone, we hypothesized that IL-33 may shift the balance from osteoclast to AAM differentiation and protect from inflammatory bone loss. Using transgenic mice overexpressing human TNF, which develop spontaneous joint inflammation and cartilage destruction, we show that administration of IL-33 or an IL-33R (ST2L) agonistic Ab inhibited cartilage destruction, systemic bone loss, and osteoclast differentiation. Reconstitution of irradiated hTNFtg mice with ST2(-/-) bone marrow led to more bone loss compared with the chimeras with ST2(+/+) bone marrow, demonstrating an important endogenous role of the IL-33/ST2L pathway in bone turnover. The protective effect of IL-33 on bone was accompanied by a significant increase of antiosteoclastogenic cytokines (GM-CSF, IL-4, and IFN-γ) in the serum. In vitro IL-33 directly inhibits mouse and human M-CSF/receptor activator for NF-κB ligand-driven osteoclast differentiation. IL-33 acts directly on murine osteoclast precursors, shifting their differentiation toward CD206(+) AAMs via GM-CSF in an autocrine fashion. Thus, we show in this study that IL-33 is an important bone-protecting cytokine and may be of therapeutic benefit in treating bone resorption.

The critical role of IL-34 in osteoclastogenesis

It has been widely believed that the cytokines required for osteoclast formation are M-CSF (also known as CSF-1) and RANKL. Recently, a novel cytokine, designated IL-34, has been identified as another ligand of CSF1R. This study was to explore the biological function, specifically osteoclastogenesis and bone metabolism, of the new cytokine. We produced recombinant mouse IL-34 and found that together with RANKL it induces the formation of osteoclasts both from splenocytes as well as dose-dependently from bone marrow cells in mouse and these cells also revealed bone resorption activity. It also promotes osteoclast differentiation from human peripheral blood mononucleated cells. Finally, we show that systemic administration of IL-34 to mice increases the proportion of CD11b+ cells and reduces trabecular bone mass. Our data indicate that IL-34 is another important player in osteoclastogenesis and thus may have a role in bone diseases. Strategies of targeting CSF1/CSF1R have been developed and some of them are already in preclinical and clinical studies for treatment of inflammatory diseases. Our results strongly suggest the need to revisit these strategies as they may provide a new potential pharmaceutical target for the regulation of bone metabolism in addition to their role in the treatment of inflammatory diseases.

Dietary supplementation with dried plum prevents ovariectomy-induced bone loss while modulating the immune response in C57BL/6J mice

This study was designed to investigate the effects of dried plum on the changes in bone metabolism and the immune response associated with ovarian hormone deficiency. Adult female C57BL/6J mice were either sham-operated (Sham) and fed AIN-93 diet (control) or ovariectomized (OVX) and fed a control diet with 0%, 5%, 15% or 25% dried plum (w/w), corresponding to control, low- (LDP), medium- (MDP) and high (HDP)-dose dried plum. Four weeks of HDP supplementation prevented the decrease in spine bone mineral density and content induced by OVX. The OVX compromise in trabecular bone of the vertebra and proximal tibia was prevented by the higher doses of dried plum, and in the vertebra these effects resulted in greater (P<.05) bone strength and stiffness. In the bone marrow, OVX suppressed granulocyte and committed monocyte populations and increased the lymphoblast population, but the MDP and HDP restored these myeloid and lymphoid populations to the level of the Sham. Dried plum also suppressed lymphocyte tumor necrosis factor (TNF)-α production ex vivo by splenocytes, in response to concanavalin (Con) A stimulation. These data indicate that dried plum's positive effects on bone structural and biomechanical properties coincide with the restoration of certain bone marrow myeloid and lymphoid populations, and suppressed splenocyte activation occurring with ovarian hormone deficiency.

Secondary osteoporosis in patients with juvenile idiopathic arthritis

Bone disease in patients with juvenile idiopathic arthritis (JIA) is associated with focal (joint erosion and juxtaarticular osteopenia) and systemic bone loss (generalized osteopenia or reduction of bone mass density). Pathophysiology of bone loss is multifactorial and involves particularly proinflammatory cytokines and deleterious effects of glucocorticoid therapy. Clinical studies in patients with JIA indicate excessive activation of osteoclastogenesis and reduction of bone formation. Reduction of physical activity, muscle atrophy caused by high disease activity, and compulsory restriction in movements are also associated with bone loss. In patients with JIA, the disease can be complicated by growth cartilage involvement and systemic or local growth retardation. In the absence of preventive measures, fragility fractures can occur even at an early age.

The increased expression of receptor activator of nuclear-kappaB ligand (RANKL) of multiple myeloma bone marrow stromal cells is inhibited by the bisphosphonate ibandronate

The receptor activator of nuclear factor-kappaB ligand (RANKL) and interleukin-1beta are osteoclast activating factors which are abnormally expressed in bone marrow stromal cells and plasma cells of multiple myeloma patients. In this work we analyzed RANKL expression in human bone marrow mesenchymal stromal cells and the effect of the bisphosphonate ibandronate on RANKL expression after IL-1beta activation of ERK pathway. Mesenchymal stromal cells were obtained from bone marrow iliac aspirates from multiple myeloma patients at stages II/III and non-osteoporotics control donors; these cells were maintained under long-term culture conditions. Cells were cultured in the presence or the absence of 5 ng/ml IL-1beta and/or 5 microM ibandronate, during selected periods. mRNA for RANKL and protein levels were assayed by RT-PCR and Western blot, respectively. Human bone marrow stromal cell line HS-5 was used for assessing IL 1beta- and ibandronate-ERK phosphorylation responses. Multiple myeloma mesenchymal stromal cells differentiate from control cells by increased basal RANKL expression. IL-1beta up regulated RANKL expression showed dependent on activated MEK/ERK pathway. Finally, the bisphosphonate ibandronate, that hindered activation of the MEK/ERK pathway significantly inhibited both basal and IL-1beta dependent RANKL expression by cells. Results indicate that RANKL expression involves the MEK/ERK pathway in multiple myeloma mesenchymal stromal cells, and that early obstruction of this path, such as that achieved with ibandronate, significantly deters RANKL protein expression.

Expression of tumor necrosis factor-α, interleukin-1α, interleukin-6 and interleukin-10 in chronic otitis media with bone osteolysis

The purpose of this study was to evaluate the expression of proinflammatory and immunoregulatory cytokines in chronic otitis media. The expression levels of TNF-α, IL-1α, IL-6 and IL-10 were determined by Western blot analysis of tissue samples obtained during ear surgery. The expression levels of TNF-α, IL-1α and IL-6 in cholesteatoma tissues were substantially higher compared to those determined in the granulation tissue. The highest levels of TNF-α, IL-1 and IL-6 proteins were observed in patients with bone destruction. There were no significant differences in the expression of IL-10 levels in cholesteatoma and normal skin, but in the granulation tissue its level was substantially higher. The level of IL-10 in cholesteatoma tissues inversely correlated with the expression of proinflammatory cytokines, the degree of bone destruction and cholesteatoma invasion. Increased expressions of TNF-α, IL-1α and IL-6 in chronic otitis media and a strong positive correlation between these cytokine levels and the degree of bone destruction indicate the destructive behavior of cholesteatoma or granulation tissue.

A novel role for TNFAIP2: its correlation with invasion and metastasis in nasopharyngeal carcinoma

Tumor necrosis factor alpha (TNFα) is an inflammatory cytokine that is present in the microenvironment of many tumors and is known to promote tumor progression. To examine how TNFα modulates the progression and metastasis of nasopharyngeal carcinoma, we used Affymetrix chips to identify TNFα-inducible genes that are dysregulated in this tumor. Elevated expression of TNFAIP2, which encodes TNFα-inducible protein 2 and not previously known to be associated with cancer, was found and confirmed by quantitative RT-PCR of TNFAIP2 expression in nasopharyngeal carcinoma and adjacent normal tissues. Immunohistochemical analysis showed that the TNFAIP2 protein was highly expressed in tumor cells. Analysis of 95 nasopharyngeal carcinoma biopsy specimens revealed that high TNFAIP2 expression was significantly correlated with high-level intratumoral microvessel density (P=0.005) and low distant metastasis-free survival (P=0.001). A multivariate analysis further confirmed that TNFAIP2 was an independent prognostic factor for nasopharyngeal carcinoma (P=0.002). In vitro, TNFα treatment of nasopharyngeal carcinoma HK1 cells was found to induce TNFAIP2 expression, and siRNA-based knockdown of TNFAIP2 dramatically reduced the migration and invasion of nasopharyngeal carcinoma HK1 cells. These results collectively suggest for the first time that TNFAIP2 is a cell migration-promoting protein and its expression predicts distant metastasis. Our data suggest that TNFAIP2 may serve as an independent prognostic indicator for nasopharyngeal carcinoma.

Fracture-associated hospitalizations in patients with inflammatory bowel disease

BACKGROUND

Maintenance of bone health is an important concern in patients with inflammatory bowel disease (IBD). They may frequently have impaired bone density resulting in greater incidence of fractures.

AIMS

To examine fracture-associated hospitalization costs in IBD patients from a nationwide representative sample, and to compare the risk factors for such fractures in IBD and non-IBD patients.

METHODS

We identified discharges with IBD and coexisting codes for hip, vertebral or wrist fractures (IBD-Fr) from the Nationwide Inpatient Sample and compared them with IBD hospitalizations without codes for these fractures. A second analysis was performed using 2008 inpatient data from the Wisconsin Hospital Association (WHA) comparing characteristics of patients with IBD-Fr and non-IBD controls hospitalized for similar fractures.

RESULTS

There were 1,653 discharges in the IBD-Fr group accounting for 10,461 days of hospital stay and US $46 million in total hospitalization charges. On multivariate analysis, age>65 years [odds ratio (OR) 28.8, 95% confidence interval (CI) 12.3-67.6] and female sex (OR 1.3, 95%CI 1.0-1.6) were associated with higher odds of hospitalization associated with fractures. We found no differences in age, gender, or race among IBD-Fr and non-IBD fracture controls. However, IBD-fractures were twice as likely to be associated with osteoporosis as non-IBD fractures (OR 2.19, 95%CI 1.10-4.33).

CONCLUSIONS

Older age, female sex, and osteoporosis were more commonly associated with hospitalization for fractures in IBD patients. Osteoporosis appears to be more common among IBD-Fr patients than non-IBD fracture controls.

Inflammation and uncoupling as mechanisms of periodontal bone loss

Periodontal disease is characterized by both inflammation and bone loss. Advances in research in both these areas have led to a new appreciation of not only each field but also the intimate relationship between inflammation and bone loss. This relationship has resulted in a new field of science called osteoimmunology and provides a context for better understanding the pathogenesis of periodontal disease. In this review, we discuss several aspects of the immuno-inflammatory host response that ultimately results in loss of alveolar bone. A proposal is made that periodontal inflammation not only stimulates osteoclastogenesis but also interferes with the uncoupling of bone formation and bone resorption, consistent with a pathologic process. Furthermore, arguments based on experimental animal models suggest a critical role of the spatial and temporal aspects of inflammation in the periodontium. A review of these findings leads to a new paradigm to help explain more fully the impact of inflammation on alveolar bone in periodontal disease so that it includes the effects of inflammation on uncoupling of bone formation from resorption.

Role of NF-κB in the skeleton

Since the discovery that deletion of the NF-κB subunits p50 and p52 causes osteopetrosis in mice, there has been considerable interest in the role of NF-κB signaling in bone. NF-κB controls the differentiation or activity of the major skeletal cell types - osteoclasts, osteoblasts, osteocytes and chondrocytes. However, with five NF-κB subunits and two distinct activation pathways, not all NF-κB signals lead to the same physiologic responses. In this review, we will describe the roles of various NF-κB proteins in basal bone homeostasis and disease states, and explore how NF-κB inhibition might be utilized therapeutically.

Osteoclastogenesis and arthritis

There is emerging interest for osteoclasts as key players in the erosive and inflammatory events leading to joint destruction in chronic arthritis. In fact, chronic inflammatory joint diseases such as psoriatic arthritis and rheumatoid arthritis are often characterized by destruction of juxta-articular bone and erosions due to the elevated activity of osteoclasts, which are involved in bone resorption. The main step in inflammatory bone erosion is an imbalance between bone resorption and bone formation: osteoclast formation is enhanced by proinflammatory cytokines such as TNF-α, IL-1β, and IL-17 and is not balanced by increased activity of bone-forming osteoblasts. T-cells, stromal cells, and synoviocytes enhance osteoclast formation via expression of RANKL and, under pathologic conditions, of proinflammatory cytokines. In rheumatoid arthritis, accumulation of osteoclasts in synovial tissues and their activation associated with osteoclastogenic cytokines and chemokines at cartilage erosion sites suggest that they could be usefully selected as therapeutic target. In particular, in consideration of the primary role of RANKL and TNF-α in osteoclastogenesis, the control of the production of RANKL and the inhibition of TNF-α represent important strategies for reducing bone damage in this disease.

Direct inhibition of human RANK+ osteoclast precursors identifies a homeostatic function of IL-1beta

IL-1β is a key mediator of bone resorption in inflammatory settings, such as rheumatoid arthritis (RA). IL-1β promotes osteoclastogenesis by inducing RANKL expression on stromal cells and synergizing with RANKL to promote later stages of osteoclast differentiation. Because IL-1Rs share a cytosolic Toll-IL-1R domain and common intracellular signaling molecules with TLRs that can directly inhibit early steps of human osteoclast differentiation, we tested whether IL-1β also has suppressive properties on osteoclastogenesis in primary human peripheral blood monocytes and RA synovial macrophages. Early addition of IL-1β, prior to or together with RANKL, strongly inhibited human osteoclastogenesis as assessed by generation of TRAP(+) multinucleated cells. IL-1β acted directly on human osteoclast precursors (OCPs) to strongly suppress expression of RANK, of the costimulatory triggering receptor expressed on myeloid cells 2 receptor, and of the B cell linker adaptor important for transmitting RANK-induced signals. Thus, IL-1β rendered early-stage human OCPs refractory to RANK stimulation. Similar inhibitory effects of IL-1β were observed using RA synovial macrophages. One mechanism of RANK inhibition was IL-1β-induced proteolytic shedding of the M-CSF receptor c-Fms that is required for RANK expression. These results identify a homeostatic function of IL-1β in suppressing early OCPs that contrasts with its well-established role in promoting later stages of osteoclast differentiation. Thus, the rate of IL-1-driven bone destruction in inflammatory diseases, such as RA, can be restrained by its direct inhibitory effects on early OCPs to limit the extent of inflammatory osteolysis.

Bone damage in rheumatoid arthritis: mechanistic insights and approaches to prevention

In rheumatoid arthritis (RA), cells within the inflamed synovium and pannus elaborate a variety of cytokines, including tumor necrosis factor (TNF) alpha, interleukin (IL)-1, IL-6, and IL-17, that contribute to inflammation, and may directly affect bone. The receptor activator of NF-kappaB (RANK) ligand/RANK/osteoprotegerin pathway plays a critical role in regulating osteoclastogenesis in articular bone erosions in RA. Proinflammatory cytokines can modulate this pathway, and may also affect the ability of the osteoblast to repair bone at sites of articular erosion. In this review, the authors discuss the current understanding of pathogenic mechanisms of bone erosion in RA and examine current therapeutic approaches to prevent this damage.