Functions of nuclear factor kappaB in bone

PC-3-Derived Exosomes Inhibit Osteoclast Differentiation by Downregulating miR-214 and Blocking NF-κB Signaling Pathway

Prostate cancer is a serious disease that can invade bone tissues. These bone metastases can greatly decrease a patient's quality of life, pose a financial burden, and even result in death. In recent years, tumor cell-secreted microvesicles have been identified and proposed to be a key factor in cell interaction. However, the impact of cancer-derived exosomes on bone cells remains unclear. Herein, we isolated exosomes from prostate cancer cell line PC-3 and investigated their effects on human osteoclast differentiation by tartrate-resistant acid phosphatase (TRAP) staining. The potential mechanism was evaluated by qRT-PCR, western blotting, and microRNA transfection experiments. The results showed that PC-3-derived exosomes dramatically inhibited osteoclast differentiation. Marker genes of mature osteoclasts, including CTSK, NFATc1, ACP5, and miR-214, were all downregulated in the presence of PC-3 exosomes. Furthermore, transfection experiments showed that miR-214 downregulation severely impaired osteoclast differentiation, whereas overexpression of miR-214 promoted differentiation. Furthermore, we demonstrated that PC-3-derived exosomes block the NF-κB signaling pathway. Our study suggested that PC-3-derived exosomes inhibit osteoclast differentiation by downregulating miR-214 and blocking the NF-κB signaling pathway. Therefore, elevating miR-214 levels in the bone metastatic site may attenuate the invasion of prostate cancer.

Analysis of Trauma Intensity during Surgical Bone Procedures Using NF-κB Expression Levels as a Stress Sensor: An Experimental Study in a Wistar Rat Model

Aim and objectives: It is well known that the transcription factor NF-κB regulates multiple aspects of innate and adaptive immune functions and functions as a pivotal mediator of inflammatory responses. In the present study, we evaluated the trauma generated (inflammatory reaction) after osteotomy bone surgical procedures and placement of implants in the femoral cortical bone of Wistar rats. Surgical stress was evaluated measuring the release and activation of the NF-κB factor. Materials and Methods: Rats were divided into four groups (n = 10) and submitted to different surgical treatments: Control Group (G1 group), only bone perforation was performed without irrigation; Implant Group (G2 group), a titanium implant was inserted after bone perforation without irrigation; Irrigated Group (G3 group) perforations were performed with intense irrigation; and Vitaminic Compound Group (G4 group) surgical perforation was performed without irrigation and a vitaminic compound containing the principal ions present in the natural bone structure was used to fill the bone defect. All animals were euthanized six hours after the surgical procedure and NF-κB levels were determined through immunohistochemical stain followed by direct counting of labeled and unlabeled osteocytes. Results: Among different treated groups, the overall mean of the NF-κB positive cell count in all positions were higher for G1 group (33.4 ± 2.45 cells). NF-κB values were lower in the G2 group (28.9 ± 2.70 cells), whereas in the G3 group (24.3 ± 2.72 cells) as well as in G4 group still lesser NF-κB positive cells were counted (26.5 ± 2.60 cells). Conclusions: The results here presented suggest that maneuvers performed during osteotomy procedures can significantly affect inflammation levels. The NF-κB activation during the surgical procedures can be minimized and/or controlled thought the adequate irrigation or application of adequate substances.

The inhibitory effects of Qingchang Wenzhong granule on the interactive network of inflammation, oxidative stress, and apoptosis in rats with dextran sulfate sodium-induced colitis

BACKGROUND

Ulcerative colitis (UC) is a kind of complex immune disease, the pathogenesis of which remains elusive. Destruction of the intestinal barrier, extreme inflammation, oxidative stress, and apoptosis might play key roles in the development of UC. In previous studies, we observed that Qingchang Wenzhong granule (QCWZG) had the exact effect on the remission of UC in the clinic; however, the underlying mechanism has not been identified. This study aimed to reveal the effects of QCWZG on the intestinal physical barrier and the interactive network of inflammation, oxidative stress, and apoptosis in rats with dextran sulfate sodium (DSS)-induced colitis.

METHODS

Sixty rats were randomly divided into six groups: blank group, model group, high/mild/low-dose QCWZG groups, and mesalazine group. The rats in the experimental group drank 4% DSS for 7 days and 1% DSS for the subsequent 7 days. Different medications or distilled water was supplied by intragastric administration for 7 days. The levels of colitis and indices related to inflammation, oxidative stress, and apoptosis were assessed.

RESULTS

Compared with the model group, the QCWZG group (P < 0.05) demonstrated attenuated disease activity index, colonic mucosa disease index, histological lesions, and colonic weights; lower levels of inflammatory substances, such as interleukin (IL)-1α, IL-6, tumor necrosis factor-α, and myeloperoxidase; lower levels of malondialdehyde; and increased levels of superoxide dismutase and glutathione peroxidase. The QCWZG group also demonstrated elevated expression of Bcl-2 and occluding but downregulated db expression of Bax and caspase 3 in the colon.

CONCLUSION

QCWZG could relieve rats with DSS-induced colitis from UC symptoms by improving the intestinal physical barrier, which resists the interactive network of inflammation, oxidative stress, apoptosis, and their overactivated interactions.

Bioactive effects of silica nanoparticles on bone cells are size, surface, and composition dependent

Silica based nanoparticles have been demonstrated to have intrinsic biologic activity towards the skeleton and to function by promoting the differentiation of bone forming osteoblasts while inhibiting the differentiation of bone resorbing osteoclasts. The excitement surrounding nanomedicine in part revolves around the almost unlimited possibilities for varying the physicochemical properties including size, composition, and surface charge. To date few studies have attempted to manipulate these characteristics in concert to optimize a complex biologic outcome. Towards this end, spherical silica nanoparticles of various sizes (50-450 nm), of different surface properties (OH, CO₂H, NR₄+, mNH₂), and of different composition (silica, gold, and polystyrene) were synthesized and evaluated for biological activity toward skeletal cells. Osteoblast activity was most influenced by composition and size variables, whereas osteoclasts were most affected by surface property variation. The study also establishes nanoparticle mediated suppression of Nfatc1, a key transcriptional regulator for osteoclast differentiation, identifying a novel mechanism of action. Collectively, the study highlights how during the design of bioactive nanoparticles, it is vital to consider not only the myriad of physical properties that can be manipulated, but also that the characteristics of the target cell plays an equally integral role in determining biological outcome. STATEMENT OF SIGNIFICANCE: Silica nanomaterials represent a promising biomaterial for beneficial effects on bone mass and quality as well as regenerative tissue engineering and are currently being investigated for intrinsic bioactivity towards the primary cells responsible for skeletal homeostasis; osteoblasts and osteoclasts. The goal of the current study was to assess the physical properties of silica nanoparticles that impart intrinsic bioactivity by evaluating size, surface charge, and composition. Results reveal differential influences of the physical properties of nanoparticles towards osteoblasts and osteoclasts. This study provides new insights into the design of nanoparticles to specifically target different aspects of bone metabolism and highlights the opportunities provided by nanotechnology to modulate a range of cell specific biological responses for therapeutic benefit.

TRIM38 regulates NF-κB activation through TAB2 degradation in osteoclast and osteoblast differentiation

The tripartite motif protein 38 (TRIM38), a member of the TRIM family, is involved in various cellular processes such as cell proliferation, differentiation, apoptosis, and antiviral defense. However, the role of TRIM38 in osteoclast and osteoblast differentiation is not yet known. In this study, we report the involvement of TRIM38 in osteoclast and osteoblast differentiation. Overexpression of TRIM38, in osteoclast precursor cells, attenuated receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast formation, RANKL-triggered NF-κB activation, and expression of osteoclast marker genes, such as NFATc1, osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP); and down-regulation of TRIM38 expression showed the opposite effects. Ectopic expression of TRIM38 in osteoblast precursors induced increased osteoblast differentiation and function. Elevated expression of alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin was also observed due to blockade of NF-κB activation. Conversely, knockdown of TRIM38 showed the opposite effects. TRIM38 also induced degradation of lysosome-dependent transforming growth factor beta-activated kinase 1 and MAP3K7-binding protein 2 (TAB2), further blocking NF-κB activation. Taken together, our data suggest that TRIM38 plays a critical role in bone remodeling as a negative regulator of NF-κB in both osteoclast and osteoblast differentiation.

MacroH2A1.2 inhibits prostate cancer-induced osteoclastogenesis through cooperation with HP1α and H1.2

Osteoclasts are multinuclear bone-resorbing cells that differentiate from hematopoietic precursor cells. Prostate cancer cells frequently spread to bone and secrete soluble signaling factors to accelerate osteoclast differentiation and bone resorption. However, processes and mechanisms that govern the expression of osteoclastogenic soluble factors secreted by prostate cancer cells are largely unknown. MacroH2A (mH2A) is a histone variant that replaces canonical H2A at designated genomic loci and establishes functionally distinct chromatin regions. Here we report that mH2A1.2, one of the mH2A isoforms, attenuates prostate cancer-induced osteoclastogenesis by maintaining the inactive state of genes encoding soluble factors in prostate cancer cells. Our functional analyses of soluble factors identify lymphotoxin beta (LTβ) as a major stimulator of osteoclastogenesis and an essential mH2A1.2 target for its anti-osteoclastogenic activity. Mechanistically, mH2A1.2 directly interacts with HP1α and H1.2 and requires them to inactivate LTβ gene in prostate cancer cells. Consistently, HP1α and H1.2 have an intrinsic ability to inhibit osteoclast differentiation in a mH2A1.2-dependent manner. Together, our data uncover a new and specific role for mH2A1.2 in modulating osteoclastogenic potential of prostate cancer cells and demonstrate how this signaling pathway can be exploited to treat osteolytic bone metastases at the molecular level.

Inflammation in bone physiology and pathology

PURPOSE OF REVIEW

Bone is constantly being remodeled throughout adult life through constant anabolic and catabolic actions that maintain tissue homeostasis. A number of hormones, cytokines growth factors, and the proximity of various cells to bone surfaces influence this process. Inflammatory changes at the bone microenvironment result in alterations leading to both excessive bone loss and bone formation. Detailed understanding of the physiological and pathological mechanisms that dictate these changes will allow us to harness inflammatory signals in bone regeneration.

RECENT FINDINGS

Recent reports have suggested that inflammatory signals are able to stimulate transcription factors that regulate osteoblast differentiation from their precursors.

SUMMARY

In this review, we summarized current understanding of the roles of inflammation in bone resorption and bone formation, which give rise to different disorders and discuss the huge potential of harnessing these inflammatory signals to achieve bone regeneration.

Flavopiridol Protects Bone Tissue by Attenuating RANKL Induced Osteoclast Formation

Bone resorption and homeostasis is carried out by osteoclasts, whose differentiation and activity are regulated by the RANK/RANKL axis. Our previous studies using a mouse model of joint injury show that joint trauma induces local inflammation followed by bone remodeling. The transcription factor cyclin-dependent kinase 9 (CDK9) is the major regulator of inflammation, as CDK9 inhibitor flavopiridol effectively suppress injury-induced inflammatory response. The objective of this study was to investigate the underlying mechanism through which flavopiridol regulates bone resorption. The effects of CDK9 inhibition, by the specific-inhibitor flavopiridol, on bone resorption were determined in vivo using two distinct and clinically relevant bone remodeling models. The first model involved titanium particle-induced acute osteolysis, and the second model was ovariectomy-induced chronic osteoporosis. The effects and mechanism of CDK9 inhibition on osteoclastogenesis were examined using in vitro culture of bone marrow macrophages (BMMs). Our results indicated that flavopiridol potently suppressed bone resorption in both in vivo bone-remodeling models. In addition, CDK9 inhibition suppressed in vitro osteoclastogenesis of BMM and reduced their expression of osteoclast-specific genes. Finally, we determined that flavopiridol suppressed RANKL signaling pathway via inhibition of p65 phosphorylation and nuclear translocation of NF-κB. Summary, CDK9 is a potential therapeutic target to prevent osteolysis and osteoporosis by flavopiridol treatment.

Activation of hypoxia-inducible factor 1 attenuates periapical inflammation and bone loss

Hypoxia (low oxygen level) is an important feature during infections and affects the host defence mechanisms. The host has evolved specific responses to address hypoxia, which are strongly dependent on the activation of hypoxia-inducible factor 1 (HIF-1). Hypoxia interferes degradation of HIF-1 alpha subunit (HIF-1α), leading to stabilisation of HIF-1α, heterodimerization with HIF-1 beta subunit (HIF-1β) and subsequent activation of HIF-1 pathway. Apical periodontitis (periapical lesion) is a consequence of endodontic infection and ultimately results in destruction of tooth-supporting tissue, including alveolar bone. Thus far, the role of HIF-1 in periapical lesions has not been systematically examined. In the present study, we determined the role of HIF-1 in a well-characterised mouse periapical lesion model using two HIF-1α-activating strategies, dimethyloxalylglycine (DMOG) and adenovirus-induced constitutively active HIF-1α (CA-HIF1A). Both DMOG and CA-HIF1A attenuated periapical inflammation and tissue destruction. The attenuation in vivo was associated with downregulation of nuclear factor-κappa B (NF-κB) and osteoclastic gene expressions. These two agents also suppressed NF-κB activation and subsequent production of proinflammatory cytokines by macrophages. Furthermore, activation of HIF-1α by DMOG specifically suppressed lipopolysaccharide-stimulated macrophage differentiation into M1 cells, increasing the ratio of M2 macrophages against M1 cells. Taken together, our data indicated that activation of HIF-1 plays a protective role in the development of apical periodontitis via downregulation of NF-κB, proinflammatory cytokines, M1 macrophages and osteoclastogenesis.

CHIP regulates bone mass by targeting multiple TRAF family members in bone marrow stromal cells

Carboxyl terminus of Hsp70-interacting protein (CHIP or STUB1) is an E3 ligase and regulates the stability of several proteins which are involved in different cellular functions. Our previous studies demonstrated that Chip deficient mice display bone loss phenotype due to increased osteoclast formation through enhancing TRAF6 activity in osteoclasts. In this study we provide novel evidence about the function of CHIP. We found that osteoblast differentiation and bone formation were also decreased in Chip KO mice. In bone marrow stromal (BMS) cells derived from Chip-/- mice, expression of a panel of osteoblast marker genes was significantly decreased. ALP activity and mineralized bone matrix formation were also reduced in Chip-deficient BMS cells. We also found that in addition to the regulation of TRAF6, CHIP also inhibits TNFα-induced NF-κB signaling through promoting TRAF2 and TRAF5 degradation. Specific deletion of Chip in BMS cells downregulated expression of osteoblast marker genes which could be reversed by the addition of NF-κB inhibitor. These results demonstrate that the osteopenic phenotype observed in Chip-/- mice was due to the combination of increased osteoclast formation and decreased osteoblast differentiation. Taken together, our findings indicate a significant role of CHIP in bone remodeling.

LRRC15 promotes osteogenic differentiation of mesenchymal stem cells by modulating p65 cytoplasmic/nuclear translocation

Background

Mesenchymal stem cells (MSCs) are a reliable resource for bone regeneration and tissue engineering, but the molecular mechanisms of differentiation remain unclear. The tumor antigen 15-leucine-rich repeat containing membrane protein (LRRC15) is a transmembrane protein demonstrated to play important roles in cancer. However, little is known about its role in osteogenesis. This study was to evaluate the functions of LRRC15 in osteogenic differentiation of MSCs.

Methods

Osteogenic-induction treatment and the ovariectomized (OVX) model were performed to investigate the potential relationship between LRRC15 and MSC osteogenesis. A loss-of-function study was used to explore the functions of LRRC15 in osteogenic differentiation of MSCs in vitro and in vivo. NF-κB pathway inhibitor BAY117082, siRNA, nucleocytoplasmic separation, and ChIP assays were performed to clarify the molecular mechanism of LRRC15 in bone regulation.

Results

Our results first demonstrated that LRRC15 expression was upregulated upon osteogenic induction, and the level of LRRC15 was significantly decreased in OVX mice. Both in-vitro and in-vivo experiments detected that LRRC15 was required for osteogenesis of MSCs. Mechanistically, LRRC15 inhibited transcription factor NF-κB signaling by affecting the subcellular localization of p65. Further studies indicated that LRRC15 regulated osteogenic differentiation in a p65-dependent manner.

Conclusions

Taken together, our findings reveal that LRRC15 is an essential regulator for osteogenesis of MSCs through modulating p65 cytoplasmic/nuclear translocation, and give a novel hint for MSC-mediated bone regeneration.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0809-1) contains supplementary material, which is available to authorized users.

Paeoniflorin ameliorates collagen-induced arthritis via suppressing nuclear factor-κB signalling pathway in osteoclast differentiation

Paeoniflorin (PF), extracted from the root of Paeonia lactiflora Pall, exhibits anti-inflammatory properties in several autoimmune diseases. Osteoclast, the only somatic cell with bone resorbing capacity, was the direct cause of bone destruction in rheumatoid arthritis (RA) and its mouse model, collagen-induced arthritis (CIA). The objective of this study was to estimate the effect of PF on CIA mice, and explore the mechanism of PF in bone destruction. We demonstrated that PF treatment significantly ameliorated CIA through inflammatory response inhibition and bone destruction suppression. Furthermore, PF treatment markedly decreased osteoclast number through the altered RANKL/RANK/OPG ratio and inflammatory cytokines profile. Consistently, we found that osteoclast differentiation was significantly inhibited by PF through down-regulation of nuclear factor-κB activation in vitro. Moreover, we found that PF suppressed nuclear factor-κB activation by decreasing its translocation to the nucleus in osteoclast precursor cells. Taken together, our new findings provide insights into a novel function of PF in osteoclastogenesis and demonstrate that PF would be a new therapeutic modality as a natural agent for RA treatment and other autoimmune conditions with bone erosion.

Dual roles of QOA-8a in antiosteoporosis: a combination of bone anabolic and anti-resorptive effects

Osteoporotic treatments have largely depended on antiresorptive or anabolic drugs; but the former also suppresses new bone formation, and the latter only includes human parathyroid hormone. There is no drug that has a dual effect to inhibit bone resorption and to stimulate bone formation simultaneously. Here, we report a small molecule, a quinoxaline derivative of oleanolic acid (QOA-8a) that plays such dual roles in osteoblasts and osteoclasts in the treatment of osteoporosis. Osteoclast differentiation was induced by incubation of primary mouse bone marrow-derived macrophages in the presence of RANKL and M-CSF, treatment with QOA-8a dose-dependently inhibited the osteoclast formation with an IC50 value of 0.098 μmol/L. QOA-8a also directly acted on osteoblasts, and stimulated new bone formation in murine calvarial bones in vitro and in vivo. In an OVX rat model, administration of QOA-8a (1, 5 mg·kg-1·d-1, po) for 16 weeks effectively prevented OVX-induced bone loss, accompanied by decreased serum levels of the bone resorption marker CTX-1 and increased serum levels of osteoblast marker N-MID-OT. Meaningfully, our preliminary study revealed that QOA-8a down-regulated the ERK1/2 signal in osteoclasts and up-regulated the signal in osteoblasts. QOA-8a showed dual functions in both animal and human osteoclastogenesis and osteoblastogenesis. Our results demonstrate that QOA-8a might serve as a lead compound with a dual function of bone anabolic and anti-resorptive effects in the development of anti-osteoporosis agents.

Inhibitory effects of melatonin on titanium particle-induced inflammatory bone resorption and osteoclastogenesis via suppression of NF-κB signaling

Wear debris-induced peri-implant osteolysis challenges the longevity of implants. The host response to wear debris causes chronic inflammation, promotes bone resorption, and impairs bone formation. We previously demonstrated that melatonin enhances bone formation and attenuates wear debris-induced bone loss in vivo. However, whether melatonin inhibits chronic inflammation and bone resorption at sites of wear debris-induced osteolysis remains unclear. In this study, we examined the potential inhibitory effects of melatonin on titanium particle-induced inflammatory osteolysis in a murine calvarial model and on RANKL-induced osteoclastic formation in bone marrow-derived macrophages. We found that the exogenous administration of melatonin significantly inhibited wear debris-induced bone resorption and the expression of inflammatory cytokines in vivo. Additionally, melatonin inhibited RANKL-induced osteoclast differentiation, F-actin ring formation, and osteoclastic resorption in a concentration-dependent manner in vitro. We also showed that melatonin blocked the phosphorylation of IκB-α and p65, but not IKKα, and significantly inhibited the expression of NFATc1 and c-Fos. However, melatonin had no effect on MAPK or PI3K/AKT signaling pathways. These results provide novel mechanistic insight into the anti-inflammatory and anti-bone resorptive effects of melatonin on wear debris-induced bone loss and provide an evidence-based rationale for the protective effects of melatonin as a treatment for peri-implant osteolysis.

STATEMENT OF SIGNIFICANCE

Wear debris-induced chronic inflammation, osteoclastic activation and osteoblastic inhibition have been identified as critical factors of peri-implant bone loss. We previously demonstrated that melatonin, a bioactive indolamine secreted mainly by the pineal gland, activates Wnt/β-catenin signaling pathway and enhances bone regeneration at osteolytic site in vivo. In the current study, we further demonstrated that melatonin significantly suppresses wear debris-induced bone resorption and inflammatory cytokine expression in vivo. In addition, melatonin inhibits receptor activator of nuclear factor kappa-B ligand induced osteoclast formation and osteoclastic bone resorption in vitro. Meanwhile, we found that melatonin mediates its anti-inflammation and anti-bone resorption effects by abrogating nuclear factor kappa-B activation. These results further support the protective effects of melatonin on wear debris-induced peri-implant bone loss, and strongly suggest that melatonin could be considered as a potential candidate for the prevention and treatment of wear debris-induced osteolysis and subsequent aseptic loosening.

Cytoskeleton and nuclear lamina affection in recessive osteogenesis imperfecta: A functional proteomics perspective

Osteogenesis imperfecta (OI) is a collagen-related disorder associated to dominant, recessive or X-linked transmission, mainly caused by mutations in type I collagen genes or in genes involved in type I collagen metabolism. Among the recessive forms, OI types VII, VIII, and IX are due to mutations in CRTAP, P3H1, and PPIB genes, respectively. They code for the three components of the endoplasmic reticulum complex that catalyzes 3-hydroxylation of type I collagen α1Pro986. Under-hydroxylation of this residue leads to collagen structural abnormalities and results in moderate to lethal OI phenotype, despite the exact molecular mechanisms are still not completely clear. To shed light on these recessive forms, primary fibroblasts from OI patients with mutations in CRTAP (n=3), P3H1 (n=3), PPIB (n=1) genes and from controls (n=4) were investigated by a functional proteomic approach. Cytoskeleton and nucleoskeleton asset, protein fate, and metabolism were delineated as mainly affected. While western blot experiments confirmed altered expression of lamin A/C and cofilin-1, immunofluorescence analysis using antibody against lamin A/C and phalloidin showed an aberrant organization of nucleus and cytoskeleton. This is the first report describing an altered organization of intracellular structural proteins in recessive OI and pointing them as possible novel target for OI treatment.

SIGNIFICANCE

OI is a prototype for skeletal dysplasias. It is a highly heterogeneous collagen-related disorder with dominant, recessive and X-linked transmission. There is no definitive cure for this disease, thus a better understanding of the molecular basis of its pathophysiology is expected to contribute in identifying potential targets to develop new treatments. Based on this concept, we performed a functional proteomic study to delineate affected molecular pathways in primary fibroblasts from recessive OI patients, carrying mutations in CRTAP (OI type VII), P3H1 (OI type VIII), and PPIB (OI type IX) genes. Our analyses demonstrated the occurrence of an altered cytoskeleton and, for the first time in OI, of nuclear lamina organization. Hence, cytoskeleton and nucleoskeleton components may be considered as novel drug targets for clinical management of the disease. Finally, according to our analyses, OI emerged to share similar deregulated pathways and molecular aberrances, as previously described, with other rare disorders caused by different genetic defects. Those aberrances may provide common pharmacological targets to support classical clinical approach in treating different diseases.

Identification of Hip BMD Loss and Fracture Risk Markers Through Population-Based Serum Proteomics

Serum proteomics analysis may lead to the discovery of novel osteoporosis biomarkers. The Osteoporotic Fractures in Men (MrOS) study comprises men ≥65 years old in the US who have had repeated BMD measures and have been followed for incident fracture. High-throughput quantitative proteomic analysis was performed on baseline fasting serum samples from non-Hispanic white men using a multidimensional approach coupling liquid chromatography, ion-mobility separation, and mass spectrometry (LC-IMS-MS). We followed the participants for a mean of 4.6 years for changes in femoral neck bone mineral density (BMD) and for incident hip fracture. Change in BMD was determined from mixed effects regression models taking age and weight into account. Participants were categorized into three groups: BMD maintenance (no decline; estimated change ≥0 g/cm2 , n = 453); expected loss (estimated change 0 to 1 SD below the estimated mean change, -0.034 g/cm2 for femoral neck, n = 1184); and accelerated loss (estimated change ≥1 SD below mean change, n = 237). Differential abundance values of 3946 peptides were summarized by meta-analysis to determine differential abundance of each of 339 corresponding proteins for accelerated BMD loss versus maintenance. Using this meta-analytic standardized fold change at cutoffs of ≥1.1 or ≤0.9 (p < 0.10), 20 proteins were associated with accelerated BMD loss. Associations of those 20 proteins with incident hip fracture were tested using Cox proportional hazards models with age and BMI adjustment in 2473 men. Five proteins were associated with incident hip fracture (HR between 1.29 and 1.41 per SD increase in estimated protein abundance). Some proteins have been previously associated with fracture risk (eg, CD14 and SHBG), whereas others have roles in cellular senescence and aging (B2MG and TIMP1) and complement activation and innate immunity (CO7, CO9, CFAD). These findings may inform development of biomarkers for future research in bone biology and fracture prediction. © 2017 American Society for Bone and Mineral Research.

The osteogenesis-promoting effects of alpha-lipoic acid against glucocorticoid-induced osteoporosis through the NOX4, NF-kappaB, JNK and PI3K/AKT pathways

Recently, accumulating evidence has indicated that glucocorticoid-induced osteoporosis (GIOP) is closely related to oxidative stress and apoptosis. Alpha-lipoic acid (LA), a naturally endogenous anti-oxidant, possesses anti-oxidative and anti-apoptosis activities, implicating LA as a therapeutic agent for the treatment of GIOP. In this study, the osteogenesis-promoting effects of LA against GIOP were investigated and the mechanisms were further probed. Here, the results showed that LA inhibited oxidative stress, suppressed apoptosis and improved osteopenia by promoting the expression of osteogenesis markers, including ALP, COL-I, OCN, BMP-2, RUNX2 and OSX. Further study revealed that the osteogenesis-promoting effects of LA likely occur via the regulation of the NOX4, NF-kappaB, JNK and PI3K/AKT pathways. The present study indicated that LA may prevent GIOP and promote osteogenesis and might be a candidate for the treatment of GIOP.

Ginsenoside Rb2 inhibits osteoclast differentiation through nuclear factor-kappaB and signal transducer and activator of transcription protein 3 signaling pathway

Ginsenoside-Rb2 (Rb2) is a 20(S)-protopanaxadiol glycoside extracted from ginseng possessing various bioactivities which has drawn considerable interest regarding the area of bone metabolism. However, the effect of Rb2 on osteoclast differentiation remains unknown. In this study, we aimed to investigate the potential role of Rb2 in regulating osteoclast differentiation and the underlying molecular mechanisms. Osteoclast differentiation was induced by receptor activator nuclear factor-kappaB (NF-κB) ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) in mouse RAW 264.7 cells. The results showed that Rb2 dose-dependently inhibited the formation of the tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells and TRAP expression. Furthermore, Rb2 promoted osteoprotegerin expression and bone resorption. The expression of osteoclast marker genes including nuclear factor of activated T cells c1 (NFATc1), c-Fos, OSCAR, and cathepsin K were also markedly inhibited by Rb2 treatment. Moreover, Rb2 significantly inhibited the RANKL-induced NF-κB activation. In addition, Rb2 also markedly suppressed the activation of signal transducer and activator of transcription protein 3 (STAT3) signaling pathway. Interestingly, the knockdown of STAT3 significantly strengthened the inhibitory effect of Rb2 on osteoclast differentiation. Taken together, our study suggests that Rb2 inhibits osteoclast differentiation associated with blocking NF-κB and STAT3 signaling pathways.

Transcriptomics, NF-κB Pathway, and Their Potential Spaceflight-Related Health Consequences

In space, living organisms are exposed to multiple stress factors including microgravity and space radiation. For humans, these harmful environmental factors have been known to cause negative health impacts such as bone loss and immune dysfunction. Understanding the mechanisms by which spaceflight impacts human health at the molecular level is critical not only for accurately assessing the risks associated with spaceflight, but also for developing effective countermeasures. Over the years, a number of studies have been conducted under real or simulated space conditions. RNA and protein levels in cellular and animal models have been targeted in order to identify pathways affected by spaceflight. Of the many pathways responsive to the space environment, the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) network appears to commonly be affected across many different cell types under the true or simulated spaceflight conditions. NF-κB is of particular interest, as it is associated with many of the spaceflight-related health consequences. This review intends to summarize the transcriptomics studies that identified NF-κB as a responsive pathway to ground-based simulated microgravity or the true spaceflight condition. These studies were carried out using either human cell or animal models. In addition, the review summarizes the studies that focused specifically on NF-κB pathway in specific cell types or organ tissues as related to the known spaceflight-related health risks including immune dysfunction, bone loss, muscle atrophy, central nerve system (CNS) dysfunction, and risks associated with space radiation. Whether the NF-κB pathway is activated or inhibited in space is dependent on the cell type, but the potential health impact appeared to be always negative. It is argued that more studies on NF-κB should be conducted to fully understand this particular pathway for the benefit of crew health in space.

Constitutive Activation of NIK Impairs the Self-Renewal of Hematopoietic Stem/Progenitor Cells and Induces Bone Marrow Failure

Previously we have shown that loss of non-canonical NF-κB signaling impairs self-renewal of hematopoietic stem/progenitor cells (HSPCs). This prompted us to investigate whether persistent activation of the non-canonical NF-κB signaling will have supportive effects on HSPC self-renewal. NF-κB-inducing kinase (NIK) is an important kinase that mainly activates the non-canonical pathway through directly phosphorylating IKKα. In contrast to our expectations, constitutive activation of NIK in the hematopoietic system leads to bone marrow (BM) failure and postnatal lethality due to intrinsic impairment of HSPC self-renewal and extrinsic disruption of BM microenvironment through enhancing osteoclastogenesis. The impaired HSPC function is associated with reduced cell proliferation and increased apoptosis and inflammatory cytokine responses. RNAseq analysis of control and NIK-activated HSPCs reveals that these effects are through non-canonical NF-κB signaling without significant changes in the canonical pathway. Gene set expression analysis of RNAseq data reveals globally decreased stem cell signature, increased maturation signature, and increased inflammatory responses. Many genes (Mpl, Tifab, Emcn, Flt3, Bcl2, and others) that regulate HSPC self-renewal, lineage commitment, and apoptosis are significantly downregulated-and those genes that regulate inflammatory responses and cell cycle inhibition (Cdkn2a and Cdkn2b) are significantly upregulated-by activation of NIK. Importantly, our data demonstrate that activation of NIK-non-canonical signaling has distinct phenotypes-smaller spleen size, decreased white blood cell counts, and reduced HSPC proliferation-compared to activation of canonical signaling. Collectively, these data indicate that the balanced non-canonical NF-κB signaling is essential for maintaining normal hematopoiesis and NIK-non-canonical signaling contributes to the development of BM failure. Stem Cells 2017;35:777-786.

Targeting IKK and NF-κB for Therapy

In addition to regulating immune responses, the NF-κB family of transcription factors also promotes cellular proliferation and survival. NF-κB and its activating kinase, IKK, have become appealing therapeutic targets because of their critical roles in the progression of many diseases including chronic inflammation and cancer. Here, we discuss the conditions that lead to pathway activation, the effects of constitutive activation, and some of the strategies used to inhibit NF-κB signaling.

Inflammation and epigenetic regulation in osteoarthritis

Osteoarthritis (OA) was once defined as a non-inflammatory arthropathy, but it is now well-recognized that there is a major inflammatory component to this disease. In addition to synovial cells, articular chondrocytes and other cells of diarthrodial joints are also known to express inflammatory mediators. It has been proposed that targeting inflammation pathways could be a promising strategy to treat OA. There have been many reports of cross-talk between inflammation and epigenetic factors in cartilage. Specifically, inflammatory mediators have been shown to regulate levels of enzymes that catalyze changes in DNA methylation and histone structure, as well as alter levels of non-coding RNAs. In addition, expression levels of a number of these epigenetic factors have been shown to be altered in OA, thereby suggesting potential interplay between inflammation and epigenetics in this disease. This review provides information on inflammatory pathways in arthritis and summarizes published research on how epigenetic regulators are affected by inflammation in chondrocytes. Furthermore, we discuss data showing how altered expression of some of these epigenetic factors can induce either catabolic or anti-catabolic effects in response to inflammatory signals. A better understanding of how inflammation affects epigenetic factors in OA may provide us with novel therapeutic strategies to treat this condition.

NF-κB as a Therapeutic Target in Inflammatory-Associated Bone Diseases

Inflammation is a defensive mechanism for pathogen clearance and maintaining tissue homeostasis. In the skeletal system, inflammation is closely associated with many bone disorders including fractures, nonunions, periprosthetic osteolysis (bone loss around orthopedic implants), and osteoporosis. Acute inflammation is a critical step for proper bone-healing and bone-remodeling processes. On the other hand, chronic inflammation with excessive proinflammatory cytokines disrupts the balance of skeletal homeostasis involving osteoblastic (bone formation) and osteoclastic (bone resorption) activities. NF-κB is a transcriptional factor that regulates the inflammatory response and bone-remodeling processes in both bone-forming and bone-resorption cells. In vitro and in vivo evidences suggest that NF-κB is an important potential therapeutic target for inflammation-associated bone disorders by modulating inflammation and bone-remodeling process simultaneously. The challenges of NF-κB-targeting therapy in bone disorders include: (1) the complexity of canonical and noncanonical NF-κB pathways; (2) the fundamental roles of NF-κB-mediated signaling for bone regeneration at earlier phases of tissue damage and acute inflammation; and (3) the potential toxic effects on nontargeted cells such as lymphocytes. Recent developments of novel inhibitors with differential approaches to modulate NF-κB activity, and the controlled release (local) or bone-targeting drug delivery (systemic) strategies, have largely increased the translational application of NF-κB therapy in bone disorders. Taken together, temporal modulation of NF-κB pathways with the combination of recent advanced bone-targeting drug delivery techniques is a highly translational strategy to reestablish homeostasis in the skeletal system.

Myeloid Deletion of Nemo Causes Osteopetrosis in Mice Owing to Upregulation of Transcriptional Repressors

The transcription factor NF-κB is central to numerous physiologic processes including bone development, and its activation is controlled by IKKγ (also called NEMO), the regulatory subunit of IKK complex. NEMO is X-linked, and mutations in this gene result in Incontinentia Pigmenti in human hemizygous females. In mice, global deficiency causes embryonic lethality. In addition, certain point mutations in the NEMO (IKBKG) human gene manifest skeletal defects implicating NEMO in the regulation of bone homeostasis. To specifically investigate such role, we conditionally deleted Nemo from osteoclast and myeloid progenitors. Morphometric, histologic, and molecular analyses demonstrate that myeloid NEMO deletion causes osteopetrosis in mice. Mechanistically, NEMO deficiency hampered activation of IKK complex in osteoclast precursors, causing arrest of osteoclastogenesis and apoptosis. Interestingly, inhibiting apoptosis by genetic ablation of TNFr1 significantly increased cell survival, but failed to rescue osteoclastogenesis or reverse osteopetrosis. Based on this observation, we analyzed the expression of different regulators of osteoclastogenesis and discovered that NEMO deletion leads to increased RBPJ expression, resulting in a decrease of Blimp1 expression. Consequently, expression of IRF8 and Bcl6 which are targets of Blimp1 and potent osteoclastogenic transcriptional repressors, is increased. Thus, NEMO governs survival and osteoclast differentiation programs through serial regulation of multiple transcription factors.

ZIP4 silencing improves bone loss in pancreatic cancer

Metabolic bone disorders are associated with several types of human cancers. Pancreatic cancer patients usually suffer from severe nutrition deficiency, muscle wasting, and loss of bone mass. We have previously found that silencing of a zinc transporter ZIP4 prolongs the survival and reduces the severity of the cachexia in vivo. However, the role of ZIP4 in the pancreatic cancer related bone loss remains unknown. In this study we investigated the effect of ZIP4 knockdown on the bone structure, composition and mechanical properties of femurs in an orthotopic xenograft mouse model. Our data showed that silencing of ZIP4 resulted in increased bone tissue mineral density, decreased bone crystallinity and restoration of bone strength through the RANK/RANKL pathway. The results further support the impact of ZIP4 on the progression of pancreatic cancer, and suggest its potential significance as a therapeutic target for treating patients with such devastating disease and cancer related disorders.

Intravenous Immunoglobulin (IVIG) Attenuates TNF-Induced Pathologic Bone Resorption and Suppresses Osteoclastogenesis by Inducing A20 Expression

Investigations on the therapeutic effects of intravenous immunoglobulin (IVIG) have focused on the suppression of autoantibody and immune complex-mediated inflammatory pathogenesis. Inflammatory diseases such as rheumatoid arthritis are often accompanied by excessive bone erosion but the effect of IVIG on osteoclasts, bone-resorbing cells, has not been studied. Here, we investigate whether IVIG directly regulates osteoclast differentiation and has therapeutic potential for suppressing osteoclast-mediated pathologic bone resorption. IVIG or cross-linking of Fcγ receptors with plate-bound IgG suppressed receptor activator of nuclear factor-κ B ligand (RANKL)-induced osteoclastogenesis and expression of osteoclast-related genes such as integrin β3 and cathepsin K in a dose-dependent manner. Mechanistically, IVIG or plate-bound IgG suppressed osteoclastogenesis by downregulating RANKL-induced expression of NFATC1, the master regulator of osteoclastogenesis. IVIG suppressed NFATC1 expression by attenuating RANKL-induced NF-κB signaling, explained in part by induction of the inflammatory signaling inhibitor A20. IVIG administration attenuated in vivo osteoclastogenesis and suppressed bone resorption in the tumor necrosis factor (TNF)-induced calvarial osteolysis model. Our findings show that, in addition to suppressing inflammation, IVIG directly inhibits osteoclastogenesis through a mechanism involving suppression of RANK signaling. Direct suppression of osteoclast differentiation may provide beneficial effects on preserving bone mass when IVIG is used to treat rheumatic disorders.

Improved Outcomes of Hematopoietic Stem Cell Transplantation in Patients With Infantile Malignant Osteopetrosis Using Fludarabine-Based Conditioning

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for infantile malignant osteopetrosis (IMO), but is associated with a high incidence of adverse outcomes. In this study, we present our experience with HSCT for IMO patients comparing different types of conditioning regimens.

METHODS

Thirty-eight patients with IMO (aged from 1 month to 6 years, median 0.66 years) who underwent allogeneic HSCT from 1983 in our hospital were included in this retrospective study. Fludarabine-based conditioning regimens were used in 26 patients and 12 patients were transplanted using other conditioning regimens.

RESULTS

The overall survival after conditioning with fludarabine was 96% (25/26) versus 58% (7/12) for the alternative regimens (P = 0.004), with significantly fewer adverse effects including hypercalcemia and veno-occlusive disease of liver. All patients who survive are clinically well.

CONCLUSIONS

We conclude that fludarabine-based conditioning regimens are safe and effective in patients with IMO, improving morbidity and mortality related to HSCT.

Genetic deletion of keratin 8 corrects the altered bone formation and osteopenia in a mouse model of cystic fibrosis

Patients with cystic fibrosis (CF) display low bone mass and alterations in bone formation. Mice carrying the F508del genetic mutation in the cystic fibrosis conductance regulator (Cftr) gene display reduced bone formation and decreased bone mass. However, the underlying molecular mechanisms leading to these skeletal defects are unknown, which precludes the development of an efficient anti-osteoporotic therapeutic strategy. Here we report a key role for the intermediate filament protein keratin 8 (Krt8), in the osteoblast dysfunctions in F508del-Cftr mice. We found that murine and human osteoblasts express Cftr and Krt8 at low levels. Genetic studies showed that Krt8 deletion (Krt8(-/-)) in F508del-Cftr mice increased the levels of circulating markers of bone formation, corrected the expression of osteoblast phenotypic genes, promoted trabecular bone formation and improved bone mass and microarchitecture. Mechanistically, Krt8 deletion in F508del-Cftr mice corrected overactive NF-κB signaling and decreased Wnt-β-catenin signaling induced by the F508del-Cftr mutation in osteoblasts. In vitro, treatment with compound 407, which specifically disrupts the Krt8-F508del-Cftr interaction in epithelial cells, corrected the abnormal NF-κB and Wnt-β-catenin signaling and the altered phenotypic gene expression in F508del-Cftr osteoblasts. In vivo, short-term treatment with 407 corrected the altered Wnt-β-catenin signaling and bone formation in F508del-Cftr mice. Collectively, the results show that genetic or pharmacologic targeting of Krt8 leads to correction of osteoblast dysfunctions, altered bone formation and osteopenia in F508del-Cftr mice, providing a therapeutic strategy targeting the Krt8-F508del-CFTR interaction to correct the abnormal bone formation and bone loss in cystic fibrosis.

NF-κB Has a Direct Role in Inhibiting Bmp- and Wnt-Induced Matrix Protein Expression

The host response to pathogens through nuclear factor κB (NF-κB) is an essential defense mechanism for eukaryotic organisms. NF-κB-mediated host responses inhibit bone and other connective tissue synthesis and are thought to affect the transcription of matrix proteins through multiple indirect pathways. We demonstrate that inhibiting NF-κB in osteoblasts increases osteocalcin expression in vivo in mice with periodontal disease. Mutating NF-κB binding sites on osteocalcin (OC) or bone sialoprotein (Bsp) promoters rescues the negative impact of NF-κB on their transcription and that NF-κB can inhibit Wnt- and Bmp-induced OC and Bsp transcription, even when protein synthesis is inhibited, indicating a direct effect of NF-κB. This inhibition depends on p65-p50 NF-κB heterodimer formation and deacetylation by HDAC1 but is not affected by the noncanonical NF-κB pathway. Moreover, NF-κB reduces Runx2 and β-catenin binding to OC/Bsp promoters independently of their nuclear localization. Thus, inflammatory signals stimulate the direct interaction of NF-κB with response elements to inhibit binding of β-catenin and Runx2 binding to nearby consensus sites and reduce expression of matrix proteins. This direct mechanism provides a new explanation for the rapid decrease in new bone formation after inflammation-related NF-κB activation.

Melatonin, bone regulation and the ubiquitin-proteasome connection: A review

Recently, investigators have shown that ubiquitin-proteasome-mediated protein degradation is critical in regulating the balance between bone formation and bone resorption. The major signal transduction pathways regulating bone formation are the RANK/NF-κB pathway and the Wnt/β-catenin pathway. These signal transduction pathways regulate the activity of mature osteoblasts and osteoclasts. In addition, the Wnt/β-catenin pathway is one of the major signaling pathways in the differentiation of osteoblasts. The ubiquitin ligases that are reported to be of major significance in regulating these pathways are the ubiquitin SCF(B-TrCP) ligase (which regulates activation of NF-κB via degradation of IkBα in osteoclasts, and regulates bone transcription factors via degradation of β-catenin), the Keap-Cul3-Rbx1 ligase (which regulates degradation of IkB kinase, Nrf2, and the antiapoptotic factor Bcl-2), and Smurf1. Also of significance in regulating osteoclastogenesis is the deubiquitinase, CYLD (cylindramatosis protein), which facilitates the separation of NF-κB from IkBα. The degradation of CYLD is also under the regulation of SCF(B-TrCP). Proteasome inhibitors influence the activity of mature osteoblasts and osteoclasts, but also modulate the differentiation of precursor cells into osteoblasts. Preclinical studies show that melatonin also influences bone metabolism by stimulating bone growth and inhibiting osteoclast activity. These actions of melatonin could be interpreted as being mediated by the ubiquitin ligases SCF(B-TrCP) and Keap-Cul3-Rbx, or as an inhibitory effect on proteasomes. Clinical trials of the use of melatonin in the treatment of bone disease, including multiple myeloma, using both continuous and intermittent modes of administration, are warranted.

Evaluating Nuclear Factor NF-κB Activation following Bone Trauma: A Pilot Study in a Wistar Rats Model

The present study investigated the moment of peak NF-kB activation and its dissipation in the cortical bone in the femur of Wistar rat stimulated by surgical trauma. Sixty-five Wistar rats were divided into 13 groups (n = 5 per group): eight experimental groups (expG 1–8) divided based on the euthanasia time point (zero, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h and 24 h) and five sham control groups (conG 1–5) killed at zero, 1 h, 2 h, 4 h and 6 h, respectively. A 1.8-mm-diameter defect was generated 0.5 mm from the femur proximal joint using a round bur to induce the surgical trauma. Overall, the activation peak of NF-κB in the cortical bone was 6 h (expG5 group) independent of the evaluated position; this peak was significantly different compared to those in the other groups (p < 0.05). The surgical trauma resulted in a spread of immune markings throughout the cortical bone with an accentuation in the knee region. The present study provides the first evidence that the NF-κB activation peak was established after 6 hours in the cortical bone of Wistar rats. The signs from a surgical trauma can span the entire cortical bone and are not limited to the damaged region.

Prednisone inhibits the focal adhesion kinase/receptor activator of NF-κB ligand/mitogen-activated protein kinase signaling pathway in rats with adriamycin-induced nephropathy

The aim of the present study was to investigate the mechanisms underlying the effects of prednisone on adriamycin-induced nephritic rat kidney damage via the focal adhesion kinase (FAK)/receptor activator of nuclear factor-κB ligand (RANKL)/mitogen‑activated protein kinase (MAPK) signaling pathway. An adriamycin‑induced nephritic rat model was established to investigate these mechanisms. A total of 30 healthy male Sprague‑Dawley rats were randomly assigned to the normal, model or prednisone group. Samples of urine were collected over the course of 24 h at days 7, 14, and 28, and renal cortex tissue samples were harvested at days 14, and 28 following nephritic rat model establishment. The total urinary protein content was measured by biuret colorimetry. Pathological changes in the kidney tissue samples were observed using an electron microscope. The mRNA expressions levels of FAK, RANKL, p38, extracellular signal‑regulated kinase (ERK), c‑Jun N‑terminal kinase (JNK), and nephrin were then quantified by reverse transcription‑quantitative polymerase chain reaction. In addition, the protein expressions levels of FAK, RANKL, p38, ERK, JNK, phosphorylated (p)‑FAK, p‑ERK, and p‑JNK were quantified by western blotting. As compared with the normal group, the protein expression levels of FAK, RANKL, p-FAK, p38 and p-ERK in the model group were increased. In the prednisone group, the protein expression levels of p-ERK decreased, as compared with the normal group. In the prednisone group, the urinary protein levels, the protein expression levels of FAK, RANKL, p38, p-FAK, p-p38 and the mRNA expression levels of FAK, p38, RANKL, ERK, JNK decreased, as compared with the model group. In the prednisone group, the mRNA and protein expression levels of nephrin and the serum expression levels of RANKL increased, the serum expression levels of osteoprotegerin (OPG) were decreased, as compared with the model group. No significant changes in the protein expression levels of JNK were observed among the groups. These results suggested that prednisone is able to protect podocytes from apoptosis, and reduce urinary protein levels by inhibiting the FAK/RANKL/MAPK signaling pathway in kidney tissue samples. Serum prednisone may induce osteoporosis via the OPG/RANK/RANKL signaling pathway.

Mst2 Controls Bone Homeostasis by Regulating Osteoclast and Osteoblast Differentiation

Mammalian sterile 20-like kinase 2 (Mst2) plays a central role in the Hippo pathway, controlling cell proliferation, differentiation, and apoptosis during development. However, the roles of Mst2 in osteoclast and osteoblast development are largely unknown. Here, we demonstrate that mice deficient in Mst2 exhibit osteoporotic phenotypes with increased numbers of osteoclasts and decreased numbers of osteoblasts as shown by micro-computed tomography (µCT) and histomorphometric analyses. Osteoclast precursors lacking Mst2 exhibit increased osteoclastogenesis and Nfatc1, Acp5, and Oscar expression in response to receptor activator of NF-κB ligand (RANKL) exposure. Conversely, Mst2 overexpression in osteoclast precursors leads to the inhibition of RANKL-induced osteoclast differentiation. Osteoblast precursors deficient in Mst2 exhibit attenuated osteoblast differentiation and function by downregulating the expression of Runx2, Alpl, Ibsp, and Bglap. Conversely, ectopic expression of Mst2 in osteoblast precursors increases osteoblastogenesis. Finally, we demonstrate that the NF-κB pathway is activated by Mst2 deficiency during osteoclast and osteoblast development. Our findings suggest that Mst2 is involved in bone homeostasis, functioning as a reciprocal regulator of osteoclast and osteoblast differentiation through the NF-κB pathway.

Understanding the local actions of lipids in bone physiology

The adult skeleton is a metabolically active organ system that undergoes continuous remodeling to remove old and/or stressed bone (resorption) and replace it with new bone (formation) in order to maintain a constant bone mass and preserve bone strength from micro-damage accumulation. In that remodeling process, cellular balances--adipocytogenesis/osteoblastogenesis and osteoblastogenesis/osteoclastogenesis--are critical and tightly controlled by many factors, including lipids as discussed in the present review. Interest in the bone lipid area has increased as a result of in vivo evidences indicating a reciprocal relationship between bone mass and marrow adiposity. Lipids in bones are usually assumed to be present only in the bone marrow. However, the mineralized bone tissue itself also contains small amounts of lipids which might play an important role in bone physiology. Fatty acids, cholesterol, phospholipids and several endogenous metabolites (i.e., prostaglandins, oxysterols) have been purported to act on bone cell survival and functions, the bone mineralization process, and critical signaling pathways. Thus, they can be regarded as regulatory molecules important in bone health. Recently, several specific lipids derived from membrane phospholipids (i.e., sphingosine-1-phosphate, lysophosphatidic acid and different fatty acid amides) have emerged as important mediators in bone physiology and the number of such molecules will probably increase in the near future. The present paper reviews the current knowledge about: (1°) bone lipid composition in both bone marrow and mineralized tissue compartments, and (2°) local actions of lipids on bone physiology in relation to their metabolism. Understanding the roles of lipids in bone is essential to knowing how an imbalance in their signaling pathways might contribute to bone pathologies, such as osteoporosis.

Increased NF-κB Activity and Decreased Wnt/β-Catenin Signaling Mediate Reduced Osteoblast Differentiation and Function in ΔF508 Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Mice

The prevalent human ΔF508 mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) is associated with reduced bone formation and bone loss in mice. The molecular mechanisms by which the ΔF508-CFTR mutation causes alterations in bone formation are poorly known. In this study, we analyzed the osteoblast phenotype in ΔF508-CFTR mice and characterized the signaling mechanisms underlying this phenotype. Ex vivo studies showed that the ΔF508-CFTR mutation negatively impacted the differentiation of bone marrow stromal cells into osteoblasts and the activity of osteoblasts, demonstrating that the ΔF508-CFTR mutation alters both osteoblast differentiation and function. Treatment with a CFTR corrector rescued the abnormal collagen gene expression in ΔF508-CFTR osteoblasts. Mechanistic analysis revealed that NF-κB signaling and transcriptional activity were increased in mutant osteoblasts. Functional studies showed that the activation of NF-κB transcriptional activity in mutant osteoblasts resulted in increased β-catenin phosphorylation, reduced osteoblast β-catenin expression, and altered expression of Wnt/β-catenin target genes. Pharmacological inhibition of NF-κB activity or activation of canonical Wnt signaling rescued Wnt target gene expression and corrected osteoblast differentiation and function in bone marrow stromal cells and osteoblasts from ΔF508-CFTR mice. Overall, the results show that the ΔF508-CFTR mutation impairs osteoblast differentiation and function as a result of overactive NF-κB and reduced Wnt/β-catenin signaling. Moreover, the data indicate that pharmacological inhibition of NF-κB or activation of Wnt/β-catenin signaling can rescue the abnormal osteoblast differentiation and function induced by the prevalent ΔF508-CFTR mutation, suggesting novel therapeutic strategies to correct the osteoblast dysfunctions in cystic fibrosis.

Suppression of NF-κB activation by gentian violet promotes osteoblastogenesis and suppresses osteoclastogenesis

Skeletal mass is regulated by the coordinated action of bone forming osteoblasts and bone resorbing osteoclasts. Accelerated rates of bone resorption relative to bone formation lead to net bone loss and the development of osteoporosis, a devastating disease that predisposes the skeleton to fractures. Bone fractures are associated with significant morbidity and in the case of hip fractures, high mortality. Gentian violet (GV), a cationic triphenylmethane dye, has long been used as an antifungal and antibacterial agent and is presently under investigation as a potential chemotherapeutic and antiangiogenic agent. However, effects on bone cells have not been previously reported and the mechanisms of action of GV, are poorly understood. In this study we show that GV suppresses receptor activator of NF-κB ligand (RANKL)-induced differentiation of RAW264.7 osteoclast precursors into mature osteoclasts, but paradoxically stimulates the differentiation of MC3T3 cells into mineralizing osteoblasts. These actions stem from the capacity of GV to suppress activation of the nuclear factor kappa B (NF-κB) signal transduction pathway that is required for osteoclastogenesis, but inhibitory to osteoblast differentiation and activity. Our data reveal that GV is an inhibitor of NF-κB activation and may hold promise for modulation of bone turnover to promote a balance between bone formation and bone resorption, favorable to gain of bone mass.

Osteoblast dysfunctions in bone diseases: from cellular and molecular mechanisms to therapeutic strategies

Several metabolic, genetic and oncogenic bone diseases are characterized by defective or excessive bone formation. These abnormalities are caused by dysfunctions in the commitment, differentiation or survival of cells of the osteoblast lineage. During the recent years, significant advances have been made in our understanding of the cellular and molecular mechanisms underlying the osteoblast dysfunctions in osteoporosis, skeletal dysplasias and primary bone tumors. This led to suggest novel therapeutic approaches to correct these abnormalities such as the modulation of WNT signaling, the pharmacological modulation of proteasome-mediated protein degradation, the induction of osteoprogenitor cell differentiation, the repression of cancer cell proliferation and the manipulation of epigenetic mechanisms. This article reviews our current understanding of the major cellular and molecular mechanisms inducing osteoblastic cell abnormalities in age-related bone loss, genetic skeletal dysplasias and primary bone tumors, and discusses emerging therapeutic strategies to counteract the osteoblast abnormalities in these disorders of bone formation.

Local administration of IKK small molecule inhibitor may enhance fracture healing in osteoporosis patient

Osteoporosis is an inflammatory bone disease affecting millions of population worldwide, which often cause increased fracture risks and prolonged fracture healing. Growing evidence suggests that IKK-NF-κB signaling exert inhibitory influence on MSCs osteogenic differentiation and bone formation. Moreover, enhance the fracture healing process in osteoporosis patient. In the current work, IKK-NF- κB differentiated osteoblasts. Thus, manipulating local inflammatory IKK-NF-κB signaling was also found to suppress the anabolic effect of signaling in osteoporotic related fracture emerge as a promising therapy to we hypothesized to use locally delivered IKK small molecule inhibitor to augment the impaired fracture healing ability in osteoporosis patient via enhancing both MSCs osteogenic differentiation and osteoblast function.

Triptolide inhibits osteoclast formation, bone resorption, RANKL-mediated NF-қB activation and titanium particle-induced osteolysis in a mouse model

The RANKL-induced NF-κB signaling pathway is required for osteoclast formation and function. By screening for compounds that inhibit RANKL-induced NF-κB activation using a luciferase reporter gene assay in RAW264.7 cells, we identified triptolide (PG490), as a candidate compound targeting osteoclast differentiation and osteoclast-mediated osteolysis. Triptolide (PG490) is an active compound of the medicinal herb Tripterygium wilfordii Hook F (TWHF) or Lei Gong Teng with known anti-inflammatory properties. We found that triptolide inhibited osteoclastogenesis and bone resorption, as well as RANKL-induced NF-қB activities as monitored by luciferase reporter gene assays and the nuclear translocation of p65. In vivo studies showed that triptolide attenuates titanium-induced osteolysis and osteoclast formation in a mouse calvarial model. Considering that drugs which protect against localized bone loss are critically needed for the effective treatment of particle-induced osteolysis, our data suggest that triptolide might have therapeutic potential for the treatment of bone lytic diseases caused by prosthetic wear particles.

Regulation of NF-κB signaling in osteoclasts and myeloid progenitors

The transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is crucial for immune responses and skeletal development. Work in recent years has shown that various members of the NF-κB family are viable targets to regulate activity and survival of bone cells and hence bone metabolism. In this regard, deletion of upstream kinases or distal NF-κB subunits resulted with bone deformities. Thus, it has become increasingly apparent that detailed investigation of NF-κB in bone cells may provide opportunities to design new therapeutic modalities. In this chapter we present modified methodology describing efficient approaches to regulate the NF-κB pathway in vitro and in vivo to assess its function in bone cells and tissues.

Osteopetrosis in TAK1-deficient mice owing to defective NF-κB and NOTCH signaling

The MAP kinase TGFβ-activated kinase (TAK1) plays a crucial role in physiologic and pathologic cellular functions including cell survival, differentiation, apoptosis, inflammation, and oncogenesis. However, the entire repertoire of its mechanism of action has not been elucidated. Here, we found that ablation of Tak1 in myeloid cells causes osteopetrosis in mice as a result of defective osteoclastogenesis. Mechanistically, Tak1 deficiency correlated with increased NUMB-like (NUMBL) levels. Accordingly, forced expression of Numbl abrogated osteoclastogenesis whereas its deletion partially restored osteoclastogenesis and reversed the phenotype of Tak1 deficiency. Tak1 deletion also down-regulated Notch intracellular domain (NICD), but increased the levels of the transcription factor recombinant recognition sequence binding protein at Jκ site (RBPJ), consistent with NUMBL regulating notch signaling through degradation of NICD, a modulator of RBPJ. Accordingly, deletion of Rbpj partially corrected osteopetrosis in Tak1-deficient mice. Furthermore, expression of active IKK2 in RBPJ/TAK1-deficient cells significantly restored osteoclastogenesis, indicating that activation of NF-κB is essential for complete rescue of the pathway. Thus, we propose that TAK1 regulates osteoclastogenesis by integrating activation of NF-κB and derepression of NOTCH/RBPJ in myeloid cells through inhibition of NUMBL.

Wnt4 signaling prevents skeletal aging and inflammation by inhibiting nuclear factor-κB

Aging-related bone loss and osteoporosis affect millions of patients worldwide. Chronic inflammation associated with aging and arthritis promotes bone resorption and impairs bone formation. Here we show that Wnt4 attenuated bone loss in osteoporosis and skeletal aging by inhibiting nuclear factor-kappa B (NF-κB) via non-canonical Wnt signaling. Transgenic mice expressing Wnt4 from osteoblasts were significantly protected from bone loss and chronic inflammation induced by ovariectomy, tumor necrosis factor or natural aging. In addition to promoting bone formation, Wnt4 could inhibit osteoclast formation and bone resorption. Mechanistically, Wnt4 inhibited transforming growth factor beta-activated kinase 1-mediated NF-κB activation in macrophages and osteoclast precursors independent of β-catenin. Moreover, recombinant Wnt4 proteins were able to alleviate osteoporotic bone loss and inflammation by inhibiting NF-κB in vivo. Taken together, our results suggest that Wnt4 might be used as a therapeutic agent for treating osteoporosis by attenuating NF-κB.

Long-term tumor necrosis factor treatment induces NFκB activation and proliferation, but not osteoblastic differentiation of adipose tissue-derived mesenchymal stem cells in vitro

The pro-inflammatory cytokine tumor necrosis factor (TNF) is well known to induce differentiation of bone matrix-resorbing osteoclasts from hematopoietic stem cells. However, the impact of TNF on differentiation of bone matrix-forming osteoblasts from mesenchymal stem cells (MSC) was only fragmentarily studied so far. Therefore, we investigated what impact long-term TNF treatment has on osteoblastic differentiation of MSC isolated from the adipose tissue (ASC) in vitro. In summary, we found continuous TNF exposure to induce the nuclear factor of kappa B pathway in ASC as well as secretion of the pro-inflammatory chemokine interleukin 8, but not the mitogen-activated protein kinase and the apoptosis pathway in ASC. Moreover, TNF neither induced nor inhibited osteoblastic differentiation of ASC, but strongly increased their proliferation rate. In that manner, pro-inflammatory conditions in vivo may generate significantly increased numbers of progenitor cells, and ASC especially, in conjunction with external stimuli, may contribute to the events of ectopic ossification observed in chronic inflammatory diseases. The substantiation of the translation of our in vitro findings to the disease context encourages further in vivo studies.