Complex regulation of tartrate-resistant acid phosphatase (TRAP) expression by interleukin 4 (IL-4): IL-4 indirectly suppresses receptor activator of NF-kappaB ligand (RANKL)-mediated TRAP expression but modestly induces its expression directly

The Evaluation of Anti-Osteoclastic Activity of the Novel Calcium Hydroxide Biodegradable Nanoparticles as an Intracanal Medicament

INTRODUCTION

The aim of this study was to evaluate the anti-osteoclastic activity of calcium hydroxide-loaded poly(lactic-co-glycolic acid) nanoparticles [Ca(OH)2-loaded PLGA NPs] in comparison to calcium hydroxide nanoparticles [Ca(OH)2 NPs].

METHODS

RAW 264.7 cell lines (third-fifth passage) were cultured and incubated with soluble receptor activator of nuclear factor kappa B ligand in triplicate. Subsequently, Ca(OH)2-loaded PLGA NPs and Ca(OH)2 NPs were added for 7 days to evaluate their effects on receptor activator of nuclear factor kappa B ligand-induced osteoclast differentiation of RAW 264.7 cells by tartrate-resistant acid phosphatase activity. Additionally, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was conducted to confirm the cytotoxicity of treatments to cells.

RESULTS

Tartrate-resistant acid phosphatase staining showed a significant reduction in the osteoclast number when treated with Ca(OH)2-loaded PLGA NPs compared with Ca(OH)2 NPs (P < .01). In comparison to the control, the number of osteoclasts significantly reduced upon treatment with Ca(OH)2-loaded PLGA NPs (P < .05), but there was no significant difference in Ca(OH)2 NPs. Furthermore, osteoclast morphology in both treatment groups exhibited smaller sizes than the control group. Neither Ca(OH)2-loaded PLGA NPs nor Ca(OH)2 NPs demonstrated cytotoxic effects on RAW264.7 cells.

CONCLUSIONS

Both Ca(OH)2 NPs with and without poly(lactic-co-glycolic acid) have the ability to inhibit osteoclast differentiation. However, Ca(OH)2-loaded PLGA NPs exhibit greater potential than Ca(OH)2 NPs, making them a promising intracanal medicament for cases of root resorption.

Exercise and osteoimmunology in bone remodeling

Bones can form the scaffolding of the body, support the organism, coordinate somatic movements, and control mineral homeostasis and hematopoiesis. The immune system plays immune supervisory, defensive, and regulatory roles in the organism, which mainly consists of immune organs (spleen, bone marrow, tonsils, lymph nodes, etc.), immune cells (granulocytes, platelets, lymphocytes, etc.), and immune molecules (immune factors, interferons, interleukins, tumor necrosis factors, etc.). Bone and the immune system have long been considered two distinct fields of study, and the bone marrow, as a shared microenvironment between the bone and the immune system, closely links the two. Osteoimmunology organically combines bone and the immune system, elucidates the role of the immune system in bone, and creatively emphasizes its interdisciplinary characteristics and the function of immune cells and factors in maintaining bone homeostasis, providing new perspectives for skeletal-related field research. In recent years, bone immunology has gradually become a hot spot in the study of bone-related diseases. As a new branch of immunology, bone immunology emphasizes that the immune system can directly or indirectly affect bones through the RANKL/RANK/OPG signaling pathway, IL family, TNF-α, TGF-β, and IFN-γ. These effects are of great significance for understanding inflammatory bone loss caused by various autoimmune or infectious diseases. In addition, as an external environment that plays an important role in immunity and bone, this study pays attention to the role of exercise-mediated bone immunity in bone reconstruction.

Biological Potential of Carnivorous Plants from Nepenthales

Since Charles Darwin and his book carnivorous plants have aroused interest and heated debate. In addition, there is growing interest in this group of plants as a source of secondary metabolites and in the application of their biological activity. The aim of this study was to trace the recent literature in search of the application of extracts obtained from families Droseraceae, Nepenthaceae, and Drosophyllaceae to show their biological potential. The data collected in the review clearly indicate that the studied Nepenthales species have great biological potential in terms of antibacterial, antifungal, antioxidant, anti-inflammatory, and anticancer use. We proposed that further investigations should include: (i) bioactivity-guided investigations of crude plant extract to connect a particular type of action with a specific compound or a group of metabolites; (ii) a search for new bioactive properties of carnivorous plants; (iii) establishment of molecular mechanisms associated with specific activity. Furthermore, further research should be extended to include less explored species, i.e., Drosophyllum lusitanicum and especially Aldrovanda vesiculosa.

Interferon-induced protein with tetratricopeptide repeats 1 (IFIT1) accelerates osteoclast formation by regulating signal transducer and activator of transcription 3 (STAT3) signalling

Osteoclasts (OCs), the main cause of bone resorption irregularities, may ultimately cause various bone diseases, including osteoarthritis. The objective of this study was to investigate the effect of interferon-induced protein with tetratricopeptide repeats 1 (IFIT1) on OC formation induced by receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) and to further explore its underlying mechanism. IFIT1 expression in Raw264.7 cells treated with macrophage colony-stimulating factor (M-CSF) and RANKL was determined by qRT-PCR. OC formation was detected using tartrate-resistant acid phosphatase (TRAP) staining. The effect of IFIT1 on STAT3 activation was detected using Western blotting. Additionally, Western blotting was used to measure the change in the expression of OC-specific proteins. IFIT1 was highly expressed in Raw264.7 cells after stimulation with M-CSF and RANKL. IFIT1 overexpression accelerated the formation of OCs, as evidenced by the increased number and size of multinuclear cells, and the upregulation of OC-specific proteins, and activated the STAT3 pathway, by inducing phosphorylation of JAK1 and STAT3. However, silencing of IFIT1 inhibited the formation of OCs and a STAT3 inhibitor Stattic weakened the effects of IFIT1. In conclusion, IFIT1 accelerates the formation of OCs, which is caused by RANKL by STAT3 pathway regulation. This study provides a potential basis for further research and for development of drugs for treating bone resorption-related diseases.

Cladophora glomerata enriched by biosorption with Mn(II) ions alleviates lipopolysaccharide-induced osteomyelitis-like model in MC3T3-E1, and 4B12 osteoclastogenesis

Chronic osteomyelitis, a bone infectious disease, is characterized by dysregulation of bone homeostasis, which results in excessive bone resorption. Lipopolysaccharide (LPS) which is a gram‐negative endotoxin was shown to inhibit osteoblast differentiation and to induce apoptosis and osteoclasts formation in vitro. While effective therapy against bacteria‐induced bone destruction is quite limited, the investigation of potential drugs that restore down‐regulated osteoblast function remains a major goal in the prevention of bone destruction in infective bone diseases. This investigation aimed to rescue LPS‐induced MC3T3‐E1 pre‐osteoblastic cell line using the methanolic extract of Cladophora glomerata enriched with Mn(II) ions by biosorption. LPS‐induced MC3T3‐E1 cultures supplemented with C. glomerata methanolic extract were tested for expression of the main genes and microRNAs involved in the osteogenesis pathway using RT‐PCR. Moreover, osteoclastogenesis of 4B12 cells was also investigated by tartrate‐resistant acid phosphatase (TRAP) assay. Treatment with algal extract significantly restored LPS‐suppressed bone mineralization and the mRNA expression levels of osteoblast‐specific genes such as runt‐related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and osteocalcin (OCN), osteopontin (OPN), miR‐27a and miR‐29b. The extract also inhibited osteoblast apoptosis, significantly restored the down‐regulated expression of Bcl‐2, and decreased the loss of MMP and reactive oxygen spices (ROS) production in MC3T3‐E1 cells induced by LPS. Furthermore, pre‐treatment with algal extract strongly decreased the activation of osteoclast in MC3T3‐E1‐4B12 coculture system stimulated by LPS. Our findings suggest that C. glomerata enriched with Mn(II) ions may be a potential raw material for the development of drug for preventing abnormal bone loss induced by LPS in bacteria‐induced bone osteomyelitis.

Ninjurin1 positively regulates osteoclast development by enhancing the survival of prefusion osteoclasts

Osteoclasts (OCs) are bone-resorbing cells that originate from hematopoietic stem cells and develop through the fusion of mononuclear myeloid precursors. Dysregulation of OC development causes bone disorders such as osteopetrosis, osteoporosis, and rheumatoid arthritis. Although the molecular mechanisms underlying osteoclastogenesis have been well established, the means by which OCs maintain their survival during OC development remain unknown. We found that Ninjurin1 (Ninj1) expression is dynamically regulated during osteoclastogenesis and that Ninj1^-/- mice exhibit increased trabecular bone volume owing to impaired OC development. Ninj1 deficiency did not alter OC differentiation, transmigration, fusion, or actin ring formation but increased Caspase-9-dependent intrinsic apoptosis in prefusion OCs (preOCs). Overexpression of Ninj1 enhanced the survival of mouse macrophage/preOC RAW264.7 cells in osteoclastogenic culture, suggesting that Ninj1 is important for the survival of preOCs. Finally, analysis of publicly available microarray data sets revealed a potent correlation between high NINJ1 expression and destructive bone disorders in humans. Our data indicate that Ninj1 plays an important role in bone homeostasis by enhancing the survival of preOCs.

Peucedanum japonicum Thunb. ethanol extract suppresses RANKL-mediated osteoclastogenesis

The constituents of Peucedanum japonicum Thunb. (PJ) exhibit biological and pharmacological activities, including anti-obesity, anti-oxidant and anti-allergic activities. The aim of the present study was to examine in vitro effects of PJ in RANKL-induced signaling pathways, which determine osteoclast differentiation. PJ ethanol extract (PEE) exhibited anti-osteoporotic activity by disrupting the phospholipase C (PLC)-Ca2+-c-Fos/cAMP response element-binding protein (CREB)-nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) signaling pathway during osteoclastogenesis. Murine bone marrow-derived macrophages (BMMs) were cultured and used to determine the effects of PJ in the receptor activator of nuclear factor κB ligand (RANKL)-mediated osteoclastogenesis. The effects of PEE in the RANKL-mediated signaling cascade were evaluated using a standard in vitro osteoclastogenesis system. PEE treatment of BMMs significantly reduced the number of RANKL-mediated tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells (P<0.05 for 5 and 10 µg/ml PEE, P<0.01 for 25 and 50 µg/ml PEE), without cytotoxic effects. Furthermore, the expression of differentiation-related marker genes, including TRAP, Oscar, Cathepsin K, dendrocyte expressed seven transmembrane protein, ATPase H+ Transporting V0 Subunit D2 and NFATc1, were markedly suppressed. PEE induced a transient increase in free cytoplasmic Ca2+ ([Ca2+]_i) mobilization via voltage-gated Ca2+ channels and PLC-sensitive pathways. Transient [Ca2+]_i increase consequently resulted in the suppression of c-Fos, CREB and NFATc1 activities. These findings highlight the potential use of PJ in treating bone disorders caused by osteoclast overgrowth.

Involvement of PU.1 in NFATc1 promoter function in osteoclast development

BACKGROUND

The transcription factors NFATc1 and PU.1 play important roles in osteoclast development. NFATc1 and PU.1 transactivate osteoclast-specific gene expression and a deficiency in NFATc1 or PU.1 genes causes osteopetrosis due to an insufficient development of osteoclasts. However, the existence of cross-regulation between NFATc1 and PU.1 is largely unknown. In the present study, the role of PU.1 in NFATc1 expression was investigated.

METHODS

Osteoclasts were generated from mouse bone marrow cells. PU.1 knockdown was performed with siRNA introduction. The mRNA levels in siRNA-introduced cells were determined by quantitative RT-PCR. The involvement of PU.1 in the NFATc1 promoter was analyzed by using a chromatin immunoprecipitation (ChIP) assay and a reporter assay. Retrovirus vector was used for enforced expression of PU.1.

RESULTS

Introduction of PU.1 siRNA into bone marrow-derived osteoclasts resulted in a decrease in NFATc1 mRNA level. A ChIP assay showed that PU.1 bound to the NFATc1 promoter in osteoclasts. NFATc1 promoter activity was reduced in PU.1 knockdown cells as assessed by a reporter assay. PU.1 siRNA introduction also downregulated the expression of osteoclast-specific genes and tartrate resistant acid phosphatase (TRAP) activity. Enforced expression of PU.1 using a retrovirus vector increased NFATc1 expression and TRAP activity. When NFATc1 expression was knocked down by using siRNA, the induction of osteoclast-specific genes and TRAP-positive cells was suppressed without affecting the expression level of PU.1.

CONCLUSIONS

These results indicate that PU.1 is involved in osteoclast development by transactivating NFATc1 expression via direct binding to the NFATc1 promoter.

SHP2 regulates osteoclastogenesis by promoting preosteoclast fusion

Genes that regulate osteoclast (OC) development and function in both physiologic and disease conditions remain incompletely understood. Shp2 (the Src homology-2 domain containing protein tyrosine phosphatase 2), a ubiquitously expressed cytoplasmic protein tyrosine phosphatase, is implicated in regulating M-CSF and receptor activator of nuclear factor-κB ligand (RANKL)-evoked signaling; its role in osteoclastogenesis and bone homeostasis, however, remains unknown. Using a tissue-specific gene knockout approach, we inactivated Shp2 expression in murine OCs. Shp2 mutant mice are phenotypically osteopetrotic, featuring a marked increase of bone volume (BV)/total volume (TV) (+42.8%), trabeculae number (Tb.N) (+84.1%), structure model index (+119%), and a decrease of trabecular thickness (Tb.Th) (-34.1%) and trabecular spacing (Tb.Sp) (-41.0%). Biochemical analyses demonstrate that Shp2 is required for RANKL-induced formation of giant multinucleated OCs by up-regulating the expression of nuclear factor of activated T cells, cytoplasmic 1 (Nfatc1), a master transcription factor that is indispensable for terminal OC differentiation. Shp2 deletion, however, has minimal effect on M-CSF-dependent survival and proliferation of OC precursors. Instead, its deficiency aborts the fusion of OC precursors and formation of multinucleated OCs and decreases bone matrix resorption. Moreover, pharmacological intervention of Shp2 is sufficient to prevent preosteoclast fusion in vitro. These findings uncover a novel mechanism through which Shp2 regulates osteoclastogenesis by promoting preosteoclast fusion. Shp2 or its signaling partners could potentially serve as pharmacological targets to regulate the population of OCs locally and/or systematically, and thus treat OC-related diseases, such as periprosthetic osteolysis and osteoporosis.

NF-κB-direct activation of microRNAs with repressive effects on monocyte-specific genes is critical for osteoclast differentiation

Background

Monocyte-to-osteoclast conversion is a unique terminal differentiation process that is exacerbated in rheumatoid arthritis and bone metastasis. The mechanisms implicated in upregulating osteoclast-specific genes involve transcription factors, epigenetic regulators and microRNAs (miRNAs). It is less well known how downregulation of osteoclast-inappropriate genes is achieved.

Results

In this study, analysis of miRNA expression changes in osteoclast differentiation from human primary monocytes revealed the rapid upregulation of two miRNA clusters, miR-212/132 and miR-99b/let-7e/125a. We demonstrate that they negatively target monocyte-specific and immunomodulatory genes like TNFAIP3, IGF1R and IL15. Depletion of these miRNAs inhibits osteoclast differentiation and upregulates their targets. These miRNAs are also upregulated in other inflammatory monocytic differentiation processes. Most importantly, we demonstrate for the first time the direct involvement of Nuclear Factor kappa B (NF-κB) in the regulation of these miRNAs, as well as with their targets, whereby NF-κB p65 binds the promoters of these two miRNA clusters and NF-κB inhibition or depletion results in impaired upregulation of their expression.

Conclusions

Our results reveal the direct involvement of NF-κB in shutting down certain monocyte-specific genes, including some anti-inflammatory activities, through a miRNA-dependent mechanism for proper osteoclast differentiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0561-5) contains supplementary material, which is available to authorized users.

Reciprocal effects of Interferon-γ and IL-4 on differentiation to osteoclast-like cells by RANKL or LPS

OBJECTIVE

LPS can induce differentiation to osteoclast-like cells independent of RANKL. In comparison with RANKL, the effects of Th1 and Th2 cytokines on LPS-induced osteoclastogenesis have not been extensively studied. In this study, we investigated the effects of IFN-γ and IL-4 on RANKL- or LPS-induced osteoclastogenesis.

MATERIALS AND METHODS

RAW 264.7 cells were induced to differentiate into osteoclast-like cells by RANKL or LPS, in the absence or presence of IFN-γ or IL-4. The number of TRAP-positive, multinucleated (≥ 3 nuclei) cells (MNCs) was counted. mRNA and protein levels of TRAP and cathepsin K were determined by quantitative RT-PCR and Western immunoblot, respectively. Expression of other genes implicated in osteoclast and macrophage differentiation and inflammation was also quantitated and was subsequently assessed in bone marrow-derived macrophages (BMMs). Phagocytic capacity of differentiated RAW264.7 was investigated by the uptake of pHrodo S. aureus bioparticles conjugates.

RESULTS

In contrast to the RANKL-treated cell population that gained more macrophage-like properties at the level of gene and protein expression as well as phagocytosis in the presence of IFN-γ or IL-4, the LPS-induced population gained more osteoclast-like properties by the addition of the same factors.

CONCLUSION

These data suggest that the adaptive immune system, through either Th1 or Th2 cytokines, is able to modify the differentiation process of osteoclasts in inflammatory situations. Moreover, the study provides an example of different regulation of osteoclast differentiation during physiological and inflammatory conditions.

Kinsenoside prevents ovariectomy-induced bone loss and suppresses osteoclastogenesis by regulating classical NF-κB pathways

Kinsenoside is able to improve bone turnover rate in ovariectomized (OVX) mice. In vitro analysis shows that kinsenoside antagonizes osteoclast development and bone resorption.

INTRODUCTION

Kinsenoside, the main active compound of the traditional Taiwanese herb Anoectochilus formosanus, has an antiinflammatory effect. This study investigates whether kinsenoside inhibits osteoporosis and osteoclastogenesis.

METHODS

OVX mice were used to examine the antiosteoporotic activity of kinsenoside. The trabecular bone microarchitecture was assessed by microcomputed tomography. In vitro experiments were performed to determine the mechanisms of the antiosteoporotic effects of kinsenoside.

RESULTS

Microcomputed tomography scanning showed that kinsenoside suppresses bone loss in OVX mice. Kinsenoside decreases plasma CTx concentration. Reverse transcription polymerase chain reaction (RT-PCR) analysis also showed that kinsenoside reduces the femoral mRNA expression of tartrate-resistant acid phosphatase (TRAP) and matrix metalloproteinase-9 (MMP-9). Kinsenoside inhibits osteoclast formation in bone marrow cells (BMs) and RAW 264.7 cells. Western blot was used to analyze osteoclast-associated signaling pathways in RAW 264.7 cells. Results show that kinsenoside does not inhibit IKK phosphorylation but suppresses the phosphorylation of IκBα and p65. Kinsenoside significantly inhibits the RANKL induction of IKK activity. Kinsenoside inhibits the RANKL-triggered nuclear translocations of NF-κB and nuclear factor of activated T cells c1 (NFATc1). RT-PCR was used to analyze osteoclast precursor fusion and resorption-associated gene expression in BMs. Kinsenoside inhibits the expression of cathepsin K (CAK), dendritic cell-specific transmembrane protein, MMP-9, and TRAP.

CONCLUSIONS

Kinsenoside inhibits osteoclastogenesis from macrophages by attenuating RANKL-induced NF-κB and NFATc1 activities, which in turn, prevents bone loss from OVX mice.

PU.1 target genes undergo Tet2-coupled demethylation and DNMT3b-mediated methylation in monocyte-to-osteoclast differentiation

BACKGROUND

DNA methylation is a key epigenetic mechanism for driving and stabilizing cell-fate decisions. Local deposition and removal of DNA methylation are tightly coupled with transcription factor binding, although the relationship varies with the specific differentiation process. Conversion of monocytes to osteoclasts is a unique terminal differentiation process within the hematopoietic system. This differentiation model is relevant to autoimmune disease and cancer, and there is abundant knowledge on the sets of transcription factors involved.

RESULTS

Here we focused on DNA methylation changes during osteoclastogenesis. Hypermethylation and hypomethylation changes took place in several thousand genes, including all relevant osteoclast differentiation and function categories. Hypomethylation occurred in association with changes in 5-hydroxymethylcytosine, a proposed intermediate toward demethylation. Transcription factor binding motif analysis revealed an over-representation of PU.1, NF-κB, and AP-1 (Jun/Fos) binding motifs in genes undergoing DNA methylation changes. Among these, only PU.1 motifs were significantly enriched in both hypermethylated and hypomethylated genes; ChIP-seq data analysis confirmed its association to both gene sets. Moreover, PU.1 interacts with both DNMT3b and TET2, suggesting its participation in driving hypermethylation and hydroxymethylation-mediated hypomethylation. Consistent with this, siRNA-mediated PU.1 knockdown in primary monocytes impaired the acquisition of DNA methylation and expression changes, and reduced the association of TET2 and DNMT3b at PU.1 targets during osteoclast differentiation.

CONCLUSIONS

The work described here identifies key changes in DNA methylation during monocyte-to-osteoclast differentiation and reveals novel roles for PU.1 in this process.

The effect of rotative stress on CAII, FAS, FASL, OSCAR, and TRAP gene expression in osteoclasts

This study was designed to explore the effects of rotative stress on carbonic anhydrase II (CAII), TNF receptor superfamily member 6 (FAS), FAS ligand (FASL), osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP) gene expression in osteoclasts. Osteoclasts were induced from RAW264.7 cells cultured in medium containing recombinant murine soluble receptor activator of NF-Kβ ligand (sRANKL). The mRNA and protein expression of CAII, FAS, FASL, OSCAR, and TRAP genes in osteoclasts was detected by RT-PCR and Western blot, respectively, after osteoclasts were loaded at various rotative stress strengths and times. No significant differences in mRNA and protein expression were observed between any of the control groups (P > 0.05). Importantly, rotative stress had a significant effect on the mRNA and protein expression of these genes (P < 0.05). We found a negative relationship between rotative stress strength and prolonged loading time and the expression of FAS/FASL genes in osteoclasts. In addition, there was a positive relationship between rotative stress strength and prolonged loading time and the expression of CAII, OSCAR, or TRAP genes in osteoclasts. Based on these results, rotative stress has a significant effect on CAII, FAS, FASL, OSCAR, and TRAP gene expression in osteoclasts.

A molecular description of acid phosphatase

Acid phosphatase is ubiquitous in distribution in various organisms. Although it catalyzes simple hydrolytic reactions, it is considered as an interesting enzyme in biological systems due to its involvement in different physiological activities. However, earlier reviews on acid phosphatase reveal some fragmentary information and do not give a holistic view on this enzyme. So, the present review summarizes studies on biochemical properties, structure, catalytic mechanism, and applications of acid phosphatase. Recent advancement of acid phosphatase in agricultural and clinical fields is emphasized where it is presented as potent agent for sustainable agricultural practices and diagnostic marker in bone metabolic disorders. Also, its significance in prostate cancer therapies as a therapeutic target has been discussed. At the end, current studies and prospects of immobilized acid phosphatase are included.

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.

Retinoic acid induces two osteocalcin isoforms and inhibits markers of osteoclast activity in Atlantic cod (Gadus morhua) ex vivo cultured craniofacial tissues

Nutritional status including vitamin A could explain some of the developmental deformities observed in cultivated teleosts, including Atlantic cod (Gadus morhua). In the present study we aimed to investigate the transcriptional effect of retinoic acid (RA) on bone related genes using Atlantic cod craniofacial explants tissue cultures. Two different osteoblast specific osteocalcin/bone gla protein isoforms were discovered in cod. Transcription of both isoforms was up-regulated following RA treatment of 65 dph cod lower jaw explants. In contrast, transcripts coding for genes related to bone resorption and osteoclast activity, matrix metalloproteinase 9 and cathepsin K were down-regulated following RA treatment. This could be linked to the decreased transcriptional ratio between receptor activator of nuclear factor kappa-B ligand rankl and osteoprotegerin observed in the same tissue samples. RA treatment of juvenile explants had no effect on runt-related transcription factor 2 and osterix mRNA levels. However, osterix was significantly down-regulated in 25 dph cod head explants following RA treatment. In situ hybridizations revealed differential spatial distribution of the two isoforms and the predominant expression of cathepsin K in bone surrounding tissues. The present study indicates that RA causes a shift in the balance between osteoclast activity and osteoblast activity in favor of the latter.

Loss of transcription factor early growth response gene 1 results in impaired endochondral bone repair

Transcription factors that play a role in ossification during development are expected to participate in postnatal fracture repair since the endochondral bone formation that occurs in embryos is recapitulated during fracture repair. However, inherent differences exist between bone development and fracture repair, including a sudden disruption of tissue integrity followed by an inflammatory response. This raises the possibility that repair-specific transcription factors participate in bone healing. Here, we assessed the consequence of loss of early growth response gene 1 (EGR-1) on endochondral bone healing because this transcription factor has been shown to modulate repair in vascularized tissues. Model fractures were created in ribs of wild type (wt) and EGR-1(-/-) mice. Differences in tissue morphology and composition between these two animal groups were followed over 28 post fracture days (PFDs). In wt mice, bone healing occurred in healing phases characteristic of endochondral bone repair. A similar healing sequence was observed in EGR-1(-/-) mice but was impaired by alterations. A persistent accumulation of fibrin between the disconnected bones was observed on PFD7 and remained pronounced in the callus on PFD14. Additionally, the PFD14 callus was abnormally enlarged and showed increased deposition of mineralized tissue. Cartilage ossification in the callus was associated with hyper-vascularity and -proliferation. Moreover, cell deposits located in proximity to the callus within skeletal muscle were detected on PFD14. Despite these impairments, repair in EGR-1(-/-) callus advanced on PFD28, suggesting EGR-1 is not essential for healing. Together, this study provides genetic evidence that EGR-1 is a pleiotropic regulator of endochondral fracture repair.

NF-κB signaling participates in both RANKL- and IL-4-induced macrophage fusion: receptor cross-talk leads to alterations in NF-κB pathways

NF-κB activation is essential for receptor activator for NF-κB ligand (RANKL)-induced osteoclast formation. IL-4 is known to inhibit the RANKL-induced osteoclast differentiation while at the same time promoting macrophage fusion to form multinucleated giant cells (MNG). Several groups have proposed that IL-4 inhibition of osteoclastogenesis is mediated by suppressing the RANKL-induced activation of NF-κB. However, we found that IL-4 did not block proximal, canonical NF-κB signaling. Instead, we found that IL-4 inhibited alternative NF-κB signaling and induced p105/50 expression. Interestingly, in nfκb1(-/-) bone marrow-derived macrophages (BMM), the formation of both multinucleated osteoclast and MNG induced by RANKL or IL-4, respectively, was impaired. This suggests that NF-κB signaling also plays an important role in IL-4-induced macrophage fusion. Indeed, we found that the RANKL-induced and IL-4-induced macrophage fusion were both inhibited by the NF-κB inhibitors IκB kinase 2 inhibitor and NF-κB essential modulator inhibitory peptide. Furthermore, overexpression of p50, p65, p52, and RelB individually in nfκb1(-/-) or nfκb1(+/+) BMM enhanced both giant osteoclast and MNG formation. Interestingly, knockdown of nfκb2 in wild-type BMM dramatically enhanced both osteoclast and MNG formation. In addition, both RANKL- and IL-4-induced macrophage fusion were impaired in NF-κB-inducing kinase(-/-) BMM. These results suggest IL-4 influences NF-κB pathways by increasing p105/p50 and suppressing RANKL-induced p52 translocation and that NF-κB pathways participate in both RANKL- and IL-4-induced giant cell formation.

Transcriptional control of rapid recall by memory CD4 T cells

Memory T cells are distinguished from naive T cells by their rapid production of effector cytokines, although mechanisms for this recall response remain undefined. In this study, we investigated transcriptional mechanisms for rapid IFN-γ production by Ag-specific memory CD4 T cells. In naive CD4 T cells, IFN-γ production only occurred after sustained Ag activation and was associated with high expression of the T-bet transcription factor required for Th1 differentiation and with T-bet binding to the IFN-γ promoter as assessed by chromatin immunoprecipitation analysis. By contrast, immediate IFN-γ production by Ag-stimulated memory CD4 T cells occurred in the absence of significant nuclear T-bet expression or T-bet engagement on the IFN-γ promoter. We identified rapid induction of NF-κB transcriptional activity and increased engagement of NF-κB on the IFN-γ promoter at rapid times after TCR stimulation of memory compared with naive CD4 T cells. Moreover, pharmacologic inhibition of NF-κB activity or peptide-mediated inhibition of NF-κB p50 translocation abrogated early memory T cell signaling and TCR-mediated effector function. Our results reveal a molecular mechanism for memory T cell recall through enhanced NF-κB p50 activation and promoter engagement, with important implications for memory T cell modulation in vaccines, autoimmunity, and transplantation.

FAM5C contributes to aggressive periodontitis

Aggressive periodontitis is characterized by a rapid and severe periodontal destruction in young systemically healthy subjects. A greater prevalence is reported in Africans and African descendent groups than in Caucasians and Hispanics. We first fine mapped the interval 1q24.2 to 1q31.3 suggested as containing an aggressive periodontitis locus. Three hundred and eighty-nine subjects from 55 pedigrees were studied. Saliva samples were collected from all subjects, and DNA was extracted. Twenty-one single nucleotide polymorphisms were selected and analyzed by standard polymerase chain reaction using TaqMan chemistry. Non-parametric linkage and transmission distortion analyses were performed. Although linkage results were negative, statistically significant association between two markers, rs1935881 and rs1342913, in the FAM5C gene and aggressive periodontitis (p = 0.03) was found. Haplotype analysis showed an association between aggressive periodontitis and the haplotype A-G (rs1935881-rs1342913; p = 0.009). Sequence analysis of FAM5C coding regions did not disclose any mutations, but two variants in conserved intronic regions of FAM5C, rs57694932 and rs10494634, were found. However, these two variants are not associated with aggressive periodontitis. Secondly, we investigated the pattern of FAM5C expression in aggressive periodontitis lesions and its possible correlations with inflammatory/immunological factors and pathogens commonly associated with periodontal diseases. FAM5C mRNA expression was significantly higher in diseased versus healthy sites, and was found to be correlated to the IL-1β, IL-17A, IL-4 and RANKL mRNA levels. No correlations were found between FAM5C levels and the presence and load of red complex periodontopathogens or Aggregatibacter actinomycetemcomitans. This study provides evidence that FAM5C contributes to aggressive periodontitis.