The alpha-isoform of p38 MAPK specifically regulates arthritic bone loss

Unveiling the Nexus: Cellular Metabolomics Unravels the Impact of Estrogen on Nicotinamide Metabolism in Mitigating Rheumatoid Arthritis Pathogenesis

Rheumatoid arthritis (RA) is a metabolic joint disorder influenced by hormonal regulation, notably estrogen, which plays a cytoprotective role against inflammation. While estrogen's impact on RA pathogenesis has been studied, the altered metabolite expression under estrogen's influence remains unexplored. This study investigated the changes in the metabolome of synovial fibroblasts isolated from RA patients under 17β-estradiol (E2) using the liquid chromatography with tandem mass spectrometry (LC-MS/MS) approach followed by multivariate and biological pathway analysis along with in vitro validation. Results identified 3624 m/z, among which eight metabolites were significant (p < 0.05). Nicotinate and nicotinamide metabolism was found to be highly correlated with the treatment of E2, with metabolites NAD+ and 1-methynicotinamide (1-MNA) upregulated by E2 induction in RA-FLS. PharmMapper analysis identified potential gene targets of 1-MNA, which were further matched with RA gene targets, and thus, STAT1, MAPK14, MMP3, and MMP9 were concluded to be the common targets. E2 treatment affected the expression of these gene targets and ameliorated the development of oxidative stress associated with RA inflammation, which can be attributed to increased concentration of 1-MNA. Thus, an LC-MS/MS-based metabolomics study revealed the prominent role of estrogen in preventing inflammatory progression in RA by altering metabolite concentration, which can support its therapeutic capacity in remitting RA.

Extracellular Signal-Regulated Kinases Play Essential but Contrasting Roles in Osteoclast Differentiation

Bone homeostasis is regulated by the balanced actions of osteoblasts that form the bone and osteoclasts (OCs) that resorb the bone. Bone-resorbing OCs are differentiated from hematopoietic monocyte/macrophage lineage cells, whereas osteoblasts are derived from mesenchymal progenitors. OC differentiation is induced by two key cytokines, macrophage colony-stimulating factor (M-CSF), a factor essential for the proliferation and survival of the OCs, and receptor activator of nuclear factor kappa-B ligand (RANKL), a factor for responsible for the differentiation of the OCs. Mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases (ERKs), p38, and c-Jun N-terminal kinases, play an essential role in regulating the proliferation, differentiation, and function of OCs. ERKs have been known to play a critical role in the differentiation and activation of OCs. In most cases, ERKs positively regulate OC differentiation and function. However, several reports present conflicting conclusions. Interestingly, the inhibition of OC differentiation by ERK1/2 is observed only in OCs differentiated from RAW 264.7 cells. Therefore, in this review, we summarize the current understanding of the conflicting actions of ERK1/2 in OC differentiation.

Iris Koreana NAKAI Inhibits Osteoclast Formation via p38-Mediated Nuclear Factor of Activated T Cells 1 Signaling Pathway

BACKGROUND

Iris Koreana NAKAI (IKN) is a flowering perennial plant that belongs to the Iridaceae family. In this study, we aimed to demonstrate the effects of IKN on osteoclast differentiation in vitro and in vivo. We also sought to verify the molecular mechanisms underlying its anti-osteoclastogenic effects.

METHODS

Osteoclasts were formed by culturing mouse bone marrow macrophage (BMM) cells with macrophage colony-stimulating factor and receptor activator of nuclear factor-κB ligand (RANKL). Bone resorption assays were performed on dentin slices. mRNA expression levels were analyzed by quantitative polymerase chain reaction. Western blotting was performed to detect protein expression or activation. Lipopolysaccharide (LPS)-induced osteoclast formation was performed using a mouse calvarial model.

RESULTS

In BMM cultures, an ethanol extract of the root part of IKN suppressed RANKL-induced osteoclast formation and bone resorptive activity. In contrast, an ethanol extract of the aerial parts of IKN had a minor effect on RANKL-induced osteoclast formation. Mechanistically, the root part of IKN suppressed RANKL-induced p38 mitogen-activated protein kinase (MAPK) activation, effectively abrogating the induction of c-Fos and nuclear factor of activated T cells 1 (NFATc1) expression. IKN administration decreased LPS-induced osteoclast formation in a calvarial osteolysis model in vivo.

CONCLUSIONS

Our study suggested that the ethanol extract of the root part of IKN suppressed osteoclast differentiation and function partly by downregulating the p38 MAPK/c-Fos/NFATc1 signaling pathways. Thus, the root part.

Network pharmacology analysis of molecular targets and related mechanisms of Guizhi decoction in treating of menopausal syndrome

Compared with hormone therapy, TCM had the advantages of overall adjustment and less side effects in the treatment of menopausal syndrome. But due to the complex pharmacodynamic composition of Guizhi decoction (GZD), the mechanism of TCM treating diseases was not clear. Network pharmacology could analyze drug action pathways through multi-pathway and multi-target, which provide a new direction for TCM mechanism research. The common targets of GZD and menopausal syndrome (MPS) were obtained by TCMSP and DisGeNET databases. And for the common targets, protein-protein interaction networks were established using the STRING database and analyzed by Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes. (Our research does not require ethical approval). One hundred forty-six active ingredients with 283 targets were obtained from GZD by network pharmacological analysis. Besides, 230 target genes were found to have interactions with MPS, 52 of which were common targets between MPS and GZD and were predicted to be potential targets for MPS treatment of GZD. GO enrichment analysis revealed that GZD could affect 51 biological processes, 15 cellular components, and 13 molecular functions. Kyoto Encyclopedia of Genes and Genomes enrichment analysis yielded a total of 223. The pathways that are closely related to the pathogenesis of MPS are MAPK, PI3K-Akt. In this study, the relevant targets and mechanisms of GZD in the treatment of MPS were discussed from the perspective of network pharmacological analysis, reflecting the characteristics of multi-component, multi-target and multiple pathways, and it provides a good theoretical basis for the clinical application of GZD.

Isoliensinine Suppresses Osteoclast Formation Through NF-κB Signaling Pathways and Relieves Ovariectomy-Induced Bone Loss

Osteoporosis is among the major contributors of pathologic fracture in postmenopausal women, which is caused by the bone metabolic disorder owing to the over-activation of osteoclasts. Inhibition of osteoclast differentiation and maturation has become a mainstream research interest in the prevention of osteoporosis. Isoliensinine (Iso) is a dibenzyl isoquinoline alkaloid with antioxidant, anti-inflammatory, and anti-cancer activities. However, whether it can be used as a potential treatment for osteoporosis remains undiscovered. Here, we investigated whether Iso might suppress the differentiation of osteoclasts in vitro and in vivo to play an anti-osteoporosis role. Our results showed that Iso inhibits the formation of mature multinuclear osteoclasts induced by RANKL, the bone resorption, and the osteoclast-specific genes expression by blocking the nuclear translocation of NF-κB p65, and the effect was in a dosage-dependent way. Furthermore, we investigated the therapeutic effect of Iso on osteoporosis in ovariectomized (OVX) mice. We found that Iso attenuated bone loss in the OVX mice and significantly promoted BS, Conn. DN, Tb.Th, TB.N, and BV/TV Index. All in all, Iso showed a prominent effect of osteoclast inhibition, with great promise for treating osteoporosis.

Bone protein analysis via label-free quantitative proteomics in patients with periprosthetic joint infection

Periprosthetic joint infection (PJI) is a catastrophic complication of arthroplasty. The treatment of PJI often requires multiple operations and long-term use of antibiotics, making PJI a substantial health and economic burden for patients. Therefore, there is an urgent need to elucidate the pathological mechanism of PJI to explore new therapeutic methods. This study aimed to explore proteomics changes in bone tissue around the prosthesis during PJI development, to explain the pathological mechanism and to provide new treatment ideas. Ten patients who underwent revision surgery at our institution were included: 5 patients with Staphylococcus aureus PJI and 5 patients with aseptic failure. The proteomics changes in bone tissues after PJI were investigated by label-free quantitative proteomics, and the pathways affected by the differential proteins were analyzed by GO annotation, GO enrichment analysis, KEGG enrichment analysis and protein-protein interaction network analysis. We identified 435 differentially expressed proteins (DEPs), with 213 upregulated and 222 downregulated proteins. Analysis revealed activation of immune-related pathways, such as complement and coagulation cascades, phagocytosis, and neutrophil activation, and inhibition of energy metabolism pathways represented by the TCA cycle. We also observed an altered balance between osteoblasts and osteoclasts during S. aureus PJI. We hope that these processes will reveal new treatment ideas. SIGNIFICANCE: PJI is a catastrophic complication of arthroplasty. When infection occurs, bacteria may invade periprosthetic bone tissue to escape immunity and cause damage. So far, only few studies focused on the changes of proteomics associated to PJI. This is the first study to describe the proteomics changes of periprosthetic bone tissue of patients with PJI. We found that the pathological process of S. aureus PJI mainly involves activation of the immune system, decreased energy metabolism, and an altered balance of osteoblasts and osteoclasts.

Bone anti-resorptive effects of coumarins on RANKL downstream cellular signaling: a systematic review of the literature

BACKGROUND

Members of the botanical families Apiaceae/Umbelliferae, Asteraceae, Fabaceae/Leguminosae, and Thymelaeaceae are rich in coumarins and have traditionally been used as ethnomedicines in many regions including Europe, Asia, and South America. Coumarins are a class of secondary metabolites that are widely present in plants, fungi, and bacteria and exhibit several pharmacological, biochemical, and therapeutic effects. Recently, many plants rich in coumarins and their derivatives were found to affect bone metabolism.

OBJECTIVE

To review scientific literature describing the mechanisms of action of coumarins in osteoclastogenesis and bone resorption.

MATERIALS AND METHODS

For this systematic review, the PubMed, Scopus, and Periodical Capes databases and portals were searched. We included in vitro research articles published between 2010 and 2020 that evaluated coumarins using osteoclastogenic markers.

RESULTS

Coumarins have been reported to downregulate RANKL-RANK signaling and various downstream signaling pathways required for osteoclast development, such as NF-κB, MAPK, Akt, and Ca²⁺ signaling, as well as pathways downstream of the nuclear factor of activated T-cells (NFATc1), including tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), and matrix metalloproteinase 9 (MMP-9).

CONCLUSIONS

Coumarins primarily inhibit osteoclast differentiation and activation by modulating different intracellular signaling pathways; therefore, they could serve as potential candidates for controlled randomized clinical trials aimed at improving human bone health.

Betulinic Acid Protects From Bone Loss in Ovariectomized Mice and Suppresses RANKL-Associated Osteoclastogenesis by Inhibiting the MAPK and NFATc1 Pathways

Osteoclasts with elevated bone resorption are commonly present in postmenopausal osteoporosis, and other osteolytic pathologies. Therefore, suppressing osteoclast generation and function has been the main focus of osteoporosis treatment. Betulinic acid (BA) represents a triterpenoid mainly purified from the bark of Betulaceae. BA shows multiple biological activities, including antitumor and anti-HIV properties, but its effect on osteolytic conditions is unknown. Here, BA suppressed receptor activator of nuclear factor‐κB ligand (RANKL)‐associated osteoclastogenesis and bone resorptive function, as assessed by tartrate‐resistant acid phosphatase (TRAP) staining, fibrous actin ring generation, and hydroxyapatite resorption assays. Mechanistically, BA downregulated the expression of osteoclastic-specific genes. Western blot analysis revealed that BA significantly interrupted ERK, JNK and p38 MAPK activation as well as intracellular reactive oxygen species (ROS) production, thus altering c-Fos and NFATc1 activation. Corroborating the above findings in cell-based assays, BA prevented ovariectomy-associated bone loss in an animal model. In conclusion, these findings suggest that BA can inhibit osteoclast generation and function as well as the RANKL signaling pathway, and might be used for treating osteoclast-related osteoporosis.

Tablysin-15 inhibits osteoclastogenesis and LPS-induced bone loss via attenuating the integrin αvβ3 pathway

Excessive osteoclast leads to the imbalance in bone reconstruction and results in osteolytic diseases, such as osteoporosis and rheumatic arthritis. Integrin α_vβ₃ abundantly expresses on osteoclast and plays a critical role in the formation and function of osteoclast, therefore, blockage of α_vβ₃ has become an attractive therapeutic option for osteolytic diseases. In this study, we find that Tablysin-15, a RGD motif containing disintegrin, concentration-dependently suppresses RANKL-induced osteoclastogenesis, F-actin ring formation and bone resorption without affecting the cell viabilities. Tablysin-15 binds to integrin α_vβ₃ and inhibits the activation of FAK-associated signaling pathways. Tablysin-15 also suppresses the activation of NF-кB, MAPK, and Akt-NFATc1 signaling pathways, which are crucial transcription factors during osteoclast differentiation. Moreover, Tablysin-15 decreases the osteoclastogenesis marker gene expression, including MMP-9, TRAP, CTSK, and c-Src. Finally, Tablysin-15 significantly inhibits LPS-induced bone loss in a mouse model. Taken together, our results indicate that Tablysin-15 significantly suppresses osteoclastogenesis in vitro and in vivo, thus it might be a excellent candidate for treating osteolytic-related diseases.

The MKK-Dependent Phosphorylation of p38α Is Augmented by Arginine Methylation on Arg49/Arg149 during Erythroid Differentiation

The activation of p38 mitogen-activated protein kinases (MAPKs) through a phosphorylation cascade is the canonical mode of regulation. Here, we report a novel activation mechanism for p38α. We show that Arg49 and Arg149 of p38α are methylated by protein arginine methyltransferase 1 (PRMT1). The non-methylation mutations of Lys49/Lys149 abolish the promotive effect of p38α on erythroid differentiation. MAPK kinase 3 (MKK3) is identified as the major p38α upstream kinase and MKK3-mediated activation of the R49/149K mutant p38α is greatly reduced. This is due to a profound reduction in the interaction of p38α and MKK3. PRMT1 can enhance both the methylation level of p38α and its interaction with MKK3. However, the phosphorylation of p38α by MKK3 is not a prerequisite for methylation. MAPK-activated protein kinase 2 (MAPKAPK2) is identified as a p38α downstream effector in the PRMT1-mediated promotion of erythroid differentiation. The interaction of MAPKAPK2 with p38α is also significantly reduced in the R49/149K mutant. Together, this study unveils a novel regulatory mechanism of p38α activation via protein arginine methylation on R49/R149 by PRMT1, which impacts partner interaction and thus promotes erythroid differentiation. This study provides a new insight into the complexity of the regulation of the versatile p38α signaling and suggests new directions in intervening p38α signaling.

Effects and Mechanisms of Exogenous Electromagnetic Field on Bone Cells: A Review

Osteoporosis, fractures, and other bone diseases or injuries represent serious health problems in modern society. A variety of treatments including drugs, surgeries, physical therapies, etc. have been used to prevent or delay the progression of these diseases/injuries with limited effects. Electromagnetic field (EMF) has been used to non-invasively treat bone diseases, such as fracture and osteoporosis, for many years. However, because a variety of cellular and molecular events can be affected by EMF with various parameters, the precise bioeffects and underlying mechanisms of specific EMF on bone cells are still obscure. Here, we summarize the common therapeutic parameters (frequency and intensity) of major types of EMF used to treat bone cells taken from 32 papers we selected from the PubMed database published in English from 1991 to 2018. Briefly, pulse EMF promotes the proliferation of osteoblasts when its frequency is 7.5-15 Hz or 50-75 Hz and the intensity is 0.40-1.55 mT or 3.8-4 mT. Sinusoidal EMF, with 0.9-4.8 mT and 45-60 Hz, and static magnetic field with 0.1-0.4 mT or 400 mT, can promote osteoblast differentiation and maturation. Finally, we summarize the latest advances on the molecular signaling pathways influenced by EMF in osteoblasts and osteoclasts. A variety of molecules such as adenosine receptors, calcium channels, BMP2, Notch, Wnt1, etc., can be influenced by EMF in osteoblasts. For osteoclasts, EMF affects RANK, NF-κB, MAPK, etc. We speculate that EMF with different frequencies and intensities exert distinct bioeffects on specific bone cells. More high-quality work is required to explore the detailed effects and underlying mechanisms of EMF on bone cells/skeleton to optimize the application of EMF on bone diseases/injuries. Bioelectromagnetics. 2020;41:263-278 © 2020 Bioelectromagnetics Society.

Rev-erbα Negatively Regulates Osteoclast and Osteoblast Differentiation through p38 MAPK Signaling Pathway

The circadian clock regulates various physiological processes, including bone metabolism. The nuclear receptors Reverbs, comprising Rev-erbα and Rev-erbβ, play a key role as transcriptional regulators of the circadian clock. In this study, we demonstrate that Rev-erbs negatively regulate differentiation of osteoclasts and osteoblasts. The knockdown of Rev-erbα in osteoclast precursor cells enhanced receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation, as well as expression of nuclear factor of activated T cells 1 (NFATc1), osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP). The overexpression of Rev-erbα leads to attenuation of the NFATc1 expression via inhibition of recruitment of c-Fos to the NFATc1 promoter. The overexpression of Rev-erbα in osteoblast precursors attenuated the expression of osteoblast marker genes including Runx2, alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OC). Rev-erbα interfered with the recruitment of Runx2 to the promoter region of the target genes. Conversely, knockdown of Reverbα in the osteoblast precursors enhanced the osteoblast differentiation and function. In addition, Rev-erbα negatively regulated osteoclast and osteoblast differentiation by suppressing the p38 MAPK pathway. Furthermore, intraperitoneal administration of GSK4112, a Rev-erb agonist, protects RANKL-induced bone loss via inhibition of osteoclast differentiation in vivo . Taken together, our results demonstrate a molecular mechanism of Rev-erbs in the bone remodeling, and provide a molecular basis for a potential therapeutic target for treatment of bone disease characterized by excessive bone resorption.

p38MAPK controls fibroblast growth factor 23 (FGF23) synthesis in UMR106-osteoblast-like cells and in IDG-SW3 osteocytes

BACKGROUND

p38 mitogen-activated protein kinase (p38MAPK) is a serine/threonine kinase activated by cellular stress stimuli including radiation, osmotic shock, and inflammation and influencing apoptosis, cell proliferation, and autophagy. Moreover, p38MAPK induces transcriptional activity of the transcription factor complex NFκB mediating multiple pro-inflammatory cellular responses. Fibroblast growth factor 23 (FGF23) is produced by bone cells, and regulates renal phosphate and vitamin D metabolism as a hormone. FGF23 expression is enhanced by NFκB. Here, we analyzed the relevance of p38MAPK activity for the production of FGF23.

METHODS

Fgf23 expression was analyzed by qRT-PCR and FGF23 protein by ELISA in UMR106 osteoblast-like cells and in IDG-SW3 osteocytes.

RESULTS

Inhibition of p38MAPK with SB203580 or SB202190 significantly down-regulated Fgf23 expression and FGF23 protein expression. Conversely, p38MAPK activator anisomycin increased the abundance of Fgf23 mRNA. NFκB inhibitors wogonin and withaferin A abrogated the stimulatory effect of anisomycin on Fgf23 gene expression.

CONCLUSION

p38MAPK induces FGF23 formation, an effect at least in part dependent on NFκB activity.

Binding Immunoglobulin Protein (BIP) Inhibits TNF-α-Induced Osteoclast Differentiation and Systemic Bone Loss in an Erosive Arthritis Model

Objective

The association between inflammation and dysregulated bone remodeling is apparent in rheumatoid arthritis and is recapitulated in the human tumor necrosis factor transgenic (hTNFtg) mouse model. We investigated whether extracellular binding immunoglobulin protein (BiP) would protect the hTNFtg mouse from both inflammatory arthritis as well as extensive systemic bone loss and whether BiP had direct antiosteoclast properties in vitro.

Methods

hTNFtg mice received a single intraperitoneal administration of BiP at onset of arthritis. Clinical disease parameters were measured weekly. Bone analysis was performed by microcomputed tomography and histomorphometry. Mouse bone marrow macrophage and human peripheral blood monocyte precursors were used to study the direct effect of BiP on osteoclast differentiation and function in vitro. Monocyte and osteoclast signaling was analyzed by Western blotting, flow cytometry, and imaging flow cytometry.

Results

BiP-treated mice showed reduced inflammation and cartilage destruction, and histomorphometric analysis revealed a decrease in osteoclast number with protection from systemic bone loss. Abrogation of osteoclast function was also observed in an ex vivo murine calvarial model. BiP inhibited differentiation of osteoclast precursors and prevented bone resorption by mature osteoclasts in vitro. BiP also induced downregulation of CD115/c-Fms and Receptor Activator of NF-κB (RANK) messenger RNA and protein, causing reduced phosphorylation of the p38 mitogen-activated protein kinases, extracellular signal-regulated kinases 1/2 and p38, with suppression of essential osteoclast transcription factors, c-Fos and NFATc1. BiP directly inhibited TNF-α- or Receptor Activator of NF-κB Ligand (RANKL)-induced NF-κB nuclear translocation in THP-1 monocytic cells and preosteoclasts by the canonical and noncanonical pathways.

Conclusion

BiP combines an anti-inflammatory function with antiosteoclast activity, which establishes it as a potential novel therapeutic for inflammatory disorders associated with bone loss.

The Novel p38 Inhibitor, Pamapimod, Inhibits Osteoclastogenesis and Counteracts Estrogen-Dependent Bone Loss in Mice

Pamapimod (PAM) is a novel selective p38 mitogen-activated protein (MAP) kinase inhibitor proved to be effective in rheumatoid arthritis in phase 2 clinical trial. However, its effect on osteoclast-associated osteoporosis and the underlying mechanisms remain unclear. In this study, we showed that PAM suppressed receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation via inhibition of p38 phosphorylation and subsequent c-Fos and nuclear factor of activated T cells c1 (NFATc1) expression. In addition, the downregulated NFATc1 leads to reduced expression of its targeting gene disintegrin and metalloproteinase domain-containing protein 12 (ADAM12), which was further proven to be critical for osteoclastic bone resorption. Therefore, we treated ovariectomized (OVX) mice with PAM and revealed a protective effect of PAM on osteoporosis in vivo. In conclusion, our results demonstrated PAM can prevent OVX-induced bone loss through suppression of p38/NFATc1-induced osteoclast formation and NFATc1/ADAM12-associated bone resorption. © 2018 American Society for Bone and Mineral Research.

Inhibition of Osteoclastogenesis by Thioredoxin-Interacting Protein-Derived Peptide (TN13)

Overactivated osteoclasts lead to many bone diseases, including osteoporosis and rheumatoid arthritis. The p38 MAPK (p38) is an essential regulator of the receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis and bone loss. We previously reported TAT conjugated thioredoxin-interacting protein-derived peptide (TAT-TN13) as an inhibitor of p38 in hematopoietic stem cells (HSCs). Here, we examined the role of TAT-TN13 in the differentiation and function of osteoclasts. TAT-TN13 significantly suppressed RANKL-mediated differentiation of RAW 264.7 cells and bone marrow macrophages (BMMs) into osteoclasts. TAT-TN13 also inhibited the RANKL-induced activation of NF-κB and nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), leading to the decreased expression of osteoclast-specific genes, including tartrate-resistant acid phosphatase (TRAP) and Cathepsin K. Additionally, TAT-TN13 treatment protected bone loss in ovariectomized (OVX) mice. Taken together, these results suggest that TAT-TN13 inhibits osteoclast differentiation by regulating the p38 and NF-κB signaling pathway; thus, it may be a useful agent for preventing or treating osteoporosis.

Osteoimmunology

Bone is a crucial element of the skeletal-locomotor system, but also functions as an immunological organ that harbors hematopoietic stem cells (HSCs) and immune progenitor cells. Additionally, the skeletal and immune systems share a number of regulatory molecules, including cytokines and signaling molecules. Osteoimmunology was created as an interdisciplinary field to explore the shared molecules and interactions between the skeletal and immune systems. In particular, the importance of an inseparable link between the two systems has been highlighted by studies on the pathogenesis of rheumatoid arthritis (RA), in which pathogenic helper T cells induce the progressive destruction of multiple joints through aberrant expression of receptor activator of nuclear factor (NF)-κB ligand (RANKL). The conceptual bridge of osteoimmunology provides not only a novel framework for understanding these biological systems but also a molecular basis for the development of therapeutic approaches for diseases of bone and/or the immune system.

Activating β-catenin/Pax6 axis negatively regulates osteoclastogenesis by selectively inhibiting phosphorylation of p38/MAPK

Balance of osteoclast formation is regulated by the receptor activator of NF-κB ligand and extracellular negative regulators such as IFN-γ and IFN-β. However, very little is known about the intrinsic negative regulatory factors of osteoclast differentiation. Recently, the paired-box homeodomain transcription factor Pax6 was shown to negatively regulate receptor activator of NF-κB ligand-mediated osteoclast differentiation. However, the mechanism underlying this regulation is still unclear. In this study, we show that a p38 inhibitor (VX-745) up-regulates the expression of Pax6 during osteoclast differentiation. Subsequently, we found that β-catenin could bind to the proximal region of Pax6 promoter to induce its expression, and this action could be impaired by p38-induced ubiquitin-mediated degradation of β-catenin. Our results suggest that Pax6 is regulated by a novel p38/β-catenin pathway. Pax6 can further regulate the nuclear translocation of NF of activated T cells, cytoplasmic 1. Our study indicates that this novel p38/β-catenin/Pax6 axis contributes to negative regulation of osteoclastogenesis. In addition, our study proposes a novel approach to treat osteoclast-related diseases through the use of VX-745 complemented with the β-catenin activator SKL2001.-Jie, Z., Shen, S., Zhao, X., Xu, W., Zhang, X., Huang, B., Tang, P., Qin, A., Fan, S., Xie, Z. Activating β-catenin/Pax6 axis negatively regulates osteoclastogenesis by selectively inhibiting phosphorylation of p38/MAPK.

Roles of Mitogen-Activated Protein Kinases in Osteoclast Biology

Bone undergoes continuous remodeling, which is homeostatically regulated by concerted communication between bone-forming osteoblasts and bone-degrading osteoclasts. Multinucleated giant osteoclasts are the only specialized cells that degrade or resorb the organic and inorganic bone components. They secrete proteases (e.g., cathepsin K) that degrade the organic collagenous matrix and establish localized acidosis at the bone-resorbing site through proton-pumping to facilitate the dissolution of inorganic mineral. Osteoporosis, the most common bone disease, is caused by excessive bone resorption, highlighting the crucial role of osteoclasts in intact bone remodeling. Signaling mediated by mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, has been recognized to be critical for normal osteoclast differentiation and activation. Various exogenous (e.g., toll-like receptor agonists) and endogenous (e.g., growth factors and inflammatory cytokines) stimuli contribute to determining whether MAPKs positively or negatively regulate osteoclast adhesion, migration, fusion and survival, and osteoclastic bone resorption. In this review, we delineate the unique roles of MAPKs in osteoclast metabolism and provide an overview of the upstream regulators that activate or inhibit MAPKs and their downstream targets. Furthermore, we discuss the current knowledge about the differential kinetics of ERK, JNK, and p38, and the crosstalk between MAPKs in osteoclast metabolism.

Identification of miR-708-5p in peripheral blood monocytes: Potential marker for postmenopausal osteoporosis in Mexican-Mestizo population

IMPACT STATEMENT

This is the first study in which hsa-miR-708-5p has been identified in peripheral blood monocytes (osteoclast precursors) and associated with postmenopausal osteoporosis through small RNA-Sequencing, in an Admixed Mexican Mestizo population. By conducting in silico and bioinformatic analyzes, we identified target genes and important signaling pathways involved in bone metabolism pointing hsa-miR-708-5p as a candidate marker for osteoporosis in Mexican population. These approaches provide a landscape of the post-transcriptional regulation, which can be useful for the management of postmenopausal osteoporosis along with the potential use of microRNAs as markers for its early detection.

Desoxyrhapontigenin inhibits RANKL‑induced osteoclast formation and prevents inflammation‑mediated bone loss

Desoxyrhapontigenin (DRG), a stilbene compound from Rheum undulatum, has been found to exhibit various pharmacological activities, however, its impact on osteoclast formation has not been investigated. The present study investigated the effect of DRG on receptor activator of nuclear factor‑κB ligand (RANKL)‑induced osteoclast differentiation in mouse bone marrow macrophages (BMMs) and inflammation‑induced bone loss in vivo. BMMs or RAW264.7 cells were treated with DRG, followed by an evaluation of cell viability, RANKL‑induced osteoclast differentiation, actin‑ring formation and resorption pits activity. The effects of DRG on the RANKL‑induced phosphorylation of MAPK and the expression of nuclear factor of activated T cells cytoplasmic 1 (NFATc1) and c‑Fos were evaluated using western blot analysis once the BMMs were exposed to RANKL and DRG. The expression levels of osteoclast marker genes were also evaluated using western blot analysis and reverse transcription‑quantitative polymerase chain reaction A lipopolysaccharide (LPS)‑induced murine bone loss model was used to evaluate the protective effect of DRG on inflammation‑induced bone‑loss. The results demonstrated that DRG suppressed the RANKL‑induced differentiation of BMMs into osteoclasts, osteoclast actin‑ring formation and bone resorption activity in a dose‑dependent manner. Furthermore, DRG significantly inhibited LPS‑induced bone loss in a mouse model. At the molecular level, DRG inhibited the RANKL‑induced activation of extracellular signal‑regulated kinase, the expression of c‑Fos, and the induction of NFATc1, a crucial transcription factor for osteoclast formation. DRG decreased the expression levels of osteoclast marker genes, including matrix metalloproteinase‑9, tartrate‑resistant acid phosphatase and cathepsin K. In conclusion, these findings suggested that DRG inhibited the differentiation of BMMs into mature osteoclasts by suppressing the RANKL‑induced activator protein‑1 and NFATc1 signaling pathways, and may be a potential candidate for treating and/or preventing osteoclast‑associated diseases, including osteoporosis.

Osteoimmunology: The Conceptual Framework Unifying the Immune and Skeletal Systems

The immune and skeletal systems share a variety of molecules, including cytokines, chemokines, hormones, receptors, and transcription factors. Bone cells interact with immune cells under physiological and pathological conditions. Osteoimmunology was created as a new interdisciplinary field in large part to highlight the shared molecules and reciprocal interactions between the two systems in both heath and disease. Receptor activator of NF-κB ligand (RANKL) plays an essential role not only in the development of immune organs and bones, but also in autoimmune diseases affecting bone, thus effectively comprising the molecule that links the two systems. Here we review the function, gene regulation, and signal transduction of osteoimmune molecules, including RANKL, in the context of osteoclastogenesis as well as multiple other regulatory functions. Osteoimmunology has become indispensable for understanding the pathogenesis of a number of diseases such as rheumatoid arthritis (RA). We review the various osteoimmune pathologies, including the bone destruction in RA, in which pathogenic helper T cell subsets [such as IL-17-expressing helper T (Th17) cells] induce bone erosion through aberrant RANKL expression. We also focus on cellular interactions and the identification of the communication factors in the bone marrow, discussing the contribution of bone cells to the maintenance and regulation of hematopoietic stem and progenitors cells. Thus the time has come for a basic reappraisal of the framework for understanding both the immune and bone systems. The concept of a unified osteoimmune system will be absolutely indispensable for basic and translational approaches to diseases related to bone and/or the immune system.

p38α MAPK regulates proliferation and differentiation of osteoclast progenitors and bone remodeling in an aging-dependent manner

Bone mass is determined by the balance between bone formation, carried out by mesenchymal stem cell-derived osteoblasts, and bone resorption, carried out by monocyte-derived osteoclasts. Here we investigated the potential roles of p38 MAPKs, which are activated by growth factors and cytokines including RANKL and BMPs, in osteoclastogenesis and bone resorption by ablating p38α MAPK in LysM+monocytes. p38α deficiency promoted monocyte proliferation but regulated monocyte osteoclastic differentiation in a cell-density dependent manner, with proliferating p38α^−/− cultures showing increased differentiation. While young mutant mice showed minor increase in bone mass, 6-month-old mutant mice developed osteoporosis, associated with an increase in osteoclastogenesis and bone resorption and an increase in the pool of monocytes. Moreover, monocyte-specific p38α ablation resulted in a decrease in bone formation and the number of bone marrow mesenchymal stem/stromal cells, likely due to decreased expression of PDGF-AA and BMP2. The expression of PDGF-AA and BMP2 was positively regulated by the p38 MAPK-Creb axis in osteoclasts, with the promoters of PDGF-AA and BMP2 having Creb binding sites. These findings uncovered the molecular mechanisms by which p38α MAPK regulates osteoclastogenesis and coordinates osteoclastogenesis and osteoblastogenesis.

Calycosin Suppresses RANKL-Mediated Osteoclastogenesis through Inhibition of MAPKs and NF-κB

Calycosin, an isoflavonoid phytoestrogen, isolated from Radix Astragali, was reported to possess anti-tumor, anti-inflammation, and osteogenic properties, but its impact on osteoclast differentiation remains unclear. In this study, we examined the effects of calycosin on osteoclastogenesis induced by RANKL. The results showed that calycosin significantly inhibited RANKL-induced osteoclast formation from primary bone marrow macrophages (BMMs). Calycosin also dose-dependently suppressed the formation of bone resorption pits by mature osteoclasts. In addition, the expression of osteoclatogenesis-related genes, including cathepsin K (CtsK), tartrate-resistant acid phosphatase (TRAP), and MMP-9, was significantly inhibited by calycosin. Furthermore, the results indicated that calycosin down-regulated the expression levels of NFATc1 and c-Fos through suppressing the activation of NF-κB and MAPKs. Our results indicate that calycosin has an inhibitory role in the bone loss by preventing osteoclast formation, as well as its bone resorptive activity. Therefore, calycosin may be useful as a therapeutic reagent for bone loss-associated diseases.

Ablation of p38α MAPK Signaling in Osteoblast Lineage Cells Protects Mice From Bone Loss Induced by Estrogen Deficiency

Estrogen deficiency causes bone loss by increasing the number of bone-resorbing osteoclasts. Selective p38α MAPK inhibitors prevent bone-wasting effects of estrogen withdrawal but implicated mechanisms remain to be identified. Here, we show that inactivation of the p38α-encoding gene in osteoblast lineage cells with the use of an osteocalcin-cre transgene protects mice from ovariectomy-induced bone loss (a murine model of postmenopausal osteoporosis). Ovariectomy fails to induce bone loss, increase bone resorption, and stimulate receptor activator of nuclear factor κB ligand and IL-6 expression in mice lacking p38α in osteoblasts and osteocytes. Finally, TNFα or IL-1, which are osteoclastogenic cytokines overproduced in the bone marrow under estrogen deficiency, can activate p38α signaling in osteoblasts, but those cytokines cannot enhance Rankl and Il6 expressions or increase osteoclast formation in p38a-deficient osteoblast cultures. These findings demonstrate that p38α MAPK signaling in osteoblast lineage cells mediates ovariectomy-induced bone loss by up-regulating receptor activator of nuclear factor κB ligand and IL-6 production.

Glucocorticoids limit acute lung inflammation in concert with inflammatory stimuli by induction of SphK1

Acute lung injury (ALI) is a severe inflammatory disease for which no specific treatment exists. As glucocorticoids have potent immunosuppressive effects, their application in ALI is currently being tested in clinical trials. However, the benefits of this type of regimen remain unclear. Here we identify a mechanism of glucocorticoid action that challenges the long-standing dogma of cytokine repression by the glucocorticoid receptor. Contrarily, synergistic gene induction of sphingosine kinase 1 (SphK1) by glucocorticoids and pro-inflammatory stimuli via the glucocorticoid receptor in macrophages increases circulating sphingosine 1-phosphate levels, which proves essential for the inhibition of inflammation. Chemical or genetic inhibition of SphK1 abrogates the therapeutic effects of glucocorticoids. Inflammatory p38 MAPK- and mitogen- and stress-activated protein kinase 1 (MSK1)-dependent pathways cooperate with glucocorticoids to upregulate SphK1 expression. Our findings support a critical role for SphK1 induction in the suppression of lung inflammation by glucocorticoids, and therefore provide rationales for effective anti-inflammatory therapies.

Endothelial damage is a major component of acute lung injury pathogenesis. Here the authors show that in a mouse model of acute lung injury, glucocorticoids induce sphingosine kinase 1 production in macrophages, promoting endothelial barrier function and ameliorating the disease.

Focus on the p38 MAPK signaling pathway in bone development and maintenance

The p38 mitogen-activated protein kinase (MAPK) signaling pathway can be activated in response to a wide range of extracellular signals. As a consequence, it can generate many different biological effects that depend on the stimulus and on the activated cell type. Therefore, this pathway has been found to regulate many aspects of tissue development and homeostasis. Recent work with the aid of genetically modified mice has highlighted the physiological functions of this pathway in skeletogenesis and postnatal bone maintenance. In this review, emphasis is given to the roles of the p38 MAPK pathway in chondrocyte, osteoblast and osteoclast biology. In particular, we describe the molecular mechanisms of p38 MAPK activation and downstream targets. The requirement of this pathway in physiological bone development and homeostasis is demonstrated by the ability of p38 MAPK to regulate master transcription factors controlling geneses and functions of chondrocytes, osteoblasts and osteoclasts.

Sexual Dimorphism in MAPK-Activated Protein Kinase-2 (MK2) Regulation of RANKL-Induced Osteoclastogenesis in Osteoclast Progenitor Subpopulations

Osteoclasts (OCs) are bone-resorptive cells critical for maintaining skeletal integrity through coupled bone turnover. OC differentiation and activation requires receptor activator of NF-kB ligand (RANKL) signaling through the p38 MAPK pathway. However the role of the p38 MAPK substrate, MAPK-activated protein kinase 2 (MK2), is not clearly delineated. Within the bone marrow exists a specific subpopulation of defined osteoclast progenitor cells (dOCPs) with surface expression of B220^-Gr1^-CD11b^lo/-CD115⁺ (dOCP^lo/-). In this study, we isolated dOCPs from male and female mice to determine sex-specific effects of MK2 signaling in osteoclastogenesis (OCgen). Male Mk2^-/- mice display an increase in the dOCP^lo cell population when compared to Mk2^+/+ mice, while female Mk2^-/- and Mk2^+/+ mice exhibit no difference. Defined OCPs from male and female Mk2^+/+ and Mk2^-/- bone marrow were treated with macrophage colony stimulation factor (M-CSF) and RANKL cytokines to promote OCgen. RANKL treatment of dOCP^lo cells stimulated p38 and MK2 phosphorylation. Tartrate-resistant acid phosphatase (TRAP) assays were used to quantify OC number, size, and TRAP enzyme activity post-RANKL stimulation. MK2 signaling was critical for male dOCP^lo OCgen, yet MK2 signaling regulated OCgen from female dOCP^- and CD11b^hi subpopulations as well. The functional gene, Ctsk, was attenuated in both male and female Mk2^-/- dOCP^lo-derived OCs. Conversely, MK2 signaling was only critical for gene expression of pre-OC fusion genes, Oc-stamp andTm7sf4, in male OCgen. Therefore, these data suggest there is a sexual dimorphism in MK2 signaling of OCP subpopulations.

Immunohistochemical evidence of stress and inflammatory markers in mouse models of cutaneous leishmaniosis

Leishmanioses are chronic parasitic diseases and host responses are associated with pro- or anti-inflammatory cytokines involved, respectively, in the control or exacerbation of infection. The relevance of other inflammatory mediators and stress markers has not been widely studied and there is a need to search for biomarkers to leishmaniasis. In this work, the stress and inflammatory molecules p38 mitogen-activated protein kinase, cyclooxygenase-2, migration inhibitory factor, macrophage inflammatory protein 2, heat shock protein 70 kDa, vascular endothelial factor (VEGF), hypoxia-inducible factors (HIF-1α and HIF-2α), heme oxygenase and galectin-3 expression were assessed immunohistochemically in self-controlled lesions in C57BL/6 mice and severe lesions in Balb/c mice infected with Leishmania amazonensis. The results indicated that the majority of molecules were expressed in the cutaneous lesions of both C57BL/6 and Balb/c mice during various phases of infection, suggesting no obvious correlation between the stress and inflammatory molecule expression and the control/exacerbation of leishmanial lesions. However, the cytokine VEGF was only detected in C57BL/6 footpad lesions and small lesions in Balb/c mice treated with antimonial pentavalent. These findings suggest that VEGF expression could be a predictive factor for murine leishmanial control, a hypothesis that should be tested in human leishmaniosis.

Tumor cell p38 MAPK: A trigger of cancer bone osteolysis

Osteolytic bone destruction is a hallmark of bone-metastatic cancers. Current therapy is unable to completely cure or prevent this disease in patients. The p38 mitogen-activated protein kinase (MAPK) affects a diverse range of intracellular responses with well-known roles in development, cell-cycle and differentiation, inflammation, apoptosis, senescence, and tumorigenesis. This article is an overview of the contribution of tumor cell-expressed p38 MAPK to the regulation of osteoclastogenesis, osteoblastogenesis, and osteolyticbone lesions.

Blockade of CD26 signaling inhibits human osteoclast development

Bone remodeling is maintained by the delicate balance between osteoblasts (OBs) and osteoclasts (OCs). However, the role of CD26 in regulating bone remodeling has not yet been characterized. We herein show that CD26 is preferentially expressed on normal human OCs and is intensely expressed on activated human OCs in osteolytic bone alterations. Macrophage-colony stimulating factor (M-CSF) and soluble receptor activator of NF-κB ligand (sRANKL) induced human OC differentiation, in association with CD26 expression on monocyte-macrophage lineage cells. CD26 expression was accompanied by increased phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), which is crucial for early human OC differentiation. The humanized anti-CD26 monoclonal antibody, huCD26mAb, impaired the formation and function of tartrate-resistant acid phosphatase (TRAP)/CD26 positive multi-nucleated (nuclei > 3) OCs with maturation in the manner of dose-dependency. It was revealed that huCD26mAb inhibits early OC differentiation via the inactivation of MKK3/6, p38 MAPK and subsequent dephosphorylation of microphthalmia-associated transcription factor (mi/Mitf). These inhibitions occur immediately after RANKL binds to RANK on the human OC precursor cells and were demonstrated using the OC functional assays. huCD26mAb subsequently impaired OC maturation and bone resorption by suppressing the expression of TRAP and OC fusion proteins. In addition, p38 MAPK inhibitor also strongly inhibited OC formation and function. Our results suggest that the blockade of CD26 signaling impairs the development of human functional OCs by inhibiting p38 MAPK-mi/Mitf phosphorylation pathway and that targeting human OCs with huCD26mAb may have therapeutic potential for the treatment of osteolytic lesions following metastasis to alleviate bone destruction and reduce total skeletal-related events (SREs).

Small-molecule inhibitors for autoimmune arthritis: success, failure and the future

Treatment of patients with aggressive autoimmune arthritis, such as rheumatoid arthritis (RA), is a considerable challenge for physicians, particularly rheumatologists. Because of the nature of autoimmune arthritis, effective and complete suppression of disease activity has been the primary therapeutic goal. Although currently available disease-modifying antirheumatic drugs (DMARDs) can successfully control the disease progression in a large proportion of patients, the benefit/risk ratio is not very much satisfied. The introduction of biologic agents such as anti-tumor necrosis factor-α, anti-interleukin-6, and anti-CD20 brings significant help to those patients with an inadequate response to treatment with DMARDs. In considering the limitation of currently available DMARDs and biologics, the development of new DMARDs, small-molecule inhibitors (SMIs), has recently emerged. In the past few years, a great volume of knowledge has been revealed from the experience of examining the usefulness of several SMIs for therapeutics of autoimmune arthritis. This paper addresses the up-to-date knowledge regarding autoimmune arthritis, therapeutics, findings from recently developed SMIs and the benefits and drawbacks of the development of SMIs. In addition, perspectives on the future development of SMIs for autoimmune arthritis will be described and discussed.

Activation of adenosine A(2A) receptor reduces osteoclast formation via PKA- and ERK1/2-mediated suppression of NFκB nuclear translocation

BACKGROUND AND PURPOSE

We previously reported that adenosine, acting at adenosine A(2A) receptors (A(2A)R), inhibits osteoclast (OC) differentiation in vitro (A(2A)R activation OC formation reduces by half) and in vivo. For a better understanding how adenosine A(2A)R stimulation regulates OC differentiation, we dissected the signalling pathways involved in A(2A)R signalling.

EXPERIMENTAL APPROACH

OC differentiation was studied as TRAP+ multinucleated cells following M-CSF/RANKL stimulation of either primary murine bone marrow cells or the murine macrophage line, RAW264.7, in presence/absence of the A(2A)R agonist CGS21680, the A(2A)R antagonist ZM241385, PKA activators (8-Cl-cAMP 100 nM, 6-Bnz-cAMP) and the PKA inhibitor (PKI). cAMP was quantitated by EIA and PKA activity assays were carried out. Signalling events were studied in PKA knockdown (lentiviral shRNA for PKA) RAW264.7 cells (scrambled shRNA as control). OC marker expression was studied by RT-PCR.

KEY RESULTS

A(2A)R stimulation increased cAMP and PKA activity which and were reversed by addition of ZM241385. The direct PKA stimuli 8-Cl-cAMP and 6-Bnz-cAMP inhibited OC maturation whereas PKI increased OC differentiation. A(2A)R stimulation inhibited p50/p105 NFκB nuclear translocation in control but not in PKA KO cells. A(2A)R stimulation activated ERK1/2 by a PKA-dependent mechanism, an effect reversed by ZM241385, but not p38 and JNK activation. A(2A)R stimulation inhibited OC expression of differentiation markers by a PKA-mechanism.

CONCLUSIONS AND IMPLICATIONS

A(2A)R activation inhibits OC differentiation and regulates bone turnover via PKA-dependent inhibition of NFκB nuclear translocation, suggesting a mechanism by which adenosine could target bone destruction in inflammatory diseases like rheumatoid arthritis.

MAPK11 in breast cancer cells enhances osteoclastogenesis and bone resorption

Breast cancer cells frequently metastasize to bone and induce osteolytic bone destruction in patients. These metastases cause severe bone pain, high risk of fractures and hypercalcemia, and are essentially incurable and fatal. Recent studies show that breast cancer cells in bone activate osteoclastogenesis and bone resorption. However the underlying mechanism is poorly understood. This study shows that the p38 MAPK (p38) isoform MAPK11 (p38β) is expressed in breast cancer cells. By using specific small hairpin RNAs for MAPK11, we demonstrated that p38β-mediated p38 activity in breast cancer cells is responsible for breast cancer-induced osteolytic bone destruction. The addition of conditioned media from breast cancer cell lines MDA-MB-231 and MDA-MB-468, which have high expression of p38β, induced osteoclast differentiation and bone resorption. In contrast, knockdown of p38β in breast cancer cells reduced osteoclast differentiation in vitro and reduced bone destruction in severe combined immunodeficiency (SCID) mouse models. The knockdown of p38β did not affect tumor growth or survival or the ability of cancer cells to home to bone. Furthermore, our results showed that p38β upregulated the expression and secretion of monocyte chemotactic protein-1 (MCP-1) in breast cancer cells, and upregulated MCP-1 activates osteoclast differentiation and activity. This study elucidates a novel molecular mechanism of breast cancer cell-induced osteolytic bone destruction. This study also indicates that targeting breast cancer cell p38β and its product MCP-1 may be a viable approach to treat or prevent bone destruction in patients with bone-metastatic breast cancer.

Hepatocyte growth factor and p38 promote osteogenic differentiation of human mesenchymal stem cells

Hepatocyte growth factor (HGF) is a paracrine factor involved in organogenesis, tissue repair, and wound healing. We report here that HGF promotes osteogenic differentiation through the transcription of key osteogenic markers, including osteocalcin, osterix, and osteoprotegerin in human mesenchymal stem cells and is a necessary component for the establishment of osteoblast mineralization. Blocking endogenous HGF using PHA665752, a c-Met inhibitor (the HGF receptor), or an HGF-neutralizing antibody attenuates mineralization, and PHA665752 markedly reduced alkaline phosphatase activity. Moreover, we report that HGF promotion of osteogenic differentiation involves the rapid phosphorylation of p38 and differential regulation of its isoforms, p38α and p38β. Western blot analysis revealed a significantly increased level of p38α and p38β protein, and reverse transcription quantitative PCR revealed that HGF increased the transcriptional level of both p38α and p38β. Using small interfering RNA to reduce the transcription of p38α and p38β, we saw differential roles for p38α and p38β on the HGF-induced expression of key osteogenic markers. In summary, our data demonstrate the importance of p38 signaling in HGF regulation of osteogenic differentiation.

Manganese overload affects p38 MAPK phosphorylation and metalloproteinase activity during sea urchin embryonic development

In the marine environment, manganese represents a potential emerging contaminant, resulting from an increased production of manganese-containing compounds. In earlier reports we found that the exposure of Paracentrotus lividus sea urchin embryos to manganese produced phenotypes with no skeleton. In addition, manganese interfered with calcium uptake, perturbed extracellular signal-regulated kinase (ERK) signaling, affected the expression of skeletogenic genes, and caused an increase of the hsc70 and hsc60 protein levels. Here, we extended our studies focusing on the temporal activation of the p38 mitogen-activated protein kinase (p38 MAPK) and the proteolytic activity of metalloproteinases (MMPs). We found that manganese affects the stage-dependent dynamics of p38 MAPK activation and inhibits the total gelatin-auto-cleaving activity of MMPs, with the exclusion of the 90-85 kDa and 68-58 kDa MMPs, whose levels remain high all throughout development. Our findings correlate, for the first time to our knowledge, an altered activation pattern of the p38 MAPK with an aberrant MMP proteolytic activity in the sea urchin embryo.

Differential roles of MAPK kinases MKK3 and MKK6 in osteoclastogenesis and bone loss

Bone mass is maintained by osteoclasts that resorb bone and osteoblasts that promote matrix deposition and mineralization. Bone homeostasis is altered in chronic inflammation as well as in post-menopausal loss of estrogen, which favors osteoclast activity that leads to osteoporosis. The MAPK p38α is a key regulator of bone loss and p38 inhibitors preserve bone mass by inhibiting osteoclastogenesis. p38 function is regulated by two upstream MAPK kinases, namely MKK3 and MKK6. The goal of this study was to assess the effect of MKK3- or MKK6-deficiency on osteoclastogenesis in vitro and on bone loss in ovariectomy-induced osteoporosis in mice. We demonstrated that MKK3 but not MKK6, regulates osteoclast differentiation from bone marrow cells in vitro. Expression of NFATc1, a master transcription factor in osteoclastogenesis, is decreased in cells lacking MKK3 but not MKK6. Expression of osteoclast-specific genes Cathepsin K, osteoclast-associated receptor and MMP9, was inhibited in MKK3−/− cells. The effect of MKK-deficiency on ovariectomy-induced bone loss was then evaluated in female WT, MKK3−/− and MKK6−/− mice by micro-CT analysis. Bone loss was partially inhibited in MKK3−/− as well as MKK6−/− mice, despite normal osteoclastogenesis in MKK6−/− cells. This correlated with the lower osteoclast numbers in the MKK-deficient ovariectomized mice. These studies suggest that MKK3 and MKK6 differentially regulate bone loss due to estrogen withdrawal. MKK3 directly mediates osteoclastogenesis while MKK6 likely contributes to pro-inflammatory cytokine production that promotes osteoclast formation.

Mitogen-activated protein kinases in innate immunity

Following pathogen infection or tissue damage, the stimulation of pattern recognition receptors on the cell surface and in the cytoplasm of innate immune cells activates members of each of the major mitogen-activated protein kinase (MAPK) subfamilies--the extracellular signal-regulated kinase (ERK), p38 and Jun N-terminal kinase (JNK) subfamilies. In conjunction with the activation of nuclear factor-κB and interferon-regulatory factor transcription factors, MAPK activation induces the expression of multiple genes that together regulate the inflammatory response. In this Review, we discuss our current knowledge about the regulation and the function of MAPKs in innate immunity, as well as the importance of negative feedback loops in limiting MAPK activity to prevent host tissue damage. We also examine how pathogens have evolved complex mechanisms to manipulate MAPK activation to increase their virulence. Finally, we consider the potential of the pharmacological targeting of MAPK pathways to treat autoimmune and inflammatory diseases.

Mitogen-activated protein kinase 2 regulates physiological and pathological bone turnover

The objective of this study was to investigate the role of the serine-threonine kinase mitogen-activated protein kinase 2 (MK2) in bone homeostasis. Primary bone cell cultures from MK2(+/+) and MK2(-/-) mice were assessed for osteoclast and osteoblast differentiation, bone resorption, and gene expression. Bone architecture of MK2(+/+) and MK2(-/-) mice was investigated by micro-computed tomography and histomorphometry. Ovariectomy was performed in MK2(+/+) and MK2(-/-) mice to assess the role of MK2 in postmenopausal bone loss. Osteoclastogenesis, bone resorption, and osteoclast gene expression were significantly impaired in monocytes from MK2(-/-) compared to MK2(+/+) mice. Mechanistically, loss of MK2 causes impaired DNA binding of c-fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) to tartrate-resistant acid phosphatase (TRAP) and the calcitonin receptor gene promoter. In addition, MK2(-/-) mice showed an age-dependent increase in trabecular bone mass and cortical thickness, fewer osteoclasts, and lower markers of bone resorption than MK2(+/+) mice. Furthermore, MK2(-/-) mice were protected from ovariectomy-induced bone loss. Osteoblastogenesis and bone formation were unchanged in MK2(-/-) mice, whereas osteoblast expression of osteoprotegerin (OPG) and serum levels of OPG were higher in MK2(-/-) than in MK2(+/+) mice. Loss of MK2 effectively blocks bone resorption and prevents the development of postmenopausal bone loss. Small-molecule inhibitors of MK2 could thus emerge as highly effective tools to block bone resorption and to treat postmenopausal bone loss.

The mitogen-activated protein kinase p38α regulates tubular damage in murine anti-glomerular basement membrane nephritis

p38 mitogen-activated protein kinase (MAPK) is thought to play a central role in acute and chronic inflammatory responses. Whether p38MAPK plays a pathogenic role in crescentic GN (GN) and which of its four isoforms is preferentially involved in kidney inflammation is not definitely known. We thus examined expression and activation of p38MAPK isoforms during anti-glomerular basement membrane (GBM) nephritis. Therefore, p38α conditional knockout mice (MxCre-p38α^Δ/Δ) were used to examine the role of p38α in anti-GBM induced nephritis. Both wild type and MxCre-p38α^Δ/Δ mice developed acute renal failure over time. Histological examinations revealed a reduced monocyte influx and less tubular damage in MxCre-p38α^Δ/Δ mice, whereas glomerular crescent formation and renal fibrosis was similar. Likewise, the levels of pro- and anti-inflammatory cytokines such as TNF, IL-1 and IL-10 were similar, but IL-8 was even up-regulated in MxCre-p38α^Δ/Δ mice. In contrast, we could detect strong down-regulation of chemotactic cytokines such as CCL-2, -5 and -7, in the kidneys of MxCre-p38α^Δ/Δ mice. In conclusion, p38α is the primary p38MAPK isoform expressed in anti-GBM nephritis and selectively affects inflammatory cell influx and tubular damage. Full protection from nephritis is however not achieved as renal failure and structural damage still occurs.

Anti-inflammatory effect and selectivity profile of AS1940477, a novel and potent p38 mitogen-activated protein kinase inhibitor

Given the key role p38 mitogen-activated protein kinase (MAPK) plays in inflammatory responses through the production of cytokines and inflammatory mediators, its inhibition is considered a promising therapeutic strategy for chronic inflammatory diseases such as rheumatoid arthritis, psoriasis, inflammatory bowel disease, and chronic obstructive pulmonary disease. Here, we evaluated the anti-inflammatory effect and selectivity profile of the novel p38 MAPK inhibitor AS1940477. AS1940477 inhibited the enzymatic activity of recombinant p38α and β isoforms but showed no effect against other 100 protein kinases including p38γ and δ isoforms. We also confirmed the selectivity of AS1940477 in the intracellular signaling pathway. In human peripheral blood mononuclear cells, AS1940477 inhibited lipopolysaccharide (LPS)- or phytohemagglutinin A (PHA)-induced production of proinflammatory cytokines, including TNFα, IL-1β, and IL-6 at low concentrations (LPS/TNFα, IC(50)=0.45n M; PHA/TNFα, IC(50)=0.40 nM). In addition, equivalent concentrations of AS1940477 that inhibited cytokine production also inhibited TNFα- and IL-1 β-induced production of IL-6, PGE(2), and MMP-3 in human synovial stromal cells. AS1940477 was also found to potently inhibit TNF production in whole blood (IC(50)=12 nM) and effectively inhibited TNFα production induced by systemically administered LPS in rats at less than 0.1mg/kg (ED(50)=0.053 mg/kg) with an anti-inflammatory effect lasting for 20h after oral administration. Overall, this study demonstrated that AS1940477 is a novel and potent p38 MAPK inhibitor and may be useful as a promising anti-inflammatory agent for treating inflammatory disorders.

Dual-specificity phosphatase 1-null mice exhibit spontaneous osteolytic disease and enhanced inflammatory osteolysis in experimental arthritis

OBJECTIVE

Bone formation and destruction are usually tightly linked; however, in disorders such as rheumatoid arthritis, periodontal disease, and osteoporosis, elevated osteoclast activity leads to bone destruction. Osteoclast formation and activation are controlled by many signaling pathways, including p38 MAPK. Dual-specificity phosphatase 1 (DUSP-1) is a factor involved in the negative regulation of p38 MAPK. The purpose of this study was to examine the effect of Dusp1 deficiency on bone destruction.

METHODS

Penetrance, onset, and severity of collagen-induced arthritis were recorded in DUSP-1+/+ and DUSP-1-/- mice. Bone destruction was assessed by histologic and micro-computed tomographic examination of the joints. The in vitro formation and activation of osteoclasts from DUSP-1+/+ and DUSP-1-/- precursors were assessed in the absence or presence of tumor necrosis factor (TNF).

RESULTS

The formation and activation of osteoclasts in vitro in the presence of TNF were enhanced by Dusp1 gene disruption. DUSP-1-/- mice exhibited higher penetrance, earlier onset, and increased severity of experimental arthritis, accompanied by greater numbers of osteoclasts in inflamed joints and more extensive loss of bone. A DUSP-1-/- mouse colony of mixed genetic background also demonstrated striking spontaneous osteolytic destruction of distal phalanges.

CONCLUSION

DUSP-1 is a critical regulator of osteoclast activity and limits bone destruction in an experimental model of rheumatoid arthritis. Defects in the expression or activity of DUSP1 in humans may correlate with a propensity to develop osteolytic lesions in arthritis.