MCP-5 suppresses osteoclast differentiation through Ccr5 upregulation.

Human monocyte chemoattractant protein-1 (MCP-1) in mice has two orthologs, MCP-1 and MCP-5. MCP-1, which is highly expressed in osteoclasts rather than in osteoclast precursor cells, is an important factor in osteoclast differentiation. However, the roles of MCP-5 in osteoclasts are completely unknown. In this study, contrary to MCP-1, MCP-5 was downregulated during receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast differentiation and was considered an inhibitory factor in osteoclast differentiation. The inhibitory role of MCP-5 in osteoclast differentiation was closely related to the increase in Ccr5 expression and the inhibition of IκB degradation by RANKL. Transgenic mice expressing MCP-5 controlled by Mx-1 promoter exhibited an increased bone mass because of a decrease in osteoclasts. This result strongly supported that MCP-5 negatively regulated osteoclast differentiation. MCP-5 also prevented severe bone loss caused by RANKL.

Nodal negatively regulates osteoclast differentiation by inducing STAT1 phosphorylation.

Several members of the transforming growth factor beta (TGF-ß) superfamily regulate the proliferation, differentiation, and function of bone-forming osteoblasts and bone-resorbing osteoclasts. However, it is still unknown whether Nodal, a member of the TGF-ß superfamily, serves a function in bone cells. In this study, we found that Nodal did not have any function in osteoblasts but instead negatively regulated osteoclast differentiation. Nodal inhibited RANKL-induced osteoclast differentiation by downregulating the expression of pro-osteoclastogenic genes, including c-fos, Nfatc1, and Blimp1, and upregulating the expression of antiosteoclastogenic genes, including Bcl6 and Irf8. Nodal activated STAT1 in osteoclast precursor cells, and STAT1 downregulation significantly reduced the inhibitory effect of Nodal on osteoclast differentiation. These findings indicate that Nodal activates STAT1 to downregulate or upregulate the expression of pro-osteoclastogenic or antiosteoclastogenic genes, respectively, leading to the inhibition of osteoclast differentiation. Moreover, the inhibitory effect of Nodal on osteoclast differentiation contributed to the reduction of RANKL-induced bone loss in vivo.

The role of Pim-1 kinases in inflammatory signaling pathways.

OBJECTIVE AND DESIGN: This observational study investigated the regulatory mechanism of Pim-1 in inflammatory signaling pathways. MATERIALS: THP-1, RAW 264.7, BV2, and Jurkat human T cell lines were used. TREATMENT: None. METHODS: Lipopolysaccharide (LPS) was used to induce inflammation, followed by PIM1 knockdown. Western blot, immunoprecipitation, immunofluorescence, and RT-PCR assays were used to assess the effect of PIM1 knockdown on LPS-induced inflammation. RESULTS: PIM1 knockdown in macrophage-like THP-1 cells suppressed LPS-induced upregulation of pro-inflammatory cytokines, inducible nitric oxide synthase, cyclooxygenase-2, phosphorylated Janus kinase, signal transducer and activator of transcription 3, extracellular signal-regulated kinase, c-Jun N-terminal kinase, p38, and nuclear factor kappa B p65 (NF-κB p65). It also suppressed upregulation of inhibitor of NF-κB kinase α/ß and enhanced the nuclear translocation of NF-κB p65. Moreover, it inhibited the upregulation of Nod-like receptor family pyrin domain-containing 3 (NLRP3) and cleavage of caspase-1 induced by co-treatment of LPS with adenosine triphosphate. Additionally, p-transforming growth factor-ß-activated kinase 1 (TAK1) interacted with Pim-1. All three members of Pim kinases (Pim-1, Pim-2, and Pim-3) were required for LPS-mediated inflammation in macrophages; however, unlike Pim-1 and Pim-3, Pim-2 functioned as a negative regulator of T cell activity. CONCLUSIONS: Pim-1 interacts with TAK1 in LPS-induced inflammatory responses and is involved in MAPK/NF-κB/NLRP3 signaling pathways. Additionally, considering the negative regulatory role of Pim-2 in T cells, further in-depth studies on their respective functions are needed.

Pirfenidone Inhibits Alveolar Bone Loss in Ligature-Induced Periodontitis by Suppressing the NF-κB Signaling Pathway in Mice.

There has been increasing interest in adjunctive use of anti-inflammatory drugs to control periodontitis. This study was performed to examine the effects of pirfenidone (PFD) on alveolar bone loss in ligature-induced periodontitis in mice and identify the relevant mechanisms. Experimental periodontitis was established by ligating the unilateral maxillary second molar for 7 days in mice (n = 8 per group), and PFD was administered daily via intraperitoneal injection. The micro-computed tomography and histology analyses were performed to determine changes in the alveolar bone following the PFD administration. For in vitro analysis, bone marrow macrophages (BMMs) were isolated from mice and cultured with PFD in the presence of RANKL or LPS. The effectiveness of PFD on osteoclastogenesis, inflammatory cytokine expression, and NF-κB activation was determined with RT-PCR, Western blot, and immunofluorescence analyses. PFD treatment significantly inhibited the ligature-induced alveolar bone loss, with decreases in TRAP-positive osteoclasts and expression of inflammatory cytokines in mice. In cultured BMM cells, PFD also inhibited RANKL-induced osteoclast differentiation and LPS-induced proinflammatory cytokine (IL-1ß, IL-6, TNF-a) expression via suppressing the NF-κB signal pathway. These results suggest that PFD can suppress periodontitis progression by inhibiting osteoclastogenesis and inflammatory cytokine production via inhibiting the NF-κB signal pathway, and it may be a promising candidate for controlling periodontitis.

The ATF3-OPG Axis Contributes to Bone Formation by Regulating the Differentiation of Osteoclasts, Osteoblasts, and Adipocytes.

Activating transcription factor 3 (ATF3) has been identified as a negative regulator of osteoblast differentiation in in vitro study. However, it was not associated with osteoblast differentiation in in vivo study. To provide an understanding of the discrepancy between the in vivo and in vitro findings regarding the function of ATF3 in osteoblasts, we investigated the unidentified roles of ATF3 in osteoblast biology. ATF3 enhanced osteoprotegerin (OPG) production, not only in osteoblast precursor cells, but also during osteoblast differentiation and osteoblastic adipocyte differentiation. In addition, ATF3 increased nodule formation in immature osteoblasts and decreased osteoblast-dependent osteoclast formation, as well as the transdifferentiation of osteoblasts to adipocytes. However, all these effects were reversed by the OPG neutralizing antibody. Taken together, these results suggest that ATF3 contributes to bone homeostasis by regulating the differentiation of various cell types in the bone microenvironment, including osteoblasts, osteoclasts, and adipocytes via inducing OPG production.

Overexpression of Neurogenin 1 Negatively Regulates Osteoclast and Osteoblast Differentiation.

Neurogenin 1 (Ngn1) belongs to the basic helix-loop-helix (bHLH) transcription factor family and plays important roles in specifying neuronal differentiation. The present study aimed to determine whether forced Ngn1 expression contributes to bone homeostasis. Ngn1 inhibited the p300/CREB-binding protein-associated factor (PCAF)-induced acetylation of nuclear factor of activated T cells 1 (NFATc1) and runt-related transcription factor 2 (Runx2) through binding to PCAF, which led to the inhibition of osteoclast and osteoblast differentiation, respectively. In addition, Ngn1 overexpression inhibited the TNF-α- and IL-17A-mediated enhancement of osteoclast differentiation and IL-17A-induced osteoblast differentiation. These findings indicate that Ngn1 can serve as a novel therapeutic agent for treating ankylosing spondylitis with abnormally increased bone formation and resorption.

Transcription Factor Lmx1b Negatively Regulates Osteoblast Differentiation and Bone Formation.

The LIM-homeodomain transcription factor Lmx1b plays a key role in body pattern formation during development. Although Lmx1b is essential for the normal development of multiple tissues, its regulatory mechanism in bone cells remains unclear. Here, we demonstrated that Lmx1b negatively regulates bone morphogenic protein 2 (BMP2)-induced osteoblast differentiation. Overexpressed Lmx1b in the osteoblast precursor cells inhibited alkaline phosphatase (ALP) activity and nodule formation, as well as the expression of osteoblast maker genes, including runt-related transcription factor 2 (Runx2), alkaline phosphatase (Alpl), bone sialoprotein (Ibsp), and osteocalcin (Bglap). Conversely, the knockdown of Lmx1b in the osteoblast precursors enhanced the osteoblast differentiation and function. Lmx1b physically interacted with and repressed the transcriptional activity of Runx2 by reducing the recruitment of Runx2 to the promoter region of its target genes. In vivo analysis of BMP2-induced ectopic bone formation revealed that the knockdown of Lmx1b promoted osteogenic differentiation and bone regeneration. Our data demonstrate that Lmx1b negatively regulates osteoblast differentiation and function through regulation of Runx2 and provides a molecular basis for therapeutic targets for bone diseases.

Bifunctional Role of CrkL during Bone Remodeling.

Coupled signaling between bone-forming osteoblasts and bone-resorbing osteoclasts is crucial to the maintenance of bone homeostasis. We previously reported that v-crk avian sarcoma virus CT10 oncogene homolog-like (CrkL), which belongs to the Crk family of adaptors, inhibits bone morphogenetic protein 2 (BMP2)-mediated osteoblast differentiation, while enhancing receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclast differentiation. In this study, we investigated whether CrkL can also regulate the coupling signals between osteoblasts and osteoclasts, facilitating bone homeostasis. Osteoblastic CrkL strongly decreased RANKL expression through its inhibition of runt-related transcription factor 2 (Runx2) transcription. Reduction in RANKL expression by CrkL in osteoblasts resulted in the inhibition of not only osteoblast-dependent osteoclast differentiation but also osteoclast-dependent osteoblast differentiation, suggesting that CrkL participates in the coupling signals between osteoblasts and osteoclasts via its regulation of RANKL expression. Therefore, CrkL bifunctionally regulates osteoclast differentiation through both a direct and indirect mechanism while it inhibits osteoblast differentiation through its blockade of both BMP2 and RANKL reverse signaling pathways. Collectively, these data suggest that CrkL is involved in bone homeostasis, where it helps to regulate the complex interactions of the osteoblasts, osteoclasts, and their coupling signals.

c-Src-Dependent and -Independent Functions of Matk in Osteoclasts and Osteoblasts.

The non-receptor tyrosine kinase c-Src participates in bone metabolism by regulating the activities of both the bone-resorbing osteoclasts and bone-forming osteoblasts. In this study, we investigated whether megakaryocyte-associated tyrosine kinase (Matk), a potent inhibitor of c-Src, affects the functions of murine osteoclasts and osteoblasts. Results revealed that the formation of osteoclasts with actin rings was attenuated by Matk overexpression in osteoclast precursor cells but was enhanced by Matk knockdown. The inhibitory effect of Matk on osteoclasts was closely related with the inhibition of c-Src activity. Intriguingly, Matk overexpression in osteoblasts reduced bone nodule formation. Conversely, Matk knockdown increased osteoblast function. Most importantly, binding of Matk to Runx2 resulted in the inhibition of Runx2 translocation into the nucleus and downregulation of Runx2 target genes. Taken together, our findings demonstrated that Matk plays a critical role in bone metabolism by impairing the functions of osteoclasts and osteoblasts via distinct mechanisms involving inhibition of c-Src-dependent and -independent signaling pathways.

Endoplasmic Reticulum-Bound Transcription Factor CREBH Stimulates RANKL-Induced Osteoclastogenesis.

Endoplasmic reticulum (ER) stress is triggered by various metabolic factors, such as cholesterol and proinflammatory cytokines. Recent studies have revealed that ER stress is closely related to skeletal disorders, such as osteoporosis. However, the precise mechanism by which ER stress regulates osteoclast differentiation has not been elucidated. In this study, we identified an ER-bound transcription factor, cAMP response element-binding protein H (CREBH), as a downstream effector of ER stress during RANKL-induced osteoclast differentiation. RANKL induced mild ER stress and the simultaneous accumulation of active nuclear CREBH (CREBH-N) in the nucleus during osteoclastogenesis. Overexpression of CREBH-N in osteoclast precursors enhanced RANKL-induced osteoclast formation through NFATc1 upregulation. Inhibiting ER stress using a specific inhibitor attenuated the expression of osteoclast-related genes and CREBH activation. In addition, inhibition of reactive oxygen species using N-acetylcysteine attenuated ER stress, expression of osteoclast-specific marker genes, and RANKL-induced CREBH activation. Furthermore, inhibition of ER stress and CREBH signaling pathways using an ER stress-specific inhibitor or CREBH small interfering RNAs prevented RANKL-induced bone destruction in vivo. Taken together, our results suggest that reactive oxygen species/ER stress signaling-dependent CREBH activation plays an important role in RANKL-induced osteoclastogenesis. Therefore, inactivation of ER stress and CREBH signaling pathways may represent a new treatment strategy for osteoporosis.

Role of CrkII Signaling in RANKL-Induced Osteoclast Differentiation and Function.

Rac1, a member of small GTPases, is a key regulator of osteoclast differentiation and function. The Crk family adaptor proteins, consisting of Src homology (SH) 2 and SH3 protein-binding domains, regulate cell proliferation, migration, and invasion through Rac1 activation. In this study, we examined the role of CrkII in osteoclast differentiation and function. Retroviral overexpression of CrkII in osteoclast precursors enhanced osteoclast differentiation and resorptive function through Rac1 activation. The knockdown of CrkII in osteoclast precursors using small interfering RNA inhibited osteoclast differentiation and its resorption activity. Unlike wild-type CrkII, overexpression of the three SH domains in mutant forms of CrkII did not enhance either osteoclast differentiation or function. Phosphorylation of p130 Crk-associated substrate (p130Cas) by osteoclastogenic cytokines in preosteoclasts increased the interaction between p130Cas and CrkII, which is known to be involved in Rac1 activation. Furthermore, transgenic mice overexpressing CrkII under control of a tartrate-resistant acid phosphatase promoter exhibited a low bone mass phenotype, associated with increased resorptive function of osteoclasts in vivo. Taken together, our data suggest that the p130Cas/CrkII/Rac1 signaling pathway plays an important role in osteoclast differentiation and function, both in vitro and in vivo.

Mucosal-associated invariant T cell deficiency in systemic lupus erythematosus.

Mucosal-associated invariant T (MAIT) cells contribute to protection against certain microorganism infections and play an important role in mucosal immunity. However, the role of MAIT cells remains enigmatic in autoimmune diseases. In this study, we examined the level and function of MAIT cells in patients with rheumatic diseases. MAIT cell, cytokine, and programmed death-1 (PD-1) levels were measured by flow cytometry. Circulating MAIT cell levels were significantly reduced in systemic lupus erythematosus (SLE) and rheumatoid arthritis patients. In particular, this MAIT cell deficiency was more prominent in CD8(+) and double-negative T cell subsets, and significantly correlated with disease activity, such as SLE disease activity index and 28-joint disease activity score. Interestingly, MAIT cell frequency was significantly correlated with NKT cell frequency in SLE patients. IFN-γ production in MAIT cells was impaired in SLE patients, which was due to an intrinsic defect in the Ca(2+)/calcineurin/NFAT1 signaling pathway. In SLE patients, MAIT cells were poorly activated by α-galactosylceramide-stimulated NKT cells, thereby showing the dysfunction between MAIT cells and NKT cells. Notably, an elevated expression of PD-1 in MAIT cells and NKT cells was associated with SLE. In rheumatoid arthritis patients, MAIT cell levels were significantly higher in synovial fluid than in peripheral blood. Our study primarily demonstrates that MAIT cells are numerically and functionally deficient in SLE. In addition, we report a novel finding that this MAIT cell deficiency is associated with NKT cell deficiency and elevated PD-1 expression. These abnormalities possibly contribute to dysregulated mucosal immunity in SLE.

Downregulation of Runx2 by 1,25-Dihydroxyvitamin D3 Induces the Transdifferentiation of Osteoblasts to Adipocytes.

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) indirectly stimulates bone formation, but little is known about its direct effect on bone formation. In this study, we observed that 1,25(OH)2D3 enhances adipocyte differentiation, but inhibits osteoblast differentiation during osteogenesis. The positive role of 1,25(OH)2D3 in adipocyte differentiation was confirmed when murine osteoblasts were cultured in adipogenic medium. Additionally, 1,25(OH)2D3 enhanced the expression of adipocyte marker genes, but inhibited the expression of osteoblast marker genes in osteoblasts. The inhibition of osteoblast differentiation and promotion of adipocyte differentiation mediated by 1,25(OH)2D3 were compensated by Runx2 overexpression. Our results suggest that 1,25(OH)2D3 induces the transdifferentiation of osteoblasts to adipocytes via Runx2 downregulation in osteoblasts.

Comparison of Topical Cyclosporine and Diquafosol Treatment in Dry Eye.

PURPOSE: To compare the treatment effects of topical cyclosporine A (CsA) and diquafosol sodium (DQS) for the treatment of moderate to severe dry eye disease (DED). METHODS: This prospective, nonrandomized, comparative study involved 60 eyes of 60 patients with moderate to severe DED who were treated with topical CsA 0.05% (group 1, 31 patients) or DQS 3% (group 2, 29 patients) in addition to artificial tears for 3 months. Before treatment, and at 1 and 3 months after treatment, the Ocular Surface Disease Index, tear breakup time, Schirmer score, tear clearance rate, and corneal and conjunctival staining scores were compared. RESULTS: Significant improvements in Ocular Surface Disease Index score, tear clearance rate, and corneal staining score were observed 1 month after treatment in group 2 (p = 0.014, p = 0.002, and p < 0.001, respectively), when compared with group 1. However, no significant differences were observed between the two groups 3 months after treatment (p > 0.05). Tear breakup times were significantly higher in group 2 compared with group 1 for the duration of the study (p < 0.001). Three months after treatment, Schirmer score was significantly higher and conjunctival staining score was significantly lower in group 1 compared with group 2 (p < 0.001). CONCLUSIONS: Both topical CsA 0.05% and DQS 3% are effective in patients with moderate to severe DED. However, the timing and degree of therapeutic effects on tear film and ocular surface parameters, as well as symptoms, can be different between the two treatments.

Akt induces osteoclast differentiation through regulating the GSK3ß/NFATc1 signaling cascade.

SHIP is an SH2-containing inositol-5-phosphatase expressed in hematopoietic cells. It hydrolyzes the PI3K product PI(3,4,5)P(3) and blunts the PI3K-initiated signaling pathway. Although the PI3K/Akt pathway has been shown to be important for osteoclastogenesis, the molecular events involved in osteoclast differentiation have not been revealed. We demonstrate that Akt induces osteoclast differentiation through regulating the GSK3ß/NFATc1 signaling cascade. Inhibition of the PI3K by LY294002 reduces formation of osteoclasts and attenuates the expression of NFATc1, but not that of c-Fos. Conversely, overexpression of Akt in bone marrow-derived macrophages (BMMs) strongly induced NFATc1 expression without affecting c-Fos expression, suggesting that PI3K/Akt-mediated NFATc1 induction is independent of c-Fos during RANKL-induced osteoclastogenesis. In addition, we found that overexpression of Akt enhances formation of an inactive form of GSK3ß (phospho-GSK3ß) and nuclear localization of NFATc1, and that overexpression of a constitutively active form of GSK3ß attenuates osteoclast formation through downregulation of NFATc1. Furthermore, BMMs from SHIP knockout mice show the increased expression levels of phospho-Akt and phospho-GSK3ß, as well as the enhanced osteoclastogenesis, compared with wild type. However, overexpression of a constitutively active form of GSK3ß attenuates RANKL-induced osteoclast differentiation from SHIP-deficient BMMs. Our data suggest that the PI3K/Akt/GSK3ß/NFATc1 signaling axis plays an important role in RANKL-induced osteoclastogenesis.

Stanniocalcin 1 and 1,25-dihydroxyvitamin D3 cooperatively regulate bone mineralization by osteoblasts.

Stanniocalcin 1 (STC1) is a calcium- and phosphate-regulating hormone that is expressed in all tissues, including bone tissues, and is involved in calcium and phosphate homeostasis. Previously, STC1 expression was found to be increased by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] administration in renal proximal tubular cells. In this study, we investigated whether STC1 directly regulates osteoblast differentiation or reciprocally controls the effects of 1,25(OH)2D3 on osteoblasts to contribute to bone homeostasis. We found that STC1 inhibited osteoblast differentiation in vitro and bone morphogenetic protein 2 (BMP2)-induced ectopic bone formation in vivo. Moreover, 1,25(OH)2D3 increased STC1 expression through direct binding to the Stc1 promoter of the vitamin D receptor (VDR). STC1 activated the 1,25(OH)2D3-VDR signaling pathway through the upregulation of VDR expression mediated by the inhibition of Akt phosphorylation in osteoblasts. STC1 further increased the effects of 1,25(OH)2D3 on receptor activator of nuclear factor-κB ligand (RANKL) secretion and inhibited osteoblast differentiation by exhibiting a positive correlation with 1,25(OH)2D3. The long-bone phenotype of transgenic mice overexpressing STC1 specifically in osteoblasts was not significantly different from that of wild-type mice. However, compared with that in the wild-type mice, 1,25(OH)2D3 administration significantly decreased bone mass in the STC1 transgenic mice. Collectively, these results suggest that STC1 negatively regulates osteoblast differentiation and bone formation; however, the inhibitory effect of STC1 on osteoblasts is transient and can be reversed under normal conditions. Nevertheless, the synergistic effect of STC1 and 1,25(OH)2D3 through 1,25(OH)2D3 administration may reduce bone mass by inhibiting osteoblast differentiation.

The Role of Receptor Activator of Nuclear Factor-κB Ligand/Osteoprotegerin Ratio in Synovial Fluid as a Potential Marker for Periprosthetic Osteolysis Following Total Ankle Arthroplasty.

Background: Periprosthetic osteolysis is a prevalent complication following total ankle arthroplasty (TAA), implicating various cytokines in osteoclastogenesis as pivotal in this process. This study aimed to evaluate the relationship between osteolysis and the concentrations of osteoclastogenesis-related cytokines in synovial fluid and investigate its clinical value following TAA. Methods: Synovial fluid samples from 23 ankles that underwent revision surgery for osteolysis following TAA were analyzed as the osteolysis group. As a control group, we included synovial fluid samples obtained from 23 ankles during primary TAA for osteoarthritis. The receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) ratio in these samples was quantified using sandwich enzyme-linked immunosorbent assay techniques, and a bead-based multiplex immunoassay facilitated the detection of specific osteoclastogenesis-related cytokines. Results: RANKL levels averaged 487.9 pg/mL in 14 of 23 patients in the osteolysis group, with no detection in the control group's synovial fluid. Conversely, a significant reduction in OPG levels was observed in the osteolysis group (p = 0.002), resulting in a markedly higher mean RANKL/OPG ratio (0.23) relative to controls (p = 0.020). Moreover, the osteolysis group had increased concentrations of various osteoclastogenesis-related cytokines (tumor necrosis factor-α, interleukin [IL]-1ß, IL-6, IL-8, IP-10, and monocyte chemotactic protein-1) in the synovial fluid relative to the control group. Conclusions: Our results demonstrated that periprosthetic osteolysis was associated with osteoclastogenesis activation through an elevated RANKL/OPG ratio following TAA. We assume that RANKL and other osteoclastogenesis-related cytokines in the synovial fluid have clinical value as a potential marker for the development and progression of osteolysis following TAA.

Sestrin2 inhibits RANKL-induced osteoclastogenesis through AMPK activation and ROS inhibition.

Sestrins are stress-responsive proteins with antioxidant properties. They participate in cellular redox balance and protect against oxidative damage. This study investigated the effects of Sestrin2 (Sesn2) on osteoclast differentiation and function. Overexpressing Sesn2 in osteoclast precursor cells significantly inhibited receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis. This was assessed as reduced expression of various osteoclast markers, including c-Fos, nuclear factor of activated T cells 1 (NFATc1), osteoclast-associated receptor, tartrate-resistant acid phosphatase, and cathepsin K. Conversely, downregulation of Sesn2 produced the opposite effect. Mechanistically, Sesn2 overexpression enhanced AMPK activation and the nuclear translocation of nuclear factor erythroid-derived factor 2-related factor 2 (Nrf2), promoting antioxidant enzymes. Moreover, azithromycin (Azm) induced Sesn2 expression, which suppressed RANKL-induced osteoclast differentiation. Specifically, Azm treatment reduced RANKL-induced production of reactive oxygen species in osteoclasts. Furthermore, intraperitoneal administration of Azm ameliorated RANKL-induced bone loss by reducing osteoclast activity in mice. Taken together, our results suggested that Azm-induced Sesn2 act as a negative regulator of RANKL-induced osteoclast differentiation through the AMPK/NFATc1 signaling pathway. Concisely, targeting Sesn2 can be a potential pharmacological intervention in osteoporosis.

Natural killer T cell deficiency in active adult-onset Still's Disease: correlation of deficiency of natural killer T cells with dysfunction of natural killer cells.

OBJECTIVE: To examine the levels and functions of natural killer (NK) and natural killer T (NKT) cells, investigate relationships between NK and NKT cells, and determine the clinical relevance of NKT cell levels in patients with adult-onset Still's disease (AOSD). METHODS: Patients with active untreated AOSD (n = 20) and age- and sex-matched healthy controls (n = 20) were studied. NK and NKT cell levels were measured by flow cytometry. Peripheral blood mononuclear cells were cultured in vitro with α-galactosylceramide (αGalCer). NK cytotoxicity against K562 cells and proliferation indices of NKT cells were estimated by flow cytometry. RESULTS: Percentages and absolute numbers of NKT cells were significantly lower in the peripheral blood of AOSD patients than in that of healthy controls. Proliferative responses of NKT cells to αGalCer were also lower in patients, and this was found to be due to proinflammatory cytokines and NKT cell apoptosis. In addition, NK cytotoxicity was found to be significantly lower in patients than in healthy controls, but NK cell levels were comparable in the 2 groups. Notably, this NKT cell deficiency was found to be correlated with NK cell dysfunction and to reflect active disease status. Furthermore, αGalCer-mediated NK cytotoxicity, showing the interaction between NK and NKT cells, was significantly lower in AOSD patients than in healthy controls. CONCLUSION: These findings demonstrate that NK and NKT cell functions are defective in AOSD patients and suggest that these abnormalities contribute to innate immune dysfunction in AOSD.

v-ATPase V0 subunit d2-deficient mice exhibit impaired osteoclast fusion and increased bone formation.

Matrix-producing osteoblasts and bone-resorbing osteoclasts maintain bone homeostasis. Osteoclasts are multinucleated, giant cells of hematopoietic origin formed by the fusion of mononuclear pre-osteoclasts derived from myeloid cells. Fusion-mediated giant cell formation is critical for osteoclast maturation; without it, bone resorption is inefficient. To understand how osteoclasts differ from other myeloid lineage cells, we previously compared global mRNA expression patterns in these cells and identified genes of unknown function predominantly expressed in osteoclasts, one of which is the d2 isoform of vacuolar (H(+)) ATPase (v-ATPase) V(0) domain (Atp6v0d2). Here we show that inactivation of Atp6v0d2 in mice results in markedly increased bone mass due to defective osteoclasts and enhanced bone formation. Atp6v0d2 deficiency did not affect differentiation or the v-ATPase activity of osteoclasts. Rather, Atp6v0d2 was required for efficient pre-osteoclast fusion. Increased bone formation was probably due to osteoblast-extrinsic factors, as Atp6v02 was not expressed in osteoblasts and their differentiation ex vivo was not altered in the absence of Atp6v02. Our results identify Atp6v0d2 as a regulator of osteoclast fusion and bone formation, and provide genetic data showing that it is possible to simultaneously inhibit osteoclast maturation and stimulate bone formation by therapeutically targeting the function of a single gene.