TNF-alpha expression is transcriptionally regulated by RANK ligand

RANKL/RANK is required for cytokine-induced beta cell death; osteoprotegerin, a RANKL inhibitor, reverses rodent type 1 diabetes

Treatment for type 1 diabetes (T1D) requires stimulation of functional β cell regeneration and survival under stress. Previously, we showed that inhibition of the RANKL/RANK [receptor activator of nuclear factor kappa Β (NF-κB) ligand] pathway, by osteoprotegerin and the anti-osteoporotic drug denosumab, induces rodent and human β cell proliferation. We demonstrate that the RANK pathway mediates cytokine-induced rodent and human β cell death through RANK-TRAF6 interaction and induction of NF-κB activation. Osteoprotegerin and denosumab protected β cells against this cytotoxicity. In human immune cells, osteoprotegerin and denosumab reduce proinflammatory cytokines in activated T-cells by inhibiting RANKL-induced activation of monocytes. In vivo, osteoprotegerin reversed recent-onset T1D in nonobese diabetic/Ltj mice, reduced insulitis, improved glucose homeostasis, and increased plasma insulin, β cell proliferation, and mass in these mice. Serum from T1D subjects induced human β cell death and dysfunction, but not α cell death. Osteoprotegerin and denosumab reduced T1D serum-induced β cell cytotoxicity and dysfunction. Inhibiting RANKL/RANK could have therapeutic potential.

Role of PPARs in Progression of Anxiety: Literature Analysis and Signaling Pathways Reconstruction

Peroxisome proliferator-activated receptor (PPAR) group includes three isoforms encoded by PPARG, PPARA, and PPARD genes. High concentrations of PPARs are found in parts of the brain linked to anxiety development, including hippocampus and amygdala. Among three PPAR isoforms, PPARG demonstrates the highest expression in CNS, where it can be found in neurons, astrocytes, and glial cells. Herein, the highest PPARG expression occurs in amygdala. However, little is known considering possible connections between PPARs and anxiety behavior. We reviewed possible connections between PPARs and anxiety. We used the Pathway Studio software (Elsevier). Signal pathways were created according to previously developed algorithms. SNEA was performed in Pathway Studio. Current study revealed 14 PPAR-regulated proteins linked to anxiety. Possible mechanism of PPAR involvement in neuroinflammation protection is proposed. Signal pathway reconstruction and reviewing aimed to reveal possible connection between PPARG and CCK-ergic system was conducted. Said analysis revealed that PPARG-dependent regulation of MME and ACE peptidase expression may affect levels of nonhydrolysed, i.e., active CCK-4. Impairments in PPARG regulation and following MME and ACE peptidase expression impairments in amygdala may be the possible mechanism leading to pathological anxiety development, with brain CCK-4 accumulation being a key link. Literature data analysis and signal pathway reconstruction and reviewing revealed two possible mechanisms of peroxisome proliferator-activated receptors involvement in pathological anxiety: (1) cytokine expression and neuroinflammation mechanism and (2) regulation of peptidases targeted to anxiety-associated neuropeptides, primarily CCK-4, mechanism.

Overview of RAW264.7 for osteoclastogensis study: Phenotype and stimuli

Bone homeostasis is preserved by the balance of maintaining between the activity of osteogenesis and osteoclastogenesis. However, investigations for the osteoclastogenesis were hampered by considerable difficulties associated with isolating and culturing osteoclast in vivo. As the alternative, stimuli‐induced osteoclasts formation from RAW264.7 cells (RAW‐OCs) have gain its importance for extensively osteoclastogenic study of bone diseases, such as rheumatoid arthritis, osteoporosis, osteolysis and periodontitis. However, considering the RAW‐OCs have not yet been well‐characterized and RAW264.7 cells are polymorphic because of a diverse phenotype of the individual cells comprising this cell linage, and different fate associated with various stimuli contributions. Thus, in present study, we provide an overview for current knowledge of the phenotype of RAW264.7 cells, as well as the current understanding of the complicated interactions between various stimuli and RAW‐OCs in the light of the recent progress.

Crocin inhibits RANKL‑induced osteoclastogenesis by regulating JNK and NF‑κB signaling pathways

Receptor activator of nuclear factor‑κB ligand (RANKL), a member of the tumor necrosis factor receptor-ligand family, is a crucial factor involved in osteoclast differentiation. Crocin, a pharmacologically active component of Crocus sativus L., has been reported to attenuate ovariectomy‑induced osteoporosis in rats. However, the molecular mechanism underlying the effect of crocin on osteoclast formation remains to be determined. The present study aimed to investigate the effect of crocin on RANKL‑induced osteoclastogenesis and its underlying molecular mechanism. Results demonstrated that crocin decreased osteoclastogenesis in bone marrow‑derived macrophages (BMMs). In addition, the expression levels of osteoclast marker proteins were downregulated by crocin. Mechanistically, crocin inhibited RANKL‑induced activation of nuclear factor‑κB (NF‑κB) by suppressing inhibitor of κBα degradation and preventing NF‑κB p65 subunit nuclear translocation, and by activating c‑Jun N‑terminal kinase (JNK) in BMMs. In summary, the results of the present study suggested that crocin downregulates osteoclast differentiation via inhibition of JNK and NF‑κB signaling pathways. Thus, crocin may be a potential therapeutic agent for the treatment of osteoclast‑associated diseases, including osteoporosis.

Alpha-1 antitrypsin inhibits RANKL-induced osteoclast formation and functions

Osteoporosis is a global public health problem affecting more than 200 million people worldwide. We previously showed that treatment with alpha-1 antitrypsin (AAT), a multifunctional protein with anti-inflammatory properties, mitigated bone loss in an ovariectomized mouse model. However, the underlying mechanisms of the protective effect of AAT on bone tissue are largely unknown. In this study, we investigated the effect of AAT on osteoclast formation and function in vitro. Our results showed that AAT dose-dependently inhibited the formation of RANKL (receptor activator of nuclear factor κB ligand) induced osteoclasts derived from mouse bone marrow macrophages/monocyte (BMM) lineage cells and the murine macrophage cell line, RAW 264.7 cells. In order to elucidate the possible mechanisms underlying this inhibition, we tested the effect of AAT on the gene expression of cell surface molecules, transcription factors, and cytokines associated with osteoclast formation. We showed that AAT inhibited M-CSF (macrophage colony-stimulating factor) induced cell surface RANK expression in osteoclast precursor cells. In addition, AAT inhibited RANKL-induced TNF-α production, cell surface CD9 expression, and dendritic cell-specific transmembrane protein (DC-STAMP) gene expression. Importantly, AAT treatment significantly inhibited osteoclast-associated mineral resorption. Together, these results uncovered new mechanisms for the protective effects of AAT and strongly support the notion that AAT has therapeutic potential for the treatment of osteoporosis.

TNFα Increases RANKL Expression via PGE₂-Induced Activation of NFATc1

Tumor necrosis factor α (TNFα) is known to upregulate the expression of receptor activator of NF-κB ligand (RANKL). We investigated the role of the calcineurin/nuclear factor of activated T-cells (NFAT) signaling pathway in TNFα-induced RANKL expression in C2C12 and primary cultured mouse calvarial cells. TNFα-induced RANKL expression was blocked by the calcineurin/NFAT pathway inhibitors. TNFα increased NFAT transcriptional activity and subsequent RANKL promoter binding. Mutations in the NFAT-binding element (MT(N)) suppressed TNFα-induced RANKL promoter activity. TNFα increased prostaglandin E2 (PGE₂) production, which in turn enhanced NFAT transcriptional activity and binding to the RANKL promoter. MT(N) suppressed PGE₂-induced RANKL promoter activity. TNFα and PGE₂ increased the expression of RANKL, NFAT cytoplasmic-1 (NFATc1), cAMP response element-binding protein (CREB), and cyclooxygenase 2 (COX2); which increment was suppressed by indomethacin, a COX inhibitor. Mutations in the CRE-like element blocked PGE₂-induced RANKL promoter activity. PGE₂ induced the binding of CREB to the RANKL promoter, whereas TNFα increased the binding of both CREB and NFATc1 to this promoter through a process blocked by indomethacin. The PGE₂ receptor antagonists AH6809 and AH23848 blocked TNFα-induced expression of RANKL, NFATc1, and CREB; transcriptional activity of NFAT; and binding of NFATc1 or CREB to the RANKL promoter. These results suggest that TNFα-induced RANKL expression depends on PGE₂ production and subsequent transcriptional activation/enhanced binding of NFATc1 and CREB to the RANKL promoter.

Soluble RANKL Cleaved from Activated Lymphocytes by TNF-α-Converting Enzyme Contributes to Osteoclastogenesis in Periodontitis

Host immune responses play a key role in promoting bone resorption in periodontitis via receptor activator of NF-κB ligand (RANKL)-dependent osteoclastogenesis. Both membrane-bound RANKL (mRANKL) expressed on lymphocytes and soluble RANKL (sRANKL) are found in periodontal lesions. However, the underlying mechanism and cellular source of sRANKL release and its biological role in periodontitis are unclear. TNF-α-converting enzyme (TACE) is reported to cleave the following: 1) precursor TNF-α with release of mature, soluble TNF-α and 2) mRANKL with release of sRANKL. Both soluble TNF-α and sRANKL are found in the periodontitis lesion, leading to the hypothesis that TACE expressed on lymphocytes is engaged in RANKL shedding and that the resulting sRANKL induces osteoclastogenesis. In the current study, upon stimulating PBLs with mitogens in vitro, RANKL expression, sRANKL secretion, and TACE expression were all upregulated. Among the four putative mRANKL sheddases examined in neutralization assays, TACE was the only functional sheddase able to cleave mRANKL expressed on PBL. Moreover, PBL culture supernatant stimulated with mitogens in the presence of anti-TACE Ab or anti-RANKL Ab showed a marked reduction of osteoclastogenesis from osteoclast precursors, indicating that TACE-mediated sRANKL may possess sufficient osteoclastogenic activity. According to double-color confocal microscopy, B cells expressed a more pronounced level of RANKL and TACE expression than T cells or monocytes in periodontally diseased gingiva. Conditioned medium of patients' gingival lymphocyte culture increased in vitro osteoclastogenic activity, which was suppressed by the addition of anti-TACE Ab and anti-RANKL Ab. Therefore, TACE-mediated cleavage of sRANKL from activated lymphocytes, especially B cells, can promote osteoclastogenesis in periodontitis.

TNFα signaling regulates cystic epithelial cell proliferation through Akt/mTOR and ERK/MAPK/Cdk2 mediated Id2 signaling

Tumor necrosis factor alpha (TNFα) is present in cyst fluid and promotes cyst growth in autosomal dominant polycystic kidney disease (ADPKD). However, the cross-talk between TNFα and PKD associated signaling pathways remains elusive. In this study, we found that stimulation of renal epithelial cells with TNFα or RANKL (receptor activator of NF-κB ligand), a member of the TNFα cytokine family, activated either the PI3K pathway, leading to AKT and mTOR mediated the increase of Id2 protein, or MAPK and Cdk2 to induce Id2 nuclear translocation. The effects of TNFα/RANKL on increasing Id2 protein and its nuclear translocation caused significantly decreased mRNA and protein levels of the Cdk inhibitor p21, allowing increased cell proliferation. TNFα levels increase in cystic kidneys in response to macrophage infiltration and thus might contribute to cyst growth and enlargement during the progression of disease. As such, this study elucidates a novel mechanism for TNFα signaling in regulating cystic renal epithelial cell proliferation in ADPKD.

Miconazole inhibits receptor activator of nuclear factor-κB ligand-mediated osteoclast formation and function

Osteoclasts are responsible for bone erosion in diseases as diverse as osteoporosis, periodontitis, and rheumatoid arthritis. Antifungal products have received recent attention as potential therapeutic and preventative drugs in human disease. Since little is known about the action of miconazole, an antifungal imidazole, on bone metabolism, we investigated the effects of miconazole on osteoclast formation using mouse bone marrow macrophages (BMMs). Miconazole inhibited RANKL-induced osteoclast formation in a dose-dependent manner without cytotoxicity. Furthermore, miconazole inhibited the bone resorptive activity of osteoclasts. Miconazole suppressed RANKL-induced expression of c-Fos and NFATc1, two essential transcription factors for osteoclast differentiation. Miconazole seemed to inhibit osteoclast formation MAPK pathways as well as Blimp1 through MafB expression. Miconazole also inhibited RANKL-induced expression of the pro-inflammatory cytokines, COX-2 and iNOS. In accordance with the in vitro study, miconazole reduced lipopolysaccharide-induced osteoclast formation in vivo. Therefore, miconazole exerted an inhibitory effect on osteoclast formation in vitro and in vivo. It could be useful for the treatment of bone diseases associated with excessive bone resorption.

Dextromethorphan inhibits osteoclast differentiation by suppressing RANKL-induced nuclear factor-κB activation

Dextromethorphan (DXM), a commonly used antitussive, is a dextrorotatory morphinan. Here, we report that DXM inhibits the receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis and bone resorption by abrogating the activation of NF-κB signalling in vitro. Oral administration of DXM ameliorates ovariectomy (OVX)-induced osteoporosis in vivo.

INTRODUCTION

DXM was reported to possess anti-inflammatory properties through inhibition of the release of pro-inflammatory factors. However, the potential role and action mechanism of DXM on osteoclasts and osteoblasts remain unclear. In this study, in vitro and in vivo studies were performed to investigate the potential effects of DXM on osteoclastogenesis and OVX-induced bone loss.

METHODS

Osteoclastogenesis was examined by the TRAP staining, pit resorption, TNF-α release, and CCR2 and CALCR gene expression. Osteoblast differentiation was analyzed by calcium deposition. Osteogenic and adipogenic genes were measured by real-time PCR. Signaling pathways were explored using Western blot. ICR mice were used in an OVX-induced osteoporosis model. Tibiae were measured by µCT and serum markers were examined with ELISA kits.

RESULTS

DXM inhibited RANKL-induced osteoclastogenesis. DXM mainly inhibited osteoclastogenesis via abrogation of IKK-IκBα-NF-κB pathways. However, a higher dosage of DXM antagonized the differentiation of osteoblasts via the inhibition of osteogenic signals and increase of adipogenic signals. Oral administration of DXM (20 mg/kg/day) partially reduced trabecular bone loss in ovariectomized mice.

CONCLUSION

DXM inhibits osteoclast differentiation and activity by affecting NF-κB signaling. Therefore, DXM at suitable doses may have new therapeutic applications for the treatment of diseases associated with excessive osteoclastic activity.

Reactive oxygen species and the cardiovascular system

Ever since the discovery of free radicals, many hypotheses on the deleterious actions of reactive oxygen species (ROS) have been proposed. However, increasing evidence advocates the necessity of ROS for cellular homeostasis. ROS are generated as inherent by-products of aerobic metabolism and are tightly controlled by antioxidants. Conversely, when produced in excess or when antioxidants are depleted, ROS can inflict damage to lipids, proteins, and DNA. Such a state of oxidative stress is associated with many pathological conditions and closely correlated to oxygen consumption. Although the deleterious effects of ROS can potentially be reduced by restoring the imbalance between production and clearance of ROS through administration of antioxidants (AOs), the dosage and type of AOs should be tailored to the location and nature of oxidative stress. This paper describes several pathways of ROS signaling in cellular homeostasis. Further, we review the function of ROS in cardiovascular pathology and the effects of AOs on cardiovascular outcomes with emphasis on the so-called oxidative paradox.

Modulation of osteoclast function in bone by the immune system

Osteoclast differentiation and function is regulated by cellular signals and cytokines that also play significant roles in the immune system. There is much scope, therefore, for immune cell influence on osteoclasts and bone metabolism. Many examples of this have been identified and T cells in particular are a source of factors affecting osteoclast formation and activity, a number which have either pro-osteolytic or anti-osteolytic actions depending on the cellular and microenvironmental context. For example, IL-12 and IL-18 participate in inflammatory processes that can lead to highly destructive osteolysis, yet these cytokines potently block osteoclast formation through mediation of T cells. IL-23 participates in chronic inflammatory processes, but lack of this cytokine results in reduced bone mass in mice, pointing to an influence on physiological regulation of bone mass. Such insights suggest that therapies that target immune responses may significantly influence osteolysis. Investigations into links between the immune system and bone metabolism are thus uncovering important information about the functioning of both systems.

Role of TNF-alpha in vascular dysfunction

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.

Interleukin-10 inhibits tumor necrosis factor-α production in lipopolysaccharide-stimulated RAW 264.7 cells through reduced MyD88 expression

The mechanism of interleukin (IL)-10-mediated inhibition of tumor necrosis factor (TNF)-α production was studied by lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells. IL-10 inhibited TNF-α production transiently at an early stage after LPS stimulation. IL-10 inhibited the activation of nuclear factor (NF)-κB, p38 and stress-activated protein kinase (SAPK) in LPS-stimulated RAW 264.7 cells. Although the level of MyD88 protein increased in response to LPS, IL-10 prevented the LPS-induced MyD88 augmentation. There was no significant difference in the MyD88 mRNA expression between the cells pretreated with or without IL-10 in response to LPS. Therefore, IL-10 was suggested to inhibit LPS-induced TNF-α production via reduced MyD88 expression.

Systems level analysis of osteoclastogenesis reveals intrinsic and extrinsic regulatory interactions

Osteoclasts are bone-resorbing cells derived from the myeloid lineage that play a central role in bone remodeling and inflammatory bone erosion diseases. The receptor activator of NF-kappaB ligand (RANKL) produced by osteoblasts and activated immune cells initiates the development of osteoclasts in the bone marrow. Using time series gene expression data, the intrinsic processes and the extrinsic factors that control osteoclastogenesis were identified. The gene expression profiles display distinct commitment and differentiation phases. Analysis of the time course revealed several mechanistic details, including the complex role of cholesterol in osteoclast development. Epistatic interactions and the coordination between cellular processes that regulate development were inferred from the coexpression network. The coexpression network indicated that osteoclasts induce angiogenesis and recruit T-cells to the site of osteoclastogenesis early in the commitment phase. The resulting model provides an essential framework for a better understanding of the epigenetic program of osteoclastogenesis.

Regulation of osteoclast differentiation and function by phosphate: potential role of osteoclasts in the skeletal abnormalities in hypophosphatemic conditions

Mice fed with a low Pi diet exhibited decreased osteoclast number. Hyp mice also showed decreased osteoclasts, and high Pi reversed it. Low Pi reduced osteoclast formation and bone resorption in vitro. Hypophosphatemia may suppress osteoclast differentiation/function, leading to skeletal abnormalities.

INTRODUCTION

Skeletal abnormalities seen in hypophosphatemic disorders indicate a critical role of phosphate (Pi) in skeletogenesis. However, the role of osteoclasts in the pathogenesis of the disturbed skeletogenesis is unclear.

MATERIALS AND METHODS

Mice fed with a low-Pi diet and Hyp mice that are characterized by hypophosphatemia and impaired osteogenesis were studied. Effects of Pi on osteoclast formation and bone resorption were also examined in vitro.

RESULTS

Histomorphometric examination showed that mice on a low-Pi diet exhibited decreased osteoclast number. Furthermore, osteoclast number in Hyp mice was also decreased compared with wildtype (WT) mice. Of note, feeding of Hyp mice with high-Pi diet significantly reversed hypophosphatemia, improved disturbed osteogenesis, and increased osteoclast number. Osteoclast-like cell (OLC) formation and bone resorption in Hyp bone marrow cells was not different from WT bone marrow cells. On the other hand, OLC formation and bone resorption were decreased in conjunction with reduced mRNA expression of RANKL in WT bone marrow cells cultured in the medium containing low Pi (0.5 mM). Recombinant human matrix extracellular phosphoglycoprotein (MEPE), a candidate for phosphatonin, also decreased osteoclast formation, whereas fibroblast growth factor 23 (FGF23), another phosphatonin candidate, showed no effects.

CONCLUSIONS

Our results suggest that Pi controls the differentiation and function of osteoclasts. These actions of Pi on osteoclasts may be associated with the pathogenesis of the skeletal abnormalities in hypophosphatemic disorders.

Toll-like receptor 9 ligand blocks osteoclast differentiation through induction of phosphatase

CpG-ODN, in addition to stimulation of osteoclastogenic signals in early osteoclast precursors, also induces phosphatase, shifting the pattern of ERK phosphorylation from sustained to transient. This shift results in the degradation of c-fos, an essential molecule for osteoclast differentiation. Therefore, CpG-ODN blocks osteoclast differentiation.

INTRODUCTION

Activation of either Toll-like receptor 9 (TLR9) or RANK induces similar responses in osteoclast precursors. Paradoxically, activation of TLR9 results in inhibition of RANKL-induced osteoclastogenesis.

MATERIALS AND METHODS

We used bone marrow-derived osteoclast precursors. Analyses of signaling molecules phosphorylation were performed using Western blotting. Different levels of gene expression analyses were performed using RT-PCR, Northern, and run-on analyses (for RNA), and EMSA, Western, and pulse-chase experiments (for protein). Phosphatase activity was measured spectrophotometrically.

RESULTS

We found that RANKL and TLR9 ligand, oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG-ODN), induce sustained and transient extracellular signal-regulated kinase (ERK) phosphorylation, respectively. Furthermore, together they induce a transient phosphorylation of ERK. The duration of ERK phosphorylation is a key factor in determining induction of c-fos, a protein critical for osteoclastogenesis. Indeed, we found that CpG-ODN does not induce c-fos and inhibits its induction by RANKL by enhancing c-fos mRNA and protein degradation. Our observation that CpG-ODN, but not RANKL, induces the expression of the phosphatase PP2A suggests that CpG-ODN exerts its inhibitory activity by induction of ERK dephosphorylation. Moreover, together with the phosphatase inhibitor okadaic acid, CpG-ODN induces sustained ERK phosphorylation and c-fos expression.

CONCLUSIONS

Our findings suggest that the increased rate of c-fos degradation by the TLR9 ligand mediates the inhibition of RANKL-induced osteoclast differentiation. The TLR9 ligand, through induction of dephosphorylation, prevents the sustained ERK phosphorylation needed for maintaining high c-fos levels that are essential for osteoclast differentiation.

Osteochondral repair in synovial joints

PURPOSE OF REVIEW

One of the major challenges in rheumatology remains the induction of osteochondral repair in synovial joints. Remarkable progress has been made in controlling the inflammatory pathways of chronic synovitis and tissue damage in rheumatoid arthritis and spondyloarthropathy. Here, we provide an overview of the current knowledge on the mechanisms involved in osteochondral repair in degenerative joint diseases, as well as in immune mediated inflammatory arthritides, with special emphasis on tumor necrosis factor alpha and IL-1.

RECENT FINDINGS

Homeostasis of articular cartilage and subchondral bone are essential for maintaining the integrity of osteochondral structures within synovial joints. This is achieved by the regulation of a delicate balance between anabolic and catabolic signals. In articular cartilage one cell type, the chondrocyte, is responsible for regulation of homeostasis. In bone, however, two distinct cell types, osteoblasts and osteoclasts, are responsible for anabolic and catabolic pathways, respectively. In inflammatory joint disorders, this tight regulation is profoundly dysregulated, with tumor necrosis factor alpha acting as an important catalyst of a disturbed homeostasis, together with IL-1. Targeting these cytokines may restore the intrinsic repair capacity of osteochondral structures.

SUMMARY

To restore catabolic cytokine balances appears to be a suitable strategy to promote osteochondral repair.

RANKL-stimulated TNFα production in osteoclast precursor cells promotes osteoclastogenesis by modulating RANK signaling pathways

Although TNFalpha is known to be an important factor for bone resorption, particularly in inflammatory bone diseases, the relevance between RANKL and TNFalpha in osteoclastogenesis remains unclear. In this study we examined the mechanism of TNFalpha induced osteoclastogenesis and its downstream signaling. We show that osteoclastogenesis is suppressed by anti-TNFalpha- and anti-TNF receptor type I (TNFRI)-antibodies and in TNFalpha- and TNFRI-deficient mice using in vitro culture systems: (1) co-culture of mouse spleen derived osteoclast precursor cells (pOCs) with osteoblasts, (2) pure pOC culture and (3) RAW264.7 cells in presence of RANKL. Furthermore, TNFalpha production in pOCs was stimulated by RANKL. Endogenous TNFalpha in pOCs induced c-Fos and NFATc1. Expression rates of NFATc1 and c-Fos were significantly decreased in TNFalpha- and TNFRI-deficient pOCs during osteoclastogenesis. These results indicate that TNFalpha is induced by RANKL in pOCs and serves as an autocrine factor promoting osteoclastogenesis through c-Fos and NFATc1 activation.

Tumor necrosis factor-alpha induces endothelial dysfunction in Lepr(db) mice

BACKGROUND

We hypothesized that the inflammatory cytokine tumor necrosis factor-alpha (TNF) produces endothelial dysfunction in type 2 diabetes.

METHODS AND RESULTS

In m Lepr(db) control mice, sodium nitroprusside and acetylcholine induced dose-dependent vasodilation, and dilation to acetylcholine was blocked by the NO synthase inhibitor N(G)-monomethyl-L-arginine. In type 2 diabetic (Lepr(db)) mice, acetylcholine- or flow-induced dilation was blunted compared with m Lepr(db), but sodium nitroprusside produced comparable dilation. In Lepr(db) mice null for TNF (db(TNF-)/db(TNF-)), dilation to acetylcholine or flow was greater than in diabetic Lepr(db) mice and comparable to that in controls. Plasma concentration of TNF was significantly increased in Lepr(db) versus m Lepr(db) mice. Real-time polymerase chain reaction and Western blotting showed that mRNA and protein expression of TNF and nuclear factor-kappaB were higher in Lepr(db) mice than in controls. Administration of anti-TNF or soluble receptor of advanced glycation end products attenuated nuclear factor-kappaB and TNF expression in the Lepr(db) mice. Immunostaining results show that TNF in mouse heart is localized predominantly in vascular smooth muscle cells rather than in endothelial cells and macrophages. Superoxide generation was elevated in vessels from Lepr(db) mice versus controls. Administration of the superoxide scavenger TEMPOL, NAD(P)H oxidase inhibitor (apocynin), or anti-TNF restored endothelium-dependent dilation in Lepr(db) mice. NAD(P)H oxidase activity, protein expression of nitrotyrosine, and hydrogen peroxide production were increased in Lepr(db) mice (compared with controls), but these variables were restored to control levels by anti-TNF.

CONCLUSIONS

Advanced glycation end products/receptor of advanced glycation end products and nuclear factor-kappaB signaling play pivotal roles in TNF expression through an increase in circulating and/or local vascular TNF production in the Lepr(db) mouse with type 2 diabetes. Increases in TNF expression induce activation of NAD(P)H oxidase and production of reactive oxidative species, leading to endothelial dysfunction in type 2 diabetes.

Concise Review: Embryonic Stem Cells: A New Tool to Study Osteoblast and Osteoclast Differentiation

Bone remodeling involves synthesis of organic matrix by osteoblasts and bone resorption by osteoclasts. A tight collaboration between these two cell types is essential to maintain a physiological bone homeostasis. Thus, osteoblasts control bone-resorbing activities and are also involved in osteoclast differentiation. Any disturbance between these effectors leads to the development of skeletal abnormalities and/or bone diseases. In this context, the determination of key genes involved in bone cell differentiation is a new challenge to treat any skeletal disorders. Different models are used to study the differentiation process of these cells, but all of them use pre-engaged progenitor cells, allowing us to study only the latest stages of the differentiation. Embryonic stem (ES) cells come from the inner mass of the blastocyst prior its implantation to the uterine wall. Because of their capacity to differentiate into all germ layers, and so into all tissues of the body, ES cells represent the best model by which to study earliest stages of bone cell differentiation. Osteoblasts are generated by two methods, one including the generation of embryoid body, the other not. Mineralizing cells are obtained after 2 weeks of culture and express all the specific osteoblastic markers (alkaline phosphatase, type I collagen, osteocalcin, and others). Osteoclasts are generated from a single-cell suspension of ES cells seeded on a feeder monolayer, and bone-resorbing cells expressing osteoclastic markers such as tartrate-resistant alkaline phosphatase or receptor activator of nuclear factor kappaB are obtained within 11 days. The aim of this review is to present recent discoveries and advances in the differentiation of both osteoblasts and osteoclasts from ES cells.

Functional link between TNF biosynthesis and CaM-dependent activation of inducible nitric oxide synthase in RAW 264.7 macrophages

Inflammatory responses stimulated by bacterial endotoxin LPS involve Ca2+-mediated signaling, yet the cellular sensors that determine cell fate in response to LPS remain poorly understood. We report that exposure of RAW 264.7 macrophage-like cells to LPS induces a rapid increase in CaM abundance, which is associated with the modulation of the inflammatory response. Increases in CaM abundance precede nuclear localization of key transcription factors (i.e., NF-κB p65 subunit, phospho-c-Jun, Sp1) and subsequent increases in the proinflammatory cytokine TNF-α and inducible nitric oxide synthase (iNOS). Cellular apoptosis after LPS challenge is blocked upon inhibition of iNOS activity using the pharmacological inhibitor 1400W. LPS-mediated iNOS expression and apoptosis also were inhibited by siRNA-mediated silencing of TNF induction, indicating TNF induction both precedes and is necessary for subsequent regulation of iNOS expression. Increasing the level of cellular CaM by stable transfection results in reductions in LPS-induced expression of TNF and iNOS, along with reduced activation of their transcriptional regulators and concomitant protection against apoptosis. Thus the level of CaM available for Ca2+-dependent signaling regulation plays a key role in determining the expression of the proinflammatory and proapoptotic cascade during cellular activation by LPS. These results indicate a previously unrecognized central role for CaM in maintaining cellular homeostasis in response to LPS such that, under resting conditions, cellular concentrations of CaM are sufficient to inhibit the biosynthesis of proinflammatory mediators associated with macrophage activation. Although CaM and iNOS protein levels are coordinately increased as part of the oxidative burst, limiting cellular concentrations of CaM due to association with iNOS (and other high-affinity binders) commit the cell to an unchecked inflammatory cascade leading to apoptosis.

Inhibitor-kappaB kinase-beta regulates LPS-induced TNF-alpha production in cardiac myocytes through modulation of NF-kappaB p65 subunit phosphorylation

TNF-alpha is recognized as a significant contributor to myocardial dysfunction. Although several studies suggest that members of the NF-kappaB family of transcription factors are essential regulators of myocardial TNF-alpha gene expression, recent developments in our understanding of the modulation of NF-kappaB activity through posttranslational modification of NF-kappaB subunits suggest that the present view of NF-kappaB-dependent cytokine expression in heart is incomplete. Therefore, the goal of the present study was to examine the role of p65 subunit phosphorylation in the regulation of TNF-alpha production in cultured neonatal ventricular myocytes. Bacterial LPS-induced TNF-alpha production is accompanied by a 12-fold increase in phosphorylation of p65 at Ser536, a modification associated with enhancement of p65 transactivation potential. Pharmacological inhibition of IKK-beta reduced LPS-induced TNF-alpha production 38-fold, TNF-alpha mRNA levels 6-fold, and IkappaB-alpha phosphorylation 5-fold and degraded IkappaB-alpha 2-fold and p65 phosphorylation 6-fold. Overexpression of dominant-negative p65 reduced TNF-alpha production 3.5-fold, whereas overexpression of dominant-negative IKK-beta reduced LPS-induced TNF-alpha production 2-fold and p65 phosphorylation 2-fold. Overexpression of dominant-negative IKK-alpha had no effect on p65 phosphorylation or TNF-alpha production, revealing that IKK-beta, not IKK-alpha, plays a central role in regulation of p65 phosphorylation at Ser536 and TNF-alpha production in heart. Finally, we demonstrated, using a chromatin immunoprecipitation assay, that LPS stimulates recruitment of Ser536-phosphorylated p65 to the TNF-alpha gene promoter in cardiac myocytes. Taken together, these data provide compelling evidence for the role of NF-kappaB signaling in TNF-alpha gene expression in heart and highlight the importance of this proinflammatory gene-regulatory pathway as a potential therapeutic target in the management of cytokine-induced myocardial dysfunction.

Organization of transcriptional regulatory machinery in osteoclast nuclei: compartmentalization of Runx1

The osteoclast is a highly polarized multinucleated cell that resorbs bone. Using high resolution immunofluorescence microscopy, we demonstrated that all nuclei of an osteoclast are transcriptionally active. Each nucleus within the osteoclast contains punctately organized microenvironments where regulatory complexes that support transcriptional and post-transcriptional control reside. Functional equivalency of osteoclast nuclei is reflected by similar representation of regulatory proteins that support ribosomal RNA synthesis (nucleolin), mRNA transcription (RNA polymerase II, bromouridine triphosphate), processing of gene transcripts (SC35), signal transduction (NF-kappaB), and phenotypic gene expression (Runx1). Our results establish that gene regulatory machinery is architecturally associated and compartmentalized within intranuclear microenvironments of the multiple nuclei of osteoclasts to support physiologically responsive modifications in cellular structural and functional properties.