Regulation of bone mass and osteoclast function depend on the F-actin modulator SWAP-70

The F-actin bundler SWAP-70 promotes tumor metastasis

Dynamic rearrangements of the F-actin cytoskeleton are a hallmark of tumor metastasis. Thus, proteins that govern F-actin rearrangements are of major interest for understanding metastasis and potential therapies. We hypothesized that the unique F-actin binding and bundling protein SWAP-70 contributes importantly to metastasis. Orthotopic, ectopic, and short-term tail vein injection mouse breast and lung cancer models revealed a strong positive dependence of lung and bone metastasis on SWAP-70. Breast cancer cell growth, migration, adhesion, and invasion assays revealed SWAP-70's key role in these metastasis-related cell features and the requirement for SWAP-70 to bind F-actin. Biophysical experiments showed that tumor cell stiffness and deformability are negatively modulated by SWAP-70. Together, we present a hitherto undescribed, unique F-actin modulator as an important contributor to tumor metastasis.

Artemisinic acid attenuates osteoclast formation and titanium particle-induced osteolysis via inhibition of RANKL-induced ROS accumulation and MAPK and NF-κB signaling pathways

Periprosthetic osteolysis (PPO) is the most common cause of joint arthroplasty failure. Its progression involves both biological and mechanical factors. Osteoclastogenesis induced by wear from debris-cell interactions, ultimately leading to excessive bone erosion, is considered the primary cause of PPO; therefore, targeting osteoclasts is a promising treatment approach. Currently available drugs have various side effects and limitations. Artemisinic acid (ArA) is a sesquiterpene isolated from the traditional herb Artemisia annua L. that has various pharmacological effects, such as antimalarial, anti-inflammatory, and antioxidant activities. Therefore, this study was aimed at investigating the effect of ArA on osteoclast formation and bone resorption function in vitro, as well as wear particle-induced osteolysis in vivo, and to explore its molecular mechanism of action. Here, we report that ArA inhibits RANKL-stimulated osteoclast formation and function. Mechanistically, ArA suppresses intracellular reactive oxygen species levels by activating the antioxidant response via nuclear factor erythroid-2-related factor 2 (Nrf2) pathway upregulation. It also inhibits the mitogen-activated kinases (MAPK) and nuclear factor-κB (NF-κB) pathways, as well as the transcription and expression of NFATc1 and c-Fos. In vivo experiments demonstrated that ArA reduces osteoclast formation and alleviates titanium particle-induced calvarial osteolysis. Collectively, our study highlights that ArA, with its osteoprotective and antioxidant effects, is a promising therapeutic agent for preventing and treating PPO and other osteoclast-mediated osteolytic diseases.

The Role of Rosavin in the Pathophysiology of Bone Metabolism

Rosavin, a phenylpropanoid in Rhodiola rosea's rhizome, and an adaptogen, is known for enhancing the body's response to environmental stress. It significantly affects cellular metabolism in health and many diseases, particularly influencing bone tissue metabolism. In vitro, rosavin inhibits osteoclastogenesis, disrupts F-actin ring formation, and reduces the expression of osteoclastogenesis-related genes such as cathepsin K, calcitonin receptor (CTR), tumor necrosis factor receptor-associated factor 6 (TRAF6), tartrate-resistant acid phosphatase (TRAP), and matrix metallopeptidase 9 (MMP-9). It also impedes the nuclear factor of activated T-cell cytoplasmic 1 (NFATc1), c-Fos, the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and mitogen-activated protein kinase (MAPK) signaling pathways and blocks phosphorylation processes crucial for bone resorption. Moreover, rosavin promotes osteogenesis and osteoblast differentiation and increases mouse runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) expression. In vivo studies show its effectiveness in enhancing bone mineral density (BMD) in postmenopausal osteoporosis (PMOP) mice, restraining osteoclast maturation, and increasing the active osteoblast percentage in bone tissue. It modulates mRNA expressions by increasing eukaryotic translation elongation factor 2 (EEF2) and decreasing histone deacetylase 1 (HDAC1), thereby activating osteoprotective epigenetic mechanisms, and alters many serum markers, including decreasing cross-linked C-telopeptide of type I collagen (CTX-1), tartrate-resistant acid phosphatase 5b (TRACP5b), receptor activator for nuclear factor κ B ligand (RANKL), macrophage-colony-stimulating factor (M-CSF), and TRAP, while increasing alkaline phosphatase (ALP) and OCN. Additionally, when combined with zinc and probiotics, it reduces pro-osteoporotic matrix metallopeptidase 3 (MMP-3), interleukin 6 (IL-6), and tumor necrosis factor α (TNF-α), and enhances anti-osteoporotic interleukin 10 (IL-10) and tissue inhibitor of metalloproteinase 3 (TIMP3) expressions. This paper aims to systematically review rosavin's impact on bone tissue metabolism, exploring its potential in osteoporosis prevention and treatment, and suggesting future research directions.

Cilengitide inhibits osteoclast adhesion through blocking the αvβ3-mediated FAK/Src signaling pathway

The remodeling of actin cytoskeleton of osteoclasts on the bone matrix is essential for osteoclastic resorption activity. A specific regulator of the osteoclast cytoskeleton, integrin αvβ3, is known to provide a key role in the degradation of mineralized bone matrixes. Cilengitide is a potent inhibitor of integrins and is capable of affecting αvβ3 receptors, and has anti-tumor and anti-angiogenic and apoptosis-inducing effects. However, its function on osteoclasts is not fully understood. Here, the cilengitide role on nuclear factor κB ligand-receptor activator (RANKL)-induced osteoclasts was explored. Cells were cultured with varying concentrations of cilengitide (0,0.002,0.2 and 20 μM) for 7 days, followed by detected via Cell Counting Kit-8, staining for tartrate resistant acid phosphatase (TRAP), F-actin ring formation, bone resorption assays, adhesion assays, immunoblotting assays, and real-time fluorescent quantitative PCR. Results demonstrated that cilengitide effectively restrained the functionality and formation of osteoclasts in a concentration-dependent manner, without causing any cytotoxic effects. Mechanistically, cilengitide inhibited osteoclast-relevant genes expression; meanwhile, cilengitide downregulated the expression of key signaling molecules associated with the osteoclast cytoskeleton, including focal adhesion kinase (FAK), integrin αvβ3 and c-Src. Therefore, this results have confirmed that cilengitide regulates osteoclast activity by blocking the integrin αvβ3 signal pathway resulting in diminished adhesion and bone resorption of osteoclasts.

Reversing the imbalance in bone homeostasis via sustained release of SIRT-1 agonist to promote bone healing under osteoporotic condition

The imbalance of bone homeostasis is the root cause of osteoporosis. However current therapeutic approaches mainly focus on either anabolic or catabolic pathways, which often fail to turn the imbalanced bone metabolism around. Herein we reported that a SIRT-1 agonist mediated molecular therapeutic strategy to reverse the imbalance in bone homeostasis by simultaneously regulating osteogenesis and osteoclastogenesis via locally sustained release of SRT2104 from mineral coated acellular matrix microparticles. Immobilization of SRT2104 on mineral coating (MAM/SRT) harnessing their electrostatic interactions resulted in sustained release of SIRT-1 agonist for over 30 days. MAM/SRT not only enhanced osteogenic differentiation and mineralization, but also attenuated the formation and function of excessive osteoclasts via integrating multiple vital upstream signals (β-catenin, FoxOs, Runx2, NFATc1, etc.) in vitro. Osteoporosis animal model also validated that it accelerated osteoporotic bone healing and improved osseointegration of the surrounding bone. Overall, our work proposes a promising strategy to treat osteoporotic bone defects by reversing the imbalance in bone homeostasis using designated small molecule drug delivery systems.

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A mineral coated acellular matrix microcarriers sustainably release SIRT2104 more than 30 days.

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This drug delivery system regulates osteogenesis and osteoclastogenesis.

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It can accelerate osteoporotic bone healing by reversing the imbalance in bone homeostasis.

Stress deprivation of tendon explants or Tpm3.1 inhibition in tendon cells reduces F-actin to promote a tendinosis-like phenotype

Actin is a central mediator between mechanical force and cellular phenotype. In tendons, it is speculated that mechanical stress deprivation regulates gene expression by reducing filamentous (F)-actin. However, the mechanisms regulating tenocyte F-actin remain unclear. Tropomyosins (Tpms) are master regulators of F-actin. There are more than 40 Tpm isoforms, each having the unique capability to stabilize F-actin subpopulations. We investigated F-actin polymerization in stress-deprived tendons and tested the hypothesis that stress fiber-associated Tpm(s) stabilize F-actin to regulate cellular phenotype. Stress deprivation of mouse tail tendon down-regulated tenogenic and up-regulated protease (matrix metalloproteinase-3) mRNA levels. Concomitant with mRNA modulation were increases in G/F-actin, confirming reduced F-actin by tendon stress deprivation. To investigate the molecular regulation of F-actin, we identified that tail, Achilles, and plantaris tendons express three isoforms in common: Tpm1.6, 3.1, and 4.2. Tpm3.1 associates with F-actin in native and primary tenocytes. Tpm3.1 inhibition reduces F-actin, leading to decreases in tenogenic expression, increases in chondrogenic expression, and enhancement of protease expression in mouse and human tenocytes. These expression changes by Tpm3.1 inhibition are consistent with tendinosis progression. A further understanding of F-actin regulation in musculoskeletal cells could lead to new therapeutic interventions to prevent alterations in cellular phenotype during disease progression.

Parkin Inhibits RANKL-Induced Osteoclastogenesis and Ovariectomy-Induced Bone Loss

Osteoporosis and osteoporotic fractures comprise a substantial health and socioeconomic burden. The leading cause of osteoporosis is an imbalance in bone formation and bone resorption caused by hyperactive osteoclasts. Therefore, a new strategy to suppress osteoclastogenesis is needed. Parkin is likely closely associated with bone metabolism, although its role in osteoclastogenesis is unclear. In this study, the Parkin protein inhibited the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation, osteoclast-specific gene expression, F-actin ring formation, and bone resorption pit formation in vitro. Moreover, depletion of Parkin enhanced RANKL-induced osteoclast formation, osteoclast-specific gene expression, F-actin ring formation, and bone resorption pit formation. Reactive oxygen species (ROS) activity was suppressed, while autophagy was upregulated with the presence of the Parkin protein. ROS activity was upregulated and autophagy was decreased due to Parkin knockdown. In addition, intravenous administration of Parkin rescued ovariectomy-induced bone loss and reduced osteoclastogenesis in vivo. Collectively, Parkin has therapeutic potential for diseases associated with overactive osteoclasts.

Prussian Blue Nanozyme Normalizes Microenvironment to Delay Osteoporosis

Osteoporosis (OP) is the most common orthopedic disease in the elderly and the main cause of age-related mortality and disability. However, no satisfactory intervention is currently available in clinical practice. Thus, an effective therapy to prevent or delay the development of OP should be devised. Osteoclastogenesis overactivation and excessive bone resorption are the main characteristics of OP. Accordingly, a paradigm for nanozyme-mediated normalization of the disease microenvironment to regulate osteoclast differentiation and delay OP is proposed. Hollow Prussian blue nanozymes (HPBZs) are prepared via template-free hydrothermal synthesis and selected as representative nanozymes. The intrinsic osteoclast activity-remodeling bioactivities of the HPBZs are explored in vitro and in vivo, focusing on their impact on osteogenesis and specific molecular mechanisms using an OP murine model. The HPBZs significantly normalize the OP microenvironment, thereby inhibiting osteoclast formation and osteoclast resorption, possibly owing to the suppression of intracellular reactive oxygen species generation, the mitogen-activated protein kinase, and nuclear factor κB signaling pathways. Consistently, in an ovariectomy-induced OP murine model, HPBZ treatment significantly attenuates osteoporotic bone loss in vivo. The findings confirm the HPBZ-mediated normalization of the disease microenvironment for the treatment of OP and suggest its application to other inflammation-related diseases.

Aminooxyacetic acid hemihydrochloride inhibits osteoclast differentiation and bone resorption by attenuating oxidative phosphorylation

Osteoclasts undergo active metabolic reprogramming to acquire the energy needed during differentiation and bone resorption. Compared with immature osteoclasts, mature osteoclasts comprise higher levels of electron transport chain enzymes and more metabolically active mitochondria. Of all energy metabolism pathways, oxidative phosphorylation is considered to be the most efficient in supplying energy to osteoclasts. We found that the malate-aspartate shuttle inhibitor aminooxyacetic acid hemihydrochloride inhibits osteoclastogenesis and bone resorption by inhibiting exchange of reducing equivalents between the cytosol and the mitochondrial matrix and attenuating mitochondrial oxidative phosphorylation in vitro. The weakening of the oxidative phosphorylation pathway resulted in reduced mitochondrial function and inadequate energy supply along with reduced reactive oxygen species production. Furthermore, treatment with aminooxyacetic acid hemihydrochloride helped recover bone loss in ovariectomized mice. Our findings highlight the potential of interfering with the osteoclast intrinsic energy metabolism pathway as a treatment for osteoclast-mediated osteolytic diseases.

Monascin abrogates RANKL-mediated osteoclastogenesis in RAW264.7 cells via regulating MAPKs signaling pathways

Osteoclasts (OCs) are multinucleated cells that play a major role in osteolytic diseases such as osteoporosis. Monascin (Ms) is one of the active substances in the traditional Chinese medicine red yeast rice. Studies have found that red yeast rice can maintain bone health. In this study, the anti-osteoclastogenesis effects of Ms on RANKL-induced RAW264.7 cells were assessed, and the underlying mechanism was investigated. Ms exhibited inhibitory effects on OC differentiation and formation in a dose-dependent manner and suppressed the bone-resorbing activity of mature OCs. Ms blocked OCs-typical genes (c-Fos, NFATc1, CSTK, MMP-9, TRAP, ITG-β3, OSCAR and DC-STAMP). Furthermore, Ms treatment considerably inhibited the activation of MAPKs, JNK and p38. Taken together, Ms suppresses RANKL-induced osteoclastogenesis of RAW264.7 cells by restraining MAPKs signaling pathways and is a potential therapeutic option as a novel OC inhibitor to mitigate bone erosion.

Switch-associated protein 70 protects against nonalcoholic fatty liver disease through suppression of TAK1

BACKGROUND AND AIMS

NAFLD is a progressive disease without known effective drug treatments. Switch-associated protein 70 (SWAP70) is a guanine nucleotide exchange factor that participates in the regulation of many cellular processes. However, the role of SWAP70 in NAFLD remains unclear. This study aimed to identify the function and mechanism of SWAP70 in NAFLD.

APPROACH AND RESULTS

The results showed that the expression of SWAP70 was significantly increased in mice and hepatocytes after metabolic stimulation. Overexpression of SWAP70 in hepatocytes suppressed lipid deposition and inflammation, and SWAP70 knockdown created the inverse effect. Using hepatocyte-specific Swap70 knockout and overexpression mice fed a high-fat, high-cholesterol diet, we demonstrated that SWAP70 suppressed the progression of nonalcoholic steatohepatitis by inhibiting lipid accumulation, inflammatory response, and fibrosis. Mechanically, RNA sequencing analysis and immunoprecipitation assays revealed that SWAP70 inhibited the interaction between transforming growth factor β-activated kinase 1 (TAK1) binding protein 1 and TAK1 and sequentially suppressed the phosphorylation of TAK1 and subsequent c-Jun N-terminal kinase/P38 signaling. Inhibition of TAK1 activation blocked hepatocyte lipid deposition and inflammation caused by SWAP70 knockdown.

CONCLUSIONS

SWAP70 is a protective molecule that can suppress the progression of NAFLD by inhibiting hepatic steatosis and inflammation. SWAP70 may be important for mitigating the progression of NAFLD.

BMPR1α promotes osteolytic lesion of oral squamous cell carcinoma by SHH‐dependent osteoclastogenesis

Oral squamous cell carcinoma (OSCC) is an aggressive tumor that usually invades the maxilla or mandible. The extent and pattern of mandibular bone invasion caused by OSCC are the most important factors determining the treatment plan and patients' prognosis. Yet, the process of mandibular invasion is not fully understood. The following study explores the molecular mechanism that regulates the mandibular invasion of OSCC by focusing on bone morphogenetic protein receptor 1α (BMPR1α) and Sonic hedgehog (SHH) signals. We found that BMPR1α was positively correlated to bone defect of OSCC patients. Mechanistically, BMPR1α signaling regulated the differentiation and resorption activity of osteoclasts through the interaction of OSCC cells and osteoclast progenitors, and this process was mediated by SHH secreted by tumor cells. The inhibition of SHH protected bone from tumor‐induced osteolytic activity. These results provide a potential new treatment strategy for controlling OSCC from invading the jawbones.

Role of Dynamic Actin Cytoskeleton Remodeling in Foxp3+ Regulatory T Cell Development and Function: Implications for Osteoclastogenesis

In T cells, processes such as migration and immunological synapse formation are accompanied by the dynamic reorganization of the actin cytoskeleton, which has been suggested to be mediated by regulators of RhoGTPases and by F-actin bundlers. SWAP-70 controls F-actin dynamics in various immune cells, but its role in T cell development and function has remained incompletely understood. CD4⁺ regulatory T (Treg) cells expressing the transcription factor Foxp3 employ diverse mechanisms to suppress innate and adaptive immunity, which is critical for maintaining immune homeostasis and self-tolerance. Here, we propose Swap-70 as a novel member of the Foxp3-dependent canonical Treg cell signature. We show that Swap-70^-/- mice have increased numbers of Foxp3⁺ Treg cells with an effector/memory-like phenotype that exhibit impaired suppressor function in vitro, but maintain overall immune homeostasis in vivo. Upon formation of an immunological synapse with antigen presenting cells in vitro, cytosolic SWAP-70 protein is selectively recruited to the interface in Treg cells. In this context, Swap-70^-/- Treg cells fail to downregulate CD80/CD86 on osteoclast precursor cells by trans-endocytosis and to efficiently suppress osteoclastogenesis and osteoclast function. These data provide first evidence for a crucial role of SWAP-70 in Treg cell biology and further highlight the important non-immune function of Foxp3⁺ Treg cells in bone homeostasis mediated through direct SWAP-70-dependent mechanisms.

Circulating osteogenic progenitors and osteoclast precursors are associated with long-term glycemic control, sex steroids, and visceral adipose tissue in men with type 2 diabetes mellitus

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is well-known to be associated with normal bone density but, concurrently, low bone turnover and increased risk for fracture. One of the proposed mechanisms is possible derangement in bone precursor cells, which could be represented by deficiencies in circulating osteogenic progenitor (COP) cells and osteoclast precursors (OCP). The objective of our study is to understand whether extent of glycemic control has an impact on these cells, and to identify other factors that may as well.

METHODS

This was a secondary analysis of baseline data from 51 male participants, aged 37-65 in an ongoing clinical trial at Michael E. DeBakey VA Medical Center, Houston, Texas, USA. At study entry serum Hemoglobin A1c was measured by high-performance liquid chromatography osteocalcin (OCN) and C-terminal telopeptide of type 1 collagen (CTx) were measured by ELISA, and testosterone and estradiol by liquid-chromatography/mass-spectrometry. Areal bone mineral density (BMD), trabecular bone score and body composition were measured by dual energy x-ray absorptiometry, while COP and OCP were measured by flow cytometry.

RESULTS

When adjusted for serum testosterone, parathyroid hormone, and 25-hydroxyvitamin D, those with poor long-term glycemic control had significantly higher percentage of COP (p = 0.04). COP correlated positively with visceral adipose tissue (VAT) volume (r = 0.37, p = 0.01) and negatively with free testosterone (r = -0.28, p = 0.05) and OCN (r = -0.28, p = 0.07), although only borderline for the latter. OCP correlated positively with age, FSH, lumbar spine BMD, and COP levels, and negatively with glucose, triglycerides, and free estradiol. Multivariable regression analyses revealed that, in addition to being predictors for each other, another independent predictor for COP was VAT volume while age, glucose, and vitamin D for OCP.

CONCLUSION

Our results suggest that high COP could be a marker of poor metabolic control. However, given the complex nature and the multitude of factors influencing osteoblastogenesis/adipogenesis, it is possible that the increase in COP is a physiologic response of the bone marrow to increased osteoblast apoptosis from poor glycemic control. Alternatively, it is also likely that a metabolically unhealthy profile may retard the development of osteogenic precursors to fully mature osteoblastic cells.

d-mannose attenuates lipopolysaccharide-induced osteolysis via CPT1A-Mediated lipid metabolic regulation in macrophages

Inflammatory osteolysis is usually linked to the activation of proinflammatory macrophage and the consequent excessive osteoclast formation. Emerging evidence indicates that agents or drugs targeting lipid metabolism in macrophages might be potential in the prevention and treatment of osteolysis. d-mannose, as a natural-existed metabolic regulator, exerts strong effects on attenuating osteopenia and inflammation. However, whether d-mannose is therapeutically effective on osteolysis and whether a metabolic mechanism counts for the effect remain to be addressed. Here, by using an in vivo lipopolysaccharide (LPS)-induced inflammatory osteolysis mouse model as well as an in vitro LPS-induced inflammatory macrophage culture system, we show that d-mannose attenuates inflammatory osteolysis and inhibits excessive osteoclastogenesis by reversing the LPS-induced activation of proinflammatory macrophage. Mechanically, d-mannose recovers LPS-suppressed Cpt1a transcription and promotes lipid metabolism of macrophage. Treatment with etomoxir, an inhibitor of CPT1A, abolishes the effects of d-mannose on LPS-treated macrophage in vitro and eliminates its protection against osteolysis in vivo. Collectively, our results imply that d-mannose attenuates LPS-induced osteolysis by manipulating CPT1A-mediated lipid metabolism in macrophages. Our results disclose the unrecognized utilization of d-mannose as an effective intervention against inflammatory osteolysis and provide evidence to manage inflammatory scenarios by therapeutically targeting lipid metabolism in macrophage.

Inhibition of Sirtuin 3 prevents titanium particle-induced bone resorption and osteoclastsogenesis via suppressing ERK and JNK signaling

Implant-derived wear particles can be phagocytosed by local macrophages, triggering an inflammatory cascade that can drive the activation and recruitment of osteoclasts, thereby inducing peri-prosthetic osteolysis. Efforts to suppress pro-inflammatory cytokine release and osteoclastsogenesis thus represent primary approaches to treating and preventing such osteolysis. Sirtuin 3 (SIRT3) is a NAD⁺-dependent deacetylases that control diverse metabolic processes. However, whether SIRT3 could mitigate wear debris-induced osteolysis has not been reported. Herein we explored the impact of the SIRT3 on titanium particle-induced osteolysis. Tartrate resistant acid phosphatase (TRAP) staining revealed that the inhibition of SIRT3 suppressed nuclear factor-κB ligand (RANKL)-mediated osteoclasts activation in a dose-dependent fashion. Notably, inhibition of SIRT3 also suppressed matrix metallopeptidase 9 (MMP9) and nuclear factor of activated T‐cell cytoplasmic 1 (NFATc1) expression at the mRNA and protein levels, while also inhibiting the mRNA expression of dendritic cell-specific transmembrane protein (DC-STAMP), ATPase H⁺ Transporting V0 Subunit D2 (Atp6v0d2), TRAP and Cathepsin K (CTSK) . In addition, inhibition of SIRT3 suppressed titanium particle-induced tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) expression and prevented titanium particle-induced osteolysis and bone loss in vivo. This inhibition of osteoclasts differentiation was found to be linked to the downregulation and reduced phosphorylation of JNK and ERK. Taken together, inhibition of SIRT3 may be a potential target for titanium particle-induced bone loss.

PERK controls bone homeostasis through the regulation of osteoclast differentiation and function

Osteoclasts are multinucleated giant cells with the ability to degrade bone tissue, and are closely related to abnormal bone metabolic diseases. Endoplasmic reticulum (ER) is an organelle responsible for protein modification, quality control, and transportation. The accumulation of unfolded or misfolded proteins in ER cavity induces ER stress. Double-stranded RNA-dependent protein kinase-like ER kinase (PERK) is an ER stress-sensing protein, which is ubiquitous in eukaryotic cells. Systemic PERK knockout mice show severe bone loss, suggesting that PERK is of great significance for maintaining the normal growth and development of bone tissue, but the role of PERK in osteoclastogenesis is still unclear. In this study, we found that PERK was significantly activated during RANKL-induced osteoclast differentiation; knockdown of PERK by siRNA and inhibition of PERK by GSK2606414, respectively, had significant negative regulatory effects on the formation and bone resorption of osteoclasts. PERK inhibitor GSK2606414 down-regulated the mRNA levels and protein expression of osteoclast differentiation marker genes, and inhibited RANKL-induced activation of Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways. Treatment with PERK inhibitor GSK2606414 in ovariectomized mouse model significantly suppressed bone loss and osteoclast formation. Thapsigargin activated ER stress to enhance autophagy, while GSK2606414 had a significant inhibitory effect on autophagy flux and autophagosome formation. Antioxidant N-acetylcysteine (NAC) could inhibit the expression of PERK phosphorylation, osteoclast-related proteins and autophagy-related proteins, but the use of PERK activator CCT020312 can reverse inhibition effect of NAC. Our findings demonstrate a key role for PERK in osteoclast differentiation and suggest its therapeutic potential.

Identification of osteoporosis markers through bioinformatic functional analysis of serum proteome

Osteoporosis is a severe chronic skeletal disorder that increases the risks of disability and mortality; however, the mechanism of this disease and the protein markers for prognosis of osteoporosis have not been well characterized. This study aims to characterize the imbalanced serum proteostasis, the disturbed pathways, and potential serum markers in osteoporosis by using a set of bioinformatic analyses. In the present study, the large-scale proteomics datasets (PXD006464) were adopted from the Proteome Xchange database and processed with MaxQuant. The differentially expressed serum proteins were identified. The biological process and molecular function were analyzed. The protein-protein interactions and subnetwork modules were constructed. The signaling pathways were enriched. We identified 209 upregulated and 230 downregulated serum proteins. The bioinformatic analyses revealed a highly overlapped functional protein classification and the gene ontology terms between the upregulated and downregulated protein groups. Protein-protein interactions and pathway analyses showed a high enrichment in protein synthesis, inflammation, and immune response in the upregulated proteins, and cell adhesion and cytoskeleton regulation in the downregulated proteins. Our findings greatly expand the current view of the roles of serum proteins in osteoporosis and shed light on the understanding of its underlying mechanisms and the discovery of serum proteins as potential markers for the prognosis of osteoporosis.

NF-κB promotes osteoclast differentiation by overexpressing MITF via down regulating microRNA-1276 expression

BACKGROUND

Nuclear factor-kappa B (NF-κB) is an important nuclear transcription factor in cells, involving in a series of processes such as cell proliferation, apoptosis, and differentiation. In this study, we explored the specific mechanism of NF-κB on the differentiation of osteoclasts.

METHODS

MicroRNAs (miRNAs) expression microarray data GSE105027 related to osteoarthritis was obtained to screen out the differentially expressed miRNA. Phorbol-12-myristate-13-acetate (PMA) was used to induce THP-1 cells to differentiate into macrophages, followed by induction to osteoclasts using macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). ELISA and RT-qPCR were conducted to examine IL-6 and IL-1β expression. The binding of NF-κB to the miR-1276 promoter region was demonstrated by ChIP assay, and targeting relationship between miR-1276 and MITF was verified by dual luciferase reporter assay. KK, iKBα, NF-kB, p-IKK, p-iKBα, p-NF-kB expression was analyzed by western blot. NF-κB and miR-1276 expression in osteoclasts was examined later. After gain- and less-of-function study, the effects on osteoclast differentiation were detected by TRAP-positive osteoclasts, TRAP activity, TRAP-5b content, F-Actin expression, as well as osteoclast differentiation marker genes expression.

RESULTS

NF-κB was activated in osteoclasts, and down-regulation of NF-κB inhibited osteoclast differentiation. Next, miR-1276 was downregulated in osteoclasts after differentiation from monocytes. Meanwhile, NF-κB decreased the expression of miR-1276 by binding to the miR-1276 promoter, thereby elevating MITF expression, thereby promoting osteoclast differentiation.

CONCLUSION

In summary, NF-κB promoted osteoclast differentiation through downregulating miR-1276 to upregulate MITF.

Anemonin Attenuates RANKL-Induced Osteoclastogenesis and Ameliorates LPS-Induced Inflammatory Bone Loss in Mice via Modulation of NFATc1

Osteoporosis is a metabolic bone disease characterized by insufficient osteoblastic function and/or excessive osteoclastic activity. One promising strategy for treating osteoporosis is inhibiting excessive osteoclast resorbing activity. Previous studies have revealed that anemonin (ANE), isolated from various types of Chinese natural herbs, has anti-inflammatory and anti-oxidative properties. However, whether ANE regulates osteoclastogenesis is unknown. This study aimed to investigate the potential effect of ANE on osteoclastogenesis and inflammatory bone loss in mice. In in vitro studies, ANE suppressed RANKL-stimulated osteoclast differentiation and function by downregulating the expression of osteoclast master transcriptor NFATc1, as well as its upstream transcriptor c-Fos, by decreasing NF-κB and ERK1/2 signaling. Interestingly, ANE did not change the phosphorylation and degradation of IκB-α and activation of JNK and p38 MAPKs. However, ANE repressed the phosphorylation of MSK-1 which is the downstream target of ERK1/2 and p38 MAPK and can phosphorylate NF-κB p65 subunit. These results implicated that ANE might suppress NF-κB activity via modulation of ERK1/2 mediated NF-κB phosphorylation. In addition, ANE directly suppressed NFATc1 transcription by inhibiting Blimp-1 expression, and the subsequent enhancement of the expression of NFATc1 negative regulators, Bcl-6 and IRF-8. Moreover, in vivo studies were conducted using an LPS-induced inflammatory bone loss mice model. Micro-CT and histology analysis showed that ANE treatment significantly improved trabecular bone parameters and bone destruction. These data indicate that ANE can attenuate RANKL-induced osteoclastogenesis and ameliorate LPS-induced inflammatory bone loss in mice through modulation of NFATc1 via ERK1/2-mediated NF-κB phosphorylation and Blimp1 signal pathways. ANE may provide new treatment options for osteoclast-related diseases.

Mechanism of control of F-actin cortex architecture by SWAP-70

F-actin binding and bundling are crucial to a plethora of cell processes, including morphogenesis, migration, adhesion and many others. SWAP-70 was recently described as an in vitro F-actin-binding and -bundling protein. Fluorescence cross-correlation spectroscopy measurements with purified recombinant SWAP-70 confirmed that it forms stable oligomers that facilitate F-actin bundling. However, it remained unclear how SWAP-70 oligomerization and F-actin binding are controlled in living cells. We addressed this by biophysical approaches, including seFRET, FACS-FRET and FLIM-FRET. PIP3-mediated association with the cytoplasmic membrane and non-phosphorylated Y426 are required for SWAP-70 to dimerize and to bind F-actin. The dimerization region was identified near the C terminus where R546 is required for dimerization and, thus, F-actin bundling. The in vitro and in vivo data presented here reveal the functional relationship between the cytoplasm-to-membrane translocation and dimerization of SWAP-70, and F-actin binding and bundling, and demonstrate that SWAP-70 is a finely controlled modulator of membrane-proximal F-actin dynamics.This article has an associated First Person interview with the first author of the paper.

SWAP70 undergoes dynamic conformational regulation at the leading edge of migrating cells

Rearrangements of the actin cytoskeleton are regulated in part by dynamic localised activation and inactivation of Rho family small GTPases. SWAP70 binds to and activates the small GTPase RAC1 as well as binding to filamentous actin and PIP3 . We have developed an encoded biosensor, which uses Forster resonance energy transfer to reveal conformational changes in SWAP70 in live cells. SWAP70 adopts a distinct conformation at the plasma membrane, which in migrating glioma cells is enriched at the leading edge but does not always associate with its PIP3 -dependent translocation to the membrane. This supports a role for SWAP70 in positive feedback activation of RAC1 at sites of filamentous actin, PIP3 and active RAC1.

Pectolinarigenin prevents bone loss in ovariectomized mice and inhibits RANKL-induced osteoclastogenesis via blocking activation of MAPK and NFATc1 signaling

Osteoporosis (OP) is a metabolic disease caused by multiple factors, which is characterized by a reduction of bone mass per unit volume and destruction of bone microstructure. Aberrant osteoclast function is the main cause of OP, therefore, regulating the differentiation and function of osteoclast is one of the treatment strategies for OP. Pectolinarigenin (PEC) is a medicinal implant isolated from Fragrant Eupatorium. Our experimental data showed that PEC was able to inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis in vitro, by tartrate-resistant acid phosphatase (TRAcP) staining, Fibrous actin ring formation, and hydroxyapatite resorption assays. In terms of mechanism, PEC inhibited the expression of the osteoclastogenesis-related gene, including cathepsin K (Ctsk), matrix metalloproteinase 9 (Mmp9), and TRAcP (Acp5). Western blot analysis demonstrated that PEC could significantly block the activation of RANKL-induced mitogen-activated protein kinase signaling cascades and was able to suppress the protein expression of nuclear factor of activated T-cells and c-Fos. Meanwhile, the intracellular reactive oxygen species levels were also reduced by PEC in a concentration-dependent manner. Further, PEC could prevent the ovariectomy-induced bone loss in vivo. Summarizing all, our data suggested that PEC inhibits osteoclast formation and function and RANKL signaling pathways, and thus could potentially be used in the treatment the osteoclast-related bone loss diseases.

Foxp3+ Regulatory T Cells in Bone and Hematopoietic Homeostasis

The bone represents surprisingly dynamic structures that are subject to constant remodeling by the concerted action of bone-forming osteoblasts and bone-resorbing osteoclasts - two cell subsets of distinct developmental origin that are key in maintaining skeletal integrity throughout life. In general, abnormal bone remodeling due to dysregulated bone resorption and formation is an early event in the manifestation of various human bone diseases, such as osteopetrosis/osteoporosis and arthritis. But bone remodeling is also closely interrelated with lympho-hematopoietic homeostasis, as the bone marrow niche is formed by solid and trabecular bone structures that provide a framework for the long-term maintenance and differentiation of HSCs (>blood lineage cells and osteoclasts) and MSCs (>osteoblasts). Numerous studies in mice and humans have implicated innate and adaptive immune cells in the dynamic regulation of bone homeostasis, but despite considerable clinical relevance, the exact mechanisms of such immuno-bone interplay have remained incompletely understood. This holds particularly true for CD4⁺ regulatory T (Treg) cells expressing the lineage specification factor Foxp3: Foxp3⁺ Treg cells have been shown to play an indispensable role in maintaining immune homeostasis, but may also exert critical non-immune functions, which includes the control of metabolic and regenerative processes, as well as the differentiation of HSCs and function of osteoclasts. Here, we summarize our current knowledge on the T cell/bone interplay, with a particular emphasis on our own efforts to dissect the role of Foxp3⁺ Treg cells in bone and hematopoietic homeostasis, employing experimental settings of gain- and loss-of-Treg cell function. These data make a strong case that Foxp3⁺ Treg cells impinge on lympho-hematopoiesis through indirect mechanisms, i.e., by acting on osteoclast development and function, which translates into changes in niche size. Furthermore, we propose that, besides disorders that involve inflammatory bone loss, the modulation of Foxp3⁺ Treg cell function in vivo may represent a suitable approach to reinstate bone homeostasis in non-autoimmune settings of aberrant bone remodeling.

SWAP70 is a universal GEF-like adaptor for tethering actin to phagosomes

We recently identified a key role for SWAP70 as the tethering factor stabilizing F-actin filaments on the surface of phagosomes in human dendritic cells by interacting both with Rho-family GTPases and the lipid phosphatidylinositol (3,4)-bisphosphate. In this study, we aimed to investigate whether this role of SWAP70 was general among immune phagocytes. Our data reveal that SWAP70 is recruited to early phagosomes of macrophages and dendritic cells from both human and mouse. The putative inhibitor of SWAP70 sanguinarine blocked phagocytosis and F-actin polymerization, supporting a key role for SWAP70 in phagocytosis as demonstrated previously with knock-down. Moreover, SWAP70 was recently shown to sequester the F-actin severing protein cofilin and we investigated this relationship in phagocytosis. Our data show an increased activation of cellular cofilin upon siRNA knockdown of SWAP70. Finally, we explored whether SWAP70 would be recruited to the immune synapse between dendritic cells and T cells required for antigen presentation, as the formation of such synapses depends on F-actin. However, we observed that SWAP70 was depleted at immune synapses and specifically was recruited to phagosomes. Our data support an essential and specific role for SWAP70 in tethering and stabilizing F-actin to the phagosomal surface in a wide range of phagocytes.

SWAP70 Organizes the Actin Cytoskeleton and Is Essential for Phagocytosis

Actin plays a critical role during the early stages of pathogenic microbe internalization by immune cells. In this study, we identified a key mechanism of actin filament tethering and stabilization to the surface of phagosomes in human dendritic cells. We found that the actin-binding protein SWAP70 is specifically recruited to nascent phagosomes by binding to the lipid phosphatidylinositol (3,4)-bisphosphate. Multi-color super-resolution stimulated emission depletion (STED) microscopy revealed that the actin cage surrounding early phagosomes is formed by multiple concentric rings containing SWAP70. SWAP70 colocalized with and stimulated activation of RAC1, a known activator of actin polymerization, on phagosomes. Genetic ablation of SWAP70 impaired actin polymerization around phagosomes and resulted in a phagocytic defect. These data show a key role for SWAP70 as a scaffold for tethering the peripheral actin cage to phagosomes.

Surface microtopography modulates sealing zone development in osteoclasts cultured on bone

Bone homeostasis is continuously regulated by the coordinated action of bone-resorbing osteoclasts and bone-forming osteoblasts. Imbalance between these two cell populations leads to pathological bone diseases such as osteoporosis and osteopetrosis. Osteoclast functionality relies on the formation of sealing zone (SZ) rings that define the resorption lacuna. It is commonly assumed that the structure and dynamic properties of the SZ depend on the physical and chemical properties of the substrate. Considering the unique complex structure of native bone, elucidation of the relevant parameters affecting SZ formation and stability is challenging. In this study, we examined in detail the dynamic response of the SZ to the microtopography of devitalized bone surfaces, taken from the same area in cattle femur. We show that there is a significant enrichment in large and stable SZs (diameter larger than 14 µm; lifespan of hours) in cells cultured on rough bone surfaces, compared with small and fast turning over SZ rings (diameter below 7 µm; lifespan approx. 7 min) formed on smooth bone surfaces. Based on these results, we propose that the surface roughness of the physiologically relevant substrate of osteoclasts, namely bone, affects primarily the local stability of growing SZs.

Def6 Restrains Osteoclastogenesis and Inflammatory Bone Resorption

Inflammatory bone resorption mediated by osteoclasts is a major cause of morbidity and disability in many inflammatory disorders, including rheumatoid arthritis (RA). The mechanisms that regulate osteoclastogenesis and bone resorption in inflammatory settings are complex and have not been well elucidated. In this study, we identify the immunoregulator differentially expressed in FDCP 6 homolog (Def6) as a novel inhibitor of osteoclastogenesis in physiological and inflammatory conditions. Def6 deficiency in Def6^-/- mice enhanced the sensitivity of osteoclast precursors to the physiological osteoclastogenic inducer receptor activator for NF-κB ligand, and Def6^-/- osteoclasts formed actin rings. Furthermore, Def6 deficiency markedly increased TNF-α-induced osteoclastogenesis in vitro and in vivo and enhanced bone resorption in an inflammatory osteolysis mouse model. TNF-α serum levels correlated negatively with Def6 expression levels in osteoclast precursors obtained from RA patients, and the osteoclastogenic capacity of the osteoclast precursors was significantly inversely correlated with their Def6 expression levels, indicating that Def6 functions as an inhibitor of excessive osteoclast formation and bone destruction in RA. Mechanistically, Def6 suppressed osteoclastogenesis and the expression of key osteoclastogenic factors NFATc1, B lymphocyte-induced maturation protein-1, and c-Fos by regulating an endogenous IFN-β-mediated autocrine feedback loop. The Def6-dependent pathway may represent a novel therapeutic target to prevent pathological bone destruction.

SWEF Proteins Distinctly Control Maintenance and Differentiation of Hematopoietic Stem Cells

SWAP-70 and DEF6, two proteins that feature similar domain and motif arrangements, are mainly known for their functions in differentiated hematopoietic cells. Both proteins interact with and regulate RhoGTPases and F-actin dynamics, yet their role in hematopoietic stem and precursor cells (HSPCs) remained unexplored. Here, the role of the SWEF proteins SWAP-70 and DEF6 in HSPCs was examined. Both SWEF proteins are expressed in HSCs. HSCs and different precursor populations were analyzed in mice deficient for SWAP-70, DEF6, SWAP-70 and DEF6 (double knockout, DKO), and wild-type controls. HSPCs isolated from these strains were used for competitive adoptive transfer into irradiated wild-type mice. Reconstitution of the myeloid and lymphoid lineages in the recipient mice was determined. The numbers of HSPCs in the bone marrow of Swap-70-/- and Swap-70-/-Def6-/- mice were >3-fold increased. When transplanted into lethally irradiated wild-type recipients, the reconstitution potential of Swap-70-/- HSPCs was intrinsically impaired in competing with wild-type HSPCs for contribution to hematopoiesis. Def6-/- HSPCs show wild type-like reconstitution potential under the same transplantation conditions. DKO HSPCs reconstituted to only 25% of wild-type levels, indicating a partial rescue by DEF6 deficiency in the Swap-70-/- background. Our study reveals the two SWEF proteins as important contributors to HSPC biology. Despite their similarity these two proteins regulate HSC/progenitor homeostasis, self-renewal, lineage contributions and repopulation in a distinct and mostly antagonistic manner.

The F-actin modulator SWAP-70 controls podosome patterning in osteoclasts

Osteoclasts are bone resorbing cells acting as key mediators of bone disorders. Upon adhesion to bone, osteoclasts polarize and reorganize their cytoskeleton to generate a ring-like F-actin-rich structure, the sealing zone, wherein the osteoclast's resorptive organelle, the ruffled border, is formed. The dynamic self-organization of actin-rich adhesive structures, the podosomes, from clusters to belts is crucial for osteoclast-mediated bone degradation. Mice lacking the protein SWAP-70 display an osteopetrotic phenotype due to defective bone resorption caused by impaired actin ring formation in Swap-70^−/− osteoclasts. To further elucidate the mechanisms underlying this defect, we investigated the specific function of SWAP-70 in the organization and dynamics of podosomes. These detailed studies show that the transition from podosome clusters to rings is impaired in Swap-70^−/− osteoclasts. Live cell imaging of dynamic F-actin turnover and SWAP-70 localization during podosome patterning indicate that SWAP-70 is dispensable for cluster formation but plays a key role in F-actin ring generation. Our data provide insights in the role of SWAP-70's F-actin binding domain and pleckstrin homology (PH) domain in the proper localization of SWAP-70 and formation of a peripheral podosome belt, respectively. Ex vivo bone analyses revealed that SWAP-70-deficient osteoclasts exhibit defective ruffled border formation and V-ATPase expression. Our findings suggest an important role of membrane binding of SWAP-70 for the regulation of actin dynamics, which is essential for podosome patterning, and thus for the resorptive activity of osteoclasts.

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SWAP-70 controls dynamic podosome patterning but not assembly of podosomes.

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PIP3 and F-actin binding are required for proper subcellular localization of SWAP-70.

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SWAP-70-deficient osteoclasts are impaired in ruffled border formation.

SWAP-70 contributes to spontaneous transformation of mouse embryo fibroblasts

Mouse embryo fibroblasts (MEFs) grow slowly after cultivation from animals, however, after an extended period of cultivation, their growth accelerates. We found that SWAP-70 deficient MEFs failed to increase growth rates. They maintain normal growth rates and proliferation cycles for at least 5 years. Complementing SWAP-70 deficiency in one of these MEF clones, MEF1F2, by expressing human SWAP-70 resulted in fast growth of the cells after further cultivation for a long period. The resulting cells show a transformation phenotype, since they grow on top of each other and do not show contact inhibition. This phenotype was reverted when sanguinarine, a putative SWAP-70 inhibitor, was added. Two SWAP-70 expressing clones were examined in detail. Even after cell density became very high their cdc2 and NFκB were still activated suggesting that they do not stop growing. One of the clones formed colonies in soft agar and formed tumors in nude mice. Lately, one more clone became transformed being able to make colonies in soft agar. We maintain 4 human SWAP-70 expressing MEF1F2 cell lines. Three out of 4 clones exhibited transforming phenotypes. The mouse SWAP-70 gene also promoted transformation of MEFs. Taken together our data suggest that SWAP-70 is not a typical oncogene, but is required for spontaneous transformation of MEFs.

Adseverin knockdown inhibits osteoclastogenesis in RAW264.7 cells

Osteoclastogenesis is a complex process that is highly dependent on the dynamic regulation of the actin cytoskeleton. Adseverin (Ads), a member of the gelsolin superfamily of actin-binding proteins, regulates actin remodeling by severing and capping actin filaments. The objective of the present study was to characterize the role of Ads during osteoclastogenesis by assessing Ads expression and using a knockdown strategy. Immunoblot analyses were used to examine Ads expression during osteoclastogenesis. A stable Ads knockdown macrophage cell line was generated using a retroviral shRNA construct. Osteoclast differentiation was morphologically examined via cell staining with osteoclast specific markers and light microscopy. The results showed that Ads expression was significantly increased in response to receptor activator of nuclear factor-κB ligand during osteoclastogenesis, and Ads was highly expressed in mature osteoclasts. Ads-knockdown macrophages showed major osteoclastogenesis defects, most likely caused by a pre-osteoclast fusion defect. These results indicate that Ads deficiency in monocytes inhibits osteoclastogenesis. Thus, in future studies it could be noteworthy to investigate the function of Ads in bone marrow monocytes during osteoclastogenesis.

Cavin-1/PTRF alters prostate cancer cell-derived extracellular vesicle content and internalization to attenuate extracellular vesicle-mediated osteoclastogenesis and osteoblast proliferation

Background

Tumour-derived extracellular vesicles (EVs) play a role in tumour progression; however, the spectrum of molecular mechanisms regulating EV secretion and cargo selection remain to be fully elucidated. We have reported that cavin-1 expression in prostate cancer PC3 cells reduced the abundance of a subset of EV proteins, concomitant with reduced xenograft tumour growth and metastasis.

Methods

We examined the functional outcomes and mechanisms of cavin-1 expression on PC3-derived EVs (PC3-EVs).

Results

PC3-EVs were internalized by osteoclast precursor RAW264.7 cells and primary human osteoblasts (hOBs) in vitro, stimulating osteoclastogenesis 37-fold and hOB proliferation 1.5-fold, respectively. Strikin gly, EVs derived from cavin-1-expressing PC3 cells (cavin-1-PC3-EVs) failed to induce multinucleate osteoblasts or hOB proliferation. Cavin-1 was not detected in EVs, indicating an indirect mechanism of action. EV morphology, size and quantity were also not affected by cavin-1 expression, suggesting that cavin-1 modulated EV cargo recruitment rather than release. While cavin-1-EVs had no osteoclastogenic function, they were internalized by RAW264.7 cells but at a reduced efficiency compared to control EVs. EV surface proteins are required for internalization of PC3-EVs by RAW264.7 cells, as proteinase K treatment abolished uptake of both control and cavin-1-PC3-EVs. Removal of sialic acid modifications by neuraminidase treatment increased the amount of control PC3-EVs internalized by RAW264.7 cells, without affecting cavin-1-PC3-EVs. This suggests that cavin-1 expression altered the glycosylation modifications on PC3-EV surface. Finally, cavin-1 expression did not affect EV in vivo tissue targeting as both control and cavin-1-PC3-EVs were predominantly retained in the lung and bone 24 hours after injection into mice.

Discussion

Taken together, our results reveal a novel pathway for EV cargo sorting, and highlight the potential of utilizing cavin-1-mediated pathways to attenuate metastatic prostate cancer.

Dendritic cell podosome dynamics does not depend on the F-actin regulator SWAP-70

In addition to classical adhesion structures like filopodia or focal adhesions, dendritic cells similar to macrophages and osteoclasts assemble highly dynamic F-actin structures called podosomes. They are involved in cellular processes such as extracellular matrix degradation, bone resorption by osteoclasts, and trans-cellular diapedesis of lymphocytes. Besides adhesion and migration, podosomes enable dendritic cells to degrade connective tissue by matrix metalloproteinases. SWAP-70 interacts with RhoGTPases and F-actin and regulates migration of dendritic cells. SWAP-70 deficient osteoclasts are impaired in F-actin-ring formation and bone resorption. In the present study, we demonstrate that SWAP-70 is not required for podosome formation and F-actin turnover in dendritic cells. Furthermore, we found that toll-like receptor 4 ligand induced podosome disassembly and podosome-mediated matrix degradation is not affected by SWAP-70 in dendritic cells. Thus, podosome formation and function in dendritic cells is independent of SWAP-70.