GM-CSF cannot substitute for M-CSF in human osteoclastogenesis

Circular RNA circIKBKB promotes breast cancer bone metastasis through sustaining NF-κB/bone remodeling factors signaling

Background

Breast cancer (BC) has a marked tendency to spread to the bone, resulting in significant skeletal complications and mortality. Recently, circular RNAs (circRNAs) have been reported to contribute to cancer initiation and progression. However, the function and mechanism of circRNAs in BC bone metastasis (BC-BM) remain largely unknown.

Methods

Bone-metastatic circRNAs were screened using circRNAs deep sequencing and validated using in situ hybridization in BC tissues with or without bone metastasis. The role of circIKBKB in inducing bone pre-metastatic niche formation and bone metastasis was determined using osteoclastogenesis, immunofluorescence and bone resorption pit assays. The mechanism underlying circIKBKB-mediated activation of NF-κB/bone remodeling factors signaling and EIF4A3-induced circIKBKB were investigated using RNA pull-down, luciferase reporter, chromatin isolation by RNA purification and enzyme-linked immunosorbent assays.

Results

We identified that a novel circRNA, circIKBKB, was upregulated significantly in bone-metastatic BC tissues. Overexpressing circIKBKB enhanced the capability of BC cells to induce formation of bone pre-metastatic niche dramatically by promoting osteoclastogenesis in vivo and in vitro. Mechanically, circIKBKB activated NF-κB pathway via promoting IKKβ-mediated IκBα phosphorylation, inhibiting IκBα feedback loop and facilitating NF-κB to the promoters of multiple bone remodeling factors. Moreover, EIF4A3, acted acting as a pre-mRNA splicing factor, promoted cyclization of circIKBKB by directly binding to the circIKBKB flanking region. Importantly, treatment with inhibitor eIF4A3-IN-2 reduced circIKBKB expression and inhibited breast cancer bone metastasis effectively.

Conclusion

We revealed a plausible mechanism for circIKBKB-mediated NF-κB hyperactivation in bone-metastatic BC, which might represent a potential strategy to treat breast cancer bone metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01394-8.

Systemic and local effects of radiotherapy: an experimental study on implants placed in rats

OBJECTIVES

Evaluate the modulating effect of ionizing radiation, blood cytokine levels, and bone remodeling of the interface around the implant to understand the radiation mechanisms which can impair the implants receptor site.

MATERIAL AND METHODS

Sixty rats were submitted to grade V titanium implants in the femurs and were divided into the following groups: no-irradiation (N-Ir): control group with implant only; early-irradiation (E-Ir): implant + irradiation after 24 h; late-irradiation (L-Ir): implant + irradiation after 4 weeks; and previous-irradiation (P-Ir): irradiation + implant after 4 weeks. The animals in the E-Ir, L-Ir, and P-Ir groups were irradiated in two fractional stages of 15 Gy. At 3 days, 2 weeks, and 7 weeks after the final procedure, five animals were randomly euthanized per group. Serum levels of TNF-ɑ, IL-1β, TGF-β, IL-6, M-CSF, and IL-10 were measured from blood collected prior to euthanasia using the ELISA test. The pieces containing the implants were subjected to immunohistochemical labeling using the tartrate acid resistant to phosphatase, osteocalcin, and caspase-3 markers and mCT. The ANOVA test was used for statistical analysis, and the Tukey multiple comparison test (p < 0.05) was applied.

RESULTS

The results indicated that ionizing radiation modifies the production of pro- and anti-inflammatory serum cytokines, the expression of proteins involved in bone remodeling and cellular apoptosis, as well as changes in bone formation.

CONCLUSIONS

The results suggests that a longer period between radiotherapy and implant placement surgery when irradiation occurs prior to implant installation would allow the recovery and renewal of bone cells and avoid future failures in osseointegration.

CLINICAL RELEVANCE

The search for modifications caused by ionizing irradiation in bone tissue can indicate the ideal period for implant placement without affecting the osseointegration process.

Regulation of Embryonic and Postnatal Development by the CSF-1 Receptor

Macrophages are found in all tissues and regulate tissue morphogenesis during development through trophic and scavenger functions. The colony stimulating factor-1 (CSF-1) receptor (CSF-1R) is the major regulator of tissue macrophage development and maintenance. In combination with receptor activator of nuclear factor κB (RANK), the CSF-1R also regulates the differentiation of the bone-resorbing osteoclast and controls bone remodeling during embryonic and early postnatal development. CSF-1R-regulated macrophages play trophic and remodeling roles in development. Outside the mononuclear phagocytic system, the CSF-1R directly regulates neuronal survival and differentiation, the development of intestinal Paneth cells and of preimplantation embryos, as well as trophoblast innate immune function. Consistent with the pleiotropic roles of the receptor during development, CSF-1R deficiency in most mouse strains causes embryonic or perinatal death and the surviving mice exhibit multiple developmental and functional deficits. The CSF-1R is activated by two dimeric glycoprotein ligands, CSF-1, and interleukin-34 (IL-34). Homozygous Csf1-null mutations phenocopy most of the deficits of Csf1r-null mice. In contrast, Il34-null mice have no gross phenotype, except for decreased numbers of Langerhans cells and microglia, indicating that CSF-1 plays the major developmental role. Homozygous inactivating mutations of the Csf1r or its ligands have not been reported in man. However, heterozygous inactivating mutations in the Csf1r lead to a dominantly inherited adult-onset progressive dementia, highlighting the importance of CSF-1R signaling in the brain.

The Alternative Faces of Macrophage Generate Osteoclasts

The understanding of how osteoclasts are generated and whether they can be altered by inflammatory stimuli is a topic of particular interest for osteoclastogenesis. It is known that the monocyte/macrophage lineage gives rise to osteoclasts (OCs) by the action of macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor-kB ligand (RANKL), which induce cell differentiation through their receptors, c-fms and RANK, respectively. The multinucleated giant cells (MGCs) generated by the engagement of RANK/RANKL are typical OCs. Nevertheless, very few studies have addressed the question of which subset of macrophages generates OCs. Indeed, two main subsets of macrophages are postulated, the inflammatory or classically activated type (M1) and the anti-inflammatory or alternatively activated type (M2). It has been proposed that macrophages can be polarized in vitro towards a predominantly M1 or M2 phenotype with the addition of granulocyte macrophage- (GM-) CSF or M-CSF, respectively. Various inflammatory stimuli known to induce macrophage polarization, such as LPS or TNF-α, can alter the type of MGC obtained from RANKL-induced differentiation. This review aims to highlight the role of immune-related stimuli and factors in inducing macrophages towards the osteoclastogenesis choice.

VEGF, FLT3 ligand, PlGF and HGF can substitute for M-CSF to induce human osteoclast formation: implications for giant cell tumour pathobiology

Giant cell tumour of bone (GCTB) is a primary bone tumour that contains numerous very large, hyper-nucleated osteoclastic giant cells. Osteoclasts form from CD14+ monocytes and macrophages in the presence of receptor activator of nuclear factor kappa B ligand (RANKL) and macrophage-colony stimulating factor (M-CSF). GCTB contains numerous growth factors, some of which have been reported to influence osteoclastogenesis and resorption. We investigated whether these growth factors are capable of substituting for M-CSF to support osteoclast formation from cultured human monocytes and whether they influence osteoclast cytomorphology and resorption. Vascular endothelial growth factor-A (VEGF-A), VEGF-D, FLT3 ligand (FL), placental growth factor (PlGF) and hepatocyte growth factor (HGF) supported RANKL-induced osteoclastogenesis in the absence of M-CSF, resulting in the formation of numerous TRAP+ multinucleated cells capable of lacunar resorption. Monocytes cultured in the presence of M-CSF, HGF, VEGF-A and RANKL together resulted in the formation of very large, hyper-nucleated (GCTB-like) osteoclasts that were hyper-resorptive. M-CSF and M-CSF substitute growth factors were identified immunohistochemically in GCTB tissue sections and these factors stimulated the resorption of osteoclasts derived from a subset of GCTBs. Our findings indicate that there are growth factors that are capable of substituting for M-CSF to induce human osteoclast formation and that these factors are present in GCTB where they influence osteoclast cytomorphology and have a role in osteoclast formation and resorption activity.

Rheumatoid and pyrophosphate arthritis synovial fibroblasts induce osteoclastogenesis independently of RANKL, TNF and IL-6

Bone destruction is a common feature of inflammatory arthritis and is mediated by osteoclasts, the only specialized cells to carry out bone resorption. Aberrant expression of receptor activator of nuclear factor kappa β ligand (RANKL), an inducer of osteoclast differentiation has been linked with bone pathology and the synovial fibroblast in rheumatoid arthritis (RA). In this manuscript, we challenge the current concept that an increase in RANKL expression governs osteoclastogenesis and bone destruction in autoimmune arthritis. We isolated human fibroblasts from RA, pyrophosphate arthropathy (PPA) and osteoarthritis (OA) patients and analyzed their RANKL/OPG expression profile and the capacity of their secreted factors to induce osteoclastogenesis. We determined a 10-fold increase of RANKL mRNA and protein in fibroblasts isolated from RA relative to PPA and OA patients. Peripheral blood mononuclear cells (PBMC) from healthy volunteers were cultured in the presence of RA, PPA and OA synovial fibroblast conditioned medium. Osteoclast differentiation was assessed by expression of tartrate-resistant acid phosphatase (TRAP), vitronectin receptor (VNR), F-actin ring formation and bone resorption assays. The formation of TRAP(+), VNR(+) multinucleated cells, capable of F-actin ring formation and lacunar resorption in synovial fibroblast conditioned medium cultures occured in the presence of osteoprotegerin (OPG) a RANKL antagonist. Osteoclasts did not form in these cultures in the absence of macrophage colony stimulating factor (M-CSF). Our data suggest that the conditioned medium of pure synovial fibroblast cultures contain inflammatory mediators that can induce osteoclast formation in human PBMC independently of RANKL. Moreover inhibition of the TNF or IL-6 pathway was not sufficient to abolish osteoclastogenic signals derived from arthritic synovial fibroblasts. Collectively, our data clearly show that alternate osteoclastogenic pathways exist in inflammatory arthritis and place the synovial fibroblast as a key regulatory cell in bone and joint destruction, which is a hallmark of autoimmune arthritis.

Inflammatory osteoclastogenesis can be induced by GM-CSF and activated under TNF immunity

In inflammatory arthritis such as RA, osteoclastic activity is severely enhanced. GM-CSF was reportedly elevated in synovial fluid, but is a strong inhibitor of osteoclastogenesis; here lies a contradiction. Our objective was to examine what type of osteoclasts generate and resorb bone with resistance to GM-CSF in an inflammatory joint. Monocyte-derived cells generated in GM-CSF were morphologically and immunophenotypically different from both the conventional DC and macrophage. They could differentiate into osteoclasts in the presence of RANKL + M-CSF, acquiring a stronger osteoclastic activity under TNF treatment. Furthermore, their differentiation was not inhibited by GM-CSF, while monocyte-derived osteoclast differentiation was completely inhibited. The resorption was suppressed by GM-CSF, and the existence of another osteoclastic pathway has been suggested. Our findings indicate another type of osteoclast exists in inflammatory arthritis.

CD34 human hematopoietic progenitor cell line, MUTZ-3, differentiates into functional osteoclasts

OBJECTIVE

CD14(+) monocyte cell lines can differentiate into an osteoclast (OC)-like lineage. However, the identification of human cell lines with stem cell characteristics, capable of differentiating into OCs, would provide a tool for the study of the molecular mechanisms regulating their commitment, differentiation, and function. Since the human acute myeloid leukemia cell line MUTZ-3 contains both CD34(+) stem cell and CD14(+) cell populations, we investigated the capacity of the stem/progenitor CD34(+) population to differentiate into functional OCs.

MATERIALS AND METHODS

Sorted MUTZ-3-CD34(+) and MUTZ-3-CD14(+) cells were cultured in presence of M-CSF, RANK-L, and TNF-alpha to generate OCs. Differentiation was evaluated by TRAP staining and RT-PCR, which assessed the expression of c-fms, RANK, MMP-9, CATK, TRAP, and CTR in -CD34(+)OC and -CD14(+)OC cells. Resorption pit formation was also evaluated. CD34, CD14, M-CSF-R, RANK, and CTR expression was assessed by FACS analysis.

RESULTS

MUTZ-3-CD34(+) differentiated into OCs, displaying the full range of differentiation markers; MMP-9, CATK, TRAP, and RANK mRNA were detected from day 3 of culture, whereas CTR from day 12. Stimulated MUTZ-3-CD34(+) generated functional osteoclasts that formed extensive resorption lacunae on both mineralized surface and bone slices. Surprisingly, in both sorted populations we identified a population M-CSF-R(+)/RANK(+) that at the same time co-expressed CD14 and CD34.

CONCLUSIONS

These findings demonstrate that MUTZ-3 cells constitute an invaluable model to study the expression pattern in different developmental stages of commitment and differentiation. Importantly, the data indicate that the CD14(+)CD34(+)M-CSF-R(+)RANK(+) population represents an intermediate stage of differentiation from CD34 precursors and monocytes to osteoclast.

Fcgamma receptors directly mediate cartilage, but not bone, destruction in murine antigen-induced arthritis: uncoupling of cartilage damage from bone erosion and joint inflammation

OBJECTIVE

To determine the relationship between synovial inflammation and the concomitant occurrence of cartilage and bone erosion during conditions of variable inflammation using various Fcgamma receptor knockout (FcgammaR(-/-)) mice.

METHODS

Antigen-induced arthritis (AIA) was introduced in the knee joints of various FcgammaR(-/-) mice and wild-type controls. Joint inflammation and cartilage and bone destruction levels were determined by histologic analysis. Cathepsin K, RANKL, and osteoprotegerin (OPG) levels were detected by immunolocalization.

RESULTS

In FcgammaRIIb(-/-) mice, which lack the inhibiting Fcgamma receptor IIb, levels of joint inflammation and cartilage and bone destruction were significantly higher (infiltrate 93%, exudate 200%, cartilage 100%, bone 156%). AIA in mice lacking activating FcgammaR types I, III, and IV, but not FcgammaRIIb (FcR gamma-chain(-/-) mice), prevented cartilage destruction completely. In contrast, levels of bone erosion and joint inflammation were comparable with their wild-type controls. Of great interest, in arthritic mice lacking activating FcgammaR types I, II, and III, but not IV (FcgammaRI/II/III(-/-) mice), levels of joint inflammation were highly elevated (infiltrate and exudate, 100% and 188%, respectively). Cartilage destruction levels were decreased by 92%, whereas bone erosion was increased by 200%. Cathepsin K, a crucial mediator of osteoclasts, showed a strong correlation with the amount of inflammation but not with the amount of activating FcgammaR, which was low in osteoclasts. RANKL, but not OPG, levels were higher in the inflammatory cells of arthritic knee joints of FcgammaRI/II/III(-/-) mice versus wild-type mice.

CONCLUSION

Activating FcgammaR are crucial in mediating cartilage destruction independently of joint inflammation. In contrast, FcgammaR are not directly involved in bone erosion. Indirectly, FcgammaR drive bone destruction by regulating joint inflammation.

Multiple roles of M-CSF in human osteoclastogenesis

Although the critical role of M-CSF in osteoclastogenesis is well documented, there has been no detailed analysis of how it regulates human osteoclast formation and function in vitro. We used a human osteoclastogenesis model employing CFU-GM osteoclast precursors cultured for 14 days on dentine with RANKL, with varying exposure to exogenous human M-CSF. Short-term treatment of precursors with M-CSF (10-100 ng/mL) resulted in increased proliferation with or without RANKL. Treatment with M-CSF (1-100 ng/mL) for 14 days caused a biphasic concentration-dependent stimulation of formation, fusion, and resorption peaking at 10-50 ng/mL and almost complete abolition of resorption at 100 ng/mL. Time-course studies using M-CSF (25 ng/mL) showed that osteoclast size, nuclei/cell, and resorption increased with longer duration of M-CSF treatment. When treatment was restricted to the first 4 days, M-CSF (25-100 ng/mL) stimulated formation of normal numbers of osteoclasts that resorbed less. Blockade of endogenous M-CSF signaling with neutralizing M-CSF antibody during the first week of culture extensively inhibited osteoclastogenesis, whereas blockade during the second week produced only a small reduction in resorption. Treatment with M-CSF during the second week of culture caused a small increase in osteoclast number and a concentration-dependent increase in cytoplasmic spreading with inhibition of resorption. We have shown that M-CSF modulates multiple steps of human osteoclastogenesis, including proliferation, differentiation and fusion of precursors. In the later stages of osteoclastogenesis, M-CSF modulates osteoclast-resorbing activity, but is not required for survival. Modulation of M-CSF signaling is a potential therapeutic target for conditions associated with excess bone resorption.

Rheumatoid synovial endothelial cells produce macrophage colony-stimulating factor leading to osteoclastogenesis in rheumatoid arthritis

OBJECTIVES

Periarticular osteoporosis and joint destruction are major complications in rheumatoid arthritis (RA), caused by osteoclast-mediated bone resorption. However, the mechanisms of monocyte/osteoclast maturation and role of RA endothelial cells (RAECs) in the control of osteoclastogenesis remain unclear. The present study was designed to determine the most important factors that influence monocyte accumulation and osteoclast formation among the many factors produced by RAEC.

METHODS

We analysed the expression profiles of various genes in human endothelial cells from various organs (RA synovium, umbilical vein, skin, liver sinusoid, renal glomerulus and brain) using oligonucleotide microarrays. Specifically, up-regulated gene in RAECs was assessed by real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and immunostaining of RA synovia. Migration of monocytes was assessed by the chemotactic chamber EZ-TAXIScan. Tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cell (MNC) formation was observed by microscopy.

RESULTS

Among many epithelial-expressed factors, macrophage colony-stimulating factor (M-CSF) gene was abundantly expressed specifically in RAECs. Genes of fibroblast growth factor-2, interleukin-6 and osteoprotegerin were also overexpressed in RAECs. Migration of monocytes and osteoclast formation in co-cultures promoted by culture supernatants of RAECs were inhibited by M-CSF neutralizing antibody.

CONCLUSIONS

M-CSF produced by RAECs is involved in osteoclastogenesis from monocytes, migration and TRAP-positive MNC formation.

Human periodontal ligament cells secrete macrophage colony-stimulating factor in response to tumor necrosis factor-alpha in vitro

BACKGROUND

Human periodontal ligament (HPDL) cells may support osteoclastogenesis by expressing receptor activator of nuclear factor-kappa B ligand (RANKL) in response to periopathogenic factors and inflammatory cytokines. Because osteoclastogenesis requires the presence of macrophage colony-stimulating factor (M-CSF), we examined whether HPDL cells secrete M-CSF in response to tumor necrosis factor-alpha (TNF-alpha).

METHODS

Cultured HPDL cells were treated with TNF-alpha in serum-free condition. The expression of M-CSF and RANKL was determined by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Inhibitors and anti-TNF receptor (TNFR) neutralizing antibodies were used for the inhibitory experiments. A migration assay was performed.

RESULTS

TNF-alpha upregulated M-CSF and RANKL in HPDL cells. The effect on M-CSF expression could be partially blocked by pyrrolidine-dithiocarbamate ammonium salt and LY294002 but not by NS398. Neutralizing antibody to TNFR1 could diminish the effect of TNF-alpha. In addition, TNF-treated culture medium exhibited chemotactic effect for RAW264.7.

CONCLUSIONS

HPDL cells are capable of secreting M-CSF and expressing RANKL in response to TNF-alpha. The upregulation of M-CSF is possibly one of the mechanisms essential for periodontal tissue destruction in response to inflammatory cytokines. The upregulation is partly through nuclear factor-kappa B (NF-kappaB) and phosphatidylinositol 3'-kinase and possibly involves TNFR1.