Differentiation Of Osteoclast Precursors Research Articles

Phosphatidylserine‐Incorporated Exosome Mimetics Encapsulating CXCR3 Antagonist Alleviate Osteoporosis

AbstractExosomes derived from mesenchymal stem cells are an active area of research due to their therapeutic potential in treating osteoporosis. To further harness their therapeutic performance in modulating bone resorption, equipped exosomes with osteoclast‐targeting moieties on their surface as well as chemokine receptor antagonists blocking osteoclast recruitment. Phosphatidylserine (PS), a membrane lipid exerting immunosuppressive and phagocytic signals, is incorporated in the membrane of exosome mimetics (EMs) to achieve a marked affinity for osteoclast precursors and potential anti‐resorptive effects. This is also aimed to tackle a CXCL9‐CXCR3 ligand‐receptor axis, a critical signaling axis in regulating osteoclast precursor recruitment and differentiation at bone resorption sites, by encapsulating a chemical antagonist of CXCR3, AMG487, in the PS‐incorporated EMs (PS‐EMs). The osteoclast‐targeting PS‐EMs loaded with AMG487 effectively protected against bone loss in an ovariectomized mouse model. These findings demonstrate the great promise of PS‐EMs as anti‐resorptive nanotherapies for alleviating osteoporosis.

Osteomesopyknosis associated with a novel ALOX5 variant that impacts the RANKL pathway.

Bone tissue homeostasis relies on the coordinated activity of the bone-forming osteoblasts and bone-resorbing osteoclasts. Osteomesopyknosis is considered a distinctive rare sclerosing skeletal disorder of unelucidated pathophysiology and presumably autosomal dominant transmission. However, the causal genes are unknown. We present a case report encompassing clinical assessments, imaging studies, and whole-exome sequencing analysis, complemented by functional invitro experiments. This new case of osteomesopyknosis was associated with a missense ALOX5 variant predicted to induce protein misfolding and proteasomal degradation. Transfection experiments demonstrated that the variant was associated with reduced protein levels restored by proteasomal inhibition with bortezomib. Likewise, gene expression analysis showed that the mutated gene was associated with a decreased RANKL/OPG ratio, which is a critical driver of osteoclast precursor differentiation. Our data indicate impaired bone resorption as the underlying mechanism of this rare osteosclerosis, implicating ALOX5 pathogenic variants as potential etiological factors.

The chromatin remodeling factor Arid1a cooperates with Jun/Fos to promote osteoclastogenesis by epigenetically upregulating Siglec15 expression.

Osteoporosis is characterized by an imbalance between osteoclast-mediated bone resorption and osteoblast-related bone formation, particularly increased osteoclastogenesis. However, the mechanisms by which epigenetic factors regulate osteoclast precursor differentiation during osteoclastogenesis remain poorly understood. Here, we show that the specific knockout of the chromatin remodeling factor Arid1a in bone marrow-derived macrophages (BMDMs) results in increased bone mass. The loss of Arid1a in BMDM inhibits cell-cell fusion and maturation of osteoclast precursors, thereby suppressing osteoclast differentiation. Mechanistically, Arid1a increases the chromatin access in the gene promoter region of sialic acid-binding Ig-like lectin 15 (Siglec15) by transcription factor Jun/Fos, which results in the upregulation of Siglec15 and promotion of osteoclast differentiation. However, the loss of Arid1a reprograms the chromatin structure to restrict Siglec15 expression in osteoclast precursors, thereby inhibiting BMDM differentiation into mature osteoclasts. Deleting Arid1a after ovariectomy (a model for postmenopausal bone loss) alleviated bone loss and maintained bone mass. In summary, epigenetic reprogramming mediated by Arid1a loss suppresses osteoclast differentiation and may serve as a promising therapeutic strategy for treating bone loss diseases.

Stable Sulforaphane Targets the Early Stages of Osteoclast Formation to Engender a Lasting Functional Blockade of Osteoclastogenesis.

Sulforaphane, the native but unstable form of SFX-01, is an antioxidant that activates the NRF2 and inhibits the NF-KB pathways to achieve its actions. Resolving the mechanism(s) by which SFX-01 serves to control the various osteoclastogenic stages may expose pathways that could be explored for therapeutic use. Here we seek to identify the stage of osteoclastogenesis targeted by SFX-01 and explore whether, like SFN, it exerts its actions via the NRF2 and NF-KB pathways. Osteoclasts generated from the bone marrow (BM) of mice were cultured with SFX-01 at different timepoints to examine each phase of osteoclastogenesis separately. This showed that SFX-01 exerted actions throughout the process of osteoclastogenesis, but had its largest effects in the early osteoclast precursor differentiation stage. Thus, treatment with SFX-01 for the duration of culture, for the initial 3 days differentiation or for as little as the first 24 h was sufficient for effective inhibition. This aligned with data suggesting that SFX-01 reduced DC-STAMP levels, osteoclast nuclear number and modified cytoskeletal architecture. Pharmacological regulation of the NRF2 pathways, via selective inhibitors/activators, supported the anti-osteoclastogenic roles of an SFX-01-mediated by NRF2 activation, as well as the need for tight NF-KB pathway regulation in osteoclast formation/function.

Isolation and Characterization of an Anti-Osteoporotic Compound from Melia toosendan Fructus.

Melia toosendan fructus, traditionally employed in traditional Chinese and Korean herbal medicine, exhibits diverse biological properties encompassing anti-tumor, anti-inflammatory, and anti-viral effects. However, its influence on bone metabolism remains largely unexplored. In this study, we investigated the impact of an ethanolic extract of Melia toosendan fructus (MTE) on osteoclast differentiation and characterized its principal active constituent in osteoclast differentiation and function, as well as its effects on bone protection. Our findings demonstrate that MTE effectively inhibits the differentiation of osteoclast precursors induced by receptor activator of nuclear factor κB ligand (RANKL). Utilizing a bioassay-guided fractionation approach coupled with UHPLC-MS/MS analysis, we isolated and identified the triterpenoid compound toosendanin (TSN) as the active constituent responsible for MTE's anti-osteoclastogenic activity. TSN treatment downregulated the expression of nuclear factor of activated T cells c1, a pivotal osteoclastogenic transcription factor, along with molecules implicated in osteoclast-mediated bone resorption, including tumor necrosis factor receptor-associated factor 6, carbonic anhydrase II, integrin beta-3, and cathepsin K. Furthermore, treatment of mature osteoclasts with TSN impaired actin ring formation, acidification, and resorptive function. Consistent with our in vitro findings, TSN administration mitigated trabecular bone loss and reduced serum levels of the bone resorption marker, C-terminal cross-linked telopeptides of type I collagen, in a mouse bone loss model induced by intraperitoneal injections of RANKL. These results suggest that TSN, as the principal active constituent of MTE with inhibitory effects on osteoclastogenesis, exhibits bone-protective properties by suppressing both osteoclast differentiation and function. These findings imply the potential utility of TSN in the treatment of diseases characterized by excessive bone resorption.

Differentiation-inducing effect of osteoclast microgrooves for the purpose of three-dimensional design of regenerated bone.

In vivo bone remodeling is promoted by the balance between osteoclast and osteoblast activity. Conventional research on bone regeneration has mainly focused on increasing osteoblast activity, with limited studies on the effects of scaffold topography on cell differentiation. Here, we examined the effect of microgroove-patterned substrate with spacings ranging from 1 to 10 μm on the differentiation of rat bone marrow-derived osteoclast precursors. Tartrate-resistant acid phosphatase (TRAP) staining and relative gene expression quantification showed that osteoclast differentiation was enhanced in substrate with 1 µm microgroove spacing compared with that in the other groups. Additionally, the ratio of podosome maturation stages in substrate with 1 μm microgroove spacing exhibited a distinct pattern, which was characterized by an increase in the ratio of belts and rings and a decrease in that of clusters. However, myosin II abolished the effects of topography on osteoclast differentiation. Overall, these showed that the reduction of myosin II tension in the podosome core by an integrin vertical vector increased podosome stability and promoted osteoclast differentiation in substrates with 1 μm microgroove spacing, including that microgroove design plays an important role in scaffolds for bone regeneration. STATEMENT OF SIGNIFICANCE: Reduction of myosin II tension in the podosome core, facilitated by an integrin vertical vector, resulted in an enhanced osteoclast differentiation, concomitant with an increase in podosome stability within 1-μm-spaced microgrooves. These findings are anticipated to serve as valuable indicators for the regulation of osteoclast differentiation through the manipulation of biomaterial surface topography in tissue engineering. Furthermore, this study contributes to the lucidation of the underlying mechanisms governing cellular differentiation by providing insights into the impact of the microtopographical environment.

Obesity, but not high-fat diet, is associated with bone loss that is reversed via CD4+CD25+Foxp3+ Tregs-mediated gut microbiome of non-obese mice

Osteoporosis is characterized by decreased bone mass, microarchitectural deterioration, and increased bone fragility. High-fat diet (HFD)-induced obesity also results in bone loss, which is associated with an imbalanced gut microbiome. However, whether HFD-induced obesity or HFD itself promotes osteoclastogenesis and consequent bone loss remains unclear. In this study, we developed HFD-induced obesity (HIO) and non-obesity (NO) mouse models to evaluate the effect of HFD on bone loss. NO mice were defined as body weight within 5% of higher or lower than that of chow diet fed mice after 10 weeks HFD feeding. NO was protected from HIO-induced bone loss by the RANKL /OPG system, with associated increases in the tibia tenacity, cortical bone mean density, bone volume of cancellous bone, and trabecular number. This led to increased bone strength and improved bone microstructure via the microbiome-short-chain fatty acids (SCFAs) regulation. Additionally, endogenous gut-SCFAs produced by the NO mice activated free fatty acid receptor 2 and inhibited histone deacetylases, resulting in the promotion of Treg cell proliferation in the HFD-fed NO mice; thereby, inhibiting osteoclastogenesis, which can be transplanted by fecal microbiome. Furthermore, T cells from NO mice retain differentiation of osteoclast precursors of RAW 264.7 macrophages ex vivo. Our data reveal that HFD is not a deleterious diet; however, the induction of obesity serves as a key trigger of bone loss that can be blocked by a NO mouse-specific gut microbiome.

IL-17A regulates autophagy and promotes osteoclast differentiation through the ERK/mTOR/Beclin1 pathway.

Bone is a frequent target of tumor metastasis, with high incidence rate and poor prognosis. Osteoclasts play a key role in the process of tumor bone metastasis. Interleukin-17A (IL-17A) is an inflammatory cytokine, highly expressed in a variety of tumor cells, that can alter the autophagic activity of other cells, thereby causing corresponding lesions. Previous studies have shown that low concentration IL-17A can promote osteoclastogenesis. The aim of this study was to clarify the mechanism of low concentration IL-17A promoting osteoclastogenesis by regulating autophagic activity. The results of our study showed that IL-17A could promote the differentiation of osteoclast precursors (OCPs) into osteoclasts in the presence of RANKL, and increase the mRNA levels of osteoclast-specific genes. Moreover, IL-17A increased the expression of Beclin1 by inhibiting the phosphorylation of ERK and mTOR, leading to enhanced autophagy of OCPs, accompanied by decreased OCP apoptosis. Furthermore, knockdown of Beclin1 and suppression of autophagy by 3-methyladenine (3-MA) significantly attenuated the enhanced osteoclastogenesis induced by IL-17A. In summary, these results indicate that low concentration IL-17A enhances the autophagic activity of OCPs through the ERK/mTOR/Beclin1 pathway during osteoclastogenesis, and further promotes osteoclast differentiation, suggesting that IL-17A may serve as a potential therapeutic target for cancer-related bone resorption in cancer patients.

In-vitro analysis of resorption processes following high hydrostatic pressure treatment of human trabecular bone

The present study focused on the investigation of the resorption behavior of high hydrostatic pressure (HHP) treated bone allografts in vitro by analyzing the differentiation and activity of osteoclast precursors. HHP is known to be an efficient method for devitalization of bone grafts and a gentle alternative compared to conventional processing. While bone resorption is part of the physiological fracture healing, highly processed allografts are prone to excessive degradation, which ultimately leads to graft failure. The influence of HHP treatment on the extent of resorption was analyzed in bone blocks cultivated with peripheral blood mononuclear cells (PBMCs). Data on gene and protein expression as well as histological alterations were obtained. The present study showed that an application of 500 MPa led to significant osteoclastic differentiation and activity which was observed already after 8 h of incubation. Whereas a treatment of 250 MPa resulted also in the differentiation of PBMCs, osteoclastic activity was similar to the untreated control. Thus, the pressure level of HHP is crucial for the extent of degradation processes. Based on our results a treatment with 500 MPa might not be suitable for allografts intended for subsequent clinical applications. This study provides a basis for further experiments including in vivo studies which should focus on the equilibrium of bone formation and bone resorption.

Structural and functional state of bone tissue in young people with a combined course of osteoarthritis and obesity

In recent years, an increase in the number of patients with osteoarthritis(ОА) against the background of obesity is considered not from the point of view of mechanicalstress on the joints by an overweight patient but by the active synthesis of hormone-likesubstances by adipose tissue, which have a metabolic effect on all processes in the body. A largenumber of different chemical compounds (calcium, phosphorus, magnesium, uronic acids,tartrate-resistant bone phosphatase, and a number of others) are involved in the remodeling ofbone tissue, the balance between which determines the strength and mobility of the bone. Among
 such biochemical markers, the glycoprotein osteoprotegerin is considered. The osteoprotegerininhibits the differentiation of osteoclast precursors into osteoclasts and also regulates theirresorption in vitro and in vivo. It works by binding to RANKL on osteoblast / stromal cells,thereby blocking the RANKL-RANK ligand interaction between osteoblasts / stromal cells andosteoclast precursors.The aim of our study to establish the content of osteoprotegerin in the blood serum of youngpatients with osteoarthritis and obesity and to analyze its role in the formation of structural andfunctional changes in bone tissue. The work was performed on 75 young patients (average age -30.92 ± 0.55 years) with OA, which was established in patients with various stages of obesity; forthe comparison group, 50 individuals with an isolated course of OA of the same age (30.95 ±0.55 years) and duration of anamnesis were selected; control indicators were obtained whenexamining 37 apparently healthy individuals. The diagnosis of OA was confirmed by acomprehensive assessment of patients' complaints, anamnesis data, objective and instrumentalstudies (X-ray examination of the affected joints) while focusing on the "Protocols for themanagement of patients with osteoarthritis." The presence and severity of obesity were assessedaccording to the criteria of the International Diabetes Federation (IDF, 2005) based on thecalculation of body mass index (BMI) according to the Kettle formula. The indicator ofosteoprotegerin (pg / ml) (bone tissue glycoprotein) was investigated in fasting blood serum byenzyme-linked immunosorbent assay (ELISA) using FineTest EH0247 reagents, China. Theprevalence of osteoporotic conditions was assessed by dual-energy X-ray absorptiometry(DEXA) using the HOLOGIC Explorer QDR W Series Bone Densitometer (USA). The content ofosteoprotegerin in blood serum was studied as a biochemical marker of damage to the bone andcartilage tissue. The data obtained allowed us to say that in both groups - patients with OA (92.3± 1.68 pg / ml) and patients with a combination of OA with obesity and increased body weight
 (124.03 ± 3.2 pg / ml) - there was an increase in this glycoprotein when compared with thecontrol values ​​(65.64 ± 0.64), (p <0.001). The performed densitometric study allowed us toobtain the following results: osteopenia was identified in 15% of patients in main group and in36% - in comparison group; osteoporosis was identified in 24% of patients in main group and in10% - in comparison group.The course of osteoarthritis in young people is accompanied by theformation of osteoporotic conditions, which more often (24% versus 10%), with the addition ofobesity, lead to the development of osteoporosis. The development of osteoporotic changes inpatients with osteoarthritis and in combination with obesity is accompanied by an increase in thesynthesis of osteoprotegerin, a glycoprotein involved in the processes of bone tissue remodeling.

Titanium surface with nanospikes tunes macrophage polarization to produce inhibitory factors for osteoclastogenesis through nanotopographic cues

Definitive prevention of inflammatory osteolysis around peri-implant bone tissue remains unestablished. M1 macrophages play a key role in the host defense against inflammatory osteolysis, and their polarization depends on cell shape. Macrophage polarization is controlled by environmental stimuli, particularly physicochemical cues and hence titanium nanosurface might tune macrophage polarization and function. This study determined whether titanium nanosurfaces with anisotropically patterned nanospikes regulates macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors. Alkaline-etching treatment with different protocols created two types of titanium nanosurfaces that had anisotropically patterned nanospikes with high or low distribution density, together with superhydrophilicity and the presence of hydroxyl groups. J774A.1 cells (mouse macrophage-like cell line), cultured on both titanium nanosurfaces, exhibited truly circulated shapes and highly expressed M1, but less M2, markers, without loss of viability. M1-like polarization of macrophages on both titanium nanosurfaces was independent of protein-mediated ligand stimulation or titanium surface hydrophilic or chemical status. In contrast, other smooth or micro-roughened titanium surfaces with little or no nanospikes did not activate macrophages under any culture conditions. Macrophage culture supernatants on both titanium nanosurfaces inhibited osteoclast differentiation of RAW264.7 cells (mouse osteoclast precursor cell line), even when co-incubated with osteoclast differentiation factors. The inhibitory effects on osteoclast differentiation tended to be higher in macrophages cultured on titanium nanosurfaces with denser nanospikes. These results showed that titanium nanosurfaces with anisotropically patterned nanospikes tune macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors, with nanotopographic cues rather than other physicochemical properties. Statement of significancePeri-implant inflammatory osteolysis is one of the serious issues for dental and orthopedic implants. Macrophage polarization and function are key for prevention of peri-implant inflammatory osteolysis. Macrophage polarization can be regulated by the biomaterial's surface physicochemical properties such as hydrophilicity or topography. However, there was no titanium surface modification to prevent inflammatory osteolysis through immunomodulation. The present study showed for the first time that the titanium nanosurfaces with anisotropically patterned nanospikes, created by the simple alkali-etching treatment polarized macrophages into M1-like type producing the inhibitory factor on osteoclast differentiation. This phenomenon attributed to nanotopographic cues, but not hydrophilicity on the titanium nanosurfaces. This nanotechnology might pave the way to develop the smart implant surface preventing peri-implant inflammatory osteolysis through immunomodulation.

Senescent RAW264.7 cells exhibit increased production of nitric oxide and release inducible nitric oxide synthase in exosomes.

Aging cells not only cease growing, but also secrete various proteins such as inflammatory cytokines. This secretory phenomenon is known as the senescence‑associated secretory phenotype (SASP). The aim of the present study was to elucidate the effects of senescence on the differentiation of osteoclast precursors (OCPs) and corresponding SASP. RAW264.7 cells were used as OCPs and were cultured to passage (P)5, P10 and P20. Cell proliferation assays, senescence‑associated β‑galactosidase staining and telomere length quantification were subsequently performed, and it was revealed that replicative senescence was induced at P20. In addition, the level of tartrate‑resistant acid phosphatase activity in P20 cells treated with receptor activator of nuclear factor‑κB ligand was significantly lower than that in P5 and P10 cells. The SASP factors interleukin‑6, tumour necrosis factor‑α and nitric oxide were significantly increased in P20 culture supernatants compared with those in P5 and P10 supernatants. Furthermore, the number of exosomes at P20 was increased compared with that at P5 and P10, and inducible nitric oxide synthase (iNOS) was expressed in exosomes at P20, but not in exosomes at P5. In conclusion, the present study revealed that senescent RAW264.7 cells exhibit increased expression of SASP factors and release iNOS in exosomes.

Aplidin (Plitidepsin) Regulates Viability and Function of Myeloma Cells and Bone Cells in Combination with Other Anti-MM Drugs

In multiple myeloma (MM) the clonal expansion of malignant plasma cells within the bone marrow results in the development of lytic bone lesions due to exacerbated bone resorption. Despite recent progress in its treatment, MM remains incurable and the associated bone disease persists even after complete remission. Thus, identification of new therapeutic approaches that suppress MM cell growth and protect the bone is an unmet need. Aplidin, a novel anti-cancer compound isolated from the marine tunicate Aplidium albicans, exhibits anti-MM activity even in MM cells resistant to conventional chemotherapy and is currently in phase III clinical trials in Europe. However, the effects of Aplidin on bone cells and MM-induced bone disease are unknown. The goal of the current study was to examine the effect of Aplidin, alone or in combination with other anti-MM drugs, on myeloma cells and bone cells (osteocytes, osteoblasts, and osteoclasts) using in vitro approaches.Aplidin decreased the number of human JJN3 and murine 5TGM1 MM cells with an EC50~10nM, determined by MTT assay, due to decreased cell viability, assessed by Trypan blue exclusion, reaching a 20% increase in MM cell death after 48h. Treatment with glucocorticoids (GC) (10-5M) or Bortezomib (3nM) also decreased MM viability and enhanced the anti-MM activity of Aplidin by 1.6-fold and 2.5-fold, respectively. In addition, Aplidin at >10nM induced MLO-A5 osteocytic dead up to 15% and in combination with GC up to 50%; whereas, in contrast, Bortezomib did not affect osteocyte viability and partially prevented the increase in MLO-A5 cell death induced by Aplidin. Further, 1nM Aplidin increased OB-6 osteoblastic cell death up to 20% and decreased their matrix mineralization capacity, quantified by Alizarin red. These effects were enhanced when Aplidin was combined with GC, but partially prevented by combination of Aplidin with Bortezomib. Cells of the osteoclastic lineage exhibited higher sensitivity to Aplidin in comparison to MM cells or osteoblastic cells, and thus it was tested at lower concentrations. Specifically, 50 pM Aplidin decreased the number of hematopoietic precursors by 15-20%, as quantified by enumerating GM-CSF colonies in cultures established from murine bone marrow. Moreover, Aplidin, at concentrations as low as 0.01 pM, reduced osteoclast precursor commitment and differentiation by 10%, as quantified by enumerating the number of osteoclast precursors maintained in the presence of M-CSF for 3 days with or without Aplidin. In addition, Aplidin decreased by 40% the number of TRAP positive osteoclasts generated after 4 days in the presence of M-CSF and sRANKL; and blunted the rapid (5-15min) increased in ERK phosphorylation induced by Rankl, but did not affect RANKL-induced p38 phosphorylation, suggesting that Aplidin inhibited RANKL-induced differentiation of osteoclast precursors by preventing ERK activation. Lastly, to test the effects of Aplidin on osteoclasts function, mature osteoclasts generated in the presence of M-CSF/sRANKL were detached by trypsinization, replated on bovine dentin slides and exposed to Aplidin for 3 and 7 days. 10pM Aplidin reduced the number of mature osteoclasts by 60% and markedly decreased the number of resorption pits.In summary, Aplidin (1nM and up) decreases MM cell viability and GC or Borteozmib enhances its anti-MM activity. In addition, Aplidin (10nM and up) decreases osteocytic cell viability and this effect is exacerbated by GC but partially prevented by Bortezomib. Moreover, Aplidin (1nM and up) induces osteoblastic cell death and decreases their mineral production, and these effects are increased by GC, but partially prevented by Bortezomib. Furthermore, Aplidin (0.01pM and up) reduces osteoclast precursor commitment and differentiation, and inhibits mature osteoclast resorption activity. Taken together these findings suggest that combining Aplidin with proteosomal inhibitors may be a novel therapy for MM to enhance anti-tumor responses, decrease bone destruction by inhibiting bone resorption, and prevent potential side effects of Aplidin on cells of the osteoblastic lineage. DisclosuresDelgado-Calle:PharmaMar: Research Funding. Galmarini:PharmaMar: Employment. Roodman:PharmaMar: Research Funding. Bellido:PharmaMar: Research Funding.

Lactic acid promotes metastatic niche formation in bone metastasis of colorectal cancer

BackgroundTo investigate the effect of lactic acid (LA) on the progression of bone metastasis from colorectal cancer (CRC) and its regulatory effects on primary CD115 (+) osteoclast (OC) precursors.MethodsThe BrdU assay, Annexin-V/PI assay, TRAP staining and immunofluorescence were performed to explore the effect of LA on the proliferation, apoptosis and differentiation of OC precursors in vitro and in vivo. Flow cytometry was performed to sort primary osteoclast precursors and CD4(+) T cells and to analyze the change in the expression of target proteins in osteoclast precursors. A recruitment assay was used to test how LA and Cadhein-11 regulate the recruitment of OC precursors. RT-PCR and Western blotting were performed to analyze the changes in the mRNA and protein expression of genes related to the PI3K-AKT pathway and profibrotic genes. Safranin O-fast green staining, H&E staining and TRAP staining were performed to analyze the severity of bone resorption and accumulation of osteoclasts.ResultsLA promoted the expression of CXCL10 and Cadherin-11 in CD115(+) precursors through the PI3K-AKT pathway. We found that CXCL10 and Cadherin-11 were regulated by the activation of CREB and mTOR, respectively. LA-induced overexpression of CXCL10 in CD115(+) precursors indirectly promoted the differentiation of osteoclast precursors through the recruitment of CD4(+) T cells, and the crosstalk between these two cells promoted bone resorption in bone metastasis from CRC. On the other hand, Cadherin-11 mediated the adhesion between osteoclast precursors and upregulated the production of specific collagens, especially Collagen 5, which facilitated fibrotic changes in the tumor microenvironment. Blockade of the PI3K-AKT pathway efficiently prevented the progression of bone metastasis caused by lactate.ConclusionLA promoted metastatic niche formation in the tumor microenvironment through the PI3K-AKT pathway. Our study provides new insight into the role of LA in the progression of bone metastasis from CRC.DasE7LVW6tcKsMdapJmhMFVideo

IL-33/Vitamin D Crosstalk in Psoriasis-Associated Osteoporosis.

Patients with psoriasis (Pso) and, in particular, psoriatic arthritis (PsoA) have an increased risk of developing osteoporosis (OP). It has been shown that OP is among the more common pathologies associated with Pso, mainly due to the well-known osteopenizing conditions coexisting in these patients. Pso and OP share common risk factors, such as vitamin D deficiency and chronic inflammation. Interestingly, the interleukin (IL)-33/ST2 axis, together with vitamin D, is closely related to both Pso and OP. Vitamin D and the IL-33/ST2 signaling pathways are closely involved in bone remodeling, as well as in skin barrier pathophysiology. The production of anti-osteoclastogenic cytokines, e.g., IL-4 and IL-10, is promoted by IL-33 and vitamin D, which are stimulators of both regulatory and Th2 cells. IL-33, together with other Th2 cytokines, shifts osteoclast precursor differentiation towards macrophage and dendritic cells and inhibits receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis by regulating the expression of anti-osteoclastic genes. However, while the vitamin D protective functions in OP and Pso have been definitively ascertained, the overall effect of IL-33 on bone and skin homeostasis, because of its pleiotropic action, is still controversial. Emerging evidence suggests a functional link between vitamin D and the IL-33/ST2 axis, which acts through hormonal influences and immune-mediated effects, as well as cellular and metabolic functions. Based on the actions of vitamin D and IL-33 in Pso and OP, here, we hypothesize the role of their crosstalk in the pathogenesis of both these pathologies.

NLRP3 regulates alveolar bone loss in ligature-induced periodontitis by promoting osteoclastic differentiation.

ObjectivesNLRP3 inflammasome is a critical part of the innate immune system and plays an important role in a variety of inflammatory diseases. However, the effects of NLRP3 inflammasome on periodontitis have not been fully studied.Materials and methodsWe used ligature‐induced periodontitis models of NLRP3 knockout mice (NLRP3KO) and their wildtype (WT) littermates to compare their alveolar bone phenotypes. We further used Lysm‐Cre/RosanTnG mouse to trace the changes of Lysm‐Cre+ osteoclast precursors in ligature‐induced periodontitis with or without MCC950 treatment. At last, we explored MCC950 as a potential drug for the treatment of periodontitis in vivo and in vitro.ResultsHere, we showed that the number of osteoclast precursors, osteoclast differentiation and alveolar bone loss were reduced in NLRP3KO mice compared with WT littermates, by using ligature‐induced periodontitis model. Next, MCC950, a specific inhibitor of the NLRP3 inflammasome, was used to inhibit osteoclast precursors differentiation into osteoclast. Further, we used Lysm‐Cre/RosanTnG mice to demonstrate that MCC950 decreases the number of Lysm‐Cre+ osteoclast precursors in ligature‐induced periodontitis. At last, treatment with MCC950 significantly suppressed alveolar bone loss with reduced IL‐1β activation and osteoclast differentiation in ligature‐induced periodontitis.ConclusionOur findings reveal that NLRP3 regulates alveolar bone loss in ligature‐induced periodontitis by promoting osteoclastic differentiation.

Circular RNA atlas in osteoclast differentiation with and without alendronate treatment

BackgroundAlendronate (AL) is the most widely used bisphosphonate in the treatment of osteoporosis (OP). However, the role of circular RNAs (circRNAs) in the treatment of OP with AL remains unclear.MethodsIn this study, we showed that osteoclast (OC) precursors (OPCSs) could be induced into OCs with macrophage colony-stimulating factor (MCSF) and receptor activator of nuclear factor-κB ligand (RANKL) treatment. Subsequently, the OCs were treated with AL. OC differentiation-related biomarkers including RANK, tartrate-resistant acid phosphatase (TRAP), and cathepsin K (CTSK) were analyzed with TRAP staining, quantitative real-time (qPCR), and western blotting. Differentially expressed circRNAs (DECs) were identified among the OPCS, OC, and OC + AL groups. In addition, the expression levels of 10 DECs related to OC differentiation were verified by qPCR.ResultsTRAP staining showed that MCSF and RANKL treatment effectively induced OPCSs to differentiate into OCs. In addition, qPCR and western blot analysis revealed that the three biomarkers of OC (RANK, TRAP, and CTSK) were expressed significantly more in the OC group than those in the OPCS group. In contrast, the mRNA and protein expression levels of these three biomarkers decreased significantly in OCs treated with AL compared with those non-treated OCs. GO analysis of the DECs in the OPCS group vs. the OC group revealed that their functions were mainly related to cell, cell part, binding, and single-organism terms. KEGG analysis of the top 20 DECs in a comparison between the OPCS and OC groups showed that genes involved in mitogen-activated protein kinase signaling were the most common. Results of functional analyses of DECs in an OC vs. OC + AL comparison were similar to those in the OPCS vs. OC comparison. Finally, qPCR showed that, in the OC + AL vs. OC group comparison, the expression levels of seven and three DECs significantly decreased and increased, respectively.ConclusionsHaving successfully induced OPCSs to differentiate into OCs, we showed that AL suppresses the differentiation of OPCS into OC and that 10 DECs were involved in the regulation of this process. This indicates that these DECs might be important to the treatment of OP.

Evaluation of genetic variants in IL-1B and its interaction with the predisposition of osteoporosis in the northwestern Chinese Han population.

Interleukin (IL)-1β stimulates the proliferation and differentiation of osteoclast precursors into mature osteoclasts. IL-1B polymorphisms may influence the gene and protein expression of IL-1β. The present study aimed to investigate the association of IL-1B variants (rs2853550, rs1143643, rs3136558, rs1143630, rs1143627, rs16944 and rs1143623) and their interaction with osteoporosis risk among the northwestern Chinese Han population. AN Agena MassARRAY system (Agena, San Diego, CA, USA) was employed for genotyping in 594 osteoporosis patients and 599 healthy controls. The possible association between IL-1B polymorphisms and risks of osteoporosis development was identified with odds ratios (OR) and 95% confidence intervals (CI) using logistic regression models. Haplotype analysis and multifactor dimension reduction analysis were used to explore the potential association between combined single nucleotide polymorphisms (SNPs) and osteoporosis risk. The AA genotype of rs2853550 was a protective factor for osteoporosis occurrence (OR = 0.11, p = 0.038), whereas rs16944 (OR = 1.19, p = 0.037) and rs1143623 (OR = 1.21, p = 0.025) conferred an increased risk of osteoporosis. Moreover, rs1143627, rs16944 and rs1143623 were associated with an elevated susceptibility to osteoporosis, especially in females and individuals aged > 60 years or with a body mass index > 24 kg/m2 . Haplotype Grs1143630 Ars1143627 Grs16944 was a risk factor of osteoporosis occurrence (OR = 1.20, p = 0.032). The best model of SNP-SNP analysis was a four-locus combination of rs1143643, rs3136558, rs1143630 and rs1143623 (testing accuracy = 0.5623). IL-1B polymorphisms and haplotype Grs1143630 Ars1143627 Grs16944 might contribute to susceptibility to osteoporosis. The SNP-SNP interaction of polymorphisms in IL-1B revealed the accumulated effect on osteoporosis risk.

An herbal formula inhibits STAT3 signaling and attenuates bone erosion in collagen-induced arthritis rats

BackgroundReceptor activator of NF-κB ligand (RANKL) facilitates differentiation of osteoclast precursors into osteoclasts, resulting in bone erosion in rheumatoid arthritis (RA) patients. Fibroblast-like synoviocytes (FLS) are the main cells for producing RANKL. Signal transducer and activator of transcription 3 (STAT3) signaling is activated in FLS of RA patients (RA-FLS), which has been linked to RANKL production. A two-herb formula (RL) comprising Rosae Multiflorae Fructus and Lonicerae Japonicae Flos is traditionally used for treating RA in China. We have found that a standardized ethanolic extract of RL (RLE for short) alleviates bone erosion in collagen-induced arthritis (CIA) rats. PurposeThis study aimed to determine whether RLE inhibits RANKL production and osteoclastogenesis in cell and rat models, and to explore the involvement of the STAT3 pathway in this inhibition. Study Design and MethodsA CIA rat model, interleukin-6/soluble interleukin-6 receptor (IL-6/sIL-6R)-stimulated RA-FLS and a co-culture system (IL-6/sIL-6R-stimulated RA-FLS/peripheral blood mononuclear cells) were used to evaluate the effects of RLE. Micro-computed tomography analysis was used to observe bone erosion in CIA rats. Tartrate-resistant acid phosphatase staining was used to evaluate osteoclastogenesis. Western blotting and ELISA assays were employed to examine protein levels. RT-qPCR was used to detect mRNA levels. STAT3-over-activated RA-FLS were used to investigate the involvement of STAT3 signaling in the anti-osteoclastogenic effects of RLE. ResultsRLE alleviated bone erosion in joints of CIA rats. In both synovial tissues of CIA rats and IL-6/sIL-6R-stimulated RA-FLS, RLE downregulated the protein level of RANKL. In the co-culture system, RLE significantly and dose-dependently inhibited IL-6/sIL-6R-induced osteoclastogenesis. Mechanistic studies revealed that RLE lowered the protein level of phospho-STAT3 (Tyr705) in synovial tissues of CIA rats. In IL-6/sIL-6R-stimulated RA-FLS, RLE inhibited the activation/phosphorylation of a STAT3 upstream kinase Janus kinase 2 (Tyr1007/1008) and STAT3 (Tyr705), decreased the nuclear localization of STAT3, lowered mRNA levels of STAT3-transcriptionally regulated genes IL-1β and TNF-α. RLE's inhibitory effects on RANKL production in RA-FLS gradually decreased when IL-6/sIL-6R doses increased. Over-activation of STAT3 diminished the inhibitory effects of RLE on RANKL production in IL-6/sIL-6R-stimulated RA-FLS, and attenuated the anti-osteoclastogenic effects of RLE in the co-culture system. ConclusionWe, for the first time, demonstrated that suppressing STAT3 signaling contributes to the inhibition of RANKL production and osteoclastogenesis, and thereby supports the mechanisms responsible for the reduction in bone erosion in RLE-treated CIA rats. This study provides further pharmacological groundwork for developing RLE as a modern anti-arthritic drug, and supports the notion that targeting STAT3 signaling is a viable strategy for managing bone erosion.

The tethering function of mitofusin2 controls osteoclast differentiation by modulating the Ca2+–NFATc1 axis

Dynamic regulation of the mitochondrial network by mitofusins (MFNs) modulates energy production, cell survival, and many intracellular signaling events, including calcium handling. However, the relative importance of specific mitochondrial functions and their dependence on MFNs vary greatly among cell types. Osteoclasts have many mitochondria, and increased mitochondrial biogenesis and oxidative phosphorylation enhance bone resorption, but little is known about the mitochondrial network or MFNs in osteoclasts. Because expression of each MFN isoform increases with osteoclastogenesis, we conditionally deleted MFN1 and MFN2 (double conditional KO (dcKO)) in murine osteoclast precursors, finding that this increased bone mass in young female mice and abolished osteoclast precursor differentiation into mature osteoclasts in vitro Defective osteoclastogenesis was reversed by overexpression of MFN2 but not MFN1; therefore, we generated mice lacking only MFN2 in osteoclasts. MFN2-deficient female mice had increased bone mass at 1 year and resistance to Receptor Activator of NF-κB Ligand (RANKL)-induced osteolysis at 8 weeks. To explore whether MFN-mediated tethering or mitophagy is important for osteoclastogenesis, we overexpressed MFN2 variants defective in either function in dcKO precursors and found that, although mitophagy was dispensable for differentiation, tethering was required. Because the master osteoclastogenic transcriptional regulator nuclear factor of activated T cells 1 (NFATc1) is calcium-regulated, we assessed calcium release from the endoplasmic reticulum and store-operated calcium entry and found that the latter was blunted in dcKO cells. Restored osteoclast differentiation by expression of intact MFN2 or the mitophagy-defective variant was associated with normalization of store-operated calcium entry and NFATc1 levels, indicating that MFN2 controls mitochondrion-endoplasmic reticulum tethering in osteoclasts.