Osteoclast formation and activity in the pathogenesis of osteoporosis in rheumatoid arthritis

Aging-Related Rotator Cuff Tears: Molecular Mechanisms and Implications for Clinical Management

Shoulder pain and disabilities are prevalent issues among the elderly population, with rotator cuff tear (RCT) being one of the leading causes. Although surgical treatment has shown some success, high postoperative retear rates remain a great challenge, particularly in elderly patients. Aging-related degeneration of muscle, tendon, tendon-to-bone enthesis, and bone plays a critical role in the development and prognosis of RCT. Studies have demonstrated that aging worsens muscle atrophy and fatty infiltration, alters tendon structure and biomechanical properties, exacerbates enthesis degeneration, and reduces bone density. Although recent researches have contributed to understanding the pathophysiological mechanisms of aging-related RCT, a comprehensive systematic review of this topic is still lacking. Therefore, this article aims to present a review of the pathophysiological changes and their clinical significance, as well as the molecular mechanisms underlying aging-related RCT, with the goal of shedding light on new therapeutic approaches to reduce the occurrence of aging-related RCT and improve postoperative prognosis in elderly patients.

In vitro osteoclastogenesis in autoimmune diseases - Strengths and pitfalls of a tool for studying pathological bone resorption and other disease characteristics

Osteoclasts play a critical role in bone pathology frequently associated with autoimmune diseases. Studying the etiopathogenesis of these diseases and their clinical manifestations can involve in vitro osteoclastogenesis, an experimental technique that utilizes osteoclast precursors that are relatively easily accessible from peripheral blood or synovial fluid. However, the increasing number of methodical options to study osteoclastogenesis in vitro poses challenges in translating findings to clinical research and practice. This review compares and critically evaluates previous research work based on in vitro differentiation of human osteoclast precursors originating from patients, which aimed to explain autoimmune pathology in rheumatic and enteropathic diseases. The discussion focuses primarily on methodical differences between the studies, including the origin of osteoclast precursors, culture conditions, and methods for identifying osteoclasts and assessing their activity. Additionally, the review examines the clinical significance of the three most commonly used in vitro approaches: induced osteoclastogenesis, spontaneous osteoclastogenesis, and cell co-culture. By analyzing and integrating the gathered information, this review proposes general connections between different studies, even in cases where their results are seemingly contradictory. The derived conclusions and future directions aim to enhance our understanding of a potential and limitations of in vitro osteoclastogenesis and provide a foundation for discussing novel methods (such as osteoclastogenesis dynamic) and standardized approaches (such as spontaneous osteoclastogenesis) for future use in autoimmune disease research.

Dlk2 interacts with Syap1 to activate Akt signaling pathway during osteoclast formation

Excessive osteoclast formation and bone resorption are related to osteolytic diseases. Delta drosophila homolog-like 2 (Dlk2), a member of the epidermal growth factor (EGF)-like superfamily, reportedly regulates adipocyte differentiation, but its roles in bone homeostasis are unclear. In this study, we demonstrated that Dlk2 deletion in osteoclasts significantly inhibited osteoclast formation in vitro and contributed to a high-bone-mass phenotype in vivo. Importantly, Dlk2 was shown to interact with synapse-associated protein 1 (Syap1), which regulates Akt phosphorylation at Ser473. Dlk2 deletion inhibited Syap1-mediated activation of the AktSer473, ERK1/2 and p38 signaling cascades. Additionally, Dlk2 deficiency exhibits increased bone mass in ovariectomized mice. Our results reveal the important roles of the Dlk2-Syap1 signaling pathway in osteoclast differentiation and osteoclast-related bone disorders.

Cholesterol sulfate inhibits osteoclast differentiation and survival by regulating the AMPK-Sirt1-NF-κB pathway

Cholesterol sulfate (CS) is an activator of retinoic acid-related orphan receptor α (RORα). CS treatment or RORα overexpression attenuates osteoclastogenesis in a collagen-induced arthritis mouse model. However, the mechanism by which CS and RORα regulate osteoclast differentiation remains largely unknown. Thus, we aimed to investigate the role of CS and RORα in osteoclastogenesis and their underlying mechanism. CS inhibited osteoclast differentiation, but RORα deficiency did not affect osteoclast differentiation and CS-mediated inhibition of osteoclastogenesis. CS enhanced adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and sirtuin1 (Sirt1) activity, leading to nuclear factor-κB (NF-κB) inhibition by decreasing acetylation at Lys310 of p65. The NF-κB inhibition was restored by AMPK inhibitor, but the effects of CS on AMPK and NF-κB were not altered by RORα deficiency. CS also induced osteoclast apoptosis, which may be due to sustained AMPK activation and consequent NF-κB inhibition, and the effects of CS were significantly reversed by interleukin-1β treatment. Collectively, these results indicate that CS inhibits osteoclast differentiation and survival by suppressing NF-κB via the AMPK-Sirt1 axis in a RORα-independent manner. Furthermore, CS protects against bone destruction in lipopolysaccharide- and ovariectomy-mediated bone loss mouse models, suggesting that CS is a useful therapeutic candidate for treating inflammation-induced bone diseases and postmenopausal osteoporosis.

Radiation Induces Bone Microenvironment Disruption by Activating the STING-TBK1 Pathway

Background and Objectives: Damage to normal bone tissue following therapeutic irradiation (IR) represents a significant concern, as IR-induced bone microenvironment disruption can cause bone loss and create a more favorable environment for tumor metastases. The aim of the present study was to explore the cellular regulatory mechanism of IR-induced bone microenvironment disruption to effectively prevent radiotherapy-associated adverse effects in the future. Materials and Methods: In this study, a mouse model of local IR was established via local irradiation of the left hind limb of BALB/c mice with 12 Gy X-rays, and an in vitro osteocyte (OCY) model was established by exposing osteocyte-like MLO-Y4 cells to 2, 4, and 8 Gy irradiation to analyze multicellular biological injuries and cellular senescence. Small interfering RNA (siRNA) transfection at the cellular level and a selective antagonist intervention C-176 at the animal level were used to explore the potential role of the stimulator of interferon genes (STING) on IR-induced bone microenvironment disruption. Results: The results showed that 12 Gy local IR induces multicellular dysfunction, manifested as ascension of OCYs exfoliation, activation of osteoclastogenesis, degeneration of osteogenesis and fate conversion of adipogenesis, as well as cellular senescence and altered senescence-associated secretory phenotype (SASP) secretion. Furthermore, the expression of STING was significantly elevated, both in the primary OCYs harvested from locally irradiated mice and in vitro irradiated MLO-Y4 cells, accompanied by the markedly upregulated levels of phosphorylated TANK-binding kinase 1 (P-TBK1), RANKL and sclerostin (SOST). STING-siRNA transfection in vitro restored IR-induced upregulated protein expression of P-TBK1 and RANKL, as well as the mRNA expression levels of inflammatory cytokines, such as IL-1α, IL-6 and NF-κB, accompanied by the alleviation of excessive osteoclastogenesis. Finally, administration of the STING inhibitor C-176 mitigated IR-induced activation of osteoclastogenesis and restraint of osteogenesis, ameliorating the IR-induced biological damage of OCYs, consistent with the inhibition of P-TBK1, RANKL and SOST. Conclusions: The STING-P-TBK1 signaling pathway plays a crucial role in the regulation of the secretion of inflammatory cytokines and osteoclastogenesis potential in IR-induced bone microenvironment disruption. The selective STING antagonist can be used to intervene to block the STING pathway and, thereby, repair IR-induced multicellular biological damage and mitigate the imbalance between osteoclastogenesis and osteoblastgenesis.

The Use of Intravenous Zoledronate May Reduce Retear Rate after Rotator Cuff Repair in Older Female Patients with Osteoporosis. A First In-Human Prospective Study

The objective of this study was to demonstrate the effect of intravenous (IV) zoledronate administration on rotator cuff healing, retear rate, and clinical outcomes in osteoporotic patients who underwent arthroscopic rotator cuff repair (ARCR) compared with patients with normal bone densities. In this prospective nonrandomized comparative study with propensity score matching, 30 patients who were postoperatively administered IV zoledronate (5 mg) were enrolled as the study group. The control group was matched using 1-to-2 propensity score matching. Radiologic and functional outcomes were evaluated 6 months after surgery. The functional scores in both groups exhibited significant improvement 6 months after surgery. Compared with Group 1 (osteoporosis with IV zoledronate injection) Group 2 (normal bone density) showed significant improvement in their University of California, Los Angeles (UCLA) shoulder score and Constant Shoulder Score (CSS) at 6 months postoperatively. The range of motion improved in both groups at 6 months after surgery. The retear rates according to Sugaya’s classification (IV and V) were 13.3% (4 of 30 patients) and 25% (15 of 60 patients) in Groups 1 and 2, respectively, which established a non-inferiority of Group 1 to the control group. The retear pattern according to Rhee’s classification in Group 1 was type I in all cases, whereas eight cases of type I and seven cases of type II patterns were observed in Group 2, which was statistically insignificant between the groups. In conclusion, anti-osteoporotic drug use is beneficial for patients with osteoporosis to reduce the failure rate after an ARCR of length > 2 cm, especially in older female patients. Moreover, thorough scrutiny is required to detect osteoporosis in patients with rotator cuff tears, especially in female patients.

Aromatic Bis[aminomethylidenebis(phosphonic)] Acids Prevent Ovariectomy-Induced Bone Loss and Suppress Osteoclastogenesis in Mice

Osteoporosis is a skeletal disease associated with excessive bone turnover. Among the compounds with antiresorptive activity, nitrogen-containing bisphosphonates play the most important role in antiosteoporotic treatment. In previous studies, we obtained two aminomethylidenebisphosphonates—benzene-1,4-bis[aminomethylidene(bisphosphonic)] (WG12399C) acid and naphthalene-1,5-bis[aminomethylidene(bisphosphonic)] (WG12592A) acid—which showed a significant antiproliferative activity toward J774E macrophages, a model of osteoclast precursors. The aim of these studies was to evaluate the antiresorptive activity of these aminobisphosphonates in ovariectomized (OVX) Balb/c mice. The influence of WG12399C and WG12592A administration on bone microstructure and bone strength was studied. Intravenous injections of WG12399C and WG12592A bisphosphonates remarkably prevented OVX-induced bone loss; for example, they sustained bone mineral density at control levels and restored other bone parameters such as trabecular separation. This was accompanied by a remarkable reduction in the number of TRAP-positive cells in bone tissue. However, a significant improvement in the quality of bone structure did not correlate with a parallel increase in bone strength. In ex vivo studies, WG12399C and WG12592A remarkably bisphosphonates reduced osteoclastogenesis and partially inhibited the resorptive activity of mature osteoclasts. Our results show interesting biological activity of two aminobisphosphonates, which may be of interest in the context of antiresorptive therapy.

Virtual screening identified natural Keap1-Nrf2 PPI inhibitor alleviates inflammatory osteoporosis through Nrf2-mir214-Traf3 axis

Overactive osteoclastogenesis is involved in the inflammatory bone loss and could be target for therapy. Here, we applied transcription factor enrichment analysis using public inflammatory osteolysis datasets and identified Nrf2 as the potential therapeutic target. Additionally, in-silico screening was performed to dig out Nrf2-Keap1 PPI inhibitor and Forsythoside-β was found to be the best-performing PHG compound. We firstly tested the effect of Forsythoside-β in inflammatory osteoporosis models and found it was able to attenuate the bone loss by inhibiting osteoclastogenesis and activating Nrf2-signaling in vivo. Forsythoside-β was capable to suppress the differentiation of osteoclast in time and dose-dependent manners in vitro. Further, Forsythoside-β could inhibit the production of reactive oxygen species and induce Nrf2 nuclear-translocation by interrupting Nrf2-Keap1 PPI. Recently, Nrf2 was identified as the epigenetic regulator modulating levels of miRNA in various diseases. We discovered that Forsythoside-β could suppress the expression of mir-214-3p, one of most variable miRNAs during osteoclastogenesis. To clarify the undermining mechanism, by utilizing chip-seq dataset, we found that Nrf2 could bind to promoter of mir-214-3p and further regulate this miRNA. Collectively, Forsythoside-β was able to prevent bone loss through Nrf2-mir-214-3p-Traf3 axis, which could be a promising candidate for treating inflammatory bone loss in the future.

Probiotic Propionibacterium freudenreichii MJ2 Enhances Osteoblast Differentiation and Mineralization by Increasing the OPG/RANKL Ratio

Osteoblast differentiation is important for the development of bone and the maintenance of bone density. Propionibacterium freudenreichii is a probiotic with an anti-inflammatory property. The aim of this study was to investigate the enhancement effect of P. freudenreichii MJ2 (MJ2) isolated from raw milk on osteoblast differentiation, mineralization, and its signaling pathway. For in vitro and in vivo experiments, human fetal osteoblastic cell line hFOB 1.19 and an ovariectomized rat model were used, respectively. Expression levels of genes and proteins related to osteoblast differentiation and mineralization were measured by real-time polymerase chain reaction (qPCR) and Western blotting, respectively. Alizarin red S staining was performed to measure osteoblast mineralization. Heat-killed MJ2 (hkMJ2)-treated cells showed significantly increased osteoblast differentiation via an increase in the osteoprotegerin (OPG)/receptor activator of nuclear factor-κB ligand (RANKL) ratio and significantly increased osteoblast mineralization by stimulating the expression of bone morphogenetic protein 2 and runt-related transcription factor 2. Additionally, oral administration of live or heat-killed MJ2 to ovariectomized rats inhibited osteoporosis-induced bone loss. Specifically, surface proteins isolated from MJ2 promoted osteoblast differentiation and mineralization. In conclusion, MJ2 enhanced osteoblast differentiation and mineralization through the OPG/RANKL signaling pathway and the effective component of MJ2 might be its surface proteins.

Mesenchymal stem cells: amazing remedies for bone and cartilage defects

Skeletal disorders are among the leading debilitating factors affecting millions of people worldwide. The use of stem cells for tissue repair has raised many promises in various medical fields, including skeletal disorders. Mesenchymal stem cells (MSCs) are multipotent stromal cells with mesodermal and neural crest origin. These cells are one of the most attractive candidates in regenerative medicine, and their use could be helpful in repairing and regeneration of skeletal disorders through several mechanisms including homing, angiogenesis, differentiation, and response to inflammatory condition. The most widely studied sources of MSCs are bone marrow (BM), adipose tissue, muscle, umbilical cord (UC), umbilical cord blood (UCB), placenta (PL), Wharton's jelly (WJ), and amniotic fluid. These cells are capable of differentiating into osteoblasts, chondrocytes, adipocytes, and myocytes in vitro. MSCs obtained from various sources have diverse capabilities of secreting many different cytokines, growth factors, and chemokines. It is believed that the salutary effects of MSCs from different sources are not alike in terms of repairing or reformation of injured skeletal tissues. Accordingly, differential identification of MSCs' secretome enables us to make optimal choices in skeletal disorders considering various sources. This review discusses and compares the therapeutic abilities of MSCs from different sources for bone and cartilage diseases.

Accumulation of synovial fluid CD19+CD24hiCD27+ B cells was associated with bone destruction in rheumatoid arthritis

Regulatory CD19⁺CD24^hiCD27⁺ B cells were proved to be numerically decreased and functionally impaired in the peripheral blood (PB) from rheumatoid arthritis (RA), with the potential of converting into osteoclast-priming cells. However, the distribution and function of CD19⁺CD24^hiCD27⁺ B cells in RA synovial fluid (SF) were unclear. In this study, we investigated whether RA SF CD19⁺CD24^hiCD27⁺ B cells were increased and associated with bone destruction. We found that the proportion of RA SF CD19⁺CD24^hiCD27⁺ B cells was increased significantly, and was positively correlated with swollen joint counts, tender joint counts and disease activity. CXCL12, CXCL13, CCL19 contributed to the recruitment of CD19⁺CD24^hiCD27⁺ B cells in RA SF. Notably, CD19⁺CD24^hiCD27⁺ B cells in the SF from RA expressed significantly more RANKL compared to OA and that in the PB from RA. Critically, RA CD19⁺CD24^hiCD27⁺ B cells promoted osteoclast (OC) differentiation in vitro, and the number of OCs was higher in cultures with RA SF CD19⁺CD24^hiCD27⁺ B cells than in those derived from RA PB. Collectively, these findings revealed the accumulation of CD19⁺CD24^hiCD27⁺ B cells in SF and their likely contribution to joint destruction in RA. Modulating the status of CD19⁺CD24^hiCD27⁺ B cells might provide novel therapeutic strategies for RA.

Anti-Osteoporotic Effects of the Herbal Mixture of Cornus officinalis and Achyranthes japonica In Vitro and In Vivo

Osteoporosis is a porous bone disease caused by bone density loss, which increases the risk of fractures. Cornus officinalis (CO) and Achyranthes japonica (AJ) have been used as traditional herbal medicine for various disorders in East Asia. Although the anti-osteoporotic effects of single extract of CO and AJ have already been reported, the synergistic effect of a combined mixture has not been studied. In this study, we investigated the effects of a CO and AJ herbal mixture on osteoporosis in in vitro and in vivo models. The results demonstrate that treatment with the CO and AJ mixture significantly promoted osteoblast differentiation of MC3T3-E1 mouse preosteoblasts through the upregulation of osteoblastic differentiation-associated genes such as alkaline phosphatase (Alpl), runt-related transcription factor 2 (Runx2), and bone gamma-carboxyglutamic acid-containing protein (Bglap), while the mixture significantly inhibited differentiation of osteoclasts isolated from primary-cultured mouse monocytes. In addition, oral administration of CO and AJ mixture significantly prevented bone mineral density loss and trabecular bone structures in an ovariectomy-induced osteoporotic mouse model. These results suggest that the combination treatment of CO and AJ mixture might be a beneficial therapy for osteoporosis.

Arctiin abrogates osteoclastogenesis and bone resorption via suppressing RANKL-induced ROS and NFATc1 activation

Osteoporosis, characterized by disrupted bone resorption and formation, is viewed as a global health challenge. Arctiin (ARC) is a main component of Arctium lappa L, which exerts chemopreventive effects against various tumor cells. However, the role of ARC in bone remodeling is still unclear. Here, we first demonstrated that ARC inhibits osteoclast formation and bone resorption function induced by the receptor activator of nuclear factor-κB ligand (RANKL) in a dose- and time-dependent manner without exerting cytotoxic effects. Mechanistic analysis revealed that ARC not only suppresses RANKL-induced mitogen-activated protein kinase (MAPK) and calcium signaling pathways, but also enhances the expression of cytoprotective enzymes that are involved in scavenging reactive oxygen species (ROS). Further, ARC inhibits the activation of the major transcription factor nuclear factor of activated T cells 1 (NFATc1) during RANKL-induced osteoclast formation. Preclinical studies showed that ARC protects bone loss in an ovariectomy (OVX) mouse model. Conclusively, our data confirmed that ARC could potentially inhibit osteoclastogenesis by abrogating RANKL-induced MAPK, calcium, and NFATc1 signaling pathway, as well as by promoting the expression of ROS scavenging enzymes in Nrf2/Keap1/ARE signaling pathway, thereby² preventing OVX-induced bone loss. Thus, ARC may serve as a novel therapeutic agent for the treatment of osteoporosis.

Modulation of Inflammation by Extracellular Granzyme A

Granzyme A (GrA) has long been recognized as one of the key players in the induction of cell death of neoplastic, foreign or infected cells after granule delivery by cytotoxic cells. While the cytotoxic potential of GrA is controversial in current literature, accumulating evidence now indicates roles for extracellular GrA in modulating inflammation and inflammatory diseases. This paper aims to explore the literature presenting current knowledge on GrA as an extracellular modulator of inflammation by summarizing (i) the presence and role of extracellular GrA in several inflammatory diseases, and (ii) the potential molecular mechanisms of extracellular GrA in augmenting inflammation.

Osteoclasts and their circulating precursors in rheumatoid arthritis: Relationships with disease activity and bone erosions

Patients with rheumatoid arthritis (RA) have very different outcomes, particularly with regard to bone erosions. Since osteoclasts are responsible for bone destruction adjacent to rheumatoid synovium, profiling osteoclasts from circulating precursors in RA could help identify patients at risk for bone destruction. In this study, we sought to determine whether the functional characteristics of osteoclasts generated from their blood precursors were modified by RA activity or were intrinsic to osteoclasts and associated with the RA phenotype (erosive or not).

Osteoclasts were generated in vitro from peripheral blood mononuclear cells (PBMCs) of subjects with RA (n = 140), as well as sex- and age-matched healthy controls (n = 101). Osteoclastic parameters were analyzed at baseline and during the follow-up for up to 4 years, with regular assessment of RA activity, bone erosions, and bone mineral density (BMD). As a validation cohort, we examined RA patients from the Early Undifferentiated PolyArthritis (EUPA) study (n = 163).

The proportion of CD14⁺ PBMC was higher in RA than in control subjects, but inversely correlated with the 28-joint disease activity score (DAS28). Also surprisingly, in osteoclast cultures from PBMCs, active RA was associated with lower osteoclastogenic capacity, while in vitro bone resorption per osteoclast and resistance to apoptosis were similar in both active and quiescent RA. In a small subgroup analysis, osteoclasts from subjects with recent RA that had progressed at four years to an erosive RA exhibited at baseline greater resistance to apoptosis than those from patients remaining non-erosive.

Our findings establish that when RA is active, circulating monocytes have a reduced potential to generate osteoclasts from PBMCs in vitro. In addition, osteoclasts associated with erosive disease had resistance to apoptosis from the start of RA.

•

Osteoclasts are derived in vitro from circulating monocytes in rheumatoid arthritis.

•

Blood CD14⁺ monocytes (%) are higher but inversely correlated with disease activity.

•

Active rheumatoid arthritis is associated with reduced osteoclast formation in vitro.

•

Inflammation alters the ability to generate osteoclasts from circulating monocytes.

•

Osteoclast resistance to apoptosis is stable and associated with long-term erosions.

Proteomic analysis of CHIKV-infected human fibroblast-like synoviocytes: Identification of host factors potentially associated with CHIKV replication and cellular pathogenesis

Chikungunya virus (CHIKV) is a mosquito-borne virus that causes arthralgic fever. Fibroblast-like synoviocytes play a key role in joint damage in inflammatory arthritides and can additionally serve as target cells for CHIKV infection. To gain a better understanding of CHIKV-induced arthralgia, the interaction between CHIKV and synoviocytes was investigated at the protein level. A gel-enhanced liquid chromatography-mass spectrometry (GeLC-MS/MS) approach was used to examine protein expression from primary human fibroblast-like synoviocytes (HFLS) infected with clinical isolates of CHIKV at 12 and 24 hr post infection. Our analysis identified 259 and 241 proteins of known function that were differentially expressed (>1.5 or <-1.5 fold change) following CHIKV infection at 12 and 24 hpi, respectively. These proteins are involved in cellular homeostasis, including cellular trafficking, cytoskeletal organization, immune response, metabolic process, and protein modification. Some of these proteins have previously been reported to participate in arthralgia/arthritis and the death of infected cells. Our results provide information on the CHIKV-induced modulation of cellular proteins of HFLS at an early stage of infection, as well as highlighting biological processes associated with CHIKV infection in the main target cells of the joint.

Benzydamine inhibits osteoclast differentiation and bone resorption via down-regulation of interleukin-1 β expression

Bone diseases such as osteoporosis and periodontitis are induced by excessive osteoclastic activity, which is closely associated with inflammation. Benzydamine (BA) has been used as a cytokine-suppressive or non-steroidal anti-inflammatory drug that inhibits the production of pro-inflammatory cytokines or prostaglandins. However, its role in osteoclast differentiation and function remains unknown. Here, we explored the role of BA in regulating osteoclast differentiation and elucidated the underlying mechanism. BA inhibited osteoclast differentiation and strongly suppressed interleukin-1β (IL-1β) production. BA inhibited osteoclast formation and bone resorption when added to bone marrow-derived macrophages and differentiated osteoclasts, and the inhibitory effect was reversed by IL-1β treatment. The reporter assay and the inhibitor study of IL-1β transcription suggested that BA inhibited nuclear factor-κB and activator protein-1 by regulating IκB kinase, extracellular signal regulated kinase and P38, resulting in the down-regulation of IL-1β expression. BA also promoted osteoblast differentiation. Furthermore, BA protected lipopolysaccharide- and ovariectomy-induced bone loss in mice, suggesting therapeutic potential against inflammation-induced bone diseases and postmenopausal osteoporosis.

Impact of Diaphyseal Cortical Thickness on Functional Outcomes After Arthroscopic Rotator Cuff Repair

PURPOSE

To study the influence of combined cortical thickness (CCT) of the proximal humerus on arthroscopic rotator cuff tear repair outcomes.

METHODS

The study included 210 patients who underwent arthroscopic repair of full-thickness supraspinatus tears. An independent reviewer measured CCT on preoperative radiographs, and patients were evaluated postoperatively at 3, 6, 12, and 24 months. Functional outcome was assessed with the Constant shoulder score (CSS), Oxford shoulder score (OSS), and University of California at Los Angeles Shoulder rating scale (UCLASS). The patients were divided based on CCT: ≥4 mm (higher CCT) and <4 mm (lower CCT). Univariate analysis and multivariate linear regressions were applied to study the effect of higher CCT on functional scores.

RESULTS

At 6 months' follow-up, CSS and UCLASS were higher in the patients with higher CCT (mean ± standard deviation, 59 ± 17 vs 54 ± 14, P = .020; and 30 ± 5 vs 28 ± 5, P = .020, respectively). At 12 months' follow-up, CSS, UCLASS, and OSS were higher in the patients with higher CCT (71 ± 13 vs 65 ± 14, P = .002; 30 ± 5 vs 28 ± 5, P = .009; and 15 ± 6 vs 18 ± 7, P = .001, respectively). At 24 months' follow-up, CSS and OSS were higher in the patients with higher CCT (74 ± 11 vs 69 ± 13, P = .006; and 14 ± 4 vs 16 ± 8, P = .041, respectively).

CONCLUSION

We conclude that although a higher CCT is not associated with clinically significant differences in functional outcomes, further studies examining postoperative imaging as well as perioperative optimization of bone mineral density may yield valuable results regarding the impact of CCT on cuff healing and functional outcomes.

LEVEL OF EVIDENCE

III (retrospective comparative therapeutic trial).

The Nrf2 activator RTA-408 attenuates osteoclastogenesis by inhibiting STING dependent NF-κb signaling

The dysregulation of ROS production and osteoclastogenesis is involved in the progress of osteoporosis. To identify novel and effective targets to treat this disease, it is important to explore the underlying mechanisms. In our study, we firstly tested the effect of the Nrf2 activator RTA-408, a novel synthetic triterpenoid under clinical investigation for many diseases, on osteoclastogenesis. We found that it could inhibit osteoclast differentiation and bone resorption in a time- and dose-dependent manner. Further, RTA-408 enhanced the expression and activity of Nrf2 and significantly suppressed RANKL-induced reactive oxygen species (ROS) production. Nrf2 regulates the STING expression and STING induces the production of IFN-β. Here, we found that RTA-408 could suppress STING expression, but that it does not affect Ifnb1 expression. RANKL-induced degradation of IκBα and the nuclear translocation of P65 was suppressed by RTA-408. Although this compound was not found to influence STING-IFN-β signaling, it suppressed the RANKL-induced K63-ubiquitination of STING via inhibiting the interaction between STING and the E3 ubiquitin ligase TRAF6. Further, adenovirus-mediated STING overexpression rescued the suppressive effect of RTA-408 on NF-κB signaling and osteoclastogenesis. In vivo experiments showed that this compound could effectively attenuate ovariectomy (OVX)-induced bone loss in C57BL/6 mice by inhibiting osteoclastogenesis. Collectively, we show that RTA-408 inhibits NF-κB signaling by suppressing the recruitment of TRAF6 to STING, in addition to attenuating osteoclastogenesis and OVX-induced bone loss in vivo, suggesting that it could be a promising candidate for treating osteoporosis in the future.

Mannan-Binding Lectin Attenuates Inflammatory Arthritis Through the Suppression of Osteoclastogenesis

Mannan-binding lectin (MBL) is a vital element in the host innate immune system, which is primarily produced by the liver and secreted into the circulation. Low serum level of MBL is reported to be associated with an increased risk of arthritis. However, the underlying mechanism by which MBL contributes to the pathogenesis of arthritis is poorly understood. In this study, we investigated the precise role of MBL on the course of experimental murine adjuvant-induced arthritis (AIA). MBL-deficient (MBL^−/−) AIA mice showed significantly increased inflammatory responses compared with wild-type C57BL/6 AIA mice, including exacerbated cartilage damage, enhanced histopathological features and high level of tartrate-resistant acid phosphatase (TRAP)-positive cells. MBL protein markedly inhibited the osteoclast formation from human blood monocytes induced by receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) in vitro. Mechanistic studies established that MBL inhibited osteoclast differentiation via down-regulation of p38 signaling pathway and subsequent nuclear translocation of c-fos as well as activation of nuclear factor of activated T-cells c1 (NFATc1) pathway. Importantly, we have provided the evidence that concentrations of MBL correlated negatively with the serum levels of amino-terminal propeptide of type I procollagen (PINP) and C-terminal telopeptide of type I collagen (β-CTX), serum markers of bone turnover, in patients with arthritis. Our study revealed an unexpected function of MBL in osteoclastogenesis, thus providing new insight into inflammatory arthritis and other bone-related diseases in patients with MBL deficiency.

Methylglyoxal activates osteoclasts through JNK pathway leading to osteoporosis

Diabetes mellitus is characterized by chronic hyperglycemia and its diverse complications. Hyperglycemia is associated with inflammatory responses in different organs, and diabetic patients have a higher risk of bone fracture due to increased bone weakness. Methylglyoxal, a reactive advanced glycation end product precursor, is known to have increased level in diabetic patients. The accumulation of methylglyoxal promotes inflammation and it may play a role in diabetes related osteoporosis. In this study, therefore, the underlying mechanism of methylglyoxal on osteoporosis was studied using both animal and cell models. In the animal model, rats were treated with either methylglyoxal or saline as control. In the cell model, the macrophage RAW264.7 was treated with methylglyoxal or vehicle control. Following the treatment, animal samples were harvested for micro-CT and real-time polymerase chain reaction analyses. Cell samples were harvested for MTT assay, RT-PCR, and Western Blotting analyses. In both animals and cell cultures, methylglyoxal was shown to induce osteoclastogenesis by increased gene expression of osteoclast bone biomarkers CTSK, OSCAR and TRACP5. Furthermore, in methylglyoxal-treated macrophages activation of the c-Jun N-terminal kinases signaling pathway was observed, and inhibition of JNK activities resulted in down-regulation of osteoclast biomarkers gene expressions. Our results therefore suggested that methylglyoxal may contribute to the progression of diabetes-related osteoporosis and imbalanced bone remodeling through JNK pathway in osteoclasts.

LY411575, a potent γ-secretase inhibitor, suppresses osteoclastogenesis in vitro and LPS-induced calvarial osteolysis in vivo

A series of osteolytic bone diseases are usually related to excessive bone resorption and osteoclast formation. Thus, agents or drugs which can target osteoclast development and attenuate bone loss are potentially considerable in preventing and treating of bone lytic diseases. In recent years, many studies have reported that Notch signaling has substantial impacts on the process of osteoclast differentiation, maturation, and bone destruction. In the present study, we showed that LY411575, a γ-secretase inhibitor, could potently suppress osteoclast differentiation, osteoclast-specific gene expression, and bone resorption via suppressing Notch/HES1/MAPK (ERK and p38)/Akt-mediated NFATc1 induction in vitro. Consistent with in vitro results, LY411575 exhibited protective effects in lipopolysaccharides-induced calvarial bone destruction in vivo. Collectively, these results indicate that LY411575 may have therapeutic potential in the treatment of osteoclast-mediated osteolytic bone diseases.

Inhibition of RANKL-stimulated osteoclast differentiation by Schisandra chinensis through down-regulation of NFATc1 and c-fos expression

Background

Schisandra chinenesis (SC) has been reported to have ameliorative effect on osteoporosis. However, the mechanisms underlying the anti-osteoporosis activity of SC have not been clearly elucidated. In the present study, we determined the effects of SC on The receptor activator of NF-kB ligand (RANKL)-induced osteoclastogenesis and its potential mechanism.

Methods

Raw 264.7 cells were treated with 0.6, 6 and 60 μg/mL SC in the presence of 100 ng/mL RANKL for 7 days. RANKL-induced osteoclast formation was analyzed by tartrate resistant acid phosphatase (TRAP) staining. The osteoclast differentiation-related factors were confirmed along with TNF-α.

Results

SC inhibits the RANKL-induced osteoclast differentiation in dose-dependent manner within non-toxic concentrations. The supernatant concentrations of TNF-α were significantly decreased by SC treatment. In addition, osteoclastogenesis-related factors, TRAP6 and NF-κB, were markedly decreased by SC in RANKL-induced osteoclasts. Mechanistically, SC reduced the RANKL-triggered NFATc1 and c-fos expressions.

Conclusions

Taken together, our data suggest that SC can modulate bone metabolism by suppressing RANKL-induced osteoclast differentiation.

Electronic supplementary material

The online version of this article (10.1186/s12906-018-2331-5) contains supplementary material, which is available to authorized users.

Stevioside Prevents Wear Particle-Induced Osteolysis by Inhibiting Osteoclastogenesis and Inflammatory Response via the Suppression of TAK1 Activation

Aseptic loosening and periprosthetic osteolysis are the leading causes of total joint arthroplasty failure, which occurs as a result of chronic inflammatory response and enhanced osteoclast activity. Here we showed that stevioside, a natural compound isolated from Stevia rebaudiana, exhibited preventative effects on titanium particle-induced osteolysis in a mouse calvarial model. Further histological assessment and real-time PCR analysis indicated that stevioside prevented titanium particle-induced osteolysis by inhibiting osteoclast formation and inflammatory cytokine expression in vivo. In vitro, we found that stevioside could suppress RANKL-induced osteoclastogenesis and titanium particle-induced inflammatory response in a dose-dependent manner. Mechanistically, stevioside achieved these effects by disrupting the phosphorylation of TAK1 and subsequent activation of NF-κB/MAPKs signaling pathways. Collectively, our data suggest that stevioside effectively suppresses osteoclastogenesis and inflammatory response both in vitro and in vivo, and it might be a potential therapy for particle-induced osteolysis and other osteolytic diseases.

Divergent roles of immune cells and their mediators in pain

Chronic pain is a major debilitating condition that is difficult to treat. Although chronic pain may appear to be a disorder of the nervous system, crucial roles for immune cells and their mediators have been identified as important contributors in various types of pain. This review focuses on how the immune system regulates pain and discusses the emerging roles of immune cells in the initiation or maintenance of chronic pain. We highlight which immune cells infiltrate damaged nerves, the dorsal root ganglia, spinal cord and tissues around free nerve endings and discuss through which mechanisms they control pain. Finally we discuss emerging roles of the immune system in resolving pain and how the immune system contributes to the transition from acute to chronic pain. We propose that targeting some of these immune processes may provide novel therapeutic opportunities for the treatment of chronic pain.

Gut Microbiota and Bone Health

The past decade has seen an explosion of research in the area of how the bacteria that inhabit the human body impact health and disease. One of the more surprising concepts to emerge from this work is the ability of the intestinal microbiota to impact virtually all systems in the body. Recently, the role of gut bacteria in bone health and disease has received more significant attention. In this chapter, we review what has been learned about how the gut microbiome impacts bone health and discuss possible mechanisms of how the gut-bone axis may be connected. We also discuss the use of therapeutic microbes in the modulation of bone health. Finally, we propose an emerging field of the gut-brain-bone axis, in which the gut drives bone physiology via regulation of key hormones that are originally synthesized in the brain.

An Optimized Method to Generate Human Active Osteoclasts From Peripheral Blood Monocytes

Osteoclasts (OCs), the bone-resorbing cells, play a key role in skeletal development and adult bone remodeling. They also participate in the pathogenesis of various bone disorders. One of the major technical difficulties in the generation of OCs, when working on human material, is the ability to achieve large differentiation of mature OCs from human peripheral blood mononuclear cells (PBMCs). Access to a standardized source of active OCs is needed to better analyze the roles of human OCs. The aim of this study was to develop a procedure yielding active and mature OCs from fresh human PBMCs. We therefore examined the differentiation of PBMCs to OCs in different cell culture media, using non-stripped and charcoal-stripped sera in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL). We also studied the effects of vitamin D3 in the differentiation level of PBMCs to OCs. Phalloidin-AlexaFluor^®488/DAPI fluorescent stainings and dentin resorption analyses by scanning electron microscopy were used to identify the number and size of differentiated OCs, number of nuclei per cell and resorption activities of OCs for a 7–14–21-day culture period. This study reports an optimized method for an efficient production of human active OCs from a low seeding density of PBMCs, after a 14-day culture period by using a medium containing fetal bovine charcoal-stripped serum in the presence of M-CSF and RANKL, and in the absence of vitamin D3.

A novel approach for correction of crosstalk effects in pathway analysis and its application in osteoporosis research

Osteoporosis is a prevalent bone metabolic disease and peripheral blood monocytes represent a major systemic cell type for bone metabolism. To identify the key dysfunctional pathways in osteoporosis, we performed pathway analyses on microarray data of monocytes from subjects with extremely high/low hip bone mineral density. We first performed a traditional pathway analysis for which different pathways were treated as independent. However, genes overlap among pathways will lead to “crosstalk” phenomenon, which may lead to false positive/negative results. Therefore, we applied correction techniques including a novel approach that considers the correlation among genes to adjust the crosstalk effects in the analysis. In traditional analysis, 10 pathways were found to be significantly associated with BMD variation. After correction for crosstalk effects, three of them remained significant. Moreover, the MAPK signaling pathway, which has been shown to be important for osteoclastogenesis, became significant only after the correction for crosstalk effects. We also identified a new module mainly consisting of genes present in mitochondria to be significant. In summary, we describe a novel method to correct the crosstalk effect in pathway analysis and found five key independent pathways involved in BMD regulation, which may provide a better understanding of biological functional networks in osteoporosis.

Production of RANKL by Memory B Cells: A Link Between B Cells and Bone Erosion in Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage. The mechanisms of bone damage in RA are complex, involving activation of bone-resorbing osteoclasts (OCs) by synoviocytes and Th17 cells. This study was undertaken to investigate whether B cells play a direct role in osteoclastogenesis through the production of RANKL, the essential cytokine for OC development.

METHODS

RANKL production by total B cells or sorted B cell subpopulations in the peripheral blood and synovial tissue from healthy donors or anti-cyclic citrullinated peptide-positive patients with RA was examined by flow cytometry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemical analysis. To define direct effects on osteoclastogenesis, B cells were cocultured with CD14+ monocytes, and OCs were enumerated by tartrate-resistant acid phosphatase staining.

RESULTS

Healthy donor peripheral blood B cells were capable of expressing RANKL upon stimulation, with switched memory B cells (CD27+IgD-) having the highest propensity for RANKL production. Notably, switched memory B cells in the peripheral blood from RA patients expressed significantly more RANKL compared to healthy controls. In RA synovial fluid and tissue, memory B cells were enriched and spontaneously expressed RANKL, with some of these cells visualized adjacent to RANK+ OC precursors. Critically, B cells supported OC differentiation in vitro in a RANKL-dependent manner, and the number of OCs was higher in cultures with RA B cells than in those derived from healthy controls.

CONCLUSION

These findings reveal the critical importance of B cells in bone homeostasis and their likely contribution to joint destruction in RA.

Monocyte Heterogeneity: Consequences for Monocyte-Derived Immune Cells

Blood monocytes are precursors of dendritic cells, macrophages, and osteoclasts. They are a heterogeneous cell population with differences in size, phenotype, and function. Although monocytes maintain several tissue-specific populations of immune cells in homeostasis, their contribution to populations of dendritic cells, macrophages, and osteoclasts is significantly increased in inflammation. Identification of a growing number of functionally different subsets of cells within populations of monocyte-derived immune cells has recently put monocyte heterogeneity into sharp focus. Here, we summarize recent findings in monocyte heterogeneity and their differentiation into dendritic cells, macrophages, and osteoclasts. We also discuss these advances in the context of the formation of functionally different monocyte-derived subsets of dendritic cells, macrophages, and osteoclasts.

Anti-IL-20 monoclonal antibody promotes bone fracture healing through regulating IL-20-mediated osteoblastogenesis

Bone loss and skeletal fragility in bone fracture are caused by an imbalance in bone remodeling. The current challenge in bone fracture healing is to promote osteoblastogenesis and bone formation. We aimed to explore the role of IL-20 in osteoblastogenesis, osteoblast differentiation and bone fracture. Serum IL-20 was significantly correlated with serum sclerostin in patients with bone fracture. In a mouse model, anti-IL-20 monoclonal antibody (mAb) 7E increased bone formation during fracture healing. In vitro, IL-20 inhibited osteoblastogenesis by upregulating sclerostin, and downregulating osterix (OSX), RUNX2, and osteoprotegerin (OPG). IL-20R1 deficiency attenuated IL-20-mediated inhibition of osteoblast differentiation and maturation and reduced the healing time after a bone fracture. We conclude that IL-20 affects bone formation and downregulates osteoblastogenesis by modulating sclerostin, OSX, RUNX2, and OPG on osteoblasts. Our results demonstrated that IL-20 is involved in osteoregulation and anti-IL-20 mAb is a potential therapeutic for treating bone fracture or metabolic bone diseases.

CLEC5A is critical for dengue virus-induced osteoclast activation and bone homeostasis

Abstract

Osteoclasts are bone tissue macrophages critical to maintain bone homeostasis. However, whether osteoclasts are susceptible to flaviviral infections and involved in dengue virus (DV)-induced disease pathogenesis is still unknown. In this study, we found that osteoclasts were preferentially susceptible to DV infection and produced similar amounts of cytokines and infectious virions as macrophages. Interestingly, DV-induced cytokine secretion and nuclear translocation of the transcription factor NFATc1 in osteoclast via the Syk-coupled myeloid C-type lectin member 5A (CLEC5A). Moreover, DV caused transient inflammatory reaction in bone tissue and upregulated osteolytic activity to release C-telopeptide of type I collagen (CTX-1) from bone tissue. Furthermore, DV-induced osteolytic activity was attenuated in CLEC5A-deficient mice, and administration of antagonistic anti-CLEC5A mAb inhibited DV-activated osteolytic activity and reduced CTX-1 serum level in vivo. This observation suggests that osteoclasts serve as a novel target for DV, and transient upregulation of osteolytic activity may contribute to the clinical symptoms in dengue patients.

Key messages

Cultured osteoclasts were susceptible to DV infection.

Osteoclasts produced similar amounts of cytokines and infectious virions as macrophages.

DV induced nuclear translocation of NFATc1 in osteoclast via CLEC5A.

DV caused transient inflammatory reaction in bone tissue and upregulated osteolytic activity.

Antagonistic anti-CLEC5A mAb inhibited DV-activated osteolytic activity in vivo.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1409-0) contains supplementary material, which is available to authorized users.

Notch2 signaling promotes osteoclast resorption via activation of PYK2

Notch signaling plays a central role in various cell fate decisions, including skeletal development. Recently, Notch signaling was implicated in osteoclast differentiation and maturation, including the resorption activity of osteoclasts. However, the specific involvement of notch signaling in resorption activity was not fully investigated. Here, we investigated the roles of Notch signaling in the resorption activity of osteoclasts by use of the gamma-secretase inhibitor dibenzazepine (DBZ). Attenuating Notch signaling by DBZ suppressed the expression of NFATc1, a master transcription factor for osteoclast differentiation. However, overexpression of a constitutively active form of NFATc1 did not fully rescue the effects of DBZ. DBZ suppressed the autophosphorylation of PYK2, which is essential for the formation of the podosome belt and sealing zone, with reduced c-Src/PYK2 interaction. We found that RANKL increases PYK2 activation accompanied by increased NICD2 production in osteoclasts. Overexpression of NICD2 in osteoclasts rescued DBZ-mediated suppression of resorption activity with promotion of PYK2 autophosphorylation and microtubule acetylation. Consistent with the in vitro results, DBZ strongly suppressed bone destruction in an interleukin-1-induced bone loss model. Collectively, these results demonstrate that Notch2 in osteoclasts plays a role in the control of resorption activity via the PYK2-c-Src-microtubule signaling pathway.

Bromo-honaucin A inhibits osteoclastogenic differentiation in RAW 264.7 cells via Akt and ERK signaling pathways

Osteoclasts are unique bone remodeling cells derived from multinucleated myeloid progenitor cells. They play homeostatic vital roles in skeletal modeling and remodeling but also destroy bone masses in many pathological conditions such as osteoporosis and rheumatoid arthritis. Receptor activation of NF-κB ligand (RANKL) is essential to osteoclastogenesis. In this study, we investigated the effects of bromo-honaucin A (Br-H A) isolated from Leptolyngbya crossbyana (cyanobacterium). To investigate the mechanism of the inhibitory effect of Br-H A on osteoclastogenesis, we employed Br-H Ain RANKL-treated murine monocyte/macrophage RAW 264.7 cells for osteoclastic differentiation in-vitro. The inhibitory effects on in-vitro osteoclastogenesis was evaluated by counting the number of Tartarate resistant acid phospatase (TRAP) positive multinucleated cells and by measuring the expression level of osteoclast-specific genes like matrix metalloproteinase 9 (MMP9), cathepsin K (CATH K), GRB2-associated-binding protein 2 (GAB2), c-terminal myc kinase (C-MYC), C-terminal Src kinase (C-SRC) and Microphthalmia-associated transcription factor (MITF). Moreover, Br-H A blocked the resorbing capacity of RAW 264.7 cells on calcium phosphate-coated plates. Finally, Br-H A clearly decreased the expression of Akt and also decreased the activation of ERK. Thus, the study identifies Br-H A as potent inhibitor potentialin the treatment of diseases involving abnormal bone lysis such as osteoporosis, rheumatoid arthritis, and periodontal bone degradation.

Circulating monocytes: an appropriate model for bone-related study

Peripheral blood monocytes (PBMs) are an important source of precursors of osteoclasts, the bone-resorbing cells and the cytokines produced by PBMs that have profound effects on osteoclast differentiation, activation, and apoptosis. So PBMs represent a highly valuable and unique working cell model for bone-related study. Finding an appropriate working cell model for clinical and (epi-)genomic studies of human skeletal disorders is a challenge. Peripheral blood monocytes (PBMs) can give rise to osteoclasts, the bone-resorbing cells. Particularly, PBMs provide the sole source of osteoclast precursors for adult peripheral skeleton where the bone marrow is normally hematopoietically inactive. PBMs can secrete potent pro- and anti-inflammatory cytokines, which are important for osteoclast differentiation, activation, and apoptosis. Reduced production of PBM cytokines represents a major mechanism for the inhibitory effects of sex hormones on osteoclastogenesis and bone resorption. Abnormalities in PBMs have been linked to various skeletal disorders/traits, strongly supporting for the biological relevance of PBMs with bone metabolism and disorders. Here, we briefly review the origin and further differentiation of PBMs. In particular, we discuss the close relationship between PBMs and osteoclasts, and highlight the utility of PBMs in study the pathophysiological mechanisms underlying various skeletal disorders.

Triterpenoid Saponin W3 from Anemone flaccida Suppresses Osteoclast Differentiation through Inhibiting Activation of MAPKs and NF-κB Pathways

Excessive bone resorption by osteoclasts within inflamed joints is the most specific hallmark of rheumatoid arthritis. A. flaccida has long been used for the treatment of arthritis in folk medicine of China; however, the active ingredients responsible for the anti-arthritis effects of A. flaccida are still elusive. In this study, W3, a saponin isolated from the extract of A. flaccida was identified as the major active ingredient by using an osteoclast formation model induced by receptor activator of nuclear factor kappa-B ligand (RANKL). W3 dose-dependently suppressed the actin ring formation and lacunar resorption. Mechanistic investigation revealed that W3 inhibited the RANKL-induced TRAF6 expression, decreased phosphorylation of mitogen-activated protein kinases (MAPKs) and IκB-α, and suppressed NF-κB p65 DNA binding activity. Furthermore, W3 almost abrogated the expression of c-Fos and nuclear factor of activated T cells (NFATc1). Therefore, our results suggest that W3 is a potential agent for treating lytic bone diseases although further evaluation in vivo and in clinical trials is needed.

Dual Effect of Chrysanthemum indicum Extract to Stimulate Osteoblast Differentiation and Inhibit Osteoclast Formation and Resorption In Vitro

The risk of bone-related diseases increases due to the imbalance between bone resorption and bone formation by osteoclasts and osteoblasts, respectively. The goal in the development of antiosteoporotic treatments is an agent that will improve bone through simultaneous osteoblast stimulation and osteoclast inhibition without undesirable side effects. To achieve this goal, numerous studies have been performed to identify novel approaches using natural oriental herbs to treat bone metabolic diseases. In the present study, we investigated the effect of Chrysanthemum indicum extract (CIE) on the differentiation of osteoclastic and osteoblastic cells. CIE inhibited the formation of TRAP-positive mature osteoclasts and of filamentous-actin rings and disrupted the bone-resorbing activity of mature osteoclasts in a dose-dependent manner. CIE strongly inhibited Akt, GSK3β, and IκB phosphorylation in RANKL-stimulated bone marrow macrophages and did not show any effects on MAP kinases, including p38, ERK, and JNK. Interestingly, CIE also enhanced primary osteoblast differentiation via upregulation of the expression of alkaline phosphatase and the level of extracellular calcium concentrations during the early and terminal stages of differentiation, respectively. Our results revealed that CIE could have a potential therapeutic role in bone-related disorders through its dual effects on osteoclast and osteoblast differentiation.

The study of mechanisms of protective effect of Rg1 against arthritis by inhibiting osteoclast differentiation and maturation in CIA mice

Ginsenoside Rg1 is a natural product extracted from Panax ginseng C.A. Although Rg1 protects tissue structure and functions by inhibiting local inflammatory reaction, the mechanism remains poorly understood. In vitro, Rg1 dose-dependently inhibited TRAP activity in receptor activator of nuclear factor-κB ligand- (RANKL-) induced osteoclasts and decreased the number of osteoclasts and osteoclast resorption area. Rg1 also significantly inhibited the RANK signaling pathway, including suppressing the expression of Trap, cathepsin K, matrix metalloproteinase 9 (MMP9), and calcitonin receptor (CTR). In vivo, Rg1 dramatically decreased arthritis scores in CIA mice and effectively controlled symptoms of inflammatory arthritis. Pathologic analysis demonstrated that Rg1 significantly attenuated pathological changes in CIA mice. Pronounced reduction in synovial hyperplasia and inflammatory cell invasion were observed in CIA mice after Rg1 therapy. Alcian blue staining results illustrated that mice treated with Rg1 had significantly reduced destruction in the articular cartilage. TRAP and cathepsin K staining results demonstrated a significant reduction of numbers of OCs in the articular cartilage in proximal interphalangeal joints and ankle joints in Rg1-treated mice. In summary, this study revealed that Rg1 reduced the inflammatory destruction of periarticular bone by inhibiting differentiation and maturation of osteoclasts in CIA mice.

Characterization of functional reprogramming during osteoclast development using quantitative proteomics and mRNA profiling

In addition to forming macrophages and dendritic cells, monocytes in adult peripheral blood retain the ability to develop into osteoclasts, mature bone-resorbing cells. The extensive morphological and functional transformations that occur during osteoclast differentiation require substantial reprogramming of gene and protein expression. Here we employ -omic-scale technologies to examine in detail the molecular changes at discrete developmental stages in this process (precursor cells, intermediate osteoclasts, and multinuclear osteoclasts), quantitatively comparing their transcriptomes and proteomes. The data have been deposited to the ProteomeXchange with identifier PXD000471.

Our analysis identified mitochondrial changes, along with several alterations in signaling pathways, as central to the development of mature osteoclasts, while also confirming changes in pathways previously implicated in osteoclast biology. In particular, changes in the expression of proteins involved in metabolism and redirection of energy flow from basic cellular function toward bone resorption appeared to play a key role in the switch from monocytic immune system function to specialized bone-turnover function. These findings provide new insight into the differentiation program involved in the generation of functional osteoclasts.