Cells of the synovium in rheumatoid arthritis. Osteoclasts

Identification the role of necroptosis in rheumatoid arthritis by WGCNA network

Rheumatoid arthritis (RA) is the predominant manifestation of inflammatory arthritis, distinguished by an increasing burden of morbidity and mortality. The intricate interplay of genes and signalling pathways involved in synovial inflammation in patients with RA remains inadequately comprehended. This study aimed to ascertain the role of necroptosis in RA, as along with their associations with immune cell infiltration. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were employed to identify central genes for RA. In this study, identified total of 28 differentially expressed genes (DEGs) were identified in RA. Utilising WGCNA, two co-expression modules were generated, with one module demonstrating the strongest correlation with RA. Through the integration of differential gene expression analysis, a total of 5 intersecting genes were discovered. These 5 hub genes, namely fused in sarcoma (FUS), transformer 2 beta homolog (TRA2B), eukaryotic translation elongation factor 2 (EEF2), cleavage and polyadenylation specific factor 6 (CPSF6) and signal transducer and activator of transcription 3 (STAT3) were found to possess significant diagnostic value as determined by receiver operating characteristic (ROC) curve analysis. The close association between the concentrations of various immune cells is anticipated to contribute to the diagnosis and treatment of RA. Furthermore, the infiltration of immune cells mentioned earlier is likely to exert a substantial influence on the initiation of this disease.

Single-cell RNA sequencing reveals that an imbalance in monocyte subsets rather than changes in gene expression patterns is a feature of postmenopausal osteoporosis

The role of monocytes in postmenopausal osteoporosis is widely recognized; however, the mechanisms underlying monocyte reprogramming remain unknown. In this study, single-cell RNA sequencing (scRNA-seq) was conducted on CD14+ bone marrow monocytes obtained from 3 postmenopausal women with normal BMD and 3 women with postmenopausal osteoporosis (PMOP). Monocle2 was used to classify the monocytes into 7 distinct clusters. The proportion of cluster 1 significantly decreased in PMOP patients, while the proportion of cluster 7 increased. Further analysis via GSEA, transcription factor activity analysis, and sc-metabolic analysis revealed significant differences between clusters 1 and 7. Cluster 7 exhibited upregulated pathways associated with inflammation, immunity, and osteoclast differentiation, whereas cluster 1 demonstrated the opposite results. Monocle2, TSCAN, VECTOR, and scVelo data indicated that cluster 1 represented the initial subset and that cluster 7 represents one of the terminal subsets. BayesPrism and ssGSEA were employed to analyze the bulk transcriptome data obtained from the GEO database. The observed alterations in the proportions of 1 and 7 were validated and found to have diagnostic significance. CD16 serves as the marker gene for cluster 7, thus leading to an increased proportion of CD16+ monocytes in women with PMOP. Flow cytometry was used to assess the consistency of outcomes with those of the bioinformatic analysis. Subsequently, an additional scRNA-seq analysis was conducted on bone marrow mononuclear cells obtained from 3 patients with PMOP and 3 postmenopausal women with normal BMD. The differential proportions of cluster 1 and cluster 7 were once again confirmed, with the pathological effect of cluster 7 may attribute to cell-cell communication. The scRNA-seq findings suggest that an imbalance in monocyte subsets is a characteristic feature of PMOP. These findings elucidate the limitations of utilizing bulk transcriptome data for detecting alterations in monocytes, which may influence novel research inquiries.

Xuetongsu attenuates bone destruction in collagen-induced arthritis mice by inhibiting osteoclast differentiation and promoting osteoclast apoptosis

Tujia ethnomedicine Xuetong (the stems of Kadsura heteroclita) have been widely used in folk for rheumatoid arthritis (RA), which can alleviate rheumatic pain through liquor soaking in folk. In this study, we aimed to evaluate the pharmacological effects and underlying mechanism of Xuetongsu (a key chemical component of Xuetong) on bone destruction. In our previous study, it was found that Xuetong extract can reduce adjuvant arthritic rats paw swelling and inhibit inflammatory factors in serum. Furthermore, Xuetongsu has been demonstrated to inhibit the proliferation of fibroblast-like synoviocytes, but its potential to inhibit bone destruction has not been explored. To address this, we employed the STRING database to predict protein interactions and utilized Autodock software to simulate the binding of Xuetongsu to target proteins. In this study, administration of Xuetongsu significantly alleviated paw swelling and bone destruction in C57BL/6 mice with collagen-induced arthritis (CIA). Mechanistic studies have indicated that Xuetongsu promotes apoptosis of mature osteoclasts in joint tissues by activating Caspase-3 and Bax, while inhibiting Bcl-2. Additionally, Xuetongsu inhibits osteoclast differentiation by suppressing RANKL, RANK, P-NF-κB, and NFATc1, and reduces bone resorption activity by inhibiting MMP-9, CTSK, and TRAP. Importantly, Xuetongsu exhibits good biocompatibility in major organs of mice. In summary, Xuetongsu has the potential to treat bone destruction by promoting apoptosis of mature osteoclasts, inhibiting osteoclast differentiation, and reducing bone resorption. This study reveals the pharmacological effects of Xuetongsu and its mechanism of action, which may contribute to the development of novel approaches for treating RA.

Rheumatoid arthritis molecular targets and their importance to flavonoid-based therapy

Rheumatoid arthritis (RA) is a progressive, chronic, autoimmune, inflammatory, and systemic condition that primarily affects the synovial joints and adjacent tissues, including bone, muscle, and tendons. The World Health Organization recognizes RA as one of the most prevalent chronic inflammatory diseases. In the last decade, there was an expansion on the available RA therapeutic options which aimed to improve patient's quality of life. Despite the extensive research and the emergence of new therapeutic approaches and drugs, there are still significant unwanted side effects associated to these drugs and still a vast number of patients that do not respond positively to the existing therapeutic strategies. Over the years, several references to the use of flavonoids in the quest for new treatments for RA have emerged. This review aimed to summarize the existing literature about the flavonoids' effects on the major pathogenic/molecular targets of RA and their potential use as lead compounds for the development of new effective molecules for RA treatment. It is demonstrated that flavonoids can modulate various players in synovial inflammation, regulate immune cell function, decrease synoviocytes proliferation and balance the apoptotic process, decrease angiogenesis, and stop/prevent bone and cartilage degradation, which are all dominant features of RA. Although further investigation is necessary to determine the effectiveness of flavonoids in humans, the available data from in vitro and in vivo models suggest their potential as new disease-modifying anti-rheumatic drugs. This review highlights the use of flavonoids as a promising avenue for future research in the treatment of RA.

Exosomal Osteoclast-Derived miRNA in Rheumatoid Arthritis: From Their Pathogenesis in Bone Erosion to New Therapeutic Approaches

Rheumatoid arthritis (RA) is an autoimmune disease that causes inflammation, pain, and ultimately, bone erosion of the joints. The causes of this disease are multifactorial, including genetic factors, such as the presence of the human leukocyte antigen (HLA)-DRB1*04 variant, alterations in the microbiota, or immune factors including increased cytotoxic T lymphocytes (CTLs), neutrophils, or elevated M1 macrophages which, taken together, produce high levels of pro-inflammatory cytokines. In this review, we focused on the function exerted by osteoclasts on osteoblasts and other osteoclasts by means of the release of exosomal microRNAs (miRNAs). Based on a thorough revision, we classified these molecules into three categories according to their function: osteoclast inhibitors (miR-23a, miR-29b, and miR-214), osteoblast inhibitors (miR-22-3p, miR-26a, miR-27a, miR-29a, miR-125b, and miR-146a), and osteoblast enhancers (miR-20a, miR-34a, miR-96, miR-106a, miR-142, miR-199a, miR-324, and miR-486b). Finally, we analyzed potential therapeutic targets of these exosomal miRNAs, such as the use of antagomiRs, blockmiRs, agomiRs and competitive endogenous RNAs (ceRNAs), which are already being tested in murine and ex vivo models of RA. These strategies might have an important role in reestablishing the regulation of osteoclast and osteoblast differentiation making progress in the development of personalized medicine.

Profiling joint tissues at single-cell resolution: advances and insights

Advances in the profiling of human joint tissues at single-cell resolution have provided unique insights into the organization and function of these tissues in health and disease. Data generated by various single-cell technologies, including single-cell RNA sequencing and cytometry by time-of-flight, have identified the distinct subpopulations that constitute these tissues. These timely studies have provided the building blocks for the construction of single-cell atlases of joint tissues including cartilage, bone and synovium, leading to the identification of developmental trajectories, deciphering of crosstalk between cells and discovery of rare populations such as stem and progenitor cells. In addition, these studies have revealed unique pathogenetic populations that are potential therapeutic targets. The use of these approaches in synovial tissues has helped to identify how distinct cell subpopulations can orchestrate disease initiation and progression and be responsible for distinct pathological outcomes. Additionally, repair of tissues such as cartilage and meniscus remains an unmet medical need, and single-cell methodologies can be invaluable in providing a blueprint for both effective tissue-engineering strategies and therapeutic interventions for chronic joint diseases such as osteoarthritis and rheumatoid arthritis.

The Role of TAM Receptors in Bone

The TAM (TYRO3, MERTK, and AXL) family of receptor tyrosine kinases are pleiotropic regulators of adult tissue homeostasis maintaining organ integrity and self-renewal. Disruption of their homeostatic balance fosters pathological conditions like autoinflammatory or degenerative diseases including rheumatoid arthritis, lupus erythematodes, or liver fibrosis. Moreover, TAM receptors exhibit prominent cell-transforming properties, promoting tumor progression, metastasis, and therapy resistance in various cancer entities. Emerging evidence shows that TAM receptors are involved in bone homeostasis by regulating osteoblastic bone formation and osteoclastic bone resorption. Therefore, TAM receptors emerge as new key players of the regulatory cytokine network of osteoblasts and osteoclasts and represent accessible targets for pharmacologic therapy for a broad set of different bone diseases, including primary and metastatic bone tumors, rheumatoid arthritis, or osteoporosis.

Distinct mast cell subpopulations within and around lymphatic vessels regulate lymph flow and progression of inflammatory-erosive arthritis in TNF-transgenic mice

Objective

Inflammatory-erosive arthritis is exacerbated by dysfunction of joint-draining popliteal lymphatic vessels (PLVs). Synovial mast cells are known to be pro-inflammatory in rheumatoid arthritis (RA). In other settings they have anti-inflammatory and tissue reparative effects. Herein, we elucidate the role of mast cells on PLV function and inflammatory-erosive arthritis in tumor necrosis factor transgenic (TNF-tg) mice that exhibit defects in PLVs commensurate with disease progression.

Methods

Whole mount immunofluorescent microscopy, toluidine blue stained histology, scanning electron microscopy, and in silico bioinformatics were performed to phenotype and quantify PLV mast cells. Ankle bone volumes were assessed by μCT, while corresponding histology quantified synovitis and osteoclasts. Near-infrared indocyanine green imaging measured lymphatic clearance as an outcome of PLV draining function. Effects of genetic MC depletion were assessed via comparison of 4.5-month-old WT, TNF-tg, MC deficient KitW-sh/W-sh (cKit-/-), and TNF-tg x cKit-/- mice. Pharmacological inhibition of mast cells was assessed by treating TNF-tg mice with placebo or cromolyn sodium (3.15mg/kg/day) for 3-weeks.

Results

PLVs are surrounded by MCT+/MCPT1+/MCPT4+ mast cells whose numbers are increased 2.8-fold in TNF-tg mice. The percentage of peri-vascular degranulating mast cells was inversely correlated with ICG clearance. A population of MCT+/MCPT1-/MCPT4- mast cells were embedded within the PLV structure. In silico single-cell RNA-seq (scRNAseq) analyses identified a population of PLV-associated mast cells (marker genes: Mcpt4, Cma1, Cpa3, Tpsb2, Kit, Fcer1a & Gata2) with enhanced TGFβ-related signaling that are phenotypically distinct from known MC subsets in the Mouse Cell Atlas. cKit-/- mice have greater lymphatic defects than TNF-tg mice with exacerbation of lymphatic dysfunction and inflammatory-erosive arthritis in TNF-tg x cKit-/- vs. TNF-Tg mice. Cromolyn sodium therapy stabilized PLV mast cells, increased TNF-induced bone loss, synovitis, and osteoclasts, and decreased ICG clearance.

Conclusions

Mast cells are required for normal lymphatic function. Genetic ablation and pharmacological inhibition of mast cells exacerbates TNF-induced inflammatory-erosive arthritis with decreased lymphatic clearance. Together, these findings support an inflammatory role of activated/degranulated peri-PLV mast cells during arthritic progression, and a homeostatic role of intra-PLV mast cells, in which loss of the latter dominantly exacerbates arthritis secondary to defects in joint-draining lymphatics, warranting investigation into specific cellular mechanisms.

A newly developed PLD1 inhibitor ameliorates rheumatoid arthritis by regulating pathogenic T and B cells and inhibiting osteoclast differentiation

Phospholipase D1 (PLD1), which catalyzes the hydrolysis of phosphatidylcholine to phosphatidic acid and choline, plays multiple roles in inflammation. We investigated the therapeutic effects of the newly developed PLD1 inhibitors A2998, A3000, and A3773 in vitro and in vivo rheumatoid arthritis (RA) model. A3373 reduced the levels of LPS-induced TNF-α, IL-6, and IgG in murine splenocytes in vitro. A3373 also decreased the levels of IFN-γ and IL-17 and the frequencies of Th1, Th17 cells and germinal-center B cells, in splenocytes in vitro. A3373 ameliorated the severity of collagen-induced arthritis (CIA) and suppressed infiltration of inflammatory cells into the joint tissues of mice with CIA compared with vehicle-treated mice. Moreover, A3373 prevented systemic bone demineralization in mice with CIA and suppressed osteoclast differentiation and the mRNA levels of osteoclastogenesis markers in vitro. These results suggest that A3373 has therapeutic potential for RA.

Evolution and immunopathology of chikungunya virus informs therapeutic development

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, is an emerging global threat identified in more than 60 countries across continents. The risk of CHIKV transmission is rising due to increased global interactions, year-round presence of mosquito vectors, and the ability of CHIKV to produce high host viral loads and undergo mutation. Although CHIKV disease is rarely fatal, it can progress to a chronic stage, during which patients experience severe debilitating arthritis that can last from several weeks to months or years. At present, there are no licensed vaccines or antiviral drugs for CHIKV disease, and treatment is primarily symptomatic. This Review provides an overview of CHIKV pathogenesis and explores the available therapeutic options and the most recent advances in novel therapeutic strategies against CHIKV infections.

Rheumatoid arthritis treatment with zoledronic acid, a potentialinhibitorofGWAS-derived pharmacogenetics STAT3 and IL2 targets

Rheumatoid arthritis (RA) is an inflammatory condition that primarily affects the joints and progress to affect other vital organs. Variety of drugs are being recommended to control the disease progression that benefits patients to perform day-to-day activities. Few of these RA drugs have noticeable side effects; therefore, it's crucial to choose the appropriate drug for treating RA with an understanding of the disease's pathophysiology. Herein, we investigated the RA genes from GWAS data to construct protein-protein interaction (PPI) network and to define appropriate drug targets for RA. The predicted drug targets were screened with the known RA drugs based on molecular docking. Further, the molecular dynamics simulations were performed to comprehend the conformational changes and stability of the targets upon binding of the selected top ranked RA drug. As a result, our constructed protein network from GWAS data revealed, STAT3 and IL2 could be potential pharmacogenetics targets that interlink most of the RA genes encoding proteins. These interlinked proteins of both the targets showed involvement in cell signaling, immune response, and TNF signaling pathway. Among the 192 RA drugs investigated, zoledronic acid had the lowest binding energy that inhibit both STAT3 (-6.307 kcal/mol) and IL2 (-6.231 kcal/mol). Additionally, STAT3 and IL2 trajectories on zoledronic acid binding exhibit notable differences in MD simulations as compared to a drug-free environment. Also, the in vitro assessment with the zoledronic acid confirms the outcome of our computational study. Overall, our study identify zoledronic acid could be potential inhibitor against these targets, that will benefits patients with RA. Comparative efficiency assessments between the RA drugs through clinical trials are needed to validate our findings in the treatment of RA.

A green-lipped mussel prevents rheumatoid arthritis via regulation of inflammatory response and osteoclastogenesis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by progressive joint destruction. Green-lipped mussel (GLM) has chondro-modulatory and anti-inflammatory properties, but the mechanism underlying the effect of GLM on RA is unclear. To investigate the roles of GLM on the pathogenesis of RA, we examined the effects of GLM in collagen-induced arthritis (CIA) mice and osteoclast differentiation. GLM was orally administrated CIA mice at 3 weeks after chicken type II collagen (CII) immunizations. GLM reduced arthritis severity and the histologic score of CIA mice compared to vehicle. The expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-17) was decreased in the ankle joints of GLM-treated CIA mice. The expression of CD4+ IL-17+ cells decreased in ex vivo splenocytes and the spleens of GLM-treated CIA mice. Moreover, GLM inhibited TRAP+ multinucleated cells among mouse bone marrow-derived monocytes/macrophages (BMM), and the expression of osteoclast-related genes in mouse BMMs and human monocytes in vitro. These results suggest that GLM has potential as a therapeutic agent that can improve disease by controlling pathologic immune cells and osteoclastogenesis.

A Scoping Review of the Skeletal Effects of Naringenin

BACKGROUND

Osteoporosis is caused by the deterioration of bone density and microstructure, resulting in increased fracture risk. It transpires due to an imbalanced skeletal remodelling process favouring bone resorption. Various natural compounds can positively influence the skeletal remodelling process, of which naringenin is a candidate. Naringenin is an anti-inflammatory and antioxidant compound found in citrus fruits and grapefruit. This systematic review aims to present an overview of the available evidence on the skeletal protective effects of naringenin.

METHOD

A systematic literature search was conducted using the PubMed and Scopus databases in August 2022. Original research articles using cells, animals, or humans to investigate the bone protective effects of naringenin were included.

RESULTS

Sixteen eligible articles were included in this review. The existing evidence suggested that naringenin enhanced osteoblastogenesis and bone formation through BMP-2/p38MAPK/Runx2/Osx, SDF-1/CXCR4, and PI3K/Akt/c-Fos/c-Jun/AP-1 signalling pathways. Naringenin also inhibited osteoclastogenesis and bone resorption by inhibiting inflammation and the RANKL pathway.

CONCLUSIONS

Naringenin enhances bone formation while suppressing bone resorption, thus achieving its skeletal protective effects. It could be incorporated into the diet through fruit intake or supplements to prevent bone loss.

Mechanism of Emodin in the Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic, systemic, and autoimmune disease, and its main pathological changes are inflammatory cell infiltration accompanied by the secretion and accumulation of a variety of related cytokines, which induce the destruction of cartilage and bone tissue. Therefore, the modulation of inflammatory cells and cytokines is a key therapeutic target for controlling inflammation in RA. This review details the effects of emodin on the differentiation and maturation of T lymphocytes, dendritic cells, and regulatory T cells. In addition, the systematic introduction of emodin directly or indirectly affects proinflammatory cytokines (TNF-α, IL-6, IL-1, IL-1β, IL-17, IL-19, and M-CSF) and anti-inflammatory cytokines (the secretion of IL-4, IL-10, IL-13, and TGF-β) through the coregulation of a variety of inflammatory cytokines to inhibit inflammation in RA and promote recovery. Understanding the potential mechanism of emodin in the treatment of RA in detail provides a systematic theoretical basis for the clinical application of emodin in the future.

Inhibition of TREM-2 Markedly Suppresses Joint Inflammation and Damage in Experimental Arthritis

The triggering receptors expressed on myeloid cells (TREMs) are a family of activating immune receptors that regulate the inflammatory response. TREM-1, which is expressed on monocytes and/or macrophages and neutrophils, functions as an inflammation amplifier and plays a role in the pathogenesis of rheumatoid arthritis (RA). Unlike TREM-1, the role in RA of TREM-2, which is expressed on macrophages, immature monocyte-derived dendritic cells, osteoclasts, and microglia, remains unclear and controversial. TREM-2 ligands are still unknown, adding further uncertainty to our understanding of TREM-2 function. Previously, we demonstrated that TREM-1 blockade, using a ligand-independent TREM-1 inhibitory peptide sequence GF9 rationally designed by our signaling chain homooligomerization (SCHOOL) model of cell signaling, ameliorates collagen-induced arthritis (CIA) severity in mice. Here, we designed a TREM-2 inhibitory peptide sequence IA9 and tested it in the therapeutic CIA model, either as a free 9-mer peptide IA9, or as a part of a 31-mer peptide IA31 incorporated into lipopeptide complexes (IA31-LPC), for targeted delivery. We demonstrated that administration of IA9, but not a control peptide, after induction of arthritis diminished release of proinflammatory cytokines and dramatically suppressed joint inflammation and damage, suggesting that targeting TREM-2 may be a promising approach for the treatment of RA.

Modulation of Differentiation and Bone Resorbing Activity of Human (Pre-) Osteoclasts After X-Ray Exposure

Low-dose radiotherapy (LD-RT) is a local treatment option for patients with chronic degenerative and inflammatory diseases, in particular musculoskeletal diseases. Despite reported analgesic and anti-inflammatory effects, cellular and molecular mechanisms related to osteoimmunological effects are still elusive. Here we test the hypothesis that X-irradiation inhibits the differentiation of precursor osteoclasts into mature osteoclasts (mOC) and their bone resorbing activity. Circulating monocytes from healthy donors were isolated and irradiated after attachment with single or fractionated X-ray doses, comparable to an LD-RT treatment scheme. Then monocytes underwent ex vivo differentiation into OC during cultivation up to 21 days, under conditions mimicking the physiological microenvironment of OC on bone. After irradiation, apoptotic frequencies were low, but the total number of OC precursors and mOC decreased up to the end of the cultivation period. On top, we observed an impairment of terminal differentiation, i.e. a smaller fraction of mOC, reduced resorbing activity on bone, and release of collagen fragments. We further analyzed the effect of X-irradiation on multinucleation, resulting from the fusion of precursor OC, which occurs late during OC differentiation. At 21 days after exposure, the observation of smaller cellular areas and a reduced number of nuclei per mOC suggest an impaired fusion of OC precursors to form mOC. Before, at 14 days, the nuclear translocation of Nuclear Factor Of Activated T Cells 1 (NFATc1), a master regulator of osteoclast differentiation and fusion, was decreased. In first results, obtained in the frame of a longitudinal LD-RT study, we previously reported a pain-relieving effect in patients. However, in a subgroup of patients suffering from Calcaneodynia or Achillodynia, we did not observe a consistent decrease of established blood markers for resorption and formation of bone, or modified T cell subtypes involved in regulating these processes. To assess the relevance of changes in bone metabolism for other diseases treated with LD-RT will be subject of further studies. Taken together, we observed that in vitro X-irradiation of monocytes results in an inhibition of the differentiation into bone-resorbing OC and a concomitant reduction of resorbing activity. The detected reduced NFATc1 signaling could be one underlying mechanism.

Glytabastan B, a coumestan isolated from Glycine tabacina, alleviated synovial inflammation, osteoclastogenesis and collagen-induced arthritis through inhibiting MAPK and PI3K/AKT pathways

The roots of Glycine tabacina are used to treat rheumatoid arthritis (RA) and joint infection in folk medicine. Glytabastan B (GlyB), a newly reported coumestan isolated from this species, was found to significantly attenuate IL-1β-induced inflammation in SW982 human synovial cells at 3 and 6 μM, as evidenced by the decreased levels of pro-inflammatory mediators and matrix metalloproteinases (MMPs). GlyB also suppressed RANKL-induced osteoclastogenesis, decreased the expression of osteoclastogenic markers (NFATc1, CTSK, MMP-9) and osteoclast-mediated bone resorption. Further, GlyB administration (12.5 and 25 mg/kg) significantly inhibited inflammation, osteoclast formation and disease progression in collagen-induced arthritis (CIA) mice. Integration of network pharmacology, quantitative phosphoproteomic and experimental pharmacology results revealed that these beneficial actions were closely associated with the blockade of GlyB on the activation of MAPK, PI3K/AKT and their downstream signals including NF-κB and GSK3β/NFATc1. Drug affinity responsive target stability (DARTS) assay, cellular thermal shift (CETSA) assay and molecular docking analysis confirmed that there were direct interactions between GlyB and its target proteins ERK2, JNK1 and class Ⅰ PI3K catalytic subunit p110 (α, β, δ and γ), which significantly contributed to the inhibition of activation of MAPK and PI3K/AKT pathways. In conclusion, these results strongly suggest GlyB is a promising multiple-target candidate for the development of agents for the prevention and treatment of RA.

Nucleotides modulate synoviocyte proliferation and osteoclast differentiation in macrophages with potential implications for rheumatoid arthritis

P2 receptors are nucleotide-activated receptors involved in inflammation, cell proliferation osteoblastogenesis, osteoclastogenesis and their function. They can be potential role players in the pathophysiology of rheumatoid arthritis (RA). Our analysis of gene expression datasets of synovial tissue biopsy from the GEO database shows changes in the expression levels of P2 receptors. HIG-82, a synovial fibroblast cell line and RAW 264.7, a macrophage cell line are good in vitro models to study RA. Nucleotide addition experiments showed UDP Glucose significantly increased the proliferation of synovial fibroblasts (HIG-82). Similarly, nucleotides such as Adenosine tri-phosphate (ATP), Adenosine di-phosphate (ADP), Uridine tri-phosphate (UTP), Uridine di-phosphate (UDP) and Uridine diphosphoglucose (UDPG) induced elevated reactive oxygen species (ROS) and tartrate Resistant Acid Phosphatase (TRAP) activity in RAW264.7 cells. The ADP-induced TRAP could be inhibited by clopidogrel a P2Y₁₂ inhibitor. ATP, ADP, UTP, UDP and UDPG also induced osteoclastogenesis as evident from fused multinucleate cells and expression of osteoclast markers (TRAP, Cathepsin K [CTSK]) as determined by Q-PCR. Apyrase (APY) a nucleotidase and an enzyme that is used to modulate extracellular nucleotide concentration is sufficient to induce osteoclastogenesis. Taken together our results show that nucleotides modulate synoviocyte proliferation and macrophage differentiation into osteoclast and play an important role in RA. Nucleotide receptors might be potential therapeutic targets in RA.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03052-8.

Interleukin-9 Facilitates Osteoclastogenesis in Rheumatoid Arthritis

In rheumatoid arthritis (RA), inflammatory cytokines play a pivotal role in triggering abnormal osteoclastogenesis leading to articular destruction. Recent studies have demonstrated enhanced levels of interleukin-9 (IL-9) in the serum and synovial fluid of patients with RA. In RA, strong correlation has been observed between tissue inflammation and IL-9 expression in synovial tissue. Therefore, we investigated whether IL-9 influences osteoclastogenesis in patients with RA. We conducted the study in active RA patients. For inducing osteoclast differentiation, mononuclear cells were stimulated with soluble receptor activator of NF-kB ligand (sRANKL) and macrophage-colony-stimulating factor (M-CSF) in the presence or absence of recombinant (r) IL-9. IL-9 stimulation significantly enhanced M-CSF/sRANKL-mediated osteoclast formation and function. Transcriptome analysis revealed differential gene expression induced with IL-9 stimulation in the process of osteoclast differentiation. IL-9 mainly modulates the expression of genes, which are involved in the metabolic pathway. Moreover, we observed that IL-9 modulates the expression of matrix metalloproteinases (MMPs), which are critical players in bone degradation. Our results indicate that IL-9 has the potential to influence the structural damage in the RA by promoting osteoclastogenesis and modulating the expression of MMPs. Thus, blocking IL-9 pathways might be an attractive immunotherapeutic target for preventing bone degradation in RA.

JTE-952 Suppresses Bone Destruction in Collagen-Induced Arthritis in Mice by Inhibiting Colony Stimulating Factor 1 Receptor

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and structural destruction of the joints. Bone damage occurs in an early stage after onset and osteoclast activation plays a substantial role in its progression. Colony stimulating factor 1 receptor (CSF1R) is a receptor protein tyrosine kinase specifically expressed in monocytic-lineage cells such as macrophages and osteoclasts. Here, we investigated the effect of JTE-952, a novel CSF1R tyrosine kinase inhibitor, on osteoclast formation in vitro and on bone destruction in a mouse model of collagen-induced arthritis. JTE-952 completely inhibited osteoclast differentiation from human monocytes, with an IC₅₀ of 2.8 nmol/L, and reduced osteoclast formation from the synovial cells of RA patients. Detectable levels of colony stimulating factor 1 (CSF1), a ligand of CSF1R, were observed in the synovial tissues of the arthritis model, similar to those observed in the pathology of human RA. JTE-952 significantly suppressed increases in the bone destruction score, the number of tartrate-resistant-acid-phosphatase-positive cells, and the severity of arthritis in the model mice. We also examined the efficacy of JTE-952 combined with methotrexate. This combination therapy more effectively reduced the severity of bone destruction and arthritis than monotherapy with either agent alone. In summary, JTE-952 potently inhibited human osteoclast formation in vitro and suppressed bone destruction in an experimental arthritis model, especially when combined with methotrexate. These results indicate that JTE-952 should strongly inhibit bone destruction and joint inflammation in RA patients and effectively prevent the progression of the structural destruction of joints.

ELMO1 signaling is a promoter of osteoclast function and bone loss

Osteoporosis affects millions worldwide and is often caused by osteoclast induced bone loss. Here, we identify the cytoplasmic protein ELMO1 as an important ‘signaling node’ in osteoclasts. We note that ELMO1 SNPs associate with bone abnormalities in humans, and that ELMO1 deletion in mice reduces bone loss in four in vivo models: osteoprotegerin deficiency, ovariectomy, and two types of inflammatory arthritis. Our transcriptomic analyses coupled with CRISPR/Cas9 genetic deletion identify Elmo1 associated regulators of osteoclast function, including cathepsin G and myeloperoxidase. Further, we define the ‘ELMO1 interactome’ in osteoclasts via proteomics and reveal proteins required for bone degradation. ELMO1 also contributes to osteoclast sealing zone on bone-like surfaces and distribution of osteoclast-specific proteases. Finally, a 3D structure-based ELMO1 inhibitory peptide reduces bone resorption in wild type osteoclasts. Collectively, we identify ELMO1 as a signaling hub that regulates osteoclast function and bone loss, with relevance to osteoporosis and arthritis.

Osteoporosis and bone fractures affect millions of patients worldwide and are often due to increased bone resorption. Here the authors identify the cytoplasmic protein ELMO1 as an important ‘signaling node’ promoting the bone resorption function of osteoclasts.

Biomarker Approach Towards Rheumatoid Arthritis Treatment

Rheumatoid arthritis is an auto-immune disorder, recognized by cartilage as well as bone destruction, which causes irreversible joint deformities, which further results in functional limitations in the patient. Genes like HLA-DRB1 and PTPN22 are likely implicated in the genetic predisposition of rheumatoid arthritis pathology. The first and foremost clinical manifestation in a person with rheumatoid arthritis is joint destruction followed by cartilage and bone destruction caused by cell-cell interactions. The cell-cell interactions are thought to be initialized through the contact of antigen-presenting cells (APC) with CD4+ cells, leading to the progression of the disease. APC includes a complex of class ІІ major histocompatibility complex molecules along with peptide antigens and binds to the receptors present on the surface of T-cells. Further, the activation of macrophages is followed by the release of various pro-inflammatory cytokines such as IL-1 and TNF-α, which lead to the secretion of enzymes that degrade proteoglycan and collagen, which in turn, increase tissue degradation. Biomarkers like IL-6, IL-12, IL-8 and IL-18, 14-3-3η, RANKL, IFN-γ, IFN-β and TGF-β have been designated as key biomarkers in disease development and progression. The study of these biomarkers is very important as they act as a molecular indicator of pathological processes that aggravate the disease.

Umbelliferone Ameliorates Complete Freund Adjuvant-Induced Arthritis via Reduction of NF-κB Signaling Pathway in Osteoclast Differentiation

Osteoclasts, bone-resorbing somatic cells, are directly responsible for bone destruction during rheumatoid arthritis. Complete Freund adjuvant (CFA) is a widely used animal model using rodents for studying rheumatoid arthritis (RA), which effectively manifests serious cartilage destruction and progressive bone erosion, affecting synovial joints and serious joint dysfunction. It was considered that joint injury in RA is induced through systemic inflammation pathway. Umbelliferone (UF), a coumarin derivative of Agele marmilosa, possesses anti-inflammatory activity. In the current study, we scrutinize the effect of umbelliferone on CFA-induced arthritis model and explore the possible mechanism on bone destruction. Intradermal administration of CFA (0.05 mL) was to induce RA manifestations in the experimental rats and the same oral administration of UF was received. The anti-arthritic activity of UF was determined by its inhibitory activity on various biochemical markers, viz., pro-inflammatory, inflammatory, antioxidant enzymes, and hematological parameters elevated during RA condition. We also estimated the mRNA expression of osteoclast parameters. Obtained result disclosed significant reduction in the paw edema and increment of the body weight after UF administration. UF reduce the inflammatory mediatory such as COX-2, PGE₂, NF-kB, and VEGF; pro-inflammatory cytokines include TNF-α, IL-1β, IL-6, IL-10, and IL-17 significantly. Moreover, UF treatment significantly reduced the osteoclast number via modulating the RANKL/RANK/OPG ratio. Furthermore, administration of umbelliferone significantly (P < 0.001) suppressed the NF-κB and VEGF. Collectively, our results indicated the novel role of umbelliferone in osteoclastogenesis and proved that umbelliferone is a modern therapeutic tool as a natural agent for treating arthritis and other autoimmune disorders with bone degradation.

Sclareol inhibits RANKL-induced osteoclastogenesis and promotes osteoblastogenesis through promoting CCN1 expression via repressing the MAPK pathway

Osteoclasts are crucial cellular components of bone and are the cause of various bone problems like osteoporosis. Various biological activities such as anti-tumorous, anti-inflammatory, antibacterial, and immunomodulatory function are influenced by Sclareol, as a natural diterpene compound. However, studies on the effect and mechanism of Sclareol on osteoporosis are rare. In the current research, the influence of Sclareol on osteoclastogenesis and osteoblastogenesis was targeted to be discovered in ovariectomy (OVX)-induced animal models and in vitro. The expression levels of osteoclast-related genes such as c-Fos, NFATc1, and CTSK were detected by RT-qPCR and western blotting to understand the inhibition of Sclareol on the creation of osteoclast. The influence of Sclareol on osteoblastogenesis and the expression of osteoblastogenic markers were also examined. Sclareol inhibited the osteoclastogenesis caused by receptor activator of nuclear factor-κB ligand (RANKL) which promoted osteoblastogenesis through upregulating the expression of cysteine-rich protein 61 (CYR61/CCN1), which is a matricellular protein of the CCN family. The p-ERK and p-P38 protein expression levels were considerably downregulated by Sclareol. Furthermore, CCN1 overexpression partially mimicked the inhibitory effect of Sclareol, while the opposite results were obtained after CCN1 silencing. Additionally, Sclareol protected against loss of bones in an osteoporosis mouse model generated by OVX. The acquired results indicated that Sclareol represses RANKL-induced osteoclastogenesis and promotes osteoblastogenesis via promoting the expression of CCN1 by constraining the mitogen-activated protein kinase (MAPK) pathway. Our findings proposed that for the avoidance and treatment of osteoclast-linked disorders, Sclareol is a potentially effective drug. A proposed model for mediated regulation of osteoclastogenesis and osteoblastogenesis by Sclareol. The basic model of the process by which Sclareol prevents osteoclastogenesis and promotes osteoblastogenesis. Sclareol may increase the expression of CCN1 through inhibiting the MAPK pathway, thereby inhibiting osteoclast differentiation and attenuating bone resorption. Sclareol represses the expression of c-Fos, which stimulates the formation of osteoclast. In contrast, Sclareol promotes osteoblast differentiation by upregulating Runx2 expression, thereby improving the formation of bones. Consequently, Sclareol protects against loss of bones by regulating the stability of bone makeover via inhibition of bone formation and stimulation of bone resorption. Graphical Headlights 1. Sclareol represses RANKL-induced osteoclastogenesis. 2. Sclareol promotes osteoblast differentiation. 3. Sclareol inhibits the MAPK pathway through induction of CCN1. 4. Sclareol protects against bone loss by regulating the balance of bone remodeling via inhibition of bone formation and stimulation of bone resorption.

Isolation and Identification of Antiarthritic Constituents from Glycine tabacina and Network Pharmacology-Based Prediction of Their Protective Mechanisms against Rheumatoid Arthritis

Glycine tabacina (Labill.) Benth is an edible medicinal herb for rheumatoid arthritis (RA) treatment in folk medicine. Current phytochemical research on this dried herb led to the isolation of eight new coumestans, named glytabastan A-H (1-8), and twenty-three known compounds 9-31. Their structures were elucidated using spectroscopic methods. The antiarthritic activities of all isolates were evaluated, and the results showed that coumestans 1-6 and 8-10 could inhibit arthritic inflammation in vitro, while coumestans 1, 2, 9, and 10 significantly blocked the osteoclastogenesis induced by receptor activator of nuclear factor (NF) κB ligand (RANKL). Moreover, network pharmacological analysis revealed that the anti-RA effect of G. tabacina involved multitargets, multipathways such as PI3K/Akt and MAPK signaling pathways, and various biological processes such as inflammatory response and cytokine-mediated signaling pathways. These results suggested that this species and its novel coumestans could serve as potential antiarthritic agents for functional food or medicinal use.

Metformin: A Potential Therapeutic Tool for Rheumatologists

Metformin is an oral antihyperglycemic drug widely used to treat type 2 diabetes, acting via indirect activation of 5′ Adenosine Monophosphate-activated Protein Kinase (AMPK). Actually, evidence has accumulated of an intriguing anti-inflammatory activity, mainly mediated by AMPK through a variety of mechanisms such as the inhibition of cytokine-stimulated Nuclear Factor-κB (NF-κB) and the downregulation of the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathways. Moreover, AMPK plays an important role in the modulation of T lymphocytes and other pivotal cells of the innate immune system. The current understanding of these AMPK effects provides a strong rationale for metformin repurposing in the management of autoimmune and inflammatory conditions. Several studies demonstrated metformin’s beneficial effects on both animal and human rheumatologic diseases, especially on rheumatoid arthritis. Unfortunately, even though data are large and remarkable, they almost exclusively come from experimental investigations with only a few from clinical trials. The lack of support from prospective placebo-controlled trials does not allow metformin to enter the therapeutic repertoire of rheumatologists. However, a large proportion of rheumatologic patients can currently benefit from metformin, such as those with concomitant obesity and type 2 diabetes, two conditions strongly associated with rheumatoid arthritis, osteoarthritis, and gout, as well as those with diabetes secondary to steroid therapy.

Sex-Based Differences in Monocytic Lineage Cells Contribute to More Severe Collagen-Induced Arthritis in Female Rats Compared with Male Rats

Monocytes' plasticity has an important role in the development of rheumatoid arthritis (RA), an autoimmune disease exhibiting greater prevalence in women. Contribution of this phenomenon to sex bias in RA severity was investigated in rat collagen-induced arthritis (CIA) model of RA. The greater severity of CIA in females (exhibiting signs of bone resorption) was accompanied by the higher blood level of advanced oxidation protein products and a more pro-oxidant profile. Consistently, in females, the greater density of giant multinuclear cells (monocytes/macrophages and osteoclasts) in inflamed joint tissue was found. This correlated with the higher frequencies of CCR2- and CX3CR1- expressing cells (precursors of inflammatory monocytes/macrophages and osteoclasts) among CD11b+ splenocytes. This in conjunction with the enhanced migratory capacity of CD11b+ monocytic cells in females compared with males could be linked with the higher frequencies of CCR2+CX3CR1-CD43^lowCD11b+ and CCR2-CX3CR1+CD43^hiCD11b+ cells (corresponding to "classical" and "non-classical" monocytes, respectively) and the greater density of CD68+ cells (monocytes/macrophages and osteoclast precursors/osteoclasts) in blood and inflamed paws from female rats, respectively. Consistently, the higher levels of GM-CSF, TNF-α and IL-6, IL-1β (driving Th17 cell differentiation), and IL-17 followed by the lower level of IL-10 were measured in inflamed paw cultures from female compared with male rats. To the greater IL-17 production (associated with enhanced monocyte immigration and differentiation into osteoclasts) most likely contributed augmented Th17 cell generation in the lymph nodes draining arthritic joints from female compared with male rats. Overall, the study suggests the sex-specific contribution of monocytic lineage cells to CIA, and possibly RA development.

Dolichosin A, a coumestan isolated from Glycine tabacina, inhibits IL-1β-induced inflammation in SW982 human synovial cells and suppresses RANKL-induced osteoclastogenesis: From network pharmacology to experimental pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Glycine tabacina (Labill.) Benth has been used as a traditional Chinese herbal medicine for the treatment of rheumatoid arthritis (RA) and joint infection. It is also one of the sources of the renowned native herbal medicine 'I-Tiao-Gung' in Taiwan.

AIM OF THE STUDY

This study aimed to investigate anti-arthritic effects and underlying mechanisms of dolichosin A (DoA), a coumestan compound isolated from G. tabacina, by the integration of network pharmacology and experimental pharmacology.

MATERIALS AND METHODS

Putative therapeutic targets and potential pharmacological mechanisms of DoA for RA treatment were predicted by network pharmacology approach. The regulated network of DoA acting on RA was constructed using Cytoscape 3.7.1. Anti-arthritic effects of DoA and predicted mechanisms were further validated using IL-1β-induced SW982 human synovial cell model and RANKL-induced osteoclastogenesis model.

RESULTS

A regulatory network of DoA-targets-pathways-RA was successfully constructed using network pharmacology approach. In this network, 65 candidate targets of DoA related to its therapeutic effect on RA were identified and the functional enrichment analysis revealed that these candidate targets were significantly involved in 12 central signaling pathways such as PI3K/AKT pathway, MAPK pathway and osteoclast differentiation. Furthermore, we found that DoA could significantly inhibit IL-1β-induced inflammation in SW982 human synovial cells, as evidenced by the decreased levels of pro-inflammatory mediators (TNF-α, IL-6 and COX-2) and MMP-3. DoA also suppressed RANKL-induced osteoclastogenesis in vitro, as evidenced by decreased number of TRAP-positive multinucleated osteoclasts and reduced TRAP activity. Further experimental mechanism evidence confirmed the predicted results of network pharmacology that the blockade of PI3K/AKT and MAPK pathways activation was closely associated with these regulated processes of DoA.

CONCLUSIONS

Our results demonstrated that DoA exhibited strong anti-arthritic activity through suppressing PI3K/AKT and MAPK pathways activation in activated synovial cells and osteoclasts, suggesting its potential as a hopeful candidate for the development of novel agents for the prevention and treatment of RA.

DMY protects the knee joints of rats with collagen-induced arthritis by inhibition of NF-κB signaling and osteoclastic bone resorption

Collagen-induced arthritis (CIA) is a widely used animal model for studying rheumatoid arthritis (RA), which manifests serious joint dysfunction, progressive bone erosion and articular cartilage destruction. Considering that joint damage in RA is caused by systemic inflammation and dihydromyricetin (DMY), the main flavonoid of Ampelopsis Michx, possesses anti-inflammatory properties, in the present study we have investigated the potential capability of DMY to inhibit inflammation-mediated joint damage and explore the underlying mechanisms. A rat model of RA induced by CIA was administered with DMY for 5 weeks. Prior to histological analysis, the knee joints were scanned by microcomputed tomography (μCT) to detect bone damage. Articular cartilage destruction was assessed by Alcian blue and Toluidine blue staining and the pathological alteration of osteoblasts and osteoclasts in joints was evaluated by hematoxylin-eosin (H&E) and tartrate-resistant acid phosphatase (TRAP) staining, respectively. The effects of DMY on osteoblast differentiation and osteoclast formation in vitro were investigated. Consistent with the in vivo results, DMY had no significant effect on osteoblast differentiation but an inhibitory effect on osteoclast formation. Furthermore, we determined that the mechanism of the DMY-suppressed osteoclast formation was blocking the phosphorylation of I-κB kinase (IKK) so as to hinder the activation of nuclear factor-κB (NF-κB). Collectively, DMY could ameliorate knee joint damage, especially in articular cartilage, which is the weight-bearing region, by inhibiting osteoclast formation through NF-κB signaling.

Phenotypic and functional characterization of natural killer cells in rheumatoid arthritis-regulation with interleukin-15

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial inflammation and joint destruction. Previous studies have shown that natural killer (NK) cells may play an important role in the pathogenesis of RA. Interleukin (IL)-15, a pro-inflammatory cytokine which induces proliferation and differentiation of NK cells, is overexpressed in RA. In this present study, we examine various NKRs and adhesion molecule expression on NK cells from RA patients and their response to IL-15 stimulation. We also sought to study cytokine-induced memory-like (CIML) NK cells in RA patients. We established that 1. RA patients had higher NK cell percentages in peripheral blood and their serum IL-15 levels were higher compared to healthy volunteers; 2. NK cells from RA patients showed lower NKp46 expression and an impaired CD69 response to IL-15; 3. NK cells from RA patients showed higher CD158b and CD158e expression but lower CD62L expression; 4. exogenous IL-15 up-regulated CD69, CD158b, CD158e but down-regulated NKp46 and CD62L expression in RA; 5. As to CIML NK cells, restimulation - induced NK cytotoxicity and IFN-γ production was impaired in RA patients, 6. Reduced NKp46, perforin, and granzyme B expression on NK cells was found in RA patients with bone deformity and erosion, 7. RA disease activity (DAS28) showed inverse correlation with the percentages of CD56⁺CD3⁻ NK cells, and NKp46 and perforin expression on NK cells, respectively. Taken together, our study demonstrated differential expression of various NK receptors in RA patients. NKp46, CD158e, and perforin expression on NK cells may serve as markers of RA severity.

Fc-gamma receptors and S100A8/A9 cause bone erosion during rheumatoid arthritis. Do they act as partners in crime?

Bone erosion is one of the central hallmarks of RA and is caused by excessive differentiation and activation of osteoclasts. Presence of autoantibodies in seropositive arthritis is associated with radiographic disease progression. ICs, formed by autoantibodies and their antigens, activate Fcγ-receptor signalling in immune cells, and as such stimulate inflammation-mediated bone erosion. Interestingly, ICs can also directly activate osteoclasts by binding to FcγRs on their surface. Next to autoantibodies, high levels of alarmins, among which is S100A8/A9, are typical for RA and they can further activate the immune system but also directly promote osteoclast function. Therefore, IC-activated FcγRs and S100A8/A9 might act as partners in crime to stimulate inflammation and osteoclasts differentiation and function, thereby stimulating bone erosion. This review discusses the separate roles of ICs, FcγRs and alarmins in bone erosion and sheds new light on the possible interplay between them, which could fuel bone erosion.

TGFβ1 Regulates Human RANKL-Induced Osteoclastogenesis via Suppression of NFATc1 Expression

Osteoclasts are multinucleated giant cells responsible for bone resorption. Various mediators involved in osteoclast differentiation have been investigated as possible therapeutic targets for osteoporosis and rheumatoid arthritis (RA). Although transforming growth factor beta1 (TGFβ1) has been described as one such multifunctional cytokine essential for bone remodeling, its effect on osteoclastogenesis remains controversial. Therefore, we sought to examine the effect of TGFβ1 on osteoclast generation induced by receptor activator of nuclear factor (NF)-κB ligand (RANKL) in humans. Peripheral blood monocytes, isolated using magnetic bead sorting, were cultured with macrophage-colony stimulating factor (M-CSF) or RANKL with or without TGFβ1. Tartrate-resistant acid phosphatase (TRAP) staining, as well as bone resorption assays, revealed that TGFβ1 suppressed RANKL-mediated human osteoclast development. Real-time reverse transcription PCR and Western blotting revealed that TGFβ1 reduced the gene and protein expression of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), the master regulator of osteoclast differentiation, respectively. Luciferase assays indicated that TGFβ1 inhibited the NF-κB p65-stimulated promoter activity of NFATc1. Immunofluorescence analysis demonstrated that TGFβ1 abrogated RANKL-induced nuclear translocation of p65. Thus, TGFβ1 regulates human RANKL-induced osteoclastogenesis via downregulation of NFATc1 by blocking nuclear translocation of NF-κB, suggesting that TGFβ1 may be a potential therapeutic target for RA.

RA-map: building a state-of-the-art interactive knowledge base for rheumatoid arthritis

Rheumatoid arthritis (RA) is a progressive, inflammatory autoimmune disease of unknown aetiology. The complex mechanism of aetiopathogenesis, progress and chronicity of the disease involves genetic, epigenetic and environmental factors. To understand the molecular mechanisms underlying disease phenotypes, one has to place implicated factors in their functional context. However, integration and organization of such data in a systematic manner remains a challenging task. Molecular maps are widely used in biology to provide a useful and intuitive way of depicting a variety of biological processes and disease mechanisms. Recent large-scale collaborative efforts such as the Disease Maps Project demonstrate the utility of such maps as versatile tools to organize and formalize disease-specific knowledge in a comprehensive way, both human and machine-readable. We present a systematic effort to construct a fully annotated, expert validated, state-of-the-art knowledge base for RA in the form of a molecular map. The RA map illustrates molecular and signalling pathways implicated in the disease. Signal transduction is depicted from receptors to the nucleus using the Systems Biology Graphical Notation (SBGN) standard representation. High-quality manual curation, use of only human-specific studies and focus on small-scale experiments aim to limit false positives in the map. The state-of-the-art molecular map for RA, using information from 353 peer-reviewed scientific publications, comprises 506 species, 446 reactions and 8 phenotypes. The species in the map are classified to 303 proteins, 61 complexes, 106 genes, 106 RNA entities, 2 ions and 7 simple molecules. The RA map is available online at ramap.elixir-luxembourg.org as an open-access knowledge base allowing for easy navigation and search of molecular pathways implicated in the disease. Furthermore, the RA map can serve as a template for omics data visualization.

RTD-1 therapeutically normalizes synovial gene signatures in rat autoimmune arthritis and suppresses proinflammatory mediators in RA synovial fibroblasts

Rhesus theta defensin-1 (RTD-1), a macrocyclic immunomodulatory host defense peptide from Old World monkeys, is therapeutic in pristane-induced arthritis (PIA) in rats, a model of rheumatoid arthritis (RA). RNA-sequence (RNA-Seq) analysis was used to interrogate the changes in gene expression in PIA rats, which identified 617 differentially expressed genes (DEGs) in PIA synovial tissue of diseased rats. Upstream regulator analysis showed upregulation of gene expression pathways regulated by TNF, IL1B, IL6, proinflammatory cytokines, and matrix metalloproteases (MMPs) involved in RA. In contrast, ligand-dependent nuclear receptors like the liver X-receptors NR1H2 and NR1H3 and peroxisome proliferator-activated receptor gamma (PPARG) were downregulated in arthritic synovia. Daily RTD-1 treatment of PIA rats for 1-5 days following disease presentation modulated 340 of the 617 disease genes, and synovial gene expression in PIA rats treated 5 days with RTD-1 closely resembled the gene signature of naive synovium. Systemic RTD-1 inhibited proinflammatory upstream regulators such as TNF, IL1, and IL6 and activated antiarthritic ligand-dependent nuclear receptor pathways, including PPARG, NR1H2, and NR1H3, that were suppressed in untreated PIA rats. RTD-1 also inhibited proinflammatory responses in IL-1β-stimulated human RA fibroblast-like synoviocytes (FLS) in vitro and diminished expression of human orthologs of disease genes that are induced in rat PIA synovium. Thus, the antiarthritic mechanisms of systemic RTD-1 include homeostatic regulation of arthritogenic gene networks in a manner that correlates temporally with clinical resolution of rat PIA.

Active roles of dysfunctional vascular endothelium in fibrosis and cancer

Chronic inflammation is the underlying pathological condition that results in fibrotic diseases. More recently, many forms of cancer have also been linked to chronic tissue inflammation. While stromal immune cells and myofibroblasts have been recognized as major contributors of cytokines and growth factors that foster the formation of fibrotic tissue, the endothelium has traditionally been regarded as a passive player in the pathogenic process, or even as a barrier since it provides a physical divide between the circulating immune cells and the inflamed tissues. Recent findings, however, have indicated that endothelial cells in fact play a crucial role in the inflammatory response. Endothelial cells can be activated by cytokine signaling and express inflammatory markers, which can sustain or exacerbate the inflammatory process. For example, the activated endothelium can recruit and activate leukocytes, thus perpetuating tissue inflammation, while sustained stimulation of endothelial cells may lead to endothelial-to-mesenchymal transition that contributes to fibrosis. Since chronic inflammation has now been recognized as a significant contributing factor to tumorigenesis, it has also emerged that activation of endothelium also occurs in the tumor microenvironment. This review summarizes recent findings characterizing the molecular and cellular changes in the vascular endothelium that contribute to tissue fibrosis, and potentially to cancer formation.

Activation of TGR5 alleviates inflammation in rheumatoid arthritis peripheral blood mononuclear cells and in mice with collagen II‑induced arthritis

Rheumatoid arthritis (RA) is characterized by chronic inflammatory synovitis resulting in progressive joint destruction. Persistent synovial inflammation is induced by activation of various inflammatory cells. G-protein-coupled bile acid receptor 1 (TGR5) is a G-protein-coupled receptor activated by various bile acids, which has been reported to act as a key adaptor in regulating various signaling pathways involved in inflammatory responses and a diverse array of physiological processes, including bile acid synthesis, lipid and carbohydrate metabolism, carcinogenesis, immunity and inflammation. In the present study, TGR5 expression was detected in RA peripheral blood mononuclear cells (PBMCs), and its association with clinical disease activity, histological synovitis severity and radiological joint destruction was analyzed. Subsequently, the role and potential underlying mechanisms of TGR5 in the PBMCs of patients with RA and mice with collagen II-induced arthritis (CIA) were investigated. PBMCs were obtained from 50 patients with RA and 40 healthy controls (HCs). The mRNA and protein expression levels of TGR5 were detected in PBMCs via reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence staining, respectively. Additionally, the levels of proinflammatory cytokines were analyzed by RT-qPCR and enzyme-linked immunosorbent assay (ELISA). The activation of nuclear factor-κB (NF-κB) and IκB kinase a was determined via western blot analysis. The anti-arthritic and anti-inflammatory effects of LCA on mice with CIA were then investigated. The arthritis score was assessed, and the protein levels of proinflammatory cytokines in the plasma of mice were detected via ELISA. TGR5 mRNA expression was significantly downregulated in the PBMCs of patients with RA compared with in those of the HCs (0.53±0.58 for patients vs. 1.49±0.83 for HCs; P<0.001); similar findings were observed at the protein level. The mRNA expression levels of TGR5 in the PBMCs of patients with RA with a high 28-Joint Disease Activity Score (DAS28) were significantly decreased compared with in patients with a low DAS28 (0.81±0.65 for low score vs. 0.35±0.46 for high score; P=0.002). Furthermore, TGR5 expression was significantly correlated with the levels of C-reactive protein (r=−0.429; P=0.002) and the DAS28 (r=−0.383; P=0.006). RT-qPCR and ELISA analyses indicated that lithocholic acid (LCA, 10 mg/kg/day) attenuated lipopolysaccharide-induced proinflammatory cytokine production via inhibition of NF-κB activity in the PBMCs of patients with RA. In addition, the arthritis score was significantly decreased in LCA-treated CIA mice compared with in non-treated CIA mice. The increased production of tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-8 was significantly reduced in the plasma of LCA-treated CIA mice compared with the control. In conclusion, TGR5 may contribute to the inflammation of PBMCs in patients with RA and mice with CIA.

Metformin one in a Million Efficient Medicines for Rheumatoid Arthritis Complications: Inflammation, Osteoblastogenesis, Cardiovascular Disease, Malignancies

BACKGROUND

Rheumatoid arthritis is a widespread autoimmune disease and inflammation and bone destruction are two main issues in rheumatoid arthritis.

OBJECTIVE

To discussing metformin effects on rheumatoid arthritis complications.

METHODS

We conducted a narrative literature search including clinical trials, experimental studies on laboratory animals and cell lines. Our search covered Medline, PubMed and Google Scholar databases from 1999 until 2018. We used the terms" Metformin; Rheumatoid arthritis; Cardiovascular disease; Cancer; Osteoblastogenesis.

DISCUSSION

Inflammatory pro-cytokines such as Interlukin-6 play important roles in T. helper 17 cell lineage differentiation. Interlukin-6 and Tumor Necrosis Factor-α activate Janus kinase receptors signal through signaling transducer and activator of transcription signaling pathway which plays important role in inflammation, bone destruction and cancer in rheumatoid arthritis patients. Interlukin-6 and Tumor Necrosis Factor-α synergistically activate signaling transducer and activator of transcription and Nuclear Factor-kβ pathways and both cytokines increase the chance of cancer development in rheumatoid arthritis patients. Metformin is AMPK activators that can suppress mTOR, STAT3 and HIF-1 so AMPK activation plays important role in suppressing inflammation and osteoclastogenesis and decreasing cancer.

CONCLUSION

Metformin effect on AMPK and mTOR pathways gives the capability to change Treg/Th17 balance and decrease Th17 differentiation and inflammation, osteoclastogenesis and cancers in RA patients. Metformin can be useful in protecting bones especially in first stages of RA and it can decrease inflammation, CVD and cancer in RA patients so Metformin beside DAMARs can be useful in increasing RA patients' life quality with less harm and cost.

Inhibition of Osteoclastogenesis by Thioredoxin-Interacting Protein-Derived Peptide (TN13)

Overactivated osteoclasts lead to many bone diseases, including osteoporosis and rheumatoid arthritis. The p38 MAPK (p38) is an essential regulator of the receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis and bone loss. We previously reported TAT conjugated thioredoxin-interacting protein-derived peptide (TAT-TN13) as an inhibitor of p38 in hematopoietic stem cells (HSCs). Here, we examined the role of TAT-TN13 in the differentiation and function of osteoclasts. TAT-TN13 significantly suppressed RANKL-mediated differentiation of RAW 264.7 cells and bone marrow macrophages (BMMs) into osteoclasts. TAT-TN13 also inhibited the RANKL-induced activation of NF-κB and nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), leading to the decreased expression of osteoclast-specific genes, including tartrate-resistant acid phosphatase (TRAP) and Cathepsin K. Additionally, TAT-TN13 treatment protected bone loss in ovariectomized (OVX) mice. Taken together, these results suggest that TAT-TN13 inhibits osteoclast differentiation by regulating the p38 and NF-κB signaling pathway; thus, it may be a useful agent for preventing or treating osteoporosis.

Macrophage migration inhibitory factor (MIF) inhibitor 4-IPP suppresses osteoclast formation and promotes osteoblast differentiation through the inhibition of the NF-κB signaling pathway

Current pharmacological intervention for the treatment of osteolytic bone diseases such as osteoporosis focuses on the prevention of excessive osteoclastic bone resorption but does not enhance osteoblast-mediated bone formation. In our study, we have shown that 4-iodo-6-phenylpyrimidine (4-IPP), an irreversible inhibitor of macrophage migration inhibitory factor (MIF), can inhibit receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis and potentiate osteoblast-mediated mineralization and bone nodule formation in vitro. Mechanistically, 4-IPP inhibited RANKL-induced p65 phosphorylation and nuclear translocation by preventing the interaction of MIF with thioredoxin-interacting protein-p65 complexes. This led to the suppression of late osteoclast marker genes such as nuclear factor of activated T cells cytoplasmic 1, resulting in impaired osteoclast formation. In contrast, 4-IPP potentiated osteoblast differentiation and mineralization also through the inhibition of the p65/NF-κB signaling cascade. In the murine model of pathologic osteolysis induced by titanium particles, 4-IPP protected against calvarial bone destruction. Similarly, in the murine model of ovariectomy-induced osteoporosis, 4-IPP treatment ameliorated the bone loss associated with estrogen deficiency by reducing osteoclastic activities and enhancing osteoblastic bone formation. Collectively, these findings provide evidence for the pharmacological targeting of MIF for the treatment of osteolytic bone disorders.-Zheng, L., Gao, J., Jin, K., Chen, Z., Yu, W., Zhu, K., Huang, W., Liu, F., Mei, L., Lou, C., He, D. Macrophage migration inhibitory factor (MIF) inhibitor 4-IPP suppresses osteoclast formation and promotes osteoblast differentiation through the inhibition of the NF-κB signaling pathway.

RIPK1 inhibition attenuates experimental autoimmune arthritis via suppression of osteoclastogenesis

Background

Rheumatoid arthritis (RA) is a chronic and systemic inflammatory disease characterized by upregulation of inflammatory cell death and osteoclastogenesis. Necrostatin (NST)-1s is a chemical inhibitor of receptor-interacting serine/threonine-protein kinase (RIPK)1, which plays a role in necroptosis.

Methods

We investigated whether NST-1s decreases inflammatory cell death and inflammatory responses in a mouse model of collagen-induced arthritis (CIA).

Results

NST-1s decreased the progression of CIA and the synovial expression of proinflammatory cytokines. Moreover, NST-1s treatment decreased the expression of necroptosis mediators such as RIPK1, RIPK3, and mixed lineage kinase domain-like (MLKL). In addition, NST-1s decreased osteoclastogenesis in vitro and in vivo. NST-1s downregulated T helper (Th)1 and Th17 cell expression, but promoted Th2 and regulatory T (Treg) cell expression in CIA mice.

Conclusions

These results suggest that NST-1s attenuates CIA progression via the inhibition of osteoclastogenesis and might be a potential therapeutic agent for RA therapy.

Gold Clusters Prevent Inflammation-Induced Bone Erosion through Inhibiting the Activation of NF-κB Pathway

Inflammation-induced bone erosion is a major pathological factor in several chronic inflammatory diseases that often cause severe outcomes, such as rheumatoid arthritis and periodontitis. Plenty of evidences indicated that the inflammatory bone destruction was attributed to an increase in the number of bone-resorbing osteoclasts. However, anti-resorptive therapy alone failed to prevent bone loss in an inflammatory condition. Conventional anti-inflammation treatments are usually intended to suppress inflammation only, but ignore debilitating the subsequent bone destruction. Therefore, inhibition of proinflammatory activation of osteoclastogenesis could be an important strategy for the development of drugs aimed at preventing inflammatory bone destruction. Methods: In this study, we synthesized a peptide coated gold cluster to evaluate its effects on inflammatory osteoclastogenesis in vitro and inflammation-induced bone destruction in vivo. The in vitro anti-inflammation and anti-osteoclastogenesis effects of the cluster were evaluated in LPS-stimulated and receptor activator of nuclear factor κB ligand (RANKL) stimulated macrophages, respectively. The LPS-induced expression of crucial pro-inflammation cytokines and RANKL-induced osteoclastogenesis as well as the activation of NF-κB pathway in both situations were detected. The inflammation-induced RANKL expression and subsequent inflammatory bone destruction in vivo were determined in collagen-immunized mice. Results: The gold cluster strongly suppresses RANKL-induced osteoclast formation via inhibiting the activation of NF-κB pathway in vitro. Moreover, treatment with the clusters at a dose of 5 mg Au/kg.bw significantly reduces the severity of inflammation-induced bone and cartilage destruction in vivo without any significant toxicity effects. Conclusion: Therefore, the gold clusters may offer a novel potent therapeutic stratagem for inhibiting chronic inflammation associated bone destruction.

Antibody-Based Tracers for PET/SPECT Imaging of Chronic Inflammatory Diseases

Chronic inflammatory diseases are often progressive, resulting not only in physical damage to patients but also social and economic burdens, making early diagnosis of them critical. Nuclear medicine techniques can enhance the detection of inflammation by providing functional as well as anatomical information when combined with other modalities such as magnetic resonance imaging, computed tomography or ultrasonography. Although small molecules and peptides were mainly used for the treatment and imaging of chronic inflammatory diseases in the past, antibodies and their fragments have also been emerging for chronic inflammatory diseases as they show high specificity to their targets and can have various biological half-lives depending on how they are engineered. In addition, imaging with antibodies or their fragments can visualize the in vivo biodistribution of the probes or help monitor therapeutic responses, thereby providing physicians with a greater understanding of drug behavior in vivo and another means of monitoring their patients. In this review, we introduce various targets and radiolabeled antibody-based probes for the molecular imaging of chronic inflammatory diseases in preclinical and clinical studies. Targets can be classified into three different categories: 1) cell-adhesion molecules, 2) surface markers on immune cells, and 3) cytokines or enzymes. The limitations and future directions of using radiolabeled antibodies for imaging inflammatory diseases are also discussed.

Induction of Krüppel-like factor 2 reduces K/BxN serum-induced arthritis

Krüppel-like factor 2 (KLF2) critically regulates activation and function of monocyte, which plays important pathogenic role in progressive joint destruction in rheumatoid arthritis (RA). It is yet to be established the molecular basis of KLF2-mediated regulation of monocytes in RA pathogenesis. Herein, we show that a class of compound, HDAC inhibitors (HDACi) induced KLF2 expression in monocytes both in vitro and in vivo. KLF2 level was also elevated in tissues, such as bone marrow, spleen and thymus in mice after infusion of HDACi. Importantly, HDACi significantly reduced osteoclastic differentiation of monocytes with the up-regulation of KLF2 and concomitant down-regulation of matrixmetalloproteinases both in the expression level as well as in the protein level. In addition, HDACi reduced K/BxN serum-induced arthritic inflammation and joint destruction in mice in a dose-dependent manner. Finally, co-immunoprecipitation and overexpression studies confirmed that KLF2 directly interacts with HDAC4 molecule in cells. These findings provide mechanistic evidence of KLF2-mediated regulation of K/BxN serum-induced arthritic inflammation.

Low-Dose Radiotherapy Has No Harmful Effects on Key Cells of Healthy Non-Inflamed Joints

Low-dose radiotherapy (LD-RT) for benign inflammatory and/or bone destructive diseases has been used long. Therefore, mechanistic investigations on cells being present in joints are mostly made in an inflammatory setting. This raises the question whether similar effects of LD-RT are also seen in healthy tissue and thus might cause possible harmful effects. We performed examinations on the functionality and phenotype of key cells within the joint, namely on fibroblast-like synoviocytes (FLS), osteoclasts and osteoblasts, as well as on immune cells. Low doses of ionizing radiation showed only a minor impact on cytokine release by healthy FLS as well as on molecules involved in cartilage and bone destruction and had no significant impact on cell death and migration properties. The bone resorbing abilities of healthy osteoclasts was slightly reduced following LD-RT and a positive impact on bone formation of healthy osteoblasts was observed after in particular exposure to 0.5 Gray (Gy). Cell death rates of bone-marrow cells were only marginally increased and immune cell composition of the bone marrow showed a slight shift from CD8⁺ to CD4⁺ T cell subsets. Taken together, our results indicate that LD-RT with particularly a single dose of 0.5 Gy has no harmful effects on cells of healthy joints.

Effects of rheumatoid arthritis associated transcriptional changes on osteoclast differentiation network in the synovium

Background

Osteoclast differentiation in the inflamed synovium of rheumatoid arthritis (RA) affected joints leads to the formation of bone lesions. Reconstruction and analysis of protein interaction networks underlying specific disease phenotypes are essential for designing therapeutic interventions. In this study, we have created a network that captures signal flow leading to osteoclast differentiation. Based on transcriptome analysis, we have indicated the potential mechanisms responsible for the phenotype in the RA affected synovium.

Method

We collected information on gene expression, pathways and protein interactions related to RA from literature and databases namely Gene Expression Omnibus, Kyoto Encyclopedia of Genes and Genomes pathway and STRING. Based on these information, we created a network for the differentiation of osteoclasts. We identified the differentially regulated network genes and reported the signaling that are responsible for the process in the RA affected synovium.

Result

Our network reveals the mechanisms underlying the activation of the neutrophil cytosolic factor complex in connection to osteoclastogenesis in RA. Additionally, the study reports the predominance of the canonical pathway of NF-κB activation in the diseased synovium. The network also confirms that the upregulation of T cell receptor signaling and downregulation of transforming growth factor beta signaling pathway favor osteoclastogenesis in RA. To the best of our knowledge, this is the first comprehensive protein–protein interaction network describing RA driven osteoclastogenesis in the synovium.

Discussion

This study provides information that can be used to build models of the signal flow involved in the process of osteoclast differentiation. The models can further be used to design therapies to ameliorate bone destruction in the RA affected joints.