Soluble Siglec-9 suppresses arthritis in a collagen-induced arthritis mouse model and inhibits M1 activation of RAW264.7 macrophages

GLI1 facilitates collagen-induced arthritis in mice by collaborative regulation of DNA methyltransferases

Rheumatoid arthritis (RA) is characterized by joint synovitis and bone destruction, the etiology of which remains to be explored. Many types of cells are involved in the progression of RA joint inflammation, among which the overactivation of M1 macrophages and osteoclasts has been thought to be an essential cause of joint inflammation and bone destruction. Glioma-associated oncogene homolog 1 (GLI1) has been revealed to be closely linked to bone metabolism. In this study, GLI1 expression in the synovial tissue of RA patients was positively correlated with RA-related scores and was highly expressed in collagen-induced arthritis (CIA) mouse articular macrophage-like cells. The decreased expression and inhibition of nuclear transfer of GLI1 downregulated macrophage M1 polarization and osteoclast activation, the effect of which was achieved by modulation of DNA methyltransferases (DNMTs) via transcriptional regulation and protein interactions. By pharmacological inhibition of GLI1, the proportion of proinflammatory macrophages and the number of osteoclasts were significantly reduced, and the joint inflammatory response and bone destruction in CIA mice were alleviated. This study clarified the mechanism of GLI1 in macrophage phenotypic changes and activation of osteoclasts, suggesting potential applications of GLI1 inhibitors in the clinical treatment of RA.

Long-Circulating Lipid Nanospheres Loaded with Flurbiprofen Axetil for Targeted Rheumatoid Arthritis Treatment

Background

Flurbiprofen axetil (FA) is a non-steroidal anti-inflammatory drug with good analgesic and anti-inflammatory effects. However, it suffers from poor solubility, short circulation time, and off-target binding profile, which significantly limit its clinical application. Here, we loaded FA into stealth lipid microspheres modified with the arginine-glycine-aspartic acid (RGD) peptide (cRGD-FA-SLM), and examined the therapeutic potential of the resulting platform for the treatment of rheumatoid arthritis (RA).

Methods

cRGD-FA-SLM was prepared by high pressure homogenization, and its toxicity and uptake by macrophages were examined using cultures of RAW264.7 cells. Hemolysis and hepatotoxicity tests were performed to assess the safety of the developed platform, while its pharmacokinetics, biodistribution, and therapeutic efficacy were investigated in a collagen-induced arthritis rat model.

Results

cRGD-FA-SLM showed homogeneous spherical morphology and efficient encapsulation of FA. The developed platform was non-toxic to normal macrophages and was selectively internalized by lipopolysaccharide-activated macrophages in vitro, while it distributed mainly to arthritic joints and significantly prolonged FA in circulation in vivo. cRGD-FA-SLM also significantly reduced the expression of prostaglandin E2 and alleviated joint edema and bone erosion, showing prolonged analgesic effects in arthritic rats.

Conclusion

cRGD-FA-SLM shows good inflammation-targeting ability and prolongs drug circulation in vivo, suggesting promise as an anti-inflammatory and analgesic agent for targeted RA treatment.

Siglec-9 is an inhibitory receptor on human mast cells in vitro

BACKGROUND

Mast cell activation is critical for the development of allergic diseases. Ligation of sialic acid-binding immunoglobin-like lectins (Siglecs), such as Siglec-6, -7, and -8 as well as CD33, have been shown to inhibit mast cell activation. Recent studies showed that human mast cells express Siglec-9, an inhibitory receptor also expressed by neutrophils, monocytes, macrophages, and dendritic cells.

OBJECTIVE

We aimed to characterize Siglec-9 expression and function in human mast cells in vitro.

METHODS

We assessed the expression of Siglec-9 and Siglec-9 ligands on human mast cell lines and human primary mast cells by real-time quantitative PCR, flow cytometry, and confocal microscopy. We used a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene editing approach to disrupt the SIGLEC9 gene. We evaluated Siglec-9 inhibitory activity on mast cell function by using native Siglec-9 ligands, glycophorin A (GlycA), and high-molecular-weight hyaluronic acid, a monoclonal antibody against Siglec-9, and coengagement of Siglec-9 with the high-affinity receptor for IgE (FcεRI).

RESULTS

Human mast cells express Siglec-9 and Siglec-9 ligands. SIGLEC9 gene disruption resulted in increased expression of activation markers at baseline and increased responsiveness to IgE-dependent and IgE-independent stimulation. Pretreatment with GlycA or high-molecular-weight hyaluronic acid followed by IgE-dependent or -independent stimulation had an inhibitory effect on mast cell degranulation. Coengagement of Siglec-9 with FcεRI in human mast cells resulted in reduced degranulation, arachidonic acid production, and chemokine release.

CONCLUSIONS

Siglec-9 and its ligands play an important role in limiting human mast cell activation in vitro.

Roles of the Siglec family in bone and bone homeostasis

Tremendous progress has been seen in the study of the role of sialic acid binding im-munoglobulin type lectins (Siglecs) in osteoimmunology in the past two decades. Interest in Siglecs as immune checkpoints has grown from the recognition that Siglecs have relevance to human disease. Siglecs play important roles in inflammation and cancer, and play key roles in immune cell signaling. By recognizing common sialic acid containing glycans on glycoproteins and glycolipids as regulatory receptors for immune cell signals, Siglecs are expressed on most immune cells and play important roles in normal homeostasis and self-tolerance. In this review, we describe the role that the siglec family plays in bone and bone homeostasis, including the regulation of osteoclast differentiation as well as recent advances in inflammation, cancer and osteoporosis. Particular emphasis is placed on the relevant functions of Siglecs in self-tolerance and as pattern recognition receptors in immune responses, thereby potentially providing emerging strategies for the treatment of bone related diseases.

Potential therapeutic targets of macrophages in inhibiting immune damage and fibrotic processes in musculoskeletal diseases

Macrophages are a heterogeneous cell type with high plasticity, exhibiting unique activation characteristics that modulate the progression and resolution of diseases, serving as a key mediator in maintaining tissue homeostasis. Macrophages display a variety of activation states in response to stimuli in the local environment, with their subpopulations and biological functions being dependent on the local microenvironment. Resident tissue macrophages exhibit distinct transcriptional profiles and functions, all of which are essential for maintaining internal homeostasis. Dysfunctional macrophage subpopulations, or an imbalance in the M1/M2 subpopulation ratio, contribute to the pathogenesis of diseases. In skeletal muscle disorders, immune and inflammatory damage, as well as fibrosis induced by macrophages, are prominent pathological features. Therefore, targeting macrophages is of great significance for maintaining tissue homeostasis and treating skeletal muscle disorders. In this review, we discuss the receptor-ligand interactions regulating macrophages and identify potential targets for inhibiting collateral damage and fibrosis in skeletal muscle disorders. Furthermore, we explore strategies for modulating macrophages to maintain tissue homeostasis.

Network pharmacology and experimental validation to identify the potential mechanism of Hedyotis diffusa Willd against rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic, autoimmune disease that may lead to joint damage, deformity, and disability, if not treated effectively. Hedyotis diffusa Willd (HDW) and its main components have been widely used to treat a variety of tumors and inflammatory diseases. The present study utilized a network pharmacology approach, microarray data analysis and molecular docking to predict the key active ingredients and mechanisms of HDW against RA. Eleven active ingredients in HDW and 180 potential anti-RA targets were identified. The ingredients-targets-RA network showed that stigmasterol, beta-sitosterol, quercetin, kaempferol, and 2-methoxy-3-methyl-9,10-anthraquinone were key components for RA treatment. KEGG pathway results revealed that the 180 potential targets were inflammatory-related pathways with predominant enrichment of the AGE-RAGE, TNF, IL17, and PI3K-Akt signaling pathways. Screened through the PPI network and with Cytoscape software, RELA, TNF, IL6, TP53, MAPK1, AKT1, IL10, and ESR1 were identified as the hub targets in the HDW for RA treatment. Molecular docking was used to identify the binding of 5 key components and the 8 related-RA hub targets. Moreover, the results of network pharmacology were verified by vitro experiments. HDW inhibits cell proliferation in MH7A cells in a dose and time-dependent manner. RT-qPCR and WB results suggest that HDW may affect hub targets through PI3K/AKT signaling pathway, thereby exerting anti-RA effect. This study provides evidence for a clinical effect of HDW on RA and a research basis for further investigation into the active ingredients and mechanisms of HDW against RA.

Semaphorin 3G exacerbates joint inflammation through the accumulation and proliferation of macrophages in the synovium

Objectives

Methotrexate (MTX) is an anchor drug for the treatment of rheumatoid arthritis (RA). However, the precise mechanisms by which MTX stalls RA progression and alleviates the ensuing disease effects remain unknown. The aim of the present study was to identify novel therapeutic target molecules, the expression patterns of which are affected by MTX in patients with RA.

Methods

CD4⁺ T cells from 28 treatment-naïve patients with RA before and 3 months after the initiation of MTX treatment were subjected to DNA microarray analyses. The expression levels of semaphorin 3G, a differentially expressed gene, and its receptor, neuropilin-2, were evaluated in the RA synovium and collagen-induced arthritis synovium. Collagen-induced arthritis and collagen antibody-induced arthritis were induced in semaphorin3G-deficient mice and control mice, and the clinical score, histological score, and serum cytokines were assessed. The migration and proliferation of semaphorin 3G-stimulated bone marrow-derived macrophages were analyzed in vitro. The effect of local semaphorin 3G administration on the clinical score and number of infiltrating macrophages during collagen antibody-induced arthritis was evaluated.

Results

Semaphorin 3G expression in CD4⁺ T cells was downregulated by MTX treatment in RA patients. It was determined that semaphorin 3G is expressed in RA but not in the osteoarthritis synovium; its receptor neuropilin-2 is primarily expressed on activated macrophages. Semaphorin3G deficiency ameliorated collagen-induced arthritis and collagen antibody-induced arthritis. Semaphorin 3G stimulation enhanced the migration and proliferation of bone marrow-derived macrophages. Local administration of semaphorin 3G deteriorated collagen antibody-induced arthritis and increased the number of infiltrating macrophages.

Conclusions

Upregulation of semaphorin 3G in the RA synovium is a novel mechanism that exacerbates joint inflammation, leading to further deterioration, through macrophage accumulation.

Systemic Administration of Neutral Electrolyzed Saline as a Novel Treatment for Rheumatoid Arthritis Reduces Mechanical and Inflammatory Damage to the Joints: Preclinical Evaluation in Mice

Rheumatoid arthritis is globally present in about 1% of the population. This autoinflammatory disease modifies the connective tissue, causing pain and inflammation of the joints. Over time, it causes the loss of joint cartilage and bone mass, decreasing the patient's quality of life. Treatment options now available either give symptomatic alleviation or alter the disease process. Nonetheless, adherence to chronic treatment is typically limited due to adverse effects. As a result, new therapy approaches, such as systemic administration of neutral electrolyzed saline to improve patients' quality of life, are being investigated. The study is a randomized prospective preclinical trial with a single-blind and a 4-arm parallel group using a collagen-induced mice model to generate rheumatoid arthritis. It was carried out on 36 male BALB/c mice, with the primary outcome measure being a scoring system for histopathologic assessment. When all groups are compared, there are significant differences. In addition, the animal model was validated by the healthy group. The animals treated with neutral electrolyzed saline had much less cartilage degradation, bone erosion, pannus development, and inflammation than the placebo-treated mice. Serum IL-6 levels were evaluated in parallel with disease severity expressed as synovitis grading of the affected joints. Spearman's rank correlation coefficient (Rs) = 0.399 (P=0.016) between serum IL-6 levels and the synovitis grading suggests a direct correlation between IL-6 production and disease severity. An additional trial of 20 male BALB/c mice (10 treated with placebo and 10 with neutral electrolyzed saline for 30 days) showed no clinical nor histopathological evidence of adverse effects. According to histopathological and blood test results, we conclude that neutral electrolyzed saline minimizes mechanical and inflammatory damage to the joint and may be helpful as an alternative to rheumatoid arthritis therapy.

Extracellular vesicle-guided in situ reprogramming of synovial macrophages for the treatment of rheumatoid arthritis

Activation state of synovial macrophages is significantly correlated with disease activity and severity of rheumatoid arthritis (RA) and provides valuable clues for RA treatment. Classically activated M1 macrophages in inflamed synovial joints secrete high levels of pro-inflammatory cytokines and chemokines, resulting in bone erosion and cartilage degradation. Herein, we propose extracellular vesicle (EV)-guided in situ macrophage reprogramming toward anti-inflammatory M2 macrophages as a novel RA treatment modality based on the immunotherapeutic concept of reestablishing M1-M2 macrophage equilibrium in synovial tissue. M2 macrophage-derived EVs (M2-EVs) were able to convert activated M1 into reprogrammed M2 (RM2) macrophages with extremely high efficiency (>90%), producing a distinct protein expression pattern characteristic of anti-inflammatory M2 macrophages. In particular, M2-EVs were enriched for proteins known to be involved in the generation and migration of M2 macrophages as well as macrophage reprogramming factors, allowing for rapid and efficient driving of macrophage polarization toward M2 phenotype. After administration of M2-EVs into the joint of a collagen-induced arthritis mouse model, the synovial macrophage polarization was significantly shifted from M1 to M2 phenotype, a process that benefited greatly from the long residence time (>3 days) of M2-EVs in the joint. This superb in situ macrophage-reprogramming ability of EVs resulted in decreased joint swelling, arthritic index score and synovial inflammation, with corresponding reductions in bone erosion and articular cartilage damage and no systemic toxicity. The anti-RA effects of M2-EVs were comparable to those of the conventional disease-modifying antirheumatic drug, Methotrexate, which causes a range of toxic adverse effects, including gastrointestinal mucosal injury. Overall, our EV-guided reprogramming strategy for in situ tuning of macrophage responses holds great promise for the development of anti-inflammatory therapeutics for the treatment of various inflammatory diseases in addition to RA.

Transgenic mouse models to study the physiological and pathophysiological roles of human Siglecs

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are important immunomodulatory receptors. Due to differences between human and mouse Siglecs, defining the in vivo roles for human Siglecs (hSiglecs) can be challenging. One solution is the development and use of hSiglec transgenic mice to assess the physiological roles of hSiglecs in health and disease. These transgenic mice can also serve as important models for the pre-clinical testing of immunomodulatory approaches that are based on targeting hSiglecs. Four general methods have been used to create hSiglec-expressing transgenic mice, each with associated advantages and disadvantages. To date, transgenic mouse models expressing hSiglec-2 (CD22), -3 (CD33), -7, -8, -9, -11, and -16 have been created. This review focuses on both the generation of these hSiglec transgenic mice, along with the important findings that have been made through their study. Cumulatively, hSiglec transgenic mouse models are providing a deeper understanding of the differences between human and mice orthologs/paralogs, mechanisms by which Siglecs regulate immune cell signaling, physiological roles of Siglecs in disease, and different paradigms where targeting Siglecs may be therapeutically advantageous.

Anti-inflammatory natural products as potential therapeutic agents of rheumatoid arthritis: A systematic review

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease causing severe locomotor disability and deterioration in the quality of life. Existing treatments for RA mainly focus on the use of immunomodulators and the suppression of synovial inflammation, and many have significant side effects. Medicinal plants are regarded as important alternative sources for treating RA.

PURPOSE

This review summarizes the bioactive compounds of medicinal plants, which have been shown to modulate the immune response by regulating interleukins in vitro and in vivo experimental models, and that may be promising substances for use in the treatment of RA.

METHODS

Articles on natural products used for the management of arthritis were retrieved from PubMed, Embase, Scopus, and Web of Science through electronic and manual search in English. In total, 576 publications were identified, and 34 were included in this systematic review.

RESULTS

Two articles presented findings on the role of natural components in the treatment of arthritis in both in vitro and in vivo studies. Nine reports defined the role of plant-derived natural molecules in the treatment of arthritis using cell lines, and 27 in vivo studies assessed the anti-arthritic efficacy and immunomodulation effects of phytoconstituents on interleukin production and inflammatory responses.

CONCLUSION

This systematic review broadly reports that, in contrast to other classes of phytochemicals, flavonoids have the greatest therapeutic potential against arthritis by modulating the expression of pro-inflammatory TNF-α, IL-1β, IL-6, IL-8, and IL-17, as well as anti-inflammatory IL-2 and IL-10 cytokines, through the suppression of dynamic inflammatory biomarkers.

Loss of α2-6 sialylation promotes the transformation of synovial fibroblasts into a pro-inflammatory phenotype in arthritis

In healthy joints, synovial fibroblasts (SFs) provide the microenvironment required to mediate homeostasis, but these cells adopt a pathological function in rheumatoid arthritis (RA). Carbohydrates (glycans) on cell surfaces are fundamental regulators of the interactions between stromal and immune cells, but little is known about the role of the SF glycome in joint inflammation. Here we study stromal guided pathophysiology by mapping SFs glycosylation pathways. Combining transcriptomic and glycomic analysis, we show that transformation of fibroblasts into pro-inflammatory cells is associated with glycan remodeling, a process that involves TNF-dependent inhibition of the glycosyltransferase ST6Gal1 and α2-6 sialylation. SF sialylation correlates with distinct functional subsets in murine experimental arthritis and remission stages in human RA. We propose that pro-inflammatory cytokines remodel the SF-glycome, converting the synovium into an under-sialylated and highly pro-inflammatory microenvironment. These results highlight the importance of glycosylation in stromal immunology and joint inflammation.

A sweet spot for macrophages: Focusing on polarization

Macrophages are a type of functionally plastic cells that can create a pro-/anti-inflammatory microenvironment for organs by producing different kinds of cytokines, chemokines, and growth factors to regulate immunity and inflammatory responses. In addition, they can also be induced to adopt different phenotypes in response to extracellular and intracellular signals, a process defined as M1/M2 polarization. Growing evidence indicates that glycobiology is closely associated with this polarization process. In this research, we review studies of the roles of glycosylation, glucose metabolism, and key lectins in the regulation of macrophages function and polarization to provide a new perspective for immunotherapies for multiple diseases.

The human sialic acid-binding immunoglobulin-like lectin Siglec-9 and its murine homolog Siglec-E control osteoclast activity and bone resorption

Regulation of osteoclast differentiation and function is a central element in bone homeostasis. While the role of soluble factors, such as cytokines, hormones and growth factors, in controlling osteoclast differentiation has been intensively characterized, the function of surface receptors is less well understood. Sialic acid-binding immunoglobulin-like lectin (Siglec)-9 and its murine homolog Siglec-E are sialic acid-recognizing inhibitory receptors from the CD33-related Siglec-family and mainly expressed on myeloid cells. We found Siglec-9 and Siglec-E to be expressed at all stages of human and murine osteoclastogenesis, respectively. Siglec-E knockout mice displayed lower bone mass despite unchanged osteoclast numbers and an increased bone formation rate. Ex vivo osteoclast assays using Siglec-E knockout cells or a blocking antibody against human Siglec-9 confirmed the suppressive effect of Siglec-9/Siglec-E on osteoclast function. Although osteoclast numbers were unchanged or even slightly decreased, the blockade/absence of Siglec-9/Siglec-E resulted in an augmented resorption activity of mature osteoclasts. This increased resorption activity was associated with enlarged actin rings. Together, our results suggest Siglec-9/Siglec-E to inhibit osteoclast activation independently from osteoclast differentiation and thereby propose a new mechanism for the control of local bone resorption.

Rapid bone staining with hair removal (RAP-B/HR): a non-destructive and rapid whole-mount bone staining protocol optimized for adult hairy mice

We developed a non-destructive and rapid whole-mount bone staining method for small fish, Xenopus laevis, and rodent fetuses (RAP-B). RAP-B does not require skin or soft tissue removal. However, RAP-B requires hair removal from hairy animals, such as adult mice and rats. In the present study, we investigated hair removal chemical treatments that did not result in soft tissue destruction. The hair removal effectiveness was investigated using a calcium mercaptoacetate or sodium mercaptoacetate solution on skin fragments obtained from the back of adult mice. A mixture of 2% sodium mercaptoacetate in 3% potassium hydroxide was found to be the most effective in complete hair removal from the skin. Using this hair removal treatment as a pretreatment for RAP-B, the preparation of fast-acting artifact-free whole-mount bone staining was possible without skin and soft tissue removal (RAP-B/HR). We performed a seamless observation from a low magnification wide-view to a high magnification without artifactacting artifacts using fluorescence zoom microscopy. Therefore, the combination of RAP-B/HR and fluorescent zoom microscopy is a novel platform for three-dimensional, wide-field, high-resolution pathological anatomical analysis.

Macrophages as a source of fibrosis biomarkers for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease/steatohepatitis (NAFLD/NASH) are becoming major liver diseases worldwide. Liver fibrosis and cirrhosis are among the most significant risk factors of hepatocellular carcinoma (HCC) and associated with the long-term prognosis of NAFLD patients. To stratify the risk of HCC in NAFLD patients clinically, the discovery of non-invasive fibrosis markers is needed urgently. Liver macrophages play critical roles in the regulation of inflammation and fibrosis by interacting with hepatic stellate cells (HSCs) and other immune cells. Thus, it is rational to explore feasible biomarkers for liver fibrosis by focusing on macrophage-related factors. We examined serum factors comprehensively in multiple cohorts of NAFLD/NASH patients to determine whether they were correlated with the biopsy-proven fibrosis stage. We found that the serum levels of interleukin (IL)-34, YKL-40 and soluble Siglec-7 (sSiglec7) were closely associated with liver fibrosis and served as diagnostic biomarkers in patients with NAFLD/NASH. In the NAFLD liver, IL-34 was produced by activated fibroblasts, and YKL-40 and sSiglec-7 were secreted from macrophages. The sensitivity and specificity of these markers to detect advanced liver fibrosis varied, supporting the notion that the combination of these markers with other modalities is an option for clinical application.

Artemisinin ameliorates intestinal inflammation by skewing macrophages to the M2 phenotype and inhibiting epithelial-mesenchymal transition

BACKGROUND

Inflammatory bowel disease (IBD) is a self-destructive intestinal disease whose etiology is unclear but complex and the effective treatment is deficient. Increasing evidences have indicated that immune dysfunction and epithelial-mesenchymal transition (EMT)-related intestinal mucosal barrier impaired hold critical position in the pathogenesis of IBD. Artemisinin (ART) is a sesquiterpenoid compound extracted from Chinese herbal medicine which has good immunomodulatory effects. Studies have shown that artemisinin and its analogues have therapeutic effects on a variety of tumors and immune-related disorders. The purpose of current study was to research the effect and mechanism about artemisinin-induced macrophage polarization to M2 phenotype and inhibiting the process of EMT.

METHODS

In vitro, the anti-inflammatory effect of artemisinin is mainly verified by RAW264.7 cells and tissue (colon tissue and PBMC) from CD patients with active intestinal inflammation. RAW264.7 cells stimulated with LPS to induce inflammatory state and ART were used as therapeutic treatment in different concentration. Then the expression levels of pro-inflammatory factors, macrophage polarization and ERK pathway were analyzed. Colon tissue and PBMC from CD patients were treated with ART in different concentrations and macrophage polarization, pro-inflammatory factors expression, EMT-related protein were analyzed. In vivo, DSS-induced colitis mice were treated by ART for seven days. The DAI score was calculated and the colons and spleens were harvested after the animals were sacrificed. The expression of macrophage markers and EMT-related markers in the intestines of mice in each group were monitored by qPCR and western blot.

RESULT

ART treatment could decrease the levels of pro-inflammatory coefficient expressed in theRAW264.7 cells and human PBMC. Moreover, ART could ameliorate the intestinal inflammation in vivo through down-regulating the expression of pro-inflammatory factors, promoting macrophage polarization to M2 phenotype and inhibiting the process of EMT.

CONCLUSION

Taken together, our findings demonstrated that artemisinin might ameliorate inflammation by inducing macrophage polarization to M2 phenotype and inhibiting the process of EMT, suggesting that ART may be applied to the rehabilitation of IBD in the future.

Tumor Derived SIGLEC Family Genes May Play Roles in Tumor Genesis, Progression, and Immune Microenvironment Regulation

Background

SIGLEC family genes can also be expressed on tumor cells in different cancer types, and though it has been found that SIGLEC genes expressed by immune cells can be exploited by tumors to escape immune surveillance, functions of tumor derived SIGLEC expression in tumor microenvironment (TME) were barely investigated, which could play roles in cancer patients' survival.

Methods

Using bioinformatic analysis, mutation status of SIGLEC family genes was explored through the cBioPortal database, and expression of them in different tumors was explored through the UALCAN database. The GEPIA database was used to compare SIGLEC family genes' mRNA between cancers and to generate a highly correlated gene list in tumors. A KM-plotter database was used to find the association between SIGLEC genes and survival of patients. The associations between SIGLEC family genes' expression, immune infiltration, and immune regulators' expression in TME were generated and examined by the TIMER 2.0 database; the differential fold changes of SIGLEC family genes in specific oncogenic mutation groups of different cancer types were also yielded by TIMER 2.0. The networks of SIGLEC family genes and highly correlated genes were constructed by the STRING database, and gene ontology and pathway annotation of SIGLEC family highly correlated genes were performed through the DAVID database.

Results

SIGLEC family genes were highly mutated and amplified in melanoma, endometrial carcinoma, non-small cell lung cancer, bladder urothelial carcinoma, and esophagogastric adenocarcinoma, while deep deletion of SIGLEC family genes was common in diffuse glioma. Alteration of SIGLEC family genes demonstrated different levels in specific tumors, and oncogenic mutation in different cancer types could influence SIGLEC family genes' expression. Most SIGLEC family genes were related to patients' overall survival and progression free survival. Also, tumor derived SIGLEC family genes were related to tumor immune cell infiltration and may regulate TME by influencing chemokine axis.

Conclusion

Our computational analysis showed SIGLEC family genes expressed by tumor cells were associated with tumor behaviors, and they may also influence TME through chemokine axis, playing vital roles in patients' survival. Further experiments targeting tumor derived SIGLEC family genes are needed to confirm their influences on tumor growth, metastasis, and immune environment regulation.

Siglec-7 is a predictive biomarker for the efficacy of cancer vaccination against metastatic colorectal cancer

Cancer immunotherapy, including vaccination, is considered a major scientific and medical breakthrough. However, cancer immunotherapy does not result in durable objective responses against colorectal cancer (CRC). To improve the efficacy of immunotherapy, the present study investigated several biomarkers for selecting patients who were expected to respond well to immunotherapy. Firstly, a comprehensive proteomic analysis was performed using tumor tissue lysates from patients enrolled in a phase II study, in which five human leukocyte antigen (HLA)-A*24:02-restricted peptides were administered. Sialic acid-binding immunoglobulin type lectin (Siglec)-7 was identified as a potential predictive biomarker. Subsequently, this biomarker was validated using western blot analysis, and immunofluorescence using tissue samples from the patients enrolled in the phase II study. The expression levels of Siglec-7 detected by immunofluorescence were quantified and their association with overall survival (OS) in patients treated with the peptide vaccine was examined. Furthermore, considering the important role of tumor-infiltrating lymphocytes (TILs) for CRC prognosis, the densities of CD3⁺, CD4^+, CD8⁺ and forkhead box P3 (FOXP3)⁺ T cells in CRC tissues were examined and compared with Siglec-7 expression. The mean expression levels of Siglec-7 were significantly higher in patients with poor prognosis, with an OS of ≤2 years, as shown in comprehensive proteomic analysis (P=0.016) and western blot analysis (P=0.025). Immunofluorescence analysis demonstrated that Siglec-7 was expressed in intratumoral macrophages. The OS in patients with high Siglec-7 expression was significantly shorter than in that in patients with low Siglec-7 expression (P=0.017) in the HLA-A*24:02-matched patients. However, this difference was not observed in the HLA-unmatched patients. There was no significant difference in OS between patients according to the numbers of TILs, nor significant correlation between TILs and Siglec-7 expression. In conclusion, Siglec-7 expression in macrophages in tumor tissue may be a novel predictive biomarker for the efficacy of immunotherapy against metastatic CRC.

MiR-130a/Ndrg2 Axis Inhibits the Proliferation of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis

Studies have found that N-myc downstream-regulated gene 2 (Ndrg2) is involved in the progression of rheumatoid arthritis (RA); however, the specific mechanism still remains unclear. Gene expression profiles in the tibial joints of the collagen-induced rheumatoid arthritis model were obtained using Gene Expression Omnibus database. Western blot and real-time PCR were respectively performed to determine the expression of Ndrg2 and gene messenger RNA. Cell viability was measured by Cell Counting Kit-8 (CCK-8) method, and cell cycle was detected by flow cytometry. Cell scratch assays were carried out to detect migration. The binding ability of miR-130a to Ndrg2-3'-UTR was predicted by TargetScan website and confirmed by dual luciferase assay. A collagen-induced arthritis rat model was constructed to observe the effects of miR-130a on arthritis index, hind limb swelling, volume of rat hind paw, and inflammation. Ndrg2 was found downregulated in RA tissues, and knockdown of Ndrg2 promoted fibroblast-like synoviocytes (FLS) proliferation and inflammation, while overexpressed Ndrg2 produced opposite results. Ndrg2 was predicted as a target gene for miR-130a, and miR-130a mimic promoted FLS proliferation, while miR-130a inhibitor suppressed FLS proliferation. Moreover, we found that miR-130a antagomir could significantly reduce the arthritis index, swelling degree, foot volume, and inflammatory factor levels; inhibit the expression of miR-130a; and promote the expression of Ndrg2. The miR-130a/Ndrg2 axis signaling pathway is involved in the progression of RA. Our findings provide a theoretical basis for the clinical treatment of RA.

Nanoparticle-facilitated delivery of BAFF-R siRNA for B cell intervention and rheumatoid arthritis therapy

The present study was designed to explore the effects of B-cell activating factor receptor (BAFF-R) siRNA encapsulated nanoparticles on collagen-induced arthritis (CIA). BAFF-R siRNA encapsulated nanoparticles (NP-_siBAFF-R) were constructed using a double emulsion method and was characterized by dynamic light scattering and transmission electron microscopy. Cellular uptake of nanoparticles was determined using flow cytometry. The CIA mouse model was established and the mice were intravenously injected with nanoparticles. NP-_siBAFF-R effectively decreased the expression of BAFF-R in B cells and facilitated the delivery of siRNA into B cells. Treatment of NP_siBAFF-R ameliorated rheumatoid arthritis (RA) symptoms in the CIA mouse model via decreasing the arthritis score, mean ankle diameter, the levels of anti-collagen IgG in serum and increasing the expression of collagen type II and osteocalcin in dissected joint tissues. Additionally, treatment of NP_siBAFF-R decreased the percentage and number of B cells and inhibited the production of pro-inflammatory cytokines in RA mice. These results demonstrate that NP-_siBAFF-R may provide an effective strategy for RA treatment.

Soluble Siglec-9 alleviates intestinal inflammation through inhibition of the NF-κB pathway

BACKGROUND

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are a superfamily of immunoreceptors recognizing sialic acid. Siglec-9 has been shown to mediate inhibitory immune responses. The aim of this study was to evaluate the effect of a soluble form of Siglec-9 (sSiglec-9) on inflamed intestinal epithelial cells (IECs), murine macrophages, and experimental murine colitis models.

METHODS

COLO 205 human IECs and RAW 264.7 murine macrophages were pretreated with sSiglec-9 and then stimulated with TNF-α or lipopolysaccharides, respectively. The expression of proinflammatory cytokines such as IL-8 and TNF-α was measured using real-time RT-PCR and ELISA. To demonstrate the inhibitory effects of sSiglec-9 on the NF-κB pathway, IκBα phosphorylation/degradation was determined using western blotting and the DNA binding activity of NF-κB was evaluated using an electrophoretic mobility shift assay. Further, mouse models with dextran sulfate sodium-induced acute colitis and piroxicam-induced IL-10^-/- chronic colitis were generated. Intraperitoneal injections of sSiglec-9 were performed, and body weight, colon length, and histopathologic findings were examined.

RESULTS

sSiglec-9 suppressed IL-8 and TNF-α gene expression in stimulated COLO 205 and RAW 264.7 cells. sSiglec-9 inhibited IκBα phosphorylation/degradation and the DNA binding activity of NF-κB. sSiglec-9 injections significantly ameliorated weight loss, colon shortening, and the severity of intestinal inflammation in acute and chronic colitis mouse models.

CONCLUSION

sSiglec-9 may inhibit NF-κB activation in IECs and macrophages and alleviate experimental colitis in mice, suggesting that sSiglec-9 is a potential therapeutic agent for the treatment of inflammatory bowel disease.

The Roles of Siglec7 and Siglec9 on Natural Killer Cells in Virus Infection and Tumour Progression

The function of natural killer (NK) cells, defending against virus infection and tumour progression, is regulated by multiple activating and inhibiting receptors expressed on NK cells, among which sialic acid-bind immunoglobulin-like lectins (Siglecs) act as a vital inhibitory group. Previous studies have shown that Siglec7 and Siglec9 are expressed on NK cells, which negatively regulate the function of NK cells and modulate the immune response through the interaction of sialic acid-containing ligands. Siglec7 and Siglec9 are very similar in distribution, gene encoding, protein sequences, ligand affinity, and functions in regulating the immune system against virus and cancers, but differences still exist between them. In this review, we aim to discuss the similarities and differences between Siglec7 and Siglec9 and analyze their functions in virus infection and tumour progression in order to develop better anti-viral and anti-tumor immunotherapy in the future.

Serum soluble sialic acid-binding immunoglobulin-like lectin-7 concentration as an indicator of liver macrophage activation and advanced fibrosis in patients with non-alcoholic fatty liver disease

AIM

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of liver disease worldwide. Because liver fibrosis is associated with the long-term prognosis of patients with NAFLD, there is an urgent need for non-invasive markers of liver fibrosis. Sialic acid-binding immunoglobulin-like lectin-7 (Siglec-7) is an immunomodulatory molecule expressed on various immune cells, including macrophages, which plays a key role in liver inflammation and fibrosis in NAFLD. We aimed to determine whether serum levels of soluble Siglec-7 (sSiglec-7) could have utility at a marker of fibrosis in this patient population.

METHODS

We examined serum samples from 93 NAFLD patients and 19 healthy donors for macrophage-associated protein, including sSiglec-7, soluble CD163, and YKL-40, and examined their correlation with liver fibrosis scores, tissue elastography, and histological findings. Independent factors associated with advanced fibrosis were analyzed using a logistic regression model and a decision tree. To clarify the source of sSiglec-7, we examined its expression in liver tissue-derived macrophages and cultured monocyte-derived macrophages.

RESULTS

Serum sSiglec-7 levels were significantly higher in NAFLD patients compared with healthy donors, and correlated positively with sCD163 and YKL-40 levels. Serum sSiglec-7 was an independent diagnostic marker with high specificity (96.3%) for advanced fibrosis (F3 and F4) in NAFLD patients. Siglec-7 was mainly expressed on CCR2⁺ macrophages in the liver, and sSiglec-7 production by monocyte-derived macrophages in vitro was increased after stimulation by pro-inflammatory factors.

CONCLUSIONS

Elevated serum sSiglec-7 could serve as an independent marker with high specificity for advanced liver fibrosis in patients with NAFLD.

Delivery of benzoylaconitine using biodegradable nanoparticles to suppress inflammation via regulating NF-κB signaling

Rheumatoid arthritis (RA) is a kind of systemic autoimmune disease, and patients with RA usually suffer serious pain, resulting in low quality of life. The development of drug delivery systems (DDSs) provides a valid approach for RA therapy via inhibiting the secretion of inflammatory cytokines from macrophages. As a prevailing drug nanocarrier with distinctive superiority, polymeric nanoparticles (NPs) have attracted much attention in recent years. However, low biocompatibility and limited exploitation of drug with high efficiency are still the main challenges in RA treatment. To overcome the limitations, we prepared a biocompatible copolymer methoxy-poly(ethylene glycol)-poly(lactide-co-glycolide) (mPEG-PLGA). Moreover, benzoylaconitine (BAC) with superior anti-inflammatory effect was selected as model drug. It was isolated from Aconitum kusnezoffii Reichb and encapsulated into mPEG-PLGA NPs (NP/BAC) to increase the bioavailablity of BAC. The NPs exhibited high cytocompatibility for activated macrophages and well compatibility with red blood cells. Furthermore, the anti-inflammatory property of NP/BAC was testified by substantially inhibiting secretion of pro-inflammatory cytokines. The TNF-α and IL-1β cytokines of NP/BAC group reduced 70 % and 66 % compared with that of activated macrophages. Especially, NP/BAC reduced the overexpression of NF-κB p65 to inhibit NF-κB signaling pathway, which was a critical regulator of inflammatory responses. NP/BAC also showed efficient in vivo anti-inflammatory effect with high ear (69.8 %) and paw (87.1 %) swelling suppressing rate. These results revealed the anti-inflammatory mechanism of NP/BAC and proved it was a suitable DDS to suppress inflammation, providing a promising strategy for RA therapy and research of Aconitum kusnezoffii Reichb.

Sialic Acid-Siglec-E Interactions During Pseudomonas aeruginosa Infection of Macrophages Interferes With Phagosome Maturation by Altering Intracellular Calcium Concentrations

Pseudomonas aeruginosa (PA) is commonly associated with nosocomial and chronic infections of lungs. We have earlier demonstrated that an acidic sugar, sialic acid, is present in PA which is recognized and bound by sialic acid binding immunoglobulin type lectins (siglecs) expressed on neutrophils. Here, we have tried to gain a detailed insight into the immunosuppressive role of sialic acid-siglec interactions in macrophage-mediated clearance of sialylated PA (PA^+Sia). We have demonstrated that PA^+Sia shows enhanced binding (~1.5-fold) to macrophages due to additional interactions between sialic acids and siglec-E and exhibited more phagocytosis. However, internalization of PA^+Sia is associated with a reduction in respiratory burst and increase in anti-inflammatory cytokines secretion which is reversed upon desialylation of the bacteria. Phagocytosis of PA^+Sia is also associated with reduced intracellular calcium ion concentrations and altered calcium-dependent signaling which negatively affects phagosome maturation. Consequently, although more PA^+Sia was localized in early phagosomes (Rab5 compartment), only fewer bacteria reach into the late phagosomal compartment (Rab7). Possibly, this leads to reduced phagosome lysosome fusion where reduced numbers of PA^+Sia are trafficked into lysosomes, compared to PA^−Sia. Thus, internalized PA^+Sia remain viable and replicates intracellularly in macrophages. We have also demonstrated that such siglec-E-sialic acid interaction recruited SHP-1/SHP-2 phosphatases which modulate MAPK and NF-κB signaling pathways. Disrupting sialic acid-siglec-E interaction by silencing siglec-E in macrophages results in improved bactericidal response against PA^+Sia characterized by robust respiratory burst, enhanced intracellular calcium levels and nuclear translocation of p65 component of NF-κB complex leading to increased pro-inflammatory cytokine secretion. Taken together, we have identified that sialic acid-siglec-E interactions is another pathway utilized by PA in order to suppress macrophage antimicrobial responses and inhibit phagosome maturation, thereby persisting as an intracellular pathogen in macrophages.

Curcumin attenuates collagen-induced rat arthritis via anti-inflammatory and apoptotic effects

Curcumin is a natural herbal product that has been popularly used to treat autoimmune diseases in China; however, its effects on rheumatoid arthritis and its mechanism are not clear. The main purposes of this study are to explore the therapeutic effects of curcumin on collagen-induced arthritis (CIA) rats and the pharmacological mechanism. In the present study, CIA rats were established by injecting bovine type II collagen. Curcumin and methotrexate were then orally administered daily, and the swelling degree of the hind limb joints was scored every two days. Histopathological changes were observed by hematoxylin-eosin staining. The levels of cytokines (TNF-α, IL-1β, IL-17 and TGF-β) were detected by radioimmunoassay, while the expression of IκBα and COX-2 was detected by Western blot. In addition, cell viability was detected by CCK-8 assay, and the effect of curcumin on macrophage apoptosis was detected by flow cytometry and TUNEL assay. The results indicated that in vivo curcumin attenuated the degree of joint swelling of rats and the further development of joint histopathology. Moreover, it downregulated the levels of cytokines. In vitro curcumin inhibited the degradation of IκBα and reduced the production of COX-2 in LPS-induced inflammatory RAW264.7 cells. Importantly, curcumin significantly induced macrophage apoptosis. In conclusion, in this study, we have demonstrated that curcumin exerts therapeutic effects on arthritis in CIA rats and has a strong pharmacological activity on reducing the inflammatory response in macrophages. Its mechanism may be related to the inhibition of the NF-κB signaling pathway and the promotion of macrophage apoptosis.

Increased expression of Siglec-9 in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common inflammatory lung disease. Sialic acid-binding immunoglobulin-type lectins 9 (Siglec-9) is predominantly expressed on innate immune cells and has been shown to exert regulatory effect on immune cells through glycan recognition. Soluble Siglec-9 (sSiglec-9), the extracellular region of Siglec-9, might fulfill its function partly by competitive inhibiting siglec-9 binding to its ligands; however, the role of Siglec-9 and sSiglec-9 in the pathogenesis COPD remain largely unknown. In this study, we showed that Siglec-9 expression in alveolar and peripheral blood neutrophil were increased in COPD patients by immunofluorescence and flow cytometry, respectively. Plasma levels of sSiglelc-9 were elevated in COPD patients by ELISA. In vitro, Siglec-9 expression and/or sSiglelc-9 levels were up-regulated by cigarette smoke extract (CSE), lipopolysaccharide (LPS), some cytokines, and dexamethasone (DEX). Recombinant sSiglce-9 increased oxidative burst in neutrophil and enhanced neutrophil chemotaxis toward IL-8 independent on CXCR1 and CXCR2 expression, but it did not affect neutrophil apoptosis or secretions of inflammatory cytokines. In conclusion, Siglec-9 was complementarily increased to induce a negative feedback loop to limit neutrophil activation in COPD, sSiglce-9 enhanced neutrophil ROS and chemotaxis toward IL-8 likely via competitively inhibiting ligands binding to Siglec-9.

Carnosic acid (CA) attenuates collagen-induced arthritis in db/db mice via inflammation suppression by regulating ROS-dependent p38 pathway

Rheumatoid arthritis (RA) is a multifactorial autoimmune disease, characterized by inflammation of synovial joints. Carnosic acid (CA) is a phenolic diterpene isolated from Rosmarinus officinailis, playing a central role in cytoprotective responses to oxidative stress and inflammation response. Our study aimed to investigate the effects of CA on RA progression in diabetic animals. Carnosic acid (CA) was used to treat collagen-induced arthritis (CIA)-induced db/db mice. Blood glucose, oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were investigated to explore insulin resistance. CA significantly down-regulated fasting blood glucose, glucose level in OGTT and ITT, ameliorated CIA-induced bone loss, and reduced pro-inflammatory cytokines and reactive oxygen species (ROS) in db/db mice with arthritis induced by CIA. In vitro, CA suppressed Receptor Activator for Nuclear Factor-κ B Ligand (RANKL)- and Macrophage colony-stimulating factor (M-CSF)-induced osteoclastogenesis. The osteoclastic specific markers were inhibited by CA. Signal transduction studies showed that CA significantly decreased the expression of molecules contributing to ROS and increased anti-oxidants. Additionally, CA inactivated the RANKL- and M-CSF-induced p38 mitogen activated protein kinases (MAPK), inhibited NF-κB phosphorylation, causing pro-inflammatory cytokines down-regulation. Together, CA ameliorated osteoclast formation and CIA-induced bone loss in db/db mice through inflammation suppression by regulating ROS-dependent p38 pathway.