Etiologies of Rheumatoid Arthritis: Update on Mucosal, Genetic, and Cellular Pathogenesis

Rheumatoid arthritis-recent advances in pathogenesis and the anti-inflammatory effect of plant-derived COX inhibitors

The majority of people with autoimmune disorders, including those with rheumatoid arthritis, osteoarthritis, and tendonitis report pain, stiffness, and inflammation as major contributors to their worse quality of life in terms of overall health. Of all the available treatment options, COX inhibitors are the ones that are utilized most frequently to ease the symptoms. Various signaling cascades have been reported to be involved in the pathogenesis of rheumatoid arthritis which includes JAK/STAT, MAPK, and NF-kB signaling pathways, and several allopathic inhibitors (tofacitinib and baricitinib) have been reported to target the components of these cascades and have received approval for RA treatment. However, the prolonged use of these COX inhibitors and other allopathic drugs can pose serious health challenges due to their significant side effects. Therefore, searching for a more effective and side effect-free treatment for rheumatoid arthritis has unveiled phytochemicals as both productive and promising. Their therapeutic ability helps develop potent and safe drugs targeting immune-inflammatory diseases including RA. Various scientific databases were used for searching articles such as NCBI, SpringerLink, BioMed Central, ResearchGate, Google Scholar, Scopus, Nature, Wiley Online Library, and ScienceDirect. This review lists various phytochemicals and discusses their potential molecular targets in RA treatment, as demonstrated by various in vitro, in vivo (pre-clinical), and clinical studies. Several pre-clinical and clinical studies suggest that various phytochemicals can be an alternative promising intervention for attenuating and managing inflammation-associated pathogenesis of rheumatoid arthritis.

[Identification of potential biomarkers and immunoregulatory mechanisms of rheumatoid arthritis based on multichip co-analysis of GEO database]

OBJECTIVE

To identify the biomarkers for early rheumatoid arthritis (RA) diagnosis and explore the possible immune regulatory mechanisms.

METHODS

The differentially expressed genesin RA were screened and functionally annotated using the limma, RRA, batch correction, and clusterProfiler. The protein-protein interaction network was retrieved from the STRING database, and Cytoscape 3.8.0 and GeneMANIA were used to select the key genes and predicting their interaction mechanisms. ROC curves was used to validate the accuracy of diagnostic models based on the key genes. The disease-specific immune cells were selected via machine learning, and their correlation with the key genes were analyzed using Corrplot package. Biological functions of the key genes were explored using GSEA method. The expression of STAT1 was investigated in the synovial tissue of rats with collagen-induced arthritis (CIA).

RESULTS

We identified 9 core key genes in RA (CD3G, CD8A, SYK, LCK, IL2RG, STAT1, CCR5, ITGB2, and ITGAL), which regulate synovial inflammation primarily through cytokines-related pathways. ROC curve analysis showed a high predictive accuracy of the 9 core genes, among which STAT1 had the highest AUC (0.909). Correlation analysis revealed strong correlations of CD3G, ITGAL, LCK, CD8A, and STAT1 with disease-specific immune cells, and STAT1 showed the strongest correlation with M1-type macrophages (R=0.68, P=2.9e-08). The synovial tissues of the ankle joints of CIA rats showed high expressions of STAT1 and p-STAT1 with significant differential expression of STAT1 between the nucleus and the cytoplasm of the synovial fibroblasts. The protein expressions of p-STAT1 and STAT1 in the cell nuclei were significantly reduced after treatment.

CONCLUSION

CD3G, CD8A, SYK, LCK, IL2RG, STAT1, CCR5, ITGB2, and ITGAL may serve as biomarkers for early diagnosis of RA. Gene-immune cell pathways such as CD3G/CD8A/LCK-γδ T cells, ITGAL-Tfh cells, and STAT1-M1-type macrophages may be closely related with the development of RA.

Global research trends in DNA methylation in rheumatoid arthritis: A bibliometric analysis and visual analysis

Rheumatoid arthritis (RA) is a prevalent autoimmune disorder with a significant global economic burden. Epigenetic modifications, particularly DNA methylation, play a crucial role in RA. This study conducted a bibliometric analysis to explore the evolving trends and predominant themes in RA and DNA methylation research over the past two decades. A total of 1800 articles met the inclusion criteria, and the analysis revealed consistent growth in the literature, with a notable increase in output after 2019. The research involved 70 countries, 2139 academic institutions, 23,365 unique authors, and 58,636 co-cited authors. The United States emerged as a dominant contributor in this research domain. The significance of DNA methylation in shaping research directions for RA management is increasingly evident. Recent investigations have shed light on the pivotal role of DNA methylation in RA, particularly in characterizing synovial tissue and exploring the underlying mechanisms of disease pathogenesis. This study provides valuable insights into the landscape of DNA methylation research in RA and highlights the importance of epigenetics in autoimmune diseases.

Circulating PCSK9 relates to aggravated disease activity, Th17/Treg imbalance, and predicts treatment outcome of conventional synthetic DMARDs in rheumatoid arthritis patients

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates inflammatory response and CD4+ T cell differentiation in autoimmune diseases, while its clinical role in rheumatoid arthritis (RA) lacks sufficient evidence. Subsequently, this study intended to explore the vertical change of PCSK9, and its linkage with T helper (Th) cells, regulatory T (Treg) cells, clinical features, and treatment outcomes in RA patients.

METHODS

This multi-center, prospective, cohort study determined serum PCSK9 in 89 RA patients who received conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs) and 50 healthy controls (HCs) after recruitment by enzyme-linked immunosorbent assay. For RA patients, serum PCSK9 was also determined at 6th week, 12th week, and 24th week; meanwhile, Th1, Th2, Th17, and Treg cells at baseline were determined through flow cytometry.

RESULTS

PCSK9 was increased in RA patients compared to HCs (median: 209.2 versus 122.0 ng/mL, P < 0.001). In RA patients, PCSK9 positively correlated with Th17 cells (P = 0.023) and Th17/Treg ratio (P = 0.018), but did not link with Th1 cells, Th2 cells, Th1/Th2 ratio, or Treg cells. Meanwhile, PCSK9 was not associated with any demographics and medication histories, while it positively correlated with C-reactive protein (P = 0.010), disease activity score in 28 joints (P = 0.009), physician's global assessment (P = 0.015), and clinical disease activity index (P = 0.040). Importantly, PCSK9 gradually reduced from baseline to 24th week; its decrement related to higher possibility of treatment response (P = 0.002), low disease activity (P = 0.001), and remission of csDMARDs (P = 0.012).

CONCLUSION

Circulating PCSK9 shows the potency as a biomarker for disease management and treatment outcome prediction of csDMARDs in RA.

Rheumatoid Arthritis Has Won the Battle but Not the War: How Many Joints Will We Save Tomorrow?

Rheumatoid arthritis refers to joint diseases of unclear etiology whose final stages can lead to unbearable pain and complete immobility of the affected joints. As one of the most widely known diseases of the joints, it serves as a study target for a large number of research groups and pharmaceutical companies. Modern treatment with anti-inflammatory drugs, including janus kinase (JAK) inhibitors, monoclonal antibodies, and botanicals (polyphenols, glycosides, alkaloids, etc.) has achieved some success and hope for improving the course of the disease. However, existing drugs against RA have a number of side effects which push researchers to elaborate on more selective and effective drug candidates. The avant-garde of research, which aims to develop treatment of rheumatoid arthritis using antisense oligonucleotides along with nonsteroidal drugs and corticosteroids against inflammation, increases the chances of success and expands the arsenal of drugs. The primary goal in the treatment of this disease is to find therapies that allow patients with rheumatoid arthritis to move their joints without pain. The main purpose of this review is to show the victories and challenges for the treatment of rheumatoid arthritis and the tortuous but promising path of research that aims to help patients experience the joy of freely moving joints without pain.

Pyroptosis by NLRP3/caspase-1/gasdermin-D pathway in synovial tissues of rheumatoid arthritis patients

We investigated the potential involvement of pyroptosis, a proinflammatory form of regulated cell death, in rheumatoid arthritis (RA). Synovial fluid, synovial tissues and/or serum were compared among 32 patients with RA, 46 patients with osteoarthritis (OA) and 30 healthy controls. Samples were assayed for interleukin (IL)-1β, IL-18 and lactate hydrogenase (LDH). Synovial expression of NLRP3, caspase-1 and cleaved gasdermin D (GSDMD) was assayed using immunohistochemistry and multiplex immunohistochemistry. Patients with RA showed significantly higher levels of IL-1β and IL-18 in synovial fluid than patients with OA, and significantly higher levels of both cytokines in serum than healthy controls. RA was associated with higher levels of LDH in synovial fluid than OA. Among patients with RA, levels of IL-1β, IL-18 and LDH were significantly higher in synovial fluid than in serum, and the levels in synovial fluid positively correlated with disease activity and inflammation. Synovial cells, particularly macrophages, showed upregulation of NLRP3, caspase-1 and cleaved GSDMD in RA compared to OA. Our results implicate pyroptosis in the pathogenesis of RA, perhaps as a driver of local inflammation in joints.

Fourier-transform infrared spectroscopy: a universal optical sensing technique with auspicious application prospects in the diagnosis and management of autoimmune diseases

Autoimmune diseases (AIDs) are poorly understood clinical syndromes due to breakdown of immune tolerance towards specific types of self-antigens. They are generally associated with an inflammatory response mediated by lymphocytes T, autoantibodies or both. Ultimately, chronic inflammation culminates in tissue damages and clinical manifestations. AIDs affect 5% of the world population, and they represent the main cause of fatality in young to middle-aged females. In addition, the chronic nature of AIDs has a devastating impact on the patient's quality of life. It also places a heavy burden on the health care system. Establishing a rapid and accurate diagnosis is considered vital for an ideal medical management of these autoimmune disorders. However, for some AIDs, this task might be challenging. Vibrational spectroscopies, and more particularly Fourier-transform infrared (FTIR) spectroscopy, have emerged as universal analytical techniques with promising applications in the diagnosis of various types of malignancies and metabolic and infectious diseases. The high sensitivity of these optical sensing techniques and their minimal requirements for test reagents qualify them to be ideal analytical techniques. The aim of the current review is to explore the potential applications of FTIR spectroscopy in the diagnosis and management of most common AIDs. It also aims to demonstrate how this technique has contributed to deciphering the biochemical and physiopathological aspects of these chronic inflammatory diseases. The advantages that can be offered by this optical sensing technique over the traditional and gold standard methods used in the diagnosis of these autoimmune disorders have also been extensively discussed.

Circular RNA CircCDKN2B−AS_006 Promotes the Tumor-like Growth and Metastasis of Rheumatoid Arthritis Synovial Fibroblasts by Targeting the miR−1258/RUNX1 Axis

Rheumatoid arthritis (RA) is an autoimmune polyarthritis in which synovial fibroblasts (SFs) play a major role in cartilage and bone destruction through tumor−like proliferation, migration, and invasion. Circular RNAs (circRNAs) have emerged as vital regulators for tumor progression. However, the regulatory role, clinical significance, and underlying mechanisms of circRNAs in RASF tumor−like growth and metastasis remain largely unknown. Differentially expressed circRNAs in synovium samples from patients with RA and patients with joint trauma were identified via RNA sequencing. Subsequently, in vitro and in vivo experiments were performed to investigate the functional roles of circCDKN2B−AS_006 in RASF proliferation, migration, and invasion. CircCDKN2B−AS_006 was upregulated in synovium samples from patients with RA and promoted the tumor-like proliferation, migration, and invasion of RASFs. Mechanistically, circCDKN2B−AS_006 was shown to regulate the expression of runt−related transcription factor 1 (RUNX1) by sponging miR-1258, influencing the Wnt/β−catenin signaling pathway, and promoting the epithelial−to−mesenchymal transition (EMT) in RASFs. Moreover, in the collagen−induced arthritis (CIA) mouse model, intra−articular injection of lentivirus−shcircCDKN2B−AS_006 was capable of alleviating the severity of arthritis and inhibiting the aggressive behaviors of SFs. Furthermore, the correlation analysis results revealed that the circCDKN2B−AS_006/miR−1258/RUNX1 axis in the synovium was correlated with the clinical indicators of RA patients. CircCDKN2B−AS_006 promoted the proliferation, migration, and invasion of RASFs by modulating the miR−1258/RUNX1 axis.

Identification and preliminary validation of synovial tissue-specific genes and their-mediated biological mechanisms in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease. It is well known that the formation of positive feedback between synovial hyperplasia and inflammatory infiltration is intimately associated with the occurrence and development of RA. However, the exact mechanisms still remain unknown, making the early diagnosis and therapy of RA difficult. This study was designed to identify prospective diagnostic and therapeutic biomarkers, as well as their-mediated biological mechanisms in RA.

METHODS

Three microarray datasets (GSE36700, GSE77298 and GSE153015) and two RNA-sequencing datasets (GSE89408 and GSE112656) of synovial tissues, as well as three other microarray datasets (GSE101193, GSE134087 and GSE94519) of peripheral blood were downloaded for integrated analysis. The differently expressed genes (DEGs) were identified by "limma" package of R software. Then, weight gene co-expression analysis and gene set enrichment analysis were performed to investigate synovial tissue-specific genes and their-mediated biological mechanisms in RA. The expression of candidate genes and their diagnostic value for RA were verified by quantitative real-time PCR and receiver operating characteristic (ROC) curve, respectively. Relevant biological mechanisms were explored through cell proliferation and colony formation assay. The suggestive anti-RA compounds were discovered by CMap analysis.

RESULTS

We identified a total of 266 DEGs, which were mainly enriched in cellular proliferation and migration, infection and inflammatory immune signaling pathways. Bioinformatics analysis and molecular validation revealed 5 synovial tissue-specific genes, which exhibited excellent diagnostic value for RA. The infiltration level of immune cells in RA synovial tissue was significantly higher than that in control individuals. Moreover, preliminary molecular experiments suggested that these characteristic genes may be responsible for the high proliferation potential of RA fibroblast-like synoviocytes (FLSs). Finally, 8 small molecular compounds with anti-RA potential were obtained.

CONCLUSIONS

We have proposed 5 potential diagnostic and therapeutic biomarkers (CDK1, TTK, HMMR, DLGAP5, and SKA3) in synovial tissues that may contribute to the pathogenesis of RA. These findings may shed light on the early diagnosis and therapy of RA.

6-Shogaol inhibits the proliferation, apoptosis, and migration of rheumatoid arthritis fibroblast-like synoviocytes via the PI3K/AKT/NF-κB pathway

BACKGROUND

Fibroblast-like synoviocytes (FLSs) are essential for joint destruction in rheumatoid arthritis (RA). 6-Shogaol, a phenolic extract isolated from ginger, has been found to have potential benefits in the treatment of diverse inflammatory and immune disorders. However, the role of 6-shogaol in RA has yet to be explored.

PURPOSE

To reveal the effect of 6-shogaol on RA FLSs and MH7A cells and to investigate the molecular mechanism of 6-shogao in RA.

METHODS

We performed MTT, EdU, cell apoptosis, cell migration and invasion, RT-qPCR, western blot analysis, and immunofluorescence to elucidate the effect of 6-shogaol on the proliferation, apoptosis, and migration of RA FLSs and MH7A cells and revealed its modulation of the PI3K/AKT/NF-κB pathway. The in vivo therapeutic effect of 6-shogaol was verified in mice with collagen-induced arthritis (CIA).

RESULTS

6-Shogaol suppressed proliferation, migration, and invasion, and induced apoptosis in RA FLSs and MH7A cells. 6-Shogaol also reduced the production of TNF-α, IL-1β, IL-6, IL-8, MMP-2, and MMP-9. Molecular analysis revealed that 6-shogaol inhibited the PI3K/AKT/NF-κB pathway by activating PPAR-γ. Treatment with 6-shogaol ameliorated joint destruction of mice with CIA.

CONCLUSION

This study revealed that 6-shogaol inhibited proliferation, migration, invasion, cytokine, and MMPs production, and induced apoptosis in RA FLSs via the PI3K/AKT/NF-κB pathway, providing a new natural potential drug for future RA treatments.

Biomarkers (mRNAs and non-coding RNAs) for the diagnosis and prognosis of rheumatoid arthritis

In recent years, diagnostic and therapeutic approaches for rheumatoid arthritis (RA) have continued to improve. However, in the advanced stages of the disease, patients are unable to achieve long-term clinical remission and often suffer from systemic multi-organ damage and severe complications. Patients with RA usually have no overt clinical manifestations in the early stages, and by the time a definitive diagnosis is made, the disease is already at an advanced stage. RA is diagnosed clinically and with laboratory tests, including the blood markers C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) and the autoantibodies rheumatoid factor (RF) and anticitrullinated protein antibodies (ACPA). However, the presence of RF and ACPA autoantibodies is associated with aggravated disease, joint damage, and increased mortality, and these autoantibodies have low specificity and sensitivity. The etiology of RA is unknown, with the pathogenesis involving multiple factors and clinical heterogeneity. The early diagnosis, subtype classification, and prognosis of RA remain challenging, and studies to develop minimally invasive or non-invasive biomarkers in the form of biofluid biopsies are becoming more common. Non-coding RNA (ncRNA) molecules are composed of long non-coding RNAs, small nucleolar RNAs, microRNAs, and circular RNAs, which play an essential role in disease onset and progression and can be used in the early diagnosis and prognosis of RA. In this review of the diagnostic and prognostic approaches to RA disease, we provide an overview of the current knowledge on the subject, focusing on recent advances in mRNA-ncRNA as diagnostic and prognostic biomarkers from the biofluid to the tissue level.

New insights into the pathogenesis and management of rheumatoid arthritis

Over the past few decades, understanding of the pathogenesis of rheumatoid arthritis (RA) has improved substantially. Insights into the cellular and molecular mechanisms involved in RA have enabled the discovery of new therapeutic targets and led to the development of biologics and targeted synthetic disease-modifying antirheumatic drugs. In parallel with the improvement in therapies, the evolution of strategies in the management of RA has also contributed considerably to better outcomes in patients. Major changes include the development of disease activity measures, formulation of the treat-to-target principles as well as increased attention to comorbidities. The presence of comorbidities such as cardiovascular diseases may increase the mortality of RA patients, affect their treatment strategies and result in worse outcomes. Therefore, prevention and management of certain high-risk comorbidities have become increasingly important in the long-term treatment of RA. In this study, we summarized new insights into the pathogenesis and management of rheumatoid arthritis and associated comorbidities, with a special focus on the 2021 update of the American College of Rheumatology (ACR) guideline for RA and key reports presented at the 2021 ACR convergence.

Phytochemicals from medicinal plants from African forests with potentials in rheumatoid arthritis management

OBJECTIVES

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by inflammation, pain, and cartilage and bone damage. There is currently no cure for RA. It is however managed using nonsteroidal anti-inflammatory drugs, corticosteroids and disease-modifying anti-rheumatic drugs, often with severe side effects. Hidden within Africa's lush vegetation are plants with diverse medicinal properties including anti-RA potentials. This paper reviews the scientific literature for medicinal plants, growing in Africa, with reported anti-RA activities and identifies the most abundant phytochemicals deserving research attention. A search of relevant published scientific literature, using the major search engines, such as Pubmed/Medline, Scopus, Google Scholar, etc. was conducted to identify medicinal plants, growing in Africa, with anti-RA potentials.

KEY FINDINGS

Twenty plants belonging to 17 families were identified. The plants are rich in phytochemicals, predominantly quercetin, rutin, catechin, kaempferol, etc., known to affect some pathways relevant in RA initiation and progression, and therefore useful in its management.

SUMMARY

Targeted research is needed to unlock the potentials of medicinal plants by developing easy-to-use technologies for preparing medicines from them. Research attention should focus on how best to exploit the major phytochemicals identified in this review for the development of anti-RA 'green pharmaceuticals'.

Nutrition and Rheumatoid Arthritis Onset: A Prospective Analysis Using the UK Biobank

Rheumatoid arthritis (RA) is a chronic inflammatory disease that affects the joints. The multifactorial etiopathogenesis of RA has been heavily investigated, but is still only partially understood. Diet can represent both a risk factor and a protective factor, based on some evidence that suggests specific properties of certain foods and their ability to increase/reduce inflammation. To date, the studies done on this topic provide discordant results and are heterogeneous in terms of design and cohort size. In this work, we investigated for the first time the relationship between nutrition and the risk of RA onset using a sample size of about half a million subjects from one of the largest publicly available biobanks that is the UK biobank. Results showed that oily fish, alcohol, coffee and breakfast cereals have protective roles in RA; whereas, tea can increase the risk of RA. In conclusion, the obtained results confirm that diet plays key roles in RA, either by promoting or by preventing RA onset and development. Future research should focus on unravelling the effects of dietary habits on immune-mediated diseases to establish better preventive strategies.

Humoral Response to Microbial Biomarkers in Rheumatoid Arthritis Patients

Background/Objective: Chronic humoral immune response against multiple microbial antigens may play a crucial role in the etiopathogenesis of rheumatoid arthritis (RA). We aimed to assess the prevalence and magnitude of antibody response against various bacterial and viral immunogen peptides in the sera of RA patients compared with the general population. Methods: Polyclonal IgG antibodies (Abs) specific for peptides derived from Porphyromonas gingivalis (RgpA, Kpg), Aggregatibacter actinomycetemcomitans (LtxA1, LtxA2), Mycobacterium avium subsp. paratuberculosis (MAP4027), Epstein–Barr virus (EBNA1, EBVBOLF), and human endogenous retrovirus (HERV-W env-su) were detected by ELISA in serum samples from 148 consecutive RA patients and 148 sex and age-matched healthy controls (HCs). In addition, the presence of a relationship between the positivity and the titer of antibodies and RA descriptors was explored by bivariate correlation analysis. Results: RA patients exhibit a higher prevalence of humoral immune response against all tested peptides compared to HCs with a statically significant difference for MAP4027 (30.4% vs. 10.1%), BOLF (25.7% vs. 8.1%), RgpA (24.3% vs. 9.4%), HERV W-env (20.3% vs. 9.4%), and EBNA1 (18.9% vs. 9.4%) peptides. Fifty-three (35.8%) out of 148 RA serum and 93 (62.8%) out of 148 HCs were negative for all pathogen-derived peptides. There was a significant correlation between OD values obtained by ELISA test against all peptides (p < 0.0001). We also found an increased titer and prevalence of Abs against LtxA1 and LtxA2 in seropositive vs. seronegative RF (p = 0.019, p = 0.018). Conclusion: This study demonstrates a significantly increased humoral response against multiple pathogens in patients with RA and implies that they could be an important factor in the pathogenesis of the disease. Therefore, the role of each individual pathogen in RA needs to be further investigated.

Integrated pharmacology reveals the mechanism of action of Bu-Shen-Tong-Du prescription against collagen-induced arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease. Bu-Shen-Tong-Du prescription (BSP) has traditionally been used in to treat RA but its underlying mechanisms remain unclear. In this study, we explored the potential mechanisms of BSP in collagen-induced arthritis (CIA) rats, a classic animal model of RA. We employed an integrated pharmacology approach in combination with network pharmacology, 1H-nuclear magnetic resonance (NMR) metabolomics, and biochemical analyses to determine the mechanisms of BSP for treating RA. We found that BSP can regulate immunity and inflammation by decreasing the spleen index; inhibiting hyperplasia of the white pulp; reducing the levels of IL-1β, IL-6, IL-17A, and IFN-γ; and increasing the levels of IL-10 in the serum. Network pharmacology was utilized to predict related signal transduction pathways of BSP in RA treatment. 1H NMR metabolomics of the serum confirmed that BSP regulated energy metabolism and amino acid metabolism. Finally, we validated the Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB signaling pathway using immunohistochemical methods, which demonstrated that BSP controlled RA-induced inflammation by inhibiting the TLR4/NF-κB signaling pathway. These results confirm the therapeutic effect of BSP in a CIA rat model, which is exerted via the inhibition of the inflammation and the improvement of the immune function, balancing energy metabolism and amino acid metabolism, and inhibiting the TLR4/NF-κB signaling pathway. This study provides an experimental basis for using BSP as a combinatorial drug to inhibit inflammation and regulate immunity in the treatment of RA.

Incidence and severity of G6PI-induced arthritis are not increased in genetically distinct mouse strains upon aging

Background

The incidence of rheumatoid arthritis is correlated with age. In this study, we analyzed the association of the incidence and severity of glucose-6-phosphate isomerase (G6PI)-induced arthritis with age in two different mouse strains.

Methods

Young and very old mice from two different arthritis-susceptible wild-type mouse strains were analyzed after a single subcutaneous injection of G6PI s.c. The metabolism and the function of synoviocytes were analyzed in vitro, the production of bioactive lipid mediators by myeloid cells and synoviocytes was assessed in vitro and ex vivo by UPLC-MS-MS, and flow cytometry was used to verify age-related changes of immune cell composition and function.

Results

While the severity of arthritis was independent from age, the onset was delayed in old mice. Old mice showed common signs of immune aging like thymic atrophy associated with decreased CD4⁺ effector T cell numbers. Despite its decrease, the effector T helper (Th) cell compartment in old mice was reactive and functionally intact, and their Tregs exhibited unaltered suppressive capacities. In homeostasis, macrophages and synoviocytes from old mice produced higher amounts of pro-inflammatory cyclooxygenase (COX)-derived products. However, this functional difference did not remain upon challenge in vitro nor upon arthritis reactions ex vivo.

Conclusion

While old mice show a higher baseline of inflammatory functions, this does not result in increased reaction towards self-antigens in arthritis-susceptible mouse strains. Together, our data from two different mouse strains show that the susceptibility for G6PI-induced arthritis is not age-dependent.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02596-7.