Chenyang Lu

Rheumatoid arthritis (RA) is a leading cause of disability globally. Although iron accumulation in arthritic lesions has been observed in patients with RA, its specific contribution to disability outcomes remains unclear. Here we demonstrate a comprehensive multiomics approach to elucidate the impact and underlying mechanisms of iron overload in RA. First, clinical radiology in an RA cohort reveals a positive correlation between elevated ferrous iron levels in synovial fluid and joint damage extent. Iron chelator DFO administration significantly alleviates bone destruction in the K/BxN serum-transfer induced arthritis mice model. In terms of cellular function, we identify the aggressive migration and invasion of fibroblast-like synoviocytes (FLSs) induced by excess iron utilizing a humanized synovitis model. Mechanistically, the multiomics integration of transcriptomics and metabolomics indicates the enriched lipid synthesis pathway in the FLS response to iron exposure. The lipid transcription factor SREBP1 is particularly highly expressed in RA-FLSs, and its genetic ablation or pharmacological inhibition markedly mitigates the pathogenic effects of iron overload both in vitro and in vivo. At the molecular level, iron regulatory protein IRP1 enhances the translation of SREBP1 adapter protein SCAP by disengaging from its mRNA 5′ untranslated region upon iron stimulation. This process facilitates SREBP1 cleavage and activation, driving the upregulation of genes involved in fatty acid and cholesterol biosynthesis. Our findings elucidate the IRP1–SCAP axis as a critical modulator of lipid metabolic reprogramming in aggressive FLSs, underscoring its potential as a therapeutic target for RA by modulating the ‘iron–lipid’ crosstalk.

Objective: To evaluate the utility of synovial iron quantification using Magnetic resonance imaging (MRI) in assessing structural joint damage in the knee of patients with rheumatoid arthritis (RA). Methods: This cross-sectional study employed a two-stage design. In the initial comparative stage, 6 patients with RA and 5 patients with osteoarthritis (OA) were recruited to compare synovial R2* values, a metric derived from iterative decomposition of water and fat with echo asymmetry and least-squares estimation quantitation (IDEAL-IQ) MRI sequences representing synovial iron content. Following this, the RA cohort was expanded to a total of 51 patients to investigate the association between R2* values and clinical parameters, including disease activity and bone erosion. Synovial fluid iron levels were measured with an Iron Assay Kit and synovial iron deposits were semi-quantified via Prussian blue staining. Associations between R2* and clinical and laboratory parameters, including inflammatory factors and joint damage indices, were analyzed using Spearman’s rank correlation. Univariate and multivariate ordered logistic regression models were employed to identify factors associated with bone erosion severity. An R2*-based nomogram was developed and validated using receiver operating characteristic (ROC) analysis and calibration curves. Results: Synovial R2* values were significantly higher in RA patients than those with osteoarthritis (53.66 S⁻¹ vs. 31.38 S⁻¹, p < 0.05), consistent with Prussian blue staining results. While synovial R2* values showed no significant correlation with systemic iron metabolic markers, inflammatory indicators, or the Disease Activity Score 28, they were positively correlated with bone erosion severity (ρ = 0.500, p < 0.001) and negatively associated with the joint space width (ρ = −0.307, p < 0.05). Multivariate analysis identified R2* as an independent indicator linked to bone erosion extent (OR = 2358.336, p < 0.001). The R2*-based nomogram demonstrated good discriminative performance. (AUC = 0.83). Conclusions: The R2* value derived from IDEAL-IQ MRI is a reliable tool for quantifying synovial iron and may represent a promising non-invasive imaging biomarker reflecting bone erosion in RA patients.

The soluble variant of the ectopeptidase CD13 (sCD13), released from the cell surface by matrix metalloproteinase 14 (MMP14), is a potent pro-inflammatory mediator, displaying chemotactic, angiogenic, and arthritogenic properties through bradykinin receptor B1 (B1R). We revealed a link between sCD13 and amplified neutrophil-mediated inflammatory responses in SARS-CoV-2 infection. sCD13 was markedly elevated in patients with COVID-19 and correlated with disease severity and variants, ethnicity, inflammation markers, and neutrophil extracellular trap formation (NETosis). Neutrophils treated with sCD13 showed heightened NETosis and chemotaxis, which were inhibited by sCD13 receptor blockade. Meanwhile sCD13 did not induce platelet aggregation. Single-cell analysis of COVID-19 lungs revealed coexpression of CD13 and MMP14 by various cell types, and higher CD13 expression compared with controls. Neutrophils with high CD13 mRNA were enriched for genes associated with immaturity, though CD13 protein expression was lower. Histological examination of COVID-19 lungs revealed CD13-positive leukocytes trapped in vessels with fibrin thrombi. Flow cytometry verified the presence of B1R and a second sCD13 receptor, protease-activated receptor 4, on monocytes and neutrophils. These findings identify sCD13 as a potential instigator of COVID-19–associated NETosis, potentiating vascular stress and thromboembolic complications. The potent pro-inflammatory effects of sCD13 may contribute to severe COVID-19, suggesting that sCD13 and its receptors might be therapeutic targets.

Objectives Obstetric antiphospholipid syndrome (OAPS) is an autoimmune disease characterised by the presence of antiphospholipid antibodies in circulation and pathological pregnancy. However, the pathogenesis of OAPS remains unknown. We aimed to reveal cellular compositions and molecular features of decidual cells involved in the development of OAPS using single-cell RNA sequencing (scRNA-seq). Methods We performed unbiased scRNA-seq analysis on the first-trimester decidua from five OAPS patients and five healthy controls (HCs), followed by validations with flow cytometry, immunohistochemical staining and immunofluorescence in a larger cohort. Serum chemokines and cytokines were measured by using ELISA. Results A higher ratio of macrophages but a lower ratio of decidual natural killer (dNK) cells was found in decidua from OAPS compared with HCs. Vascular endothelial cells shrinked in OAPS decidua while having upregulated chemokine expression and conspicuous responses to IFN-γ and TNF-α. Macrophages in OAPS had stronger phagocytosis function, complement activation signals and relied more on glycolysis. dNK cells were more activated in OAPS and had enhanced cytotoxicity and IFN-γ production. Downregulation of granules in OAPS dNK cells could be associated with suppressed glycolysis. Moreover, stromal cells had a prosenescent state with weakened immune surveillance for senescent cells in OAPS. In addition, the cellular interactions between decidual immune cells and those of immune cells with non-immune cells under disease state were altered, especially through chemokines, IFN-γ and TNF-α. Conclusion This study provided a comprehensive decidual cell landscape and identified aberrant decidual microenvironment in OAPS, providing some potential therapeutic targets for this disease.

IgG4-related disease (IgG4-RD) is a systemic autoimmune disease with unclear pathogenesis. We performed single-cell RNA-seq and surface proteome analyses on 61,379 PBMCs from 9 treatment-naive IgG4-RD patients and 7 age- and sex-matched healthy controls. Integrative analyses were performed for altered gene expression in IgG4-RD, and flow cytometry and immunofluorescence were used for validation. We observed expansion of plasmablasts with enhanced protein processing and activation, which correlated with the number of involved organs in IgG4-RD. Increased proportions of CD4 ⁺ cytotoxic T lymphocytes (CTLs), CD8 ⁺ CTLs-GNLY (granulysin), and γδT cells with enhanced chemotaxis and cytotoxicity but with suppressed inhibitory receptors characterize IgG4-RD. Prominent infiltration of lymphocytes with distinct compositions were found in different organs of IgG4-RD patients. Transcription factors (TFs), including PRDM1/XBP1 and RUNX3, were upregulated in IgG4-RD, promoting the differentiation of plasmablasts and CTLs, respectively. Monocytes in IgG4-RD have stronger expression of genes related to cell adhesion and chemotaxis, which may give rise to profibrotic macrophages in lesions. The gene activation pattern in peripheral immune cells indicated activation of multiple interaction pathways between cell types, in part through chemokines or growth factors and their receptors. Specific upregulation of TFs and expansion of plasmablasts and CTLs may be involved in the pathogenesis of IgG4-RD, and each of these populations are candidate targets for therapeutic interventions in this disease.

CD13, an ectoenzyme on myeloid and stromal cells, also circulates as a shed, soluble protein (sCD13) with powerful chemoattractant, angiogenic, and arthritogenic properties, which require engagement of a G protein–coupled receptor (GPCR). Here we identify the GPCR that mediates sCD13 arthritogenic actions as the bradykinin receptor B1 (B1R). Immunofluorescence and immunoblotting verified high expression of B1R in rheumatoid arthritis (RA) synovial tissue and fibroblast-like synoviocytes (FLSs), and demonstrated binding of sCD13 to B1R. Chemotaxis, and phosphorylation of Erk1/2, induced by sCD13, were inhibited by B1R antagonists. In ex vivo RA synovial tissue organ cultures, a B1R antagonist reduced secretion of inflammatory cytokines. Several mouse arthritis models, including serum transfer, antigen-induced, and local innate immune stimulation arthritis models, were attenuated in Cd13^–/– and B1R^–/– mice and were alleviated by B1R antagonism. These results establish a CD13/B1R axis in the pathogenesis of inflammatory arthritis and identify B1R as a compelling therapeutic target in RA and potentially other inflammatory diseases.

Letters to the Editor; Authors: Y. Hu, Y. Zhao, H. Zeng, Q. Jin, T. Liu, Q. Yang, D. Fox, C. Lu

Antiviral therapies targeting the pandemic coronavirus disease 2019 (COVID-19) are urgently required. We studied an already-approved botanical drug cepharanthine (CEP) in a cell culture model of GX_P2V, a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-related virus. RNA-sequencing results showed the virus perturbed the expression of multiple genes including those associated with cellular stress responses such as endoplasmic reticulum (ER) stress and heat shock factor 1 (HSF1)-mediated heat shock response, of which heat shock response-related genes and pathways were at the core. CEP was potent to reverse most dysregulated genes and pathways in infected cells including ER stress/unfolded protein response and HSF1-mediated heat shock response. Additionally, single-cell transcriptomes also confirmed that genes of cellular stress responses and autophagy pathways were enriched in several peripheral blood mononuclear cells populations from COVID-19 patients. In summary, this study uncovered the transcriptome of a SARS-CoV-2-related coronavirus infection model and anti-viral activities of CEP, providing evidence for CEP as a promising therapeutic option for SARS-CoV-2 infection.