Distinct fibroblast subsets drive inflammation and damage in arthritis

A 10-year knowledge mapping of T cells in rheumatoid arthritis: A bibliometric analysis

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease of autoimmune origin. T cells play crucial roles in the initiation and progression of RA. Although bibliometric methods have been widely used to synthesize knowledge trajectories across different biomedical fields, it has hardly been used to underscore the knowledge trends in relation to T cell and RA. This study used bibliometric methods to delineate the evolution of research on T cells and RA. Data were sourced from the Web of Science™ Core Collection and were scientometrically analyzed using CiteSpace and VOSviewer. From 2014 to 2023, 7037 papers on T cells and RA were retrieved. The number of annual publications is stable between 600 and 800, and the citation frequency continues to rise. The United States, China, the United Kingdom and Japan were the most productive countries. Karolinska Institute, and Harvard Medical School were the institutions that published the most research papers. Wei W, Cho ML, and Park SH were the most prolific authors. Mclnnes IB and Smolen JS were the most frequently cited authors. The journals with the most articles are Frontiers in Immunology, Arthritis Research & Therapy, and Arthritis & Rheumatology. Current research hotspots include pathogenic factors and targeted biological therapy, immune mechanisms, inflammatory mechanisms, and bone destruction mechanisms. The current research frontiers in this field are gut microbiota, identification, fibroblast-like synoviocytes, biologic therapy, mesenchymal stem cells, and risk. This work provides new insights into the scientific research and clinical application of T cells to develop therapeutic targets for RA.

Aging microvasculature: Effects on immune cell trafficking and inflammatory diseases

Leukocyte recruitment to sites of inflammation is vital for orchestrating an effective immune response. Key to this process is the ability of leukocytes to migrate through venular walls, engaging in sequential interactions with endothelial cells, pericytes, and the venular basement membrane. The aging process exerts profound effects on the molecular and functional properties of the vasculature, thereby influencing the profile and dynamics of leukocyte trafficking during inflammation. In this review, by focusing mainly on neutrophils, we summarize key examples of how the aged microvasculature and perivascular stroma cells promote dysregulated leukocyte-venular wall interactions and present the associated molecular mechanisms. Additionally, we discuss the functional implications of such aberrant leukocyte behavior to age-related and chronic inflammatory pathologies.

Current cutting-edge omics techniques on musculoskeletal tissues and diseases

Musculoskeletal disorders, including osteoarthritis, rheumatoid arthritis, osteoporosis, bone fracture, intervertebral disc degeneration, tendinopathy, and myopathy, are prevalent conditions that profoundly impact quality of life and place substantial economic burdens on healthcare systems. Traditional bulk transcriptomics, genomics, proteomics, and metabolomics have played a pivotal role in uncovering disease-associated alterations at the population level. However, these approaches are inherently limited in their ability to resolve cellular heterogeneity or to capture the spatial organization of cells within tissues, thus hindering a comprehensive understanding of the complex cellular and molecular mechanisms underlying these diseases. To address these limitations, advanced single-cell and spatial omics techniques have emerged in recent years, offering unparalleled resolution for investigating cellular diversity, tissue microenvironments, and biomolecular interactions within musculoskeletal tissues. These cutting-edge techniques enable the detailed mapping of the molecular landscapes in diseased tissues, providing transformative insights into pathophysiological processes at both the single-cell and spatial levels. This review presents a comprehensive overview of the latest omics technologies as applied to musculoskeletal research, with a particular focus on their potential to revolutionize our understanding of disease mechanisms. Additionally, we explore the power of multi-omics integration in identifying novel therapeutic targets and highlight key challenges that must be overcome to successfully translate these advancements into clinical applications.

Complementing muscle regeneration-fibro-adipogenic progenitor and macrophage-mediated repair of elderly human skeletal muscle

The capacity to regenerate skeletal muscle after injury requires a complex and well-coordinated cellular response, which is challenged in aged skeletal muscle. Here, we unravel the intricate dynamics of elderly human skeletal muscle regeneration by combining spatial, temporal, and single cell transcriptomics. Using spatial RNA sequencing (n = 3), we profile the expression of human protein-coding genes in elderly human skeletal muscle biopsies before as well as 2-, 8-, and 30-day post injury (NCT03754842). Single Cell-Spatial deconvolution analysis highlights monocytes/macrophages and fibro-adipogenic progenitors (FAPs) as pivotal players in human muscle regeneration. By utilizing flow cytometry (n = 9) and cell sorting we confirm the increased cellular content and activity during regeneration. Spatial correlation analysis unveils FAPs and monocytes/macrophages co-localization and intercellular communication, mediated by complement factor C3. Immunostaining confirms C3 expression in FAPs and FAP secretion of C3, suggesting a role in phagocytosis of necrotic muscle cells. Finally, functional assays demonstrate C3's impact on human monocyte metabolism, survival and phagocytosis, unveiling its involvement in skeletal muscle regeneration. These insights elucidate the FAP-macrophage interplay in aged human muscle with perspectives for future therapeutic interventions to reduce the age-induced decline in regenerative capacity.

Can we cure rheumatoid arthritis?

Rheumatoid arthritis (RA) persists as a chronically progressive autoimmune disorder, notwithstanding significant advancements in early intervention and precision-targeted therapeutics. While treat-to-target paradigms and disease-modifying antirheumatic drugs ameliorate clinical outcomes, sustained drug-free remission (SDFR) or even cure remains elusive, underscoring the need for innovative strategies addressing underlying immunopathogenic mechanisms. Prolonged SDFR implies cure or eradication of disease, but there is no consensus definition of cure because it has rarely been contemplated in RA. Pathogenic immune circuit resilience, stromal hyperactivation, persistent structural abnormalities, and genetic susceptibilities constitute multifactorial barriers to a cure. Emerging therapies - including novel biologics, cellular interventions, and gene editing - aim to reprogram pathogenic immune responses rather than suppress symptoms and may have the potential for both SDFR and possibly cure. Whereas preclinical and early clinical data suggest the potential to modify disease trajectories, durable resetting of the RA immune system toward normal has not yet been conclusively demonstrated or uniformly achieved in RA. The 'window of opportunity' paradigm postulates that early-stage immunomodulatory interventions may alter the disease trajectory. However, the optimal therapeutic approaches for capitalizing on this temporal window remain debated, particularly regarding the integration of personalized biomarkers and mechanistic targets. This review summarizes advancements in RA therapeutics, evaluating whether emerging modalities can pivot the clinical paradigm from symptomatic management to the induction of persistent immunological normalization and cure. Although definitive cure remains on the far horizon, the rapid convergence of precision medicine, next-generation immunotherapy, and translational research underscores a paradigm shift toward curative strategies.

Feasibility assessment of radiolabeled FAPI-04 for diagnostic and therapeutic use in rheumatoid arthritis

OBJECTIVE

Fibroblast activation protein alpha (FAPα) plays a key role in cartilage degradation, inflammation, and bone erosion, particularly in rheumatoid arthritis (RA) where fibroblast-like synoviocytes in synovial tissue show elevated FAPα expression. This study explored radiolabeled FAP inhibitors for arthritis diagnosis and therapy.

DESIGN

We used the radiotracer 68Ga-FAPI-04 for PET/CT imaging to predict collagen-induced arthritis (CIA) onset. Weekly scans quantified tracer uptake via SUV values, correlating results with disease scores and incidence. For therapeutic evaluation, 177Lu-FAPI-04 targeted FAPα-expressing cells, and arthritis scores of treated CIA mice were compared with untreated controls using one-way ANOVA.

RESULTS

CIA mice with elevated SUV one week post-booster immunization had a 94.6 % arthritis incidence. SUV correlated with arthritis severity, reflecting increased FAPα expression. Treatment with 177Lu-FAPI-04 reduced arthritis scores by 64 % compared to controls (p < 0.005).

CONCLUSION

Radiotracer 68Ga-FAPI-04 effectively targets FAPα, enabling PET imaging to identify CIA severity and onset sites in mice. Additionally, 177Lu-FAPI-04 demonstrated therapeutic potential by mitigating disease activity, suggesting its promise for RA treatment.

Synovium-on-a-Chip Reveals Fibroblast-Macrophage Crosstalk Underpinning Joint Homeostasis and Evaluation of Gout Therapies

The synovium maintains joint homeostasis and regulates immune responses through fibroblast-like synoviocytes (FLS) and macrophage-like synoviocytes (MLS). However, investigation of the intricate FLS-MLS interactions is limited by the lack of physiologically relevant in vitro models. Here, this work presents a synovium-on-a-chip model that faithfully mimics the structural and functional properties of the human synovial lining, established with collagen/alginate hybrid hydrogel (CAHG). The functional phenotype of FLS observed in vivo is replicated on chip when cultured with CAHG. Moreover, co-culture with M2c macrophages derived from CD14+ monocytes enables the reconstruction of key immune functions of the synovial lining, including expression of junction proteins (ZO-1 and CLD5) and immunoregulatory markers (TREM2 and VSIG4). CD44 blockade, disrupting FLS-MLS interactions, significantly suppresses inflammasome-related pathways, underscoring the regulatory role of FLS in synovial immune responses. Our model is further validated by modeling gout, where treatment with monosodium urate crystals trigger NLRP3 inflammasome activation, macrophage polarization, and neutrophil extravasation. Pharmacological interventions with MCC950 and entrectinib effectively inhibit the inflammasome activation, demonstrating the platform's utility for preclinical drug evaluation. This synovium-on-a-chip provides a reliable in vitro model for studying synovial inflammation and serves as a valuable tool for the therapeutic discovery of inflammatory joint diseases.

CD4+ tissue-resident memory Th17 cells are a major source of IL-17A in Spondyloarthritis synovial tissue

OBJECTIVES

Interleukin (IL)-17A is a key driver of spondyloarthritis (SpA) joint pathology. We aimed to identify its cellular source in synovial tissue from patients with 2 forms of SpA, namely axial SpA (AxSpA) and psoriatic arthritis (PsA).

METHODS

Synovial tissue from patients with SpA was profiled using single-cell RNA sequencing (scRNA-seq; AxSpA, n = 5; PsA, n = 6) or spatial RNA profiling (PsA, n = 4). CellPhoneDB was used to infer cell-cell communication. Tissue-resident memory Th17 (TRM17)-like cells were generated in vitro using blood memory CD4+ T cells from SpA patients. An epigenetic inhibitor library, siRNA, and clustered regularly interspaced short palindromic repeats (CRISPR) were used to identify epigenetic regulator(s) for TRM17.

RESULTS

scRNA-seq showed that CD4+CXCR6+ TRM17 cells are the predominant spontaneous IL17A producers in SpA synovium. Cell-cell communication and single-cell spatial analysis support the interaction between TRM17 and CLEC10A+ dendritic cells, which were activated in SpA. Both sublining and lining fibroblasts in SpA synovium showed evidence of interleukin (IL)-17A activation. In vitro-generated CD4+ TRM17-like cells phenocopied joint tissue TRM17, producing IL-17A/F upon T cell-receptor (TCR) stimulation, which was further enhanced by cytokines. Perturbation of BRD1 inhibited the generation of TRM17-like cells.

CONCLUSIONS

CD4+ TRM17 cells are the predominant source of IL-17A in SpA synovial tissue. TCR stimulation is essential for the secretion of IL-17A by CD4+TRM17-like cells. The epigenetic regulator bromodomain-containing protein 1 (BRD1) contributes to the generation of CD4+TRM17. Depleting CD4+TRM17 cells in SpA is thus a therapeutic strategy with potential to induce long-term remission.

Characterization of a pathogenic nonmigratory fibroblast population in systemic sclerosis skin

Fibroblasts are central to pathogenesis of systemic sclerosis (SSc). However, studies of conventional explant fibroblast cultures incompletely reflect disease biology and treatment response. We isolated a second nonmigratory "resident" population of fibroblasts from skin biopsies after outgrowth of explant "migratory" cells. These nonmotile resident fibroblasts were compared with migratory cells from the same biopsy, using functional studies, bulk and single-cell RNA-seq, and localized in situ by multichannel immunofluorescence. Migratory and resident fibroblast populations in SSc showed distinct profibrotic characteristics and gene expression for pathogenic pathways differing by stage and autoantibody subgroup. TGF-β signaling was highly active in migratory fibroblasts in early-stage diffuse cutaneous SSc (dcSSc). Conversely, resident fibroblasts had less upregulated TGF-β signaling, especially in late-stage dcSSc. Increased chemokine expression was a hallmark of resident fibroblasts at all stages. In vitro studies confirmed differential response to TGF-β1 and CCL2 between migratory and resident cells. We suggest that migratory fibroblasts are especially important in early skin disease, whereas nonmigratory fibroblasts may have a regulatory role and contribute more to fibrosis in later-stage disease. Thus, we have identified a pathogenic fibroblast population in SSc, not isolated by conventional explant culture, that could play an important role in fibrosis and be targeted therapeutically.

Fibroblasts in immune responses, inflammatory diseases and therapeutic implications

Once regarded as passive bystander cells of the tissue stroma, fibroblasts have emerged as active orchestrators of tissue homeostasis and disease. From regulating immunity and controlling tissue remodelling to governing cell growth and differentiation, fibroblasts assume myriad roles in guiding normal tissue development, maintenance and repair. By comparison, in chronic inflammatory diseases such as rheumatoid arthritis, fibroblasts recruit and sustain inflammatory leukocytes, become dominant producers of pro-inflammatory factors and catalyse tissue destruction. In other disease contexts, fibroblasts promote fibrosis and impair host control of cancer. Single-cell studies have uncovered striking transcriptional and functional heterogeneity exhibited by fibroblasts in both normal tissues and diseased tissues. In particular, advances in the understanding of fibroblast pathology in rheumatoid arthritis have shed light on pathogenic fibroblast states in other chronic diseases. The differentiation and activation of these fibroblast states is driven by diverse physical and chemical cues within the tissue microenvironment and by cell-intrinsic signalling and epigenetic mechanisms. These insights into fibroblast behaviour and regulation have illuminated therapeutic opportunities for the targeted deletion or modulation of pathogenic fibroblasts across many diseases.

Synergistic induction of PGE2 by oral pathogens and TNF promotes gingival fibroblast-driven stromal-immune cross-talk in periodontitis

The interaction between pathogenic microorganisms and stromal cells, in particular fibroblasts, significantly contributes to the pathogenesis of many bacterially driven diseases. In periodontitis, oral pathogens penetrate the epithelial barrier and aggravate ongoing gingival inflammation by promoting the production of inflammatory mediators, such as prostaglandin E2 (PGE2). This study aimed to investigate the functional consequences of the interplay between oral pathogens and a pro-inflammatory environment in the activation of the PGE2 pathway in primary human gingival fibroblasts (GFs). GF infection with Fusobacterium nucleatum, Porphyromonas gingivalis, or Filifactor alocis in the presence of tumor necrosis factor (TNF) led to synergistic induction of cyclooxygenase-2 (COX-2), a key enzyme in the PGE2 synthesis pathway, as well as secretion of PGE2. A similar synergy in COX-2 upregulation was observed upon GF infection with oral pathogens in the presence of IL-1α, IL-1β, and interferon-α (IFN-α). This effect required toll-like receptor-2 (TLR2) and the p38 MAP kinase activation and was specific for fibroblasts as infection of macrophages or keratinocytes with oral pathogens in the proinflammatory environment did not cause synergistic COX-2 induction. Finally, we demonstrated that conditioned media from GFs infected with F. nucleatum under inflammatory conditions amplified the expression of the neutrophil chemokine IL8 in macrophages and confirmed that this effect was mediated by synergistic induction of PGE2 in GFs. Collectively, we identify a new mechanism of stromal-immune cross-talk that is driven by synergistic PGE2 induction by oral pathogens and inflammatory cytokines in GFs and may contribute to excessive macrophage activation and neutrophil infiltration in periodontitis.IMPORTANCEPeriodontitis is a highly prevalent, dysbiosis-driven chronic inflammatory disease that not only leads to tooth loss but also is associated with severe systemic diseases. In this work, we describe a novel mechanism responsible for excessive production of PGE2, which is a potent inflammatory mediator that significantly contributes to the pathogenesis of periodontitis. We found that infection of GFs with many species of oral pathogens in the presence of inflammatory cytokines produced by the host leads to synergistic induction of COX-2 expression and PGE2 production. We found that this fibroblast-specific amplification of the COX-2-PGE2 axis by oral pathogens and cytokines is driven by the p38 MAP kinase and promotes enhanced expression of a key neutrophil chemokine by macrophages. These studies have thus enabled the identification of a new mechanism of host-pathogen interactions in periodontitis, improving our understanding of the roles of GFs and their cross-talk with immune cells in disease pathogenesis.

Understanding rheumatic disease through continuous cell state analysis

Autoimmune rheumatic diseases are a heterogeneous group of conditions, including rheumatoid arthritis (RA) and systemic lupus erythematosus. With the increasing availability of large single-cell datasets, novel disease-associated cell types continue to be identified and characterized at multiple omics layers, for example, 'T peripheral helper' (TPH) (CXCR5- PD-1hi) cells in RA and systemic lupus erythematosus and MerTK+ myeloid cells in RA. Despite efforts to define disease-relevant cell atlases, the very definition of a 'cell type' or 'lineage' has proven controversial as higher resolution assays emerge. This Review explores the cell types and states involved in disease pathogenesis, with a focus on the shifting perspectives on immune and stromal cell taxonomy. These understandings of cell identity are closely related to the computational methods adopted for analysis, with implications for the interpretation of single-cell data. Understanding the underlying cellular architecture of disease is also crucial for therapeutic research as ambiguity hinders translation to the clinical setting. We discuss the implications of different frameworks for cell identity for disease treatment and the discovery of predictive biomarkers for stratified medicine - an unmet clinical need for autoimmune rheumatic diseases.

A brief overview of chikungunya-related pain

Pain is an important symptom associated with the arboviral disease caused by the Chikungunya virus (CHIKV). For a significant number of patients, this symptom can persist for months or even years, negatively affecting their quality of life. Unfortunately, pharmacological options for this condition are limited and only partially effective, as the underlying mechanisms associated with CHIKV-induced pain are still poorly understood. The re-emergence of CHIKV has led to new outbreaks, and the expected high prevalence of pain in these global events requires new scientific advances to find more effective solutions. Here we review the main aspects of pain caused by CHIKV infection, such as the anatomy of the affected sites, the prevalence and management of this symptom, the diversity of possible cellular and molecular mechanisms, and finally highlight a promising meningeal pathway to elucidate the mechanisms involved in the unsolved problem of CHIKV-associated pain.

68Ga-FAPI and 18F-NaF PET/CT in psoriatic arthritis: a comparative study

OBJECTIVES

As fibroblast-like synoviocyte activation and bone formation are associated with PsA, PET using the tracers of 68Ga-fibroblast activation protein inhibitor (FAPI) and 18F-sodium fluoride (NaF) may sensitively detect the disease. In this prospective study, we aimed to evaluate the performance of 68Ga-FAPI PET/CT in PsA and to compare it with 18F-NaF PET/CT.

METHODS

Sixteen participants (female 7/16, age 42.31 ± 10.66 years) with PsA were prospectively enrolled and underwent dual-tracer PET/CT, clinical assessment and ultrasonography. PET/CT images were scored for PET-positive lesions at the peripheral joints, entheses, and axial joints.

RESULTS

The positivity rate of 68Ga-FAPI in peripheral joints was higher than that in entheses and axial joints (21.84% vs 12.15% vs 0%), whereas high positivity rates of 18F-NaF in peripheral joints, entheses, and axial joints were observed (85.23%, 78.13% and 75%, respectively). The DAS 28 was higher in the PET-positive than in the PET-negative group with 68Ga-FAPI (5.25 ± 1.84 vs 2.55 ± 0.94, P = 0.037), but not with 18F-NaF. In addition, the PET joint count at 68Ga-FAPI PET/CT was positively correlated with the tender joint count (r = 0.604, P = 0.017), swollen joint count (r = 0.773, P = 0.001), DAS28-CRP (r = 0.556, P = 0.032), Psoriatic Arthritis Disease Activity Score (PASDAS) (r = 0.540, P = 0.038) and PsASon13 (r = 0.701, P = 0.005), while no correlation was observed in 18F-NaF PET/CT.

CONCLUSION

The positivity rates of 68Ga-FAPI- and 18F-NaF PET/CT were different in patients with PsA in peripheral joints, entheses, and axial joints. The extent of joint involvement as shown in 68Ga-FAPI PET/CT correlated with clinical and US variables as well as with disease activity.

TRIAL REGISTRATION

ClinicalTrials.gov, http://clinicaltrials.gov, NCT05686876.

Effects of embryonic origin, tissue cues and pathological signals on fibroblast diversity in humans

Fibroblasts, once perceived as a uniform cell type, are now recognized as a mosaic of distinct populations with specialized roles in tissue homeostasis and pathology. Here we provide a global overview of the expanding compendium of fibroblast cell types and states, their diverse lineage origins and multifaceted functions across various human organs. By integrating insights from developmental biology, lineage tracing and single-cell technologies, we highlight the complex nature of fibroblasts. We delve into their origination from embryonic mesenchyme and tissue-resident populations, elucidating lineage-specific behaviours in response to physiological cues. Furthermore, we highlight the pivotal role of fibroblasts in orchestrating tissue repair, connective tissue remodelling and immune modulation across diverse pathologies. This knowledge is essential to develop novel fibroblast-targeted therapies to restore steady-state fibroblast function and advance regenerative medicine strategies across multiple diseases.

Fibroblast activation protein-targeted PET/CT with 68Ga-FAPI-46 for evaluation of structural damage and inflammation in axial spondyloarthritis: a prospective study

OBJECTIVE

Axial spondyloarthritis (axSpA) is characterized by active inflammation and structural damage. To date, there is no imaging tool can alone visualize all those changes well. PET/CT imaging with gallium-68-labeled fibroblast activation protein inhibitor (68Ga-FAPI) provide extra ability for CT in detecting active inflammation in addition to its advantage in assessing structural damage. This study aims to explore the utility of 68Ga-FAPI-46 PET/CT for assessing active inflammation in axSpA.

METHODS

Between July 2023 to July 2024, 22 patients with axSpA and 12 healthy volunteers were prospectively enrolled. Disease activity and parameters associated with inflammation were evaluated at enrollment. Participants then underwent 68Ga-FAPI-46 PET/CT for assessment of FAPI uptake across joints. 68Ga-FAPI-46 uptake was semi-quantitatively evaluated by using a three-point scale. The sum of points was calculated to generate 68Ga-FAPI-46 PET/CT-derived FAPI uptake scores. Patients receiving biologics therapy were grouped as responders or non-responders according to clinical follow-up.

RESULTS

Compared to healthy volunteers, patients with axSpA exhibited significantly higher 68Ga-FAPI-46 uptake in several joints, especially in spine (p < 0.001). 68Ga-FAPI-46 PET/CT scores in spine showed strong correlation with the Ankylosing Spondylitis Disease Activity Score (ASDAS), inflammatory indicators such as c-reactive protein (CRP), and inflammation visualized by magnetic resonance imaging (MRI). Biologic responders displayed markedly higher baseline 68Ga-FAPI-46 PET/CT scores in the spine (median: 36.5 vs. 4.0, p = 0.017) and total joints (median: 53.5 vs. 11.0, p = 0.015) compared to non-responders.

CONCLUSION

68Ga-FAPI-46 PET/CT has the potential to serve as a dual-function imaging tool, integrating the structural imaging capabilities of CT with the ability to detect inflammation.

CLINICAL TRIAL REGISTRATION

NCT05999643.

Plasma haem oxygenase-1 may represent a first-in-class biomarker of oxidative stress in rheumatoid arthritis

OBJECTIVES

This study explores the early identification of rheumatoid arthritis (RA) patients at elevated risk of progression. Haem-oxygenase-1 (HO-1) is a marker of oxidative stress in inflammation. Here, we investigate HO-1 as a biomarker of oxidative stress and its association with clinical disease activity and radiographic progression in RA.

METHOD

Baseline HO-1 was measured sequentially in plasma samples from patients with early rheumatoid arthritis (eRA) (n = 80). Disease Activity Score based on 28-joint count-C-reactive protein, Clinical Disease Activity Index, and total Sharp score were used to evaluate the disease course serially over 2 years. Paired plasma and synovial fluid samples were examined for HO-1 in active established rheumatoid arthritis (esRA) (n = 20). Plasma from healthy control subjects was also included (n = 35).

RESULTS

Plasma HO-1 levels were increased in eRA {1373 pg/mL [interquartile range (IQR) 1110-2050]} and esRA [2034 pg/mL (IQR 1630-2923)] compared with controls [1064 pg/mL (IQR 869.5-1378)]. HO-1 plasma levels decreased with treatment. Baseline HO-1 correlated with disease activity and radiographic progression. A strong, linear correlation was found between synovial and plasma HO-1 levels (r = 0.75, p < 0.001).

CONCLUSION

In eRA, plasma levels of HO-1 were increased and correlated with disease and radiographic progression. A baseline measurement of plasma HO-1 levels demonstrated superior performance to currently used clinical and serological disease markers in the prediction of radiographic progression. Plasma HO-1 may function as a first-in-class biomarker of synovial oxidative stress in RA.

Dominant Role of Distinct Microenvironments on Cartilage Regeneration Fate Using PLGA-Hydrogel Composite Scaffolds

Currently, bioactive composite scaffolds provide an ideal regenerative microenvironment for cartilage tissue engineering. However, the dominant regulatory role of the microenvironment in cartilage regeneration fate remains elusive, such as in situ auricle, ex situ subcutaneous, and osteogenic regions. Therefore, investigating the influence of distinct microenvironments on cartilage regeneration and long-term outcomes is important. In this study, a universal composite scaffold is developed combining 3D-printed poly(lactic-co-glycolic acid) frameworks with cartilage-specific matrix hydrogels and then systematically explored the crucial role of the microenvironment in determining the fate of cartilage regeneration. These results indicate that the in situ auricular microenvironment effectively promotes the maturation of the regenerative cartilage and maintains its chondrogenic phenotype. In contrast, ex situ subcutaneous microenvironment leads to chondrogenic phenotype loss owing to intense immune-inflammatory responses and vascularization conditions. In the osteogenic microenvironments of cranial sites, although autologous chondrocytes show good cartilage regenerative quality within 12 weeks, they are gradually replaced by regenerative bone, ultimately achieving successful cranial defect repair. Interestingly, these findings provide critical theoretical foundations for revealing the long-term outcomes of engineered cartilage and offer practical guidance for optimizing cartilage regeneration strategies in various microenvironments.

Formyl-peptide receptor type 2 activation mitigates heart and lung damage in inflammatory arthritis

Rheumatoid arthritis (RA) is associated with heart and lung dysfunction. Current therapies fail to attenuate such complications. Here, we identify formyl-peptide receptor type 2 (FPR2) as a therapeutic target to treat heart and lung dysfunction associated with inflammatory arthritis. Arthritic mice on high levels of dietary homocysteine develop cardiac diastolic dysfunction and reduced lung compliance, mirroring two comorbidities in RA. Therapeutic administration of a small molecule FPR2 agonist (BMS986235) to hyper-homocysteine arthritic mice prevented diastolic dysfunction (monitored by echocardiography) and restored lung compliance. These tissue-specific effects were secondary to reduced neutrophil infiltration, modulation of fibroblast activation and phenotype (in the heart) and attenuation of monocyte and macrophage numbers (in the lung). A dual FPR1/2 agonist (compound 43) failed to prevent the reduction in lung compliance of arthritic mice and promoted the accumulation of inflammatory monocytes and pro-fibrotic macrophages in lung parenchyma. This cellular response lies downstream of FPR1-mediated potentiation of CCL2-dependent monocyte chemotaxis and activation. This finding supports the therapeutic development of selective FPR2 agonists to mitigate two impactful comorbidities associated with inflammatory arthritides.

Personalised treatment of rheumatoid arthritis based on cytokine profiles and synovial tissue signatures: potentials and challenges

BACKGROUND

Rheumatoid arthritis (RA) is an autoimmune, chronic inflammatory disease that mainly affects the joints and periarticular soft tissues. Although there have been significant advances in RA treatment over the past two decades, approximately 40% of patients do not respond to first-line biological disease-modifying antirheumatic drugs (bDMARDs). Physicians often use an empirical, trial-and-error approach to select bDMARDs to treat patients with RA. This is inefficient and can be costly for healthcare systems which have limited resources. Unlike in oncology, where molecular pathology helps guide targeted therapies, reliable, predictive biomarkers for drug response in RA are yet to be identified. This narrative review aims to summarise current knowledge on novel biomarkers of disease activity and drug response in RA, with a particular focus on serum cytokine profiles and macrophage and fibroblast subsets in synovial tissue. We also highlight key areas of further research that could advance the development of targeted therapies for patients with RA.

METHODS

We searched PubMed to identify studies pertaining to biomarkers of disease activity and drug response in the treatment of RA.

RESULTS

We present a detailed overview of the key studies that have identified serum cytokine profiles and synovial macrophage and fibroblast subsets as novel biomarkers of disease activity and drug response in RA.

CONCLUSION

A novel, evidence-based approach to precision medicine in RA, which involves tailoring treatment based on cytokine profiles and synovial tissue signatures, shows promise for improving patient care. However, more research is needed to identify biomarkers that predict drug response.

Fibroblast activation imaging in rheumatoid arthritis: evaluating disease activity and treatment response using [18F]FAPI PET/CT

OBJECTIVES

To evaluate the utility of fibroblast activation protein (FAP) imaging using [¹⁸F]FAPI PET/CT for assessing disease activity and monitoring treatment response in rheumatoid arthritis (RA).

MATERIALS AND METHODS

A prospective, single-center study was conducted with 42 RA patients and 8 healthy controls. Participants underwent clinical assessment and [¹⁸F]FAPI PET/CT imaging. Semiquantitative parameters, including standardized uptake value maximum (SUVmax), lesion-to-muscle ratio (LMR), [¹⁸F]FAPI-avid lesion volume (FLV), and total lesion FAP expression (TLF), were analyzed. Disease activity was stratified by the disease activity score-28 using C-reactive protein (DAS28-CRP) into three groups (low, moderate, and high). Correlations between PET/CT parameters and disease acitivity were examined, and follow-up imaging was performed in ten patients to assess treatment response.

RESULTS

[¹⁸F]FAPI PET/CT identified 201 RA-affected joints with significantly higher SUVmax in positive joints compared to controls (median 3.6 vs 2.4; p < 0.01). High disease activity was associated with increased SUVmax (median 5.6 vs 3.3 vs 2.8; p < 0.05), TBR (median 8.4 vs 3.0 vs 3.6; p < 0.05), FLV (162.2 vs 11.5 vs 9.8; p < 0.01), and TLF (569.1 vs 27.3 vs 22.7; p < 0.01). Positive correlations were observed between DAS28-CRP and both FLV (r = 0.50, p < 0.01) and TLF (r = 0.51, p < 0.01). Follow-up imaging revealed significant associations between changes in disease activity and FAP burden.

CONCLUSION

[¹⁸F]FAPI PET/CT is a promising tool for non-invasive assessment of RA disease activity. It provides quantitative insights into fibroblast activation, offering potential to enhance disease management and therapeutic planning.

KEY POINTS

Question What is the potential of fibroblast activation imaging using [18F]FAPI PET/CT for assessing RA disease activity and monitoring treatment response? Findings 18F]FAPI PET/CT effectively identifies joint involvement and quantifies fibroblast activation, correlating closely with clinical disease activity in RA. Clinical relevance [18F]FAPI PET/CT provides a non-invasive, comprehensive assessment of RA activity, and possible cutoff values for identifying high disease activity.

Acidosis regulates immune progression in rheumatoid arthritis by promoting the expression of cytokines and co-stimulatory molecules in synovial fibroblasts

BACKGROUND

Tissue acidosis is a key characteristic of RA. It remains unclear whether acidosis promotes the formation of the complex adaptive immune landscape mainly characterized by T cell activation in RA by influencing synovial fibroblasts. This study aims to investigate the influence of acidosis on the immune microenvironment of RA by exploring the cytokine secretion and expression of co-stimulatory factors of RA synovial fibroblasts.

METHODS

The Bulk RNA-seq dataset (GSE89408, Normal = 23, RA = 150) was utilized for cytokine screening and the immune state assessment based on disease stage. RNA-seq was employed to investigate cytokine and co-stimulatory molecule expression following 6 h of acid stimulation, combined with Bulk RNA-seq data to evaluate contributions to RA. Human cytokine arrays were used to confirm cytokine accumulation in supernatants after 12 h of acid stimulation. Proteomics was applied to explore cellular functional states in RASFs under 6 h of acid stress, with joint RNA-seq analysis elucidating transcription factor activation. Validation of select high-throughput data was performed using qRT-PCR and immune-based assays.

RESULTS

Bulk RNA-seq and RNA-seq identified 56 differentially expressed cytokines at their intersection. Functional enrichment analysis demonstrated that acid stimulation enhanced cytokine secretion and T cell chemotaxis in RA synovial fibroblasts (RASFs). Cytokine array revealed that acid exposure increased the accumulation of growth factors (e.g., FGF, VEGF) by over twofold and promoted the expression of multiple inflammatory and chemotactic factors. Immune state analysis indicated that acid stimulation induced a complex immune landscape by upregulating co-stimulatory and antigen-presenting molecules. Proteomics showed that acid stress enhanced mitochondrial function and triggered metabolic reprogramming in RASFs. Integrated transcriptomic and proteomic analyses revealed that AP1 regulates gene expression in RASFs, with its activation further confirmed by Western blotting and immunofluorescence.

Engineered Exosomes Loaded in Intrinsic Immunomodulatory Hydrogels with Promoting Angiogenesis for Programmed Therapy of Diabetic Wounds

Inducing rapid angiogenesis by delivering specific biological cues is critical for diabetic wound healing. Nevertheless, the angiogenesis is hindered by the inflammatory microenvironment, and the immune cells fail to orchestrate immune responses to wound healing. Herein, vascular endothelial growth factor (VEGF) plasmids-loaded macrophage exosomes (Exos) were fabricated and enfolded in injectable self-healing hydrogels for programmed therapy of diabetic wounds through sequentially intrinsically modulating the inflammatory microenvironment and promoting angiogenesis. The hydrogels, formed via dynamical Schiff base reactions using modified polysaccharides, intrinsically regulate the inflammatory microenvironment via broad-spectrum antioxidant activity and macrophage phenotype regulation, restoring tissue redox and immune homeostasis. Furthermore, the hydrogels can stabilize and release the engineered exosomes. By integration of generation and release of VEGF by plasmids-loaded macrophage Exos, VEGF secretion by M2 macrophages, and enhanced binding of VEGF to VEGF receptor 2 by high affinity of sulfated chitosan, the intrinsic immunomodulatory hydrogels effectively promote the angiogenesis and accelerate the diabetic wound healing process.

Aging platelets shift their hemostatic properties to inflammatory functions

ABSTRACT

Platelets are crucial players in hemostasis and thrombosis but also contribute to immune regulation and host defense, using different receptors, signaling pathways, and effector functions, respectively. Whether distinct subsets of platelets specialize in these diverse tasks is insufficiently understood. Here, we used a pulse-labeling method in Mus musculus models for tracking in vivo platelet aging and its functional implications. Using in vitro and in vivo assays, we reveal that young, reticulated platelets show heightened responses in the setting of clot formation, with corresponding, increased responses to agonists, adhesion, and retractile function. Unexpectedly, aged platelets lose their hemostatic proficiency but are more prone to react to inflammatory challenge: compared with reticulated platelets, this cohort was more likely to form platelet-leukocyte aggregates and showed increased adhesion to neutrophils in vitro, as well as enhanced bactericidal function. In vivo, this was reflected in increased pulmonary recruitment of aged platelets in an acute lung injury model. Proteomic analyses confirmed the upregulation of immune pathways in this cohort, including enhanced procoagulant function. In mouse models of prolonged platelet half-life, this resulted in increased pulmonary leukocyte infiltration and inflammation upon acute lung injury. Similarly, human platelet concentrates decreased their hemostatic function and elevated their putative immunomodulatory potential in vitro over time, and in a mouse model of platelet transfusion, aged platelet concentrates resulted in augmented inflammation. In summary, we show that platelets exhibit age-dependent phenotypic shifts, allowing them to fulfill their diverse tasks in the vasculature. Because functional alterations of aging platelets extend to platelet concentrates, this may hold important implications for transfusion medicine.

Fibroblast activation protein inhibitor positron emission tomography imaging in muscles of patients with idiopathic inflammatory myopathy

OBJECTIVES

Mesenchymal stromal cells in muscles participate in regeneration following muscle injury. This study explored the potential of [18F]fibroblast activation protein inhibitor (FAPI)-42 PET targeting mesenchymal stromal cells to evaluate disease activity of idiopathic inflammatory myopathy (IIM).

METHODS

Patients with IIM (n = 26) were prospectively included and underwent [18F]FAPI-42 PET/CT and whole-body MRI between January 2023 and July 2023. Patients with malignancies were retrospectively included in the control group and only underwent [18F]FAPI-42 PET/CT (n = 28). [18F]FAPI-42 PET/CT images were evaluated using for avid-FAPI uptake and the target-to-background ratio (TBR). Whole-body MRI was evaluated for oedema, fatty infiltration and atrophy in 42 muscles in the IIM group. The global FAPI- and MRI-derived parameters were calculated for each patient. Clinical assessment of disease activity and muscle strength were collected.

RESULTS

Patients with IIM had significantly higher global FAPI-avid muscle ratios (0.68 [IQR: 0.45, 0.79] vs 0.06 [IQR: 0, 0.11], P < 0.001) and global muscle TBR (2.26 [IQR: 1.71, 2.75] vs 1.23 [IQR: 1.02, 1.52], P < 0.001) compared with controls. In the IIM group, the median TBR was higher in muscles with oedema than in those without (2.44 [IQR: 1.46, 3.27] vs 1.31 [IQR: 0.95, 1.99], P < 0.001). Global FAPI-avid muscle ratios significantly correlated with global oedema score (r = 0.833), muscle strength (r = -0.649), serum creatine kinase (r = 0.456) and disease activity index (r = 0.495-0.621).

CONCLUSION

Increased [18F]FAPI-42 uptake was associated with muscle oedema in IIM. FAPI-derived parameters correlated with IIM disease activity. [18F]FAPI-42 is a promising PET tracer for evaluating IIM disease activity.

Eosinophilic esophagitis drives tissue fibroblast regenerative programs toward pathologic dysfunction

BACKGROUND

Pathologic tissue remodeling with scarring and tissue rigidity has been demonstrated in inflammatory, autoimmune, and allergic diseases. Eosinophilic esophagitis (EoE) is an allergic disease that is diagnosed and managed by repeated biopsy procurement, allowing an understanding of tissue fibroblast dysfunction. While EoE-associated tissue remodeling causes clinical dysphagia, food impactions, esophageal rigidity, and strictures, molecular mechanisms driving these complications remain under investigation.

OBJECTIVE

We hypothesized that chronic EoE inflammation induces pathogenic fibroblasts with dysfunctional tissue regeneration and motility.

METHODS

We used single-cell RNA sequencing, fluorescence-activated cell sorting analysis, and fibroblast differentiation and migration assays to decipher the induced and retained pathogenic dysfunctions in EoE versus healthy esophageal fibroblasts.

RESULTS

Differentiation assays demonstrated that active EoE fibroblasts retain regenerative programs for rigid cells such as chondrocytes (P < .05) but lose healthy fibroblast capacity for soft cells such as adipocytes (P < .01), which was reflected in biopsy sample immunostaining (P < .01). EoE, but not healthy, fibroblasts show proinflammatory and prorigidity transcriptional programs on single-cell RNA sequencing. In vivo, regenerative fibroblasts reside in perivascular regions and near the epithelial junction, and during EoE, they have significantly increased migration (P < .01). Flow analysis and functional assays demonstrated that regenerative EoE fibroblasts have decreased surface CD73 expression and activity (both P < .05) compared to healthy controls, indicating aberrant adenosine triphosphate handling. EoE fibroblast dysfunctions were induced in healthy fibroblasts by reducing CD73 activity and rescued in EoE using adenosine repletion.

CONCLUSION

A normalization of perturbed extracellular adenosine triphosphate handling and CD73 could improve pathogenic fibroblast dysfunction and tissue regeneration in type 2 inflammatory diseases.

Stem and progenitor cells in the synovial joint as targets for regenerative therapy

Damage to articular cartilage, tendons, ligaments and entheses as a result of trauma, degeneration or inflammation in rheumatic diseases is prevalent. Regenerative medicine offers promising strategies for repairing damaged tissues, with the aim of restoring both their structure and function. While these strategies have traditionally relied on tissue engineering approaches using exogenous cells, interventions based on the activation of endogenous repair mechanisms are an attractive alternative. Key to advancing such approaches is a comprehensive understanding of the diversity of the stem and progenitor cells that reside in the adult synovial joint and how they function to repair damaged tissues. Advances in developmental biology have provided a lens through which to understand the origins, identities and functions of these cells, and insights into the roles of stem and progenitor cells in joint tissue repair, as well as their complex relationship with fibroblasts, have emerged. Integration of knowledge obtained through studies using advanced single-cell technologies will be crucial to establishing unified models of cell populations, lineage hierarchies and their molecular regulation. Ultimately, a more complete understanding of how cells repair tissues in adult life will guide the development of innovative pro-regenerative drugs, which are poised to enter clinical practice in musculoskeletal medicine.

Pursuing Precision Medicine in Managing Rheumatoid Arthritis

Rheumatoid arthritis, characterized by immune dysregulation and joint destruction, is managed through a stepwise algorithm that combines methotrexate with biological and targeted synthetic disease-modifying antirheumatic drugs. Despite considerable advances, the lack of reliable biomarkers for selecting the most effective medication, especially in Phase II and beyond, remains a significant obstacle. As a result, achieving early clinical remission in all patients continues to be challenging. Rheumatoid arthritis demonstrates considerable clinical and molecular diversity, influenced by both genetic predispositions and environmental factors. Recent scientific and technological advances have shed light on the pathogenesis of rheumatoid arthritis, facilitating the stratification of patients into distinct phenotypic subgroups and potentially optimizing the choice of targeted therapies. However, persistent challenges include the high costs and logistical demands of these methodologies, as well as the complexities of conducting large-scale clinical trials. This review highlights the intricate pathogenesis of rheumatoid arthritis and underscores the need to address the disease's heterogeneity through precision medicine. Moving forward, a deeper investigation into rheumatoid arthritis pathogenesis, encompassing both genetic and environmental factors, is crucial. Pursuing precision medicine, grounded in accurate patient stratification, should be embraced as a "moonshot" objective in rheumatoid arthritis treatment, aiming to achieve transformative breakthroughs in management.

High-Strength Gelatin Hydrogel Scaffold with Drug Loading Remodels the Inflammatory Microenvironment to Enhance Osteoporotic Bone Repair

Osteoporosis is a widespread condition that induces an inflammatory microenvironment, limiting the effectiveness of conventional therapies and presenting significant challenges for bone defect repair. To address these issues, a high-strength gelatin hydrogel scaffold loaded with roxadustat is developed, specifically designed to remodel the inflammatory microenvironment and enhance osteoporotic bone regeneration. By incorporating minimal methacrylated hyaluronic acid (HAMA) into an o-nitrobenzyl functionalized gelatin (GelNB) matrix, a gelatin hydrogel with a fracture strength of 10 MPa is achieved, providing exceptional structural stability and enabling precise scaffold fabrication through digital light processing (DLP) 3D printing. Validated through cell experiments and animal studies, the hydrogel scaffold supports cell adhesion and migration, offers excellent tissue compatibility, and is fully degradable, meeting the requirements of a therapeutic scaffold. Including roxadustat further enhances the scaffold's functionality by regulating the inflammatory microenvironment via hypoxia-inducible factor-1α (HIF-1α) signaling, significantly improving bone defect repair in osteoporotic models. This drug-loaded scaffold effectively addresses inflammation-induced limitations and enhances the regenerative capacity of the affected area, paving the way for improved therapeutic outcomes in osteoporotic bone repair.

The role of the immune system in osteoarthritis: mechanisms, challenges and future directions

Osteoarthritis (OA) is a chronic joint disease that has long been considered a simple wear-and-tear condition. Over the past decade, research has revealed that various inflammatory features of OA, such as low-grade peripheral inflammation and synovitis, contribute substantially to the pathophysiology of the disease. Technological advances in the past 5 years have revealed a large diversity of innate and adaptive immune cells in the joints, particularly in the synovium and infrapatellar fat pad. Notably, the presence of synovial lymphoid structures, circulating autoantibodies and alterations in memory T cell and B cell populations have been documented in OA. These data indicate a potential contribution of self-reactivity to the disease pathogenesis, blurring the often narrow and inaccurate line between chronic inflammatory and autoimmune diseases. The diverse immune changes associated with OA pathogenesis can vary across disease phenotypes, and a better characterization of their underlying molecular endotypes will be key to stratifying patients, designing novel therapeutic approaches and ultimately ameliorating treatment allocation. Furthermore, examining both articular and systemic alterations, including changes in the gut-joint axis and microbial dysbiosis, could open up novel avenues for OA management.

Metabolic Reprogramming in Stromal and Immune Cells in Rheumatoid Arthritis and Osteoarthritis: Therapeutic Possibilities

Metabolic reprogramming of stromal cells, including fibroblast-like synoviocytes (FLS) and chondrocytes, as well as osteoclasts (OCs), are involved in the inflammatory and degenerative processes underlying rheumatoid arthritis (RA) and osteoarthritis (OA). In RA, FLS exhibit mTOR activation, enhanced glycolysis and reduced oxidative phosphorylation, fuelling inflammation, angiogenesis, and cartilage degradation. In OA, chondrocytes undergo metabolic rewiring, characterised by mTOR and NF-κB activation, mitochondrial dysfunction, and increased glycolysis, which promotes matrix metalloproteinase production, extracellular matrix (ECM) degradation, and angiogenesis. Macrophage-derived immunometabolites, including succinate and itaconate further modulate stromal cell function, acting as signalling molecules that modulate inflammatory and catabolic processes. Succinate promotes inflammation whilst itaconate is anti-inflammatory, suppressing inflammatory joint disease in models. Itaconate deficiency also correlates inversely with disease severity in RA in humans. Emerging evidence highlights the potential of targeting metabolic processes as promising therapeutic strategies for connective tissue disorders.

Neutrophils: a Central Point of Interaction Between Immune Cells and Nonimmune Cells in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease involving activation of the immune system and the infiltration of immune cells. As the first immune cells to reach the site of inflammation, neutrophils perform their biological functions by releasing many active substances and forming neutrophil extracellular traps (NETs). The overactivated neutrophils in patients with RA not only directly damage tissues but also, more importantly, interact with various other immune cells and broadly activate innate and adaptive immunity, leading to irreversible joint damage. However, owing to the pivotal role and complex influence of neutrophils in maintaining homoeostasis, the treatment of RA by targeting neutrophils is very difficult. Therefore, a comprehensive understanding of the interaction pathways between neutrophils and various other immune cells is crucial for the development of neutrophils as a new therapeutic target for RA. In this study, the important role of neutrophils in the pathogenesis of RA through their crosstalk with various other immune cells and nonimmune cells is highlighted. The potential of epigenetic modification of neutrophils for exploring the pathogenesis of RA and developing therapeutic approaches is also discussed. In addition, several models for studying cell‒cell interactions are summarized to support further studies of neutrophils in the context of RA.

Resolution of inflammation during rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes synovial joint inflammation as well as bone destruction and erosion, typically characterized by joint pain, swelling, and stiffness, with complications and persistent pain after remission posing a significant health burden for RA patients. The etiology of RA has not yet been fully elucidated, but a large number of studies have shown that the initiation of inflammation in RA is closely related to T-cell activation, the production of a variety of pro-inflammatory cytokines, macrophage M1/M2 imbalance, homeostatic imbalance of the intestinal flora, fibroblast-like synoviocytes (FLSs) and synovial tissue macrophages (STMs) in the synovial lumen of joints that exhibit an aggressive phenotype. While the resolution of RA is less discussed, therefore, we provided a systematic review of the relevant remission mechanisms including blocking T cell activation, regulating macrophage polarization status, modulating the signaling pathway of FLSs, modulating the subpopulation of STMs, and inhibiting the relevant inflammatory factors, as well as the probable causes of persistent arthritis pain after the remission of RA and its pain management methods. Achieving resolution in RA is crucial for improving the quality of life and long-term prognosis of patients. Thus, understanding these mechanisms provide novel potential for further drug development and treatment of RA.

Combination treatment with anti-RANKL and antibiotics for preventing joint destruction in septic arthritis

Septic arthritis, the most severe joint disease, is frequently caused by Staphylococcus aureus (S. aureus). A substantial proportion of patients with septic arthritis experience poor joint outcomes, often necessitating joint replacement surgery. Here, we show that monocyte depletion confers full protection against bone erosion in a septic arthritis mouse model. In the infected synovium, Ly6Chi monocytes exhibited increased expression of osteoclastogenesis-related molecules, including CCR2, c-Fms, and RANK. S. aureus lipoproteins induced elevated levels of RANKL, MCSF, and CCL2 in joints, with synovial fibroblasts identified as the major RANKL producer. Anti-RANKL treatment prevented bone destruction in both local and hematogenous septic arthritis murine models. Importantly, combining anti-RANKL treatment with antibiotics provided robust protection against joint damage. Our results indicate that the infiltration and transformation of monocytes into bone-destructive, osteoclast-like cells are key mechanisms in septic arthritis. Combining anti-RANKL and antibiotic therapy represents a promising therapy against this devastating disease.

Identification of immune characteristic biomarkers and therapeutic targets in cuproptosis for rheumatoid arthritis by integrated bioinformatics analysis and single-cell RNA sequencing analysis

Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disorder intricately liked with inflammation. Cuproptosis, an emerging type of cell death, has been implicated in the initiation and development of RA. However, the exact alterations in the expression and biological function of cuproptosis-related genes (CRGs) in RA remain poorly understood. Therefore, our study aims to elucidate the potential association between CRGs and RA, with the goal of identifying novel biomarkers for the treatment and prognosis of RA.

Methods

In this study, we identified ten differentially expressed cuproptosis-related genes (DE-CRGs) between patients with RA and controls. Through comprehensive functional enrichment and protein-protein interaction (PPI) network analysis, we explored the functional roles of the DE-CRGs. Additionally, we investigated the correlation between DE-CRGs and immune infiltration, immune factors, diagnostic efficacy, and potential therapeutic drugs.

Results

Leveraging single-cell RNA sequencing data, we conducted a detailed analysis to elucidate alterations in various cell clusters associated with RA. Our study unveiled a significant association between DE-CRGs and diverse biological functions, as well as potential drug candidates.

Discussion

These findings provide crucial insights into the involvement of DE-CRGs in the pathogenesis of RA and shed light on potential therapeutic strategies.

Spatial patterning of fibroblast TGFβ signaling underlies treatment resistance in rheumatoid arthritis

Treatment-refractory rheumatoid arthritis (RA) is a major unmet need, and the mechanisms driving treatment resistance are poorly understood. To identify molecular determinants of RA non-remission, we performed spatial transcriptomic profiling on pre- and post-treatment synovial tissue biopsies from treatment naïve patients who received conventional DMARDs or adalimumab for 6 months. In the baseline biopsies of non-remission patients, we identified significant expansion of fibrogenic fibroblasts marked by high expression of COMP, a fibrosis-associated extracellular matrix protein. COMPhi fibroblasts localized to perivascular niches that, unexpectedly, served as transcriptional hubs for TGFβ activity. We identified endothelial-derived Notch signaling as an upstream regulator of fibroblast TGFβ signaling via its dual role in driving TGFβ isoform expression and suppressing TGFβ receptors, generating a proximal-distal gradient of TGFβ activity. Further, disruption of steady-state Notch signaling in vitro enabled fibrogenic fibroblast activation. Analysis of post-treatment biopsies revealed marked expansion of COMPhi fibroblasts in non-remission RA patients, despite evidence of successful immune cell depletion, suggesting a spatiotemporal process of fibrogenic remodeling linked to treatment resistance. Collectively, our data implicates targeting of TGFβ signaling to prevent exuberant synovial tissue fibrosis as a potential therapeutic strategy for refractory RA.

ER O-glycosylation in synovial fibroblasts drives cartilage degradation

How arthritic synovial fibroblasts (SFs) activate cartilage ECM degradation remains unclear. GALNT enzymes initiate O-glycosylation in the Golgi; when relocated to the ER, their activity stimulates ECM degradation. Here, we show that in human rheumatoid and osteoarthritic synovial SFs, GALNTs are relocated to the ER. In an RA mouse model, GALNTs relocation occurs shortly before arthritis symptoms and abates as the animal recovers. An ER GALNTs inhibitor prevents cartilage ECM degradation in vitro and expression of this chimeric protein in SFs results in the protection of cartilage. One of the ER targets of GALNTs is the resident protein Calnexin, which is exported to the cell surface of arthritic SFs. Calnexin participates in matrix degradation by reducing ECM disulfide bonds. Anti-Calnexin antibodies block ECM degradation and protect animals from RA. In sum, ER O-glycosylation is a key switch in arthritic SFs and glycosylated surface Calnexin could be a therapeutic target.

Biomimetic Nanoparticles Inhibit the HIF-1α/iNOS/NLRP3 Pathway to Alleviate Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease distinguished by inflammatory synovitis. Chrysin can alleviate the inflammatory response and inhibit the progression of RA. However, unfavorable physicochemical properties and nonselective biodistribution of chrysin make it difficult to achieve good therapeutic efficacy. To address these challenges, we developed a biomimetic nanocarrier to enhance the targeted delivery of chrysin to synoviocytes, a key cellular component in RA pathology. Our nanodrug, FMPlipo@C, was engineered by integrating fibroblast-like synoviocyte (FLS) membrane proteins into chrysin-loaded liposomes. This innovative approach harnesses homologous targeting mediated by FLS membrane proteins to direct liposomes to inflamed joints, facilitating cargo release within synoviocytes. We showed that FMPlipo@C reduces inflammation in collagen-induced rheumatoid arthritis (CIA) model mice by inhibiting the HIF-1α/iNOS/NLRP3 pathway, protecting cartilage, and preventing bone erosion, thus reducing swelling and stiffness. This study offers valuable insights into the development of novel therapeutic strategies for the treatment of RA.

Advances in Extracellular Matrix-Associated Diagnostics and Therapeutics

The extracellular matrix (ECM) is the common denominator of more than 50 chronic diseases. Some of these chronic pathologies lead to enhanced tissue formation and deposition, whereas others are associated with increased tissue degradation, and some exhibit a combination of both, leading to severe tissue alterations. To develop effective therapies for diseases affecting the lung, liver, kidney, skin, intestine, musculoskeletal system, heart, and solid tumors, we need to modulate the ECM's composition to restore its organization and function. Across diverse organ diseases, there are common denominators and distinguishing factors in this fibroinflammatory axis, which may be used to foster new insights into drug development across disease indications. The 2nd Extracellular Matrix Pharmacology Congress took place in Copenhagen, Denmark, from 17 to 19 June 2024 and was hosted by the International Society of Extracellular Matrix Pharmacology. The event was attended by 450 participants from 35 countries, among whom were prominent scientists who brought together state-of-the-art research on organ diseases and asked important questions to facilitate drug development. We highlight key aspects of the ECM in the liver, kidney, skin, intestine, musculoskeletal system, lungs, and solid tumors to advance our understanding of the ECM and its central targets in drug development. We also highlight key advances in the tools and technology that enable this drug development, thereby supporting the ECM.

NaHS@Cy5@MS@SP nanoparticles improve rheumatoid arthritis by inactivating the Hedgehog signaling pathway through sustained and targeted release of H2S into the synovium

BACKGROUND

Aberrant proliferation and inflammation of fibroblast-like synoviocytes (FLSs) significantly contribute to the pathogenesis of rheumatoid arthritis (RA). Deficiency of hydrogen sulfide (H2S) is a driving force for the development of RA, and the short half-life of the H2S-releasing donor sodium hydrosulfide (NaHS) limits its clinical application in RA therapy. Designing a targeted delivery system with slow-release properties for FLSs could offer novel strategies for treating RA.

METHODS

Herein, we designed a strategy to achieve slow release of H2S targeted to the synovium, which was accomplished by synthesizing NaHS-CY5@mesoporous silic@LNP targeted peptide Dil (NaHS@Cy5@MS@SP) nanoparticles.

RESULTS

Our results demonstrated that NaHS@Cy5@MS@SP effectively targets FLSs, upregulates H2S and its-producing enzyme cystathionine-γ-lyase (CSE) in the joints of arthritic mice. Overexpression of CSE inhibited the proliferation, migration, and inflammation of FLSs upon lipopolysaccharide (LPS) exposure, effects that were mimicked by NaHS@Cy5@MS@SP. In vivo studies showed that NaHS@Cy5@MS@SP achieved a threefold higher AUCinf than that of free NaHS, significantly improving the bioavailability of NaHS. Further, NaHS@Cy5@MS@SP inhibited synovial hyperplasia and reduced bone and cartilage erosion in the DBA/1J mouse model of collagen-induced arthritis (CIA), which was superior to NaHS. RNA sequencing and molecular studies validated that NaHS@Cy5@MS@SP inactivated the Hedgehog signaling pathway in FLSs, as evidenced by reductions in the protein expression of SHH, SMO, GLI1 and phosphorylated p38/MAPK.

CONCLUSION

This study highlights NaHS@Cy5@MS@SP as a promising strategy for the controlled and targeted delivery of H2S to synoviocytes, offering potential for RA management.

Ferrostatin-1 reduces the inflammatory response of rheumatoid arthritis by decreasing the antigen presenting function of fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a systemic chronic autoimmune disease with complex mechanism. Currently, ferroptosis is believed to play a role in it, but the specific mechanism is unknown, especially in immune response. In this study, we demonstrated that the high expression of major histocompatibility complex I (MHC-I) molecules in RA fibroblast-like synoviocytes (FLSs) is an antigen-presenting cell property and that this property is closely related to the increase in antigens after citrullination. Moreover, we detected higher levels of ferroptosis among FLSs from RA patient than among FLSs from OA patients. Ferroptosis can increase the expression of citrullinated histone H3 (cit-h3) by promoting the production of peptidyl arginine deiminase 4 (PAD4), which further promotes the expression of MHC-I molecules. We cocultured RA-FLSs treated with ferroptosis drugs with selected CD8 + T cells to assess the effect of ferroptosis on the endogenous antigen-presenting function of RA-FLSs. Ferroptosis promoted the proliferation of CD8 + T cells and the release of the inflammatory factors Tumor necrosis factor-α (TNF-α) and Interferon-gamma (IFN-γ), which enhanced the inflammatory effect. This phenomenon was also observed in a collagen-induced arthritis (CIA) mouse model. Finally, ferrostatin-1 (fer-1), a ferroptosis inhibitor, inhibited the above effects and reduced the release of inflammatory factors, indicating that ferroptosis may play a therapeutic role in RA and providing new ideas for the treatment of RA in the field of immunity.

Single cell immunoprofile of synovial fluid in rheumatoid arthritis with TNF/JAK inhibitor treatment

Numerous patients with rheumatoid arthritis (RA) manifest severe syndromes, including elevated synovial fluid volumes (SF) with abundant immune cells, which can be controlled by TNF/JAK inhibitors. Here, we apply single-cell RNA sequencing (scRNA-seq) and subsequent validations in SF from RA patients. These analyses of synovial tissue show reduced density of SF-derived pathogenic cells (e.g., SPP1+ macrophages and CXCL13+CD4+ T cells), altered gene expression (e.g., SPP1 and STAT1), molecular pathway changes (e.g., JAK/STAT), and cell-cell communications in drug-specific manners in samples from patients pre-/post-treated with adalimumab/tofacitinib. Particularly, SPP1+ macrophages exhibit pronounced communication with CXCL13+CD4+ T cells, which are abolished after treatment and correlate with treatment efficacy. These pathogenic cell types alone or in combination can augment inflammation of fibroblast-like synoviocytes in vitro, while conditional Spp1 knocking-out reduces RA-related cytokine expression in collagen-induced arthritis mice models. Our study shows the functional role of SF-derived pathogenic cells in progression and drug-specific treatment outcomes in RA.

Preclinical RA: How to halt its progression

Rheumatoid arthritis (RA) is a chronic autoimmune disorder with a complex pathogenesis that evolves through various stages before clinical symptoms emerge. This review outlines the natural history of RA, starting from genetic predisposition and environmental triggers to preclinical autoimmunity and subsequent joint inflammation. Key genetic factors interact with environmental elements like smoking and infections, producing autoantibodies such as anti-citrullinated protein antibodies (ACPA) and rheumatoid factor, which precede clinical manifestations by several years. The preclinical phases offer critical opportunities for intervention aiming at halting disease progression. Preventive strategies including lifestyle modifications, dietary interventions, and targeted immune modulation may halt the progression to clinical RA in those at-risk individuals.

Single-cell RNA sequencing in autoimmune diseases: New insights and challenges

Autoimmune diseases involve a variety of cell types, yet the intricacies of their individual roles within molecular mechanisms and therapeutic strategies remain poorly understood. Single-cell RNA sequencing (scRNA-seq) offers detailed insights into transcriptional diversity at the single-cell level, significantly advancing research in autoimmune diseases. This article explores how scRNA-seq enhances the understanding of cellular heterogeneity and its potential applications in the etiology, diagnosis, treatment, and prognosis of autoimmune diseases. By revealing a comprehensive cellular landscape, scRNA-seq illuminates the functional regulation of different cell subtypes during disease progression. It aids in identifying diagnostic and prognostic markers, and analyzing cell communication networks to uncover potential therapeutic targets. Despite its valuable contributions, addressing the limitations of scRNA-seq is essential for making further advancements.

Regulation of pathologic fibroblast functions in digestive diseases: a role for hypoxia?

The recent uncovering of fibroblast heterogeneity has given great insight into the versatility of the stroma. Among other cellular processes, fibroblasts are now thought to contribute to the coordination of immune responses in a range of chronic inflammatory diseases and cancer. Although the pathologic roles of myofibroblasts, inflammatory fibroblasts, and cancer-associated fibroblasts in disease are reasonably well understood, the mechanisms behind their activation remain to be uncovered. In the gastrointestinal (GI) tract, several interleukins and tumor necrosis factor superfamily members have been identified as possible mediators driving the acquisition of inflammatory and fibrotic properties in fibroblasts. In addition to cytokines, other microenvironmental factors such as nutrient and oxygen availability are likely contributors to this process. In this respect, the phenomenon of low cellular oxygen levels known as hypoxia is common in a plethora of GI diseases. Indeed, the cross talk between hypoxia and inflammation is well-documented, with an abundance of studies suggesting that oxygen-sensing enzymes may have regulatory effects on inflammatory signaling pathways such as NF-κB. However, the impact that this has in GI fibroblasts in the context of chronic diseases has not been fully uncovered. Here we discuss the role of fibroblasts in GI diseases, the mediators that have emerged as regulators of their functions and the potential impact of hypoxia in this process, highlighting areas that require further investigation.

SPP1hi macrophages, NKG7 T cells, CCL5hi fibroblasts, and IgM plasma cells are dominant features of necrobiosis

Necrobiosis is a histologic term used to describe abnormal deposits of "degenerating" collagen within the skin. It can be found as an incidental finding in various granulomatous conditions, but is a hallmark of necrobiosis lipoidica (NL) and necrobiotic xanthogranuloma (NXG). There is limited prior research on necrobiosis. Here, we employed single-cell analysis of lesional and nonlesional skin to study the pathophysiology of necrobiosis. Our findings demonstrate that necrobiotic lesional skin is characterized by SPP1hi macrophages expressing MARCO; NKG7-expressing effector CD8+ T cells coexpressing CCL5, IFNG, GZMs, and PRF1; CCL5hi fibroblasts coexpressing CXCL9, diverse collagens (e.g., COL4A4, COL11A1, COL8A1), and TIMP1; and IGHM-expressing plasma cells. Integrative analysis of signaling ligands and receptor expression identified strong cell-cell communication between NKG7+ T cells, CCL5hi fibroblasts, and SPP1-expressing macrophages. In contrast, these cell populations were not dominant features of systemic sclerosis, another collagen deposition disease. Furthermore, although SPP1-expressing macrophages were detectable in sarcoidosis, IFNG-expressing T cells were a more defining feature of sarcoidosis compared with NL and NXG. From these findings, we speculate that necrobiosis results from the deposition of diverse collagens and ECM proteins through a process driven by CCL5-expressing fibroblasts and SPP1-expressing macrophages.

CCN2 mediates fibroblast-macrophage interaction in knee arthrofibrosis based on single-cell RNA-seq analysis

Knee arthrofibrosis, characterized by excessive matrix protein production and deposition, substantially impairs basic daily functions, causing considerable distress and financial burden. However, the underlying pathomechanisms remain unclear. Here, we characterized the heterogeneous cell populations and cellular pathways by combination of flow cytometry and single-cell RNA-seq analysis of synovial tissues from six patients with or without knee arthrofibrosis. Increased macrophages and fibroblasts were observed with decreased numbers of fibroblast-like synoviocytes, endothelial cells, vascular smooth muscle cells, and T cells in the arthrofibrosis group compared with negative controls. Notably, fibroblasts were discovered to interact with macrophages, and lead to fibrosis through TGF-β pathway induced CCN2 expression in fibroblasts. CCN2 was demonstrated to be required for fibroblast pro-fibrotic functions (activation, proliferation, and migration) through TGFBR/SMAD pathway. The expression of CCN2 was positively correlated with the collagen volume and TGF-β expression and negatively associated with patient-reported outcome measures in another cohort of patients with knee arthrofibrosis. Our study reveals the role of CCN2 in the fibroblast-macrophage interaction through TGF-β pathway which might help to shed light on CCN2 as a potential biomarker.

Spatial transcriptomics in autoimmune rheumatic disease: potential clinical applications and perspectives

Spatial transcriptomics is a cutting-edge technology that analyzes gene expression at the cellular level within tissues while integrating spatial location information. This concept, which combines high-plex RNA sequencing with spatial data, emerged in the early 2010s. Spatial transcriptomics has rapidly expanded with the development of technologies such as in situ hybridization, in situ sequencing, in situ spatial barcoding, and microdissection-based methods. Each technique offers advanced mapping resolution and precise spatial assessments at the single-cell level. Over the past decade, the use of spatial transcriptomics on clinical samples has enabled researchers to identify gene expressions in specific diseased foci, significantly enhancing our understanding of cellular interactions and disease processes. In the field of rheumatology, the complex and elusive pathophysiology of diseases such as rheumatoid arthritis, systemic lupus erythematosus, and Sjögren's syndrome remains a challenge for personalized treatment. Spatial transcriptomics provides insights into how different cell populations interact within disease foci, such as the synovial tissue, kidneys, and salivary glands. This review summarizes the development of spatial transcriptomics and current insights into the pathophysiology of autoimmune rheumatic diseases, focusing on immune cell distribution and cellular interactions within tissues. We also explore the potential of spatial transcriptomics from a clinical perspective and discuss the possibilities for translating this technology to the bedside.

Application trends of hydrogen-generating nanomaterials for the treatment of ROS-related diseases

Reactive oxygen species (ROS) play essential roles in both physiological and pathological processes. Under physiological conditions, appropriate amounts of ROS play an important role in signaling and regulation in cells. However, too much ROS can lead to many health problems, including inflammation, cancer, delayed wound healing, neurodegenerative diseases (such as Parkinson's disease and Alzheimer's disease), and autoimmune diseases, and oxidative stress from excess ROS is also one of the most critical factors in the pathogenesis of cardiovascular and metabolic diseases such as atherosclerosis. Hydrogen gas effectively removes ROS from the body due to its good antioxidant properties, and hydrogen therapy has become a promising gas therapy strategy due to its inherent safety and stability. The combination of nanomaterials can achieve targeted delivery and effective accumulation of hydrogen, and has some ameliorating effects on diseases. Herein, we summarize the use of hydrogen-producing nanomaterials for the treatment of ROS-related diseases and talk about the prospects for the treatment of other ROS-induced disease models, such as acute kidney injury.