Arthritis Research & Therapy

ObjectiveTo evaluate the Cartilage Thickness Score (CTh-Score) as a quantitative measure of cartilage damage severity by assessing its association with three osteoarthritis (OA) milestones and comparing its performance with conventional morphometric measures: radiographic minimum joint space width (JSW) and regional average cartilage thickness. MethodsData were obtained from the Osteoarthritis Initiative (OAI) and the publicly available OAI CTh-Maps and CTh-Score dataset. Three matched case-control designs were used to represent major OA milestones: (i) incident radiographic OA onset, (ii) combined pain and structural progression, and (iii) knee replacement (KR) in the coming 2 years. Progression subjects were extracted from the FNIH Biomarkers Consortium cohort. Cases and controls were compared at 4 years (T-4Y), 2 years (T-2Y), and 0 years (T0) before the milestone. MRI-based CTh-Score and regional average cartilage thickness, as well as JSW, were analyzed cross-sectionally and longitudinally. Associations with case status were assessed using adjusted logistic regression models, and responsiveness was evaluated using longitudinal change and standardized response means. ResultsThe onset cohort included 307 matched case-control pairs, the progression cohort 164 cases and 369 controls, and the KR cohort 81 cases and 324 controls. Across all three study designs, the CTh-Score significantly differentiated cases from controls at all timepoints. In the onset cohort, the CTh-Score was higher in future cases than controls at T-4Y (16.2 vs 12.6, p=0.007), T-2Y (23.5 vs 16.7, p<0.001), and T0 (39.8 vs 18.6, p<0.001), whereas JSW and regional thickness measures showed limited or later discrimination. Similar findings were observed for progression (43.2 vs 33.0 at T-4Y; p<0.001) and KR (55.4 vs 46.1 at T-4Y; p=0.02) cohorts. Longitudinally, CTh-Score changes differentiated cases from controls earlier and more consistently than JSW or regional average thickness, and its responsiveness was consistently the highest across OA milestones and time intervals. In adjusted models, the CTh-Score was independently associated with all outcomes at T-4Y and T-2Y, with odds ratios per standard deviation increase ranging from 1.3 to 2.2. ConclusionThe CTh-Score captures high-resolution cartilage thickness patterns associated with OA onset, progression, and future knee replacement, outperforming conventional morphometric measures in early discrimination, responsiveness, and predictive association. These findings support CTh-Score as a sensitive quantitative marker of cartilage damage severity across the OA continuum.

Purpose To determine whether clinically significant weight loss (>5% of body weight) is associated with slower 2-year knee cartilage degeneration in individuals with and without radiographic osteoarthritis. This study used a cartilage structural assessment score derived from the spatial distribution of cartilage thickness, referred to as the Cartilage Thickness Score (CTh-Score). It is based on cartilage thickness patterns and scores the cartilage between 0 and 100, with higher scores indicating greater severity. Methods We conducted a retrospective matched cohort study within the Osteoarthritis Initiative. High-resolution cartilage thickness maps (CTh-Maps), along with their corresponding CTh-Score, were extracted from a public repository. Participants with complete radiographic and MRI data at baseline and 24 months were stratified by baseline Kellgren-Lawrence (KL) grade into non-radiographic OA (non-ROA; KL<2) and radiographic OA (ROA; KL>=2). Within strata, cases (>5% 2-year weight loss) were propensity score-matched 1:2 to weight-stable controls on age, sex, height, weight, KL grade, joint space width (JSW), KOOS Pain, baseline CTh-Score, and mean cartilage thickness in the medial and lateral femoral and tibial compartments. The primary outcome was 2-year change (delta) in CTh-Score, where higher values indicate worsening. Secondary outcomes were delta JSW, delta regional mean cartilage thickness, and delta KOOS Pain. Non-parametric tests were used. Results We included 164 cases and 328 controls in non-ROA, and 266 cases and 532 controls in ROA. Median (interquartile range) weight loss was -6.10 kg (-8.90, -4.70) versus +0.30 kg (-1.30, 2.20) in non-ROA and -6.80 kg (-9.10, -5.02) versus +0.40 kg (-1.40, 2.82) in ROA (both p<0.001). Weight loss was associated with significantly smaller 2-year increases in CTh-Score: in non-ROA, median 1.58 (0.61, 6.53) vs 3.14 (0.44, 7.12) (p=0.005); in ROA, median 1.69 (0.97, 6.71) vs 2.90 (0.19, 7.38) (p=0.004). No between-group differences were detected for delta JSW or delta regional mean cartilage thickness in any of the 4 ROIs. A trend toward greater KOOS Pain improvement with weight loss was observed in ROA: 2.75 (-3.35, 13.40) vs 0.00 (-5.60, 8.40) (p=0.06). Conclusions Achieving >5% weight loss over 2 years is associated with approximately 50% lower progression in median cartilage degeneration, as assessed by CTh-Score, in both non-ROA and ROA. No change was observed with conventional structural metrics. These findings support weight management as a structural disease-modifying strategy and highlight CTh-Score as a sensitive endpoint.

BackgroundPain is one of the most prevalent and distressing symptoms in juvenile idiopathic arthritis (JIA) and often persists despite treatment. Damage-associated molecular patterns (DAMPs), such as high mobility group box 1 (HMGB1) and S100A8/A9, have been implicated in inflammatory activation and nociceptive sensitization, but their associations with pain are not fully characterized in JIA. MethodsPlasma and paired synovial fluid (SF) samples were obtained from patients with oligoarticular and polyarticular JIA from the Juvenile Arthritis Biobank (JABBA). A discovery cohort (n = 79) was used to investigate associations between biomarkers and pain, and these associations were subsequently examined in a validation cohort (n = 38). Levels of HMGB1, S100A8/A9, IL-6, IL-8, C2C, and TRAP5b were measured using ELISA. Associations between biomarkers and patient-reported pain scores were assessed using multivariable linear regression analyses. ResultsPlasma and SF levels of most biomarkers did not show significant correlations, except for TRAP5b, which demonstrated a moderate correlation. In the discovery cohort, as multivariable linear regression analyses, both CRP and SF HMGB1 ({beta} = 1.14, 95% CI: 0.21-2.08; {beta} = 1.54, 95% CI: 0.06-3.01 respectively in fully adjusted model) were independently associated with higher pain scores. SF S100A8/A9 ({beta} = 1.00, 95% CI: 0.10-1.89) was additionally associated with pain in fully adjusted models. Sensitivity analyses confirmed the robustness of these findings. These associations were further supported in the validation cohort. ConclusionsPain in JIA is associated with both systemic CRP and local alarmin markers, with SF HMGB1 showing a particularly robust association. These findings highlight the importance of local joint HMGB1 in pain mechanisms and suggest a potential role for DAMP-mediated pathways in persistent pain in JIA.

BackgroundChildren with juvenile idiopathic arthritis (JIA) are reported to exhibit increased rates of symptoms affecting emotional regulation and behavior. However, underlying biological mechanisms remain unclear. Neuroinflammation in the central nervous system (CNS) can be triggered by peripheral immune effects and may contribute to these observations. In this study, we aimed to investigate if neurobiological alterations are present in systemic JIA (sJIA), and if CNS neuroinflammation occurs during arthritis, and to explore the potential mechanisms involved. MethodsPlasma samples from patients with active sJIA (n = 16) and sex- and age-matched healthy controls (HCs, n = 16), together with paired samples from the same sJIA patients during inactive disease (n = 12), were analyzed using Olink proteomics to determine the peripheral neurobiological and inflammation protein profiles. Clinical data was retrieved from the Swedish Pediatric Rheumatology Register and medical charts. CNS Neuroinflammatory responses and underlying mechanisms were further explored through in vivo and in vitro experiments. FindingsActive sJIA patients exhibited altered neurobiological protein profiles compared with HCs. These alterations correlated with higher scores of pain and life impact in patients, suggesting that the altered profiles may reflect neurofunctional changes in the patients. Notably, the neurobiological protein profile remained altered even during the inactive phase of the disease. In chronic arthritic mice, microglial activation and impaired neurogenesis were observed in hippocampus, with no significant cortical changes. RNA-seq analysis implicated mitochondrial dysfunction and oxidative stress in mediating neuroinflammation during chronic arthritis in mice. Heme oxygenase 2 (HMOX2) was identified as a peripheral biomarker indicating hippocampal microglia activation. Combined neurobiological and inflammation profiling in sJIA patients implicated Interleukin-6 (IL-6) and Interleukin-18 (IL-18) as key drivers of hippocampal microglia activation during arthritis. InterpretationChronic arthritis is associated with neuroinflammation and altered neurobiological protein profiles in sJIA. HMOX2 emerges as a promising plasma biomarker of CNS changes. IL-6 and especially IL-18 are indicated as key drivers of neuroinflammatory processes. These findings offer insights for clinical monitoring and targeted therapies. FundingThis study was funded by grants from the Swedish Research Council and The Swedish Rheumatism Association. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSChildren with juvenile idiopathic arthritis (JIA) have increased rates of emotional and behavioral disturbances compared with healthy peers. Systemic inflammation and chronic arthritis are suspected to affect the central nervous system, but biological mechanisms in systemic JIA (sJIA) are poorly understood. Added value of this studyIn this study, we demonstrate patients with sJIA have a distinct plasma neurobiological protein profile compared with healthy controls, which correlate with higher pain and life impact scores. In chronic arthritic mice, hippocampal microglial activation, impaired neurogenesis, and mitochondrial dysfunction with oxidative stress are presented. By combining patient and mouse data, we identify heme oxygenase 2 (HMOX2) as a candidate plasma biomarker of hippocampal neuroinflammation and implicate IL-6, and especially IL-18, as key mediators linking chronic arthritis to neurobiological changes. Implications of all the available evidenceThis study provides molecular evidence that neurobiological alterations in sJIA patients and supports incorporating neurobiological and neuropsychiatric monitoring into the clinical follow-up of children with sJIA. We highlight the mechanistic targets and measurable biomarkers (e.g. HMOX2) for future studies and trials aiming to modulate neuroinflammation in chronic arthritis. This study may inform the development of personalized treatment strategies, including IL-18-directed therapies, for patients at risk of neurological or psychosocial complications.

ObjectiveRecently, alternatives to animal testing, such as new approach methodologies, are being developed in the orthopedic research field; animal models still provide valuable insights into the pathogenesis of knee osteoarthritis (OA). However, commonly used models develop OA much more rapidly and severely than those observed in human patients. We aimed to develop a novel murine model that closely mimics the slow progression of human OA with posterior Cruciate ligament (PCL) rupture. Design12-week-old C57BL/6 mice were induced to PCL-rupture (PCL-R) by manually applying an external tibial posterior translation force. We analyzed joint kinematics, histological observations, and bone structure to confirm the absence of concurrent injury on day 0. Then, joint stability and the pathophysiological progression of knee OA were analyzed at 8, 16, and 34 weeks post-PCL-R. The destabilized medial meniscus (DMM) model was also analyzed to compare the OA progression. ResultsNon-invasive PCL-R intervention induced the complete rupture in the central region of PCL without concurrent injury. The PCL-R group showed larger posterior tibial deviation than the INTACT (P=0.008). Regarding the range of motion in the PCL-R group, there was no limitation in range of motion on day 0, but extension limitations occurred at weeks 16 and 34 weeks. Histologically, articular cartilage degeneration in PCL-R was milder than DMM. In the subchondral bone, micro-CT reconstruction images indicated that, compared with the INTACT group, the DMM group observed progressive subchondral bone formation from 16 weeks post-surgery. In contrast, the PCLR group maintained the subchondral bone structure even at 34 weeks. ConclusionsPCL-R model induced mild abnormal mechanical stress depending on posterior instability, and cartilage degeneration occurred more slowly in this model than in DMM models.

ObjectivesMechanical cues are essential for maintaining cartilage function, yet how they integrate with molecular pathways dysregulated in osteoarthritis (OA) remains poorly defined in human tissue. Canonical Wnt signalling influences cartilage biology and cell-matrix interactions, but its role in integrin-dependent mechanoregulation in human cartilage is not fully understood. This study aimed to determine how Wnt activation affects chondrocyte responses to physiological mechanical loading, with a focus on 5{beta}1integrin and cytoskeletal organisation. MethodsHuman cartilage explants from non-OA and OA donors were subjected to short-term physiological cyclic compression. Canonical Wnt signalling was activated with CHIR99021, and integrin-mediated adhesion was modulated using the 5{beta}1 blocking peptide ATN-161 during loading. Chondrocyte responses were assessed by analysing mechanoresponsive and matrix-related gene expression, 5{beta}1 complex formation via proximity ligation assay and actin cytoskeletal organisation by confocal microscopy. ResultsOA chondrocytes exhibited a distinct integrin profile, characterised by increased ITGA5 and ITGB1 but reduced ITGA10 expression. In non-OA cartilage, canonical Wnt activation increased ITGB1 expression and 5{beta}1 integrin complex formation, while mechanical loading further enhanced ITGA5 and ITGB1 transcription under Wnt-activated conditions. Under control conditions, loading induced mechanoresponsive and anabolic gene expression in non-OA cartilage; these responses were attenuated following Wnt-activation and partially restored by 5{beta}1 blockade. Mechanical loading induced F-actin reorganization toward a more cortical distribution across cartilage zones, irrespective of disease status or treatment. Wnt activation did not result in distinct cytoskeletal phenotypes under load, and load-induced actin remodelling was comparable between groups. ConclusionThese findings identify 5{beta}1integrin as a key mediator linking canonical Wnt signalling to altered chondrocyte mechanoresponsiveness in human cartilage. While mechanical loading consistently induced cortical F-actin reorganization, Wnt-associated changes in load responsiveness arose primarily from integrin-dependent mechanisms rather than major alterations in actin organization. This study highlights the complexity of cartilage mechanoregulation and identifies integrin-mediated signaling as important contributors to canonical Wnt-driven alterations in load responsiveness relevant to OA.

Over half of patients with rheumatoid arthritis (RA) report clinically meaningful pain, despite treatment with disease-modifying antirheumatic drugs (DMARDs). While joint inflammation is a known cause of pain in patients with rheumatic diseases, emerging data indicate that many patients also suffer from centralized or nociplastic pain. There is a critical unmet need to characterize the altered cellular state that distinguishes patients with centralized pain. In the IMPACT study, 39 RA patients with minimal joint inflammation but varying levels of pain underwent quantitative sensory testing (QST) to assess nociplastic pain, completed patient-reported outcome (PRO) surveys, and provided blood samples for immune profiling. Supervised and unsupervised analysis of the multi-parameter spectral flow cytometry data identified immune cell populations correlated with nociplastic pain and patient-reported pain intensity. Moreover, analyses of single-cell RNA-seq from a subset of 22 patients revealed differences in cell type proportions and differential expression between the high and low pain groups. These studies provide novel insights into the role of circulating immune cells in altered central nervous system (CNS) pain regulation in adults with RA.

BackgroundExcessive accumulation of fibrillar collagen causes pathological scarring and fibrosis. A promising anti-fibrotic strategy targets the extracellular assembly of collagen fibrils rather than intracellular synthesis pathways. We previously developed a chimeric monoclonal antibody targeting the C-terminal telopeptide of the 2(I) chain of human collagen I that effectively disrupts fibrillogenesis. This study details the engineering of a humanized antibody variant optimized for therapeutic application, augmented with a collagen-binding peptide (CBP) to enhance targeted retention in fibrotic tissues. MethodsA humanized ACA was engineered by in silico homology modeling, complementarity-determining region grafting, and sequence optimization to eliminate chemical liabilities. Variants were expressed in mammalian cells and evaluated for binding kinetics and specificity. To improve spatial localization, the CBP was fused to the antibody. The lead variant was assessed for in vitro cytotoxicity, matrix retention, and in vivo efficacy using a rabbit model of post-traumatic knee arthrofibrosis. ResultsThe humanized ACA variants maintained high specificity and affinity for the 2Ct target domain. Fusing the CBP to the C-terminus of the light chain (C-cbpACA) successfully enhanced matrix retention without compromising target engagement or causing cellular toxicity. In the rabbit arthrofibrosis model, intra-articular C-cbpACA delivery significantly reduced flexion contracture and decreased total collagen deposition in the joint capsule compared to untreated controls. ConclusionWe successfully engineered a clinically viable, humanized, and matrix-targeted anti-fibrotic antibody that specifically inhibited extracellular collagen assembly and exhibited enhanced localization within fibrotic tissues. This construct represents a promising therapeutic strategy for mitigating pathological scarring and improving post-traumatic functional outcomes.

ObjectivesPatients with osteoarthritis (OA) affecting multiple joints have poorer health outcomes than those without, yet most research examines isolated joints, leaving a gap in multi-joint disease. This study aimed to describe radiographically defined hip (rHOA) and knee OA (rKOA) within UK Biobank (UKB), exploring interrelationships across joints, and associations with joint pain, obesity, race and deprivation. MethodsAutomated machine learning was applied to left and right hip and knee dual-energy X-ray absorptiometry scans. Radiographic OA (rOA) was defined as custom grades [&ge;]2. Joint pain was assessed through self-reported questionnaires. Descriptive statistics summarised the population characteristics. Logistic regression models examined bilateral and cross-joint associations, as well as associations with joint pain. Adjustments were made for age, sex, race, height, weight and deprivation. Other models examined the associations between body size and OA. ResultsAmong 59,475 individuals (mean age 65 years; 52.8% female), rHOA prevalence was 4,098 (6.9%)) and 4,841 (8.1%) for the right and left joints, respectively. The corresponding estimates for rKOA were 3,750 (6.3%) and 4,220 (7.1%). Overall, increasing grades of rOA and number of joints affected were more strongly associated with joint pain. Regarding joint-interrelationships, bilateral associations were stronger at the knee, whereas cross-joint associations (hip-knee) were weaker. Associations with BMI and height differed between the hip and knee. ConclusionsRadiographic hip and knee OA exhibit distinct patterns of interrelationship, associations with symptoms and risk factors, suggesting heterogeneity in disease process and the need for joint-specific treatment. Key MessagesO_ST_ABSWhat is already known on this topic?C_ST_ABSO_LIOsteoarthritis (OA) commonly affects the hip and knee and is associated with pain and disability, with recognised risk factors such as age, obesity and deprivation. C_LIO_LIIncreasing interest in multi-joint OA challenges the traditional concept of lower-limb OA as a monoarthritis, but most research examines joints in isolation. C_LIO_LIGenetic evidence suggests that hip and knee OA may differ in underlying mechanisms, yet population-scale comparisons are limited. C_LI What this study adds?O_LIAmong 59,574 individuals, this study identifies that radiographic OA captures structurally and clinically relevant disease with increasing severity and greater number of joints affected, positively associated with chronic joint pain. C_LIO_LIRadiographic hip and knee OA demonstrated strong bilateral but weaker cross-joint associations, indicating preferential within-joint symmetry. C_LIO_LIRisk factors differed by anatomical site with BMI and weight strongly associated with knee OA and weakly associated with hip OA. Height showed the opposite associations. C_LI How this study might affect research, practice or policy?O_LIThese findings support that hip and knee OA may partially represent different disease processes rather than a single condition. C_LIO_LIClinical practice should consider cumulative joint involvement and joint-specific risk factors. C_LIO_LIFuture research should consider the development of more targeted treatment to prevent multi-joint progression. C_LI

ObjectivesKnee osteoarthritis (KOA) is a leading cause of disability, yet which patients will experience structural decline remains unclear. Body mass index (BMI) and lower limb alignment are established risk factors for KOA, but their independent and interactive effects on compartment-specific cartilage loss and total knee replacement (TKR) have not been characterized at scale. MethodsWe analyzed 5,832 limbs from 3,016 participants in the Osteoarthritis Initiative followed over 7 years. Cartilage thickness in the weight-bearing medial and lateral femur and tibia was quantified, and lower limb alignment was measured using hip-knee-ankle (HKA) angle obtained from full-limb radiographs. Linear mixed-effects models estimated the independent and interactive effects of BMI and lower limb alignment on longitudinal cartilage thinning, and mixed-effects logistic regression modeled TKR risk. ResultsIn the medial compartment, BMI and varus alignment interacted multiplicatively, with their combined effect exceeding the sum of independent contributions (femur: p = 0.011; tibia: p < 0.001). At +10 kg/m{superscript 2} BMI and +10{degrees} varus, the rate of medial femur cartilage thinning was 243.5% faster than the reference rate. In the lateral compartment, BMI and valgus alignment were independently associated with faster cartilage thinning, with no significant interaction. TKR risk increased exponentially with HKA deviation (odds ratio [OR] = 1.38 per 1{degrees}; [~]five-fold at 5{degrees} malalignment) but was not associated with BMI. ConclusionBMI and lower limb alignment influence structural KOA progression through compartment-specific pathways. The multiplicative interaction in the medial compartment identifies high BMI combined with varus malalignment as a discrete high-risk phenotype, with implications for clinical risk stratification and disease-modifying intervention design.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that causes joint destruction along with extra-articular morbidity and early mortality. Abatacept (CTLA-4 Ig), a blocker of lymphocyte co-stimulation, has become a well-accepted biologic treatment with proven efficacy in established-RA and for preventing disease onset in predisposed individuals. To investigate the immunologic implications of abatacept treatment, we conducted a prospective, open-label trial with multi-omic single-cell analyses of lymphocytes and BCR repertoire profiling at predefined intervals. Treatment-induced low-disease activity correlated with coordinated depletion of circulating peripheral helper cells (Tph), late-activated naive cells (late-aNAV), and of CD27-IgD- (Double negative, DN) Zeb2+CD11c+ T-box transcription factor 21 (Tbet+) DN2 unconventional memory B cells, implicated in the tertiary lymphoid structures responsible for the propagation of pathologic autoimmune responses and joint destruction. Among B-cell subsets, DN2 had the greatest representation of molecular machinery for antigen-uptake, processing, and presentation. Among memory B-cell subsets, DN2 had the lowest representation of somatically generated N-glycosylation sites and somatic hypermutation. Yet abatacept induced DN2 cells to express elevated CXCR4 levels, which normalized upon drug withdrawal, suggesting that abatacept treatment may cause these cells to traffic out of pathologic synovial infiltrates. In conclusion, we have documented that abatacept affects the circulating immune cellular drivers of disease activity, Tph, late-aNAV and DN2. Therapeutic depletion of these pathologic lymphocyte subsets is associated with clinical benefits that can persist after therapy cessation. Hence, levels of these subsets may serve as surrogates for the overall burden of disease and potential response to abatacept therapy. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=62 SRC="FIGDIR/small/26348386v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@b44131org.highwire.dtl.DTLVardef@241f4eorg.highwire.dtl.DTLVardef@18361f6org.highwire.dtl.DTLVardef@9470b7_HPS_FORMAT_FIGEXP M_FIG C_FIG One Sentence SummaryMulti-omics analyses showed costimulatory blockade depletes trafficking DN2 B cells and Tph cells that correlates with rheumatoid disease response.

Abstract: Objective This study aimed to systematically screen for potential candidate biomarkers and identify therapeutic targets associated with gouty arthritis (GA) through integrated analyses of single-cell and bulk RNA sequencing (RNA-seq) data. Methods The single-cell dataset GSE211783 and the bulk RNA-seq dataset GSE160170 were analyzed using a series of bioinformatic approaches, including cell clustering, differential expression analysis, immune cell infiltration assessment, protein-protein interaction network construction, gene set enrichment analysis, as well as drug sensitivity evaluation. To establish an animal model of GA, monosodium urate crystals were injected intra-articularly into experimental mice. Joint swelling was evaluated, and morphological changes in joint tissues were analyzed through hematoxylin-eosin staining. The presence of TREM1-positive cells was detected by immunohistochemistry and the level of TREM1 protein expression in joint tissues were assessed by Western blotting. Results We identified 102 differentially expressed genes (DEGs) and 14 signaling pathways associated with GA. The PPI network revealed 25 hub genes, of which 17 (including TREM1, TNF, PTGS2, and NLRP3) were highly expressed and 8 (including FCGR3B and CXCR6) showed low expression in the GA samples. These genes correlated significantly with the infiltration levels of macrophages. Among the hub genes, TREM1 was selected for further validation because it correlated significantly with all 14 differential pathways. In animal experiments, GA mice developed marked joint swelling and inflammatory tissue injury, along with a significant increase in TREM1-positive cells and TREM1 protein expression. Conclusion Integrative analysis of single-cell and bulk RNA-seq data identified 102 GA-related DEGs and 14 key pathways, from which 25 hub genes were screened. TREM1 is significantly upregulated in GA and may be linked to macrophage function, providing new insights into biomarker and therapeutic target discovery for GA.

Background and purposeIn the QUADX-1 trial, we randomized 140 patients with severe knee osteoarthritis (OA) eligible for a knee arthroplasty to home-based exercise for 12 weeks. Seventy-nine (68%) of the 117 patients, who completed the exercise intervention, postponed surgery. Here, we report how many patients, who completed the 12-week exercise intervention, had received a knee arthroplasty at 2 years and describe their initial exercise response. MethodsFrom the QUADX-1 trial, we had the following: isometric knee-extensor strength, Oxford Knee Score (OKS), Knee Osteoarthritis Outcome Score (KOOS), average knee pain last week (0-10 numeric rating scale [NRS]), 6-minute walk test, stair climbing test, and self-reported exercise behaviour. ResultsAt the 2-year follow-up, 50 (43%) of the 117 patients had received a knee arthroplasty (KA group) and 67 (57%) had not (NO-KA group). Compared with the KA group, the NO-KA group had less severe radiographic OA at baseline (KL grade 4: 38% vs 55%) and showed greater-- and often clinically relevant--improvements after the 12-week exercise intervention, including knee pain (-2.1 vs -0.1 NRS points), OKS (+6.9 vs +0.5 points), and KOOS ADL (+13.9 vs +1.3 points). ConclusionTwo years after completing the initial 12-week QUADX-1 exercise intervention, more than half the cohort had not received a knee arthroplasty despite initially being considered eligible. Those who had not received a knee arthroplasty at two years had less severe radiographic OA at baseline and generally responded better to 12-week exercise two years earlier, compared to those who had. ClinicalTrials.gov-IDNCT02931058.

ObjectivesCirculating monocytes from rheumatoid arthritis (RA) patients are pre-primed for inflammatory activation, but their disease-intrinsic features have not been systematically characterized. Given the important role of metabolism in shaping immune cell function, we aimed to determine how this pre-primed state is underpinned metabolically and whether these changes persist across different activation states, using an unbiased multi-omics approach. MethodsPeripheral blood CD14 monocytes from RA patients and matched healthy donors were analyzed in an undifferentiated state (M0) and after differentiation into classically activated M(IFN{gamma}+LPS) and alternatively activated M(IL-4) macrophages, followed by acute lipopolysaccharide (LPS) stimulation. Metabolomic (untargeted LC-MS/MS), transcriptomic (RNA-seq), and proteomic (label-free mass LC-MS/MS) profiling were performed. Data was comprehensively analyzed by weighted gene correlation network analysis, differential analysis, gene set enrichment analysis, multi-omics factor analysis and metabolic flux modeling. ResultsRA monocytes exhibited a stable disease-driven signature across activation states. Integration of metabolomic, transcriptomic and proteomic data revealed an unexpected convergence on metabolic-secretory coupling, with depletion of nucleotide and redox metabolites, downregulation of mitochondrial and translational pathways, and remodeling of the secretory apparatus, including loss of cis-Golgi components. Consistently, metabolic modeling predicted reduced glycosylation fluxes, connecting metabolic changes to altered secretory capacity. ConclusionsRA monocytes adopt a stable, disease-intrinsic state that persists across activation conditions. Multi-omics data identify a linked metabolic and secretory defect, with reduced glycosylation capacity as a potential functional consequence. This metabolic-secretory coupling represents a defining feature of RA monocyte dysfunction and a potential therapeutic target.

Background: Rheumatoid arthritis (RA) has a preclinical period characterised by elevations in serum autoantibodies. Identifying the timing and magnitude of autoantibody trajectory changes may inform screening strategies and preventative interventions. Methods: Using a Bayesian multivariate segmented regression, we jointly modelled longitudinal autoantibody trajectories from two Department of Defense Serum Repository cohorts (Sample A: 209 matched case-control pairs, 1566 samples, six biomarkers; Sample B: 309 cases with two matched controls each, 2758 samples, eight biomarkers). Change-points and magnitudes of change were estimated simultaneously under a multivariate likelihood with an unstructured residual correlation matrix. Results: In Sample A, five of six biomarkers exhibited pre-diagnostic trajectory shifts with 95% highest posterior density intervals excluding zero. RF-IgM demonstrated the earliest change-point at 8.10 years before diagnosis (95% HPDI: -10.47, -5.73), followed by ACPA-IgG at 7.43 years (95% HPDI: -9.33, -5.76). In Sample B, only the four IgG isotypes showed pre-diagnostic shifts, with anti-CCP3 (IgG) earliest at 7.00 years (95% HPDI: -8.48, -5.29). A composite metric integrating timing and magnitude reordered rankings. Conclusions: This Bayesian framework enables simultaneous estimation of change-points and magnitudes across correlated autoantibodies while fully characterising uncertainty, offering a complementary approach to prior divergence-based methods for understanding preclinical RA autoimmunity.

BackgroundRheumatoid arthritis (RA) is a chronic immune-mediated inflammatory disease characterized by a heterogeneous clinical course with periods of remission and flare. Although biologic DMARDs (bDMARDs) have revolutionized RA treatment by enabling sustained disease control, their long-term use is associated with adverse effects and high costs, making dose tapering an attractive but clinically challenging strategy. The lack of reliable biomarkers to predict flare risk limits safe implementation of treatment de-escalation. This study aimed to identify novel circulating protein biomarkers associated with flare risk in RA patients undergoing bDMARDs tapering, useful to enable biomarker-guided treatment optimization strategies. MethodsA discovery proteomic analysis using mass spectrometry was performed on baseline serum samples from a subset of the OPTIBIO clinical trial (n=44), followed by validation in the full cohort (n=194) using ELISA. Functional pathway analysis explored biological processes associated with candidate biomarkers. In parallel, anti-cytokine autoantibodies were profiled using multiplex immunoassays. Logistic and Cox regression models were used to assess associations with flare risk. Predictive models integrating biomarkers and clinical variables were evaluated using receiver operating characteristic (ROC) analysis, sensitivity and specificity metrics, and decision curve analysis to assess clinical utility. ResultsMass spectrometry identified 806 proteins, of which 87 were differentially expressed at baseline between patients who flared and those who maintained remission during follow-up within the intervention (tapering) arm. Functional enrichment analysis highlighted immune-regulatory and innate immune pathways. Among the candidates, V-set immunoglobulin-domain-containing 4 (VSIG4) was validated as a biomarker associated with increased flare risk. Anti-interferon-{gamma} (anti-IFN{gamma}) autoantibodies were also associated with flare. A combined model including VSIG4, anti-IFN{gamma}, and the clinical variable DAS28-CRP improved predictive performance compared with clinical variables alone (AUC 0.76 vs 0.66), achieving significantly higher sensitivity. Decision curve analysis demonstrated higher net benefit of the combined model, indicating improved clinical decision-making. In a secondary analysis focused on patients with prolonged remission, representing the most suitable candidates for safe treatment tapering, the model performance further improved (AUC 0.84). ConclusionIntegration of novel serum proteomic and autoantibody biomarkers with clinical parameters improves prediction of flare during biologic tapering in RA and provides clinically relevant benefit for patient stratification. These findings support further development of biomarker-driven approaches for personalized treatment optimization strategies.

ObjectivesTo identify synovial transcriptional clusters in human knee osteoarthritis (OA) and determine how these relate to synovial histologic features, cell-type-associated gene expression, and cartilage degeneration severity. MethodsBulk RNA sequencing (RNA-seq) of synovial tissue from n = 135 patients with knee OA was analyzed using consensus clustering. Clusters were compared by clinical and histologic features, including cartilage degeneration severity (OARSI score). Single-cell RNA-seq (n = 18) and spatial transcriptomics were used to relate cartilage degeneration-associated gene expression patterns to synovial cell populations. ResultsFour synovial transcriptional clusters that differed in synovial histologic features and cartilage degeneration severity were identified. Greater cartilage degeneration was associated with enrichment of lining fibroblast- and inflammatory myeloid-associated gene expression, whereas lesser cartilage degeneration was associated with enrichment of sublining fibroblast, endothelial, mural cell, and adipocyte-associated gene expression. ConclusionsHuman knee OA synovium segregates into transcriptional clusters associated with cartilage degeneration severity. Synovial transcriptional heterogeneity corresponds to cell-type-associated gene expression. Key messagesO_ST_ABSWhat is already known on this topicC_ST_ABSO_LIOsteoarthritis synovium exhibits marked histologic and molecular heterogeneity. C_LIO_LISynovial inflammation detected by MRI correlates with cartilage degeneration and predicts progressive cartilage loss in knee OA. C_LIO_LIPrior transcriptomic studies have identified molecular subsets of OA synovium, but their relationship to cartilage degeneration severity remains unclear. C_LI What this study addsO_LIOA synovium segregates into four transcriptional clusters: Sublining (C1), Lymphomyeloid (C2), Myeloid (C3), and Major trauma (C4). C_LIO_LIGreater cartilage degeneration is associated with enrichment of inflammatory myeloid and lining fibroblast gene expression, whereas lesser degeneration is associated with enrichment of adipocyte, sublining fibroblast, endothelial, and mural cell-associated gene expression. C_LI How this study might affect research, practice or policyO_LIProvides a framework for a clinically relevant biological stratification of OA patients based on synovial molecular features. C_LIO_LIInforms future efforts to link synovial biology with OA prognosis, cartilage degeneration, treatment allocation, and development of targeted therapeutic strategies. C_LI

ObjectivesThe inositol phosphatase SHIP2 plays a crucial role in skeletal development and chondrocyte differentiation, and mutations in INPPL1 (encoding SHIP2) cause opsismodysplasia, a chondrodysplasia with marked cartilage abnormalities. We investigated whether SHIP2 contributes to structural joint remodeling in osteoarthritis (OA). MethodsA cartilage-specific conditional knockout of SHIP2 was generated using Ship2fl/fl mice crossed with AggrecanCreERT2 mice. OA was induced at 9 weeks of age via destabilization of the medial meniscus (DMM). Sham surgery served as control. Mice were sacrificed 12 weeks post-surgery. Histological evaluation of articular cartilage, synovium, osteophytes, and subchondral bone was performed. Chondrocyte hypertrophy was assessed by type X collagen (COLX) staining, and SHIP1 was evaluated as a potential compensatory mechanism. ResultsDMM surgery induced OA-like changes in all genotypes, including cartilage damage, synovial inflammation, osteophyte formation, and subchondral bone thickening. However, Ship2cCART-KO mice showed no differences in OA-related parameters compared to control littermates. COLX expression increased following DMM surgery, independent of SHIP2 deletion. SHIP1 protein levels were not elevated in SHIP2-deficient mice. ConclusionThese findings indicate that SHIP2, while essential for cartilage development, does not act as a structural disease modifier in post-traumatic OA, suggesting that within this context, SHIP2 is not required for maintaining adult articular cartilage structure and is unlikely to represent a major therapeutic target for modifying structural disease progression.

Rett syndrome is a severe neurodevelopmental disorder caused predominantly by loss-of-function mutations in the X-linked gene MECP2. Besides a vast array of neurological and physiological impairments, patients also frequently develop severe osteopenia with increased fracture risk, however, the mechanisms underlying these skeletal defects are not completely understood. Previous work in Mecp2-null mouse models has suggested that osteopenia is mainly due to impaired osteoblast function and reduced bone formation. Here, we examined bone mass, microarchitecture, and remodeling parameters in a Mecp2-null mouse model during postnatal development, with a particular focus on osteoclast involvement. Micro-computed tomography and histomorphometric analyses showed reduced bone mineral density and trabecular bone volume, associated with increased trabecular separation and cortical thinning. These structural alterations were accompanied by increased osteoclast number per bone surface, elevated urinary deoxypyridinoline, and higher expression of osteoclast-associated genes, including Cathepsin K. Furthermore, gene expression analysis revealed an age-dependent shift in bone remodeling. At postnatal day 35, mutant mice showed reduced expression of Dlx5 and Dlx6, consistent with low bone turnover. By postnatal day 55, Rankl and Cathepsin K were markedly upregulated, suggesting an increase in osteoclast resorptive activity, while key osteoblast markers and the RANKL/OPG ratio did not change significantly. A potential cell-autonomous contribution of Mecp2 to osteoclast maturation is also suggested by the analysis of public transcriptomic datasets on human osteoclast differentiation. Together, our findings identify increased osteoclast activity as a significant contributor to Rett-associated osteopenia and suggest that skeletal pathology in Mecp2 deficiency progresses from an early low-turnover state to a later phase of increased osteoclast resorption. HIGHLIGHTSO_LIWhat are the main findings. O_LIMecp2-null mice display reduced bone mass and altered bone microarchitecture during postnatal development, associated not only with reduced osteoblast activity, but also with increased osteoclast number, elevated urinary deoxypyridinoline, and increased expression of osteoclast-associated genes. C_LIO_LIBone remodelling shows an age-dependent shift in Mecp2 deficiency, from an early low-turnover state at postnatal day 35 to increased osteoclast resorptive activity at postnatal day 55. C_LI C_LIO_LIWhat are the implications of the main findings? O_LIRett-associated osteopenia is not explained solely by impaired osteoblast function, but also involves a significant osteoclast contribution to skeletal deterioration. C_LIO_LIThese findings refine the pathophysiological model of bone involvement in Rett syndrome and support the idea that skeletal alterations evolve dynamically during disease progression. C_LI C_LI

Protein kinase A (PKA) is involved in bone biology and is a key mediator of parathyroid hormone signaling in the osteoblast. However, the consequences of sustained PKA activation in bone are unclear. In this study, we inducibly activated PKA in osteoblasts by deleting its major regulatory subunit, Prkar1a, using a Col11-driven Cre system. Prkar1aob-/-mice demonstrated rapid and profound bone pathologies in their femurs, lumbar and caudal vertebrae with cortical bone breakdown and cortical trabecularization. This phenotype was characterized by increased bone turnover and elevated osteoblastic and osteoclastic activities. Transcriptomic and qPCR analyses showed an impairment of osteoblast differentiation with a defect in ossification, expansion of stromal cells, and numbers of both osteoblastic and osteoclastic precursors. Moreover, there were alterations in gene expression of chemokines and Wnt members with enhanced osteoclastogenesis. Altogether, activation of PKA in osteoblasts by inducible deletion of Prkar1a causes a profound high bone turnover phenotype resembling several human bone diseases.