Seillier, C. | Search bioRxiv

bioRxiv2025

Systemic immune alterations in a murine experimental model of osteoarthritis

Osteoarthritis (OA) is accompanied by an inflamed synovium containing macrophages, dendritic cells, T and B lymphocytes. Macrophages predominate and drive cytokine-mediated cartilage catabolism, while T cells and B cells, though fewer, may shape chronic adaptive responses. However, systemic immune contributions, particularly within peripheral lymphoid organs such as the spleen, remain poorly characterized. Our study aims to profile systemic immune changes in experimental OA induced by injection of mono-iodoacetate (MIA) in mouse paw. At day 56 post-OA induction, analysis of splenocytes showed that macrophages and conventional dendritic cells (cDC1 and cDC2) displayed a significant downregulation of MHCII expression, suggesting a negative feedback mechanism that limits chronic T cell activation. OA is also associated with an increase in total DCs including mainly MHCII negative tolerogenic DCs. Notably, while the proportion of CD11b- tolerogenic DCs was reduced, CD11blow tolerogenic DCs markedly expanded in OA animals. Expression level of the CD11b integrin was upregulated on macrophages and cDC2 in MIA-induced OA mice potentially facilitating their adhesion and migration toward inflamed joint. OA mice showed a significant reduction in total splenic leukocytes, primarily due to a loss of B cells, while total T cell numbers remained stable. However, T cell composition shifted: CD4+ T cells including activated and regulatory subsets decreased, whereas activated CD8+ T cells increased. This indicates a systemic imbalance favoring cytotoxic over regulatory immune activity, possibly linked to chronic immune stress or redistribution of lymphocytes to inflamed joint. In conclusion, our data reveals that chronic OA induces a coordinated remodeling of systemic innate and adaptive immunity. These systemic immune dysregulations could reveal new biomarkers or therapeutic targets.

physiology↗

bioRxiv2025

Inhibiting EZH2 Alleviates Osteoarthritis and Pain in an Experimental Murine Model Through Modulating Synovial and Macrophage Inflammation, Axon Guidance, and Osteoclastogenesis

Enhancer of zeste homolog 2 (EZH2), a histone methyltransferase responsible for H3K27 trimethylation, has emerged as a potential therapeutic target in osteoarthritis (OA). However, its contribution to the multicellular mechanisms driving joint degeneration and pain remains poorly understood. Here, we investigated the effects of pharmacological EZH2 inhibition in a pain-relevant murine OA model and explored its cellular and molecular consequences across OA-associated cell populations. OA was induced in mice by intra-articular monosodium iodoacetate (MIA) injection followed by local administration of the EZH2 inhibitor EPZ-6438. Joint pathology and pain-related behaviors were assessed by histological and functional analyses. Mechanistic studies were performed in primary human OA fibroblast-like synoviocytes and bone marrow-derived cells using targeted gene expression analyses, proteomics and ChIP-seq approaches. EZH2 inhibition reduced cartilage damage, synovial inflammation and pain-related behavioral alterations in vivo. In OA synoviocytes, EPZ-6438 decreased the expression of inflammatory, catabolic and pain-associated mediators while promoting autophagy-related responses. Proteomic and ChIP-seq analyses revealed EZH2-dependent regulation of inflammatory pathways, cellular homeostasis and neuronal-associated processes, including axon guidance-related pathways. ChIP-seq further identified inflammation-dependent EZH2 recruitment to promoters of neurodevelopmental regulators, including PAX6, suggesting a potential contribution of EZH2 to neuronal-associated mechanisms in OA. In addition, EZH2 inhibition reduced macrophage inflammatory activation and osteoclast differentiation. Together, these findings identify EZH2 as a candidate epigenetic regulator linking inflammatory, neuroimmune and osteoimmune pathways across the osteoarthritic joint. Targeting EZH2 may represent a therapeutic strategy to simultaneously modulate joint inflammation, remodeling and pain-associated pathways.

physiology↗