Transcript profiling reveals IL-1β and TGF-β1 regulation of chemokine expression in fibroblast-like synoviocytes

Fibroblast-like synoviocytes (FLS) are crucial in maintaining joint homeostasis under normal physiological conditions. However, under inflammatory settings, they release factors contributing to tissue damage and osteoarthritis (OA). This study evaluates FLS as a disease-relevant model by profiling transcriptome-wide responses following IL-1β exposure and assessing whether TGF-β1 can antagonize these responses.

Primary FLS from synovial explants of patients undergoing anterior cruciate ligament reconstruction were expanded and exposed to recombinant human IL-1β (10 ng/mL) for 24 h to simulate an inflammatory microenvironment characteristic of OA. Transcriptomic changes were profiled using the Illumina NovaSeq-6000 platform and validated through Fluidigm multiplex digital PCR. To assess the immunomodulatory effects of TGF-β1, FLS were treated with recombinant human TGF-β1 (10 ng/mL) for 48 h following IL-1β exposure, and chemokine gene expression was analyzed by digital PCR.

IL-1β-treated FLS exhibited marked upregulation of several chemokines (e.g., CCL20, CXCL8) and other arthritis-related genes (CSF2, MMP12, IL1B, LIPM), while downregulation of KRT14, KRT19, KRT18, and other anabolic and cytoskeletal genes. Highly expressed genes were enriched in NFκB, cytokine/chemokine, TNF signaling, and necroptosis/ferroptosis pathways. Notably, TGF-β1 treatment significantly reduced IL-1β-induced chemokine expression. Mechanistically, this suppression correlated with about a 50% reduction in the expression of NF-κB and C/EBPβ transcription factors, suggesting that TGF-β1 mediates anti-chemokine effects in part through transcriptional repression of NF-κB and C/EBPβ.

IL-1β induces exuberant inflammatory responses in FLS, akin to chondrocytes, highlighting that FLS can effectively model inflammatory OA. Importantly, TGF-β1 emerges as a potent modulator capable of suppressing these responses, positioning it as a potential therapeutic candidate for restoring joint homeostasis.