Pharmacological targeting of the TLR8/AP-1 axis ameliorates scleroderma skin inflammation and fibrosis by suppressing monocyte-mediated endothelial injury.

AIMS: Toll-like receptor 8 (TLR8) is implicated in systemic sclerosis (SSc) pathogenesis, but its precise cellular mechanisms remain elusive. This study elucidates TLR8's role in monocyte-endothelial crosstalk and evaluates the therapeutic potential of targeting the TLR8/AP-1 axis in SSc.

MATERIALS AND

METHODS

TLR expression in peripheral blood mononuclear cells (PBMC) from SSc patients and healthy controls was assessed via flow cytometry. Single-cell RNA-sequencing datasets were analyzed for monocyte TLR8 profiling. In vitro, CD14+ monocytes and human dermal microvascular endothelial cells (HDMC) were co-cultured using specific pharmacological modulators (TLR8 agonist VTX-2337; AP-1 inhibitor T5224). In vivo efficacy of AP-1 inhibition was evaluated in a bleomycin-induced SSc mouse model.

KEY FINDINGS: TLR8 was predominantly expressed and significantly upregulated in SSc CD14+ monocytes, positively correlating with vascular manifestations like Raynaud's phenomenon. In vitro, VTX-2337-mediated TLR8 activation induced inflammatory cytokines and adhesion molecules (ITGB1/ITGB2) in monocytes via AP-1. These activated monocytes enhanced monocyte-endothelial adhesion, accelerated endothelial migration, disrupted tube formation, and induced endothelial-to-mesenchymal transition (EndoMT). Crucially, AP-1 inhibition with T5224 abrogated these pathogenic interactions. In vivo, T5224 significantly ameliorated endothelial injury, dermal inflammation, and skin fibrosis in bleomycin-treated mice.

SIGNIFICANCE: The TLR8/AP-1 axis drives monocyte-mediated endothelial injury in SSc. Pharmacological AP-1 inhibition disrupts this pathogenic monocyte-endothelial crosstalk, offering a promising therapeutic strategy against SSc skin inflammation and fibrosis.