Transmembrane TNF-α signalling of macrophages drives pathological osteogenesis in radiographic axial spondyloarthritis.

Abstract

This study aimed to elucidate the molecular mechanism uncoupling inflammation from pathological osteogenesis in radiographic axial spondyloarthritis (r-axSpA), specifically investigating the role of transmembrane TNF (tmTNF) reverse signalling. We established a tmTNF-overexpressing transgenic mouse model that spontaneously recapitulates spinal ankylosis characteristic of r-axSpA. Single-cell RNA sequencing, genetic knockout (TNFR1/2), and macrophage depletion strategies were employed to identify cellular effectors. A mannose-modified nanoparticle system delivering Ikbkb siRNA was developed to assess targeted therapeutic intervention. Macrophages were identified as the core drivers of osteogenesis, promoting bone formation via TGF-β3 (transforming growth factor beta 3) and BMP2 (bone morphogenetic protein 2) upregulation. Mechanistically, we discovered a novel reverse signalling axis wherein soluble TNFR1 binds to tmTNF, inducing the interaction of the tmTNF intracellular domain with the proteasome subunit alpha type-1 (PSMA1). This interaction activates the IKKβ/NF-κB (inhibitor of nuclear factor kappa B kinase subunit beta / nuclear factor kappa B) pathway to upregulate TGF-β3 and BMP2, instructing macrophages to drive mesenchymal stem cell ossification. Crucially, targeted silencing of Ikbkb in macrophages significantly inhibited new bone formation. This study reveals a distinct sTNFR1-tmTNF-PSMA1-NF-κB reverse signalling axis that empowers macrophages to drive pathological osteogenesis in r-axSpA. Targeting this axis offers a precise therapeutic strategy to arrest structural damage beyond solely controlling systemic inflammation.