Inflammation-triggered Gli1+ stem cells engage with extracellular vesicles to prime aberrant neutrophils to exacerbate periodontal immunopathology

Periodontitis is a prevalent and progressive detrimental disease characterized by chronic inflammation, and the immunopathological mechanisms are not yet fully understood. Mesenchymal stem cells (MSCs) play crucial roles as immunoregulators and maintain tissue homeostasis and regeneration, but their in vivo function in immunopathology and periodontal tissue deterioration is still unclear. Here, we utilized multiple transgenic mouse models to specifically mark, ablate and modulate Gli1(+) cells, a critical and representative subset of MSCs in the periodontium, to explore their specific role in periodontal immunopathology. We revealed that Gli1(+) cells, upon challenge with an inflammatory microenvironment, significantly induce rapid trafficking and aberrant activation of neutrophils, thus exacerbating alveolar bone destruction. Mechanistically, extracellular vesicles (EVs) released by Gli1(+) cells act as crucial immune regulators in periodontal tissue, mediating the recruitment and activation of neutrophils through increased neutrophil generation of reactive oxygen species and stimulation of nuclear factor kappa-B signaling. Furthermore, we discovered that CXC motif chemokine ligand 1 (CXCL1) is exposed on the surface of EVs derived from inflammation-challenged Gli1(+) cells to prime aberrant neutrophils via the CXCL1-CXC motif chemokine receptor 2 (CXCR2) axis. Importantly, specific inhibition of EV release from Gli1(+) cells or pharmacological therapy with GANT61 ameliorates periodontal inflammation and alveolar bone loss. Collectively, our findings identify previously unrecognized roles of Gli1(+) cells in orchestrating infiltration and promoting aberrant activation of neutrophils under inflammation, which provides pathological insights and potential therapeutic targets for periodontitis.