Dental follicle stem cell-derived small extracellular vesicles ameliorate pulpitis by reprogramming macrophage metabolism

Vital pulp therapy (VPT) is considered a conservative means of preserving the vitality and function of the dental pulp after injury. However, current VPT has unfavorable effects on inflamed pulp. Mesenchymal stem cell (MSC)-derived small extracellular vesicles (MSC-sEVs) show powerful immunomodulatory capacities and exert therapeutic effects on a variety of inflammatory diseases. However, whether MSC-sEVs ameliorate the inflammatory response and promote inflammatory pulp repair in pulpitis is largely unknown. In this study, we show that sEVs derived from dental follicle stem cells (typical dental MSCs, DFSC-sEVs) alleviate lipopolysaccharide-induced pulpitis in rats and enhance pulp repair by inducing M2 macrophage polarization. Mechanistically, heat shock protein 70 (HSP70) within DFSC-sEVs can be supplemented into lysosomes to directly protect lysosomal function and induce mitophagy to promote the degradation of depolarized mitochondria, thereby preprogramming inflammatory macrophages to commit to oxidative phosphorylation, which fuels M2 polarization. Furthermore, DFSC-sEVs also transfer antioxidant miRNAs, including miR-24-3p and let-7c-5p, to inhibit mitochondrial reactive oxygen species production, thereby indirectly stabilizing lysosomes to induce M2 macrophage generation. Our study reveals a promising immunotherapeutic potential of DFSC-sEVs for VPT in inflamed pulp and a novel role for DFSC-sEVs in inhibiting the macrophage inflammatory response by protecting lysosomes and inducing mitophagy-mediated metabolic shifts toward oxidative phosphorylation.