Mechanistic Insights Into UC-MSC Therapy in a BAC-Induced Dry Eye Model: TSG-6-Dependent Inhibition of the Th17/CCL20-CCR6 Chemotactic Axis

Purpose: This study aims to investigate the therapeutic potential of umbilical cord-derived mesenchymal stem cells (UCMSCs) for dry eye disease (DED) and elucidate the underlying mechanisms, with particular focus on the role of TSG-6 in modulating the pathogenic Th17/CCL20-CCR6 inflammatory axis. Methods: Using in vitro hyperosmolar-stressed corneal epithelial cells and a benzalkonium chloride-induced murine DED model, UCMSCs were administered via eye drops in vivo and via Transwell co-culture in vitro. The role of the tumor necrosis factor α stimulated gene/protein 6 (TSG-6) was examined using knockdown UCMSCs (shTSG-6). Functional, histological, and molecular analyses were performed, including human tear samples. Results: UCMSCs improved tear secretion, reduced corneal damage, increased goblet cell density, and suppressed pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) and Th17 cells. These benefits were TSG-6-dependent. Mechanistically, TSG-6 inhibited hyperosmolarity-induced CCL20 in the epithelia by suppressing NF-κB (not MAPK), disrupting Th17 recruitment. TSG-6 also suppressed dendritic cell (DC) maturation and antigen presentation, reducing Th17 differentiation. Clinically, the tears of patients with DED showed elevated CCL20, IL-17A, and IL-6, correlating with severity. Conclusions: This study demonstrates that UCMSCs alleviate DED primarily through the secretion of TSG-6. The TSG-6 mediates the therapeutic effects by dually targeting the CCL20/CCR6 axis, inhibiting NF-κB-dependent CCL20 production in ocular surface epithelia, and suppressing DC maturation and function, leading to reduced Th17 cell migration and differentiation. These findings highlight TSG-6 as a critical mechanistic mediator and suggest the UCMSCs-secreted TSG-6/Th17/CCL20-CCR6 axis as a promising therapeutic target for DED.