IL-33 Promotes ST2-Dependent Fibroblast Maturation via P38 and TGF-β in a Mouse Model of Epidural Fibrosis

ABSTRACT

BACKGROUND@#Recent evidence suggests that IL-33, a novel member of the IL-1b family, is involved in organ fibrosis. However, the roles of IL-33 and its receptor ST2 in epidural fibrosis post spine operation remain elusive. @*METHODS@#A mouse model of epidural fibrosis was established after laminectomy. IL-33 in the wound tissues post laminectomy was measured with Western blotting, ELISA and imaging. The fibroblast cell line NIH-3T3 and primary fibroblasts were treated with IL-33 and the mechanisms of maturation of fibroblasts into myofibroblasts were analyzed. To explore roles of IL-33 and its receptor ST2 In vivo, IL-33 knockout (KO) and ST2 KO mice were employed to construct the model of laminectomy. The epidural fibrosis was evaluated using H&E and Masson staining, western-blotting, ELISA and immunohistochemistry. @*RESULTS@#As demonstrated in western blotting and ELISA, IL-33 was increased in epidural wound tissues post laminectomy. The immunoflurosence imaging revealed that endothelial cells (CD31 + ) and fibroblasts (a-SAM +) were major producers of IL-33 in the epidural wound tissues. In vitro, IL-33 promoted fibroblast maturation, which was blocked by ST2 neutralization antibody, suggesting that IL-33-promoted-fibroblasts maturation was ST2 dependent. Further, IL-33/ ST2 activated MAPK p38 and TGF-β pathways. Either p38 inhibitor or TGF-β inhibitor decreased fibronectin and a-SAM production from IL-33-treated fibroblasts, suggesting that p38 and TGF-β were involved with IL-33/ST2 signal pathways in the fibroblasts maturation. In vivo, IL-33 KO or ST2 KO decreased fibronectin, a-SMA and collagen deposition in the wound tissues of mice that underwent spine surgery. In addition, TGF-β 1 was decreased in IL-33 KO or ST2 KO epidural wound tissues. @*CONCLUSION@#In summary, IL-33/ST2 promoted fibroblast differentiation into myofibroblasts via MAPK p38 and TGF-β in a mouse model of epidural fibrosis after laminectomy.