The NLRP3 Activation in Infiltrating Macrophages Contributes to Corneal Fibrosis by Inducing TGF-β1 Expression in the Corneal Epithelium

PURPOSE. To explore the effect and mechanism of NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes on corneal fibrosis. METHODS. The wild-type, NLRP3 knockout (KO), and myeloid cell-specific NLRP3 KO (NLRP3 Lyz-KO) C57 mice were used to establish a corneal scarring model. NLRP3 inhibitor, IL-1 beta neutralizing antibody, and an IL-1R antagonist were used to investigate the role of NLRP3 and IL-1 beta in corneal fibrosis. The expression of the NLRP3 signaling pathway related proteins, alpha-smooth muscle actin, TGF-beta was determined by quantitative real-time polymerase chain reaction, Western blotting, and immunofluorescence staining. Flow cytometry was used to detect the infiltration of macrophages during corneal fibrosis. RESULTS. The components of the NLRP3 inflammasomes were elevated and activated during corneal scarring. Additionally, genetic or chemical-mediated blocking of NLRP3 as well as IL-1 beta significantly alleviated corneal fibrosis. Moreover, neutrophil (CD45(+)Ly6G(+)) and macrophage (CD45(+)F4/80(+)) accumulation increased in the cornea during the progression of corneal fibrosis. Intriguingly, the increased concentrations of NLRP3 and IL-1 beta were prominently colocalized with the infiltrating F4/80(+) macrophages. Expectedly, NLRP3 Lyz-KO mice exhibited a marked decrease in their corneal fibrosis symptoms. Mechanistically, the activation of IL-1 beta or macrophage NLRP3 stimulated the expression of TGF-beta 1 in the corneal epithelial cells, whereas an NLRP3 deficiency decreased its expression in the corneal epithelium. CONCLUSIONS. These observations revealed that the NLRP3 inflammasome activation in infiltrating macrophages contributes to corneal fibrosis by regulating corneal epithelial TGF-beta 1 expression. Targeting the NLRP3 inflammasome might be a promising strategy for the treatment of corneal scarring.