Protective roles of the TIR/BB-loop mimetic AS-1 in alkali-induced corneal neovascularization by inhibiting ERK phosphorylation

Abstract Hydrocinnamoyl-L-valylpyrrolidine (AS-1), a synthetic low-molecule mimetic of myeloid differentiation primary response gene 88 (MyD88), inhibits inflammation by disrupting the interaction between the interleukin-1 receptor (IL-1R) and MyD88. Here, we describe the effects of AS-1 on injury-induced increases in inflammation and neovascularization in mouse corneas. Mice were administered a subconjunctival injection of 8 μL AS-1 diluent before or after corneal alkali burn, followed by evaluation of corneal resurfacing and corneal neovascularization (CNV) by slit-lamp biomicroscopy and clinical assessment. Corneal inflammation was assessed by whole-mount CD45+ immunofluorescence staining, and corneal hemangiogenesis and lymphangiogenesis following injury were evaluated by immunostaining for the vascular markers isolectin B4 (IB4) and the lymphatic vascularized marker lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), respectively. Additionally, corneal tissues were collected to determine the expression of 35 cytokines, and we detected activation of IL-1RI, MyD88, and mitogen-activated protein kinase (MAPK). The results showed that alkali conditions increased the number of CD45+ cells and expression of vascular endothelial growth factor (VEGF)-A, VEGF-C, and LYVE1 in corneas, with these levels decreased in the AS-1-treated group. Moreover, AS-1 effectively prevented alkali-induced cytokine production, blocked interactions between IL-1RI and MyD88, and inhibited MAPK activation post-alkali burn. These results indicated that AS-1 prevented alkali-induced corneal hemangiogenesis and lymphangiogenesis by blocking IL-1RI–MyD88 interaction, as well as extracellular signal-regulated kinase phosphorylation, and could be efficacious for the prevention and treatment of corneal alkali burn.