Purpose: The synthesis of cytokines and adhesion molecules by corneal fibroblasts contributes to the innate immune response to corneal infection. The effects of the antimicrobial peptide LL37 on cytokine and adhesion molecule expression induced by bacterial lipopolysaccharide (LPS) in human corneal fibroblasts were examined.
Methods: The release of the cytokines IL-6 and IL-8 into culture supernatants and the expression of intercellular adhesion molecule (ICAM)-1 at the cell surface were measured with ELISAs and by flow cytometry. The abundance of mRNAs was quantitated by RT and real-time PCR analysis, and the phosphorylation of signaling proteins was examined by immunoblot analysis. The subcellular localization of ICAM-1 and the transcription factor nuclear factor (NF)-κB was determined by immunofluorescence analysis. Neutrophil infiltration in a mouse model of LPS-induced keratitis was evaluated by immunohistofluorescence analysis.
Results: The antimicrobial peptide LL37 inhibited the up-regulation of IL-6, IL-8, and ICAM-1 both at protein and mRNA levels in corneal fibroblasts induced by LPS without affecting those elicited by TNF-α. Furthermore, LL37 attenuated the LPS-induced phosphorylation of the NF-κB inhibitor IκBα and the mitogen-activated protein kinases extracellular signal-regulated kinase, p38, and c-Jun NH2-terminal kinase, as well as the translocation of NF-κB to the nucleus in corneal fibroblasts. Lipopolysaccharide-induced keratitis in mice was also suppressed by topical application of LL37.
Conclusions: The inhibition of LPS-induced cytokine and adhesion molecule expression in human corneal fibroblasts by LL37 suggests that this peptide might promote the resolution of corneal inflammation associated with bacterial infection.