Keratocan and lumican regulate neutrophil infiltration and corneal clarity in lipopolysaccharide-induced keratitis by direct interaction with CXCL1

Abstract

Keratocan and lumican are keratan-sulfate proteoglycans (KSPG), which have a critical role in maintaining corneal clarity. To determine whether these KSPGs have a role in corneal inflammation, we examined Kera-/- and Lum-/- mice in a model of lipopolysaccharide (LPS)-induced keratitis in which wild-type mice develop increased corneal thickness and haze due to neutrophil infiltration to the corneal stroma. Corneal thickness increases caused by LPS mice were significantly lower in Kera-/- and Lum -/- than wild-type mice. Further, LPS-injected Lum-/- mice had elevated corneal haze levels compared with that of Kera-/- and wild-type. At 24 h post-injection, total enhanced green fluorescent protein-positive bone marrow-derived inflammatory cells in chimeric mice was significantly lower in Kera-/- mice and Lum-/- mice compared with wild-type mice. Neutrophil infiltration was inhibited in Kera -/- and Lum-/- mice at 6 and 24 h post-stimulation, with Lum-/- corneas having the most profound defect in neutrophil migration. Reconstitution of keratocan and lumican expression in corneas of Kera-/- and Lum-/- mice using adeno-keratocan and adeno-lumican viral vectors, respectively, resulted in normal neutrophil infiltration in response to LPS. Immunoprecipitation/Western blot analysis showed that lumican and keratocan core proteins bind the CXC chemokine KC during a corneal inflammatory response, indicating that corneal KSPGs mediate neutrophil recruitment to the cornea by regulating chemokine gradient formation. Together, these data support a significant role for lumican and keratocan in a corneal inflammatory response with respect to edema, corneal clarity, and cellular infiltration. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.