Lumican Modulates Keratocan Gene Expression

Abstract

Abstract: : Purpose: Corneal transparency is dependent upon the regulation of collagen fibrillogenesis resulting in small, uniform fibril diameters and regular interfibrillar spacing in part by keratan–sulfate proteoglycans (KSPG) i.e., lumican and keratocan. Lumican–null (Lum^–/–) and keratocan–null (Kera^–/–) mice exhibited corneal opacity and misarranged collagen matrices with the lumican–null animals having a more severe corneal phenotype. Previous reports also have indicated the role of lumican is not restricted to extracellular matrix generation, but is involved in wound healing, cellular migration and tumorigenesis. Here we examined whether lumican could modulate keratocan expression in the adult mouse cornea. Methods: Expression of keratocan in Lum^–/–, Lum^+/+, and Kera–Lum/Lum^+/+ mice was determined by northern hybridization, and western blot analysis and immunohistochemistry with anti–Lum and anti–Kera antibodies. Results: Kera–Lum transgenic mice that overexpress lumican in the cornea also have an increased expression of keratocan. Electron microscopy and confocal microscopy did not detect significant alterations of collagen fibril diameter and fibril spacings, and corneal haze respectively. Keratocan expression was down regulated in corneas of Lum^–/– mice. The coupling of keratocan expression with lumican also was observed after intrastromal injection of pSecTag–Lum minigene into the corneas of Lum^–/– mice. Conclusion: Our results reveal the ability of lumican to modulate gene expression of another KSPG family member in the adult cornea, indicating a novel regulatory interaction of these two closely related PGs. Furthermore, we show the potential of intrastromal injection of minigenes to serve as a therapeutic agent for ocular surface disease. Our observations also provide an explanantion for the more severe corneal stromal abnormaility of Lum^–/– mice than that of Kera^–/– mice.

Keywords: proteoglycans/glycosaminoglycans • cornea: stroma and keratocytes • gene/expression