Defective keratocyte apoptosis in response to epithelial injury in Stat 1 null mice

Defects in apoptosis have been noted in signal transducer and activator of transcription (Stat) 1-null cells in vitro. The purpose of this study was t o analyse the keratocyte apoptosis response that occurs in vivo in response to corneal epithelial injury in Stat 1null compared with control mice and to determine whether Stat 1null corneal fibroblasts have a defective respon se to death receptor activation in vitro. Corneal epithelial scrape injuries were performed in Stat 1-null and wild-t ype mice. Keratocyte apoptosis was monitored with the quantitative TUNEL as say and confirmed using transmission electron microscopy. Corneal fibroblas t apoptosis in response to tumor necrosis factor (TNF) alpha, with and with out inhibitors of nuclear factor kappa 13 (NF-kappa B) activation, was moni tored using DNA laddering and the methylene blue assay. Significantly less keratocyte apoptosis was noted in Stat 1-null mice compa red with wild-type controls. TNF alpha-induced apoptosis only occurred in w ild-type mice in the presence of inhibitors of NF-kappa B activation. Corne al fibroblast TNF alpha-induced apoptosis was defective in Stat 1null corne al fibroblasts whether NF-kappa B activation was blocked or not. Stat 1 has an important role in the keratocyte apoptosis that occurs in res ponse to corneal epithelial injury. Previous studies suggest that the defec t is due to a lack of constitutive expression of caspases. This study demon strates that this defect in apoptosis in Stat 1-null mice is present in viv o in Stat 1-null mice and suggests that Stat 1 could be a therapeutic targe t for transient inhibition of keratocyte apoptosis to modulate corneal woun d healing, (C) 2000 Academic Press.