Chitinase-like protein YKL-40 regulates hyperoxia-induced apoptosis in human airway epithelial cells

Abstract

YKL-40 is chitinase-like protein that lacks chitinase activity. Prolonged exposure to 100% oxygen causes hyperoxic acute lung injury characterized by alveolar epithelial cell injury and death. We investigated the role of YKL-40 regulating hyperoxia-induced apoptosis in human airway epithelial cells. Human airway epithelial cell line, BEAS-2B, was exposed to > 93% oxygen for 24-72 hours. Hyperoxia induced apoptosis was confirmed by flow cytometry with Annexin-V and PI staining. The mRNA and protein expression of YKL-40, caspase 3 and caspase 7 was determined by real time PCR and Western blotting. YKL-40 short hairpin RNA (shRNA) and over-expression vectors were transfected to cells to examine the requirement of YKL-40. Hyperoxia increased FITC-Annexin V positive cells compared with room air. Caspase 3 and 7 , representative apoptosis regulators, were increased by hyperoxia on mRNA and protein level. YKL-40 expression was also increased. YKL-40 shRNA transfected cells expressed lower level of caspase 3 and 7 mRNA and protein than untransfected cells after exposing to hyperoxia, whereas YKL-40 over-expression vector transfected cells showed higher level of caspase 3 and 7 than untransfected cells. We concluded that hyperoxia induced apoptosis associates with YKL-40 expression and that YKL-40 could be considered as one of apoptosis regulators in oxidative stressed human airway epithelial cells.