The NS1 protein of avian influenza virus H9N2 induces oxidative-stress-mediated chicken oviduct epithelial cells apoptosis

The pathogenesis of H9N2 subtype avian influenza virus infection (AIV) in hens is often related to oviduct tissue damage. The viral non-structural NS1 protein is thought to play a key role in regulating the pathogenicity of AIV, but its exact function in this process remains elusive. In this study, the pro-apoptosis effect of H9N2 NS1 protein was examined on chicken oviduct epithelial cells (COECs) and our data indicated that NS1-induced oxidative stress was a contributing factor in apoptosis. Our data indicate that NS1 protein level was correlated with reactive oxygen species (ROS) in COECs transfected with NS1 expression plasmids. Interestingly, decreased activities of antioxidant enzymes, superoxide dismutase and catalase, were observed in NS1-transfected COECs. Treatment of COECs with antioxidants, such as pyrrolidine dithiocarbamate (PDTC) or N-acetylcysteine (NAC), significantly inhibited NS1-induced apoptosis. Moreover, although antioxidant treatment has little effect on the activation of caspase-8 in NS1-transfected cells, the activation of caspase-3/9 and Bax/Bcl-2 were significantly downregulated. Taken together, the results of our study demonstrated that expression of H9N2 NS1 alone is sufficient to trigger oxidative stress in COECs. Additionally, NS1 protein can induce cellular apoptosis via activating ROS accumulation and mitochondria-mediated apoptotic signalling in COECs.