Reciprocal induction of hepatitis C virus replication and stimulation of hepatic profibrogenic cytokine release and cellular viability by YKL-40

BACKGROUND: Previous studies have suggested the YKL-40/chitinase 3-like protein 1 protein is upregulated in chronic hepatitis C virus (HCV) infection with fibrosis. We sought to determine whether HCV regulates YKL-40 expression and to elucidate the mechanisms by which YKL-40 mediates the liver fibrosis caused by HCV infection. METHODS: We used purified protein, small molecule inhibitors and short-interfering RNAs to over-express or knock down certain kinases to explore the mechanisms underlying the regulation by HCV of YKL-40 expression in the Japanese fulminant hepatitis 1 (JFH1) model. RESULTS: HCV induced YKL-40 production in hepatic parenchymal cells. Further, HCV-mediated upregulation of YKL-40 through cooperative induction of tumor necrosis factor-α (TNF-α) and reactive oxygen species (ROS)-mitogen-activated protein kinase MAPKs, which are nuclear factor-κB (NF-κB)-dependent pathways. YKL-40 protein also mildly increased HCV replication, triggering hepatic profibrogenic cytokine release and cellular viability as feedback. Additionally, hepatic parenchymal cells were the sole source of YKL-40 production in the infectious JFH1 model, whereas YKL-40 was under-detected in hepatic stellate cells (HSCs) in the presence or absence of the JFH1 supernatant, which was not investigated so far. CONCLUSIONS: HCV induced and maintained secretion of YKL-40 through sustained activation of NF-κB via cooperative induction of the TNF-α and ROS-MAPKs pathways. HCV interacted with YKL-40 to enhance the progression of hepatic fibrosis. These findings support a potential role for blockade of YKL-40 as an antifibrotic strategy.