Thrombin Cleavage of Osteopontin Controls Activation of Hepatic Stellate Cells and is Essential for Liver Fibrogenesis

Liver biopsy is the current reliable way of evaluating liver fibrosis. However, no specific sera biomarker could be applied in clinical diagnosis. As the pivotal role of osteopontin (OPN) reported in numerous liver diseases, thrombin-cleaved OPN (Thr-OPN) exposes an integrin-binding motif that promoted biological functions. Herein, we investigated the potential of Thr-OPN in liver fibrosis. Using patient samples, mouse models and hepatic stellate cells (HSCs), we analyzed the involvement of Thr-OPN in liver fibrosis. The result showed that, first, Thr-OPN level was significantly higher in patients with liver cirrhosis than that in patients with chronic hepatitis B and healthy controls. Thr-OPN level was positively correlated with liver fibrosis degree in clinical samples. Then in mouse models, it showed a similar correlation between hepatic Thr-OPN levels and liver fibrosis degree. Thr-OPN peptides exacerbated liver fibrosis in OPN-deficient mice, whereas the neutralization of Thr-OPN alleviated liver fibrosis in wild-type mice. Furthermore, when compared with full-length OPN (FL-OPN), Thr-OPN exhibited a greater ability to promote HSC activation, proliferation, and migration via mitogen-activated protein (MAP) kinase and nuclear factor (NF)-κB pathways. In conclusion, Thr-OPN, not FL-OPN, was critically involved in the exacerbation of liver fibrosis by α9 and α4 integrins via MAP kinase and NF-κB signaling pathway, thus representing a novel diagnostic biomarker and treatment target for liver cirrhosis.