Osteopontin Contributes to TGF-β1 Mediated Hepatic Stellate Cell Activation

Liver fibrosis is characterized by accumulation of extracellular matrix. Our previous study found that osteopontin (OPN) increased in plasma of cirrhotic patients and indicative of cirrhosis staging. The present study was designed to investigate the expression of OPN in liver tissues and plasma of cirrhotic patients and further explore the role of OPN in human hepatic stellate cell (HSC) activation. We used immunohistochemical staining and enzyme-linked immunosorbent assay to evaluate the expression level of OPN in liver tissues and plasma from cirrhotic patients, respectively. We produced lentivirus particles and infected target cell to manipulate OPN expression. Infection efficiency was determined by real-time RT-PCR and western blot. Cell proliferation was determined using CCK8 assay, and phenotypes of HSC activation were determined by real-time RT-PCR. OPN promoter activity was determined by dual luciferase reporter assay. We found that OPN expression in human cirrhotic liver tissues was upregulated compared to normal controls. In addition, its expression correlated with Child-Pugh classification, MELD score and the occurrence of complications. We further explored OPN level in patients' plasma and showed that its level correlated with transforming growth factor-beta 1 (TGF-beta 1). In human HSC cell line LX-2, we found that change of OPN expression level could not only affect the proliferation of cells but also the TGF-beta 1 mediated HSC activation. Moreover, OPN was increased by TGF-beta 1 stimulation and regulated by TGF-beta 1 at transcription level. OPN is upregulated in liver tissues and plasma of cirrhotic patients and promotes TGF-beta 1 mediated HSC activation.