The Role of Neuropilin-1 Glycosylation in Galectin-1 Induced Activation of Hepatic Stellate Cells and Liver Fibrosis

Liver fibrosis is a response of abnormal wound-healing with accumulation of extracellular matrix (ECM) proteins in liver. The activation of hepatic stellate cell (HSC) is a rate-limiting step in hepatic fibrosis because they secret excessive ECM which alters the normal architecture of liver and causes many complications. Unfortunately, there is no effective treatment for cirrhosis, the advanced stage of liver fibrosis. Therefore, developing approaches to destroy or normalize activated HSCs has become an important issue in the therapy of liver fibrosis. We previously reported that galectin-1 (Gal-1), a β-galactoside binding protein, plays an important role in oral fibroblast activation but the role of Gal-1 in liver fibrosis is unclear. Our preliminary result showed Gal-1 was highly expressed in the fibrotic livers and loss of Gal-1 suppressed thioacetamide (TAA) induced liver fibrosis in mice. Gal-1 modulated the proliferation, migration and activation of HSCs and thiodigalactoside (TDG), a lactose analogue, inhibits Gal-1 induced HSC migration which indicates the carbohydrate-recognition domain (CRD) is required for the effect of Gal-1 on HSCs. In addition, we found that neuropilin-1 (NRP-1) is required for Gal-1 induced HSC migration suggesting that the CRD of Gal-1 could interact with the glycan of NRP-1 in HSCs. Interestingly, NRP-1 has been reported as a “co-receptor” of PDGF and TGF-β in HSCs (two important cytokines for HSC activation) and we found that Gal-1 was essential for PDGF and TGF-1 induced HSC activation. Therefore, it is hypothesized that Gal-1 binds to the glycan of NRP-1 and co-clusters the PDGFRs (PDGF receptors) or TGFRs (TGF-receptors). The Gal-1 mediated co-clustering of NRP-1/PDGFRs and NRP-1/TGFRs could enhance the PDGF and TGF- induced signal transduction and could promote HSC activation and liver fibrosis. Three specific aims are proposed to verify our hypothesis: Aim 1: To investigate whether the O- or N-glycan modification of NRP-1 affects the interaction between Gal-1 and NRP-1 and regulates Gal-1 induced HSC activation. Aim 2: To examine the involvement of Gal-1 in the co-clustering of NRP-1/PDGFRs and NRP-1/TGFRs; To examine whether this co-clustering regulates PDGF and TGF- induced signaling and HSC activation. Aim 3: To investigate the effect of Gal-1 on the progression of liver fibrosis using Gal-1 null mouse model and thiodigalactoside treatment. Since Gal-1 is crucial in HSC activation and liver fibrosis, the dissection of the interaction between Gal-1 and the glycosylated NRP-1 will help us to develop the glycan inhibitors to disrupt the interaction and to suppress PDGF/TGF-induced signaling. It is believed that Gal-1 induces the co-clustering of NRP-1/PDGFRs and NRP-1/TGFRs. Targeting Gal-1 is like“hitting three birds with one stone”namely NRP-1, PDGFRs and TGFRs. This study may open a new avenue for the therapy of liver fibrosis in the future.