Abstract
Vitronectin (VN) is a multifunctional glycoprotein present in plasma and the extracellular matrix (ECM). VN binds to various biological ligands and it plays a key role in tissue remodeling by regulating cell adhesion and fibrinolysis. The present study attempted to determine the glycan structures and how alternations of glycans modulate the biological activity of VN during liver regeneration. Plasma VN was purified from partially hepatectomized (PH) and sham-operated (SH) rats at 24 hours after operation and non-operated (NO) rats. The liquid chromatography/ multiple-stage mass spectrometry analysis of glycopeptides of each VN determined the site-specific glycosylation. With the major complex-type N-glycans, hybrid-type N-glycans were site-specifically present. The complex-type N-glycans decreased in PH-VN while the fucosylation ratio was increased. Highly sialylated O-glycans were found to be present in the Thr110-Thr124 region, which contained α2,8-linked disialic acid and dramatically decreased after PH. Further study using ultracentrifugation demonstrated that the multimer sizes of PH-VN significantly increased compared with NO-VN. In accordance with this, PH-VN exhibited remarkably enhanced collagen-binding than NO-VN. The results indicate that glycan alterations during tissue remodeling induce increased multimerization state to enhance collagen-binding of VN.Adhesion of rat hepatic stellate cells (HSCs), together with phosphorylation of focal adhesion kinase (FAK), in PH-VN was decreased to half of that in NO- or SH-VN. Adhesion of HSCs in desialylated NO-VN decreased to 1/2 of that of control VN, indicating the importance of sialylation of VN for activation of HSCs. This study proposes that the alteration of glycosylation of VN is very significant in the modulation of the biological activity of VN during many steps of tissue remodeling processes. The elucidation of the molecular mechanisms of liver regeneration from the viewpoint of alterations in glycosylation of VN may contribute to the development of a strategy to regulate matrix deposition in liver cirrhosis.
