Hepatocyte Growth Factor Immobilized onto Culture Substrates through Heparin and Matrigel Enhances DNA Synthesis in Primary Rat Hepatocytes

Abstract

Newly prepared phosphatidylethanolamine (PE) conjugates of glycosaminoglycans can be immobilized to solid phase through hydrophobic interaction. Primary rat hepatocytes were cultured on type I collagen or laminin substrates containing heparin-PE and assayed for DNA synthesis initiated by hepatocyte growth factor (HGF). Hepatocytes responded to HGF that had been added to culture media by active DNA synthesis and pronounced cell spreading, regardless of the presence of heparin-PE on the substrates. The preincubation with HGF, but not with epidermal growth factor, of the substrates containing heparin-PE significantly enhanced DNA synthesis and cell spreading in the absence of these mitogens in culture media. The enhancements were abolished by omitting heparin-PE or washing the HGF-treated substrates with 1 M NaCl, suggesting the immobilization of HGF to substrates through heparin. These phenomena were more evident with laminin substrates than with type I collagen substrates. Chondroitin sulfate-PE only partly substituted for heparin-PE, but Matrigel gave results similar to those of the substrates containing heparin-PE. Both type I collagen and laminin substrates containing heparin-PE bound higher amounts of HGF than the respective control substrates, whereas neither of the substrates containing chondroitin sulfate-PE did. However, the increase in HGF binding to the substrates was not as evident as the increase in DNA synthesis, suggesting that the latter is not simply due to the former but due to a concerted action of the immobilized HGF and heparin. Taken together, these results suggest that HGF can be trapped in extracellular matrix, probably through heparan sulfate in vivo, thereby acting as a mitogen for hepatocytes in cooperation with heparan sulfate.