Endotoxin modulation of hepatocyte secretory and cellular protein synthesis is mediated by Kupffer cells

We hypothesize that alterations of hepatocyte function in sepsis are modulated by endotoxin (lipopolysaccharide)-triggered Kupffer cells. In the present experiments the effect of lipopolysaccharide on secreted and cellular proteins synthesized by hepatocytes cultured alone or cocultured with Kupffer cells was investigated using polyacrylamide gel electrophoresis. Lipopolysaccharide had no direct effect on the types or amounts of secreted proteins synthesized by hepatocytes alone. Kupffer cells coculturing resulted in increased synthesis of some hepatocyte proteins (68k and 23k) whose production was not altered by lipopolysaccharide. In contrast, addition of lipopolysaccharide to the hepatocyte-Kupffer cell coculture substantially decreased synthesis of several proteins (73k, 66k, and 35k). Despite an overall decrease in protein synthesis of hepatocytes cocultured with Kupffer cells after the addition of lipopolysaccharide, there was increased synthesis of several individual proteins (58k and 44k). Similar effects were seen in synthesis of cellular protein. The addition of recombinant interleukin 1 to hepatocytes alone or in coculture had no effect on the amount or type of protein synthesized. We conclude that Kupffer cells regulate the types and amounts of individual proteins synthesized by hepatocytes via mediators other than interleukin 1.