Cell-cell interactions: Clues to hepatocyte heterogeneity and beyond?



We previously demonstrated that glutamine synthetase (GS) and ornithine aminotransferase (OAT) mRNAs are expressed in the mouse liver acinus preferentially in pericentral hepatocytes, that is, those immediately surrounding terminal central veins (A. L. Bennett, K. E. Paulson, R. E. Miller, and J. E. Darnell, Jr., J. Cell Biol. 105:1073–1085, 1987, and F. C. Kuo, W. L. Hwu, D. Valle, and J. E. Darnell, Jr., Proc. Natl. Acad. Sci. USA, (in press). We now show that hepatocytes surrounding large collecting hepatic veins but not portal veins also express these two mRNAs. The pericentral hepatocytes are the most distal hepatocytes with respect to acinar blood flow, whereas this is not necessarily the case for hepatocytes next to the large collecting hepatic veins. This result implies that it is contact with some hepatic venous element which signals positional expression. In an effort to induce conditions that change relationships between hepatocytes and blood vessels, regenerating liver was studied. After surgical removal of two-thirds or more of the liver, there was no noticeable change in GS or OAT expression in the remaining liver tissue during regeneration. However, treatment with carbon tetrachloride (CCl4), which specifically kills pericentral hepatocytes, completely removed GS- and OAT-containing cells and promptly halted hepatic transcription of GS. Repair of CCl4 damage is associated with invasion of inflammatory and scavenging cells, which remove dead hepatocytes to allow regrowth. Only when hepatocytes resumed contact with pericentral veins were the pretreatment levels of OAT and GS mRNA and high levels of GS transcription restored.