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Toll-like Receptor 4 on Macrophage Promotes the Development of Steatohepatitis-related Hepatocellular Carcinoma in Mice*

Kouichi Miura,Mitsuaki Ishioka,Shinichiro Minami,Y. Horie,Shigetoshi Ohshima,T. Goto,H. Ohnishi

Published 2016 in Journal of Biological Chemistry

ABSTRACT

The role of Toll-like receptor (TLR) signaling has attracted much attention in the development of hepatic inflammation and hepatocellular carcinoma (HCC). We herein sought to determine the role of TLRs and responsible cells in steatohepatitis-related HCC. We used hepatocyte-specific Pten-deficient (PtenΔhep) mice, which exhibit steatohepatitis followed by liver tumor formation, including HCC. We then generated PtenΔhep/Tlr4−/− and PtenΔhep/Tlr2−/− double-mutant mice and investigated the role of macrophages using reconstitution of bone marrow (BM)-derived cells, chemical depletion of macrophages, and isolated macrophages. Tlr4 but not Tlr2 deficiency in the PtenΔhep mice suppressed tumor growth as well as hepatic inflammation. Gut sterilization by an antibiotic mixture reduced the portal LPS levels as well as tumor growth in the PtenΔhep mice. Tumor growth was also decreased by reconstitution of BM-derived cells to Tlr4−/− BM cells. In addition, chemical depletion of macrophages significantly reduced tumor size and numbers. Macrophages expressing Ly6C were increased in number, which was associated with inflammation and tumor progression in the PtenΔhep mice. Hepatic macrophages isolated from the PtenΔhep mice abundantly expressed the Ly6C gene and produced much more IL-6 and TNFα in response to LPS. These proinflammatory cytokines induced the proliferation of HCC cells as well as oval cells, putative cancer progenitor cells. Indeed, putative cancer progenitor cells emerged before the development of macroscopic liver tumors and then increased in number under sustained inflammation. TLR4 on macrophages contributes to the development of steatohepatitis-related HCC in mice.

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