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Keywords:

  • Innate Immunity;
  • Lipopolysaccharide;
  • Alcoholic Steatohepatitis;
  • Alcoholic Liver Fibrosis

Background:  Excessive alcohol intake causes an increase in intestinal permeability that induces translocation of gut-derived lipopolysaccharide (LPS) to the portal vein. Increased LPS in the portal vein stimulates Kupffer cells through Toll-like receptor (TLR) 4 in the liver. Activated TLR4 signaling in Kupffer cells induces various inflammatory mediators including TNF-α, IL-1β, and reactive oxygen species, resulting in liver injury. Hepatic stellate cells (HSCs) also express TLR4. This study investigates whether TLR4 on bone marrow (BM)-derived cells, including Kupffer cells, or non–BM-derived endogenous liver cells, including HSCs, contributes to the progression of alcohol-induced steatohepatitis and fibrogenesis in mice.

Methods:  TLR4 BM chimera (wild-type [WT] mice with TLR4−/− BM or TLR4−/− mice with WT BM) were generated by the combination of liposomal clodronate injection with whole body irradiation and BM transplantation, followed by treatment with intragastric alcohol feeding.

Results:  WT mice transplanted with WT BM exhibited liver injury, steatosis, inflammation, and a fibrogenic response. Conversely, TLR4−/− mice with TLR4−/− BM displayed less steatosis, liver injury, and inflammation. Notably, steatosis, macrophage infiltration, and alanine aminotransferase levels in both TLR4-chimeric mice showed intermediate levels between WT mice transplanted with WT BM and TLR4−/− mice transplanted with TLR4−/− BM. Hepatic mRNA expression of fibrogenic markers (collagen α1(I), TIMP1, TGF-β1) and inflammatory cytokines (IL-1β, IL-6) were markedly increased in WT mice with WT BM, but there was less of an increase in both TLR4-chimeric mice and in TLR4−/− mice transplanted with TLR4−/− BM.

Conclusions:  TLR4 signaling in both BM-derived and non–BM-derived liver cells is required for liver steatosis, inflammation, and a fibrogenic response after chronic alcohol treatment.