Toll-Like Receptor 4 Mediates Alcohol-Induced Steatohepatitis Through Bone Marrow-Derived and Endogenous Liver Cells in Mice

Abstract

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. Method 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 (BMT), 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 ALT 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. Conclusion 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.

Protective effect of low molecular fraction of MGN-3, a modified arabinoxylan from rice bran, on acute liver injury by inhibition of NF-κB and JNK/MAPK expression

“…In recent research, upregulated TLR4 expression and function was reported in various liver models, such as partial hepatectomy [50], ischemia-reperfusion [20,51], and alcohol loading [52,53].…”

Acute organ failure following the loss of anti-apoptotic cellular FLICE-inhibitory protein involves activation of innate immune receptors

“…29 Interestingly, TLR4 is required both on parenchymal and on hematopoietic derived cells for liver injury in the context of NASH indicating that these compartments synergize in the induction of liver injury. 30 Despite the involvement of TLR4 and elevated levels of plasma endotoxins, selective gut decontamination was not sufficient to block liver injury implying that other mechanisms may coexist. Also, data by Wittkopf et al 4 support this hypothesis.…”

Inflammasome activation and function in liver disease

“…Gut-derived lipopolysaccharide, which signals through TLR4, 7,88 is likely to be the first signal that induces IL-1β expression. 18,89 Experiments using chimeric mice with cell-specific deficiency of Casp-1 demonstrated that inflammasome activation and Il-1β secretion in ALD is specific to Kupffer cells. 18 The nature of the second activating signal that releases active IL-1β is elusive, but alcohol-induced mitochondrial dysfunction is associated with changes in the metabolism of uric acid and ATP, two known activators of the NLRP3 inflammasome, raising the possibility that they could be the source of the activating signal.…”