Toll-like receptor 4 involvement in hepatic ischemia/reperfusion injury in mice

Toll-like receptor 4 (TLR4) is involved in innate immunity by recognizing endotoxin resulting in a burst of inflammatory cascade. We investigated the relation between activation of TLR4 and liver injury in partial hepatic ischemia/reperfusion (I/R) injury in mice.

TLR4-deficient mice (C3H/Hej) and wild type mice (WT, C3H/Heouj) were used in the model of I/R injury. Partial hepatic ischemia was produced by occlusion of inflow to the median and left lobes for 45 minutes. Blood was drawn at 1 and 3 hours after reperfusion. The blood was analyzed for aspartate aminotransferase (AST) and tumor necrosis factor alpha (TNF-alpha). TNF-alpha mRNA expression and myeloperoxidase (MPO) level in the ischemic lobes were examined by northern blot and myeloperoxidase assay respectively.

AST levels were significantly decreased in TLR4deficient mice compared with WT mice at both time points (WT: 1215.5+/-174.03, 2958.17+/-186.81 IU/L at 1 and 3 hours respectively vs TLR4def: 661.83+/-106.09, 1145.17+/-132.43 IU/L at 1 and 3 hours, mean+/-SD, 6 mice/group, t=-6.65 and -5.57, P<0.001). Consistent with the role of TNF-alpha in hepatic I/R, serum TNF-alpha was decreased in TLR4 deficient mice at 3 hours after reperfusion compared with WT (152.39+/-43.3 vs 249.12+/-51.89, n=6, t=-3.13, P<0.05). MPO level in the ischemic lobes in TLR4 deficient mice at 3 hours after reperfusion was significantly lower than that in WT mice (0.059 +/-0.004 vs 0.173+/-0.025, n=6, F=33.49, P<0.001). This difference appears to be mediated at the gene level since TLR4 deficient mice had decreased TNF-alpha mRNA expression at 1 hour after reperfusion compared with WT mice (80.3+/-28.8 vs 189.4+/-24.6, t=-3.25, P<0.05).

Compared with WT mice, TLR4-deficient mice appear to have a mild I/R injury. Regulation of TNF-alpha at mRNA level seems to have a critical effect. These suggest TLR4 be involved in the mechanism of hepatic I/R injury in mice.