The Contribution of Toll-Like Receptor Signaling to the Development of Hepatic Fibrosis and Carcinogenesis in Hepatocyte Specific TAK1 Deleted Mice
Jingyi Song, Sayaka Inokuchi, Yoonseok Roh, Ling Yang, Ekihiro Seki
Medicine, University of California, San Diego, School of Medicine, La Jolla, CA
Background: TGF-β -activated kinase 1(TAK1) is critical to activate the JNK and NF-kB signaling pathways. Gene disruption of TAK1 in hepatocytes has demonstrated that TAK1 is a key regulator of inflammation, fibrosis, cell survival, and carcinogenesis. We will examine the roles of Toll-like receptor 4, 9 (TLR4, TLR9), MyD88, IL1 receptor (IL1R), and TNF receptor (TNFR) in the development of liver fibrosis and carcinogenesis in hepatocyte-specific TAK1 deleted mice (TAK1 AH). Methods: TAK1 AH were crossed with mice deficient in TNFR, TLR4, TLR9, MyD88, and IL1R, to generate double knockout mice. Liver morphologies and functions were studied in mice at 1, 4, and 9 months of age. Results: TAK1 AH mice had increased ALT levels, inflammatory cell infiltration, collagen deposition, and development of visible liver tumors. At 1 month of age, ALT levels reduced significantly to 577U/L in TAK1ΔH/TNFR-/-, but remained at 1670U/L in TAK1ΔH/TLR4-/-, compared to 1608U/L in TAK1 AH mice. The deletion of TNFR and TLR4 in TAK1 AH mice significantly reduced macrophage infiltration assessed by immunohistochemistry (IHC) for F4/80 (35 and 39% reduction vs. TAK1 AH). Myofibroblast activation, as assessed by IHC for αSMA, was reduced in 1-month-old TAK1 AH/TNFR-/- and TAK1ΔH/TLR4-/- by 49 and 57%, respectively, compared with TAK1 AH. Liver fibrosis was reduced in 9-month-old TAK1 ΔH/TNFR-/- and TAK1ΔH/TLR4-/(54 and 77% reduction vs. TAK1 AH). Subsequent studies made in TAK1ΔH/TLR9-/- and TAK1 ΔH /MyD88-/- showed reductions in ALT levels (744 and 887 vs. 1608U/L in TAK1 AH), macrophage infiltration (46% and 24% reduction vs. TAK1 AH), myofibroblast activation (64 and 52% reduction vs. TAK1 AH) at 1 month of age, and hepatic fibrosis at 9 months of age (36 and 42% reduction vs. TAK1 ΔH). Compared with TAK1 AH mice, levels of related mRNAs such as Col1a, Timp1, Ccl2, and Tnfα were suppressed by additional deletions of TNFR, TLR4, TLR9, and MyD88 in 1-month-old mice. At 9 months of age, TAK1 AH/TNFR-/-, TAK1ΔH/TLR4-/-, TAK1ΔH/TLR9-/- and TAK1 ΔH/MyD88-/- mice displayed fewer and smaller tumors compared with TAK1 AH mice (by numbers, 4, 10, 11, 5 vs. 18 in TAK1 AH; by max sizes 1. 2, 3. 5, 4. 3, and 3. 1 vs 7. 1mm in TAK1 AH). Although 1-month-old TAK1ΔH/IL1 R mice had reduced macrophage infiltration and hepatic fibrosis (25 and 37% vs. TAK1 AH), tumor numbers and sizes were not reduced in comparison with TAK1 AH. Conclusions: TNFR, TLR4, TLR9, and MyD88 signaling may promote liver injury, inflammation, fibrosis, and compensatory proliferation in TAK1 AH mice. IL1R signaling may be critical for the formation of hepatic fibrosis but not for liver injury and carcinogenesis.
The following people have nothing to disclose: Jingyi Song, Sayaka Inokuchi, Yoonseok Roh, Ling Yang, Ekihiro Seki