MyD88-dependent signaling in non-parenchymal cells promotes liver carcinogenesis.

In Western countries, a rising incidence of obesity and type 2 diabetes correlates with an increase of non-alcoholic steatohepatitis (NASH)-a major risk factor for liver cirrhosis and hepatocellular carcinoma (HCC). NASH is associated with chronic liver injury, triggering hepatocyte death and enhanced translocation of intestinal bacteria, leading to persistent liver inflammation through activation of Toll-like receptors and their adapter protein myeloid differentiation factor 88 (MyD88). Therefore, we investigated the role of MyD88 during progression from NASH to HCC using a mouse model of chronic liver injury (hepatocyte-specific deletion of nuclear factor κB essential modulator, Nemo; NemoΔhepa). NemoΔhepa; NemoΔhepa/MyD88-/- and NemoΔhepa/MyD88Δhepa were generated and the impact on liver disease progression was investigated. Ubiquitous MyD88 ablation (NemoΔhepa/MyD88-/-) aggravated the degree of liver damage, accompanied by an overall decrease in inflammation, whereas infiltrating macrophages and natural killer cells were elevated. At a later stage, MyD88 deficiency impaired HCC formation. In contrast, hepatocyte-specific MyD88 deletion (NemoΔhepa/MyD88Δhepa) did not affect disease progression. These results suggest that signaling of Toll-like receptors through MyD88 in non-parenchymal liver cells is required for carcinogenesis during chronic liver injury. Hence, blocking MyD88 signaling may offer a therapeutic option to prevent HCC formation in patients with NASH.

Hepatic overexpression of cAMP-responsive element modulator α induces a regulatory T-cell response in a murine model of chronic liver disease.

OBJECTIVE: Th17 cells are a subset of CD4+ T-helper cells characterised by interleukin 17 (IL-17) production, a cytokine that plays a crucial role in inflammation-associated diseases. The cyclic AMP-responsive element modulator-α (CREMα) is a central mediator of T-cell pathogenesis, which contributes to increased IL-17 expression in patients with autoimmune disorders. Since an increased Th17 response is associated with a poor prognosis in patients with chronic liver injury, we investigated the relevance of Th17 cells for chronic liver disease (CLD) and hepatocarcinogenesis. DESIGN: Transgenic mice overexpressing CREMα were crossed with hepatocyte-specific Nemo knockout mice (NemoΔhepa) to generate NemoΔhepa/CREMαTg mice. The impact of CREMαTg on CLD progression was examined. Additionally, soft agar colony formation assays, in vitro studies, adoptive transfer of bone marrow-derived cells (BMDCs) and T cells, and gene arrays in T cells were performed. RESULTS: 8-week-old NemoΔhepa/CREMαTg mice presented significantly decreased transaminase levels, concomitant with reduced numbers of CD11b+ dendritic cells and CD8+ T cells. CREMαTg overexpression in NemoΔhepa mice was associated with significantly reduced hepatic fibrogenesis and carcinogenesis at 52 weeks. Interestingly, hepatic stellate cell-derived retinoic acid induced a regulatory T-cell (Treg) phenotype in CREMαTg hepatic T cells. Moreover, simultaneous adoptive transfer of BMDCs and T cells from CREMαTg into NemoΔhepa mice ameliorated markers of liver injury and hepatitis. CONCLUSIONS: Our results demonstrate that overexpression of CREMα in T cells changes the inflammatory milieu, attenuating initiation and progression of CLD. Unexpectedly, our study indicates that CREMα transgenic T cells shift chronic inflammation in NemoΔhepa livers towards a protective Treg response.

Functional role of CCL5/RANTES for HCC progression during chronic liver disease.

BACKGROUND & AIMS: During liver inflammation, triggering fibrogenesis and carcinogenesis immune cells play a pivotal role. In the present study we investigated the role of CCL5 in human and in murine models of chronic liver inflammation leading to hepatocellular carcinoma (HCC) development. METHODS: CCL5 expression and its receptors were studied in well-defined patients with chronic liver disease (CLD) and in two murine inflammation based HCC models. The role of CCL5 in inflammation, fibrosis, tumor initiation and progression was analyzed in different cell populations of NEMOΔhepa/CCL5-/- animals and after bone marrow transplantation (BMT). For therapeutic intervention Evasin-4 was injected for 24h or 8weeks. RESULTS: In CLD patients, CCL5 and its receptor CCR5 are overexpressed - an observation confirmed in the Mdr2-/- and NEMOΔhepa model. CCL5 deletion in NEMOΔhepa mice diminished hepatocyte apoptosis, compensatory proliferation and fibrogenesis due to reduced immune cell infiltration. Especially, CD45+/Ly6G+ granulocytes, CD45+/CD11b+/Gr1.1+/F4/80+ pro-inflammatory monocytes, CD4+ and CD8+ T cells were decreased. One year old NEMOΔhepa/CCL5-/- mice displayed smaller and less malignant tumors, characterized by reduced proliferative capacity and less pronounced angiogenesis. We identified hematopoietic cells as the main source of CCL5, while CCL5 deficiency did not sensitise NEMOΔhepa hepatocytes towards TNFα induced apoptosis. Finally, therapeutic intervention with Evasin-4 over a period of 8weeks ameliorated liver disease progression. CONCLUSION: We identified an important role of CCL5 in human and functionally in mice with disease progression, especially HCC development. A novel approach to inhibit CCL5 in vivo thus appears encouraging for patients with CLD. LAY SUMMARY: Our present study identifies the essential role of the chemoattractive cytokine CCL5 for liver disease progression and especially hepatocellular carcinoma development in men and mice. Finally, the inhibition of CCL5 appears to be encouraging for therapy of human chronic liver disease.