Deletion of tumor progression locus 2 attenuates alcohol-induced hepatic inflammation

Abstract

Background: The pathogenesis of alcoholic liver disease (ALD) involves the interaction of several inflammatory signaling pathways. Tumor progression locus 2 (TPL2), also known as Cancer Osaka Thyroid (COT) and MAP3K8, is a serine-threonine kinase that functions as a critical regulator of inflammatory pathways by up-regulating production of inflammatory cytokines. The present study aims to fill the gap in knowledge regarding the involvement of TPL2 in the mechanism of alcohol-induced hepatic inflammation.

Methods: Male TPL2(-/-) knockout (TPL2KO) mice and TPL2(+/+) wild-type (WT) mice were group pair-fed with Lieber-DeCarli liquid ethanol diet (EtOH diet, 27% energy from EtOH) or control diet (ctrl diet) for 4 weeks. Both histological and molecular biomarkers involved in the induction of hepatic inflammation by alcohol consumption were examined.

Results: Consumption of the EtOH diet in WT mice lead to a significant induction of TPL2 mRNA expression as compared with WT mice fed ctrl diet. A significant induction in inflammatory foci and steatosis was also observed in WT mice fed EtOH diet. The deletion of TPL2 significantly reduced inflammatory foci in the liver of mice consuming both ctrl and EtOH diets as compared to their respective WT controls. This reduction was associated with suppression of hepatic inflammatory gene expression of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) and macrophage marker F4/80. In addition, histological analysis of livers revealed that TPL2 deletion resulted in reduced steatosis in both ctrl (significant) and EtOH (non-significant) diet-fed mice as compared to their respective WT controls.

Conclusions: The demonstration that TPL2 deletion attenuates alcohol-induced hepatic inflammation provides evidence of a novel role for TPL2 in the pathogenesis of ALD.

Keywords: Alcohol; inflammation; liver disease; tumor progression locus 2 (TPL2).

Figure 1

Hepatic TPL2 mRNA expression is significantly increased with EtOH diet. TPL2 mRNA expression was examined in livers of WT and TPL2KO mice. No mRNA expression was detected in any of the TPL2KO mice. Values expressed as mean ± SEM and n=5–9. The t-test was performed on log transformed data for each treatment group. (*, P<0.05). Abbreviations: N.D., not determined; ctrl diet, control diet; EtOH diet, ethanol diet; TPL2, tumor progression locus 2; WT, wild-type; GAPDH, glyceraldehyde 3-phosphate dehydrogenase.

Figure 2

Deletion of TPL2 reduces hepatic inflammatory foci in mice fed both ctrl and EtOH diet. Twenty images at 100× magnification were captured for each section and blindly evaluated twice regarding the severity of liver inflammation by two separate investigators. Severity of liver inflammation was estimated by the number of inflammatory foci present. Values are expressed as means ± SEM. ANOVA followed by Tukey’s HSD was performed on log transformed data. A,B,C, data not sharing a common superscript letter are statistically significant from each other (P<0.05). Insert: representative inflammatory foci as seen on a H&E stained slide. Abbreviations: ctrl diet, control diet; EtOH diet, ethanol diet; WT, wild-type; TPL2KO, tumor progression locus 2 knock-out.

Figure 3

TPL2 deletion decreases inflammatory and macrophage marker gene expression. TPL2 deletion decreases relative mRNA expression of inflammatory and macrophage markers in liver tissue in mice fed ctrl and EtOH diet. Values expressed as mean ± SEM and n=5–9. The t-test was performed on log transformed data for each treatment group. (*, P<0.05). Abbreviations: ctrl diet, control diet; EtOH diet, ethanol diet; WT, wild-type; TPL2KO, tumor progression locus 2 knock-out; TNFα, tumor necrosis factor α; IL-6, interleukin 6; IL-1β, interleukin 1β; MCP1, monocyte chemoattractant protein 1; TLR4, toll-like receptor 4; GAPDH, glyceraldehyde 3-phosphate dehydrogenase.