Mice with Endogenously Increased ωPUFAs are Resistant to Alcohol‐Mediated Down‐Regulation of Wnt Signaling
Authors: Warner Dennis Ray , Song Ying , Warner Jeffrey , McClain Craig , Kirpich Irina 
Published: April 2020

Background/Objectives

Chronic alcohol consumption can lead to a plethora of detrimental health effects, including alcoholic liver disease (ALD), which is characterized by steatosis and steatohepatitis with varying degrees of fibrosis and cirrhosis. Unresolved inflammation and impaired mechanisms of liver tissue repair and regeneration are among major contributors to disease progression. Canonical Wnt signaling is important for tissue regeneration following hepatocellular damage and regulation of inflammation. It has been shown that hepatic Wnt signaling is down‐regulated in rodent models of ALD and that restoration of this pathway can ameliorate this disease. Our group is focused on nutritional interventions as a treatment/prevention paradigm for ALD, specifically with ω3 polyunsaturated fatty acids (PUFAs), which have numerous beneficial effects, including metabolism to specialize pro‐resolving mediators (SPM), a class of lipid molecules that are important for limiting the inflammatory response and a return to homeostasis. The objective of the current study was to test the hypothesis that ω3 PUFAs are beneficial in ALD via improving EtOH‐induced alterations in Wnt signaling.

Methods

Male WT and fat‐1+/− mice (that endogenously convert ω6 PUFAs to ω3) were provided a liquid diet that was supplemented with ethanol (EtOH) as follows: 0–3% (v/v) over the course of 1 week, 4% for 1 week, 5% for 1 week, and 6% for 3 weeks. To simulate human ALD associated with endotoxemia, LPS was administered to mice 24h before euthanasia (5 mg/kg, i.p.). Liver injury was assessed by plasma ALT activity, histopathology, and the expression of pro‐inflammatory cytokines. Liver RNA was extracted and the expression of 84 genes in the Wnt signaling pathway was determined by PCR array.

Results

We found that EtOH‐fed, LPS‐challenged fat‐1 mice had attenuated liver injury (reduced ALT levels), with reduced hepatic neutrophil accumulation, significant reduction in the expression of proinflammatory Pai‐1 and an increase in anti‐inflammatory Il‐10 levels, compared to WT mice. We also found that EtOH+LPS treated WT mice had a greater decrease in the expression of Axin2 (an endogenous readout of canonical Wnt signaling) than fat‐1 mice (8‐fold vs. 3‐fold, respectively, vs. control, pair‐fed mice). EtOH+LPS treated WT mice also had a significant increase in hepatic expression of the Wnt inhibitor, Dkk3, whereas fat‐1 mice had decreased expression of this gene when compared to pair‐fed controls. Finally, the expression of the repressor protein, Nfatc1, was increased to a greater extent in EtOH‐LPS treated WT vs. fat‐1 mice. Taken together, these data suggest that EtOH+LPS‐mediated downregulation of Wnt signaling was attenuated in fat‐1 mice.

Conclusions

fat‐1 mice are partially protected from alcohol‐induced liver disease. Canonical Wnt signaling was reduced to a greater extent in WT than in fat‐1 mice and was associated with increased liver damage and inflammation. These data provide evidence that restoration of the Wnt signaling pathway through dietary means may be a viable strategy to treat or prevent ALD.

Support or Funding Information

The work presented in this study was supported by the National Institutes of Health and the Department of Veterans Affairs.