Early Transcriptome Changes Associated with Western Diet Induced NASH in Ldlr-/- Mice Points to Activation of Hepatic Macrophages and an Acute Phase Response

BackgroundNonalcoholic fatty liver disease (NAFLD) is a global health problem. Identifying early gene indicators contributing to the onset and progression of NAFLD has the potential to develop novel targets for early therapeutic intervention. We report on the early and late transcriptomic signatures of western diet (WD)-induced nonalcoholic steatohepatitis (NASH) in female and male Ldlr(-/-) mice, with time-points at 1 week and 40 weeks on the WD. Control Ldlr(-/-) mice were maintained on a low-fat diet (LFD) for 1 and 40 weeks. MethodsThe approach included quantitation of anthropometric and hepatic histology markers of disease as well as the hepatic transcriptome. ResultsOnly mice fed the WD for 40 weeks revealed evidence of NASH, i.e., hepatic steatosis and fibrosis. RNASeq transcriptome analysis, however, revealed multiple cell-specific changes in gene expression after 1 week that persisted to 40 weeks on the WD. These early markers of disease include induction of acute phase response (Saa1-2, Orm2), fibrosis (Col1A1, Col1A2, TGF & beta;) and NASH associated macrophage (NAM, i.e., Trem2 high, Mmp12 low). We also noted the induction of transcripts associated with metabolic syndrome, including Mmp12, Trem2, Gpnmb, Lgals3 and Lpl. Finally, 1 week of WD feeding was sufficient to significantly induce TNF & alpha;, a cytokine involved in both hepatic and systemic inflammation. ConclusionThis study revealed early onset changes in the hepatic transcriptome that develop well before any anthropometric or histological evidence of NALFD or NASH and pointed to cell-specific targeting for the prevention of disease progression.