The EGFR Liver Regeneration Pathway is Downregulated in Alcoholic Hepatitis

Abstract

BackgroundAlcoholic liver disease (ALD) is a spectrum of progressive alcohol‐induced liver disorders including steatosis, steatohepatitis, and fibrosis. Alcoholic Hepatitis (AH), a clinical manifestation of severe liver damage, is associated with a hyper‐activated inflammatory immune response. The liver has an innate ability to regenerate after injury and inflammation. In severe liver diseases, including AH, this regenerative process becomes impaired. Not all the mechanisms are fully understood in the development/progression of AH, including the molecular events involved in alterations of liver tissue repair and regeneration. Recently, the epidermal growth factor receptor (EGFR) signaling pathway has been implicated in liver regeneration. The downstream effector, the E3 ubiquitin protein ligase, NEDD4, was demonstrated to be essential for EGFR internalization and signaling in vivo. NEDD4 facilitates EGFR internalization and downstream extracellular regulated kinase 1/2(ERK1/2) and signal transducer and activator 3 (STAT3) activity. The role of this pathway in liver regeneration in AH is not well defined.ObjectiveTo identify alterations of EGFR signaling in the liver of AH patients by proteomic and phosphoproteomic approach.MethodsLiquid chromatography and tandem mass spectrometry analysis were performed to measure proteomic and phosphoproteomic changes in liver tissue samples from AH patients (n=6, 44.3 ± 11.1 year old with MELD 37.2 ± 4.3, ABIC 9.61 ± 2.2, and Lille Score 0.57 ± 0.3), and age‐ and sex‐matched controls (individuals without ALD, n=12). A Student’s two‐tailed unpaired t‐test was used to determine statistical significance between the two groups (p<0.05). Linear regression analysis was performed between proteomic/phosphoproteomic data and markers of AH severity/prognosis (MELD, ABIC, and Lille Scores).ResultsEGFR protein was downregulated in AH relative to controls (1.2‐fold, p=0.02). Phosphorylation of EGFR at Y1069 was reduced 1.7‐fold, p=0.05 demonstrating decreased receptor activity. Hepatic EGFR was negatively associated with MELD (R2=0.2646), ABIC (R2=0.6719), and Lille Score (R2=0.4768). Hepatic NEDD4 was trending downward in AH relative to controls, and was negatively correlated with MELD (R2=0.8472), ABIC (R2=0.2982) and Lille Score (R2=0.52). Phosphorylated T202/Y204 relative to total ERK1 was decreased 1.5‐fold, p=0.0007 in AH relative to controls. Phospho‐ERK1 was also negatively associated with ABIC (R2=0.4523) and Lille Score (R2=0.4446). STAT3, the transcription factor that transcriptionally regulates proliferation genes in hepatocytes was decreased in AH relative to controls (1.2‐fold, p=0.01). Activation of STAT3 via phosphorylation of S714 was negatively correlated with ABIC (R2=0.8327, p=0.01) and Lille Score (R2=0.94, p<0.002).ConclusionCollectively, the data demonstrated that EGFR signaling was downregulated in AH patients which was negatively associated with disease severity. Downregulation of the EGFR pathway may potentially contribute to compromised liver regeneration in AH patients.Support or Funding InformationNIH NIAAA