IL-6 trans-Signaling Regulates Neutrophilic Inflammation in Alcohol-Associated Hepatitis.

Abstract

Alcohol-associated hepatitis (AH) is a form of acute-on-chronic liver failure characterized by intrahepatic neutrophilic inflammation. In hepatocytes, IL-6 can signal through membrane-bound (classical signaling) or soluble (trans-signaling; TS) IL-6 receptors (IL-6Rs) to regulate liver injury responses. This study determined the role of IL-6TS in the pathophysiology of AH. Liver RNA sequencing in alcohol-related liver disease patients demonstrated declining IL-6R expression with increasing AH severity, and transforming growth factor (TGF)-β1 was the strongest negative regulator of IL-6R expression; however, STAT3-dependent gene expression was increased in severe AH. In vitro, HepG2 cells were exposed to TGF-β1 to inhibit IL-6R expression, followed by STAT3 activation with either IL-6 to stimulate classical signaling, or hyper-IL-6, a recombinant IL-6/IL-6R α peptide, to activate trans-signaling. Hyper-IL-6, but not IL-6, restored STAT3 activation in the face of suppressed IL-6R. RNA sequencing was performed on hyper-IL-6 stimulated cells, yielding a gene signature that identified a subset of AH patients with: i) enhanced IL-6TS activity, ii) increased intrahepatic neutrophilic infiltration, and iii) transcriptional enrichment of leukocyte migration pathways. Female mice treated with 10-day chronic-plus-binge ethanol exhibited enhanced STAT3 activation despite reduced hepatic IL-6R expression, leading to increased expression of neutrophilic activators, with colocalization of Ly6G⁺ leukocytes and STAT3⁺ hepatocytes. IL-6TS preserves hepatocyte STAT3-dependent gene expression and neutrophilic inflammation in AH.