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

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) IL-6 receptors to regulate liver injury responses. The goal of this study was to determine the role of IL-6 trans signaling in the pathophysiology of AH. Liver RNA-Seq from alcohol-related liver disease patients demonstrated declining IL-6 receptor (IL-6R) expression with increasing AH severity, and TGF-β1 was the strongest negative regulator of IL-6R expression; however, STAT3-dependent gene expression increased in severe AH. In vitro, HepG2 cells were exposed to TGF-β1 to inhibit IL-6R expression, followed by STAT3 activation with 1) IL-6 to stimulate classical signaling or 2) hyper-IL-6, a recombinant IL-6/IL-6Rα peptide, to activate trans signaling. Only hyper-IL-6, but not IL-6, restored STAT3 activation in the face of suppressed IL-6R. RNA-Seq was performed on hyper-IL-6-stimulated cells, yielding a gene signature identifying a subset of AH patients with 1) enhanced IL-6TS activity 2) increased intrahepatic neutrophilic infiltration and 3) transcriptional enrichment of leukocyte migration pathways. Female mice treated with a 10-day chronic-plus binge ethanol model exhibited enhanced STAT3 activation despite reduced hepatic IL-6R expression, leading to increased expression of neutrophilic activators with colocalization of Ly6G+ leukocytes and STAT3-positive hepatocytes. IL-6 trans signaling preserves hepatocyte STAT3-dependent gene expression and neutrophilic inflammation in AH.