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 signals through either membrane-bound (classical signaling) or soluble (trans-signaling; TS) IL-6 receptors (IL-6Rs) to regulate liver injury responses. This study investigated the role of IL-6TS in the pathophysiology of AH. RNA sequencing of liver biopsies from patients with alcohol-related liver disease demonstrated a progressive decline in IL-6R expression correlating with increasing AH severity. Transforming growth factor (TGF)-β1 emerged as the most potent negative regulator of IL-6R expression. Notably, STAT3-dependent gene expression was increased in severe AH. In vitro, treatment of HepG2 cells with TGF-β1 suppressed IL-6R expression. Subsequent treatment with either IL-6 to stimulate classical signaling, or hyper-IL-6, a recombinant IL-6/IL-6R α peptide, to activate trans-signaling activated STAT3. Hyper-IL-6, but not IL-6, restored STAT3 activation in the face of suppressed IL-6R. RNA sequencing of hyper-IL-6 stimulated cells identified a gene signature that stratified 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. Collectively, these results indicate that IL-6TS preserves hepatocyte STAT3-dependent gene expression and promotes neutrophilic inflammation in AH.