Lipotoxicity Amplifies IL‐6 Trans‐Signaling in Sinusoidal Endothelial Cells to Promote Endotheliopathy and Liver Injury

BACKGROUND AND AIMS: Metabolic dysfunction-associated steatotic liver disease (MASLD) affects approximately 25% of the global population and is a major health concern. Liver sinusoidal endothelial cells (LSECs) undergo morphological and functional alterations during MASLD progression, resulting in endotheliopathy characterized by pro-inflammatory phenotypes. We hypothesize that lipotoxicity synergistically exacerbates LSEC dysfunction in MASLD via IL-6 trans-signaling. METHODS: Human adipocytes were treated with palmitic acid (PA). Human LSECs were treated with PA and the IL-6/soluble IL-6 receptor (sIL-6R) complex. Western blotting, qRT-PCR, RNA sequencing, transwell assays, and immunofluorescence were performed to examine inflammatory responses. MASLD model mice were established using a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) to validate the in vivo results. Alterations in LSEC morphology were examined by western blotting, histology, and electron microscopy. RESULTS: PA promoted IL-6 secretion from adipocytes. In LSECs, PA increased NFκB phosphorylation, whereas co-stimulation with PA and IL-6/sIL-6R complex synergistically enhanced activator of transcription 3 (STAT3) phosphorylation and upregulated inflammatory cytokines, chemokines, and adhesion molecules, including VCAM1. Furthermore, RNA sequencing showed concurrent NFκB and Janus kinase (JAK)/STAT pathway activation. This synergistic effect promoted neutrophil migration and VCAM1 expression under in vitro conditions. In the MASLD mouse model, hepatic IL-6 expression was elevated, accompanied by steatosis, increased transaminase levels, and inflammatory cell infiltration, along with increased VCAM1 expression and sinusoidal capillarization characterized by upregulated CD34 and downregulated CD32b and LYVE-1. CONCLUSION: Lipotoxicity-amplified IL-6 trans-signaling synergistically exacerbates LSEC endotheliopathy and promotes leukocyte recruitment and liver injury, contributing to MASLD progression and providing novel insights into its pathogenesis.