IL-18 but Not IL-1 Signaling Is Pivotal for the Initiation of Liver Injury in Murine Non-Alcoholic Fatty Liver Disease.

Doris Mayr,Ralf Wimmer,Hans Zischka,Jutta Nagel,Simon Hohenester,Christian Rust,Florian P Reiter,Max Schnurr,Alexander L Gerbes,Christian Bauer,Gerald Denk,Andreas Geier,Lesca Holdt,Claudia Einer,Tobias Schiergens,Veronika Kanitz,Enrico N De Toni

doi:10.3390/ijms21228602

Abstract

Non-alcoholic fatty liver disease (NAFLD) is rising in prevalence, and a better pathophysiologic understanding of the transition to its inflammatory phenotype (NASH) is key to the development of effective therapies. To evaluate the contribution of the NLRP3 inflammasome and its downstream effectors IL-1 and IL-18 in this process, we applied the true-to-life “American lifestyle-induced obesity syndrome” (ALiOS) diet mouse model. Development of obesity, fatty liver and liver damage was investigated in mice fed for 24 weeks according to the ALiOS protocol. Lipidomic changes in mouse livers were compared to human NAFLD samples. Receptor knockout mice for IL-1 and IL-18 were used to dissect the impact of downstream signals of inflammasome activity on the development of NAFLD. The ALiOS diet induced obesity and liver steatosis. The lipidomic changes closely mimicked changes in human NAFLD. A pro-inflammatory gene expression pattern in liver tissue and increased serum liver transaminases indicated early liver damage in the absence of histological evidence of NASH. Mechanistically, Il-18r−/−- but not Il-1r−/− mice were protected from early liver damage, possibly due to silencing of the pro-inflammatory gene expression pattern. Our study identified NLRP3 activation and IL-18R-dependent signaling as potential modulators of early liver damage in NAFLD, preceding development of histologic NASH.

Highlights

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has become a leading cause of chronic liver disease in many regions of the world [1], is still on the rise [2,3] and has been termed the “first pandemic” of the 21st century [4]
Our study identified NLRP3 activation and IL-18R-dependent signaling as potential modulators of early liver damage in NAFLD, preceding development of histologic non-alcoholic steatohepatitis (NASH)
NAFLD comprises a wide spectrum from simple hepatic steatosis to non-alcoholic steatohepatitis (NASH), characterized byinflammation and fibrosis that develop in 20% of patients with NASH

Summary

Introduction

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has become a leading cause of chronic liver disease in many regions of the world [1], is still on the rise [2,3] and has been termed the “first pandemic” of the 21st century [4]. This diet has been shown to induce obesity, glucose intolerance, hyperinsulinemia and substantial hepatic steatosis associated with necroinflammation and a profibrogenic response in mice [22] Applying this model, we revisited the contribution of the NLRP3 inflammasome, i.e., its effector cytokines IL-1 and IL-18, for the development of liver damage in NAFLD. Downstream of the activation of the inflammasome, the pro-inflammatory gene expression profile that had developed upon ALiOS diet feeding in wildtype animals was abrogated in Il-18r −/−mice (Figure 4C). In Il-18r −/− animals, activation of the inflammasome in steatotic livers was abrogated and the development of a pro-inflammatory environment in the liver was prevented independently of fatty acid composition or mitochondrial dysfunction in hepatic steatosis

Discussion

Animal Experiments

Human Tissue

Serum Biochemistry

Analysis of Fatty Acids by Gas Chromatography

Isolation of Mitochondria

Multiplex Assay

Findings

Statistical Testing