The role of hepatic cholesterol crystals and NLRP3 inflammasome in ABCG5/G8-deficient mice

 

The NLRP3 inflammasome plays an important role in metabolic fatty liver diseases (MAFLD). Hepatic damage is attributed, at least in part, to the accumulation of lipid molecules and/or cholesterol crystals. During non-alcoholic steatohepatitis (NASH) Nlrp3 is upregulated, leading to hepatic inflammation and progression to liver fibrosis, cirrhosis, and hepatocellular carcinoma. The hepatobiliary cholesterol transporter Abcg5/g8 protects the hepatocyte from cholesterol overload and is an important mediator of whole-body cholesterol homeostasis. The aim of the present study was to analyze the sterile inflammatory response by NLRP3/IL-1b in liver- and intestine-specific ABCG5/G8-deficient mice.

Using BAC-recombineering, conditional Abcg5/g8 knock-out mice were generated allowing tissue-specific deletion of the first two exons of Abcg5 and the first exon of Abcg8 by Cre-mediated recombination. Abcg5/g8 flox mice were crossed to Villin-Cre mice, expressing Cre in the intestine under the control of the Villin promoter (Int-KO), and Albumin-Cre mice, allowing hepatocyte-specific deletion of the transporter (Hep-KO). Mice were either fed chow or lithogenic diet (15 % butter fat, 1 % cholesterol, 0.5 % cholic acid), respectively. Expression analyses for Nlrp3 and Il1b as well as histological determination of neutral lipids by Oil Red O staining and cholesterol crystals using polarizing light microscopy were performed.

Under chow diet, Nlrp3 was decreased in both knock-out mice compared to wild-type (WT) controls, whereas Nlrp3 was significantly induced when challenged with the lithogenic diet. Il1b was not affected in chow-fed mice and showed no difference in HepKO mice upon lithogenic diet feeding but was increased in IntKO mice. Hepatic lipid contents were increased in both knockout groups fed chow but increased irrespective of genotype on the lithogenic diet. Of note, the amount of cholesterol crystals increased significantly in HepKO upon lithogenic diet challenge, but were not altered in IntKO as compared to WT.

The results show that tissue-specific deletion of Abcg5/g8 in liver or intestine leads to elevated levels of Nlrp3, Il1b and hepatic lipid contents as well as cholesterol crystallization under lithogenic diet. Intrahepatic cholesterol crystals are drivers of hepatic inflammation during NASH by activating the inflammasome. Liver- and intestine-specific ABCG5G5/G8-deficient mice might serve as a new model to study MAFLD/NASH in mice.

Publication History

Article published online:
04 January 2021

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