The hepatocyte IKK:NF-κB axis promotes liver steatosis by stimulating de novo lipogenesis and cholesterol synthesis

Andries Heida; Nanda Gruben; Leen Catrysse; Martijn Koehorst; Mirjam Koster; Niels J Kloosterhuis; Albert Gerding; Rick Havinga; Vincent W Bloks; Laura Bongiovanni; Justina C Wolters; Theo van Dijk; Geert van Loo; Alain de Bruin; Folkert Kuipers; Debby P Y Koonen; Bart van de Sluis

doi:10.1016/j.molmet.2021.101349

The hepatocyte IKK:NF-κB axis promotes liver steatosis by stimulating de novo lipogenesis and cholesterol synthesis

Mol Metab. 2021 Dec:54:101349. doi: 10.1016/j.molmet.2021.101349. Epub 2021 Oct 6.

Authors

Andries Heida¹, Nanda Gruben¹, Leen Catrysse², Martijn Koehorst¹, Mirjam Koster¹, Niels J Kloosterhuis¹, Albert Gerding¹, Rick Havinga¹, Vincent W Bloks¹, Laura Bongiovanni³, Justina C Wolters¹, Theo van Dijk⁴, Geert van Loo², Alain de Bruin⁵, Folkert Kuipers⁶, Debby P Y Koonen⁷, Bart van de Sluis⁸

Affiliations

¹ Departments of Pediatrics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.
² VIB Inflammation Research Center, Ghent University, Ghent, Belgium; Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
³ Department of Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, the Netherlands; Faculty of Veterinary Medicine, University of Teramo, Teramo, Italy.
⁴ Departments of Laboratory Medicine, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.
⁵ Departments of Pediatrics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands; Department of Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, the Netherlands.
⁶ Departments of Pediatrics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands; Departments of Laboratory Medicine, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.
⁷ Departments of Pediatrics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands. Electronic address: D.P.Y.Koonen@umcg.nl.
⁸ Departments of Pediatrics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands. Electronic address: A.J.A.van.de.Sluis@umcg.nl.

Abstract

Objective: Obesity-related chronic inflammation plays an important role in the development of Metabolic Associated Fatty Liver Disease (MAFLD). Although the contribution of the pro-inflammatory NF-κB signaling pathway to the progression from simple steatosis to non-alcoholic steatohepatitis (NASH) is well-established, its role as an initiator of hepatic steatosis and the underlying mechanism remains unclear. Here, we investigated the hypothesis that the hepatocytic NF-κB signaling pathway acts as a metabolic regulator, thereby promoting hepatic steatosis development.

Methods: A murine model expressing a constitutively active form of IKKβ in hepatocytes (Hep-IKKβca) was used to activate hepatocyte NF-κB. In addition, IKKβca was also expressed in hepatocyte A20-deficient mice (IKKβca;A20^LKO). A20 is an NF-κB-target gene that inhibits the activation of the NF-κB signaling pathway upstream of IKKβ. These mouse models were fed a sucrose-rich diet for 8 weeks. Hepatic lipid levels were measured and using [1-¹³C]-acetate de novo lipogenesis and cholesterol synthesis rate were determined. Gene expression analyses and immunoblotting were used to study the lipogenesis and cholesterol synthesis pathways.

Results: Hepatocytic NF-κB activation by expressing IKKβca in hepatocytes resulted in hepatic steatosis without inflammation. Ablation of hepatocyte A20 in Hep-IKKβca mice (IKKβca;A20^LKO mice) exacerbated hepatic steatosis, characterized by macrovesicular accumulation of triglycerides and cholesterol, and increased plasma cholesterol levels. Both De novo lipogenesis (DNL) and cholesterol synthesis were found elevated in IKKβca;A20^LKO mice. Phosphorylation of AMP-activated kinase (AMPK) - a suppressor in lipogenesis and cholesterol synthesis - was decreased in IKKβca;A20^LKO mice. This was paralleled by elevated protein levels of hydroxymethylglutaryl-CoA synthase 1 (HMGCS1) and reduced phosphorylation of HMG-CoA reductase (HMGCR) both key enzymes in the cholesterol synthesis pathway. Whereas inflammation was not observed in young IKKβca;A20^LKO mice sustained hepatic NF-κB activation resulted in liver inflammation, together with elevated hepatic and plasma cholesterol levels in middle-aged mice.

Conclusions: The hepatocytic IKK:NF-κB axis is a metabolic regulator by controlling DNL and cholesterol synthesis, independent of its central role in inflammation. The IKK:NF-κB axis controls the phosphorylation levels of AMPK and HMGCR and the protein levels of HMGCS1. Chronic IKK-mediated NF-κB activation may contribute to the initiation of hepatic steatosis and cardiovascular disease risk in MAFLD patients.

Keywords: Cardiovascular disease; Hypercholesterolemia; Inflammation; Lipid metabolism; Mevalonate pathway; Steatosis.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Cholesterol / biosynthesis*
Disease Models, Animal
Hepatocytes / metabolism
I-kappa B Kinase / metabolism*
Lipogenesis*
Mice
Mice, Congenic
Mice, Transgenic
NF-kappa B / metabolism*
Non-alcoholic Fatty Liver Disease / metabolism*

Substances

NF-kappa B
Cholesterol
I-kappa B Kinase
Ikbkb protein, mouse