Inflammation-induced TRIM21 represses hepatic steatosis by promoting the ubiquitination of lipogenic regulators
Kostas C. Nikolaou, Svenja Godbersen, Muthiah Manoharan, Stefan Wieland, Markus H. Heim, Markus Stoffel
Kostas C. Nikolaou, Svenja Godbersen, Muthiah Manoharan, Stefan Wieland, Markus H. Heim, Markus Stoffel
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Research Article Hepatology

Inflammation-induced TRIM21 represses hepatic steatosis by promoting the ubiquitination of lipogenic regulators

Abstract

Nonalcoholic steatohepatitis (NASH) is a leading cause for chronic liver diseases. Current therapeutic options are limited due to an incomplete mechanistic understanding of how steatosis transitions to NASH. Here we show that the TRIM21 E3 ubiquitin ligase is induced by the synergistic actions of proinflammatory TNF-α and fatty acids in livers of humans and mice with NASH. TRIM21 ubiquitinates and degrades ChREBP, SREBP1, ACC1, and FASN, key regulators of de novo lipogenesis, and A1CF, an alternative splicing regulator of the high-activity ketohexokinase-C (KHK-C) isoform and rate-limiting enzyme of fructose metabolism. TRIM21-mediated degradation of these lipogenic activators improved steatosis and hyperglycemia as well as fructose and glucose tolerance. Our study identifies TRIM21 as a negative regulator of liver steatosis in NASH and provides mechanistic insights into an immunometabolic crosstalk that limits fatty acid synthesis and fructose metabolism during metabolic stress. Thus, enhancing this natural counteracting force of steatosis through inhibition of key lipogenic activators via TRIM21-mediated ubiquitination may provide a therapeutic opportunity to treat NASH.

Authors

Kostas C. Nikolaou, Svenja Godbersen, Muthiah Manoharan, Stefan Wieland, Markus H. Heim, Markus Stoffel

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Figure 3

TNF and fatty acids, ER- and oxidative stress induce TRIM21 in hepatocytes.

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TNF and fatty acids, ER- and oxidative stress induce TRIM21 in hepatocyt...
(A and B) Immunoblot analysis of TRIM21 and A1CF expression in HepG2 cells stimulated with either TNF-α (20 ng/mL) (A) or with TNF-α and fatty acids (B) (0.5 mM mixture of oleic and palmitic acid, FA+TNF) for the indicated time. (C and D) Endogenous A1CF ubiquitination levels in HepG2 cells stimulated for 48 hours with either TNF-α (C) or with TNF-α and FA (D). (E) Endogenous A1CF ubiquitination levels in HepG2 cells challenged with TNF-α and FA for 72 hours and transfected with si-Trim21 or Scramble (control) for 48 hours. Input levels show TRIM21-knockdown efficiency and A1CF levels. (F) Ubiquitination assay determining total and K63-linked endogenous A1CF ubiquitination in liver extracts from mice challenged with LPS (5 mg/kg) for the indicated time points (n = 2 livers pooled per time point). (G) Expression levels of the indicated proteins in HepG2 cells stimulated with TNF-α (20 ng/mL) for 48 hours in the presence of inhibitors for NF-κB (10 μM, BAY-11) or TAK1 (1 μM, 5z-7-oxozeaenol) (n = 2 replicates per time point). (H) Expression levels of indicated proteins in HepG2 cells that were pretreated with the JNK inhibitor SP600125 (5 μM) and stimulated with TNF-α (20 ng/mL) for 24 hours; vehicle (DMSO) was used as control. (I and J) Expression levels of indicated proteins in HepG2 cells stimulated with 1 mM hydrogen peroxide (H2O2) (I) or with 0.2 μM thapsigargin (J) for the indicated time points (n = 3 replicates per time point each).