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Covalent Binding of Thioredoxin to TXNIP is Required for Diet-induced Hepatic Insulin Resistance

ABSTRACT: Among vertebrate animals, mammals have retained a unique molecular change that allows an intracellular arrestin domain-containing protein to bind covalently to thioredoxin. This interaction of Thioredoxin-Interacting Protein (TXNIP) with thioredoxin can only occur when thioredoxin is in the reduced state, allowing TXNIP to "sense" the cellular oxidized environment1. Here we show that a single cysteine in TXNIP mediates the development of hepatic insulin resistance in the setting of a high fat diet (HFD). Mice with exchange of TXNIP Cysteine 247 for Serine (C247S) showed improved whole-body and hepatic insulin sensitivities compared to wildtype (WT) controls following an 8-week HFD. The inhibition of the TXNIP-thioredoxin interaction under chow and HFD also regulated plasma and liver lipids and reduced free fatty acid accumulation in the livers following HFD. We also show molecularly that in HFD-fed TXNIP C247S mice livers, Toll-like Receptor 4 (TLR4)-mediated Nuclear factor kappa B (NFkB) activation and TLR4-mediating WD repeat and FYVE domain containing 1 (wdfy1) mRNA expressions were decreased, as well as PKC activity as a potential molecular mechanism to improve insulin/Akt signaling. These data show that mammals have a single amino acid enabling interaction of redox state with TXNIP that mediates insulin resistance in the setting of a high-fat diet. This reveals a potential evolutionarily-conserved mechanism for hepatic insulin resistance in metabolic syndromes.

ORGANISM(S): Mus musculus

PROVIDER: GSE253334 | GEO | 2024/01/20

REPOSITORIES: GEO

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Project description:Individuals with hepatic steatosis often display several metabolic abnormalities including insulin resistance and muscle atrophy. Previously, we found that hepatic steatosis results in an altered hepatokine secretion profile, thereby inducing skeletal muscle insulin resistance via inter-organ crosstalk. In this study, we aimed to investigate whether the altered secretion profile in the state of hepatic steatosis also induces skeletal muscle atrophy via effects on muscle protein turnover. To investigate this, eight-week-old male C57BL/6J mice were fed a chow (4.5% fat) or a high-fat diet (HFD; 45% fat) for 12 weeks to induce hepatic steatosis, after which the livers were excised and cut into ~200 µm slices. Slices were cultured to collect secretion products (conditioned medium; CM). Differentiated L6-GLUT4myc myotubes were incubated with chow or HFD CM to measure glucose uptake. Differentiated C2C12 myotubes were incubated with chow or HFD CM to measure protein synthesis and breakdown, and gene expression via RNA sequencing. Furthermore, proteomics analysis was performed in chow and HFD CM. It was found that HFD CM caused insulin resistance in L6-GLUT4myc myotubes compared with chow CM, as indicated by a blunted insulin-stimulated increase in glucose uptake. Furthermore, protein breakdown was increased in C2C12 cells incubated with HFD CM, while there was no effect on protein synthesis. RNA profiling of C2C12 cells indicated that 197 genes were differentially expressed after incubation with HFD CM, compared with chow CM, and pathway analysis showed that pathways related to anatomical structure and function were enriched. Proteomic analysis of the CM showed that 32 proteins were differentially expressed in HFD CM compared with chow CM. Pathway enrichment analysis indicated that these proteins had important functions with respect to insulin-like Growth Factor transport and uptake, and affect post-translational processes, including protein folding, protein secretion and protein phosphorylation. In conclusion, the results of this study support the hypothesis that secretion products from the liver contribute to the development of muscle atrophy in individuals with hepatic steatosis.

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Covalent Binding of Thioredoxin to TXNIP is Required for Diet-induced Hepatic Insulin Resistance

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