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MRG15 orchestrates circadian epigenomic remodeling and controls hepatic lipid metabolism

ABSTRACT: Rhythmic regulation of transcriptional processes is intimately linked to lipid homeostasis, to anticipate daily changes in energy access. Rev-erbα/HDAC3 complex was previously discovered to execute the rhythmic repression of lipid genes, however, the epigenetic switch that turns on these genes is less clear. Here, we show that genomic recruitment of MRG15 displays a significant circadian rhythm and activates lipid genes in mouse liver. Pol II recruitment and histone acetylation correspond to MRG15 binding, and the rhythm is impaired upon MRG15 depletion, establishing MRG15 as a key modulator in global rhythmic transcriptional regulation. Rather than known core clock proteins, MRG15 interacts with nuclear receptor LRH-1, and is recruited to genomic loci near lipid genes via its association with LRH-1. Blocking MRG15 by CRISPR targeting or FDA-approved drug argatroban, which is an antagonist to MRG15, attenuates liver steatosis. This work highlights MRG15 as a targetable master regulator in rhythmic regulation of hepatic lipid metabolism.

TISSUE(S): Liver

SUBMITTER: Qiurong,Ding

PROVIDER: OEX002226 | NODE |

REPOSITORIES: NODE

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Project description:To determine the effects of age and lipoic acid supplementation on hepatic gene expression, we fed young (3 months) and old (24 months) male Fischer 344 rats a diet with or without 0.2% (w/w) R-?-lipoic acid (LA) for two weeks. Total RNA isolated from liver tissue was analyzed by Affymetrix microarray to examine changes in transcriptional profile. Results showed an increase in pro-inflammatory gene expression in the aging liver, with increased immune cell function and tissue remodeling genes, representing 45% of the age-related transcriptome changes. Increased inflammation was corroborated by increases in soluble ICAM1 levels with age. There were also observed age-related increases in transcription of genes related to lipid and cholesterol synthesis including Acetyl CoA Carboxylase (Acacb) and Fatty acid Synthase (Fasn). Supplementation of old animals with LA did not reverse this necro-inflammatory phenotype, yet limited age-associated hepatic dyslipidemia. Dietary LA further affected a small but concerted number of hepatic genes regardless of age. These included declines in lipid and bile synthesis genes. Decline in lipid synthesis genes was further corroborated by a decrease in Fasn and Acc protein levels. Intriguingly, LA also altered the expression of genes governing circadian rhythm, most notably Bmal1, Npas2, and Per2, which changed in a coordinated manner with respect to their rhythmic transcription. Thus, advanced age is associated with a necro-inflammatory phenotype and increased lipid synthesis, while chronic LA supplementation influences hepatic genes associated with energy metabolism and circadian rhythm regardless of age. Young (3 months) and old (24 months) Fischer 344 male rats were fed an AIN-93M diet ± 0.2% (w/w) R-?-lipoic acid for two weeks prior to sacrifice. Total RNA was extracted from the median lobe of the liver and analyzed using Affymetrix Rat Genome 230 2.0 Genechips. There were hybridizations for 8 animals in each of the young control, young LA-supplemented, and old control groups, and 6 animals in the old LA-supplemented group. There are only 6 animals in the old LA group because two animals died during the two-week feeding period. This is the reason for nonsequential numbering of animals in this group.

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MRG15 orchestrates circadian epigenomic remodeling and controls hepatic lipid metabolism

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