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ABSTRACT: Metabolic dysfunction-associated steatotic liver disease (MASLD) affects one third of the global population. Understanding metabolic pathways involved can provide insights into disease progression and treatment. Untargeted metabolomics of livers from mice with early-stage steatosis uncovered decreased methylated metabolites, suggesting altered one-carbon metabolism. The levels of glycine, a central component of one-carbon metabolism, were lower in mice with hepatic steatosis, consistent with clinical evidence. Stable-isotope tracing demonstrated that increased serine synthesis from glycine via reverse serine hydroxymethyltransferase (SHMT) is the underlying cause for decreased glycine in steatotic livers. Consequently, limited glycine availability in steatotic livers impaired glutathione synthesis under acetaminophen-induced oxidative stress, enhancing acute hepatotoxicity. Glycine supplementation or hepatocyte-specific ablation of the mitochondrial SHMT2 isoform in mice with hepatic steatosis mitigated acetaminophen-induced hepatotoxicity by supporting de novo glutathione synthesis. Thus, early metabolic changes in MASLD that limit glycine availability sensitize mice to xenobiotics even at the reversible stage of this disease.

INSTRUMENT(S): Orbitrap Exploris 240, Q Exactive

ORGANISM(S): Mus Musculus (ncbitaxon:10090)

SUBMITTER: Eyal Gottlieb Oren Rom Inbal Mor

PROVIDER: MSV000093653 | GNPS | Tue Dec 12 18:36:00 GMT 2023

REPOSITORIES: GNPS

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Project description:Background & Aims: Inflammation in chronic liver diseases induces oxidative stress and thus may contribute to progression of liver injury, fibrosis, and carcinogenesis. The KEAP1/NRF2 axis is a major regulator of cellular redox balance. In the present study, we investigated whether the KEAP1/NRF2 system is involved in liver disease progression in human and mice. Methods: The clinical relevance of oxidative stress was investigated in a well-characterized cohort of NAFLD patients (n=63) by liver RNA sequencing and correlated with histological and clinical parameters. For functional analysis hepatocyte-specific NEMO knock-out (NEMO∆hepa) mice were crossed with hepatocyte-specific KEAP1 knock-out (KEAP1∆hepa) mice. Results: Immunohistochemical analysis of human liver sections showed increased oxidative stress and high NRF2 expression in patients with chronic liver disease. RNA sequencing of liver samples in a human pediatric NAFLD cohort revealed a significant increase of NRF2 activation correlating with the grade of inflammation, but not with the grade of steatosis, which could be confirmed in a second adult NASH cohort. In mice, microarray analysis revealed that KEAP1 deletion induces NRF2 target genes involved in glutathione metabolism and xenobiotic stress (e.g., Nqo1). Furthermore, deficiency of one of the most important antioxidants, glutathione (GSH), in NEMO∆hepa livers was rescued after deleting KEAP1. As a consequence, NEMO∆hepa/KEAP1∆hepa livers showed reduced apoptosis compared to NEMO∆hepa livers as well as a dramatic downregulation of genes involved in cell cycle regulation and DNA replication. Consequently, NEMO∆hepa/KEAP1∆hepa compared to NEMOΔhepa livers displayed decreased fibrogenesis, lower tumor incidence, reduced tumor number, and decreased tumor size. Conclusions: NRF2 activation in NASH patients correlates with the grade of inflammation, but not steatosis. Functional analysis in mice demonstrated that NRF2 activation in chronic liver disease is protective by ameliorating fibrogenesis, initiation and progression of hepatocellular carcinogenesis.

Project description:Purpose: We examined the impact of niacin on muscle gene expression in mitochondrial myopathy patients and healthy controls. Methods: Muscle transcriptomics profiles were generated using global transcriptomics analysis by RNA sequencing which was performed by the Beijing Genomic Institute (BGI) using their standard protocols Results: The pathway enrichment analysis of RNA-sequencing data indicated that phagosome formation, serine/glycine/one-carbon pathways (de novo serine biosynthesis, purine degradation, glutathione metabolism), LXR/RXR activation, eicosanoid, glycoprotein 6, atherosclerosis, iron homeostasis and cAMP-mediated signalling pathways were among the most significantly changed in patients. Only five and two of the disease associated pathways remained significantly changed after 4- and 10-month supplementation, respectively, in patients as compared to controls. The most prominent niacin-related transcriptomic change in patients’ muscle (patient 10-months on niacin vs patient baseline) was wide-spread downregulation of mTOR-dependent cytoplasmic translation, involving a large number of cytoplasmic ribosome subunits as well as translation initiation factor eIF1. In patients, niacin activated also the peroxisome proliferator-activated receptor signaling pathway, known to induce mitochondrial biogenesis. Niacin also led to decreased atherosclerosis signaling including lowered apolipoprotein expression in patients. The healthy control muscles showed only few changes after 4-months of niacin. To examine in detail the effects of NAD-booster niacin in the mitochondrial integrated stress response (ISRmt), we studied the effects NAD+ boosting for the expression of 24 ISRmt target genes in the patients’ muscle. The analysis confirmed wide-spread induction of these genes, but their expression was unaffected by niacin (ATF5 and its targets ASNS, TRIB3, FGF21, GDF15, MTHFD2, and MTHFD1L; de novo synthesis of serine, PSAT1, PHGDH and SHMT2; glutathione metabolism GPX3 and GSR; and unfolded protein response ER CHOP). Conclusions: These results showed that niacin modulated the expression of disease associated pathways and suppressed mTOR signalling in patients but niacin did not affect disease-related ISRmt signalling.

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