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Hepatic dysregulation of glyoxalase 1 in preclinical models and patients with non-alcoholic fatty liver disease

ABSTRACT: Background & Aims: Although non-alcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide, aspects of its molecular pathogenesis are unknown and clinical biomarkers for early diagnosis and accurate disease staging remain scarce. The aims of these experiments were to identify and characterize liver protein alterations in an animal model of NAFLD and explore the utility of novel candidate biomarkers in NAFLD patients. Methods: Liver protein fractions were analyzed in a relative quantitative proteomic approach utilizing isobaric tags for relative and absolute quantitation (iTRAQ) labeling combined with nano-liquid chromatography and tandem mass spectrometry (nLC-MS/MS). Differential expression was confirmed independently by western blotting and immunohistochemistry, first in mouse sections and then in biopsies from paediatric NAFLD patients. Candidate serum biomarkers were analyzed by enzyme-linked immunosorbent assay in serum from adult NAFLD patients. Results: Through proteomic profiling we identified decreased expression of hepatic glyoxalase 1 (GLO1) in an animal model of NAFLD. GLO1 protein levels were also found reduced in tissue biopsies from pediatric NAFLD patients. In vitro experiments demonstrated that, in response to lipid-loading in hepatocytes, GLO1 is first hyper-acetylated then ubiquitinylated and degraded, leading to an increase in reactive methylglyoxal. In a cohort of 62 biopsy-confirmed adult NAFLD patients serum levels of the primary methylglyoxal-derived advanced glycated endproduct, hydroimidazolone (MG-H1) were found strongly correlated with body mass index (r=0.619, p<0.0001). Conclusions: We characterize, for the first time, the post-translational modification and regulation of GLO1 expression in response to hepatic lipid loading with functional consequences in NAFLD patients.

INSTRUMENT(S): 6520 Quadrupole Time-of-Flight LC/MS

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Liver

SUBMITTER: Christos Spanos

LAB HEAD: Jennifer Bernadette Moore

PROVIDER: PXD001442 | Pride | 2018-02-16

REPOSITORIES: Pride

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Project description:Background & Aims: Cirrhosis and liver cancer are potential outcomes of advanced nonalcoholic fatty liver disease (NAFLD). It is not clear what factors determine whether patients will develop advanced or mild NAFLD, limiting non-invasive diagnosis and treatment before clinical sequelae emerge. We investigated whether DNA methylation profiles can distinguish patients with mild disease from those with advanced NAFLD, and how these patterns are functionally related to hepatic gene expression. Methods: We collected frozen liver biopsies and clinical data from patients with biopsy-proven NAFLD (56 in the discovery cohort and 34 in the replication cohort). Samples were divided into groups based on histologic severity of fibrosis: F0?1 (mild) and F3?4 (advanced). DNA methylation profiles were determined and coupled with gene expression data from the same biopsies; differential methylation was validated in subsets of the discovery and replication cohorts. We then analyzed interactions between the methylome and transcriptome. Results: Clinical features did not differ between patients known to have mild or advanced fibrosis based on biopsy analysis. There were 69,247 differentially methylated CpG sites (76% hypomethylated, 24% hypermethylated) in patients with advanced vs mild NAFLD (P<.05). Methylation at FGFR2, MAT1A, and CASP1 was validated by bisulfite pyrosequencing and the findings were reproduced in the replication cohort. Methylation correlated with gene transcript levels for 7% of differentially methylated CpG sites, indicating that differential methylation contributes to differences in expression. In samples with advanced NAFLD, many tissue repair genes were hypomethylated and overexpressed, whereas genes in certain metabolic pathways, including 1-carbon metabolism, were hypermethylated and under-expressed. Conclusions: Functionally relevant differences in methylation can distinguish patients with advanced vs mild NAFLD. Altered methylation of genes that regulate processes such as steatohepatitis, fibrosis, and carcinogenesis indicate the role of DNA methylation in progression of NAFLD. Three technical replicates were included for quality control along with 35 mild NAFLD (33 unique samples) and 24 advanced NAFLD (23 unique sample). One sample per technical duplication was randomly included for a total of 56 NAFLD samples used for study.

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Hepatic dysregulation of glyoxalase 1 in preclinical models and patients with non-alcoholic fatty liver disease

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