Highlights
- •Our ‘response-eQTL' approach aimed to discover novel SNP-gene pairs that only function in NAFLD.
- •NAFLD-specific repression of AGXT2 was prominent in rs2291702:CC carriers.
- •Lower AGXT2 expression was associated with worse histological and metabolic features in rs2291702:CC carriers.
- •The reduction of AGXT2 mimicked human NAFLD features in mice, whereas overexpression rescued them.
- •The reduced AGXT2 caused increased cell death due to ER stress activation in HepG2 cells.
Background & Aims
Non-alcoholic fatty liver disease (NAFLD) poses an increasing clinical burden. Genome-wide
association studies have revealed a limited contribution of genomic variants to the
disease, requiring alternative but robust approaches to identify disease-associated
variants and genes. We carried out a disease-specific expression quantitative trait
loci (eQTL) screen to identify novel genetic factors that specifically act on NAFLD
progression on the basis of genotype.
Methods
We recruited 125 Korean patients (83 with biopsy-proven NAFLD and 42 without NAFLD)
and performed eQTL analyses using 21,272 transcripts and 3,234,941 genotyped and imputed
single nucleotide polymorphisms. We then selected eQTLs that were detected only in
the NAFLD group, but not in the control group (i.e., NAFLD-eQTLs). An additional cohort of 162 Korean individuals with NAFLD was used
for replication. The function of the selected eQTL toward NAFLD development was validated
using HepG2, primary hepatocytes and NAFLD mouse models.
Results
The NAFLD-specific eQTL screening yielded 242 loci. Among them, AGXT2, encoding alanine-glyoxylate aminotransferase 2, displayed decreased expression in
patients with NAFLD homozygous for the non-reference allele of rs2291702, compared
to no-NAFLD individuals with the same genotype (p = 4.79 × 10-6). This change was replicated in an additional 162 individuals, yielding a combined
p value of 8.05 × 10-8 from a total of 245 patients with NAFLD and 42 controls. Knockdown of AGXT2 induced palmitate-overloaded hepatocyte death by increasing endoplasmic reticulum
stress, and exacerbated NAFLD diet-induced liver fibrosis in mice, while overexpression
of AGXT2 attenuated liver fibrosis and steatosis.
Conclusions
We identified a new molecular role for AGXT2 in NAFLD. Our overall approach will serve
as an efficient tool for uncovering novel genetic factors that contribute to liver
steatosis and fibrosis in patients with NAFLD.
Lay summary
Elucidating causal genes for non-alcoholic fatty liver disease (NAFLD) has been challenging
due to limited tissue availability and the polygenic nature of the disease. Using
liver and blood samples from 125 Korean individuals (83 with NAFLD and 42 without
NAFLD), we devised a new analytic method to identify causal genes. Among the candidates,
we found that AGXT2-rs2291702 protects against liver fibrosis in a genotype-dependent manner with the
potential for therapeutic interventions. Our approach enables the discovery of causal
genes that act on the basis of genotype.
Graphical abstract
Graphical Abstract
Keywords
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Article info
Publication history
Published online: April 20, 2021
Accepted:
April 7,
2021
Received in revised form:
March 22,
2021
Received:
August 24,
2020
Footnotes
Author names in bold designate shared co-first authorship
Identification
Copyright
© 2021 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
