We wished to understand the metabolic reprogramming underlying
liver fibrosis progression in mice. Administration to male C57BL/6J mice of the hepatotoxins
carbon tetrachloride (CCl4),
thioacetamide (TAA), or a 60% high-fat diet,
choline-deficient,
amino-acid-defined diet (HF-
CDAA) was conducted using standard protocols. Livers collected at different times were analyzed by gas chromatography-mass spectrometry-based metabolomics.
RNA was extracted from liver and assayed by qRT-PCR for
mRNA expression of 11 genes potentially involved in the synthesis of
ascorbic acid from
hexoses, Gck, Adpgk, Hk1, Hk2, Ugp2, Ugdh, Ugt1a1, Akr1a4, Akr1b3, Rgn and Gulo. All hepatotoxins resulted in similar metabolic changes during active fibrogenesis, despite different etiology and resultant
scarring pattern. Diminished hepatic
glucose,
galactose,
fructose, pentose phosphate pathway intermediates,
glucuronic acid and long-chain
fatty acids were compensated by elevated ascorbate and the product of
collagen prolyl 4-hydroxylase,
succinate and its downstream metabolites
fumarate and
malate. Recovery from the HF-
CDAA diet challenge (F2 stage
fibrosis) after switching to normal chow was accompanied by increased
glucose,
galactose,
fructose,
ribulose 5-phosphate,
glucuronic acid, the ascorbate metabolite
threonate and diminished ascorbate. During the administration of CCl4, TAA and HF-
CDAA,
aldose reductase Akr1b3 transcription was induced six- to eightfold, indicating increased conversion of
glucuronic acid to
gulonic acid, a precursor of ascorbate synthesis. Triggering hepatic
fibrosis by three independent mechanisms led to the hijacking of
glucose and
galactose metabolism towards ascorbate synthesis, to satisfy the increased demand for ascorbate as a cofactor for
prolyl 4-hydroxylase for mature
collagen production. This metabolic reprogramming and causal gene expression changes were reversible. The increased flux in this pathway was mediated predominantly by increased transcription of
aldose reductase Akr1b3.