Abstract
Methionine is an essential sulfur amino acid that is engaged in key cellular functions such as protein synthesis and is a precursor for critical metabolites involved in maintaining cellular homeostasis. In mammals, in response to nutrient conditions, the liver plays a significant role in regulating methionine concentrations by altering its flux through the transmethylation, transsulfuration, and transamination metabolic pathways. A comprehensive understanding of how hepatic methionine metabolism intersects with other regulatory nutrient signaling and transcriptional events is, however, lacking. Here, we show that methionine and derived-sulfur metabolites in the transamination pathway activate the GCN5 acetyltransferase promoting acetylation of the transcriptional coactivator PGC-1α to control hepatic gluconeogenesis. Methionine was the only essential amino acid that rapidly induced PGC-1α acetylation through activating the GCN5 acetyltransferase. Experiments employing metabolic pathway intermediates revealed that methionine transamination, and not the transmethylation or transsulfuration pathways, contributed to methionine-induced PGC-1α acetylation. Moreover, aminooxyacetic acid, a transaminase inhibitor, was able to potently suppress PGC-1α acetylation stimulated by methionine, which was accompanied by predicted alterations in PGC-1α-mediated gluconeogenic gene expression and glucose production in primary murine hepatocytes. Methionine administration in mice likewise induced hepatic PGC-1α acetylation, suppressed the gluconeogenic gene program, and lowered glycemia, indicating that a similar phenomenon occurs in vivo These results highlight a communication between methionine metabolism and PGC-1α-mediated hepatic gluconeogenesis, suggesting that influencing methionine metabolic flux has the potential to be therapeutically exploited for diabetes treatment.
Highlights
MAY 13, 2016 VOLUME 291 NUMBER 20 between methionine metabolism and PGC-1␣-mediated hepatic gluconeogenesis, suggesting that influencing methionine metabolic flux has the potential to be therapeutically exploited for diabetes treatment
Methionine Induces PGC-1␣ Acetylation in Primary Hepatocytes—PGC-1␣ responds to nutrient and hormonal cues and plays a critical role in the regulation of energy metabolism in various tissues
To identify which of the essential amino acids (EAAs) contributed to the induction of PGC-1␣ acetylation, we incubated hepatocytes with individual EAAs (1 mM)
Summary
HEK293A and HepG2 cell lines were purchased from ATCC (CRL-1573 and HB-8065) and cultured in DMEM supplemented with 10% FBS. Cell cultures were maintained at 37 °C in a humidified incubator containing 5% CO2. Primary hepatocytes were isolated from 7–10-week-old male C57BL/6 mice by perfusion with liver digest medium (Life Technologies, 17703034) followed by 70-m mesh filtration. Primary hepatocytes were isolated from debris and other cell types by Percoll (Sigma, P7828) gradient centrifugation. Isolated hepatocytes were seeded in 6-well plates (4 ϫ 105 cells per well) in plating medium (DMEM supplemented with 10% FBS, 2 mM sodium pyruvate, 1 M dexamethasone, 100 nM insulin, and 1% penicillin/streptomycin). The medium was changed to maintenance medium (DMEM supplemented with 0.2% BSA, 2 mM sodium pyruvate, 0.1 M dexamethasone, 1 nM insulin, and 1% penicillin/streptomycin) 3 h post-seeding. Medium was replaced daily with fresh maintenance medium for the duration of the experiment
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