Glutamate-oxaloacetate transaminase activity promotes palmitate lipotoxicity in rat hepatocytes by enhancing anaplerosis and citric acid cycle flux.

Egnatchik RA, Leamy AK, Sacco SA, Cheah YE, Shiota M, Young JD
J Biol Chem. 2019 294 (9): 3081-3090

PMID: 30563841 · PMCID: PMC6398133 · DOI:10.1074/jbc.RA118.004869

Hepatocyte lipotoxicity is characterized by aberrant mitochondrial metabolism, which predisposes cells to oxidative stress and apoptosis. Previously, we reported that translocation of calcium from the endoplasmic reticulum to mitochondria of palmitate-treated hepatocytes activates anaplerotic flux from glutamine to α-ketoglutarate (αKG), which subsequently enters the citric acid cycle (CAC) for oxidation. We hypothesized that increased glutamine anaplerosis fuels elevations in CAC flux and oxidative stress following palmitate treatment. To test this hypothesis, primary rat hepatocytes or immortalized H4IIEC3 rat hepatoma cells were treated with lipotoxic levels of palmitate while modulating anaplerotic pathways leading to αKG. We found that culture media supplemented with glutamine, glutamate, or dimethyl-αKG increased palmitate lipotoxicity compared with media that lacked these anaplerotic substrates. Knockdown of glutamate-oxaloacetate transaminase activity significantly reduced the lipotoxic effects of palmitate, whereas knockdown of glutamate dehydrogenase (Glud1) had no effect on palmitate lipotoxicity. C flux analysis of H4IIEC3 cells co-treated with palmitate and the pan-transaminase inhibitor aminooxyacetic acid confirmed that reductions in lipotoxic markers were associated with decreases in anaplerosis, CAC flux, and oxygen consumption. Taken together, these results demonstrate that lipotoxic palmitate treatments enhance anaplerosis in cultured rat hepatocytes, causing a shift to aberrant transaminase metabolism that fuels CAC dysregulation and oxidative stress.

© 2019 Egnatchik et al.

MeSH Terms (15)

Animals Aspartate Aminotransferases Cell Death Cell Line Citric Acid Cycle Extracellular Space Glutamine Hepatocytes Ketoglutaric Acids Male Oxidative Stress Oxygen Palmitates Rats Rats, Sprague-Dawley

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