Ethanol up-regulates fatty acid uptake and plasma membrane expression and export of mitochondrial aspartate aminotransferase in HepG2 cells.

To explain the increased plasma mitochondrial aspartate aminotransferase (mAspAT) observed in alcoholics, we cultured HepG2 hepatoma cells in ethanol. Acute (24 hour) exposure to 0, 20, 40, or 80 mmol/L ethanol produced a dose-dependent (r = .98) increase in mAspAT messenger RNA (mRNA) of < or = thirteen-fold, with no significant change in the cellular content of mAspAT or of several other enzymes. The recovery of mAspAT in the medium over 24 hours of ethanol exposure correlated with both ethanol concentration and with mAspAT mRNA (r = .90), reaching 808% of cellular enzyme content/24 hours at 80 mmol/L. Recovery of all other enzymes studied was < or = 20% of cellular content and unaffected by ethanol. Plasma membrane mAspAT content also correlated with mAspAT mRNA (r = .96) and mitochondrial levels were unchanged. No mitochondrial morphologic abnormalities were observed at any ethanol concentration studied. In cells cultured chronically at 0 to 80 mmol/L ethanol, fatty acid uptake Vmax increased in parallel with plasma membrane expression of mAspAT (r = .98). Cellular triglyceride content was highly correlated with Vmax. Thus, the data suggest that: 1) the increased plasma mAspAT observed in alcoholics may reflect pharmacologic upregulation of mAspAT mRNA and of mAspAT synthesis by ethanol; and 2) increased mAspAT-mediated fatty acid uptake may contribute to alcoholic fatty liver.