Impact on fatty acid metabolism and differential localization of FATP1 and FAT/CD36 proteins delivered in cultured human muscle cells

We compared the intracellular distribution and regulatory role of fatty acid transporter protein (FATP1) and fatty acid translocase (FAT/CD36) on muscle cell fatty acid metabolism. With the use of adenoviruses, FATP1 and FAT genes were delivered to primary cultured human muscle cells. FATP1 and FAT moderately enhanced palmitate and oleate transport evenly at concentrations of 0.05, 0.5, and 1 mM. Long-term (16 h) consumption of palmitate and oleate from the media, and particularly incorporation into triacylglyceride (TAG), was stimulated equivalently by FATP1 and FAT at all fatty acid concentrations tested. In contrast, long-term CO2 production was reduced by FATP1 and FAT at all doses of palmitate and at the lower concentrations of oleate. Neither FATP1 nor FAT markedly altered the production of acid-soluble metabolic intermediates from palmitate or oleate. The intracellular localization of fusion constructs of FATP1 and FAT with enhanced green fluorescent protein (EGFP) was examined. Independently of fatty acid treatment, FATPGFP was observed throughout the cytosol in a reticular pattern and concentrated in the perinuclear region, partly overlapping with the Golgi marker GM-130. FATGFP was found in the extracellular membrane and in cytosolic vesicles not coincident with GM-130. Neither FATP1 nor FAT proteins colocalized with lipid droplets in oleate-treated cells. We conclude that whereas FAT is localized on the extracellular membrane, FATP1 is active in the cytosol and imports fatty acids into myotubes. Overall, both FATP1 and FAT stimulated transport and consumption of palmitate and oleate, which they channeled away from complete oxidation and toward TAG synthesis.