Evidence for vesicles that mediate long-chain fatty acid uptake by human microvascular endothelial cells

This study analyzes the mechanisms of long-chain fatty acid (LCFA) uptake by human microvascular endothelial cells (HMEC). The time course revealed the presence of an early, carrier-mediated uptake component and a later component mediated by clathrin-coated vesicles (CCV) and caveolae, as evidenced by three different experimental approaches: 1) significant reduction of [3H]oleate uptake over 5 min by either inhibition of CCV formation by potassium depletion or hypertonic medium, or disruption of caveolae by filipin III or cyclodextrin. 2) Co-localization of intracellular 12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]octadecanoic acid with CCV and caveolae using confocal laser scanning microscopy. 3) Enrichment of [3H]oleate in a subcellular fraction containing CCV and caveolae. Within 10 min, more than 75% of intracellular [3H]oleate remained unmetabolized, suggesting that HMEC preferentially shuttle LCFA through the cell using CCV and caveolae as carriers. The uptake of albumin paralleled that of oleate within the first 10 min, suggesting internalization of at least some LCFA bound to albumin. Compared to oleate and albumin, the uptake of sucrose and dextran was low, indicating a potential minor contribution of fluid-phase endocytosis to the total vesicular LCFA uptake. The data indicate a previously unrecognized role of both CCV and caveolae for the uptake of LCFA by HMEC.