Acute regulation of fatty acid oxidation and AMP-activated protein kinase in human umbilical vein endothelial cells

It is generally accepted that endothelial cells generate most Of their ATP by anaerobic glycolysis and that very little ATP is derived from the oxidat ion of fatty acids or glucose. previously, we have reported that, in cultur ed human umbilical vein endothelial cells (HUVECs), activation of AMP-activ ated protein kinase (AMPK by the cell-permeable activator 5-aminoimidazole- 4-carboximide riboside (AICAR) is associated with an increase in the oxidat ion of H-3-palmitate. In the present study, experiments carried out with cu ltured HUVECs revealed the following. (1) AICAR-induced increases in palmit ate oxidation during a 2-hour incubation are associated with I decrease in the concentration of malonyl coenzyme A (CoA) tan inhibitor of carnitine pa lmitoyl transferase 1), which temporally parallels the increase in AMPK act ivity and a decrease in the activity of acetyl CoA carboxylase (ACC), (2) A ICAR does not stimulate either palmitate oxidation when carnitine is omitte d from the medium or oxidation of the medium-chain fatty acid octanoate. (3 ) When intracellular lipid pools are prelabeled with H-3-palmitate, the mea sured rate of palmitate oxidation is 3-fold higher, and in the presence of AICAR, it accounts for nearly 40% of calculated ATP generation. (4) Incubat ion of HUVECs in a glucose-fret medium for 2 hours causes the same changes in AMPK, ACC, malonyl CoA, and palmitate oxidation as does AICAR. (5) Under all conditions studied, the contribution of glucose oxidation to ATP produ ction is minimal. The results indicate that the AMPK-ACC-malonyl CoA-carnit ine palmitoyl transferase 1 mechanism plays a key role in the physiological regulation of fatty acid oxidation in HUVECs. They also indicate that HUVE Cs oxidize fatty acids from both intracellular and extracellular sources, a nd that when this is taken into account, fatty acids can be a major substra te for ATP generation. Finally, they suggest that AMPK is likely to be a ma jor factor in modulating the response of the endothelium to stresses that a lter its energy state.