Abstract 266: N-Acetyl-Cysteine Can Alter the Endothelial Cell Lipid Microenvironment

Abstract

The endothelial cell (EC) lipid microenvironment can directly impact post-translational lipid modification of critical intracellular signaling proteins, which has important vascular disease implications. The antioxidant N-Acetyl-Cysteine (NAC) is a well-known thiol that regulates intracellular glutathione levels, activates various intracellular kinases, and promotes EC proliferation. In erythrocytes, NAC alters cellular lipid content and modulates generation of plasma membrane phosphatidylserine (PS). To test the hypothesis that NAC similarly alters the lipid microenvironment in ECs, we evaluated the effect of NAC on S(cysteine)-protein lipidation, as well as its effects on cellular lipid content in HUVECs. Increasing the duration of NAC treatment (from 2 to 16 hours) and increasing the concentration of NAC (from 1 to 5 mM) robustly decreased S-protein lipidation of the heterotrimeric G protein subunit, Gaq, by 80% (p<0.05) without affecting Gaq protein levels. There was no effect of NAC on lipidation of the Caveolin-1, a lipid raft protein known to be involved in vascular function. NAC also suppressed expression (by 55%, p<0.05) of Fatty Acid Synthase (FAS), a critical lipogenic enzyme implicated in generating palmitate utilized for the lipidation of vascular proteins. Since Gaq-mediated regulation of downstream phospholipases affects cytosolic phospholipids, we characterized lipidomic profiles of NAC-treated ECs using electrospray ionization mass spectrometry analysis. Preliminary findings demonstrated that treatment with NAC 5mM alters global PS and phosphatidylcholine (PC) content in HUVECs, with a 160% increase in total PS lipid species and a 140% increase in total PC lipid species. These findings suggest that NAC remodels the lipid milieu of endothelial cells in a manner likely to impact signaling pathways relevant to inflammation, proliferation, and repair in the vasculature.