Activation of NF-κB by Palmitate in Endothelial Cells

Abstract

Objective— We investigated whether NADPH oxidase–dependent production of superoxide contributes to activation of NF-κB in endothelial cells by the saturated free fatty acid palmitate. Methods and Results— After incubation of human endothelial cells with palmitate at a concentration known to induce cellular inflammation (100 μmol/L), we measured superoxide levels by using electron spin resonance spectroscopy and the spin trap 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH). Palmitate exposure induced a >2-fold increase in superoxide levels, an effect associated with activation of NF-κB signaling as measured by phospho-IκBα, NF-κB activity, IL-6, and ICAM expression. Reduction in superoxide levels by each of 3 different interventions—pretreatment with superoxide dismutase (SOD), diphenylene iodinium (DPI), or knockdown of NADPH oxidase 4 (NOX4) by siRNA—attenuated palmitate-mediated NF-κB signaling. Inhibition of toll like receptor-4 (TLR4) signaling also suppressed palmitate-mediated superoxide production and associated inflammation, whereas palmitate-mediated superoxide production was not affected by overexpression of a phosphorylation mutant IκBα (NF-κB super repressor) that blocks cellular inflammation downstream of IKKβ/NF-κB. Finally, high-fat feeding increased expression of NOX4 and an upstream activator, bone morphogenic protein (BMP4), in thoracic aortic tissue from C57BL/6 mice, but not in TLR4 ^−/− mice, compared to low-fat fed controls. Conclusions— These results suggest that NADPH oxidase–dependent superoxide production links palmitate-stimulated TLR4 activation to NF-κB signaling in endothelial cells.