Abstract 893: Free Fatty Acids lead to Endothelial VEGF Resistance
Elevation of free fatty acids (FFA) and their intermediates underlies abnormalities in insulin signaling observed in obesity, metabolic syndrome and type 2 diabetes mellitus, and has been associated with increased cardiovascular mortality in subjects with clinical atherosclerosis. FFA cause NF-kappaB and PKC activation which are involved in receptor tyrosine kinase (RTK) signaling defects, in particular with the insulin receptor. Our study examines the effect of FFA on endothelial signaling and consequent angiogenic responses associated with the vascular endothelial growth factor (VEGF) RTK, VEGFR2. In vitro matrigel tube formation as well as in vivo angiogenic assays (adenoviral-VEGF ear injections or subcutaenous matrigel plugs) are utilized to show that angiogenic responses are reduced by 60% in fat-fed rodents. In vitro assays show a dose-dependent decrease in angiogenic tube formation with palmitic and linoleic acids (50microM-600microM). Functional assays also demonstrate the reduction in VEGF-induced nitric oxide release (70%) as well as an increase in reactive oxygen species generation and activation of NF-kappaB. Multiple signaling abnormalities have also been identified: reduced VEGFR2 tyrosine phosphorylation and reduction in downstream phosphorylation of Akt, ERK1/2 and eNOS. Thus signaling responses resulting in cell proliferation, migration and survival are all blunted. The underlying basis of these abnormalities is an increase in ceramide formation leading to activation of ceramide-activated protein phosphatases (CAPP) and atypical PKC-zeta. Inhibition of CAPP and PKC-zeta partially reverses FFA-induced endothelial angiogenic and signaling defects. This is the first report that FFA cause resistance to VEGF-stimulated signaling similar to the documented abnormalities with insulin. This suggests that FFA can lead to a vascular phenotype with multiple signaling abnormalities, each contributing to endothelial dysfunction and the acceleration of vascular disease development with increased morbidity and mortality. Furthermore, we believe that this work could be vital to understanding the failure of VEGF-induced angiogenic therapies in clinical trials.