Regulation of forskolin-induced cAMP production by cytochrome P450 epoxygenase metabolites of arachidonic acid in HEK293 cells
Endothelial cells play a vital role in the maintenance of cardiovascular homeostasis. Epoxyeicosatrienoic acids (EETs), cytochrome P-450 (CYP) epoxygenase metabolites of arachidonic acid in endothelial cells, possess potent and diverse biological effects within the vasculature. We evaluated the effects of overexpression of CYP epoxygenases on tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis in bovine aortic endothelial cells. CYP epoxygenase overexpression significantly increased endothelial cell viability and inhibited TNF-alpha induction of endothelial cell apoptosis as evaluated by morphological analysis of nuclear condensation, DNA laddering, and fluorescent-activated cell sorting (FACS) analysis. CYP epoxygenase overexpression also significantly inhibited caspase-3 activity and downregulation of Bcl-2 expression induced by TNF-alpha. The antiapoptotic effects of CYP epoxygenase overexpression were significantly attenuated by inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK signaling pathways; however, inhibition of endothelial nitric oxide synthase activity had no effect. Furthermore, CYP epoxygenase overexpression significantly attenuated the extent of TNF-alpha-induced ERK1/2 dephosphorylation in a time-dependent manner and significantly increased PI3K expression and Akt phosphorylation in both the presence and absence of TNF-alpha. Collectively, these results suggest that CYP epoxygenase overexpression, which is known to increase EET biosynthesis, significantly protects endothelial cells from apoptosis induced by TNF-alpha. This effect is mediated, at least in part, through inhibition of ERK dephosphorylation and activation of PI3K/Akt signaling.