Lipid-induced Ceramide Accrual Decreases Vascular Function in a Protein Phosphatase 2A Mediated Manner

Diet-induced obesity (DIO) and type 2 diabetes mellitus (T2DM) are conditions associated with elevated free fatty acids (FFAs) and arterial dysfunction. The precise mechanisms are unknown. When FFAs accrue in tissues not suited for their storage (e.g., blood vessels), toxic sphingolipids (e.g., ceramide) can accumulate.  Protein phosphatase 2A (PP2A) is a cytosolic phosphatase shown previously to be activated by ceramide. PP2A can impair endothelial nitric oxide synthase, an important enzyme for arterial vasorelaxation. We hypothesized that ceramide-induced arterial dysfunction is secondary to PP2A activation. Mice with heterozygous deletion of one allele of dihydroceramide desaturase (des 1 +/-) and their wild type littermates (des 1 +/+) were infused with 20% lard-oil (lipid) or vehicle (glycerol) for 6h. Des 1 +/- mice cannot convert metabolically inactive dihydroceramide into active ceramide. A subgroup of des1 +/+ mice was pre-treated with the PP2A inhibitor LB1 (1.5 mg/kg IP) two days prior to, and immediately before lipid infusion. Percent vasorelaxation to acetylcholine (ACh, 3 x 10^-8M), an endothelium-dependent vasodilator, was assessed in isolated vessels using isometric tension procedures. Compared to vehicle (74±11%; n=2 mice, 7 vessels), ACh-induced vasorelaxation was impaired by lipid infusion (44±4%; n= 3 mice, 9 vessels), but was restored in des1+/- mice (68±4%; n=3 mice, 9 vessels) and in LB1-treated mice (63±5%;n=3 mice, 9  vessels). These preliminary data implicate both ceramide and PP2A as contributing factors to lipid-induced arterial dysfunction.