High-fat/high-cholesterol diet promotes a S1P receptor-mediated antiapoptotic activity for VLDL

Withdrawing growth factors or serum from endothelial cells leads to the activation of effector caspases 3 and 7, resulting in apoptotic cell death. HDL protects against caspase induction through sphingosine-l-phosphate (SIP) receptors. This anti-caspase activity of HDL is antagonized by VLDL from apolipoprotein E4 (apoE4) (genotype, APOE4/4; apolipoprotein, apoE) targeted replacement (TR) mice, but not by VLDL from TR APOE3/3 mice, and requires the binding of apoE4-VLDL to an LDL receptor family member. In the absence of HDL, apoE4-VLDL and apoE3-VLDL from TR mice have limited antiapoptotic activity. In contrast, we show here that a high-fat/highcholesterol/cholate diet (HFD) radically alters this biological activity of VLDL. On HFD, both apoE3-VLDL and apoE4-VLDL (MD VLDL) inhibit caspase 3/7 activation initiated by serum withdrawal. This activity of HYD VLDL is independent of an LDL receptor family member but requires the activation Of S1P(3) receptors, as shown by the ability of pharmacological block of SIP receptors by VPC 23019 and by small interfering RNA-mediated down-regulation Of S1P(3) receptors to inhibit HYD VLDL anticaspase activity.