Acute activation of eNOS by statins involves scavenger receptor-B1, G protein subunit Gi, phospholipase C and calcium influx

Background and purpose: Statins (HMG CoA reductase inhibitors) have beneficial effects independent of reducing cholesterol synthesis and this includes their ability to acutely activate endothelial nitric oxide synthase (eNOS). The mechanism by which this occurs is largely unknown and thus we characterized the pathways by which statins activate NOS, including involvement of scavenger receptor-B1 (SR-B1), which is expressed in endothelial cells and maintains cholesterol concentrations. Experimental approach: Nitric oxide production was monitored in bovine aortic endothelial cells (BAECs) exposed to lovastatin (LOV) or pravastatin (PRA) for 10-20 min, alone or following pre-exposure to the end product of HMG-CoA reductase (mevalonate), G protein inhibitors (pertussis/cholera toxins), phospholipase C (PLC) inhibitor (U-73122), or intracellular and extracellular calcium chelators - BAPTA-AM and EGTA (respectively), or a function blocking antibody to SR-B1. Key results: Both statins increased NO production in a rapid, dose-dependent and HMG-CoA reductase-independent manner. Inhibiting Gi protein or PLC almost completely blocked statin-induced NO generation. Additionally, removing extracellular calcium inhibited statin-induced NO production. COS-7 cells co-transfected with eNOS and SR-B1 increased NO production when exposed to LOV or high-density lipoprotein (HDL), an agonist of SR-B1. These effects were not observed in COS-7 cells with eNOS alone or co-transfected with bradykinin receptor 2, indicating specificity for SR-B1. Further, pretreatment of BAEC with blocking antibody for SR-B1 blocked NO responses to statins and HDL. Conclusions and implications: LOV and PRA acutely activate eNOS through pathways that include the cell surface receptor SR-B1, Gi protein, phosholipase C and entry of extracellular calcium into endothelial cells.