My lab uses biochemical and cell biological approaches to explore signal transduction pathways in the cells and tissues of the cardiovascular system, with a particular focus on nitric oxide synthase pathways in endothelial cells and cardiac myocytes and their alterations in cardiovascular disease states.
Nitric oxide (NO) has been studied for many years as the active compound formed from drugs such as nitroglycerin, but endogenous nitric oxide synthases have been discovered that catalyze the formation of NO in diverse mammalian tissues. The endothelial isoform of nitric oxide synthase (eNOS) is a key signaling enzyme that is activated by a variety of cell surface receptors and is involved in the control of vascular smooth muscle relaxation and platelet aggregation.
Post-translational modifications of eNOS modulate the enzyme’s subcellular targeting to specialized lipid-rich signal-transducing microdomains in the plasma membrane termed caveolae. We study the intracellular pathways that regulate eNOS post-translational modification and subcellular targeting, and are exploring novel protein-protein interactions that modulate eNOS enzyme activity. We also investigate the interplay among protein kinases, G protein subunits and eNOS in plasmalemmal caveolae, and are studying the receptor-regulated translocation of eNOS, G protein subunits and associated signaling proteins using biochemical, biophysical, and cellular imaging approaches. We have applied RNA interference methodologies to “knock down” a broad range of endothelial signaling proteins and have identified new pathways involved in the regulation of angiogenesis. We have exploited novel biosensors in cellular imaging studies to explore the relationship between nitric oxide synthase and reactive oxygen species. We are also exploring the role of the AMP-activated protein kinase (AMPK) in eNOS regulation in endothelial cells and in the heart, with a particular interest in the perturbations of these pathways in diabetes and in response to oxidative stress.
Some of our recent studies are exploring the roles of “statin” drugs (HMG CoA reductase inhibitors commonly used in the treatment of cardiovascular disease) on the subcellular targeting and protein associations of eNOS. We found that statins markedly activate the small GTPase Rac1, a cytoskeleton-associated regulatory protein with key roles both in eNOS regulation and in the generation of reactive oxygen species implicated in vascular pathobiology, We are seeking to understand the roles of statins in the differential modulation of eNOS activity and in the regulation of reactive oxygen species.
Kou R, Sartoretto J and Michel T. Regulation of Rac1 by simvastatin in endothelial cells: differential roles of AMP-activated protein kinase and calmodulin-dependent kinase kinase-β. J Biol Chem 2009, 284: 14734-43.
Sugiyama T, Levy B and Michel T. Tetrahydrobiopterin recycling: a key determinant of eNOS-dependent signaling pathways in vascular endothelium. J Biol Chem, 2009, 284: 12691 - 12700.
Jin B, Sartoretto J, Gladyshev V, and Michel T. Endothelial nitric oxide synthase negatively regulates hydrogen peroxide-induced AMP-activated protein kinase activation in endothelial cells. Proc Natl Acad Sci USA 2009, 106:17343-17348.
Hess CN, Kou R, Johnson R, Li GK and Michel T. ADP signaling in vascular endothelial cells: ADP-dependent eNOS activation requires the expression but not the kinase activity of AMP-activated protein kinase. J Biol Chem 2009, 284:32209-32224.
Kalwa H and Michel T. The MARCKS protein plays a critical role in phosphatidylinositol 4,5-bisphosphate metabolism and directed cell movement in vascular endothelial cells. J Biol Chem 2011, 286: 2320-2333.