Redox biology is fundamental to both normal cellular homeostasis and pathological states associated with excessive oxidative stress. In the vascular system, redox reactions help regulate key physiological responses such as cell adhesion, vasoconstriction, platelet aggregation, angiogenesis, inflammatory gene expression, and apoptosis. During pathological states, altered redox balance can cause vascular cell dysfunction and contribute to disease. It is well known that vascular diseases are associated with increased generation of reactive oxygen species (ROS). However, little is known about the molecular mechanisms connecting elevated vascular ROS and disease pathogenesis. A growing number of vascular and hemostatic proteins are recognized to undergo reversible methionine oxidation, in which methionine residues are post-translationally oxidized to methionine sulfoxide (MetO). Protein methionine oxidation can be reversed by the action of stereospecific enzymes known as methionine sulfoxide reductases (MSR). The work presented in this thesis focuses on the mechanistic role of reversible protein methionine oxidation in vascular disease.
Chapter 1 discusses our current understanding of the role of ROS and redox reactions in vascular disease, highlighting the potential role of protein methionine oxidation. Chapter 2 investigates the significance of protein methionine oxidation in the prothrombotic phenotype of vascular disease. We focused primarily on thrombomodulin (TM), an endothelial surface protein critically involved in anticoagulation, and tested the hypothesis that oxidation of TM Met388 is a reversible process that contributes to vascular thrombosis. We found that methionine oxidation can inhibit TM anticoagulant function and contribute to thrombotic vascular disease although this process was not physiologically reversed by MSR. Overall, these results support a role of methionine oxidation as a redox regulator of thrombotic vascular disease. Chapter 3 examines the pathophysiologic role of protein methionine oxidation in the proinflammatory mechanisms of acute ischemic stroke. Both inflammation and oxidative pathways are activated during cerebral ischemia/reperfusion. We tested the hypothesis that protein methionine oxidation potentiates neurovascular inflammation and contributes to cerebral ischemia/reperfusion injury. We found that deficiency of methionine sulfoxide reductase A (MsrA) exacerbates cerebral ischemia/reperfusion injury through activation of redox-regulated proinflammatory pathways. These results support a novel role of methionine oxidation as a reversible redox regulator of acute ischemic stroke. An overall discussion is presented in Chapter 4 and highlights potential applications and future directions of this thesis project. Also discussed are additional targets of protein methionine oxidation and the increasing number of tools being developed to identify and quantify MetO in proteins. The work presented in this thesis contributes to the growing body of research showing the pathophysiologic role of reversible methionine oxidation. These data also advance our understanding of the mechanisms regulating vascular disease.