Background:
Dysregulated platelet activation in an ischemic microvascular environment may play a role in myocardial infarction (MI). Platelet receptor signaling is well-characterized, but mechanisms of receptor-independent activation, such as by reactive oxygen species (ROS) generated in ischemic conditions, are less well understood. We discovered that ERK5, a nuclear protein which is ROS-activated in others cells, is abundantly present in platelets. We investigated whether ERK5 could regulate platelet activation and thrombosis in healthy and diseased states.
Methods:
Human and mouse platelets were stimulated with agonists including ADP, U46619, TRAP, convulxin, or ROS (H
2
O
2
or 5% O
2
). ERK5 activity was assessed by immunoblotting. Platelet activation was assessed via fluorescent-activated cell sorting (FACS) for P-selectin or activated GPIIb/IIIa. Intravascular thrombus (pulmonary embolus) or mesenteric thrombus (oxidative injury) formation was assessed by
ex vivo
fluorescent imaging and
in vivo
intravital microscopy, respectively. MI was performed in wild-type (WT) and in platelet specific ERK5 deficient (ERK5
-/-
) mice by LAD coronary artery ligation. Left ventricular (LV) function was determined by echocardiography. Matrix metalloproteinase (MMP) activity was determined by in-gel zymography.
Results:
Human and platelet ERK5 was activated by ROS and via the thrombin and thromboxane receptors, but not via the purinergic or collagen receptors. Murine
in vivo
thrombosis was regulated by platelet ERK5 only if the injury involved oxidative stress. MI in mice promoted sustained platelet activation over one week in an ERK5-dependent manner. Following MI, platelet ERK5
-/-
mice had less reactive platelets, less platelet MMP activity and thromboxane production, attenuated MMP activity in the LV, less remodeling with smaller infarcts, and enhanced myocardial systolic performance.
Conclusions:
ERK5 is an ischemic sensor in platelets which regulates ongoing platelet activation after MI as well as remodeling via myocardial microvasculature. These observations may explain ischemic microvascular aberrations like the no-reflow phenomenon following percutaneous coronary intervention, suggesting a novel pharmacologic target.
Correction to: PCSK9 (Proprotein Convertase Subtilisin/Kexin 9) Enhances Platelet Activation, Thrombosis, and Myocardial Infarct Expansion by Binding to Platelet CD36
