Red blood cell-derived semaphorin 7A promotes thrombo-inflammation in myocardial ischemia-reperfusion injury through platelet GPIb.

Myocardial ischemia is one of the leading health problems worldwide. Therapy consists of the restitution of coronary perfusion which is followed by myocardial inflammation. Platelet-neutrophil interaction is a crucial process during inflammation, yet its consequences are not fully understood. Here, we show that platelet-neutrophil complexes (PNCs) are increased in patients with acute myocardial infarction and that this is associated with increased levels of neuronal guidance protein semaphorin 7A (SEMA7A). To investigate this further, we injected WT animals with Sema7a and found increased infarct size with increased numbers of PNCs. Experiments in genetically modified animals identify Sema7a on red blood cells to be crucial for this condition. Further studies revealed that Sema7a interacts with the platelet receptor glycoprotein Ib (GPIb). Treatment with anti-Sema7a antibody protected from myocardial tissue injury. In summary, we show that Sema7a binds to platelet GPIb and enhances platelet thrombo-inflammatory activity, aggravating post-ischemic myocardial tissue injury

Exogenous Administration of a Recombinant Variant of TWEAK Impairs Healing after Myocardial Infarction by Aggravation of Inflammation

Background: Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factorinducible 14 (Fn14) are upregulated after myocardial infarction (MI) in both humans and mice. They modulate inflammation and the extracellular matrix, and could therefore be important for healing and remodeling after MI. However, the function of TWEAK after MI remains poorly defined. Methods and results: Following ligation of the left coronary artery, mice were injected twice per week with a recombinant human serum albumin conjugated variant of TWEAK (HSA-Flag-TWEAK), mimicking the activity of soluble TWEAK. Treatment with HSA-Flag-TWEAK resulted in significantly increased mortality in comparison to the placebo group due to myocardial rupture. Infarct size, extracellular matrix remodeling, and apoptosis rates were not different after MI. However, HSA-Flag-TWEAK treatment increased infiltration of proinflammatory cells into the myocardium. Accordingly, depletion of neutrophils prevented cardiac ruptures without modulating all-cause mortality. Conclusion: Treatment of mice with HSA-Flag-TWEAK induces myocardial healing defects after experimental MI. This is mediated by an exaggerated neutrophil infiltration into the myocardium

Platelet Function and Coronary Microvascular Dysfunction

The ability of platelets to activate and aggregate to form blood clots in response to endothelial injury is well established. They are therefore critical contributors to ischaemia in atherothrombosis [1]. However, their role in cardiovascular disease is not limited to end-stage thrombosis in large vessels [2]. Abundant experimental evidence has established that activated platelets are also important mediators of microvascular thrombosis and promote the inflammatory response during ischaemia-reperfusion (IR) injury [3–5]. While platelets do not physically interact with the healthy endothelium, they can bind to the wall of hypoxic microvessels and release a plethora of inflammatory mediators that further enhance the activation of the endothelial monolayer and the recruitment of circulating leukocytes (monocytes, neutrophils, T-cells) [2]. In addition, deposition of platelets to the dysfunctional endothelium can lead to vasoconstriction which accelerates microvascular occlusion, thereby impairing tissue perfusion [3]. In this chapter, we discuss the role of platelets in promoting microvascular dysfunction and inflammation during IR injury. Focus is placed on the cross-talk between platelets and other cell types (endothelial cells [ECs] and leukocytes) via platelet adhesion receptors and platelet-derived proinflammatory mediators. We also consider new paradoxical functionalities of platelets promoting cardiac recovery after myocardial infarction (MI)