Rationale: After myocardial infarction, neutrophils rapidly and massively infiltrate the heart, where they promote both tissue healing and damage. Objective: To characterize the dynamics of circulating and cardiac neutrophil diversity after infarction. Methods and Results: We employed single-cell transcriptomics combined with cell surface epitope detection by sequencing (CITE-seq) to investigate temporal neutrophil diversity in the blood and heart after murine myocardial infarction. At day 1, 3, and 5 after infarction, cardiac Ly6G + neutrophils could be delineated into six distinct clusters with specific time-dependent patterning and proportions. At day 1, neutrophils were characterized by a gene expression profile proximal to bone marrow neutrophils (Cd177, Lcn2, Fpr1), and putative activity of transcriptional regulators involved in hypoxic response (Hif1a) and emergency granulopoiesis (Cebpb). At 3 and 5 days two major subsets of Siglecf hi (enriched for e.g. Icam1 and Tnf) and Siglecf low (nSlpi, Ifitm1) neutrophils were found. CITE-seq analysis in blood and heart revealed that while circulating neutrophils undergo a process of ageing characterized by loss of surface CD62L and upregulation of Cxcr4, heart infiltrating neutrophils acquired a unique SiglecF hi signature. SiglecF hi neutrophils were absent from the bone marrow and spleen, indicating local acquisition of the SiglecF hi signature. Reducing the influx of blood neutrophils by anti-Ly6G treatment increased proportions of cardiac SiglecF hi neutrophils, suggesting accumulation of locally aged neutrophils. Computational analysis of ligand/receptor interactions revealed putative pathways mediating neutrophil to macrophage communication in the myocardium. Finally, SiglecF hi neutrophils were also found in atherosclerotic vessels, revealing that they arise across distinct contexts of cardiovascular inflammation. Conclusions: Altogether, our data provide a time-resolved census of neutrophil diversity and gene expression dynamics in the mouse blood and ischemic heart at the single-cell level, and reveal a process of local tissue specification of neutrophils in the ischemic heart characterized by the acquisition of a SiglecF hi signature.

Background-Lower mortality rates among women with chronic heart failure than among men may depend in part on the action of female sex hormones, especially estrogens. The biological effects of estrogens are mediated by 2 distinct estrogen receptor (ER) subtypes (ER␣ and ER␤). The present study was undertaken to determine the role of ER␤ in the development of chronic heart failure after experimental myocardial infarction (MI of heart failure, and contributes to impaired expression of Ca 2ϩ -handling proteins in chronic heart failure after MI. Further studies are required to delineate the relative importance of cardiac and vascular effects of ER␤ and the role of ER␣ in the development of heart failure.

A t sites of vascular injury, the subendothelial extracellular matrix is exposed to the blood and triggers sudden platelet activation and the formation of a fibrin containing thrombus. This process is essential to prevent excessive posttraumatic blood loss, but if it occurs inappropriately, for example, at sites of atherosclerotic plaque rupture, it can lead to vessel occlusion and ischemic infarction. In the clinical context of myocardial infarction, timely reopening of an occluded coronary artery by pharmacological thrombolysis or coronary intervention constitutes an effective therapeutic mean to limit cardiac damage. However, restoration of blood flow causes further cardiac damage, the so-called reperfusion injury (RI). The mechanisms of myocardial RI are not fully understood; thus, it is possible that thrombus formation by platelets in reperfused microvessels could contribute to this process. Furthermore, thrombus fragmentation by thrombolysis or coronary balloon angioplasty might add to the occlusion of microvessels by distal embolization. Additionally, platelets release factors that potentially increase RI without mechanical obstruction of microvessels. Activated © 2016 American Heart Association, Inc. Objective-The objective of this study was to investigate the effects of platelet inhibition on myocardial ischemia-reperfusion (IR) injury. Approach and Results-Timely restoration of coronary blood flow after myocardial infarction is indispensable but leads to additional damage to the heart (myocardial IR injury). Microvascular dysfunction contributes to myocardial IR injury. We hypothesized that platelet activation during IR determines microvascular perfusion and thereby the infarct size in the reperfused myocardium. The 3 phases of thrombus formation were analyzed by targeting individual key platelet-surface molecules with monoclonal antibody derivatives: (1) adhesion (anti-glycoprotein [GP]-Ib), (2) activation (anti-GPVI), and (3) aggregation (anti-GPIIbIIIa) in a murine in vivo model of left coronary artery ligation (30 minutes of ischemia followed by 24 hours of reperfusion). Infarct sizes were determined by Evans Blue/2,3,5-triphenyltetrazolium chloride staining, infiltrating neutrophils by immunohistology. Anti-GPVI treatment significantly reduced infarct size versus control, whereas anti-GPIb or anti-GPIIbIIIa antibody fragments showed no significant differences. Mechanistically, anti-GPVI antibody-mediated reduction of infarct size was not because of impaired Ca 2+ signaling or platelet degranulation because mice deficient in store-operated calcium channels (stromal interaction molecule 1, ORAI1), α-granules (Nbeal2