Novel Therapeutics Modulate Cardiac Leukocyte Populations Following Myocardial Infarction

Abstract

Myocardial infarction (MI) triggers an inflammatory response that transitions from pro‐inflammatory to reparative over time, a progression that is essential for cardiac healing. Sympathetic nerve loss in the heart after MI predicts the probability of serious ventricular arrhythmias, and restoring nerves prevents arrhythmias. Although noradrenergic transmission is pro‐inflammatory in several contexts, acetylcholine (ACh) can be anti‐inflammatory; and cardiac sympathetic nerves release ACh along with norepinephrine after MI. Recent studies have discovered sympathetic regulation of global inflammatory responses, and our lab has shown previously that treatment with either Intracellular Sigma Peptide (ISP) or the small molecule HJ‐02 following ischemia‐reperfusion (IR) injury restores sympathetic innervation to the cardiac scar and prevents arrhythmias. However, whether sympathetic reinnervation modulates leukocyte homing and function in the heart post‐IR was unknown.C57BL/6J mice were treated on days 3‐10 after IR with ISP or HJ‐02, and we used quantitative multiplex immunohistochemistry (mIHC) to identify the leukocyte phenotypes present in the heart two weeks following IR. Reinnervated hearts had decreased inflammatory (M1‐like) macrophage levels [Percent of total macrophages ± SEM: VEH, 47.29%±1.446; ISP, 37.97%±1.590; HJ‐02, 29.72%±1.226] and elevated reparative (M2‐like) macrophages [VEH, 52.71%±1.446; ISP, 62.03%±1.590; HJ‐02, 70.28%±1.226]. HJ‐02 stimulated a significantly greater shift from inflammatory to reparative cell types compared to ISP.However, it is unknown whether it is a direct effect of the treatments on immune cells or the restoration of sympathetic nerves in the infarct causing the changes in leukocyte populations. To answer whether the treatments are the instigator, we isolated and cultured primary peritoneal macrophages from unoperated C57BL/6J mice, treated with ISP or HJ‐02, and examined macrophage marker expression using flow cytometry. Preliminary results suggest that both ISP and HJ‐02 expand isolated peritoneal macrophages in situ, with a predominantly M2‐like phenotype. M2‐like macrophages promote wound‐healing, suggesting these novel therapeutics may be beneficial for the heart after MI.