Activation of Aryl Hydrocarbon Receptor by ITE Improves Cardiac Function in Mice After Myocardial Infarction

Background The immune and inflammatory responses play a considerable role in left ventricular remodeling after myocardial infarction (MI). Binding of AhR (aryl hydrocarbon receptor) to its ligands modulates immune and inflammatory responses; however, the effects of AhR in the context of MI are unknown. Therefore, we evaluated the potential association between AhR and MI by treating mice with a nontoxic endogenous AhR ligand, ITE (2-[1'H-indole-3'-carbonyl]-thiazole-4-carboxylic acid methyl ester). We hypothesized that activation of AhR by ITE in MI mice would boost regulatory T-cell differentiation, modulate macrophage activity, and facilitate infarct healing. Methods and Results Acute MI was induced in C57BL/6 mice by ligation of the left anterior descending coronary artery. Then, the mice were randomized to daily intraperitoneal injection of ITE (200 µg/mouse, n=19) or vehicle (n=16) to examine the therapeutic effects of ITE during the postinfarct healing process. Echocardiographic and histopathological analyses revealed that ITE-treated mice exhibited significantly improved systolic function (<0.001) and reduced infarct size compared with control mice (<0.001). In addition, we found that ITE increased regulatory T cells in the mediastinal lymph node, spleen, and infarcted myocardium, and shifted the M1/M2 macrophage balance toward the M2 phenotype in vivo, which plays vital roles in the induction and resolution of inflammation after acute MI. In vitro, ITE expanded the Foxp3 (forkhead box protein P3-positive) regulatory T cells and tolerogenic dendritic cell populations. Conclusions Activation of AhR by a nontoxic endogenous ligand, ITE, improves cardiac function after MI. Post-MI mice treated with ITE have a significantly lower risk of developing advanced left ventricular systolic dysfunction than nontreated mice. Thus, the results imply that ITE has a potential as a stimulator of cardiac repair after MI to prevent heart failure.