β2-Adrenergic receptor-dependent chemokine receptor 2 expression regulates leukocyte recruitment to the heart following acute injury

Following cardiac injury, early immune cell responses are essential for initiating cardiac remodeling and tissue repair. We previously demonstrated the importance of beta 2-adrenergic receptors (beta 2ARs) in the regulation of immune cell localization following acute cardiac injury, with deficient leukocyte infiltration into the damaged heart. The purpose of this study was to investigate the mechanism by which immune cell-expressed beta 2ARs regulate leukocyte recruitment to the heart following acute cardiac injury. Chemokine receptor 2 (CCR2) expression and responsiveness to C-C motif chemokine ligand 2 (CCL2)-mediated migration were abolished in beta 2AR knockout (KO) bone marrow (BM), both of which were rescued by beta 2AR reexpression. Chimeric mice lacking immune cell-specific CCR2 expression, as well as wild-type mice administered a CCR2 antagonist, recapitulated the loss of monocyte/ macrophage and neutrophil recruitment to the heart following myocardial infarction (MI) observed in mice with immune cell-specific beta 2AR deletion. Converse to beta 2AR ablation, beta 2AR stimulation increased CCR2 expression and migratory responsiveness to CCL2 in BM. Mechanistically, G proteindependent beta 2AR signaling was dispensable for these effects, whereas beta-arrestin2-biased beta 2AR signaling was required for the regulation of CCR2 expression. Additionally, activator protein 1 (AP-1) was shown to be essential in mediating CCR2 expression in response to beta 2AR stimulation in both murine BM and human monocytes. Finally, reconstitution of beta 2ARKO BM with rescued expression of a beta-arrestin-biased beta 2AR in vivo restored BM CCR2 expression as well as cardiac leukocyte infiltration following MI. These results demonstrate the critical role of beta-arrestin2/AP-1-dependent beta 2AR signaling in the regulation of CCR2 expression and recruitment of leukocytes to the heart following injury.