Brain‐Derived Neurotrophic Factor Precursor Contributes to a Proinflammatory Program in Monocytes/Macrophages After Acute Myocardial Infarction

BACKGROUND: The imbalance of monocyte/macrophage polarization toward the preferential proinflammatory phenotype and a lack of normal inflammation resolution are present in acute myocardial infarction (AMI). Our previous study showed that upregulation of brain‐derived neurotrophic factor precursor (proBDNF) in M2‐like monocytes may contribute to the proinflammatory response in the Stanford type‐A acute aortic dissection. The present study aimed to investigate the role of proBDNF signaling in monocytes/macrophages in the progress of AMI. METHODS AND RESULTS: We observed the upregulation of proBDNF in the proinflammatory monocytes of patients with AMI. The upregulation of proBDNF was also observed in the circulating proinflammatory Ly6C(high) monocytes and cardiac F4/80(+)CD86(+) macrophages 3 days after AMI in a mice model. To neutralize proBDNF, the mice subjected to AMI were injected intraperitoneally with a monoclonal anti‐proBDNF antibody. Echocardiography, 2,3,5‐triphenyltetrazolium chloride staining, and positron emission tomography/computed tomography results demonstrate that monoclonal anti‐proBDNF antibody treatment further impaired cardiac functions, increased infarct size, and exacerbated the proinflammatory state. Moreover, the level of proinflammatory Ly6C(high) in the blood and F4/80(+)CD86(+) in the heart was further increased in monoclonal anti‐proBDNF antibody mice. RNA sequencing revealed that matrix metalloprotease‐9 protein level was dramatically increased, along with the activated proinflammatory‐related cytokines. Matrix metalloprotease‐9 inhibitor treatment attenuated the deteriorated effect of monoclonal anti‐proBDNF antibody on cardiac function and infarct areas. CONCLUSIONS: Our study shows that endogenous proBDNF in monocytes/macrophages may exert protective roles in cardiac remodeling after AMI by regulating matrix metalloprotease‐9 activity.