Silencing collapsin response mediator protein-2 reprograms macrophage phenotype and improves infarct healing in experimental myocardial infarction model

BACKGROUND: Delayed M1 toward M2 macrophage phenotype transition is considered one of the major causes for the impaired healing after myocardial infarction (MI). While searching for molecules that modulate M1 and M2 macrophage polarization, we identified collapsin response mediator protein-2 (CRMP2) as a novel molecule involved in macrophage polarization to M1. In this study, we evaluated the effect of silencing CRMP2 on macrophage polarization, inflammation and fibrosis post myocardial infarction. METHODS: CRMP2 expression was assessed with Western blotting or immunohistochemistry. Macrophage phenotypes were measured with flow cytometry, quantitative real-time PCR (qPCR), Western blotting or immunohistochemistry. CRMP2 siRNA was delivered into the macrophages infiltrated in the wound of ApoE(−/−) mice through lipidoid nanoparticle, and fibrosis, leukocyte infiltration and inflammation parameters were measured with qPCR. Infarct size was measured with Masson’s trichrome staining. Echocardiography was performed to assess ventricular systolic dimension, left ventricular diastolic dimension, anterior wall thickness and posterior wall thickness. Student’s t-test (for 2 groups) and ANOVA (for > 2 groups) were used for statistical analyses. RESULTS: CRMP2 was expressed in a higher level in M1 macrophages than M2 subsets, and CRMP2 RNA interference (RNAi) resulted in a switch of bone marrow-derived macrophages from M1 to M2 phenotype. High level of CRMP2 was also observed in the macrophages infiltrated in the infarct area 3 days post MI in both wildtype (WT) and ApoE(−/−) mice, and the expression of CRMP2 retained in the infiltrated macrophages of ApoE(−/−) mice but not in that of WT mice 10 days after MI. Nanoparticle-mediated delivery of CRMP2 siRNA to ApoE(−/−) mice with MI resulted in dramatic switch of wound macrophages from M1 to M2 phenotype, marked decrease in inflammation and fibrosis, and significant attenuation of post-MI heart failure and mortality. CONCLUSION: CRMP2 is highly expressed in M1 macrophages and silencing CRMP2 reprograms macrophage phenotype and improves infarct healing in atherosclerotic mice.