Macrophage PRMT9 Ameliorates Acute Myocardial Infarction by Promoting Symmetric Dimethylation and Degradation of STAT1

BACKGROUND: During myocardial infarction (MI), M1-like macrophages exacerbate myocardial injury by excessively secreting inflammatory cytokines. Therefore, modulating the activity of M1-like macrophages may represent a novel therapeutic strategy for MI. PRMTs (protein arginine methyltransferases) primarily regulate protein function via asymmetric dimethylation, but PRMT9 does so through symmetric dimethylation. However, its role in cardiovascular diseases has yet to be established. In this study, we investigated the role of PRMT9 in macrophage polarization in the context of MI and explored its therapeutic effect for MI. METHODS: knockout mice and macrophage-specific overexpression adeno-associated virus vectors. We explored the underlying mechanisms through flow cytometry, transcriptome analysis, immunoprecipitation/mass spectrometry analysis, and functional experiments. RESULTS: We discovered that PRMT9 was highly expressed in murine and human peripheral blood mononuclear cells in the early stages of MI. PRMT9 deficiency enhanced M1-like polarization and exacerbated cardiac damage in murine models of MI. Conversely, PRMT9 overexpression in macrophages reduced infarct size, accelerated inflammation resolution, and improved cardiac function after MI. Our findings established that PRMT9-catalyzed methylation played an important role in STAT1 (signal transducer and activator of transcription 1)-mediated macrophage polarization. Mechanistically, PRMT9 directly binds to STAT1 and facilitates its symmetric dimethylation at R588 and R736. Further analysis revealed that PRMT9-mediated symmetric dimethylation facilitated STAT1 ubiquitination, which promoted STAT1 recognition by SQSTM1/p62 (sequestosome-1) and NDP52/CALCOCO2 (nuclear dot protein 52), facilitating STAT1-selective autophagic degradation and suppressing excessive M1-like macrophage responses. Moreover, we demonstrated that the STAT1 inhibitor fludarabine, a clinically used chemotherapeutic agent, mitigated the exacerbation of post-MI myocardial injury induced by PRMT9 deletion in macrophages. CONCLUSIONS: This study discovered a novel PRMT9-driven symmetric dimethylation of STAT1, resulting in its ubiquitination and lysosomal degradation, which suppresses the proinflammatory polarization of macrophages and mitigates myocardial damage following MI.