Metrnl Reduces Thrombosis and Acute Myocardial Injury Through Inhibition of Platelet Activation via CD36 Receptor Degradation

BACKGROUND: Metrnl (Meteorin-like) is a secreted protein that plays a pivotal role in regulating insulin sensitivity, angiogenesis, and atherosclerosis. The circulating Metrnl levels are mainly derived from the endothelium and associated with atherosclerosis and arterial thrombotic disease in patients. However, Metrnl effects on platelets and thrombosis are not yet fully understood. METHODS: By using global Metrnl knockout mice, platelet-specific Metrnl knockout mice, recombinant Metrnl protein, and Metrnl-neutralizing antibody, combined with visualization techniques, we investigated the effects of Metrnl on human and rodent platelet activation in vitro, and thrombosis in vivo as well as its action mode. To screen and verify receptor-mediated mechanisms for Metrnl, we used immunoprecipitation-based mass spectrometry, protein-protein interaction tests, and functional assays under antagonist and knockout conditions. Receptor binding domains, functional sites, and downstream mechanisms were further explored using various protein mutations, specific interventions, and signaling examinations. A myocardial ischemia/reperfusion model was used to better understand the effects of Metrnl on microvascular thrombosis obstruction and acute myocardial injury. RESULTS: Metrnl deficiency potentiated thrombosis via platelet activation rather than coagulation or the fibrinolysis system. Exogenous Metrnl administration could directly inhibit platelet activation and thrombosis without causing bleeding risk when using Metrnl alone or in combination with clopidogrel. Metrnl in platelets also inhibited platelet activation and thrombosis in a secretory manner. In a molecular mechanism, CD36 was identified as a receptor for Metrnl on platelets. Metrnl induced CD36 degradation via interaction with a previously uncharacterized domain (amino acids 280-439) and acetylation at lysine 403 of CD36, thereby decreasing the downstream signaling pathway (SRC-extracellular signal-related kinase 5 [ERK5]) in platelets. Further, mouse model experiments demonstrated Metrnl protein's antiplatelet function in mitigating microvascular thrombosis and acute myocardial ischemia/reperfusion injury. CONCLUSIONS: We identify Metrnl in both endogenous secretion and exogenous administration as a novel inhibitor of platelet activation and thrombus formation without causing bleeding risk. Metrnl is a novel ligand for the CD36 receptor, which has a specific Metrnl binding domain. Metrnl inhibits platelet activation by promoting CD36 degradation via acetylation at lysine 403 of CD36. Metrnl holds promise to be a novel therapeutic target for thrombotic disease, such as in the treatment of acute myocardial infarction.