Abstract
Purpose: Cardiomyocyte death is a major cytopathologic response in acute myocardial infarction (AMI) and involves complex inflammatory interactions. Although existing reports indicating that mixed lineage kinase domain-like protein (MLKL) is involved in macrophage necroptosis and inflammasome activation, the downstream mechanism of MLKL in necroptosis remain poorly characterized in AMI. Methods: MLKL knockout mice (MLKLKO), RIPK3 knockout mice (RIPK3KO), and macrophage-specific MLKL conditional knockout mice (MLKLM-KO) were established. AMI was induced by coronary artery ligation. The role of MLKL in regulating myocardial morphological necroptosis was evaluated using immunofluorescence staining, flow cytometry, qRT-PCR, Western blot, CCK-8 assay, and ELISA. Results: Our findings revealed that myocardial segmental necroptosis (MSN), a unique morphological characteristics of cell death observed post-AMI, was promoted by intercellular inflammatory adhesion mediated by MLKL. The key features of MSN included localized cytomembrane perforation, segmental attenuation of myofilaments, MLKL-mediated filling, and macrophage inflammatory adhesion. In a mouse model of AMI, we observed MSN, which was absent in immunosuppressed mice. Pharmacological depletion of macrophages or genetic knockout of macrophage-specific MLKL (MLKLM-KO) reduced the occurrence of MSN. This reduction was reversed upon reinfusion of wild-type macrophages. Additionally, myocardial injury was significantly ameliorated in MLKLM-KO mice following AMI. In a macrophage-cardiomyocyte co-culture system, MLKLM-KO attenuated hypoxia-induced MSN and inhibited macrophage-mediated inflammatory adhesion. Furthermore, MLKL was found to trigger the formation of membrane pores and the polymerization of integrin αvβ1, thereby enhancing inflammatory adhesion in the co-culture system. Notably, MLKL-enhanced inflammatory adhesion was not entirely dependent on RIPK3. Conclusion: Our study demonstrates that MLKL is directly involved in myocardial segmental necroptosis by interacting with macrophages through inflammatory adhesion, and possibly independently of RIPK3.