Fibroblast‐Derived Microfibrillar‐Associated Protein 5 Exerts Cardioprotective Effects After Myocardial Infarction by Activating the NOTCH2 Signaling in Cardiomyocytes

BACKGROUND: Myocardial infarction (MI) remains a major cause of morbidity and mortality worldwide. MFAP5 (microfibrillar-associated protein 5) is an extracellular-matrix associated secreted glycoprotein whose cardiac function is unknown. This study aimed to explore the origin, expression, function, and potential mechanisms of MFAP5 in MI. METHODS: Single-cell analysis and immunohistochemistry were used to determine the origin and expression of MFAP5. Global MFAP5-knockout (KO) mice and adeno-associated virus 9-mediated cardiac fibroblast-specific overexpression mice were used to investigate the function of MFAP5 in vivo. RNA sequencing and ingenuity pathway analysis revealed potential mechanisms. Coimmunoprecipitation and confocal microscopy identified molecular interaction domains. rMFAP5 (recombinant MFAP5 protein) and plasmid-mediated intracellular overexpression revealed the effects of MFAP5 on cardiomyocytes under oxygen-glucose deprivation conditions. RESULTS: MFAP5 was significantly increased in both human and mouse heart tissues during MI, predominantly derived from activated cardiac fibroblasts. In vivo, MFAP5-knockout exacerbated cardiac dysfunction, enlarged infarct size and increased cardiomyocyte apoptosis during the acute phase of MI. Cardiac fibroblast-specific overexpression of MFAP5 exerted a protective effect. In vitro, MFAP5 significantly inhibited apoptosis in cardiomyocytes under oxygen-glucose deprivation stimulation. Mechanistically, MFAP5 derived from fibroblasts interacted with the extracellular EGF (epidermal growth factor) repeats of the NOTCH2 receptor on the surface of cardiomyocytes via its MBD domain, promoting shedding of the extracellular fragment of NOTCH2 and generation of the NICD2 (NOTCH2 intracellular domain). MFAP5 inhibited cardiomyocyte apoptosis by activating NOTCH2 signaling. CONCLUSIONS: Fibroblast-derived MFAP5 engages cardiomyocyte NOTCH2 to inhibit apoptosis and exerts cardioprotective effects after MI.