Small Extracellular Vesicles from Young Healthy Human Plasma Inhibit Cardiac Fibrosis After Myocardial Infarction via miR-664a-3p Targeting SMAD4.

Purpose: Cardiac fibrosis, a key contributor to ventricular pathologic remodeling and heart failure, currently lacks effective therapeutic approaches. Patients and Methods: Small extracellular vesicles from young healthy human plasma (Young-sEVs) were characterized via protein marker, transmission electron microscopy, and nanoparticle tracking analysis, then applied in cellular models and mouse models of cardiac fibrosis. Western blotting and qRT-PCR were used to identify protective signaling pathways in cardiac fibroblasts (CFs). Results: Young-sEVs significantly inhibited cardiac fibrosis and subsequent cardiac dysfunction post-myocardial infarction (MI) in mice. The main findings included that echocardiographic assessments four weeks post-MI indicated that Young-sEVs improved left ventricular ejection fraction (LVEF) and fractional shortening (LVFS), and reduced left ventricular internal diameter in diastole (LVIDd) and systole (LVIDs). Treatment with Young-sEVs also decreased Masson-positive fibroblast areas and collagen synthesis in cardiac tissue. However, sEVs from the old control group did not achieve the above effect. Consistent with in vivo results, Young-sEVs could also inhibit the proliferation, migration, and collagen synthesis of CFs in the TGF-β1-induced cellular fibrosis model. High-throughput microRNA (miRNA) sequencing and qRT-PCR analysis revealed that miR-664a-3p was abundant in Young-sEVs. The high expression of miR-664a-3p significantly inhibited the proliferation, migration, and collagen synthesis of TGF-β1-induced CFs. However, suppressing the expression of miR-664a-3p in Young-sEVs eliminated their therapeutic effect on cardiac fibrosis in mice. Further studies confirmed SMAD4 as a direct downstream target of miR-664a-3p, whose overexpression could reverse the anti-fibrotic effects of miR-664a-3p. Conclusion: In summary, these findings firstly revealed that Young-sEVs could directly bind to the 3'-untranslated region of SMAD4 mRNA through miR-664a-3p, thereby inhibiting the TGF-β/SMAD4 signaling pathway to protect heart from fibrosis and improve cardiac function. Considering the ease of obtaining plasma-derived sEVs, our study offers a promising therapeutic strategy for heart failure, with the potential for rapid clinical translation in the near future.