Notch1 Overexpression in Cardiac Mesenchymal Stem Cells Renders their Exosomes Highly Effective in Promoting Angiogenesis and Cardiac Regeneration

Objective Notch1 signaling is critical in postnatal angiogenesis. Cardiac mesenchymal stem cells (C‐MSC) are endogenous cardiac stromal cells which are believed to facilitate cardiac regeneration via paracrine effects. Here, we investigated the effects of exosomes from Notch1 engineered C‐MSC on angiogenesis and cardiac myocyte proliferation in ischemic myocardium. Methods and results C‐MSC were isolated from conditional Notch1 knock out mice. For Notch1 knockout C‐MSC generation, Notch1 gene was deleted via adenoviral vector mediated Cre recombination. For Notch1 overexpression, cells were modified with Notch1 intracellular domain (NICD). Myocardial infarction (MI) mouse model was generated by LAD ligation. Exosomes from C‐MSC (Exo‐C‐MSC), Notch1 knockout C‐MSC (Exo‐C‐MSC NICD KO ) and Notch1 overexpressing C‐MSC (Exo‐C‐MSC NICD ) were isolated and characterized. Both Exo‐C‐MSC and Exo‐C‐MSC NICD were strongly pro‐angiogenic under in vitro and in vivo conditions. Compared with Exo‐C‐MSC, Exo‐C‐MSC NICD treatment led to dense tube formation and higher vessel density in peri‐infarct area. Moreover, knockout of Notch1 significantly abrogated the pro‐angiogenetic effect of Exo‐C‐MSC. Compared with control group, pretreatment of Exo‐C‐MSC and Exo‐C‐MSC NICD also exerted anti‐apoptotic effects on endothelial cells stressed with 300 μM H 2 O 2 , for 8h. Exo‐C‐MSC NICD KO had no anti‐apoptotic effect in H 2 0 2 treated cells. As expected, intramyocardial injection of Exo‐C‐MSC NICD were strongly cardioprotective on cardiomyocytes (CMs) and vessel cells 24h after MI. Though both Exo‐C‐MSC and Exo‐C‐MSC NICD treatment improved cardiac function and decreased fibrosis in mice one‐month post‐MI, Exo‐C‐MSC NICD were more effective in improving cardiac function and reducing fibrosis. On the other hand, Exo from Notch1 knockout MSC had no effects on fibrosis or function. A significant effect on vessel density and CMs proliferation (ki67 and α‐actinin double positive cells) in peri infarct area was observed with the treatment of Exo‐C‐MSC NICD in comparison with PBS, Exo‐C‐MSC and Exo‐C‐MSC NICD KO groups. Conclusion Notch1 overexpression in C‐MSC produced highly effective exosomes in preventing cell death, promoting angiogenesis, cardiomyocyte proliferation and in restoring cardiac function after MI. These data suggest that Notch1 activation may further enhance the effectiveness of exosomes from C‐MSC in cell‐free therapy. Support or Funding Information R01 HL134354 and R01 AR070029 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .