Oxidative stress-induced Notch1 signaling promotes cardiogenic gene expression in mesenchymal stem cells

Introduction: Administration of bone marrow-derived mesenchymal stem cells (MSCs) after myocardial infarction (MI) results in modest functional improvements. However; the effect of microenvironment changes after MI, such as elevated levels of oxidative stress on cardiogenic gene expression of MSCs, remains unclear. Methods: MSCs were isolated from the bone marrow of adult rats and treated for 1 week with H2O2 (0.1 to 100 mu M) or 48 hours with glucose oxidase (GOX; 0 to 5 mU/ml) to mimic long-term pulsed or short-term continuous levels of H2O2, respectively. Results: In 100 mu M H2O2 or 5 mU/ml GOX-treated MSCs, mRNA expression of selected endothelial genes (Flt1, vWF, PECAM1), and early cardiac marker (nkx2-5, aMHC) increased significantly, whereas early smooth muscle markers (smooth muscle a-actin and sm22 alpha) and fibroblast marker vimentin decreased, as measured with real-time PCR. Interestingly, mRNA expression and activity of the cell-surface receptor Notch1 were significantly increased, as were its downstream targets, Hes5 and Hey1. Co-treatment of MSCs with 100 mu M H2O2 and a.-secretase inhibitor that prevents Notch signaling abrogated the increase in cardiac and endothelial genes, while augmenting the decrease in smooth muscle markers. Further, on GOX treatment, a significant increase in Wnt11, a downstream target of Notch1, was observed. Similar results were obtained with adult rat cardiac-derived progenitor cells. Conclusions: These data suggest that H2O2-or GOX-mediated oxidative stress upregulates Notch1 signaling, which promotes cardiogenic gene expression in adult stem/progenitor cells, possibly involving Wnt11. Modulating the balance between Notch activation and H2O2-mediated oxidative stress may lead to improved adult stem cell-based therapies for cardiac repair and regeneration.