Abstract 5442: Oxidative Stress Regulates Cardiac Stem Cell Differentiation in a MicroRNA-Mediated Mechanism

Abstract

Oxidative stress, specifically hydrogen peroxide (H 2 O 2 ) is significantly increased following myocardial infarction and its effect on adult cardiac stem cell (CSC) differentiation is largely unknown. To promote endogenous and implanted CSC differentiation into functional cardiac cells in ischemic tissue, mechanisms of deleterious redox signaling on cardiomyogenesis must be determined. Our data demonstrate that H 2 O 2 time- and dose-dependently inhibits Nkx2.5 expression in CSCs exposed to differentiating medium. Since overexpression of microRNA (miR)-1 increases embryonic stem cell cardiac differentiation, we hypothesized that H 2 O 2 regulates CSC differentiation in a miRNA-mediated mechanism. CSCs exposed to H 2 O 2 (1–100 μ M) in differentiating media demonstrated time-dependent, decreased expression of miR1 compared to cells exposed to differentiating media alone (1 μ M: 37±7.6% decrease from Day 5 control; 100 μ M: 47±11% decrease from Day 8 control). MiR133a, essential for normal cardiac development, was not time-dependently regulated by H 2 O 2 , suggesting it is not redox sensitive. Since cardiac differentiation in Drosophila is regulated by miR-1 binding to the Notch ligand Delta and Notch activation attenuates embryonic stem cell cardiogenesis, we next examined the effect of miR1 on the Notch pathway in CSCs. Delta1 expression increased 24±5% above the time-matched control exposed to differentiating media alone after 8 days exposure to H 2 O 2 (0.1 μ M). Since miR1 exhibited the inverse response to H 2 O 2 , the data support Delta1 as a target for miR1-mediated silencing in CSCs. In summary, our data suggest a mechanism for redox-mediated attenuation of CSC differentiation. H 2 O 2 decreases miR1 expression, which prevents normal Delta1 silencing by miR-1 that occurs during differentiation. This failure of Delta1 degradation increases Notch activation, which subsequently suppresses cardiogenic differentiation. This study underscores the importance of H 2 O 2 scavenging following cardiac injury to promote CSC differentiation, and suggests that targeting anti-cardiogenic miRNA regulation may be a promising strategy for successful CSC-based therapy.