Abstract 19908: 5-oxoprolinase: a Novel Cardiac Mediator of the Oxidative Stress Response in the Failing Heart

Introduction: A hallmark of Heart Failure (HF) is the re-emergence of the fetal gene program. The aim of this study was to identify novel genes associated with the fetal gene program in HF, by utilizing a mouse embryonic stem (mES) cell based micro-array. Methods/Results: The micro-array analysis was performed on mES cells, early and late mES-derived cardiac progenitors, and mouse neonatal right ventricular tissue. As expected, our screen effectively identified established fetal genes, including alpha smooth muscle actin. We further uncovered several novel genes behaving like fetal genes. The top 5 hits were validated in an in vivo pressure overload HF model. 5-oxoprolinase (OPLAH) was found to be the most significantly differentially expressed gene in the HF model. In a human organ panel, OPLAH gene expression was highest in cardiac tissue, and found to be expressed mainly in the cytosol of cardiomyocytes. Additionally OPLAH protein levels were reduced by 50-70% in both pressure overload and ischemia induced HF (p=0.001 and p=0.009, respectively). OPLAH is an ATP-hydrolyzing enzyme involved in the γ-Glutamyl cycle, responsible for the conversion of the metabolite 5-oxoproline into glutamate. To study OPLAH function we used siRNA and/or over-expression by means of viral transfection of neonatal rat ventricular myocytes. In vitro silencing of OPLAH resulted in an increased susceptibility towards oxidative stress induced apoptosis (40% increase in cleaved caspase-3 positive cells, p=0.02). Furthermore, exogenous administration of 5-oxoproline increased apoptosis in cardiomyocytes (40% increase in cleaved caspase-3 positive cells, p=0.04). Conclusions: We identified OPLAH as a novel enzyme associated with HF, behaving like fetal genes, which is involved in the innate protection against oxidative stress, by scavenging excess 5-oxoproline.