INTRODUCTION P OSTNATAL CARDIAC MYOCYTES are terminally differenti- ated and are unable to proliferate. Certain pathophysio- logical conditions leading to cardiac overload elicit an adap- tive response by increasing myocyte volume, a condition termed hypertrophy (17, 37). Physiological modulators of cardiac function, such as, endothelin-1, and angiotensin II (Ang II), can mimic hypertrophic response(s) in neonatal and adult myocytes cultured ex vivo (40). Signal transducing ki- nases (e.g., S6, Ras, Raf, ERK, p38), phosphatases (e.g., cal- cineurin), and downstream transcriptional regulators (e.g., NFAT, GATA-4, NF-B and MEF-2) have been identified as the mediators of hypertrophic responses (2, 25, 49, 53). It is often observed that some of these agonists (Ang II and NE) also cause apoptosis at higher doses (41, 43). Such transition from hypertrophic to apoptotic “mode” also occurs during end-stage heart failure and is of immense clinical relevance (4, 17, 37). A paradox in the activities of a number of the above-mentioned signaling molecules such as ERK and cal- cineurin is that these mediate both anti- and proapoptotic re- sponses (6, 36). It remains to be explored how cardiac my- ocytes utilize apparently similar signaling molecules and still achieve distinctly variable biological consequences. During recent years, reactive oxygen species (ROS) have drawn considerable attention as a determinant of various bio- f-1 1 School of Life Sciences and 2 Special Centre for Molecular Medicine, Jawaharlal Nehru University; and 3 Department of Pathology and 4 De- partment of Pharmacology, All India Institute of Medical Sciences, New Delhi, India. *Both authors have equally contributed to this study. An Assessment of the Role of Reactive Oxygen Species and Redox Signaling in Norepinephrine-induced Apoptosis and Hypertrophy of H9c2 Cardiac Myoblasts MANVEEN K. GUPTA,* 2 T.V. NEELAKANTAN,* 1 MISHRA SANGHAMITRA, 1 RAKESH K. TYAGI, 2 AMIT DINDA, 3 SUBIR MAULIK, 4 CHINMAY K. MUKHOPADHYAY, 2 and SHYAMAL K. GOSWAMI 1,2 ABSTRACT Cardiac myocytes, upon exposure to increasing doses of norepinephrine (NE), transit from hypertrophic to apoptotic phenotype. Since reactive oxygen species (ROS) generation is attributed to both phenomena, the au- thors tested whether an elevation in intracellular ROS level causes such transition. H9c2 cardiac myoblasts upon treatment with hypertrophic and apoptotic doses of NE (2 and100 μM, respectively) transiently induced intracellular ROS at a comparable level, while 200 μM H 2 O 2 , another proapoptotic agonist, showed robust and sustained ROS generation. Upon analysis of a number of redox-responsive transcription factors as the downstream targets of ROS signaling, the authors observed that NE (2 and 100 μM) and H 2 O 2 (200 μM) were ineffective in inducing NF-B while both the agonists upregulated AP-1 and Nrf-2. However, the extents of in- duction of AP-1 and Nrf-2 were not in direct correlation with the respective ROS levels. Also, AP-1 activities induced by two doses of NE were intrinsically different, since at 2 μM, it primarily induced FosB, and at 100 μM it activated Fra-1. Differential induction of FosB and Fra-1 was also reiterated in adult rat myocardium injected with increasing doses of NE. Therefore, NE induces hypertrophy and apoptosis in cardiac myocytes by distinct redox-signaling rather than a general surge of ROS. Antioxid. Redox Signal. 8, 0000–0000. FORUM ORIGINAL RESEARCH COMMUNICATION ANTIOXIDANTS & REDOX SIGNALING Volume 8, Numbers 5 & 6, 2006 © Mary Ann Liebert, Inc. AQ1. Please check names of all authors. 14260c36.pgs 5/10/06 3:26 PM Page f-1