Oxidative Stress–Dependent Sphingosine Kinase-1 Inhibition Mediates Monoamine Oxidase A–Associated Cardiac Cell Apoptosis

Abstract

Abstract-The mitochondrial enzyme monoamine oxidase (MAO), its isoform MAO-A, plays a major role in reactive oxygen species-dependent cardiomyocyte apoptosis and postischemic cardiac damage. In the current study, we investigated whether sphingolipid metabolism can account for mediating MAO-A-and reactive oxygen speciesdependent cardiomyocyte apoptosis. In H9c2 cardiomyoblasts, MAO-A-dependent reactive oxygen species generation led to mitochondria-mediated apoptosis, along with sphingosine kinase-1 (SphK1) inhibition. These phenomena were associated with generation of proapoptotic ceramide and decrease in prosurvival sphingosine 1-phosphate. These events were mimicked by inhibition of SphK1 with either pharmacological inhibitor or small interfering RNA, as well as by extracellular addition of C 2 -ceramide or H 2 O 2 . In contrast, enforced expression of SphK1 protected H9c2 cells from serotonin-or H 2 O 2 -induced apoptosis. Analysis of cardiac tissues from wild-type mice subjected to ischemia/reperfusion revealed significant upregulation of ceramide and inhibition of SphK1. It is noteworthy that SphK1 inhibition, ceramide accumulation, and concomitantly infarct size and cardiomyocyte apoptosis were significantly decreased in MAO-Adeficient animals. In conclusion, we show for the first time that the upregulation of ceramide/sphingosine 1-phosphate ratio is a critical event in MAO-A-mediated cardiac cell apoptosis. In addition, we provide the first evidence linking generation of reactive oxygen species with SphK1 inhibition. Key Words: sphingosine kinase-1 Ⅲ monoamine oxidases Ⅲ ischemia/reperfusion Ⅲ ROS Ⅲ serotonin T he ischemia/reperfusion (I/R) syndrome occurring during revascularization results in the progressive loss of cardiac myocytes, ultimately leading to heart failure. 1 A wealth of reports indicate a pivotal role for apoptosis in cardiac myocyte death after I/R. 2-4 Indeed, cardiomyocyte apoptosis was found during the early phase of reperfusion after myocardial ischemia in animal models 5,6 and after cardiac transplantation in humans. 7,8 In addition, prevention of apoptosis strongly reduced postischemic cardiac damage.Abundant evidence suggests that reactive oxygen species (ROS) play an important role in the development and progression of postischemic myocardial damage, leading to apoptosis. 9,10 The induction of oxidative stress is related to an activation of several enzymatic systems including monoamine oxidases (MAOs). 11-13 MAOs catalyze oxidative deamination of several monoamines (eg, serotonin [5-hydroxytryptamine{5-HT}], noradrenaline, dopamine), resulting in significant ROS production. 14 Based on their substrate preference and inhibitor specificity, 2 functional isoenzymes, MAO-A and MAO-B, have been identified. 15 In the heart, MAO-A is a predominant enzyme involved in the deamination of endogenous or exogenous amines. 16 Recently, we have shown that oxidative stress induced by MAO-A is responsible for receptor-independent, serotonin-mediated apoptosis during postischemic myocardial injury....

Ceramide: A common pathway for atherosclerosis?

“…Ceramide may play an important role in ischemia/reperfusion injury, which is responsible for provoking cell injury [61,62]. There is significant evidence to support an important role for ROS in the reperfusion myocardial damage [63,64].…”

Lipopolysaccharide pretreatment protects against ischemia/reperfusion injury via increase of HSP70 and inhibition of NF-κB

“…A substantial amount of evidence supports the idea that ischemia/reperfusion (I/R)-induced injury to the heart is due to the release of reactive oxygen species (ROS; Pchejetski et al 2007;Oshima et al 2005). As an intracellular target of ROS, nucleus factor-κB (NF-κB) is sequestered in the cytoplasm in an inactive state due to its association with a class of inhibitory proteins termed inhibitory κB (IκB).…”

Monoamine Oxidase B Prompts Mitochondrial and Cardiac Dysfunction in Pressure Overloaded Hearts

“…Together, these events concur to maintain proper left ventricular (LV) morphology and function, even under conditions of chronic cardiac stress due to pressure overload (3,4,39). As a major source of reactive oxygen species (ROS), MAO-A contributes to in vitro myocyte hypertrophy (6), ischemia/reperfusion (I/R) injury both in ex vivo (10) and in vivo models (5,31), heart failure and LV remodeling (25,42).…”