Myocardial infarction and resulting congestive heart failure remain the number one cause of mortality in the United States and affect the aging veteran population particularly. Published findings from our laboratory and compelling preliminary results support our central hypothesis that the sphingosine kinase/sphingosine 1- phosphate (S1P) pathway is a potent mediator of cardioprotection that can reduce acute tissue injury, chronic pathological remodeling, and mortality caused by ischemia and reperfusion. Thus, prevention of these consequences of myocardial infarction have direct bearing on the health of both the veterans we serve and of the general public. In prior studies, we determined that pharmacological activation of endogenous S1P production or administration of exogenous S1P was sufficient to decrease infarction and enhance contractility in mouse hearts subjected to ischemia-reperfusion injury. We also developed a rapid and accurate radioassay for measurement of sphingosine kinase activity and established an essential role for this enzyme in preconditioning-induced cardioprotection using pharmacological and gene targeting approaches. In adult mouse ventricular myocytes exposed to hypoxia-reoxygenation, we showed that S1P1 receptor function, Akt activation, and cell substrates interacting with mitochondria contribute to S1P-mediated prosurvival effects. The current proposal is designed to explore new functions of S1P receptor agonism and their mechanisms, and to perform translational studies in animal models.
In Specific Aim 1, we will study effects of the selective S1P1 receptor agonist SEW 2871 in two models of myocardial infarction. Model 1 is the Scavenger Receptor Class B Type I-deficient, hypomorphic apolipoprotein ER61 (SR-BI KO/ApoeR61h/h) mouse. These mice rapidly develop occlusive coronary atherosclerosis, myocardial infarction, heart failure, and premature death in response to high-fat feeding. In the second model, we will study the efficacy of SEW 2871 on ventricular dysfunction caused by ligation of the left anterior descending coronary artery in mice. We shall also test the hypothesis that inhibition of S1P lyase, the enzyme that catalyzes irreversible S1P breakdown, leads to cardioprotection by raising intracellular S1P content.
In Specific Aim 2, we shall employ the models studied in Specific Aim 1 to focus on the effects of chronic S1P1 receptor agonism. These studies will include use of sphingosine kinase-1 and -2 null mice, measurements of downstream signaling pathways, and determination of the S1P receptor subtypes that mediate chronic signals. Studies of S1P1 receptor localization and signaling in myocyte nuclear compartments after chronic agonist exposure will also be carried out, as will investigation of the regulation of gap junction trafficking and function by S1P in ventricular myocytes under physiological and stress conditions.
Relevance to Veterans Health Coronary heart disease is the single leading cause of mortality in the United States, accounting for one of every five deaths (1). Thousands of veterans are hospitalized each year with myocardial infarction (heart attack) caused by coronary heart disease. Impairment of the main pumping chamber of the heart, the left ventricle, is common in those who survive infarction. Such left ventricular dysfunction often leads to congestive heart failure which results in substantial part from efforts of the heart to maintain its impaired pumping ability caused by muscle loss. As noted in a recent editorial, there is a worsening heart failure hospitalization epidemic that """"""""We do not know how to prevent and we do not know how to treat"""""""" (2). It is estimated that 27% of veterans over the age of 65 suffer from heart disease (3), most of which is the result of coronary artery obstruction that leads to myocardial infarction. Our prior work has shown that activation of a molecular pathway not previously studied in the heart (sphingosine kinase/sphingosine 1-phosphate - mediated signaling) can rescue heart muscle subjected to acute oxygen deprivation. We now propose to use intact animal models to study the ability of this pathway to prevent death and congestive heart failure, which are both short- and long-term consequences of myocardial infarction. We plan to use drugs that mimic the action of the naturally occurring chemical sphingosine 1-phosphate and to study their effects in mouse models that resemble human disease. We also plan to investigate new biochemical mechanisms by which these drugs act to protect the heart in the setting of chronic myocardial infarction. The relevance of the proposed experiments is that an understanding of these processes in pertinent animal models can potentially lead to new therapeutic approaches in veteran and other patients who suffer from this common disorder, which accounts for over 400,000 bed-days of care in VA hospitals annually throughout the nation. 1. American Heart Association. Heart Attack and Angina Statistics. www.americanheart.org/presenter.jhtml?identifier=4591(2008). 2. Butler J and Kalogeropoulos A. Worsening heart failure hospitalization epidemic. J Amer Coll Cardiol. 2008;435-437. 3. National Survey of Veterans, National Center for Veterans Analysis and Statistics. http://www1.va.gov/vetdata/docs/survey_final.htm (2001).
