Effects And Mechanisms Of Ischemic Postconditioning On Hypertrophic Myocardium By Sphingosin-1-phosphate Signal Transduction Pathways

Objectives:To investigate the effects and mechanisms of ischemic postconditioning (IPost) in protecting hypertrophic myocardium subjected to ischemic re-perfusion (I/R) and to study the role of Sphingosine-1-phosphate in mediating such protection. Methods: Transverse aortic constriction (TAC) operation was performed on12-week-old C57/BL mice to establish left ventricular hypertrophy models. Seventy-two isolated TAC mouse hearts were mounted onto the Langendorff perfusion system and randomly divided into4equal group:(1)I/R group undergoing stable perfusion for30min, ischemic for30min, and re-perfusion for60min (an I/R cycle) to cause hypertrophic myocardium I/R injury.(2)IPost group undergoing ischemic for10s and re-perfusion10s,totally3cycles (60s) before re-perfusion for60min.(3)IPost+inhibitor group[join the VPC23019(a S1P1inhibitor) and PD98059(an ERK1/2inhibitor) respectively] group undergoing perfusion of Krebs-Henseleit (KH) buffer with VPC23019and PD98059respectively for15min and perfusion of KH buffer without VPC23019and PD98059at the beginning of re-perfusion.Hemodynamic examination was conducted60min after re-perfusion to measure the left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), maximal uprising velocity of left ventricle pressure (dp/dtmax), and minimal uprising velocity of left ventricle pressure (dp/dtmin) After the I/R procedure the myocardium of the left ventricle was isolated to detect the infarction size (IS) and to detect the ultrastructure. Apoptosis was measured by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining.Western blotting was used to detect the protein expression of S1P1,ERK1/2and phosphorylated ERK1/2. Results:The LVSP and dp/dtmax levels of the IPost group were (85±5)mmHg and (3778±230)mmHg,both significantly higher than those of the I/R group [(66±6)mmHg and(2820±220)mmHg, respectively, both P<0.05],ihe IS was smaller(both P<0.05).Compared with the I/R group, the protein levels of S1P1、phosphorylated ERK1/2of the IPost group were all significantly higher, IPost+VPC23019group and IPost+PD98059group with the I/R group,respectively,showed no effects on the above-mentioned parameters. However,the results of the IPost+inhibitor groups showed that in the first15min of re-perfusion addition of VPC23019and PD98059reversed all changes observed in the IPost group and eliminated the IPost protection by increasing IS to a level similar to that in the I/R group. Conclusion:IPost has protective effect in hypertrophic myocardium with I/R injury in vitro.The cardioprotective effects of IPost may involve in the regulation of ERK1/2signaling pathway through SIP signal transduction pathway.