Abstract 17412: Ultrasound-Mediated S100A6 Gene Therapy Ameliorates Ischemia-Reperfusion Injury

Abstract

Introduction: Myocardial ischemia-reperfusion (I/R) produces cellular damage, apoptosis and necrosis. S100A6, a member of EF-hand Ca2+-binding proteins, is upregulated after I/R, and over-expression of S100A6 prevents cardiomyocyte apoptosis in vitro. We determined the time course of S100A6 gene expression, myocyte apoptosis and left ventricular (LV) dysfunction after I/R, and investigated the protective effect of S100A6 gene therapy by ultrasound-targeted microbubble destruction (UTMD) on I/R in rats.

Methods: 10-12 weeks old Fischer-344 male rats (n=46) underwent acute I/R injury, induced by a 30-minute ligation of the left anterior descending coronary artery followed by reperfusion. Serial echocardiography was performed out to day 28, and animals were sacrificed at multiple time points after I/R. Tissues were harvested from various regions for analysis. UTMD of human S100A6 plasmid to the LV myocardium was performed 2 days prior to I/R, with control animals receiving no therapy (n=6 each). Cell culture studies were performed to examine S100A6 effects on apoptosis, in vitro.

Results: After I/R injury, LV end-diastolic and end-systolic dimensions progressively increased, and LV fractional shortening (FS) (LVFS 0.47±0.06 vs 0.19±0.05, p<0.001) and ejection fraction (EF) (LVEF 73.5±2.8 vs 43.5±9.3%, p<0.001) decreased. S100A6 mRNA increased progressively in the infarct regions after I/R injury. Caspase 3/7 activity and apoptosis by TUNEL increased after I/R. In S100A6-treated animals, LVFS after I/R was significantly greater than controls (day 7: LVFS 0.29±0.05 vs 0.22±0.05, p<0.05), and circumferential extent of akinesis, a measure of infarct size, was significantly less compared to controls (day 7: 22.7±7.3 vs 32.2±4.2%, p<0.05). In vitro studies showed S100A6 transfection of cardiomyoblasts was associated with lower TNF-α induced apoptosis (1% vs 8% by TUNEL), and lower caspase 3 activity compared to non-transfected control cells.

Conclusions: After I/R the LV dilates, LVEF declines, and is associated with increased S100A6 expression and myocyte apoptosis. S100A6 gene delivery by UTMD helps ameliorate I/R injury, resulting in attenuation in LV systolic dysfunction post I/R.