Abstract 18317: E2F2/4 Regulated by Serine 21 Phosphorylation of GSK-3α Plays Compensatory Roles Under Pressure Overload
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase with two isoforms, α and β, which have distinct functions in cardiomyocytes (CMs). GSK-3α is phosphorylated at S21 under pressure overload (PO), and inhibition of S21 phosphorylation in GSK-3α S21A knock-in (α-KI) mice promotes hypertrophy and heart failure under PO accompanied by decreases in the total number of CMs in the heart and downregulation of genes involved in mitochondrial electron transport chain complex I. Since GSK-3α downregulates cyclinD1 in the nucleus, we hypothesized that GSK-3α negatively regulates E2F-mediated transcription. Reporter gene assays showed that the transcriptional activity of E2F was increased by shRNA-mediated knock-down of GSK3α (1.75 fold, p<0.05). To evaluate the role of endogenous E2F isoforms in mediating cardiac hypertrophy and function during PO, E2F2−/+, E2F4−/+, and wild type (WT) mice were subjected to transverse aortic constriction (TAC). After two weeks of TAC, left ventricular (LV) weight/ tibial length was significantly greater (LVW/TL; E2F2−/+=7.1±0.3*, E2F4−/+=7.0±0.4*, WT=5.9±0.3, *p<0.05 vs. WT) and LV systolic function evaluated by LV ejection fraction was significantly decreased (LVEF; E2F2−/+=53±1%*, E2F4−/+=61±2%*, WT=75±1%, *p<0.05 vs. WT) in both E2F2−/+ and E2F4−/+ compared to WT mice, mimicking the cardiac phenotype in α-KI mice in response to TAC. In order to examine the causative role of E2F2/E2F4 downregulation in mediating the cardiac phenotype in α-KI mice, rescue experiments were conducted with injection of adenovirus (Ad) harboring either E2F2 or E2F4 into α-KI hearts. Rescue with either E2F2 or E2F4 dramatically attenuated cardiac hypertrophy (LVW/TL; α-KI+E2F2=7.1±0.4*, α-KI+E2F4=7.3±0.3*, α-KI+LacZ =8.7±0.4, *p<0.05 vs. α-KI+LacZ) and improved LV dysfunction (LVEF; α-KI+E2F2=66±3%*, α-KI+E2F4=60±2%*, α-KI+LacZ =39±2%, *p<0.05 vs. α-KI+LacZ) in α-KI mice under PO. Injection of either Ad-E2F2 or E2F4, but not of Ad-LacZ, significantly increased the number of Ki67-positive myocytes in the α-KI mice. These results suggest that maintaining the activity of E2F2 and E2F4 through S21 phosphorylation of GSK-3α plays an essential role in preserving cardiac function during PO.
- © 2010 by American Heart Association, Inc.