Abstract 11389: CyclinD1/E2F Signaling Attenuates Adverse Effects Caused by Activated GSK-3α Under Pressure Overload by Enhancing the Expression and Activity of Complex I
Glycogen synthase kinase-3 (GSK-3) has two isoforms, α and β, with distinct functions. Phosphorylation of GSK-3α at S21 is increased under pressure overload (PO), and the lack of S21 phosphorylation in GSK-3αS21A knock-in mice (αKI) exacerbates cardiac dysfunction, accompanied by downregulation of NADH-ubiquinone oxidoreductase (Complex I) subunits in the mitochondrial electron transport chain. After PO, the expression of NDUFS1 and NDUFS4 subunits of Complex I was decreased by 35% (p<0.05) and 26% (p<0.05), respectively, in αKI hearts. Myocardial Complex I activity was decreased by 30% (p<0.05) in αKI after PO. In order to study the underlying mechanisms of the adverse effects observed in αKI, transcription factor binding site analysis showed that E2F-mediated transcription was significantly inhibited (p<0.05) in αKI subjected to PO. E2F binding sites were found in the promoter regions of many subunits of Complex I. Reporter gene assays showed that the transcriptional activity of E2F was increased 1.75 fold by knock-down of GSK-3α, and, importantly, overexpression of E2F4 abrogated GSK-3αS21A-induced inhibition of the transcriptional activity of Complex I subunit NDUFS1. Rescue experiments with injection of either adenovirus (Ad) harboring cyclin D1 with a nuclear localization signal (CycD1-NLS), which activates E2F signaling, or Ad harboring E2F2 or E2F4 into αKI myocardium revealed that they dramatically attenuated cardiac dysfunction in αKI after PO (LVEF; αKI+CycD1-NLS=67±2%*, αKI+E2F2=66±3%*, αKI+E2F4=60±2%*, αKI+LacZ=39±2%, *p<0.05 vs αKI+LacZ), suggesting a causative role of downregulation of CycD1/E2F signaling in mediating cardiac dysfunction in αKI. Moverover, injection of Ad-CycD1-NLS, Ad-E2F2, or Ad-E2F4 significantly increased NDUFS1 and NDUFS4 expression and Complex I activity, indicating that Complex I may be involved in the protective effects afforded by CycD1/E2F activation. In summary, activated GSK-3α inhibited expression and activity of Complex I under PO through suppression of E2F. Maintainance of the activity of CycD1/E2F signaling through S21 phosphorylation of endogenous GSK-3α is a compensatory mechanism which preserves cardiac function during PO by restoring the expression and activity of Complex I.
- © 2011 by American Heart Association, Inc.