Abstract 220: The Cardioprotective Kinase, Akt, Modulates Mitochondrial Dynamics
Mitochondria exist in a dynamic state of fragmentation (fission) and elongation (fusion), termed mitochondrial dynamics. Studies suggest that mitochondrial fragmentation precedes apoptosis and that inhibiting fragmentation reduces apoptotic cell death. Simulated ischemia also induces mitochondrial fragmentation and promotes apoptosis. The anti-apoptotic kinase, Akt, confers powerful cardioprotection when activated, the mechanism of which is unclear. We hypothesized that the activation of Akt inhibits mitochondrial fragmentation, and that this action may underlie its cardioprotective effect. The effect of Akt over-expression on mitochondrial dynamics was determined in mouse embryonic fibroblasts (MEF’s) transfected with mitochondrial red fluorescent protein plus either empty vector, an Akt dominant-negative gene construct (Akt-dn) or a constitutively-active Akt gene construct (Akt-ca). Twenty four hours later, cells were assigned to two groups using confocal microscopy: those demonstrating elongated mitochondria and those displaying fragmented mitochondria (N > 150). Previous published data suggest that MEF’s comprise 20% of cells showing mitochondrial elongation and 80% of cells displaying mitochondrial fragmentation. Cells transfected with the empty vector comprised 21.4 ± 1.4% of cells displaying elongated mitochondria. In cells transfected with Akt-ca, the % of cells displaying mitochondrial elongation was markedly increased to 60.4 ± 11.3% (P < 0.01), indicating a reduction in cells containing fragmented mitochondria by 50%. In contrast, cells transfected with Akt-dn, the % of cells showing elongation was 14.6 ± 4.6%. In conclusion, this is the first study to report that the activation of Akt has the ability to influence mitochondrial dynamics, as indicated by the inhibition of mitochondrial fragmentation and/or the promotion of mitochondrial elongation, effects which may underlie the cardioprotective properties of Akt.