Abstract 15378: Mitochondrial Fission Plays a Crucial Role in Cardiomyocyte Adaptation to Energy Stress via Mitophagy
Mitochondria are dynamic organelles that undergo fusion and fission. This study aims to clarify the role of mitochondrial dynamics on energetic stress resistance in cardiomyocytes (CMs).
Dynamin-related protein 1 (Drp-1) which mediates mitochondrial fission was localized primarily in the cytosol in CMs. Glucose deprivation (GD) induced modest mitochondrial accumulation of Drp1 in CMs within 4 hours. Four-hour GD increased the proportion of CMs with fused mitochondria (23.5±6.9 to 35.0±10.8%, p<0.05), but also increased that of CMs with fission (2.1±0.3 to 15.5±4.8%, p<0.05) in Ad-shScr-transduced CMs, whereas mitochondria with fission did not increase after GD in Ad-shDrp1-transduced CMs (0.3±0.6 to 0.8±0.5%). These results suggest that GD induces both mitochondrial fusion and fission, and Drp1 plays an essential role in mitochondrial fission in response to GD. Transduction with Ad-shDrp1 significantly increased TUNEL-positive CMs and reduced cell viability after 4 hours of GD compared to transduction with Ad-shScr, suggesting that endogenous Drp1 protects CMs against cell death during GD. We evaluated the role of Drp1 in mediating mitophagy using mitochondria-targeted Keima fluorescence. Keima has a bimodal excitation spectrum peaking at 440 and 560 nm, corresponding to the neutral and acidic pH states, respectively. Puncta with high 560/440, indicating the presence of mitochondria in lysosomes, were significantly increased after 4 hours of GD in CMs transduced with Ad-shScr, but not in CMs transduced with Ad-shDrp, suggesting that Drp1 is necessary for stimulating autophagic mitochondrial degradation. Next, we examined the role of fission on energy stress in vivo using cardiac specific Drp1 hetero knockout (Drp1-hetCKO) mouse. Translocation of Drp1 from cytosol to mitochondria significantly increased in response to 48-hour fasting in control mice but not in Drp1-hetCKO mice. Left ventricular ejection fraction did not change after fasting in control mice (79.8±6.4 to 78.6±8.3%). However that in Drp1-hetCKO mice decreased after GD (79.4±9.7 to 48.3±11.6%, p<0.05), suggesting that Drp1 acts to preserve cardiac function during fasting.
In conclusion, mitochondrial fission is crucial to adapt CMs to energy stress through mitophagy.
Author Disclosures: Y. Ikeda: None. Y. Maejima: None. M. Ohishi: None. J. Sadoshima: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.