Abstract 3944: A Case of Supply and Demand: The Cellular Fuel Gauge Controls Regulators of Protein Degradation in the Heart
To preserve its function, the stressed heart activates AMPK. The role of AMPK in the regulation of metabolism and protein synthesis is well established, while it is currently unknown whether AMPK plays a role in protein degradation in the heart. Because the ubiquitin proteasome system (UPS) provides the raw material for energy provision, we hypothesize that AMPK plays a role in regulating this system. The UPS degrades specific proteins by tagging them with ubiquitin for degradation by ubiquitin ligases. Two muscle-specific ubiquitin ligases, Muscle atrophy F-box protein (Atrogin-1) and Muscle Ring Finger-1 (MuRF-1) are known as regulators of protein degradation in the heart. To determine whether AMPK regulates Atrogin-1 and MuRF-1, AMPK was activated and inhibited in cardiomyocytes. Activation of AMPK with AICAR increased the transcript and protein levels of Atrogin-1 and MuRF-1 in a dose- and time-dependent manner, while the pharmacological inhibition of AMPK abrogated these changes. Use of a constitutively active AMPK (caAMPK) adenovirus resulted in significant increases in the transcript and protein levels of these ubiquitin ligases, independent of Akt and Foxo3a activation, while an inactive AMPK (dnAMPK) adenovirus had no affect on their expression. All in vitro experiments were performed three different times and in triplicate. AMPK activation in vivo (n=6) also increased Atrogin-1 and MuRF-1 mRNA. In transplanted hearts in vivo, AMPK activation was significantly increased, which correlated with increases in Atrogin-1 and MuRF-1 mRNA. The data suggest that AMPK regulates these ligases during atrophic remodeling. In conclusion, AMPK independently controls the expression of Atrogin-1 and MuRF-1 in three different systems: in cardiomyocytes in vitro, in the intact heart in vivo, and in the intact unloaded heart in vivo. The data also suggest that intracellular protein degradation is controlled by the metabolic signals.