Department of Internal Medicine, Division of Cardiology, University of Texas Health Science Center, Houston, TX 77030, USA.
Circ Res. 2011 Oct 28;109(10):1153-61. doi: 10.1161/CIRCRESAHA.111.252742. Epub 2011 Sep 15.
The degradation of proteins by the ubiquitin proteasome system (UPS) is required for the maintenance of cellular homeostasis in the heart. An important regulator of metabolic homeostasis is AMP-activated protein kinase (AMPK). AMPK activation inhibits protein synthesis and activates autophagy, but whether AMPK plays a role in regulating protein breakdown through the UPS in the heart is not known.
To determine whether AMPK enhances UPS-mediated protein degradation by directly regulating the ubiquitin ligases Atrogin-1 and muscle RING finger protein 1 (MuRF1) in the heart.
Nutrient deprivation and pharmacological or genetic activation of AMPK increased mRNA expression and protein levels of Atrogin-1 and MuRF1 and consequently enhanced protein degradation in neonatal cardiomyocytes. Inhibition of AMPK abrogated these effects. Using gene reporter and chromatin immunoprecipitation assays, we found that AMPK regulates MuRF1 expression by acting through the myocyte enhancer factor 2 (MEF2). We further validated these findings in vivo using MEF2-LacZ reporter mice. Furthermore, we demonstrated in adult cardiomyocytes that MuRF1 is necessary for AMPK-mediated proteolysis through the UPS in the heart. Consequently, MuRF1 knockout mice were protected from severe cardiac dysfunction during fasting.
AMPK regulates the transcription of Atrogin-1 and MuRF1 and enhances UPS-mediated protein degradation in heart. Specifically, AMPK regulates MuRF1 through the transcription factor MEF2. The absence of MuRF1 in the heart preserves cardiac function during fasting. The results strengthen the hypothesis that AMPK serves as a modulator of intracellular protein degradation in the heart.
泛素蛋白酶体系统（UPS）对蛋白质的降解是维持心脏细胞内环境稳定所必需的。代谢稳态的一个重要调节剂是 AMP 激活的蛋白激酶（AMPK）。AMPK 的激活抑制蛋白质合成并激活自噬，但 AMPK 是否通过心脏中的 UPS 发挥作用来调节蛋白质分解尚不清楚。
确定 AMPK 是否通过直接调节心脏中的泛素连接酶 Atrogin-1 和肌肉环指蛋白 1（MuRF1）来增强 UPS 介导的蛋白质降解。
营养剥夺和 AMPK 的药理学或遗传学激活增加了新生心肌细胞中 Atrogin-1 和 MuRF1 的 mRNA 表达和蛋白水平，从而增强了蛋白质降解。AMPK 的抑制消除了这些作用。使用基因报告和染色质免疫沉淀测定，我们发现 AMPK 通过肌细胞增强因子 2（MEF2）调节 MuRF1 的表达。我们使用 MEF2-LacZ 报告基因小鼠进一步验证了这些发现。此外，我们在成年心肌细胞中证明，MuRF1 是 AMPK 通过 UPS 在心脏中介导蛋白质水解所必需的。因此，MuRF1 敲除小鼠在禁食期间免受严重的心脏功能障碍的影响。
AMPK 调节 Atrogin-1 和 MuRF1 的转录，并增强心脏中 UPS 介导的蛋白质降解。具体而言，AMPK 通过转录因子 MEF2 调节 MuRF1。心脏中 MuRF1 的缺失在禁食期间保护心脏功能。结果加强了 AMPK 作为心脏细胞内蛋白质降解调节剂的假说。
