Cardiology Division of the Department of Medicine, Gazes Cardiac Research Institute, Medical University of South Carolina, South Caroline, USA.
Am J Physiol Heart Circ Physiol. 2011 May;300(5):H1696-706. doi: 10.1152/ajpheart.00545.2010. Epub 2011 Feb 25.
Ubiquitin-mediated protein degradation is necessary for both increased ventricular mass and survival signaling for compensated hypertrophy in pressure-overloaded (PO) myocardium. Another molecular keystone involved in the hypertrophic growth process is the mammalian target of rapamycin (mTOR), which forms two distinct functional complexes: mTORC1 that activates p70S6 kinase-1 to enhance protein synthesis and mTORC2 that activates Akt to promote cell survival. Independent studies in animal models show that rapamycin treatment that alters mTOR complexes also reduces hypertrophic growth and increases lifespan by an unknown mechanism. We tested whether the ubiquitin-mediated regulation of growth and survival in hypertrophic myocardium is linked to the mTOR pathway. For in vivo studies, right ventricle PO in rats was conducted by pulmonary artery banding; the normally loaded left ventricle served as an internal control. Rapamycin (0.75 mg/kg per day) or vehicle alone was administered intraperitoneally for 3 days or 2 wk. Immunoblot and immunofluorescence imaging showed that the level of ubiquitylated proteins in cardiomyocytes that increased following 48 h of PO was enhanced by rapamycin. Rapamycin pretreatment also significantly increased PO-induced Akt phosphorylation at S473, a finding confirmed in cardiomyocytes in vitro to be downstream of mTORC2. Analysis of prosurvival signaling in vivo showed that rapamycin increased PO-induced degradation of phosphorylated inhibitor of κB, enhanced expression of cellular inhibitor of apoptosis protein 1, and decreased active caspase-3. Long-term rapamycin treatment in 2-wk PO myocardium blunted hypertrophy, improved contractile function, and reduced caspase-3 and calpain activation. These data indicate potential cardioprotective benefits of rapamycin in PO hypertrophy.
泛素介导的蛋白降解对于压力超负荷（PO）心肌中的心室质量增加和代偿性肥大的存活信号都是必要的。另一个涉及肥大生长过程的分子关键是哺乳动物雷帕霉素靶蛋白（mTOR），它形成两个不同的功能复合物：mTORC1 激活 p70S6 激酶-1 以增强蛋白质合成，而 mTORC2 激活 Akt 以促进细胞存活。动物模型中的独立研究表明，改变 mTOR 复合物的雷帕霉素治疗也会减少肥大生长并通过未知机制增加寿命。我们测试了肥厚心肌中生长和存活的泛素介导调节是否与 mTOR 途径有关。对于体内研究，通过肺动脉结扎进行大鼠右心室 PO；正常负荷的左心室作为内部对照。雷帕霉素（0.75mg/kg/天）或单独载体通过腹膜内给药 3 天或 2 周。免疫印迹和免疫荧光成像显示，在 PO 后 48 小时增加的心肌细胞中泛素化蛋白的水平被雷帕霉素增强。雷帕霉素预处理还显著增加了 PO 诱导的 Akt 在 S473 处的磷酸化，这一发现在体外心肌细胞中被证实是 mTORC2 的下游。体内生存信号分析表明，雷帕霉素增加了 PO 诱导的磷酸化 IκB 的降解，增强了细胞凋亡抑制蛋白 1 的表达，并降低了活性 caspase-3。在 2 周 PO 心肌中的长期雷帕霉素治疗减弱了肥大，改善了收缩功能，并减少了 caspase-3 和钙蛋白酶的激活。这些数据表明雷帕霉素在 PO 肥大中具有潜在的心脏保护益处。
