Schröder D, Heger J, Piper H M, Euler G
Institute of Physiology, Justus Liebig University, Aulweg 129, 35392, Giessen, Germany.
J Mol Med (Berl). 2006 Nov;84(11):975-83. doi: 10.1007/s00109-006-0090-0. Epub 2006 Aug 19.
Elevations in angiotensin II (AngII) and transforming growth factor (TGF-beta1) levels are often found under conditions leading to progression of heart failure. From several studies, it is evident that AngII enhances TGF-beta1 expression via activator protein 1 (AP-1) activation, and that this pathway is involved in hypertrophic growth of the heart muscle and in the development of cardiac fibrosis. We now continued characterization of the signaling pathway stimulated by AngII in ventricular cardiomyocytes of rat and analyzed if the enhancement of TGF-beta1 expression by AngII may also contribute to apoptosis induction, which is another predictor of heart failure progression. Stimulation of cardiomyocytes with 100 nM AngII for 2 h activated the transcription factors AP-1 and GATA by 68.6+/-23.9 or 70.7+/-9.8%. Induction of both factors was mediated by p38 mitogen-activated protein kinase (MAPK) because it was totally blocked using a specific inhibitor of the kinase (SB202190). When GATA was inhibited by transformation of cardiomyocytes with decoy oligonucleotides, AngII could not enhance TGF-beta1 expression. This inhibition was observed on the mRNA level in real-time polymerase chain reaction and on the protein level in Western blots. As a consequence, upon AngII stimulation for 24 h, release of TGF-beta1 from cardiomyocytes was also reduced from 240.5+/-50.4 to 130.5+/-22.1% (p<0.05). In contrast to the early induction of GATA and AP-1, the transcription factor similar to mothers against decapentaplegic homolog (SMAD) was induced by AngII after 24 h. This stimulation was dependent on TGF-beta1 because it was blocked by antibodies specific for TGF-beta1. Twenty-four hours after AngII addition, the number of apoptotic cardiomyocytes increased by 6.5+/-1.2%, and this apoptosis induction was blocked when SMAD activity was inhibited by transformation of cardiomyocytes with SMAD decoy oligonucleotides. In conclusion, the transcription factors AP-1 and GATA are activated by p38 MAPK upon AngII stimulation, and both are needed to enhance TGF-beta1 expression in ventricular cardiomyocytes. TGF-beta1 acts in an autocrine loop on the cells to induce apoptosis via SMAD signaling. Thus, the often-found correlation between AngII, TGF-beta1, AP-1, and SMAD in pathogenesis of heart disease reflects the proapoptotic signaling pathway induced by AngII in cardiomyocytes.
在导致心力衰竭进展的情况下，常发现血管紧张素II（AngII）和转化生长因子（TGF-β1）水平升高。多项研究表明，AngII通过激活蛋白1（AP-1）激活来增强TGF-β1表达，且该途径参与心肌肥厚生长及心脏纤维化的发展。我们现在继续对大鼠心室心肌细胞中由AngII刺激的信号通路进行表征，并分析AngII对TGF-β1表达的增强是否也可能促成细胞凋亡诱导，而细胞凋亡是心力衰竭进展的另一个预测指标。用100 nM AngII刺激心肌细胞2小时，使转录因子AP-1和GATA分别激活68.6±23.9%或70.7±9.8%。这两种因子的诱导均由p38丝裂原活化蛋白激酶（MAPK）介导，因为使用该激酶的特异性抑制剂（SB202190）可完全阻断其诱导。当用诱饵寡核苷酸转染心肌细胞抑制GATA时，AngII无法增强TGF-β1表达。在实时聚合酶链反应的mRNA水平和蛋白质印迹的蛋白质水平上均观察到这种抑制。因此，在AngII刺激24小时后，心肌细胞中TGF-β1的释放也从240.5±50.4%降至130.5±22.1%（p<0.05）。与GATA和AP-1的早期诱导不同，类似于果蝇抗五体不全同源蛋白（SMAD）的转录因子在AngII刺激24小时后被诱导。这种刺激依赖于TGF-β1，因为它被TGF-β1特异性抗体阻断。添加AngII 24小时后，凋亡心肌细胞数量增加了6.5±1.2%，当用SMAD诱饵寡核苷酸转染心肌细胞抑制SMAD活性时，这种凋亡诱导被阻断。总之，在AngII刺激下，转录因子AP-1和GATA由p38 MAPK激活，并都需要增强心室心肌细胞中TGF-β1的表达。TGF-β1通过SMAD信号在细胞上以自分泌环的方式诱导细胞凋亡。因此，在心脏病发病机制中经常发现的AngII、TGF-β1、AP-1和SMAD之间的相关性反映了AngII在心肌细胞中诱导的促凋亡信号通路。
