Intermolecular failure of L-type Ca2+ channel and ryanodine receptor signaling in hypertrophy.
Intermolecular failure of L-type Ca2+ channel and ryanodine receptor signaling in hypertrophy.
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DOI：
10.1371/journal.pbio.0050021
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发表时间：
2007-02
期刊：
影响因子：
9.8
通讯作者：
Wang, Shi-Qiang
中科院分区：
文献类型：
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作者：
Xu, Ming;Zhou, Peng;Xu, Shi-Ming;Liu, Yin;Feng, Xinheng;Bai, Shu-Hua;Bai, Yan;Hao, Xue-Mei;Han, Qide;Zhang, Youyi;Wang, Shi-Qiang
压力超载引起的肥厚是导致心力衰竭的关键步骤。Ca2+诱导的Ca2+释放（CICR）控制心脏收缩的过程在肥厚/心力衰竭中是有缺陷的，但分子机制仍然难以捉摸。为了研究肥厚过程中CICR的分子间性，我们利用松片共聚焦成像来观察代偿性（CHT）和失代偿性（DHT）肥厚的主动脉狭窄大鼠模型中单个l型Ca2+通道（LCC）和ryanodine受体（RyRs）之间的信号传导。我们发现LCC-RyR分子间偶联在DHT中显示偶联潜伏期延长49%，命中几率降低47%，未命中几率增加72%，显示出“分子间失败”状态。出乎意料的是，这些修饰也在CHT中大量发生，至少部分是由于亲结膜蛋白的表达减少，这表明分子间失败发生在细胞表现之前。结果，细胞范围内的Ca2+释放，被可视化为“Ca2+尖峰”，变得不同步，这与CHT中未改变的尖峰积分和全细胞Ca2+瞬态形成鲜明对比。这些数据表明，在一定限度内，称为“稳定边际”，轻微的分子间故障不会破坏细胞的兴奋-收缩耦合的完整性。只有当修正超出稳定裕度时，才会发生全局失效。发现CHT中“隐藏的”分子间故障具有重要的临床意义。高血压导致心肌肥大，心肌增厚，最终导致心力衰竭，这是发病率和死亡率的主要原因。心脏的收缩能力部分取决于细胞膜上的钙通道（l型Ca2+通道）和肌浆网上的钙释放通道之间的信号传导。这种信号传导过程在心力衰竭中是有缺陷的。我们发现，在肥厚到心力衰竭的过渡过程中，单个l型通道与其控制的Ca2+释放通道之间的信号传导效率降低。此外，我们意外地发现，甚至在心肌细胞收缩能力出现任何明显缺陷之前，通道之间的信号传导失败就发生了。在正常细胞中，钙流入和释放之间的时间间隔很短；但在心力衰竭前的肥厚中，这个信号传导过程有延迟。在寻找这种分子间失败的潜在机制时，我们发现一种被称为结膜蛋白的蛋白质，它将肌浆网锚定在细胞膜系统上，在较低水平上表达。这些结果揭示了与肥厚进展相关的早期分子事件，并可能为开发早期诊断和治疗方法以预防心力衰竭提供新的见解。作者表明，尽管l型钙通道的全细胞偶联和ryanodine受体电流激活在代谢性肥厚期间（在心力衰竭出现之前）保持完整，但分子水平上的分子间偶联已经在下降。
Pressure overload–induced hypertrophy is a key step leading to heart failure. The Ca2+-induced Ca2+ release (CICR) process that governs cardiac contractility is defective in hypertrophy/heart failure, but the molecular mechanisms remain elusive. To examine the intermolecular aspects of CICR during hypertrophy, we utilized loose-patch confocal imaging to visualize the signaling between a single L-type Ca2+ channel (LCC) and ryanodine receptors (RyRs) in aortic stenosis rat models of compensated (CHT) and decompensated (DHT) hypertrophy. We found that the LCC-RyR intermolecular coupling showed a 49% prolongation in coupling latency, a 47% decrease in chance of hit, and a 72% increase in chance of miss in DHT, demonstrating a state of “intermolecular failure.” Unexpectedly, these modifications also occurred robustly in CHT due at least partially to decreased expression of junctophilin, indicating that intermolecular failure occurs prior to cellular manifestations. As a result, cell-wide Ca2+ release, visualized as “Ca2+ spikes,” became desynchronized, which contrasted sharply with unaltered spike integrals and whole-cell Ca2+ transients in CHT. These data suggested that, within a certain limit, termed the “stability margin,” mild intermolecular failure does not damage the cellular integrity of excitation-contraction coupling. Only when the modification steps beyond the stability margin does global failure occur. The discovery of “hidden” intermolecular failure in CHT has important clinical implications. High blood pressure induces hypertrophy, a thickening of the cardiac muscle that eventually leads to heart failure, a leading cause of morbidity and mortality. The contractile power of the heart depends in part on signaling between calcium channels on the cell membrane (L-type Ca2+ channels) and calcium release channels on a specialized calcium-regulating organelle called the sarcoplasmic reticulum. This signaling process is defective in heart failure. We have found that the signaling efficiency between a single L-type channel and its controlled Ca2+ release channels decreases during the transition from hypertrophy to heart failure. Moreover, we find unexpectedly that the signaling failure between channels occurs even before any obvious defect in the cardiac cell's ability to contract is seen. In normal cells, the timing between calcium influx and release is rapid; but in hypertrophy before heart failure manifests, there is a delay in this signaling process. In seeking the underlying mechanisms of this intermolecular failure, we find that a protein known as junctophilin, which anchors the sarcoplasmic reticulum to the cell membrane system, is expressed at a lower level. These results reveal early molecular events associated with the progression of hypertrophy, and may provide new insights for developing methods of early diagnosis and treatment to prevent heart failure. The authors show that although whole-cell coupling of L-type calcium channels and ryanodine receptor current activation remains intact during compensated hypertrophy (before heart failure manifests), intermolecular coupling at a molecular level is already slipping.