Zhao Claire Y, Greenstein Joseph L, Winslow Raimond L
Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
J Mol Cell Cardiol. 2016 Feb;91:215-27. doi: 10.1016/j.yjmcc.2016.01.004. Epub 2016 Jan 7.
The balanced signaling between the two cyclic nucleotides (cNs) cAMP and cGMP plays a critical role in regulating cardiac contractility. Their degradation is controlled by distinctly regulated phosphodiesterase isoenzymes (PDEs), which in turn are also regulated by these cNs. As a result, PDEs facilitate communication between the β-adrenergic and Nitric Oxide (NO)/cGMP/Protein Kinase G (PKG) signaling pathways, which regulate the synthesis of cAMP and cGMP respectively. The phenomena in which the cAMP and cGMP pathways influence the dynamics of each other are collectively referred to as cN cross-talk. However, the cross-talk response and the individual roles of each PDE isoenzyme in shaping this response remain to be fully characterized. We have developed a computational model of the cN cross-talk network that mechanistically integrates the β-adrenergic and NO/cGMP/PKG pathways via regulation of PDEs by both cNs. The individual model components and the integrated network model replicate experimentally observed activation-response relationships and temporal dynamics. The model predicts that, due to compensatory interactions between PDEs, NO stimulation in the presence of sub-maximal β-adrenergic stimulation results in an increase in cytosolic cAMP accumulation and corresponding increases in PKA-I and PKA-II activation; however, the potentiation is small in magnitude compared to that of NO activation of the NO/cGMP/PKG pathway. In a reciprocal manner, β-adrenergic stimulation in the presence of sub-maximal NO stimulation results in modest cGMP elevation and corresponding increase in PKG activation. In addition, we demonstrate that PDE2 hydrolyzes increasing amounts of cAMP with increasing levels of β-adrenergic stimulation, and hydrolyzes increasing amounts of cGMP with decreasing levels of NO stimulation. Finally, we show that PDE2 compensates for inhibition of PDE5 both in terms of cGMP and cAMP dynamics, leading to cGMP elevation and increased PKG activation, while maintaining whole-cell β-adrenergic responses similar to that prior to PDE5 inhibition. By defining and quantifying reactions comprising cN cross-talk, the model characterizes the cross-talk response and reveals the underlying mechanisms of PDEs in this non-linear, tightly-coupled reaction system.
两种环核苷酸（cNs），即环磷酸腺苷（cAMP）和环磷酸鸟苷（cGMP）之间的平衡信号传导在调节心脏收缩力方面起着关键作用。它们的降解由调控方式各异的磷酸二酯酶同工酶（PDEs）控制，而这些同工酶反过来也受这些环核苷酸调节。因此，磷酸二酯酶促进了β-肾上腺素能信号通路与一氧化氮（NO）/环磷酸鸟苷/蛋白激酶G（PKG）信号通路之间的通讯，这两条信号通路分别调节环磷酸腺苷和环磷酸鸟苷的合成。环磷酸腺苷和环磷酸鸟苷信号通路相互影响动态变化的现象统称为环核苷酸串扰。然而，串扰反应以及每种磷酸二酯酶同工酶在形成这种反应中的具体作用仍有待全面阐明。我们构建了一个环核苷酸串扰网络的计算模型，该模型通过两种环核苷酸对磷酸二酯酶的调控，从机制上整合了β-肾上腺素能信号通路和NO/环磷酸鸟苷/蛋白激酶G信号通路。各个模型组件以及整合后的网络模型重现了实验观察到的激活-反应关系和时间动态变化。该模型预测，由于磷酸二酯酶之间的代偿性相互作用，在次最大β-肾上腺素能刺激存在的情况下，NO刺激会导致胞质内环磷酸腺苷积累增加以及蛋白激酶A-I（PKA-I）和蛋白激酶A-II（PKA-II）激活相应增加；然而，与NO激活NO/环磷酸鸟苷/蛋白激酶G信号通路相比，这种增强的幅度较小。反之，在次最大NO刺激存在的情况下，β-肾上腺素能刺激会导致环磷酸鸟苷适度升高以及蛋白激酶G激活相应增加。此外，我们证明随着β-肾上腺素能刺激水平的增加，磷酸二酯酶2（PDE2）水解的环磷酸腺苷量增加，而随着NO刺激水平的降低，其水解的环磷酸鸟苷量增加。最后，我们表明，在环磷酸鸟苷和环磷酸腺苷动态变化方面，磷酸二酯酶2都能补偿磷酸二酯酶5（PDE5）的抑制作用，从而导致环磷酸鸟苷升高和蛋白激酶G激活增加，同时维持与磷酸二酯酶5抑制之前相似的全细胞β-肾上腺素能反应。通过定义和量化构成环核苷酸串扰的反应，该模型表征了串扰反应，并揭示了在这个非线性、紧密耦合的反应系统中磷酸二酯酶的潜在机制。
