Cardiovascular Research Group, Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
Acta Physiol (Oxf). 2013 Jan;207(1):173-82. doi: 10.1111/j.1748-1716.2012.02470.x. Epub 2012 Aug 13.
β-Adrenergic receptor activation increases myocardial contractility, in part through protein kinase A (PKA)-dependent modification of cardiac myofilaments. PKA regulation of cardiac myofilaments is contingent influenced by protein kinase C (PKC) phosphorylation of troponin I (TnI). Reductions in the cardiac Z-disc protein CapZ attenuate PKC regulation of myofilament activation. We hypothesized that CapZ-deficient transgenic mouse hearts respond poorly to β-adrenergic receptor activation, as a result of impaired PKC activation.
Wild-type and CapZ-deficient transgenic mice were treated with the β-adrenergic receptor agonist isoproterenol (ISO) and whole heart function assessed by echocardiography. Cardiac myofilaments were isolated post-ISO treatment and subjected to an actomyosin MgATPase assay and protein phosphorylation gels.
CapZ-deficient transgenic mouse hearts exhibited increased contractility and myofilament calcium sensitivity at baseline, as compared to wild-type mice. In wild-type mice, ISO increased myocardial contractility and decreased myofilament calcium sensitivity, along with an increase in TnI phosphorylation. CapZ-deficient transgenic mice responded to ISO treatment, and myocardial functional differences between transgenic and wild-type mice were abolished. ISO-dependent changes in myofilament activation in transgenic mice were similar to those observed in wild-type. TnI phosphorylation was similarly increased in wild-type and transgenic mice following ISO treatment, while CapZ-deficient transgenic mouse myofilaments also exhibited increased myosin-binding protein C phosphorylation. Differences in myofilament protein phosphorylation patterns suggest the intracellular mechanisms utilized by β-adrenergic receptor activation are different than that seen in wild-type hearts.
These data further support the concept that the cardiac Z-disc protein is a regulator of myofilament function and intracellular signalling transduction.
β肾上腺素能受体激活可增加心肌收缩力，部分是通过蛋白激酶 A（PKA）依赖性修饰心肌纤维实现的。PKA 对心肌纤维的调节受到肌钙蛋白 I（TnI）蛋白激酶 C（PKC）磷酸化的影响。Z 盘蛋白 CapZ 的减少会减弱 PKC 对肌球蛋白激活的调节。我们假设，由于 PKC 激活受损，CapZ 缺乏的转基因小鼠心脏对β肾上腺素能受体激活的反应较差。
用β肾上腺素能受体激动剂异丙肾上腺素（ISO）处理野生型和 CapZ 缺乏的转基因小鼠，并通过超声心动图评估全心功能。在 ISO 处理后分离心肌纤维，并进行肌球蛋白 MgATP 酶测定和蛋白质磷酸化凝胶分析。
与野生型小鼠相比，CapZ 缺乏的转基因小鼠心脏在基础状态下表现出收缩力增加和肌球蛋白钙敏感性增加。在野生型小鼠中，ISO 增加心肌收缩力并降低肌球蛋白钙敏感性，同时 TnI 磷酸化增加。CapZ 缺乏的转基因小鼠对 ISO 处理有反应，转基因和野生型小鼠之间的心肌功能差异被消除。转基因小鼠中肌球蛋白激活的 ISO 依赖性变化与野生型相似。ISO 处理后，野生型和转基因小鼠的 TnI 磷酸化均增加，而 CapZ 缺乏的转基因小鼠肌球蛋白结合蛋白 C 的磷酸化也增加。肌球蛋白蛋白磷酸化模式的差异表明，β肾上腺素能受体激活所利用的细胞内机制与野生型心脏不同。
这些数据进一步支持了心脏 Z 盘蛋白是肌球蛋白功能和细胞内信号转导的调节因子的概念。
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