Beta-Adrenergic Control of the Pathological Cardiac Microtubule Network

描述(申请人提供)：我们对血流动力学挑战下病理性与生理性肥厚心脏反应的负荷特异性的研究导致发现[Science，260：682-687,1993]在由严重的压力超负荷引起的病理性、高室壁应激性肥厚期间，致密的心脏微管网络导致显著的收缩和细胞内运输功能障碍。在试图确定这种细胞骨架异常的原因时，提供了一个重要的提示，即我们从未见过微管网络的变化具有同等程度和持续时间的完全代偿性生理性肥厚，其中室壁应力保持正常。这一提示，加上以下三个进一步的考虑，导致了本申请中提出的研究。首先，失代偿性病理性心肌肥厚的一个特征是循环和神经儿茶酚胺的持续升高，因此人们认为这在病理性肥厚中存在，但在代偿性生理性肥厚中不存在。其次，最近的数据表明，b-肾上腺素能输入在增加p21-激活的激酶或pak1的活性方面发挥了关键作用，p21-激活的激酶进而启动了一系列磷酸酶的激活，特别是在心脏中PP2A和PP1的激活。第三，我们自己的数据表明，病理性心肌肥厚中出现的异常微管网络是由MAP4的微管结合驱动的，MAP4是主要的心脏微管相关结构蛋白，而这反过来又是由磷酸酶依赖的位点特异性MAP4去磷酸化驱动的。我们建议在这里将这些信息用于两个具体目标。在具体目标#1中，我们将试图通过比较我们非常典型的猫生理性容量超负荷性肥厚模型和我们同样特征的病理性压力超负荷性肥厚伴或不伴慢性b肾上腺素能阻断模型，来确定b-肾上腺素能输入在引起肥大相关心脏微管表型中的病因学作用。如果我们的假设正确，我们的假设将预测，在没有b-肾上腺素能阻断的压力超负荷性肥厚中将存在异常的微管网络，但在有b-肾上腺素能阻断的这个模型中和在没有药物治疗的生理性容量超负荷模型中都没有。在特定的目标#2中，如果我们能够在先前的目标中，通过使用慢性b-肾上腺素能受体阻滞剂，在以其为特征的严重压力超负荷模型中阻止致密的、MAP4装饰的微管网络的形成，我们将确定这是否也阻止了相关的收缩和基于微管的运输的功能异常。 公共卫生相关性：在65岁或以上的美国人中，充血性心力衰竭是住院和再次住院的主要原因。以收缩性心力衰竭为特征的收缩功能障碍和心脏生长异常是一种对几种病理挑战的不适应性心肌反应，包括持续的心脏压力超负荷。这项研究将确定导致衰竭心脏功能障碍的一个重要原因的机制：心肌细胞细胞骨架微管网络的变化。

DESCRIPTION (provided by applicant): Our studies of the load-specificity of pathological versus physiological hypertrophic cardiac responses to hemodynamic challenges led to the discovery [Science, 260: 682-687, 1993] of a dense cardiocyte microtubule network during pathological, high ventricular wall stress hypertrophy caused by severe pressure-overloading that contributes to the striking contractile and intracellular transport dysfunction that occur in this setting. In attempting to identify the cause for this cytoskeletal abnormality, a crucial hint was provided by the fact that we have never seen microtubule network changes with an equivalent degree and duration of fully compensated physiological hypertrophy wherein ventricular wall stress remains normal. This hint, coupled with the following three further considerations, led to the studies proposed in this application. First, a hallmark of decompensated pathological cardiac hypertrophy is a persistent elevation of circulating and neural catecholamines, such that one would expect this to be present in pathological hypertrophy but absent from compensated physiological hypertrophy. Second, very recent data establish a critical role of b-adrenergic input in increasing the activity of p21-activated kinase, or Pak1, which in turn initiates a cascade of phosphatase activation, specifically of PP2A and then PP1, in the heart. Third, our own data indicate that the abnormal microtubule network seen in pathological cardiac hypertrophy is driven by binding to microtubules of MAP4, the predominant cardiac microtubule-associated structural protein, and that this in turn is driven by phosphatase-dependent site-specific MAP4 dephosphorylation. We propose to use this information here in two specific aims. In Specific Aim #1, we will attempt to establish the etiological role of b-adrenergic input in causing the hypertrophy- associated cardiac microtubule phenotype by comparing our very well characterized model of feline physiological volume-overload hypertrophy to our equally well characterized model of pathological pressure-overload hypertrophy with or without chronic b-adrenergic blockade. If correct, our hypothesis would predict that the abnormal microtubule network will be present in pressure-overload hypertrophy without b-adrenergic blockade but absent both in this model with b-adrenergic blockade and in the physiological volume-overload model with no drug treatment. In Specific Aim #2, if we are able in the previous aim to prevent formation of the dense, MAP4-decorated microtubule network by using chronic b-adrenergic blockade in the severe pressure-overload model of which it is characteristic, we will determine whether this also prevents the associated functional abnormalities of contraction and microtubule-based transport. PUBLIC HEALTH RELEVANCE: Congestive heart failure is the leading cause of hospital admission and readmission in Americans aged 65 or greater. The contractile dysfunction and cardiac growth abnormalities that characterize systolic heart failure are a maladaptive myocardial response to several pathological challenges, including sustained cardiac pressure overloading. This study will identify the mechanism underlying one important cause for this dysfunction in the failing heart: alterations in the microtubule network of the cardiac muscle cell cytoskeleton.