Beta-Adrenergic Control of the Pathological Cardiac Microtubule Network

描述（由申请人提供）：我们对病理性与生理性肥大心脏对血流动力学挑战的反应的负荷特异性的研究导致了以下发现[Science，260：682-687，1993]在病理过程中致密的心肌细胞微管网络，严重压力引起的高心室壁应力肥大-超负荷导致在这种情况下发生的显著的收缩和细胞内转运功能障碍。在试图确定这种细胞骨架异常的原因，一个重要的提示是，我们从来没有见过微管网络的变化与完全代偿的生理性肥大，其中心室壁应力保持正常的同等程度和持续时间的事实。 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，失代偿性病理性心脏肥大的标志是循环和神经儿茶酚胺的持续升高，使得人们预期这存在于病理性肥大中，但不存在于代偿性生理性肥大中。第二，最近的数据建立了一个关键的作用，β-肾上腺素能输入增加p21激活激酶的活性，或Pak 1，这反过来又启动了一个级联的磷酸酶激活，特别是PP 2A，然后PP 1，在心脏。第三，我们自己的数据表明，在病理性心脏肥大中观察到的异常微管网络是由MAP 4（主要的心脏微管相关结构蛋白）与微管结合驱动的，而这反过来又是由磷酸酶依赖性位点特异性MAP 4去磷酸化驱动的。 我们建议在此将此信息用于两个具体目标。在具体目标#1中，我们将尝试通过比较我们非常充分表征的猫生理性容量超负荷肥大模型与我们同样充分表征的病理性压力超负荷肥大模型（伴或不伴慢性β-肾上腺素能阻滞），确定β-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。如果正确，我们的假设将预测，异常微管网络将存在于压力超负荷肥大没有β-肾上腺素能阻滞，但不存在于此模型与β-肾上腺素能阻滞和生理容量超负荷模型，没有药物治疗。在具体目标#2中，如果我们能够在之前的目标中通过在严重压力超负荷模型中使用慢性β-肾上腺素能阻滞来防止致密的、MAP 4修饰的微管网络的形成，我们将确定这是否也防止了收缩和基于微管的运输的相关功能异常。 公共卫生相关性：充血性心力衰竭是65岁或以上美国人入院和再入院的主要原因。收缩功能障碍和心脏生长异常是收缩性心力衰竭的特征，是对几种病理挑战（包括持续心脏压力超负荷）的适应不良心肌反应。这项研究将确定在衰竭的心脏中这种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改变。

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.