PKA Signaling and Metabolic Inflexibility in the Diabetic Heart

 描述(由申请者提供)：该项目的长期目标是了解糖尿病如何影响心脏，并获得更好的治疗方案。考虑到糖尿病和随之而来的心血管并发症的高发病率，这一点尤其重要。事实上，在没有其他危险因素的情况下，糖尿病可以通过尚不完全清楚的机制引起心脏功能的变化。这项建议的重点是了解糖尿病是如何影响β-肾上腺素能信号通路的，以及这些变化如何加剧和增加心脏的压力。通过β-肾上腺素能受体信号通路激活cAMP依赖的蛋白激酶(PKA)是提高心肌收缩能力的主要途径。该通路的过度激活或失调是糖尿病心肌病、危及生命的心律失常和心力衰竭的主要驱动因素。然而，这一途径被破坏的机制在很大程度上是未知的。在健康的心脏中，PKA通过放大钙循环来增加收缩能力，并协同激活磷酸果糖激酶-2(PFK-2)以促进葡萄糖氧化。通过这种方式，工作负荷和新陈代谢需求得到了很好的协调。对此应用程序的研究解决了这种编排是如何被打乱的。这项工作的基础是我们最近的发现，在糖尿病心脏中，PFK-2对直接激活PKA没有反应，这表明受体后信号转导受到了影响。此外，我们的结果表明，PFK-2的这种无反应性是由PKA抑制物(PKI)的减少所介导的，PKI是一种核蛋白家族，可以抑制PKA并促进其向细胞质的运输。这些发现导致了我们的总体假设，即糖尿病导致PKI缺乏，导致PKA的异常定位和活性，从而取消PFK2的激活并促进心肌病。这一假设正在用糖尿病小鼠模型和成人原代心肌细胞进行测试和探索。在目标1中，我们正在研究PKA信号在糖尿病心脏中的不同以及这种信号在心功能中的变化。机制研究正在进行，以了解糖尿病代谢状况如何调节这些变化。在目标2中，我们正在定义公钥基础设施水平下降的原因和后果。这一目标建立在我们最近发现的这些蛋白质的动态性质上。在目标3中，我们正在验证这样的假设，即PFK-2在维持β-肾上腺素能刺激后的代谢灵活性方面发挥着重要作用。我们正在定义糖尿病是如何影响PFK-2水平的，以及这如何使这种酶对PKA激活不敏感。这些研究将调查一个完全未被探索但关键的PKA调节和信号传递领域，以及它们如何受到糖尿病心功能障碍的影响，并可能导致糖尿病心功能不全。这项研究的结果可能有助于开发β受体下游的治疗靶点。

 DESCRIPTION (provided by applicant): The long term goal of this project is to understand how diabetes affects the heart and derive better treatment options. This is especially important given the high incidence of diabetes and ensuing cardiovascular complications. Indeed, diabetes can induce changes to cardiac function in the absence of other risk factors through mechanisms that are not completely clear. The focus of this proposal is to understand how the beta-adrenergic signaling pathway is affected by diabetes, and how these changes may exacerbate and enhance stress on the heart. Activation of cAMP-dependent protein kinase (PKA) via beta-adrenergic receptor signaling is a primary means of increasing cardiac contractility. Over- activation or dysregulation of this pathway is a major driver of diabetic cardiomyopathy, life threatening arrhythmias, and heart failure. However, the mechanisms by which this pathway becomes disrupted are largely unknown. In the healthy heart, PKA increases contractility by amplifying calcium cycling and concertedly activates phosphor-fructose kinase-2 (PFK-2) to promote glucose oxidation. In this manner, workload and metabolic demand are finely orchestrated. The studies of this application address how this orchestration becomes disrupted. The foundation for this work is based on our recent discovery that in the diabetic heart PFK-2 is unresponsive to direct PKA activation, suggesting that post-receptor signaling is compromised. Moreover, our results indicate that this unresponsiveness of PFK-2 is mediated by a decrease in PKA inhibitors (PKIs), a family of nuclear proteins that inhibit PKA and facilitate its transport to the cytoplasm. These findings have led to our overarching hypothesis that diabetes-induces a deficiency of PKI, resulting in aberrant localization and activity of PKA that abrogates PFK2 activation and promotes cardiomyopathy. This hypothesis is being tested and explored using murine models of diabetes and adult primary cardiomyocytes. In Aim 1, we are examining how PKA signaling differs in the diabetic heart and how this changes in cardiac function. Mechanistic studies are being performed to understand how diabetic metabolic conditions mediate these changes. In Aim 2, we are defining the cause and consequence of decreased PKI levels. This aim builds off our recent discovery of the dynamic nature of these proteins. In Aim 3, we are testing the hypothesis that PFK-2 plays an essential role in maintaining metabolic flexibility following beta-adrenergic stimulation. We are defining how PFK-2 levels are affected by diabetes and how this desensitizes this enzyme to PKA activation. These studies will investigate a completely unexplored but critical area of PKA regulation and signaling and how they are impacted by, and perhaps contribute to, diabetic cardiac dysfunction. Results from this study may aid in developing therapeutic targets downstream of beta-receptors.