Metabolic mechanisms of cardioprotection through alpha-1A adrenergic receptor activation

心脏比其他任何器官消耗更多的ATP，其中绝大多数是由线粒体中的脂肪酸氧化(FAO)和氧化磷酸化(OXPHOS)产生的。交感神经系统(SNs)通过激活心肌细胞中的α-1-肾上腺素能受体(α1-AR)和β-AR(β-AR)来调节线粒体功能的许多方面，我们最近综述了这一点。持续刺激心脏β-AR导致病理结构和代谢改变，导致心肌能量耗竭和心力衰竭(HF)，但α-1-AR在衰竭心脏发挥适应性作用，减轻慢性β-AR激活的毒性。这种心脏保护的机制在很大程度上仍不清楚。α1-AR有三种亚型：A、B和D。越来越多的证据表明，α1A亚型保护心肌细胞免受多种类型的损伤。我们先前发表的研究表明，一种选择性的α-1A激动剂可以增加暴露于蒽环类药物的衰竭小鼠心脏中的ATP值。我们的初步数据显示，缺乏αA-AR(α1AKO)的基因敲除小鼠的通透性心肌纤维和分离的线粒体显示出粮农组织降低，电子传输链(ETC)复合体I和II的活性降低。我们最近还发现，选择性α1A激动剂治疗可以增强未受损伤的小鼠心脏的复合体I、II和IV的活性，并保护实验性心肌梗死小鼠的心脏能量能力和收缩功能。总而言之，这些发现表明了α1A介导的心脏保护的一种新机制，因为先前还没有研究过β1-ARs对粮农组织和氧磷酸盐的调节。我们现在提出三个具体目标，以建立在我们已发表的发现和新的初步数据的基础上，以验证中心假设，即α1A-ARs通过增强线粒体氧化能力来代谢支持未受损的心脏并保护衰竭的心脏。目的1将确定α1A-ARs是否通过我们的心肌细胞特异性β1A基因敲除小鼠的心肌自主效应、α1A骨骼肌粮农组织调节的新的重点研究以及高脂饮食模型来增强心脏中的氧合酶。目的2将发现α1A-Ars是否通过维持长链粮农组织和调节ETC酶活性，结合体外机械性方法对α1A基因敲除和α1A激动剂处理的小鼠心脏进行体内图谱分析来保持能量能力。目的3将使用三种临床相关的小鼠模型来测试选择性α1A-AR激动剂是否起到促有丝分裂作用--增强线粒体功能的药物--对HF的保护作用：慢性异丙肾上腺素输注，心肌细胞特异性粮农组织丢失(肉碱棕榈酰转移酶2基因敲除)，以及杜氏肌营养不良模型，在该模型中，复合体I活性受损。如果成功完成，拟议的实验将有可能极大地扩展我们对三七总皂苷调节心肌细胞线粒体功能的理解，阐明在临床和生理相关的小鼠模型中α1A介导的心脏保护的新机制。这些研究也代表了我们正在努力推进α1A-AR激动剂作为新型心力衰竭疗法的下一步。

The heart consumes more ATP than any other organ, the vast majority of which is generated by fatty acid oxidation (FAO) coupled to oxidative phosphorylation (OXPHOS) in mitochondria. The sympathetic nervous system (SNS) regulates numerous aspects of mitochondrial function through activation of alpha-1-adrenergic receptors (α1-ARs) and beta-ARs (β-ARs) in cardiomyocytes, as we recently reviewed. Persistent stimulation of cardiac β-ARs causes pathological structural and metabolic changes resulting in myocardial energy depletion and heart failure (HF), but α1-ARs exert adaptive effects in the failing heart, mitigating the toxicity of chronic β-AR activation. The mechanisms underlying this cardioprotection remain largely unclear. There are three α1-AR subtypes: A, B, and D. Mounting evidence indicates that the α1A subtype protects cardiomyocytes against multiple types of injury. We previously published that a selective α1A agonist increases ATP content in anthracycline-exposed failing mouse hearts. Our preliminary data now show that permeabilized cardiac muscle fibers and isolated mitochondria from knockout mice lacking the αA-AR (α1AKO) exhibit decreased FAO and diminished activity of electron transport chain (ETC) Complex I and II. We also recently found that treatment with a selective α1A agonist enhances Complex I, II and IV activity in uninjured mouse hearts and protects cardiac energetic capacity and contractile function in mice subjected to experimental myocardial infarction. Collectively, these findings suggest a novel mechanism for α1A-mediated cardioprotection, as regulation of neither FAO nor OXPHOS by β1-ARs has been studied previously. We now propose three Specific Aims to build upon our published findings and novel preliminary data to test the central hypothesis that α1A-ARs metabolically support the uninjured heart and protect the failing heart by enhancing mitochondrial oxidative capacity. Aim 1 will determine whether α1A-ARs enhance OXPHOS in the heart through cardiomyocyte-autonomous effects using our cardiomyocyte-specific β1A knockout mice, novel focused studies of α1A skeletal muscle FAO regulation, and a high fat diet model. Aim 2 will find if α1A-ARs preserve energetic capacity through maintenance of long chain FAO and regulation of ETC enzyme activity, coupling in vivo profiling of α1A knockout and α1A agonist treated mouse hearts with mechanistic in vitro approaches. Aim 3 will test whether selective α1A-AR agonists act as mitotropes—drugs that enhance mitochondrial function--to protect against HF using three clinically relevant mouse models: chronic isoproterenol infusion, cardiomyocyte-specific loss of FAO (Carnitine palmitoyl transferase 2 knockout), and a Duchenne Muscular Dystrophy model in which Complex I activity is impaired. If successfully completed, the proposed experiments have the potential to significantly expand our understanding of SNS regulation of cardiomyocyte mitochondrial function, elucidating new mechanisms of α1A-mediated cardioprotection in clinically and physiologically relevant mouse models. These studies also represent the next step in our ongoing efforts to advance α1A-AR agonists as novel HF therapies.