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

心脏比任何其他器官消耗更多的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。我们最近回顾了交感神经系统（SNS）通过激活心肌细胞中的α -1-肾上腺素能受体（α1-ARs）和β-ARs （β-ARs）来调节线粒体功能的许多方面。持续刺激心脏β-AR可引起病理结构和代谢变化，导致心肌能量耗竭和心力衰竭（HF），但α - ar在心力衰竭中发挥适应性作用，减轻慢性β-AR激活的毒性。这种保护心脏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亚型可以保护心肌细胞免受多种类型的损伤。我们之前发表了选择性α1A激动剂可增加蒽环类药物暴露的衰竭小鼠心脏中ATP含量。我们的初步数据现在表明，缺乏αA-AR （α1AKO）的敲除小鼠的渗透心肌纤维和分离线粒体表现出FAO降低和电子传递链（ETC）复合物I和II活性降低。我们最近还发现，选择性α1A激动剂可以增强未损伤小鼠心脏中复合物I、II和IV的活性，并保护实验性心肌梗死小鼠的心脏能量容量和收缩功能。总的来说，这些发现表明α 1a介导的心脏保护的新机制，因为β1-ARs对FAO和OXPHOS的调节都没有被研究过。我们现在提出三个具体目标，以我们已发表的研究结果和新的初步数据为基础，来验证α1A-ARs通过增强线粒体氧化能力来代谢支持未损伤心脏和保护衰竭心脏的中心假设。目的1将通过心肌细胞特异性β1A敲除小鼠、α1A骨骼肌FAO调控的新重点研究和高脂肪饮食模型，确定α1A- ars是否通过心肌细胞自主效应增强心脏中的OXPHOS。目的2将发现α1A- ars是否通过维持长链FAO和调节ETC酶活性来保持能量容量，并通过体外机制方法耦合α1A敲除和α1A激动剂处理小鼠心脏的体内分析。目的3将测试选择性α1A-AR激动剂是否作为促核因子（增强线粒体功能的药物）来预防心衰，使用三种临床相关的小鼠模型：慢性异丙肾上腺素输注、心肌细胞特异性丢失FAO（肉碱palmitoyl transferase 2敲除）和Duchenne肌营养不良模型，其中复合物I活性受损。如果成功完成，本实验有可能显著扩展我们对SNS调节心肌细胞线粒体功能的理解，阐明α 1a介导的心脏保护在临床和生理相关小鼠模型中的新机制。这些研究也代表了我们正在努力推进α1A-AR激动剂作为新型心衰治疗的下一步。

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.