Role of PI3K in Atrial Myopathy: Insights from Transgenic Mouse Models and Identification of a Dysregulated PI3K Lipid Profile in Individuals with Atrial Fibrillation

In a serendipitous discovery, we identified atrial enlargement, fibrosis and thrombi in a subset of transgenic mice with reduced phosphoinositide 3-kinase (PI3K, class IA) in cardiac myocytes. Understanding mechanisms underlying atrial myopathy has important implications for understanding and preventing atrial fibrillation (AF). Prior work had shown that PI3K is an essential regulator of exercise-induced ventricular enlargement and protection, but the role in the atria was unknown. Further, while targeting IGF1-PI3K-Akt signaling has been considered a potential therapeutic strategy for the failing heart, growing evidence suggests fine-tuning IGF1-PI3K signaling would be necessary. Here, we undertook comprehensive physiological and molecular analyses in cardiac-specific transgenic mice with increased or decreased PI3K to assess the dose response impact of directly regulating PI3K. Elevated PI3K was associated with a dose-dependent increase in heart size, and preserved/enhanced function. In contrast, reduced PI3K led to cardiac dysfunction, fibrosis, arrhythmia, and increased susceptibility to atrial enlargement and thrombi. This phenotype was associated with dysregulation of a lipid species (GM3) that regulates the IGF1-PI3K pathway, cardiac stress and contractility genes. Proteomic profiling identified distinct signatures across atria with varying degrees of atrial dysfunction, enlargement, and presence of atrial thrombi. To assess the potential relevance in humans we assessed circulating PI3K-related lipids in plasma from athletes with/without AF. Dysregulation of GM3 and PI3K-related lipids were identified in athletes with AF. Collectively, this work advances our understanding of mechanisms underpinning atrial pathophysiology, offers new insights for therapeutic approaches targeting atrial myopathy and AF, and has identified potential new lipid markers for identifying individuals at risk of AF. Overall design: Target-locus-amplification of genomic DNA from dnPI3K transgenic mice to reveal transgene insertion site

本研究在一次偶然发现中，于心肌细胞内磷酸肌醇3-激酶（phosphoinositide 3-kinase, PI3K，IA型）表达降低的转基因小鼠亚群中，观察到心房扩大、心肌纤维化及血栓形成。理解心房肌病的发病机制，对于认识并预防心房颤动（atrial fibrillation, AF）具有重要意义。既往研究表明，PI3K是运动诱导心室增大及心脏保护的关键调控因子，但其在心房中的作用尚不明确。此外，尽管靶向IGF1-PI3K-Akt信号通路曾被视为心力衰竭的潜在治疗策略，但越来越多的证据提示，需对IGF1-PI3K信号通路进行精准调控。本研究构建了心肌细胞特异性PI3K表达上调或下调的转基因小鼠模型，并开展全面的生理与分子学分析，以评估直接调控PI3K所产生的剂量依赖性效应。研究发现，PI3K表达升高与心脏体积呈剂量依赖性增大，并伴随心功能的保留与增强。与之相反，PI3K表达降低会导致心功能障碍、心肌纤维化、心律失常，并增加心房扩大及血栓形成的易感性。该表型与调控IGF1-PI3K通路、心肌应激及收缩功能相关基因的脂质分子GM3的表达失调密切相关。蛋白质组学分析显示，在心房功能障碍程度、心房扩大程度不同且存在心房血栓的样本中，存在独特的分子特征谱。为评估该研究结果在人类中的潜在相关性，我们对伴/不伴心房颤动的运动员血浆中的PI3K相关脂质进行了检测，结果在心房颤动运动员体内发现了GM3及PI3K相关脂质的表达失调。综上，本研究加深了我们对心房病理生理机制的认识，为心房肌病及心房颤动的靶向治疗提供了新的思路，并鉴定出可用于识别心房颤动高危人群的潜在新型脂质标志物。整体实验设计：对dnPI3K转基因小鼠的基因组DNA进行靶位点扩增，以明确转基因插入位点。