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

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE243115 | GEO | 2025/01/09

REPOSITORIES: GEO

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Project description:Obscurins are giant, modular, cytoskeletal proteins that regulate striated muscle structure and function. Immunoglobulin domains 58/59 (Ig58/59) of obscurin interact with diverse proteins including titin variants and phospholamban. Mutations within Ig58/59 that alter these binding interactions have been linked to the development of myopathy in humans, underscoring the pathophysiological significance of this module. We previously generated a constitutive deletion mouse model, Obscn-ΔIg58/59, that expresses obscurin lacking Ig58/59 and comprehensively characterized the effects of this deletion on cardiac morphology and function through aging. Our findings demonstrated that Obscn-ΔIg58/59 male animals develop severe arrhythmia characterized by spontaneous atrial fibrillation/junctional escape by 6-months of age, with atrial enlargement and ventricular remodeling manifesting by 12-months. Herein, we aim to mechanistically evaluate the impact of the Ig58/59 deletion in atria at the cellular level and determine the molecular basis for atrial enlargement and arrhythmia due to the physiological process of aging. Ultrastructural evaluation of sedentary aging male Obscn-ΔIg58/59 atria revealed prominent Z-disk streaming and misalignment. More importantly, Obscn-ΔIg58/59 atrial cardiomyocytes exhibited increased Ca2+ spark frequency and age-specific alterations in Ca2+ cycling kinetics and sarcoplasmic reticulum Ca2+ content that preceded those observed in Obscn-ΔIg58/59 ventricular cardiomyocytes. Proteomic and phospho-proteomic analyses revealed extensive and novel alterations in the expression and phosphorylation profile of major cytoskeletal proteins, Ca2+ regulators, and Z-disk associated protein complexes in Obscn-ΔIg58/59 atria through aging that likely underlie the observed atrial pathologies. These studies are the first to evaluate the role of obscurin in atria and to reveal chamber-specific molecular alterations due to Ig58/59 deletion. Moreover, our findings provide new molecular insights into a genetic model of spontaneous atrial fibrillation and remodeling where atrial dysfunction precedes ventricular maladaptation.

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

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