PROJECT 2 SUMMARY Atrial fibrillation (AF) risk is increased by a variety of cardiovascular stressors, including obesity, hypertension, coronary or valve disease, heart failure, metabolic syndrome, sleep apnea, excessive alcohol, and extreme exertion. AF is a progressive condition, and risk of stroke and other complications increases with increasing AF burden. Identification of drugs or interventions that can slow or reverse the progression of AF would have a significant clinical impact. In RNA sequencing studies, we have identified mitochondrial dysfunction and oxidative phosphorylation pathways among the most prominent pathways associated with development of persistent AF. In Project 2, Genes and Metabolism: Targeting Mitochondrial Dysfunction in Atrial Fibrillation (P2), our central hypothesis is that metabolic stressors and aging increase mitochondrial oxidant production, promoting atrial mitochondrial DNA damage, dysfunction and metabolic heterogeneity. We hypothesize that metabolic heterogeneity underlies electrical instability, and that interventions that promote mitochondrial resilience and limit metabolic heterogeneity will reduce atrial ectopy and slow AF progression. We propose two specific aims. Aim 1 seeks to evaluate the role of metabolic stressors on an in vitro model of engineered heart tissues (EHTs), derived from atrial-like cardiac myocytes differentiated from human induced pluripotent stem cells. We will study the transcriptional and functional impact of 4 distinct metabolic stressors relevant to the etiology of AF on EHT cellular composition and mitochondrial, contractile and electrical function of human atrial EHTs. Stressors include: chronic exposure to isoproterenol, palmitate, ethanol and endothelin-1; the same stressors will be used to test the protective effect of metabolic/mitochondrial targeted drugs in EHTs. In Aim 2, we will evaluate the metabolic mechanisms that underlie progression of AF in the heterozygous CREM-IbCX transgenic mouse model of spontaneous AF and AF progression, employing a high fat diet as a metabolic stress with which we can study the functional and transcriptomic impact of obesity on the development and rate of progression of AF. We hypothesize that progression of AF in this model is also caused by mitochondrial dysfunction, resulting in metabolic, transcriptional and electrophysiologic dysfunction. We thus propose that obese mice will develop AF more quickly, earlier, and with a greater burden than in lean transgenic mice. Finally, using obese transgenic mice, we will evaluate the impact of drugs that protected EHTs from mitochondrial dysfunction and downstream effects, to determine if these drugs can slow the development and progression of AF. We expect both the atrial EHT and obese CREM-IbCX mouse models will be useful for preclinical testing of new and existing metabolic drugs that can improve AF treatment and slow its progression. This project is highly collaborative with the other PPG pro...