Our human genetic and left atrial transcriptomic studies identified two atrial fibrillation (AF) genome wide association study genes that are the focus of this project, FAM13B and SYNE2. Aim 1 will focus on FAM13B. We discovered that the FAM13B AF-risk allele is associated with lower FAM13B expression. FAM13B knockdown in human induced pluripotent stem cell derived cardiomyocytes (iCM) led to reduced expression of several mitochondrial proteins, including those needed for the clearance of dysfunctional mitochondria by mitophagy. The accumulation of dysfunctional mitochondria and decreased mitophagy are hallmarks of cardiac aging. We hypothesize that the FAM13B risk allele works in conjunction with aging to lead to impaired mitophagy, increased reactive oxygen species, depleted ATP, and altered ion conductance. We propose to determine the effects of aging and FAM13B knockdown on mitochondrial dysfunction and mitophagy and explore their downstream effects related to AF pathogenesis, both in human iCM cells and in atrial cardiomyocytes from young and old, wildtype and Fam13b knockout mice. In collaborative studies we will determine if Fam13b knockout mice are more susceptible to pacing induced atrial arrhythmia. We will also test metformin, an inducer of mitophagy that is used in the Clinical Project, to see if it can ameliorate FAM13B or aging associated changes. Aim 2 will focus on SYNE2, a nuclear membrane protein that connects the nucleus to the cytoskeleton. We discovered that the SYNE2 AF-risk allele is associated with lower expression of a short isoform of SYNE2. This short isoform lacks its actin binding domain, decreasing nuclear-cytoskeletal coupling, and thus may protect the nucleus from physical stress during cell contraction. We hypothesize that the SYNE2 risk allele leads to changes in nuclear morphology and stiffness and increased cardiomyocyte nuclear injury and cell death. We propose to determine the effects of SYNE2 short isoform expression on nuclear dysfunction by genetic methods to over and under express the SYNE2 short isoform in iCM cells followed by assays for nuclear morphology, stiffness, protein import, injury, and the responses to stress and pacing. Finally we will combine knockdown of FAM13B and SYNE2 short isoform in iCM to generate a novel cell culture model for testing potential AF therapeutics.
|Program type||Strategically Focused Research Network|
|Effective start/end date||07/01/2018 → 06/30/2022|