PROJECT SUMMARY/ ABSTRACT
Atrial Fibrillation (AF) is an arrhythmia characterized by the aberrant, unorganized initiation and
propagation of electrical impulses across the atria. The most common serious arrhythmia, AF affected an
estimated 33.5 million globally in 2010, with a lifetime risk of 1 in 3 individuals older than 55 years old. A
greater understanding of the mechanisms of AF is required to design more effective treatment strategies.
Genome-wide association studies have linked AF with over 143 genomic loci, including the transcription
factor (TF) TBX5. In our previous study, we integrated single-nucleus RNA- and ATAC- sequencing
(multiomics) of control and Tbx5 KO aCMs with TBX5 chromatin occupancy in aCMs to identify direct TBX5
targets that might contribute to AF. In the process, we uncovered a novel function for TBX5 in maintaining
genomic accessibility at enhancer elements, likely by recruiting chromatin modifying proteins. TBX5 interacts
with chromodomain helicase DNA binding protein 4 (CHD4), a component of the nucleosome remodeling and
histone deacetylase (NuRD) complex. Although conventionally viewed as a transcriptional repressor, our
Preliminary Data reveal an exciting, alternative role for CHD4 as a transcriptional activator.
To better understand gene expression changes central to AF, we performed multiomics on a second AF
mouse model caused by Liver Kinase B1 (LKB1) inactivation in aCMs, a gene decreased in human AF patient
aCMs, revealing 632 core atrial rhythm (AR) genes that are commonly downregulated in aCMs from both
models. 61% of AR genes were adjacent to regions co-occupied by CHD4-TBX5, and include the Na+ channel
SCN5A, regulators FGF12/13 and the gap junction channels Connexin 43 (GJA1) and Connexin 45 (GJA5).
These data lead to our central hypothesis that CHD4 maintains rhythm homeostasis in healthy atria by
complexing with TBX5 to maintain the accessibility of TBX5-dependent enhancers, promoting the expression
of genes that are critical for normal aCM electrical function.
To determine the mechanisms by which the CHD4-TBX5 complex regulates the atrial enhancer network,
we will characterize the phenotypic and genomic consequences of Chd4 inactivation in aCMs, identify CHD4-
interacting proteins required for aCM gene activation, and uncover other cis-activating factors that function
cooperatively with CHD4-TBX5 to regulate aCM gene expression. To identify core atrial genes required for
atrial rhythm, we will test the requirement of select AR genes to maintain atrial rhythm by inactivation. Genes
identified as critical regulators of rhythm will then be evaluated for therapeutic efficacy in AF prevention and
reversal in our established AF mouse models. This proposal is significant because it will mechanistically
characterize genes required for atrial function, determine how they are regulated, and test their potential as
therapies in multiple models, laying the groundwork for the development of more effective treatment strategies.