The Pitx2 homeodomain transcription factor is a central transcriptional regulator in left right asymmetry that functions within the heart to contro cardiac morphogenesis. It is now clear that Pitx2 is fundamentally connected to AF although the basis for this connection remains obscure. The first evidence for the Pitx2-AF link was made in a Genome Wide Association Study (GWAS) implicating a region of chromosome 4q25 in early onset familial AF. Pitx2 was the gene in closest proximity to the disease associated single nucleotide polymorphism (SNP). AF patients with the 4q25 SNP were free of hypertension, diabetes and valve defects. Moreover, patients with the 4q25 SNP were more prone to cardioembolic stroke adding further urgency to gain insight to the underlying molecular mechanisms associated with the 4q25 SNP. We were the first group to report that Pitx2 heterozygous mice were predisposed to AF indicating that reduced levels of Pitx2 led to AF. Three different groups have subsequently replicated our findings. Because of its critical role in AF, we hypothesized that genome wide analysis of Pitx2 transcriptional target genes would provide novel and fundamentally important insight into the molecular mechanisms for AF in the Pitx2 haplo-insufficient state. Our preliminary Chromatin Immuno Precipitation (ChIP) sequence (seq) data indicate that Pitx2 directly binds to a number of genes that have been implicated in AF and also PR interval in human GWAS studies. Moreover, motif analysis of our ChIPseq data further suggests that Pitx2 coordinately regulates gene expression with other transcription factors such as Nkx2.5 that are implicated in AF. Lastly, our ChIP seq and other preliminary data suggest that Pitx2 regulates microRNAs that are important for AF predisposition. We propose to thoroughly investigate the molecular basis for Pitx2 regulated conduction system development and maintenance. There is poor understanding of the genetic mechanisms underlying AF. New genetic insights will be critical for diagnostic testing and family counseling i the future. Moreover, an in depth knowledge of genetics of AF will provide critical resources for patient management as human genome sequencing becomes more commonplace. Finally, there is the long term goal to develop novel therapeutic strategies based on solid scientific information that will come from work in model organisms and human genetics.

Public Health Relevance

Atrial fibrillation (AF), the most prevalent sustained cardiac arrhythmia in the human population, is associated with a high incidence of stroke leading to substantial disability, suffering, and enormous health care costs. Because AF prevalence increases with age, affecting approximately 5% of the human population over 65, the incidence of AF will increase and continue to be a large public burden. In this proposal, we will perform an in depth study of genes that are important in AF.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
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Cardiovascular Differentiation and Development Study Section (CDD)
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Lathrop, David A
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Baylor College of Medicine
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