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TBX5 G125R induces profound transcriptional deregulation and atrial dysfunction in vivo [CUT&RUN]

ABSTRACT: Rationale: Pathogenic variants in the gene for T-box transcription factor (TF) 5 (TBX5) cause Holt-Oram syndrome (HOS), characterized by congenital heart defects and limb abnormalities. A particular missense variant in TBX5 (G125R) in a Dutch family causes atypical HOS as well as early onset atrial fibrillation (AF). Understanding the effects of such an altered key cardiac TF on the transcription regulatory network and cardiac physiology provides a unique opportunity to gain insight into the mechanisms underlying diseases such as AF. Objective: To determine the in vivo TBX5-G125R-induced changes in the transcriptional regulatory network and epigenetic state underlying the atypical HOS with early onset AF found in an extended pedigree. Methods and Results: We modeled the TBX5-G125R pathogenic variant in vivo in the mouse and found severe cardiac defects and fetal lethality in Tbx5G125R/G125R mice, whereas Tbx5G125R/+ mice were viable and morphologically unaffected. Electrophysiological analysis of adult Tbx5G125R/+ mice revealed variable RR interval, atrial extra systole and susceptibility to AF upon pacing. These characteristics were also observed in the patient family. Additionally, calcium homeostasis as well as conduction were changed in the mutant atrial cardiomyocytes. Single-nucleus transcriptional profiling of right atria revealed the most profound changes in expression in the cardiomyocytes of Tbx5G125R/+ mice. Transcriptional profiling of atrial tissue identified differential expression of over a thousand genes, whereas expression levels of several genes known to respond to Tbx5 insufficiency did not change. Epigenetic profiling revealed shifts in sites associated with acetylated H3K27 as well as in chrom atin accessibility in Tbx5G125R/+ atrial cardiomyocytes indicating Tbx5-G125R has altered DNA binding and TF interaction properties.

ORGANISM(S): Mus musculus

PROVIDER: GSE167081 | GEO | 2022/02/07

REPOSITORIES: GEO

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Project description:Rationale: The most significantly associated atrial fibrillation (AF) risk loci in humans map to a noncoding gene desert upstream of the evolutionarily conserved left-right (LR) transcription factor Pitx2, a master regulator of LR asymmetric organ development. Pitx2 dosage is fundamentally linked to the development of sinus node dysfunction (SND) and AF, the most common cardiac arrhythmia affecting adults, but the mechanistic basis for this remains obscure. We identified a conserved long noncoding RNA (lncRNA), Playrr, which is exclusively transcribed on the embryo’s right side, opposite to Pitx2 on the left, that participates in mutually antagonistic transcriptional regulation with Pitx2. Objective: The objective of this study was to investigate a role of Playrr in regulating Pitx2 transcription and protecting against the development of cardiac rhythm disturbances. Methods and Results: Playrr expression in the developing heart was analyzed with RNA in situ hybridization. Playrr was expressed asymmetrically (on the right) to Pitx2 (on the left) in developing mouse embryos, including in mouse embryonic sinoatrial node cells. We utilized CRISPR/Cas9 genome editing in mice to target Playrr, generating mice lacking Playrr RNA transcript (PlayrrEx1sj allele). Using qRT-PCR we detected upregulation of the cardiac isoform, Pitx2c, during visceral organ morphogenesis in PlayrrEx1sj mutant embryos. Surface ECG (AliveCor®) and 24-hour telemetry ECG detected bradycardia and irregular interbeat (R-R) intervals suggestive of SND in PlayrrEx1sj mutant adults. Programmed stimulation of PlayrrEx1sj mutant adults resulted in pacing-induced AF. Within the right atrium of PlayrrEx1sj mutant hearts, Masson’s trichrome stain revealed increased collagen deposition indicative of fibrosis, and immunofluorescence demonstrated mis-localization of Connexin 43 in atrial cardiomyocytes. These findings suggested an altered atrial substrate in PlayrrEx1sj adult mice. Finally, transcriptomic analysis by chromatin run-on and sequencing (ChRO-seq) in atria of PlayrrEx1sj mutant mice compared to wild type controls revealed differential expression of genes involved in cell-cell adhesion and motility, fibrosis, and dysregulation of the key cardiac genes Tbx5 and Hcn1. Conclusions: Adult mice lacking functional Playrr lncRNA transcript have baseline bradyarrhythmia and increased susceptibility to AF. These cardiac phenotypes are similar to those observed in Pitx2 heterozygous mice. Interactions between Pitx2 and Playrr may provide a genetic mechanism for modulating Pitx2 dosage and susceptibility to SND and AF.

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TBX5 G125R induces profound transcriptional deregulation and atrial dysfunction in vivo [CUT&RUN]

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