Impacts of transcription elongation on cardiac gene regulation during homeostasis and regeneration

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Project Summary Heart failure is a major cause of death in the US, contributing significantly to the burden of the healthcare system every year. Despite the heterogeneity of the causes of heart failure, the heart undergoes gene expression changes during failure resulting in structural and functional defects. Our long-term goal is to understand the transcriptional regulatory mechanisms that sustain the structure and function of the heart in homeostasis and that can induce cardiac protective effects or promote cardiac repair upon injury. In this application, we will use the transcription regulator Rtf1 as a point of entry to address this critical question in cardiac biology. Critical roles for transcription elongation in cellular RNA biogenesis have gained increasing attention in recent years, but how they contribute to the maintenance of cardiac homeostasis and how modulating transcription elongation might promote cardiac repair in damaged hearts remain elusive. Using both zebrafish and mouse genetics, we have previously shown that Rtf1 activity is essential for myocardial development. Rtf1 depletion destabilizes promoter-proximal pausing of RNA Pol II, blocks activation of the myocardial gene program and prevents myocardial progenitor cell formation resulting in a heartless embryo. In preliminary data leading to this proposal, we have found that Rtf1 plays important roles in normal and stressed adult hearts. Ablation of Rtf1 activity in adult cardiomyocytes leads to rapid heart failure with dysregulated cardiac gene expression and a loss of contractility. In stressed hearts, we observed elevated Rtf1 expression within cardiomyocytes after injury, suggesting a role for Rtf1 in the cardiac stress response. Overexpression of Rtf1 also promotes cardiomyocyte proliferation in a zebrafish ventricular resection model. The dysregulated cardiac gene expression and reduction of epigenetic marks of active transcription in Rtf1-deficient failing hearts suggest that Rtf1 functions as a key transcriptional regulator for cardiomyocytes. These findings lead to our central hypothesis that Rtf1 modulates transcriptional pausing and co-transcriptional histone modification to facilitate efficient mRNA synthesis in cardiomyocytes and thereby sustains cardiac structure and function in normal and stressed hearts. We have delineated three Aims to interrogate this hypothesis. Specifically, we will investigate Rtf1-dependent gene expression in cardiomyocytes and decipher the progressive molecular, cellular, physiological and metabolomic changes occurring during heart failure (Aim 1). We will use an array of molecular approaches to uncover the molecular basis by which Rtf1 impacts the transcriptome in cardiomyocytes (Aim 2). We will also investigate how Rtf1 responds to cardiac damage and the potential of manipulating Rtf1 activity to promote cardiac repair (Aim 3). Accomplishing these aims will not only provide significant new insights into the regulatory network of cardiac gene expression but also a possible therapeutic target to promote cardiac health and post-injury repair.