My recent study identified Serum response factor (SRF), an obligatory cardiogenic transcription factor, as a prominent caspase-3 target in human failing hearts. SRF cleavage led to the generation of a dominant negative inhibitor, SRF-N (N-terminus of SRF). This novel discovery is provocative, and raises the question of potential pathogenic role of SRF-N in cardiac dysfunction. To address this question, I generated multiple independent lines of transgenic mice that expressed SRF-N specifically in the heart. Mice with high expression level of SRF-N developed a dilated, hypertrophic cardiomyopathy and eventually died of heart failure. This provides a mouse model that mimics the progression of human heart disease. Microarray and quantitative PCR (Q-PCR) analyses revealed a significant downregulation of miR-133a and miR-1 in the SRF-N transgenic hearts, which coincided with overt upregulation of Mef2a, CaM and NFATc4. Together with recent discovery of RhoA and Cdc42 as miR-133a targets, we believe that the dysregulation of miR-133a and miR-1 and the consequent upregulation of a group of hypertrophy-associated genes may constitute one of the potential mechanisms contributing to SRF-N-mediated cardiomyopathy. These preliminary results underpin the application's central hypothesis that the dominant negative SRF-N directs the onset of cardiomyopathy and facilitates the progression to overt heart failure through the downregulation of miR-133a and miR-1 gene.
Three aims are proposed.
Aim I is to characterize the transgenic mouse phenotype. The transgenic mice will be assessed by comprehensive studies including functional, morphological and molecular assessments.
Aim II and III are to elucidate the molecular mechanism of SRF-N-mediated cardiomyopathy. Dysregulation of the two cardiac microRNAs will be assessed. A group of miR-133a and miR-1 regulated target genes will be evaluated. Two new enhancers directed for miR-133a expression and one new target for miR-133a will be verified. Rescue experiments will be conducted to test if the introduction of miR-133a and -1 could correct/rescue the murine heart phenotype. The ultimate outcome of the application will be to establish a direct link between the dominant negative SRF-N and the development of heart failure. The novelty includes 1) the demonstration of SRF-N-mediated cardiomyopathy in intact heart;2) the identification of two SRF-dependent enhancers regulating miR-133a expression;and 3) the elucidation of the molecular mechanism directing disease progression.
The study is focused on the mechanistic view of dominant negative cardiogenic transcription factor SRF-N (N-terminus of serum response factor) in propelling heart failure.
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