Abstract 19553: Med12 is a Transcriptional “Mediator” of Cardiac Contractile Function
Introduction: The Mediator complex regulates gene transcription by linking the basal transcriptional machinery with DNA bound transcription factors. The activity of the Mediator complex is modulated by a kinase submodule comprised of 4 proteins, including MED12. Although ubiquitously expressed, studies suggest that these proteins differentially regulate gene expression in a tissue-specific manner. MED12 regulates development in a variety of cell types through the regulation of different gene programs. Consequently, MED12 null mice are embryonically lethal, however the function of MED12 in the heart is not yet known.
Hypothesis: We tested the hypothesis that MED12 is required for normal cardiac function.
Methods: Mice harboring conditional cardiac-specific deletion of MED12 (cKO) were generated. We performed serial echocardiography on male cKO mice and controls through 12 weeks of age. RNAseq was performed on P1 ventricles, and calcium transients were measured using fluo-4 AM in P1 cardiomyocytes (CM). Chromatin immunoprecipitation (ChIP) experiments were performed in CMs using a MED12 antibody.
Results: Fractional shortening was significantly decreased in male cKO mice compared to controls at 1 week (42.3 ± 3.1 vs. 59.4 ± 4.2, n=10), and 12 weeks (33.6 ± 5.6 vs. 56.7 ± 6.1, n=10). Downregulation of calcium handling genes by at least 2-fold in cKO ventricles was determined by RNAseq (n=3), and include SERCA2a, phospholamban (PLN), ryanodine receptor 2 (RyR2), and multiple calcium channel and gap junction genes (including Kcnn1 and Gja1). The Ca2+ transient amplitude was increased in cKO CMs (1.97 ± 0.05 vs. 1.42 ± 0.07, n=15), and cKO CMs displayed faster Ca2+ decay rates (0.19 ± 0.009 vs. 0.39 ± 0.06, n=15). Finally, ChIP experiments demonstrated that MED12 interacts with promoters of SERCA2a, PLN, Kcnn1 and Gja1.
Conclusions: MED12 governs the transcriptional network of calcium handling genes in the heart and is required to maintain normal cardiac function and calcium homeostasis. Dysregulation of calcium cycling not only alters cardiac contractility, but also contributes to development of pathological cardiac hypertrophy and heart failure. Thus activation of MED12 may restore cardiac calcium homeostasis in the setting of cardiovascular disease.
Author Disclosures: K.K. Baskin: None. S. DeLeon: None. C. Makarewich: None. R. Bassel-Duby: None. E.N. Olson: None.
- © 2016 by American Heart Association, Inc.