Cardiomyocyte-Specific Ablation of Med1 Subunit of the Mediator Complex Causes Lethal Dilated Cardiomyopathy in Mice

Abstract

Mediator, an evolutionarily conserved multi-protein complex consisting of about 30 subunits, is a key component of the polymerase II mediated gene transcription. Germline deletion of the Mediator subunit 1 (Med1) of the Mediator in mice results in mid-gestational embryonic lethality with developmental impairment of multiple organs including heart. Here we show that cardiomyocyte-specific deletion of Med1 in mice (csMed1-/-) during late gestational and early postnatal development by intercrossing Med1fl/fl mice to α-MyHC-Cre transgenic mice results in lethality within 10 days after weaning due to dilated cardiomyopathy-related ventricular dilation and heart failure. The csMed1-/- mouse heart manifests mitochondrial damage, increased apoptosis and interstitial fibrosis. Global gene expression analysis revealed that loss of Med1 in heart down-regulates more than 200 genes including Acadm, Cacna1s, Atp2a2, Ryr2, Pde1c, Pln, PGC1α, and PGC1β that are critical for calcium signaling, cardiac muscle contraction, arrhythmogenic right ventricular cardiomyopathy, dilated cardiomyopathy and peroxisome proliferator-activated receptor regulated energy metabolism. Many genes essential for oxidative phosphorylation and proper mitochondrial function such as genes coding for the succinate dehydrogenase subunits of the mitochondrial complex II are also down-regulated in csMed1-/- heart contributing to myocardial injury. Data also showed up-regulation of about 180 genes including Tgfb2, Ace, Atf3, Ctgf, Angpt14, Col9a2, Wisp2, Nppa, Nppb, and Actn1 that are linked to cardiac muscle contraction, cardiac hypertrophy, cardiac fibrosis and myocardial injury. Furthermore, we demonstrate that cardiac specific deletion of Med1 in adult mice using tamoxifen-inducible Cre approach (TmcsMed1-/-), results in rapid development of cardiomyopathy and death within 4 weeks. We found that the key findings of the csMed1-/- studies described above are highly reproducible in TmcsMed1-/- mouse heart. Collectively, these observations suggest that Med1 plays a critical role in the maintenance of heart function impacting on multiple metabolic, compensatory and reparative pathways with a likely therapeutic potential in the management of heart failure.

Ectopic expression of Cdk8 induces eccentric hypertrophy and heart failure

“…As Mediator function is closely associated with energy utilization and homeostasis (22,24,(39)(40)(41), it is not entirely unexpected that overexpression of Cdk8 results in a large enrichment of downregulated mitochondrial-based metabolic genes and pathways (Figures 6 and 7). In fact, we see considerable overlap between the RNA-seq results presented here (885 of 1,160 genes expressed >1.5-fold, r 2 = 0.61) and those from cardiac deletion of the core Mediator subunit Med1 (Med1cKO) that we recently reported (24).…”

MED12 regulates a transcriptional network of calcium-handling genes in the heart

“…It was recently reported by two independent groups that cardiac-specific deletion of Med1 leads to severe DCM and premature death in mice. Although many calcium-handling genes were downregulated in the Med1 -/-heart, they were measured after the onset of DCM, which has been associated with decreased calcium-handling gene expression, as discussed above (49,50).…”

Mediator 1 Is Atherosclerosis Protective by Regulating Macrophage Polarization

“…15 In addition, cardiomyocyte-specific ablation of MED1 in mice results in lethality due to dilated cardiomyopathy-related ventricular dilation and heart failure, suggesting that MED1 may play a role in cardiovascular diseases. 16 Overall, MED1 may have pivotal but distinct roles in various pathophysiological states depending on the tissue.…”