Targeting Mediator Kinase Attenuates Cardiac Hypertrophy by Regulating Enhancer Utilization

Background Cardiac hypertrophy is characterized by extensive transcriptional remodeling that contributes to the progression of heart failure. Preclinical models demonstrate that therapies targeting hypertrophic responses can mitigate disease severity. Recent evidence shows that failing human and murine hearts exhibit elevated mediator kinase expression, sufficient to drive eccentric hypertrophy and heart failure through activation of hypertrophic gene programs. Mediator kinase inhibition suppresses oncogenic transcription by altering enhancer utilization, suggesting similar mechanisms may attenuate pathological remodeling in the heart. This study investigates whether mediator kinase inhibition can blunt cardiomyocyte hypertrophy, offering a potential therapeutic strategy for heart failure. Methods Two structurally unrelated mediator kinase inhibitors, Senexin A (SxnA) and CCT251545, were tested in neonatal rat cardiomyocytes. Hypertrophy was assessed by cell size measurements, RNA sequencing, and H3K27ac chromatin immunoprecipitation sequencing. Results Mediator kinase inhibition significantly reduced hypertrophic growth, attenuating cell size increases induced by phenylephrine (PE) and endothelin‐1. Transcriptomic profiling revealed a dose‐dependent suppression of PE‐induced differentially expressed genes in Senexin A‐treated cells. Mechanistically, PE stimulation enhanced RNA polymerase II pause release, whereas Mediator kinase inhibition did not alter this process. Epigenomic analysis showed that PE markedly increased the number of super‐enhancers relative to vehicle treatment, while co‐treatment with Senexin A reduced the total number of active enhancers. Nearest‐neighbor analysis linked putative regulatory enhancers to key PE‐responsive genes, and these enhancer signatures were blunted by SxnA. Conclusions These findings demonstrate that Mediator kinase inhibition counteracts hypertrophic growth and transcriptional reprogramming, highlighting its potential as a therapeutic strategy to modulate pathological gene regulation in cardiac hypertrophy.