Transcription factor CREM mediates high glucose response in cardiomyocytes and in a male mouse model of prolonged hyperglycemia

This study aims at investigating the epigenetic landscape of cardiomyocytes exposed to long elevated glucose levels in vitro and in vivo Exposure of mouse HL-1 and rat differentiated H9C2 cardiomyocyte cell lines to high glucose (30 mM) for 72 hours determined some epigenetic changes including upregulation of class I and III HDAC protein levels and activity, inhibition of histone acetylase p300 activity, increase in histone H3 lysine (K) 27 trimethylation (H3K27me3) and reduction in H3K9 acetylation (H3K9Ac). Gene expression analysis focused on cardiotoxicity, revealed that high glucose induced markers associated with tissue damage, fibrosis and cardiac remodelling such as Nexilin, Versican, CREM and ADRA2. Notably, the transcription factor CREM was found to be important in the regulation of cardiotoxicity-associated genes as assessed by specific siRNA and chromatin immunoprecipitation experiments. In CD1 mice, made hyperglycaemic by STZ injection, cardiac structural alterations were evident at six months after STZ treatment and were associated with a significant increase of H3K27me3 and reduction of H3K9Ac. Consistently, Nexilin, CREM and ADRA2 expression was significantly induced at RNA and protein level. Confocal microscopy analysis of Nexilin localization showed this protein irregularly distributed along the sarcomeres in the heart of hyperglycaemic mice. This evidence suggested for a structural alteration of cardiac Z-disk with potential consequences on contractility. In conclusion, high glucose may alter the epigenetic landscape of cardiac cells. Sildenafil, restoring cGMP levels, counteracted the increase of CREM and Nexilin providing a protective effect in the presence of hyperglycemia.