Differential regulation of DNA methylation versus histone acetylation in cardiomyocytes during HHcy in vitro and in vivo: an epigenetic mechanism.

The mechanisms of homocysteine-mediated cardiac threats are poorly understood. Homocysteine, being the precursor to S-adenosyl methionine (a methyl donor) through methionine, is indirectly involved in methylation phenomena for DNA, RNA, and protein. We reported previously that cardiac-specific deletion of N-methyl-d-aspartate receptor-1 (NMDAR1) ameliorates homocysteine-posed cardiac threats, and in this study, we aim to explore the role of NMDAR1 in epigenetic mechanisms of heart failure, using cardiomyocytes during hyperhomocysteinemia (HHcy). High homocysteine levels activate NMDAR1, which consequently leads to abnormal DNA methylation vs. histone acetylation through modulation of DNA methyltransferase 1 (DNMT1), HDAC1, miRNAs, and MMP9 in cardiomyocytes. HL-1 cardiomyocytes cultured in Claycomb media were treated with 100 μM homocysteine in a dose-dependent manner. NMDAR1 antagonist (MK801) was added in the absence and presence of homocysteine at 10 μM in a dose-dependent manner. The expression of DNMT1, histone deacetylase 1 (HDAC1), NMDAR1, microRNA (miR)-133a, and miR-499 was assessed by real-time PCR as well as Western blotting. Methylation and acetylation levels were determined by checking 5'-methylcytosine DNA methylation and chromatin immunoprecipitation. Hyperhomocysteinemic mouse models (CBS+/-) were used to confirm the results in vivo. In HHcy, the expression of NMDAR1, DNMT1, and matrix metalloproteinase 9 increased with increase in H3K9 acetylation, while HDAC1, miR-133a, and miR-499 decreased in cardiomyocytes. Similar results were obtained in heart tissue of CBS+/- mouse. High homocysteine levels instigate cardiovascular remodeling through NMDAR1, miR-133a, miR-499, and DNMT1. A decrease in HDAC1 and an increase in H3K9 acetylation and DNA methylation are suggestive of chromatin remodeling in HHcy.