An epigenetic circuit linking oxidative stress and DNA hydroxymethylation in heart failure

Background

Heart failure is a major cause of morbidity and mortality worldwide, but the underlying molecular mechanisms remain not well defined. Reactive oxygen species (ROS) in heart failure (HF) alter multitudes of mitochondrial enzymes and metabolites, such as α-ketoglutarate and its oxidised form L-2-hydroxyglutarate (L-2HG). These metabolites are cofactors for ten eleven translocation (TET) enzymes that convert DNA's 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC).

Aim

We hypothesize that oxidative stress during heart failure alters mitochondrial function through epigenetic remodeling, and that reduction of oxidative stress will improve cardiac function.

Methods and results

Targeted LC-MS/MS analysis of dilated cardiomyopathy (DCM) hearts obtained from MLP−/− and WT littermate controls showed a significant increase in the oxidized metabolite L-2HG (∼30%, p=0.004), with significant reduction of multiple TCA cycle intermediates. RNA sequencing revealed a significant reduction in mRNA levels of IDH2 in human TTN related DCM and MLP−/− HF mice. The altered activity of IDH2 contributes to ROS production in these hearts and to the production of L-2HG. No alteration in the mitochondria structures was observed. HF biopsies show decreased TET activity most likely due to increased L-2HG levels. Whole genome single base pair 5mC and 5hmC deep sequencing of gDNA from explanted human DCM heart biopsies and MLP−/− mouse model revealed significantly altered global distribution of both 5mC and 5hmC in comparison to control samples. Genes involved in hypertrophy, such as Myh7 and Fhl2 were among the top genes with differential 5mC levels. Global loss of 5hmC level was observed, especially in the intronic regions of genes involved in redox hemostasis. Reducing oxidative stress in vivo in MLP−/− using a small molecule (AZ14117925) improves heart function (EF) by 13% [EF=(Treated:47,44%, Placebo: 34,54%), n=5 (males per group), p=0.0373, unpaired t-test]. Additional bioinformatic analysis revealed that reduction of ROS most likely leads to activation of TET and activation of pro-survival pathways, anti-oxidative stress response, and significantly less activation of apoptotic pathways.

Conclusion

Alterations in TCA cycle metabolites may underlie changes in DNA methylation and gene expression in end-stage human DCM and mouse models and indicate a role for epigenetic regulation of mitochondrial function in HF. NRF2 activation may pose a novel therapeutic approach to treat this devastating disease.

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): AstraZeneca

P5435Epigenetic modifications and gene expressions in Mybpc3 knockout mice

Background

DNA methylation and hydroxymethylation plays critical role in important biological processes, including differentiation of tissues in the embryo and cellular response to different diseases and diverse environmental factors. The epigenetic landscape in heart failure might be altered.

Purpose

Our objective was to determine how Mybpc3 deficiency, which produces hypertrophic cardiomyopathy, affects epigenetic landscape, gene expression, and regulation.

Methods

We generated and analysed genome-wide DNA methylomes and hydroxymethylomes from cardiac tissues of 12-week old Mybpc3−/− mice and littermate controls, and performed whole genome RNA sequencing (RNA-seq) for gene expression and validated the findings using qPCR.

Results

Single base resolution revealed overall lower 5-mC level in Mybpc3 deficient mice. In deficient mice, different genic regions including transcription start site, exons, and introns, had low levels of 5-mC. Although there was no overall difference in 5-hmC content, knockout mice had lower levels of 5-hmC in the distal part of the genes (last exon, transcription termination site, and 3'-flanking regions). The 5-hmC enrichment in the intronic regions was associated with higher gene expression, whereas, the presence of 5-mC in the 5'-flanking regions was associated with lower gene expression in both knockout and wildtype mice. Ingenuity pathway analysis (IPA) of differentially expressed genes revealed overrepresentation of genes involved in axonal-guidance pathway. Tet activity was downregulated in Mybpc3−/− mice, and it may explain the overall difference of 5-mC in deficient mice. We also observed that Mybpc3 ablation affected alternative splicing of Myh6 and Myh7.

Conclusion

This study establishes that knocking out of Mybpc3 changes epigenetic landscape in cardiac tissue, which is tightly linked to gene expression and regulation.

Acknowledgement/Funding

LeDucq 13CVD04, Hjärt och Lungfonden (Sweden)

[The ethmoido-maxillary plate and paranasal sinuses--a study by HRCT]

The ethmoido-maxillary plate is a thin layer of bone separating the maxillary sinus from the ethmoidal cells or sphenoidal sinus. The plate was studied using axial HRCT images obtained from various otological lesions. One hundred forty-one adults were included in this study. The ethmoido-maxillary plate was first classified into four groups of configurations, namely, straight or near-straight, anterior-concave, posterior-concave and ant. and post. concave forms. The incidences of these forms were 55%, 23%, 13%, and 9%, respectively. A symmetrical configuration between the two sides was seen in 50%. The numbers of ethmoidal cells and/or sphenoidal sinus in contact with the plate and their incidences were 2 cells (47%), 3 cells (30%), 1 cell (15%), 4 cells (5%), and 5 cells (1%). The straight form showed lower numbers of cells than the other forms. The sphenoidal sinus and the maxillary sinus were in direct contact with each other at the ethmoido-maxillary plate in 19% of cases.