Remodeling is at the heart of chromatin: the heartaches of chromatin

Genomics and Epigenomics of Congenital Heart Defects: Expert Review and Lessons Learned in Africa

Congenital heart defects (CHD) are structural malformations found at birth with a prevalence of 1%. The clinical trajectory of CHD is highly variable and thus in need of robust diagnostics and therapeutics. Major surgical interventions are often required for most CHDs. In Africa, despite advances in life sciences infrastructure and improving education of medical scholars, the limited clinical data suggest that CHD detection and correction are still not at par with the rest of the world. But the toll and genetics of CHDs in Africa has seldom been systematically investigated. We present an expert review on CHD with lessons learned on Africa. We found variable CHD phenotype prevalence in Africa across countries and populations. There are important gaps and paucity in genomic studies of CHD in African populations. Among the available genomic studies, the key findings in Africa were variants in GATA4 (P193H), MTHFR 677TT, and MTHFR 1298CC that were associated with atrial septal defect, ventricular septal defect (VSD), Tetralogy of Fallot (TOF), and patent ductus arteriosus phenotypes and 22q.11 deletion, which is associated with TOF. There were no data on epigenomic association of CHD in Africa, however, other studies have shown an altered expression of miR-421 and miR-1233-3p to be associated with TOF and hypermethylation of CpG islands in the promoter of SCO2 gene also been associated with TOF and VSD in children with non-syndromic CHD. These findings signal the urgent need to develop and implement genetic and genomic research on CHD to identify the hereditary and genome-environment interactions contributing to CHD. These projected studies would also offer comparisons on CHD pathophysiology between African and other populations worldwide. Genomic research on CHD in Africa should be developed in parallel with next generation technology policy research and responsible innovation frameworks that examine the social and political factors that shape the emergence and societal embedding of new technologies.

SWI/SNF chromatin remodeling enzymes are associated with cardiac hypertrophy in a genetic rat model of hypertension

Pathological cardiac hypertrophy is characterized by a sustained increase in cardiomyocyte size and re-activation of the fetal cardiac gene program. Previous studies implicated SWI/SNF chromatin remodeling enzymes as regulators of the fetal cardiac gene program in surgical models of cardiac hypertrophy. Although hypertension is a common risk factor for developing cardiac hypertrophy, there has not yet been any investigation into the role of SWI/SNF enzymes in cardiac hypertrophy using genetic models of hypertension. In this study, we tested the hypothesis that components of the SWI/SNF complex are activated and recruited to promoters that regulate the fetal cardiac gene program in hearts that become hypertrophic as a result of salt induced hypertension. Utilizing the Dahl salt-sensitive (S) rat model, we found that the protein levels of several SWI/SNF subunits required for heart development, Brg1, Baf180, and Baf60c, are elevated in hypertrophic hearts from S rats fed a high salt diet compared with normotensive hearts from Dahl salt-resistant (R) rats fed the same diet. Furthermore, we detected significantly higher levels of SWI/SNF subunit enrichment as well as evidence of more accessible chromatin structure on two fetal cardiac gene promoters in hearts from S rats compared with R rats. Our data implicate SWI/SNF chromatin remodeling enzymes as regulators of gene expression in cardiac hypertrophy resulting from salt induced hypertension. Thus we provide novel insights into the epigenetic mechanisms by which salt induced hypertension leads to cardiac hypertrophy.

Glycemic memories and the epigenetic component of diabetic nephropathy

A strong case for the deregulation of epigenetic chromatin modifications in the development and progression of various chronic complications of diabetes has emerged from recent experimental observations. Clinical trials of type 1 and type 2 diabetes patients highlight the importance of early and intensive treatment and the prolonged damage of hyperglycemia on organs such as the kidney. The functional relationship between the regulation of chromatin architecture and persistent gene expression changes conferred by prior hyperglycemia represents an important avenue of investigation for explaining diabetic nephropathy. While several studies implicate epigenetic changes at the chromatin template in the deregulated gene expression associated with diabetic nephropathy, the molecular determinants of metabolic memory in renal cells remain poorly understood. There is now strong evidence from experimental animals and cell culture of persistent glucose-driven changes in vascular endothelial gene expression that may also have relevance for the microvasculature of the kidney. Exploration of epigenetic mechanisms underlying the hyperglycemic cue mediating persistent transcriptional changes in renal cells holds novel therapeutic potential for diabetic nephropathy.

From cell phenotype to epigenetic mechanisms: new insights into regenerating myocardium

The self-regenerating property of the adult myocardium is not a new discovery. Even though we could not confirm that the adult myocardium is a post-mitotic tissue, we should consider that its plasticity is extremely low. Studies are still in progress to decipher the mechanisms underlying the abovementioned potential fetal features of the adult heart. The modest results of several clinical trials based on the transplantation of millions of autologous stem cells into the dysfunctional heart have confirmed that the cross-talk of different signals, such as the microenvironment, promotes the regeneration of adult myocardium. Recent scientific evidence has revealed that cellular cross-talk does not depend on the action of a single cell phenotype. It is conceivable that the limited turnover of cardiomyocytes is ensured by the interplay of adult cardiac cells in response to environmental changes. The epigenetic state of a cell serves as a dynamic interface between the environment and phenotype. The epigenetic modulation of the adult cardiac cells by natural active compounds encourages further studies to improve myocardial plasticity. In this review, we will highlight the most relevant studies demonstrating the epigenetic modulation of myocardial regeneration without the use of stem cell transplantation.