Atherosclerosis: cell biology and lipoproteins--panoramic views of DNA methylation landscapes of atherosclerosis

Improving myocardial fractional flow reserve in coronary atherosclerosis via CX37 gene silence: a preclinical validation study in pigs

OBJECTIVES

The purpose of this study was to evaluate the effect of CX37 gene silence on myocardial fractional flow reserve (FFR).

METHODS

A total of 90 male pigs were randomly divided into saline, mock and 3 different doses (5, 10 and 20 µl) of CX37 viral suspension groups that could induce coronary plaque formation with high-fat diet. After performing myocardial FFR by intravascular ultrasound, different doses of CX37 viral suspension, saline and mock small interfering RNA (siRNA) were transfected into the related coronary. The FFR, the myocardial enzymes and the cardiac structures and functions of the pigs were detected at baseline, 4th, 8th and 12th week after transfection, respectively.

RESULTS

Repeated measures analysis of variance comparison showed that the difference in the FFR among the 5 groups was statistically significant (F = 27.0, P < 0.01). Post hoc analysis showed that FFR were highest in the siRNA CX37 group (20 µl), followed by the siRNA CX37 group (10 µl) and the siRNA CX37 group (5 µl), and lowest in the mock and saline groups. Left ventricular end-diastolic diameter was significantly smaller and ejection fraction was obviously higher in the 3 siRNA CX37 groups compared with the untreated groups.

CONCLUSIONS

Our study showed that FFR levels increased along with decreased doses of siRNA CX37 lentivirus, indicating that siRNA CX37 lentivirus may reduce the risk of coronary atherosclerosis and provide a potential approach to treat coronary heart disease.

Epigenetics of the failing heart

With the impressive advancement in high-throughput 'omics' technologies over the past two decades, epigenetic mechanisms have emerged as the regulatory interface between the genome and environmental factors. These mechanisms include DNA methylation, histone modifications, ATP-dependent chromatin remodeling and RNA-based mechanisms. Their highly interdependent and coordinated action modulates the chromatin structure controlling access of the transcription machinery and thereby regulating expression of target genes. Given the rather limited proliferative capability of human cardiomyocytes, epigenetic regulation appears to play a particularly important role in the myocardium. The highly dynamic nature of the epigenome allows the heart to adapt to environmental challenges and to respond quickly and properly to cardiac stress. It is now becoming evident that histone-modifying and chromatin-remodeling enzymes as well as numerous non-coding RNAs play critical roles in cardiac development and function, while their dysregulation contributes to the onset and development of pathological cardiac remodeling culminating in HF. This review focuses on up-to-date knowledge about the epigenetic mechanisms and highlights their emerging role in the healthy and failing heart. Uncovering the determinants of epigenetic regulation holds great promise to accelerate the development of successful new diagnostic and therapeutic strategies in human cardiac disease.

Reduction of connexin 37 expression by RNA interference decreases atherosclerotic plaque formation

The aim of this study was to examine the effects of connexin 37 (Cx37) interference on atherosclerotic plaques. Lentiviruses expressing small interfering RNA (siRNA) of Cx37 were constructed, and were shown to significantly knockdown the mRNA and protein expression of Cx37 in vitro. Sixty pigs on a high‑fat diet were randomly divided into three treatment groups of saline, mock or Cx37 siRNA, to induce plaque formation. The Cx37 lentiviral suspension was transfected into the abdominal aortic plaques of pigs. Plaque characteristics were detected by intravascular ultrasound and the expression of Cx37 mRNA was detected by semi‑quantitative polymerase chain reaction. The expression of Cx37 protein was analyzed by western blot analysis. Two months after lentivirus transfection, Cx37 mRNA levels were decreased by 38% in the Cx37 siRNA group, by 60% in the mock‑siRNA group and by 63% in the saline group (P<0.05). The mock group showed no significant changes in Cx37 expression as compared with the saline group. Cx37 protein expression was lower in the Cx37 siRNA‑treated group as compared with the other groups (0.21±0.07 vs. 0.65±0.06 vs. 0.54±0.07). The percentage of plaque necrosis at 10 months (two months following RNAi) was decreased in the Cx37 siRNA group as compared with that at eight months, prior to RNAi (5.26±2.11 vs. 7.83±1.03%, P<0.05). In the mock‑siRNA and saline groups, no differences (P=0.074, 0.061, respectively) were observed. In the Cx37 siRNA group, plaque volumes following 10 months decreased relative to those following eight months, prior to RNAi (21.03±6.24 vs. 31.23±10.23, P<0.01). By contrast, in the mock siRNA and saline groups, plaque volumes after 10 months were increased relative to those following eight months (38.54±13.56 vs. 32.12±11.21 mm3, 37.36±14.21 vs. 30.21±12.02 mm3, P=0.031, P=0.027). Atherosclerotic plaque formation was effectively decreased through the downregulation of Cx37 mRNA using Cx37 siRNA.

Integrated analysis of microarray data of atherosclerotic plaques: modulation of the ubiquitin-proteasome system

Atherosclerosis is a typical complex multi-factorial disease and many molecules at different levels and pathways were involved in its development. Some studies have investigated the dysregulation in atherosclerosis at mRNA, miRNA or DNA methylation level, respectively. However, to our knowledge, the studies that integrated these data and revealed the abnormal networks of atherosclerosis have not been reported. Using microarray technology, we analyzed the omics data in atherosclerosis at mRNA, miRNA and DNA methylation levels. Our results demonstrated that the global DNA methylation and expression of miRNA/mRNA were significantly decreased in atherosclerotic plaque than in normal vascular tissue. The interaction network constructed using the integrative data revealed many genes, cellular processes and signaling pathways which were widely considered to play crucial roles in atherosclerosis and also revealed some genes, miRNAs or signaling pathways which have not been investigated in atherosclerosis until now (e.g. miR-519d and SNTB2). Moreover, the overall protein ubiquitination in atherosclerotic plaque was significantly increased. The proteasome activity was increased early but decreased in advanced atherosclerosis. Our study revealed many classic and novel genes and miRNAs involved in atherosclerosis and indicated the effects of ubiquitin-proteasome system on atherosclerosis might be closely related to the course of atherosclerosis. However, the efficacy of proteasome inhibitors in the treatment of atherosclerosis still needs more research.

Unraveling the DNA methylome of atherosclerosis

PURPOSE OF REVIEW

Epigenetic mechanisms of transcriptional regulation in atherosclerosis have gained an increasing interest in recent years. We focus on the relevance of DNA methylation, a well characterized epigenetic modification of the genome, as a biomarker and underlying mechanism of atherosclerosis.

RECENT FINDINGS

A growing number of loci have been identified, which are good candidate biomarkers for atherosclerosis and provide novel insights into the molecular changes taking place in the diseased vessel. Understanding the global change in DNA methylation during atherosclerosis remains a challenge. Novel unfolding research avenues include the interplay between genetic variants and DNA methylation patterns, and the role of long noncoding RNAs as epigenetic regulators.

SUMMARY

Epigenetics continues to represent a promising area of research in atherosclerosis. The full exploitation of cutting edge epigenomics will be decisive to define whether epigenetics will contribute to lower the burden of cardiovascular diseases.