Expression Profile of Circular RNAs in Epicardial Adipose Tissue in Heart Failure
Circular RNAs (circRNAs) are a novel class of non-coding RNAs characterized by their covalently closed loop structure, which distinguishes them from linear RNAs. These molecules have garnered significant attention due to their roles in gene regulation and their involvement in various physiological and pathological processes. Recent studies have explored circRNA expression profiles across different tissue types, yet the expression patterns of circRNAs in human epicardial adipose tissue (EAT) remain largely undefined. This study aimed to compare circRNA expression profiles in EAT between patients with heart failure (HF) and those without HF, shedding light on the potential roles of circRNAs in the pathogenesis of HF.
Epicardial adipose tissue, a type of visceral fat surrounding the heart, has emerged as a critical player in cardiovascular health. EAT is known to secrete various bioactive molecules, including adipokines, cytokines, and micro-particles carrying proteins, lipids, and RNAs. These secretions exert both vasocrine and paracrine effects on the myocardium, influencing heart function. Given the established correlation between EAT and HF, independent of metabolic status or coronary artery disease (CAD), understanding the molecular mechanisms underlying this relationship is of paramount importance. This study sought to fill this gap by examining circRNA expression patterns in EAT from patients with CAD, comparing those with and without HF.
The study enrolled ten patients with CAD undergoing coronary artery bypass grafting, divided into HF and non-HF groups (n=5 each). HF was defined based on elevated brain natriuretic peptide (BNP) levels (>500 ng/L) and abnormal echocardiographic findings, including increased left ventricular end-diastolic diameter (LVEDD) and reduced left ventricular ejection fraction (LVEF). The non-HF group comprised individuals with normal BNP levels (<100 ng/L) and echocardiograms. RNA sequencing was performed on ribosomal-depleted total RNAs extracted from EAT specimens, followed by quantitative real-time polymerase chain reaction (qRT-PCR) for validation of selected circRNAs.
RNA sequencing revealed a total of 2278 circRNAs in the EAT of the ten patients with CAD. The lengths of these circRNAs predominantly ranged within 2000 nucleotides (nt), with an average of three exons per circRNA. Notably, 9.3% of the circRNAs were single-exon, while 2.8% spanned at least ten exons. The circRNA hsa_circ_0087255, with 21 exons, was the longest identified. The majority of circRNAs (90.0%) had average read counts of less than 10, while a small fraction (0.5%) exhibited read counts exceeding 50, indicating high expression levels in human EAT. These highly expressed circRNAs corresponded to genes such as GSE1, RHOBTB3, HIPK3, UBXN7, PCMTD1, N4BP2L2, CFLAR, EPB41L2, FCHO2, FNDC3B, and SPECC1.
Hierarchical clustering analysis of differentially expressed circRNAs revealed significant differences between the HF and non-HF groups. A total of 1240 circRNAs exhibited significant level changes (P<0.05), with 561 up-regulated and 679 down-regulated in the HF group. Further analysis identified 141 circRNAs with substantial differences between the two groups (P2), including 56 up-regulated and 85 down-regulated circRNAs. Among these, hsa_circ_0005565 stood out with the highest fold change (27.4) and was significantly up-regulated in all five HF patients. qRT-PCR validation confirmed the increased expression of hsa_circ_0005565 in the HF group (P=0.008), suggesting its potential as a biomarker for HF.
Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were conducted to explore the functional roles of the differentially expressed circRNAs. The top enriched GO terms included positive regulation of metabolic processes, positive regulation of cellular metabolic processes, and macromolecule metabolic processes. The most significant KEGG pathways were insulin resistance, transcriptional misregulation in cancer, and platinum drug resistance. These findings suggest that the differentially expressed circRNAs in EAT may play roles in metabolic regulation and inflammatory responses, which are critical in the pathogenesis of HF.
The study also highlighted the top 11 highly expressed circRNAs in human EAT, including hsa_circ_0000722, hsa_circ_0007444, hsa_circ_0000284, hsa_circ_0001380, hsa_circ_0001801, hsa_circ_0000471, hsa_circ_0001092, hsa_circ_0001640, hsa_circ_0002490, hsa_circ_0006156, and hsa_circ_0000745. These circRNAs corresponded to genes involved in cell proliferation and inflammatory response, further emphasizing their potential roles in cardiovascular health and disease.
The findings of this study contribute to the growing body of evidence on the involvement of circRNAs in cardiovascular diseases. Previous research has demonstrated the presence of circRNAs in various cardiovascular tissues, including the right atrium, vena cava, and heart, as well as in cardiomyocytes, cardiac fibroblasts, vascular smooth muscle cells, endothelial cells, macrophages, and blood monocytes. However, the expression profiles of circRNAs in human EAT had not been thoroughly investigated prior to this study.
EAT has been increasingly recognized as a link between metabolic disorders and HF. Its thickness, independent of body mass index (BMI), is positively associated with left ventricular mass. Epicardial fat amounts correlate with impaired left ventricular function and myocardial fibrosis, regardless of metabolic status or CAD. EAT is implicated in the pro-inflammatory polarization and fibrotic transformation observed in HF. Similar to other visceral adipose tissues, EAT secretes numerous molecules that exert exocrine and paracrine effects on adjacent organs, potentially influencing cardiac cell metabolism, endothelial and arterial smooth muscle functions, and inflammatory cell activities, all of which contribute to HF.
In conclusion, this study provides a comprehensive analysis of circRNA expression profiles in human EAT, with a particular focus on their roles in HF. The identification of differentially expressed circRNAs, along with their associated GO terms and KEGG pathways, offers valuable insights into the molecular mechanisms underlying HF. These findings also highlight potential biomarkers for HF, which warrant further investigation. The study underscores the importance of EAT in cardiovascular health and disease and opens new avenues for research into the therapeutic potential of circRNAs in HF.
doi.org/10.1097/CM9.0000000000001056
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