In this study, we integrated the gene expression profiles of AF and control groups (11 and 8 samples, respectively) from GSE31821 and GSE79768 datasets, then used bioinformatics tools to analyze the data. Compared with control groups, there were 114 DEGs with | log2 FC | ≥ 0.5 in AF. In addition, 8 potential key genes (CXCL10, TLR7, DDX58, CCR2, RSAD2, KIT, LYN, CXCL11) and several important pathways were found to be associated with AF risk, suggesting that they may play an important role in the pathogenesis of AF. Two DEGs (RSAD2 and CXCL11) were randomly selected for further verification in AF. The results showed that the expression of RSAD2 and CXCL11 was significantly lower in the tissues of patients with AF compared to controls, indicating the reliability of DEGs, which can be used as potential biomarkers for the diagnosis and treatment of AF.
CXCL10 and CXCL11 are both inflammatory chemokines with effects on vascular dysfunction, remodeling, oxidative stress and fibrosis . CXCL10, also known as IP-10, is involved in biological processes by binding to CXCR3. After activation by interferon (IFN) or lipopolysaccharide (LPS), CXCL10 has chemotactic effects in monocytes, T cells and smooth muscle cells . The CXCL10/CXCR3 axis is involved in cardiac inflammatory or non-inflammatory infections playing a role in cardiac remodeling . CXCL10 may be a predictor of cardiovascular disease in the elderly, as elevated CXCL10 levels were observed in the aorta of elderly rats . Furthermore, CXCL10 is found to be a marker of circulating inflammation in patients with advanced HF,which is involved in cardiac remodeling in a study in a rat HF mode . Chen et al. found that MIAT-containing serum extracellular vesicles in AF patients promoted atrial remodeling and exacerbated AF by eliminating miR-485-5p-mediated CXCL10 inhibition .
CXCL11, also known as interferon-inducible T cell alpha chemoattractant(I-TAC), is another chemokine that binds to CXCR3 and also to Ackr3 . Elevated CXCL11 levels have been observed in patients with nonalcoholic cirrhotic portal hypertension as well as in patients with severe graft coronary artery disease . CXCL11 and CXCL10 receptor antagonists attenuate phenylephrine-dependent cardiac remodeling , they also involve in the pathogenesis of hypertension . Gang et al. have identified CXCL11 as a key AF gene .
DDX58 is a member of the retinoic acid-induced receptor , which can recognize exogenous RNA from many viruses, including coronavirus, Zika virus, and rubella .DDX58 signaling downstream through the mitochondrial activation complex culminates in activation of TANK-binding kinase (TBK1), leading to transcriptional activation of interferon-responsive genes and release of pro-inflammatory cytokines .Mutations in the DDX58 gene may be associated with features typical of Singleton-Merten syndrome, including dental hypoplasia, tendon rupture and severe cardiac sequelae .In patients with acute respiratory distress syndrome (ARDS), the DDX58 is found to be highly expressed after infection and significantly enriched in ARDS-related pathways, scoring high in PPI analysis, suggesting that they may be associated with ARDS, providing a new biomarker for the diagnosis, treatment and monitoring of ARDS .The role of DDX58 in AF is not reported at present and needs to be further investigated.
Toll-like receptors (TLRs) are congenital pathogen recognition receptors that recognize exogenous microorganisms, including bacteria and viruses, through pathogen associated molecular patterns (PAMPs) to protect the host from infection. The activation of TLRs activation leads to an inflammatory response, resulting in the release of cytokines and chemokines and an influx of inflammatory cells . TLR7 belongs to the TLRs within the cytosol. The TLR7 ligands identified so far are single-stranded RNA and imidazoquinoline derivatives . Interestingly, TLR7 has been shown to have a protective effect against atherosclerosis . In a mouse model of acute myocardial infarction TLR7 is found to mediate the response to acute myocardial injury and chronic remodeling, possibly by regulating post-infarction scar formation and myocardial inflammatory infiltration . In terms of AF, the use of gene therapy TLR2and TLR7 / TLR8 involved in CD14 + monocytes, blocking the proteasome proteolysis, reducing pro-inflammatory cytokine response, thereby reducing the heart-specific immune response in autoimmune myocarditis animal model .
As a chemokine receptor, C-C chemokine receptor 2 (CCR2) regulates the immune response by inducing the recruitment of macrophages and monocytes to sites of inflammation , and studies have demonstrated that CCR2 knockdown or treatment with CCR2 inhibitors can protect cardiac function in diabetic patients . In a mouse study, the expression of chemokines or cytokines in CCR2 + macrophages increased after myocardial injury, indicating that monocytes are recruited to the injured sit . A recent study found that CCR2 is a key gene associated with AF progression . The high number of CCR2-positive monocytes/macrophages in the LAA of patients with progressive atrial remodeling in AF may suggest enhanced monocyte/macrophage infiltration. Infiltrating monocytes may differentiate into macrophages and then activate pro-inflammatory processes by releasing cytokines or chemokines to further recruit monocytes/macrophages or induce repair function by promoting tissue fibrosis .
Lyn is a non-receptor tyrosine kinase of the Src family, mainly found in myeloid cells and B lymphocytes, and the lack of Lyn and p110δ (an isoform of PI3K) resulte in a significant decrease in autoimmune-mediated renal pathology and improved survival .Wang et al. have identified the Lyn gene as a potential diagnostic marker for coronary artery disease (CAD) by bioinformatic methods and therapeutic targets , and Lyn gene is identified as a biomarker associated with hypertrophic cardiomyopathy using co-expression analysis .Therefore, we speculate that Lyn may also play a role in AF and needs to be further investigated.
The protein encoded by the KIT gene is the stem cell factor receptor (SCFR), also known as the proto-oncogene c-KIT or tyrosine protein kinase KIT or CD117, a receptor tyrosine kinase. c-KIT positivity is a general marker for the identification of cardiac stem cells (CSC), and the protein plays a central role in the ability to self-renew and differentiate in cardiac myocytes . Importantly, c-KIT expression is increased in damaged myocardial tissue such as in myocardial infarction or end-stage HF . It is found that a decrease in c-KIT positive cardiac stem cells in cell cultures derived from left ventricular (LA) tissue of AF patients may be involved in LA remodeling .
RSAD2 is commonly considered an antiviral protein, also known as Viperin or Cig5, that plays a key role in the innate immune response system. RSAD2 can be induced by interferon to resist viral infection . The miR-200 family are found to promote podocyte differentiation and discover its novel role as a regulator of cell differentiation possibly by suppressing RSAD2 expression. STAT1-mediated epigenetic control of RSAD2 is found to be a key mechanism for promoting NK cell survival and death during viral infection. It is found that in the presence of IFNc and LPS (or any other exogenous or endogenous TLR4 ligand), RSAD2 can be overproduced in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). This may in turn regulate leukocyte attraction, adhesion, and the proliferation and migration of VSMCs, which are important features of vascular dysfunction and early triggers of atherosclerosis . We had observed the differential expression of RSAD2 in AF patients and need to further understand its mechanism.
Although the results based on bioinformatics methods are enlightening, the present study still has limitations. Firstly, We only randomly selected two genes for qRT-PCR validation in a small sample of tissues, which may bias the results, and a larger, multicenter study is needed to complete experimental validation. Secondly, we currently do not know how these genes contribute to atrial fibrillation, and more evidence is needed to identify their biological basis.