In the present study, we integrated gene expression profiles of 46 AF samples and 31 SR samples from 5 GEO datasets and analyzed the data using bioinformatics tools. A total of 27 DEGs with |log2 FC| ≥ 0.58 and 5 with |log2 FC| ≥ 1 in AF compared with SR samples were selected. Furthermore, 9 potential crucial genes (IGFBP2, IGFBP3, CHGB, CXCR4, HTR2B, FHL2, C1orf105, ATP1B4 and SLC26A9), and several important pathways, which were associated with AF risk, were identified, suggesting these may play important role in the mechanism of AF.
IGFBP2, located in chromosome 2q35, encodes the second most abundant circulating IGF-binding protein. IGFBP2, secreted by differentiating white adipocytes, regulates the functions of IGFs . In the Framingham heart study, IGFBP2 was significantly associated with all-cause mortality . Our study revealed that the IGFBP2 expression level was up-regulated in AF samples compared to SR samples. The enrichment analysis results of IGFBP2 were all correlated with IGFBP3.
The functional gene IGFBP3 encodes the primary carrier of IGFs (IGFBP3) in the circulation. IGFBP3 is involved in oxidative stress, atherosclerosis and left ventricular hypertrophy [21, 22]. More important, a previous study revealed low IGFBP3 serum level as an independent determinant of AF . Enrichment analyses in the present study indicated that IGFBP2 and IGFBP3 were enriched in GO term of insulin-like growth factor binding and pathway of IGF transport and uptake by IGFBPs. Thus, IGFBP2 and IGFBP3 might bind and regulate the functions of IGFs through IGF transport and uptake by IGFBPs pathway, and then affect the susceptibility of AF .
Our study revealed that CHGB was involved in IGF transport and uptake by IGFBPs pathway including IGFBP2 and IGFBP3, and the gene expression of CHGB was higher in AF patients. Chromogranin B (CHGB) is an emerging cardiovascular biomarker, which is encoded by CHGB . CHGB can regulate B-type natriuretic peptide (BNP) production through polycystin 2(PC2)-CGB-BNP signaling axis in cardiomyocyte, and integrate information from myocardial stress and neuro-endocrine activation [23, 24]. CHGB level was significantly increased in heart failure patients . These findings suggested that IGF transport and uptake by IGFBPs pathway with IGFBP2, IGFBP3 and CHGB may participate in the occurrence and development of AF. A more thorough understanding of IGF transport and uptake by IGFBPs pathway in AF is necessary.
With PPI analysis, IGFBP2, IGFBP3 and CXCR4 were divided into a group according to protein-protein interactions. There was evidence that CXCR4 was overexpressed in chronic AF patients, and might contribute to the process of AF through regulating atrial fibrosis and structural remodeling . In the present study, CXCR4 was also found to be potential crucial gene related to AF. KEGG pathway enrichment analysis showed that the CXCR4 and HTR2B were enriched in calcium signaling pathway, which had been extensively characterized in the role in cardiac hypertrophy and remodeling processes . HTR2B is located in chromosome 2q37.1. 5-HT2B (5-hydroxytryptamine receptor 2B) receptor coded by HTR2B, is presented in the cardiovascular system, and may indirectly produce life-threatening arrhythmias and cardiodepression [27, 28]. In auricular myocytes of newborn rat, the activation of 5-HT2B enhances gap junctional intercellular communication (GJIC) in a receptor subtype-specific manner, and prolongs 5-HT exposure to alter the Cx expression pattern which associated with AF .
Increasing evidence demonstrated that FHL2 and its protein product has a function in cardiovascular disease [29, 30]. FHL2, located at the sarcomere, interacted with extracellular signal regulated kinase (ERK) and regulated cardiac growth, suggesting FHL2 a protective role in adrenergic-mediated cardiac hypertrophy [31, 32]. We found that FHL2 was up-regulated in AF samples compared to SR, and was involved in cardiac muscle cell differentiation. These results indicated that FHL2 might be a potential biomarker of AF.
In this study, C1orf105 and ATP1B4 had 2 fold lower and higher gene expression, respectively in AF patients than SR control. SLC26A9 and ATP1B4 were enriched in KEGG pathways of mineral absorption and proximal tubule bicarbonate reclamation. Previous study showed that a SNP on C1orf105 was associated with remodeling response to atherosclerosis . Slc26a9 encodes transporters with diverse functional attributes and RT-PCR showed that Slc26a9 is detectable in heart . The above evidence revealed that C1orf105, SLC26A9 and ATP1B4 were related with cardiovascular disease and might have a function in AF.
In current study, we have discussed that 9 potential crucial genes are involved in the occurrence and development of AF, suggesting these genes may serve as potential biomarkers and therapeutic targets for AF. However, the limitations of this study should be considered. Firstly, it is difficult to consider some important factors such as regions, races and age. Considering that the development of AF results from various environmental and genetic factors, some unmeasured factors including region, family history and risk factors of AF should be evaluated in further research. In addition, the potential crucial genes need further validation by RT-qPCR in clinical samples. Finally, the mechanisms in which these genes play are not completely clear. More evidence is required to find out the biological foundation.