circRNAs have received increasing attention due to their highly stable and specific spatiotemporal expression patterns. circRNAs are a transcriptional product in various tissue and cell types in humans, mice, drosophila, and nematodes, among other species. circRNAs can be classified into three types: exonic (circRNA arising from the exons of the linear transcript); intergenic (circRNA located outside of a known gene locus); and sense-overlapping (circRNA whose gene locus overlaps with linear RNA but is transcribed from the opposite strand). The differentially expressed hosting genes of the circRNAs and the disordered splicing machinery will lead to circRNAs differentially expressed. So far, numerous circRNAs have been reported in different animals. The majority of circRNAs showing specific expression patterns are related to tissue development and disease [19]. Therefore, circRNA has potential as a biomarker for some diseases [11]. Thus far, many studies have reported abnormal expression levels of circRNAs in a number of cancers, such as gastric [20, 21], colorectal [22, 23], breast [24, 25], and lung cancers [26, 27]. However, few studies have focused on the development of ACLF.
In this study, we detected several circRNAs in HC, CHB and ACLF subjects. The circRNAs were initially identified by reference to a database or website. circBase, (http://circbase.org/) which includes merged genomic data on circRNAs from humans, mice, nematode worms, pike, and coelacanth, provides evidence of their expression[28]. Therefore, we identified the circRNAs detected herein using circBase. A flow diagram of circRNA prediction is shown in Supplemental Fig. 5.
CHB is mainly caused by aberrant cellular immunity, due for example to natural killer (NK) cells, cytotoxic T cells and antibody-dependent lymphocytes. When infected with hepatitis B, three types of lymphocytes target antigens of the hepatocyte membrane: HBsAg, HBcAg, and other immunoregulatory cells. Auxiliary and inhibitory T cells take part in the immune response, which can lead to immune disorder hypofunction. Many researchers have reported dysfunction and inhibition of T cells in CHB. For example, Raziorrouh et al. [29] reported that tetramer + CD4 + T cell numbers were reduced during CHB. Zhang et al. reported that HBV-specific T cell responses to recombinant HBV core protein were reduced in CHB patients and positively correlated with HBV viral load in co-infected, chronic HBV patients [30]. Therefore, the progression of ACLF from CHB may be related to the BP of immunodeficiency or dysfunction, which can in turn be caused by HTLV-I infection, Staphylococcus aureus infection or other diseases. The process of immunity dysfunction may be related to the NOD-like receptor signaling pathway, the NF-kappa B signaling pathway, and/or the interleukin-1-mediated signaling pathway.
Since circRNAs contain multiple miRNA-binding sites, the function of individual circRNAs can be predicted by their miRNA target gene, and annotated according to the function of their miRNA target gene. The circRNA-miRNA co-expression network identified two up-regulated circRNAs and nine down-regulated circRNAs in this study. After combining the results from the GO and KEGG analyses, circRNA_00389, circRNA_07734, circRNA_08533, circRNA_ 15699, and circRNA_16083 were identified as the most important circRNAs during the progression of ACLF. Among them, circRNA_00389 had the highest enrichment score in the KEGG analysis, consistent with the GO analysis. The top term in BP analysis was regulation of lymphocyte activation, which corresponded to down-regulated circRNA_00389. However, the expression of circRNA_00389 had no statistical significance between ACLF and HC group. Therefore, combined with the results of spearman's correlation analysis, circRNA_07734, circRNA_08533, and circRNA_16083, which are related to immune dysfunction and correlate with ALT, AST, TBIL, and IBIL, are important circRNAs in ACLF.
However, our study had limitation, there are only 3 samples in each group. Therefore, in the further work, we should perform qRT-PCR to determine the expression levels of these circRNAs and carry out research on mechanisms.