Polymorphism of key genes in RIG-I/MAVS signaling pathway
In the RIG-I/MAVS signaling pathway, the INTS10 rs28413168 polymorphism was statistically associated with HBV intrauterine transmission. There is no research report on the association between the INTS10 rs28413168 gene polymorphism and intrauterine transmission of HBV or other diseases, but there have been related reports on the association study between the INTS10 gene polymorphisms at other loci and diseases. A South African study found that three polymorphisms (rs55830938, rs73599609, rs73667448) located between the INTS10/LPL gene are associated with systolic blood pressure. The results of another American study suggest that the INTS10/LPL rs149352150 gene polymorphism is associated with male BMI.
INTS10 is a member of the integration factor complex family, which can affect the splicing of RNA precursors, which in turn affects the synthesis and expression of mRNA in the cell. A study found that INST10 has an effect of inhibiting virus infection that has never been discovered before. The study found that the INTS10 rs7000921 locus polymorphism is closely related to the chronicity of HBV infection through the genome-wide association study. Subsequently, the team also found in vitro cell culture experiments that INTS10 was significantly related to HBV replication. In the RIG-I/MAVS pathway, overexpression of INST10 can increase the phosphorylation of IRF3, which in turn activates the activity of downstream IFN-stimulated response element (ISRE), increases the expression level of IFN-λ, and ultimately inhibits HBV replication. Since no functional study on INST10 rs28413168 has been found so far, we found that this site is located in the 5'non-transcribed region through the Ensembl database, suggesting that this site may be involved in the translation, transcription, and stability maintenance of INST10 mRNA. Through the website of rSNP and Fast SNP gene function prediction, our study found that INST10 rs28413168 gene polymorphism may directly participate in gene transcription regulation, and then affect the anti-HBV function of INST10 in the body.
Polymorphism of key genes in cGAS-STING signaling pathway
In the cGAS-STING pathway, there were significant differences in the genotype distribution of MB21D1 rs311678 infants between the case group and the control group. MB21D1, also known as cGAS, can be used as a cytoplasmic DNA sensor to participate in the recognition of different viruses. The combination of cGAS and DNAs can activate the interferon-stimulating gene STING, which in turn stimulates the production of IFN-I and antiviral ISGs. The lack of cGAS will lead to the reduction of the early antiviral inherent response to the body's viral infection. Dansako reported that cGAS and its adaptor protein (STING) recognize and bind dsDNA derived from the HBV genome to generate an innate immune response. In addition, the study also proved that HBV infection can induce the production of interferon-inducible gene 56 (ISG56) through the cGAS-STING signaling pathway, thereby inhibiting the assembly of HBV virus particles. A Japanese study found that daunorubicin can trigger an endogenous cGAS-dependent innate immune response to inhibit the production of HBV. Therefore, the antiviral effect induced by the cGAS-STING signaling pathway plays an important role in identifying and controlling HBV infection.
rs311678 is located in the 5th exon coding region of the cGAS gene. The mutation at this site is synonymous and will not cause any changes in the amino acids it encodes. However, Xiao reported that the cGAS rs311678 locus polymorphism is associated with cervical precancerous lesions, and the cGAS rs311678 G allele reduces the risk of cervical precancerous lesions. Our research used the SNP function prediction website rSNP for function prediction, and the results suggested that this site is involved in post-transcriptional regulation and can bind to a variety of RNA-binding proteins, thereby affecting the expression level and function of cGAS.
Polymorphism of IL-10 genes
Previous studies have shown that IL-10 can regulate the immune response and inflammatory response by inhibiting the activity of antigen-presenting cells. In addition, IL-10 can inhibit the maturation of various immune cells and the production of cytokines, reducing the immune response level. The IL-10 promoter is highly polymorphic, but currently, only the rs1800871 (-819) and rs1800872 (-592) polymorphisms in the promoter region have been extensively studied. The main reason is that these two sites are respectively related to the Msll and Rsal restriction enzyme (re) sites, which may change the activity of the IL-10 gene. It is reported that IL-10 promoter region polymorphism can affect IL-10 gene transcription and translation, leading to abnormal cell proliferation and cancer development. Wu reported that IL-10 rs1800872 (-592a/c) gene polymorphism is associated with spontaneous HBsAg seroconversion and good outcome of hepatitis B. Compared with hepatitis B carriers of CA and CC genotypes, patients with IL-10 rs1800872 AA genotype have higher serum IL-10 levels. In addition, Li found that IL-10 levels in patients with chronic hepatitis B were significantly higher than those in the general population. These results were confirmed by another research. However, a Japanese study showed that the IL-10rs1800872 genotype is not significantly associated with the risk of HBV infection. Our study found that compared with infants with CC genotype, infants with AA genotype at this locus have a significantly higher risk of intrauterine transmission of HBV. We speculate that infants with the AA genotype may have higher levels of IL-10, which inhibits the maturation of various immune cells and the synthesis of cytokines. This will reduce the body's immune response level, leading to a significant increase in the risk of HBV intrauterine infection.
Polymorphism of TLR3 genes
TLR3 can recognize type I IFN, double-stranded RNA (dsRNA) viruses and dsRNA produced during virus replication, activate IRF3 and NF-κB, and also promote the expression of IFN-β and other pro-inflammatory factors. TLR3 is mainly expressed in hepatocytes, macrophages, NK cells, and biliary epithelial cells, located in the plasma membrane or acidic endosome. And macrophages and NK cells play a vital role in the process of clearing HBV[45, 46]. In addition, during HBV infection, TLR3 can activate hepatic non-parenchymal cells, produce interferon β, and inhibit virus replication.
This study found that the SNP at rs3775291 of neonatal TLR3 is closely related to the intrauterine transmission of HBV, which is similar to the results of previous studies. Fischer found that compared with HBeAg-positive patients, the CC genotype of TLR3 rs3775291 appeared more frequently in patients with HBeAg seroclearance, while the TT genotype was more common in HBeAg-positive patients. This further supports that the rs3775291 mutation is related to the innate immune response during HBV infection. In addition, Rong's research also showed that compared with the CC genotype, subjects carrying CT genotype and TT genotype at this locus had an increased risk of chronic HBV infection by 1.42 folds and 2.31 folds, respectively. The specific mechanism of this phenomenon is not yet clear. It may be that mutations at this site cause changes in protein or gene expression, affecting the function and efficiency of signal transduction and thereby altering the immune response.
SNPs rs3775291 is a non-synonymous mutant gene locus located in the fourth exon region of TLR3. The mutation at this locus reduces the location of the soluble outer domain and the dimerization of TLR3 on the membrane, resulting in a decrease in its ability to bind to dsRNA and the signal transduction efficiency. Svensson A detected the expression level of TLR3 mRNA in peripheral blood mononuclear cells (PBMC) of multiple patients infected with human herpesvirus type 2 (HSV-2). It was found that the appearance of the T allele increased the expression of TLR3 mRNA in PBMC relative to the allele C. However, a study showed that the polymorphism of TLR3 rs3775291 locus does not affect the expression of TLR3 in the cell and the localization in the cell, but it will affect the activity of TLR3 and the expression of the receptor on the cell surface.
Multiple genes and HBV intrauterine transmission
According to the theory of common diseases-common mutations, common complex diseases are affected by multiple common mutations, and the effect of each common mutation is weak. As a complex disease, the MTCT of HBV is often affected by multiple genes or multiple sites during its occurrence and development. These genes or loci may interact with each other. This study explored the cumulative effect of multiple positive gene loci on the risk of HBV intrauterine transmission. It was found that infants carrying the INTS10 rs28413168 C allele, MB21D1 rs311678 A allele, IL10 rs1800872 A allele, and TLR3 rs3775291 T allele at the same time significantly increased the risk of intrauterine transmission of HBV. This suggested that these four sites may have an additive effect on the risk of HBV intrauterine transmission, but the specific biological mechanism depends on the elucidation of the function of each gene and in-depth functional experimental research.