Association of TLR8 gene polymorphisms with Hepatitis C virus infection

• Main Authors: Chiou-Huey Wang, 王秋惠
• Other Authors: Kuei-Hsiang Lin
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/9s3u9s

博士 === 高雄醫學大學 === 醫學研究所-基礎醫學組 === 102 === Toll-like receptors (TLRs) play pivotal roles in the innate immune system and control inflammatory responses and adaptive immunity. Growing amounts of data suggest that the ability of individuals to respond to TLR ligands may be different due to single nucleotide polymorphisms (SNPs) within TLR genes, resulting in an altered susceptibility to infectious diseases. TLR8 located in X chromosome, activates downstream signals to induce inflammatory cytokines and type I interferon through recognizing single-stranded RNA. In our previous study, we found that a TLR8 Met/Val substitution at the start codon and a G>C change at the -129 position in the promoter region were in complete linkage disequilibrium. In this study, we found that the promoter activity and competitive DNA-binding ability of TLR8-129G were higher than those of TLR8-129C in THP-1 cells. Moreover, TLR8-129G mRNA stability was significantly lower than that of TLR8-129C. Nuclear factor-kappa B (NF-κB)-driven luciferase activity in HEK293 cells transfected with the TLR8 variants demonstrated TLR8+1G plasmids induced more NF-κB signaling than those transfected with TLR8+1A after 20 μM CL075 (p = 0.011) stimulation. Take together, our data indicate that TLR8 129G/+1G genotype had stronger ability to modulate TLR8 gene and inflammation response. The clinical outcome of hepatitis C virus (HCV) infection is highly variable, and genetic factors involving innate immunity are likely to affect disease susceptibility and progression. We evaluated associations between TLR8 gene SNPs and susceptibility to HCV infection. TLR8-129G alleles were present at higher frequency in males of an HCV-infected group as compared to a control group (17.6% vs. 6.8%, p = 0.004). In addition, the functional effects of these polymorphisms by analyzing the TLR8 mRNA expressions and cytokine production ex vivo by TLR8-specific agonists stimulation of healthy subjects with different genotypes. The percentage of CD14+ cells from those with TLR8-129C/+1A that expressed TLR8 was significantly lower, but higher in intensity compared to cells from those with TLR8-129G/+1G. Cells from those with TLR8-129G/+1G haplotype produced more IFN-α, but less amounts of pro-inflammatory cytokines upon stimulation. Collectively, our data show that individuals with TLR8 -129G/+1G genotype may have stronger innate immunity to clear HCV in the beginning of HCV infection correlating with the susceptibility to HCV infection in male population. To study TLR8 functional effects on HCV-infected patients, we revealed that the patients presented significantly higher TLR8 transcript variant 2 mRNA as compared to healthy controls, and chronic hepatitis C and hepatocellular carcinoma patients induced significantly more TLR8 V1 mRNA but less TLR8 V2 mRNA as compared to healthy control group (p<0.001; p=0.001, respectively) after CL075 stimulation. In conclusion, variations in the TLR8 gene may modulate immune responses during HCV infection. The results of the present study might have implications for assessing the risk profile of individual patients and for the illustration of TLR8 in the prevention of, or therapy for HCV infection.