Genetic Association Analysis And Subsea Uent Functional Studies Of Genetic Variants In Susceptibility Genes For Hepatitis B Infection

Hepatitis B virus(HBV)infection seriously affects human health,with 240 million persons infected chronically throughout the world.Twin study indicates that host genetic factors greatly influence HBV-related liver diseases.Recently,genome-wide association study(GWAS)reveals that STAT4 is a plausible candidate for an association study with HBV-related liver diseases.In the first part of this thesis,we examined the roles of STAT4 polymorphisms on HBV-related liver diseases in a Chinese Han population.We selected 13 SNPs in STAT4 based on the HapMap database to investigate their association in 3033 participants.We found that SNP rs7574865 was significantly associated with HBV infection(OR =1.15,95%CI = 1.00-1.31,P = 0.046)and clearance(OR = 1.17,95%CI=1.02-1.33,P = 0.028).Meta-analyses of this SNP,incorporating all the data from 8944 chronic HBV infection(CHBVI)patients,8451 healthy and 2081 clearance individuals,also indicated SNP rs7574865 to be significantly associated with HBV infection(fixed-effects and random-effects models:pooled OR = 1.14,pooled P =3.8×10-5)and clearance(fixed-effects:pooled OR = 1.20,pooled P = 0.002;random-effects models:pooled OR = 1.25,pooled P = 0.044).Further,haplotype-based association analysis showed that the haplotype CTCTT,formed by SNPs rs8179673,rs7574865,rs4274624,rsl 1889341,and rs10168266,was significantly associated with HBV infection(OR =0.87,95%CI=0.76-0.99,P = 0.022)and clearance(OR = 0.86,95%CI=0.75-0.99,P = 0.018).Bioinformatics analysis of these five SNPs predicted that they participate in transcriptional regulation of the STAT4 gene,further functional study is required to validate these predictions.Taken together,our findings demonstrate that variants in STAT4 play a critical role in HBV infection and clearance in the Chinese Han population.However,HBV susceptibility SNPs identified by GWAS only explain a limited heritability,indicating more genetic variants remain to be discovered.In the second part of this thesis,we adopted a new research strategy to identify more susceptibility genes and variants for HBV infection.We first performed a genetic association analysis of 300 sib-pairs and 3087 case-control samples,which revealed that 36 SNPs located in 31 genes showed nominal associations with HBV infection in both samples.Of these genes,we selected SEC24D for further analysis according to the following two main evidences.First,the time course analysis of expression profiles from HBV-infected primary human hepatocytes(PHH)indicated that SEC24D expression was markedly increased as the time goes on after HBV infection(P = 4.0 × 10-4).Second,SNP rs76459466 in SEC24D was negatively associated with HBV risk(ORmeta=0.82,Pmeta = 2.0 ×10-3)which again indicated SEC24D represents a novel susceptibility gene for HBV infection.Based on these data,we designed the in vitro experiments to investigate the association between SEC24D and HBV infection.In the cell culture expriments,we found that the HBV markers were significantly reduced when enhancing the SEC24D expression levels.However,when inhibiting its expression,the HBV markers were significantly increased.These findings suggested SEC24D appeared to be protective against HBV infection in vitro.Consistently,in the woodchuck models,we found that the SEC24D expression levels were markly enhanced in the non-infected liver tissues(S = 2.0 ×10-3).Taken together,we concluded that SEC24D represents a novel candidate gene for HBV infection.Conclusion,firstly,we not only replicated STAT4 polymorphisms are significantly associated with HBV infection,but also found that it plays an important role in HBV clearance.Secondly,besides STAT4,we also found a novel potential susceptibility gene on HBV infection using integraive genomic functional genomics strategy.All the findings still need to be further replicated and functional assessment for the gene.