Genome-wide haplotype association analysis of primary biliary cholangitis risk in Japanese

Zebrafish ppp1r21 mutant as a model for the study of primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune cholestatic liver disease that progresses to fibrosis and cirrhosis, resulting from the gradual destruction of intrahepatic bile ducts. Exploring genetic variants associated with PBC is essential to understand the pathogenesis of PBC. Here we identify a zebrafish balloon dog (blg) mutant with intrahepatic bile duct branching defects, exhibiting several key pathological PBC-like features, including immunodominant autoantigen PDC-E2 production, cholangiocyte apoptosis, immune cell infiltration, inflammatory activation, and liver fibrosis. blg encodes the protein phosphatase 1 regulatory subunit 21 (Ppp1r21), which is enriched in the liver and its peripheral tissues and plays a vital role in the early intrahepatic bile duct formation stage. Further studies show an excessive activation of the PI3K/AKT/mTOR pathway in the hepatic tissues in the mutant, while treatment with the pathway inhibitor LY294002 and rapamycin partially rescues intrahepatic bile duct branching defects and alleviates the PBC-like symptoms. These findings implicate the potential role of the Ppp1r21-mediated PI3K/AKT/mTOR pathway in the pathophysiology of PBC.

Several genetic variants associated with systemic sclerosis in a Chinese Han population

BACKGROUND

Systemic sclerosis (SSc) is a connective tissue disease with ethnic differences. Single-nucleotide polymorphisms (SNPs) in the ARID3A, CXCR5, and TNFSF8 genes have been reported to be associated with various autoimmune diseases. The aim of this study was to investigate the association between these SNPs and susceptibility to SSc in a Chinese Han population.

METHODS

A case-control study was conducted in 342 patients with SSc and 694 ethnically matched healthy controls. SNPs in ARID3A, CXCR5, and TNFSF8 were genotyped using a Sequenom MassArray iPLEX system, and allele association analyses were performed using the PLINK v1.90 software.

RESULTS

Our study demonstrated that the ARID3A rs10415976 G and CXCR5 rs77871618 T alleles were suggestively associated with patients with SSc (P = 0.049 and P = 0.024, respectively) and TNFSF8 rs1555457 T allele was strongly associated with SSc (P = 0.003). Patients carrying the ARID3A rs350146 TT and TNFSF8 rs1555457 TT genotypes had a significant increased risk of SSc (P = 0.03 and P = 0.004, respectively). Moreover, rs10415976, rs77871618, and rs1555457 were associated with SSc in an additive genetic model (P < 0.05). rs62132345 and rs1555457 were associated with SSc in the dominant genetic model (P < 0.05). rs350146 was associated with SSc in the recessive genetic model (P = 0.029).

CONCLUSIONS

ARID3A rs10415976, ARID3A rs350146, and CXCR5 rs77871618 were suggestively associated with SSc and TNFSF8 rs1555457 was strongly associated with SSc in the Chinese Han population in this study. Key Points • This case-control study determined that ARID3A rs10415976, ARID3A rs350146 and CXCR5 rs77871618 were suggestively associated with SSc and TNFSF8 rs1555457 was strongly associated with SSc in the Chinese Han population. • The differences in these results compared with previous studies may be a result of ethnic and racial differences.

Regional heritability mapping identifies several novel loci (STAT4, ULK4, and KCNH5) for primary biliary cholangitis in the Japanese population

While the advent of GWAS more than a decade ago has ushered in remarkable advances in our understanding of complex traits, the limitations of single-SNP analysis have also led to the development of several other approaches. Simulation studies have shown that the regional heritability mapping (RHM) method, which makes use of multiple adjacent SNPs jointly to estimate the genetic effect of a given region of the genome, generally has higher detection power than single-SNP GWAS. However, thus far its use has been mostly limited to agricultural settings, and its potential for the discovery of new genes in human diseases is yet to be fully exploited. In this study, by applying the RHM method to primary biliary cholangitis (PBC) in the Japanese population, we identified three novel loci (STAT4, ULK4, and KCNH5) at the genome-wide significance level, two of which (ULK4 and KCNH5) have not been found associated with PBC in any population previously. Notably, these genes could not be detected by using conventional single-SNP GWAS, highlighting the potential of the RHM method for the detection of new susceptibility loci in human diseases. These findings thereby provide strong empirical evidence that RHM is an effective and practical complementary approach to GWAS in this context. Also, liver tissue mRNA microarray analysis revealed higher gene expression levels in ULK4 in PBC patients (P < 0.01). Lastly, we estimated the common SNP heritability of PBC in the Japanese population (0.210 ± 0.026).

No difference in TCRβ repertoire of CD4+ naive T cell between patients with primary biliary cholangitis and healthy control subjects

Primary biliary cholangitis (PBC) is considered as a model of organ-specific autoimmune disease based on the serological findings of anti-mitochondrial antibodies (AMA), infiltrates of T cells, and selective destruction of epithelial cells in the liver. T-cell-mediated autoimmune mechanisms are considered to be involved in the pathogenesis of primary biliary cholangitis (PBC). In this context, we used a combination of multiplex-PCR, Illumina sequencing and IMGT/HighV-QUEST for a standardized analysis of the T cell receptor β-chain (TCRβ) repertoire of CD4^＋naive T cells in PBC patients compared with healthy volunteers. Nonfunctional TCRs were used to study the pre-selection TCR repertoire, as they are not subject to functional selection (positive and negative selection). Functional TCRs were used to study the post-selection TCR repertoire. The results showed that there was not significant difference between PBC patients and healthy volunteers in TCRβ diversity, CDR3 length distributions, degree of sequence sharing, and usage frequency of TRBV and TRBJ segments, no matter in Pre-selection or Post-selection repertoires. In conclusion, early events in thymic T cell development and repertoire generation are not abnormality in PBC patients. The breakdown of self-tolerance to autoantigen may be derived from other immunological dysregulation or environmental agents.