Sex-specific association of X-linked Toll-like receptor 7 (TLR7) with male systemic lupus erythematosus

Abstract

Systemic lupus erythematosus (SLE) is a multisystem, autoimmune disease that predominantly affects women. Previous findings that duplicated Toll-like receptor 7 (Tlr7) promotes lupus-like disease in male BXSB mice prompted us to evaluate TLR7 in human SLE. By using a candidate gene approach, we identified and replicated association of a TLR7 3'UTR SNP, rs3853839 (G/C), with SLE in 9,274 Eastern Asians (P(combined) = 6.5 x 10(-10)), with a stronger effect in male than female subjects [odds ratio, male vs. female = 2.33 (95% CI = 1.64-3.30) vs. 1.24 (95% CI = 1.14-1.34); P = 4.1 x 10(-4)]. G-allele carriers had increased TLR7 transcripts and more pronounced IFN signature than C-allele carriers; heterozygotes had 2.7-fold higher transcripts of G-allele than C-allele. These data established a functional polymorphism in type I IFN pathway gene TLR7 predisposing to SLE, especially in Chinese and Japanese male subjects.

Fig. 1.

A functional SNP rs3853839 in 3′UTR of TLR7 is associated with SLE in a Chinese population. (A) TLR7 and TLR8 gene structure. (B) Eleven TLR7 SNPs and 12 TLR8 SNPs were genotyped in 1,434 SLE cases and 1,591 healthy controls of Eastern Asian descent. The two SNPs (rs5935436, rs3853839) that showed significant association after Bonferroni correction are highlighted. (C) Two haplotype blocks were constructed based on the strength of LD in each gene region. The R² values of each SNP pair are depicted. The protective haplotype GAACAC is highlighted.

Fig. 2.

TLR7 SNP rs3853839 plays a functional role in TLR7 regulation. (A) Correlation of the TLR7 transcript levels in PBMCs from Chinese individuals with rs3853839 genotypes. G represents the major allele and C represents the minor allele of rs3853839. Each symbol represents an individual, and horizontal lines indicate mean values. (B) Allelic specific transcriptional expression of TLR7 in Chinese female subjects heterozygous for rs3853839 (G/C genotype) by pyrosequencing. TLR7 transcripts containing risk G allele were significantly elevated in PBMCs compared with those containing C allele. (C) XCI analysis in Chinese female individuals was performed by measuring the degree of methylated CAG repeats in AR gene and revealed no significant skewing XCI among SLE cases (n = 21) and normal controls (n = 16). (D) Comparison of IFN signature in PBMCs from clinically inactive female patients with SLE carrying various genotypes using IFN score. IFN score was calculated by combination of mRNA expression levels of four IFN-regulated genes including LY6E, MX1, IFIT1, and IFIT3 as described in Materials and Methods. Patients with SLE carrying GG genotype showed a more pronounced IFN signature in PBMCs compared with those carrying GC and CC genotypes.