Background
Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease characterized by ANCA production and inflammation in small vessels [
1]. There are substantial differences in the epidemiology of AAV between European and Asian populations. Microscopic polyangiitis (MPA) and myeloperoxidase (MPO)-ANCA positive AAV (MPO-AAV) are predominant in East Asian populations, while granulomatosis with polyangiitis (GPA) and proteinase 3 (PR3)-ANCA positive AAV (PR3-AAV) are common in the populations of European ancestry [
2]. Another striking difference is that the prevalence of AAV-associated interstitial lung disease (AAV-ILD), a complication associated with poor prognosis, is considerably higher in Japanese than in European populations [
3]. Among the AAV subsets, ILD was predominantly observed in MPA and MPO-AAV as compared with GPA and PR3-AAV [
3]; however, significantly higher complication rate of ILD in the Japanese than in the European population is also observed when only MPA patients were compared [
4], suggesting that genetic factors may contribute to the susceptibility to AAV-ILD.
Genome-wide association studies (GWAS) on AAV have been reported in European populations, and associations of
HLA-DP,
SERPINA1,
PRTN3, and
PTPN22 with GPA and PR3-AAV;
HLA-DQ and
PTPN22 with MPA and MPO-AAV; and
HLA-DQ,
BCL2L11, and
TSLP with eosinophilic granulomatosis with polyangiitis (EGPA) were identified [
5‐
8]. In a Japanese population, we reported that
HLA-DRB1*09:01-DQB1*03:03 haplotype and
DRB1*13:02 were associated with risk and protection for MPA/MPO-AAV, respectively [
9,
10]. However, genetic factors of AAV have not been fully determined.
Little is known on the genetic factors associated with the occurrence of ILD among the patients with autoimmune rheumatic diseases. Recently, we reported that a single nucleotide variant (SNV) rs35705950 in the upstream region of
MUC5B gene, the strongest susceptibility variant to idiopathic pulmonary fibrosis (IPF) [
11‐
13], was associated with ILD in the patients with rheumatoid arthritis (RA) in a multinational collaborative study [
14]. Subsequently, we also reported association of rs35705950 with AAV-ILD [
15]. Based on the histological and radiographic patterns of idiopathic interstitial pneumonia (IIP), ILD in AAV and RA is most frequently classified into usual interstitial pneumonia (UIP), typically observed in IPF [
3]. These findings suggest a possibility that there may be shared pathological processes between IPF and AAV-ILD.
Although the association between
MUC5B rs35705950 and AAV-ILD is striking (odds ratio [OR] 11.6 when compared with AAV patients without ILD) [
15], this allele alone cannot account for the high complication rate of ILD in Japanese AAV, because the population frequency of the risk allele is substantially lower as compared with European populations [
14,
15]. Thus, other genetic factors are likely to play a role in the occurrence of ILD among AAV patients in Japan.
In addition to
MUC5B,
TERT and
DSP have been reported to be associated with IPF and IIPs in GWAS [
11‐
13,
16].
TERT gene encodes telomerase reverse transcriptase, which is the catalytic subunit of telomerase, and contributes to maintenance of telomere length [
17]. Desmoplakin, encoded by
DSP, is one of desmosomal components and has a role in cell-cell adhesion and tissue integrity [
18]. Although the mechanisms by which these susceptibility genes contribute to development of IPF remain unclear,
TERT and
DSP could be considered candidate genes which might be associated with ILD among the patients with AAV, in a similar manner to
MUC5B.
This study was carried out to examine whether the IPF risk SNVs in TERT and DSP genes are associated with AAV subsets and presence of ILD among AAV patients in a Japanese population. Unexpectedly, TERT and DSP SNVs turned out to be significantly associated with susceptibility to MPA and MPO-AAV regardless of the presence of ILD.
Discussion
Here, we report that
TERT rs2736100A and
DSP rs2076295G, both of which are the risk alleles for IPF [
12,
13,
16], are associated with susceptibility to MPA and MPO-AAV in a Japanese population. Unexpectedly, association of these alleles with occurrence of ILD among the patients with MPO-AAV was not detected. These are new findings which have not been reported in the populations of European nor of Asian ancestry.
It has been recognized that some patients with IPF are positive for MPO-ANCA and develop MPA [
24], and hypothesized that IPF and AAV may share some pathogenic mechanisms. Our current finding that the IPF risk alleles of
TERT and
DSP are associated with MPA and MPO-AAV is in line with such hypothesis. This is also supported by the reports that silica contributes to the pathogenesis of both IPF and AAV [
25,
26].
On the other hand, significant association of
TERT and
DSP IPF risk SNVs was not detected when MPO-AAV patients with and without ILD were compared. This finding was unexpected, but similar finding has been reported in RA, where association of these genes was not observed in RA-ILD when compared with RA patients without ILD [
14]. This is in contrast to
MUC5B, which shows association in the patients with AAV and RA only when they are complicated by ILD [
14,
15]. These results might suggest a possibility that some IPF associated genes (e.g.,
MUC5B) may play a role in the process of lung disease, and others (e.g.,
TERT and
DSP) may be involved in the shared molecular background between AAV/RA and IPF. Further studies are required to validate this hypothesis.
The association of
TERT rs2736100 was reported in GWAS on IPF in a Japanese population [
16], and also in GWAS on IIPs, among which IPF was the most common subset, in European populations [
12].
TERT rs2736100 is located in intron 2 of the
TERT gene. Wei et al. reported that the
TERT risk allele, rs2736100A, showed lower enhancer activity compared with rs2736100C, using a luciferase assay in primary lung epithelial cells [
27]. They also found that rs2736100A showed decreased expression of
TERT mRNA [
27], suggesting a functional significance of this SNV. Moreover, rs2736100A was associated with shorter leukocyte telomere length [
28], previously shown to contribute to risk of IPF [
29]. With respect to AAV, a proportion of T cells was reported to show short telomeres in GPA patients [
30], although telomere length abnormality has not been reported in MPA or MPO-AAV. Because
TERT has an anti-apoptotic effect [
31], decreased expression of
TERT associated with the risk allele may result in an enhancement of apoptosis. Indeed, in AAV patients, an enhanced rate of apoptosis was observed in neutrophils [
32]. Apoptotic neutrophils may be opsonized with anti-MPO and anti-PR3 antibodies which recognize MPO and PR3 on the surface, engulfed by macrophages, and lead to secretion of pro-inflammatory cytokines such as interleukin-1 and interleukin-8. These processes may induce inflammation in vessel and tissue injury [
33,
34].
Interestingly, association of
TERT rs7726159A has been shown to be associated with systemic lupus erythematosus (SLE) in East Asian populations [
35]. The risk SNV for SLE is in moderate linkage disequilibrium (
r2 = 0.773) with that for MPO-AAV and IPF, although the risk allele is the opposite. Nevertheless, this finding may suggest that
TERT variants may be functional and associated with multiple autoimmune conditions either in a predispositional or in a protective manner, regardless of the presence of ILD.
The association of
DSP with IIPs and IPF has been identified by GWAS in the European populations [
12,
13].
DSP rs2076295 is located in intron 5, and the risk allele was reported to be associated with decreased expression of
DSP in the lung [
12]. Expression quantitative trait locus (eQTL) analysis using the GTEx Portal database [
36] shows that rs2076295G is the most strongly associated variant with
DSP expression in the lung (
P = 3.7 × 10
−75, normalized effect size = − 0.73, Additional file
2: Figure S1).
DSP was reported to modulate Wnt/beta-catenin signaling, which is involved in cell proliferation, differentiation, immune responses, and carcinogenesis [
37,
38]. In
Dsp-deficient atrial myocyte cell lines and HEK293T cells transfected with
DSP frameshift variant, the Wnt/beta-catenin signaling was suppressed [
39,
40]. Although contribution of the Wnt signaling to the pathogenesis of AAV is unclear, Wnt signaling has been reported to play a role in autoimmune diseases such as SLE and RA [
41]. In this study, association of
DSP was observed in male but not in female AAV. Although the reason of such difference remains unclear, sex hormone or genes located in sex chromosomes might affect the association of
DSP.
Our study has several limitations. Due to rarity of AAV, a replication study was not conducted. The annual incidence/million in Japan has been reported to be 22.6 and 18.2 for AAV and MPA, respectively [
2]. As shown in Additional file
1: Supplementary Table S1, when OR is less than 1.4, we cannot detect the association with power ≥ 0.8 in the case-case analysis comparing AAV patients with and without ILD. Therefore, the results in this study should be confirmed in larger sample size in the future. In addition, not all AAV patients with ILD were diagnosed by HRCT, and lung biopsy was not performed in most of the patients. Thus, we cannot exclude the possibility that ILD with a specific histological pattern such as UIP might show association with
TERT or
DSP IPF risk SNVs.
Competing interests
Dr. Sada has received speaker’s honoraria from Chugai Pharmaceutical Co. Ltd.
Dr. Hirano has received research grants and/or speaker’s honoraria from Chugai Pharmaceutical Co. Ltd., Ono Pharmaceuticals, CSL Behring, Towa Pharmaceutical Co. Ltd., Abbvie Japan Co. Ltd., Japan Blood Products Organization, Ayumi Pharmaceutical Co., Nippon Kayaku Co. Ltd., Astellas Pharma Inc., Sumitomo Dainippon Pharma, and UCB Japan.
Dr. Nagasaka has received speaker’s honoraria from Bristol-Myers Squibb Co. Ltd., Chugai Pharmaceutical Co. Ltd., and Teijin Pharma Ltd.
Dr. Makino is a consultant for AbbVie, Teijin, and Boehringer-Ingelheim.
Dr. Harigai has received research grants and/or honoraria from AbbVie Japan Co. Ltd., Bristol-Myers Squibb K.K., Chugai Pharmaceutical Co. Ltd., Eisai Co. Ltd., Mitsubishi Tanabe Pharma Co., Ono Pharmaceutical Co. Ltd., Taisho Toyama Pharmaceutical Co. Ltd., Ayumi Pharmaceutical Co. Ltd., Takeda Pharmaceutical Co. Ltd., Teijin Pharma Ltd., and Pfizer Japan Inc. Dr. Harigai serves as a consultant for Bristol-Myers Squibb K.K., Chugai Pharmaceutical Co. Ltd., CIMIC Co. Ltd., Kissei Pharmaceutical Co. Ltd., Ono Pharmaceutical Co. Ltd., and Pfizer Japan Inc.
Dr. Tsuchiya has received research fund from H.U. Group Research Institute G.K. for a collaborative research unrelated to this study, and research grants from Bristol-Myers Squibb, 2015 Japan College of Rheumatology Award from Japan College of Rheumatology, 2017 Novartis Rheumatology Award from Japan Rheumatism Association with research funding, and speaker’s honoraria from Teijin.
Other authors declare no potential conflict of interest.
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