In the current study, we investigated the association between the ANRIL gene polymorphisms, including rs1333048 and rs10757278, with susceptibility to AR in the kurdish population of Kermanshah, Iran. Our results showed no significant association between these two polymorphisms and AR risk.
From an etiopathological point of view, AR is considered a complex multi-factorial inflammatory disease in which the genetic factors are critically involved in the activation of inflammatory responses (Broide, 2010). Although many studies have identified a large number of genetic factors involved in the pathogenesis of AR, the underlying mechanisms of gene dysregulation have not yet been identified. Recently, non-coding RNAs (ncRNAs), like microRNAs (miRNAs) and lncRNAs, as crucial regulators of gene expression, have been suggested to be involved in the regulation of immune responses and the pathogenesis of several immune-related disorders (Ghafouri-Fard et al., 2020; Mulrane et al., 2013; Rakhshan et al., 2020; Rezazadeh et al., 2018; Wei et al., 2017).
Regarding the nature of AR as Th2-mediated responses and the role of lncRNAs and miRNAs in the regulation of Th2 responses, no wonder that altered expression of these ncRNAs might contribute to the pathogenesis of AR. Intriguingly, the importance of miRNAs was determined in AR pathogenesis. For example, upregulation of miR-126-5p, miR-19a-5p, and miR-26a-5p was reported in the nasal mucosa of AR patients compared to healthy control (Rakhshan et al., 2020). Recently, a study indicated that lncRNA ANRIL expression in the nasal mucosa of AR patients was remarkably increased, and it was positively associated with upregulation of pro-inflammatory cytokines (IL- 4, IL-6, IL-13, and IL-17) as well as disease severity such as itching and congestion. Hence, these observations suggest that the lncRNA ANRIL might be involved in the pathogenesis of AR (Qian et al., 2019). Although it is not clear how lncRNA ANRIL might play a role in regulating AR-related cytokines and miRNAs, it appears that the sponging of anti-inflammatory miRNAs, such as miR-Let7e and miR-18b by lncRNA ANRIL might be an explanation. Interestingly, the binding of ANRIL to an ANRIL binding transcriptional factor (Yin Yang 1) may be considered another mechanism, leading to upregulating IL-6 and IL-8 expression in human endothelial cells. (Hori et al., 2017; Huo et al., 2016; Li et al., 2018; Qian et al., 2019). It is worth emphasizing that Signal transducer and activator of transcription 1 (STAT1) signaling contributed to ANRIL expression, which participates in the regulation of immune response through induction of the pro-inflammatory cytokine IFN-γ (Harismendy et al., 2011). Given the association between nuclear factor (NF)-κB pathway and the crucial role of ANRIL in the expression of several pro-inflammatory genes regulated by NF-κB (Wee et al., 2017; Zhou et al., 2016), ANRIL might be a missing puzzle piece in the pathogenesis of AR. However, this speculation should be further investigated.
One of SNPs within the ANRIL gene has been reported to change the phenotypic traits and function of the genes, such as changes in the binding site for proteins involved in signaling pathways (Harismendy et al., 2011; Taheri et al., 2017). For instance, the polymorphism rs10757278 of the ANRIL gene has been demonstrated to disturb the binding of the STAT1 (Harismendy et al., 2011). In recent years, different studies have demonstrated the association of SNPs of ANRIL gene with the susceptibility to different diseases(Hariri et al., 2020; Rezazadeh et al., 2018; Taheri et al., 2017).
Taheri and colleagues revealed that the GG genotype of rs10757278 and AA genotype of rs1333048 A > C were associated with prostate cancer and benign prostate hyperplasia (BPH) risk in an Iranian population (Taheri et al., 2017). Besides, rs10757278 was significantly associated with coronary artery disease (CAD) risk in patients from Iraq, Iran, and Poland (Hariri et al., 2020; Niemiec et al., 2012; Suleiman et al., 2019). Additionally, ANRIL gene rs10757278 and rs1333048 SNPs were shown to confer a risk for psoriasis development in an Iranian population (Rakhshan et al., 2020). In accordance with our study, there was no significant association of ANRIL gene rs1333048 and rs10757278 SNPs with both multiple sclerosis (MS) and breast cancer (Khorshidi et al., 2017; Rezazadeh et al., 2018). However, haplotype analysis of ANRIL gene polymorphisms (rs1333045, 1333048, rs4977574, and rs10757278) indicated a protective effect of CCGG and TAAA haplotypes in MS while TAGG and CCGA haplotypes were significantly associated with increased risk of MS (Rezazadeh et al., 2018). Moreover, haplotype analysis (with an order of rs1333045, 1333048, rs4977574, and rs10757278 SNPs) demonstrated that TCGA haplotype was associated with breast cancer risk (Khorshidi et al., 2017). The discrepancy in the reports concerning the contribution of ANRIL polymorphisms to different diseases might stem from population-specific genetic stratification, sample size, different genotyping methods, and the involvement of other genetic factors.
Several potential limitations in our study should be pointed out. First, we did not investigate the lncRNA ANRIL expression in the study groups, and therefore were unable to determine a link between the SNPs and transcription of lncRNA ANRIL. Second, the small sample size and inclusion of only one Iranian population can decrease the statistical power of our study, thus we recommended replication studies with a larger sample size to assess the involvement of ANRIL polymorphisms in AR pathogenesis. Third, the present study did not cover all of the genetic polymorphisms on ANRIL, and thus, further studies are required to identify potential causative variants. Fourth, the distribution of genotypes of rs10757278 was not in accordance with HWE in the study groups, probably due to inbreeding or small population sizes. Therefore, the obtained results should be interpreted with caution.