Interaction between ELMO1 gene polymorphisms and environment factors on susceptibility to diabetic nephropathy in Chinese Han population

Diabetic nephropathy (DN) is one of the most destructive microvascular complications of all the complications of diabetes, and it is the main cause of end-stage renal disease (ESRD), which accounts for a large proportion of the morbidity and mortality of diabetes [1]. DN is also an important risk factor for the development of cardiovascular disease and chronic kidney disease [2] and one of the main causes of death [3]. The pathogenesis of DN was multifactorial and was also not been well known. Previous studies have reported that some genetic and environmental risk factors may lead to its progress, including hyperglycemia, hypertension and hyperlipidemia, which were common modifiable risk factors. In addition, some unmodifiable risk factors should also draw public attentions, such as genetic factors [4, 5].

Genome-Wide Association Studies (GWAS) and meta-analysis [6, 7] have reported some genes related with susceptibility to DN in different populations. In 2005, a Japanese GWAS study [8] confirmed that Engulfment and Cell Motility 1 (ELMO1) gene is a new candidate gene. In this study, they evaluated more than 80,000 loci and found that one SNP locus in intron 18 of ELMO1 gene was closely related to DN. Then, some studies also reported that this gene was associated with kidney disease attributed to T2DM in different populations [9‐11], including Chinese populations [11]. The detailed mechanism for association between ELMO1 gene polymorphisms and DN susceptibility was not well known. However, a previous study [12] showed that mutations in elmo1 gene can lead to the disorder of extracellular matrix (ECM) metabolism, which leads to the accumulation of ECM, thickening of renal tubules and glomerular basement membrane, thus increasing the risk of DN. However, to date, the association between DN risk and SNPs within ELMO1 gene have not been extensively examined in Chinese populations. Strong evidences [13, 14] have suggested the important role for the combination of environmental exposures and genetic factors for development or progression of the DN. However, till now, no study investigated the ELMO1 gene–environment interaction. Therefore, the present study aimed to evaluate the impact of four SNPs in the ELMO1 gene, and its interaction with environmental risk factors on susceptibility to DN.

A description for DN patients and normal controls regarding demographic and general or clinical characteristics is shown in Table 1. A total of 1325 participants including 660 T2DM patients with DN and 665 T2DM patients without DN (controls). The average age for all participants was 66.0 ± 12.8 years. There was no significant difference found in several parameters, including gender, smoking rates, age, duration of diabetes, FPG and BMI between the two groups (all p-values were more than 0.05). In contrast, the percentages of participants who consumed alcohol, hypertension patients, means of HbA1c, creatinine, urea and urine albumin/creatinine ratios (ACR) were higher in the DN patients than that in controls.

The genotype frequencies in the control of the current study were all distributed accordingly to HWE (Table 2). The frequency of the rs741301-G allele was 30.7% in DN patients and 20.2% in normal controls, in addition, the frequency of the rs10255208-G allele was 28.3% in DN patients and 20.4% in normal controls, which was also indicating a significantly statistical difference. The rs741301-G allele and the rs10255208-GG genotype were associated with an increased risk of DN risk, adjusted ORs (95% CI) were 1.75 (1.19–2.28) and 1.41 (1.06–1.92), respectively. We also found that the others SNPs-rs1345365 and rs7782979 were not correlated with DN susceptibility significantly.

The gene–hypertension or alcohol drinking interaction test were determined by GMDR model (Table 3). We found a significant gene–alcohol drinking interaction combination, but no significant gene–hypertension interaction combinations, after adjusting for age, gender, BMI, smoking and alcohol drinking covariates. A two-locus including rs741301 and alcohol drinking was significantly in the GMDR model. In order to obtain the odds ratios and 95% CI for the joint effects of gene–alcohol drinking on DN, we conducted stratified analysis for interaction effect using logistic regression. We found that alcohol drinkers with rs741301-AG/GG genotype also have the highest DN risk, compared to never drinkers with rs741301-AA genotype, OR (95% CI) 3.52 (1.93–4.98) (Fig. 1).

In the current study, we found that rs741301-G allele and the rs10255208-GG genotype were associated with an increased risk of DN risk respectively. We also found that the others SNPs-rs1345365 and rs7782979 were not significantly associated with susceptibility to DN. DN is the most common cause of ESRD and the most common microvascular complication of diabetes mellitus [17]. However, its detailed pathogenesis was not well known yet, and both environmental and genetic factors were reported involving in the occurrence and development of DN susceptibility [18, 19]. ELMO1 is a protein composed of 720 amino acids, encoded by elmo1 gene and located on chromosome 7p14.2-14.1. It may be a new and powerful candidate gene of DN, which has influence on the movement and phagocytosis of apoptotic cells [20]. Animal studies in mice [21] suggest that ELMO1 protein plays an important role in the pathogenesis of DN and proteinuria. Over the last decade, some studies were performed to test the relationship between ELMO1 gene SNPs and DN risk, but these studies concluded inconsistent results, and few studies were performed in Chinese populations. Mehrabzadeh et al. [22] investigated the relationship between ELMO1-rs741301 and the risk of DN in Iranian population, and considered that ELMO1-rs741301 is an important candidate gene for DN susceptibility. Bodhini et al. [23] reported a significant association of the ELMO1 rs741301 SNPs with DN in south Indians. Wu et al. [11] also verified the association of rs741301 with DN, and rs1345365 was not associated with DN risk, however the sample size for this study was very small, just 200 unrelated Chinese subjects were enrolled. Some studies including GWAS and replication studies were performed in Japanese type 2 diabetic patients [8], replication studies in American Indian study [10] and GoKinD collection study [9], African American cohorts [24]. The key role of ELMO1 as a DN susceptibility gene has been verified. Although many studies have confirmed that elmo1 is a candidate gene for DN, the risk locus and risk allele are not consistent in all populations [25]. Different perspectives also existed in some studies. Yahya et al. [26] suggested that ELMO1-rs74130 was not associated with susceptibility to DN. Hanson et al. [10] indicated that ELMO1-rs1345365, but not rs741301 associated with DN risk. In terms of rs10255208, which was less studies previously, but this SNP has been reported association with T2DM in Tunisian Arabs [27].

The pathogenesis and process of DN are very complex. The factors of DN susceptibility mainly include genetic factors, environmental factors and the synergistic effect of genetic and environmental factors [28, 29]. Some studies have showed that the interaction between gene and environment factors were associated with the DN risk. This study is the first to confirm the synergistic effect of elmo1 gene polymorphism and environmental factors on DN susceptibility. We found a significant gene–alcohol drinking interaction combination, but no significant gene–hypertension interaction combinations. Alcohol drinkers with rs741301-AG/GG genotype also have the highest DN risk, compared to never drinkers with rs741301-AA genotype. The detailed mechanism for ELMO1 gene-DN association was not well known. However, a previous study [12] showed that mutations in elmo1 gene can lead to the disorder of ECM metabolism, the accumulation of which could thicken of renal tubules and glomerular basement membrane, thus increasing the risk of DN. Another study [21] suggested that ELMO1 also could plays an important role in the development of DN by increasing oxidative stress (OS), the level of elmo1 gene expression in diabetic mice was consistent with the degree of renal fibrosis and urinary albumin excretion. There was also a positive correlation between ROS and ELMO1 expression.

The limitations of this study were: Firstly, more environment factors should be included in the interaction analysis; secondly, the study population were all Chinese Han, which may not present on behalf of the Chinese populations, because there were 56 races in China. Secondly, just four SNPs were selected for genotyping, more SNPs should be included, and gene–gene interaction should be investigated in the future.

In conclusion, we found that the rs741301-G allele and the rs10255208-GG genotype, gene–environment interaction between rs741301 and alcohol drinking were all associated with increased DN risk. This study not only investigated whether the ELMO1 gene was related to DN susceptibility, but also investigated whether the interaction effect existed between this gene and some significant environmental factors, such as hypertension, alcohol drinking. Previous studies merely investigated this interaction effect between ELMO1 gene and alcohol drinking, especially in Chinese Han populations.