Correlation between SEPS1 gene polymorphism and type 2 diabetes mellitus: A preliminary study

Abstract Background The protein encoded by the selenoprotein S gene is considered to be an anti‐inflammatory and antioxidant protein and is involved in a variety of diseases. Therefore, we want to study the distribution characteristics of this gene in Chinese diabetic population. Methods A total of 170 patients with DM (including 100 patients with T2DM and 70 patients with diabetic nephropathy [DN]) and 100 healthy controls (HC) were selected from Haikou People's Hospital (China) between January 2017 and July 2017. The polymorphisms of three SEPS1 genes (SNP ID: rs4965814, rs28665122, and rs34713741) were measured by massARRAY method, while the polymorphisms of SEPS1 genes (SNP ID: rs4965373) were detected by Sanger sequencing. Results Comparing three groups, the results were the following: (a) There was a significant difference in the genotype and allele distribution of rs34713741 between DN group and HC group and between T2DM group and DN group; For this gene locus, the risk of diabetic nephropathy in healthy individuals with T allele was 0.6 times higher than that in individuals with GG genotype (OR = 0.60, 95% CI: 0.46 ~ 0.77). (b) There was a significant difference in the distribution of rs4975814 genotype between DN group and HC group; for this gene locus, the risk of diabetic nephropathy in healthy individuals with T allele was 2.71 times higher than that in individuals with GG genotype (OR = 2.71, 95% CI: 1.66 ~ 4.45). Conclusion We conclude that rs34713741 (GT + TT) may be a protective gene for DN and the rs4975814 (GT + TT) may be a susceptibility gene for DN.

resistance to inflammation, through "selenide" glutathione peroxidase and thioredoxin reductase. 1 Currently, it has been found that selenoprotein gene polymorphism is closely associated with inflammatory and immune diseases. Over the recent years, five kinds of selenoproteins, that is, glutathione peroxidase (GPx), thioredoxin protein reductase 2 (TrxR2), selenoprotein (relative molecular mass 15 000; SEP15), selenoprotein P (SelP), and selenoprotein S (SEPS1, also known as SelS) have been intensively studied. As a transmembrane protein, 2 SEPS1 constitutes a reverse transport channel for endoplasmic reticulum (ER)-associated protein degradation together with ER-associated protein 1, which reversely transports misfolded proteins from the ER to the cytoplasm for degradation, and also inhibits and regulates the inflammatory and immune response caused by misfolded proteins in the ER. 3 In the human genome, 25 selenoprotein genes have been identified. 4 In 2002, SEPS1 was discovered as a novel gene that produces a protein that interacts with serum amyloid protein (SAA). SAA is an acute phase protein involved in insulin resistance, which has an important role in the development of diabetes and atherosclerosis. 5 So far, there have been few reports on the polymorphism of SEPS1 gene in T2DM, especially in the Chinese population.
The following study investigates the correlation between SEPS1 gene polymorphism and T2DM in Chinese population.

| Patients
A total of 100 patients with T2DM, 70 patients with diabetic nephropathy and 100 healthy controls were selected from Haikou People's Hospital (China) between October 2017 and January 2018. The information that could identify individual participants during or after data collection can be access to by us. The specific clinical data for each patient are shown in Table 1 and Table 2. The inclusion criteria for patients with T2DM and diabetic nephropathy were as follows: (a) The T2DM was diagnosed according to the criteria of American Diabetes Association (ADA) in 2016 6 and (b) clinical diagnosis of T2DM or diabetic nephropathy. Healthy controls with primary diseases of important organs (heart, liver, kidney, brain), or with history of drug abuse or allergic constitution were excluded from the study.

| Genomic DNA extraction from peripheral blood
Genomic DNA was extracted from peripheral blood using DNA extraction kit (Beijing Sunbiotech Company); EDTA anticoagulated venous blood. The obtained DNA solution was stored at −20°C.

| Statistical analysis
SPSS 21.0 statistical software was used for data processing and statistical analysis. The frequency of each allele and genotype of SEPS1 was calculated. Hardy-Weinberg equilibrium test and linkage disequilibrium test were carried out with SHEsis software to check whether each group accorded with the equilibrium. The SEPS1 gene polymorphism between the groups was compared by independent sample chisquare test. P < 0.05 was considered statistically significant.

| RE SULTS
In the study of healthy control group and diabetes mellitus group, Compared to the control group, no significant difference in the genotype and allele distribution was found for rs4965373, rs28665122, rs34713741, and rs4975814 of the DM group (Table 3 and Table 4).
Next, we compared the difference in the genotype and allele distribution between three groups (T2DM, DN, and HC). Briefly, we found no significant differences in the genotypes and alleles distribution for rs4965373 and rs28665122 between groups. Moreover, statistically significant difference in the genotype and alleles distribution of rs34713741 was found between DN group and HC group (χ 2 = 6.495,  (Table 5 and

| D ISCUSS I ON
The SEPS1 gene, which is located on 15q26.3, contains 6 exons and 5 introns. 7 It is expressed in different tissues, including adipose tissue, muscle, and liver. 5 13 On the contrary, Li and his team have performed a study of HT patients in China and have found that 2 SEPS1 SNPs (rs2009895-rs28665122) were significantly associated with female HT, but not in male population, 14 confirming the propulsive role of this gene in chronic inflammation. The expression product of the SEPS1 gene also revealed to have an important role in the progression of diabetes.
Studies have shown that the expression of SEPS1 in omental adipose tissue of patients with T2DM was higher than that of non-diabetic patients, and Pearson's correlation analysis confirmed that the expression of SEPS1 in omental adipose tissue was positively correlated with SAA and HOMA-IR. 15   is correlated with the risk of CKD. Nevertheless, the SEPS1 SNP they studied was mainly 105G-A (rs34713741), while our study demonstrated that there was a significant association between the polymorphism of rs4713741 and rs4975814 and diabetic nephropathy, which was in line with the observations made by Hishida.
TA B L E 6 Comparison of genotypes and alleles distribution in three other gene locus polymorphisms between two groups of T2DM and DN and HC groups  Note: 2 1 and P 1 were compared between T2DM and HC groups; 2 2 and P 2 were compared between DN and HC groups; 2 3 and P 3 were compared between T2DM and DN groups. In some samples, the amount of DNA remaining was insufficient after first generation sequencing of Sanger, and the cases of actual measurement were 198. P value: chi-square test. Abbreviations: DN, Diabetic nephropathy; HC, Healthy controls; T2DM, Type 2 diabetes mellitus.
While the cause of diabetes still remains unknown, it is certain that it involves a variety of factors and that it is affected by the external environment and internal genetic factors.

This study was supported by the Finance Science and Technology
Project of Hainan Province (No.ZDYF2018132). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

CO N FLI C T O F I NTE R E S T
All authors declare no competing interests.

E TH I C A L A PPROVA L
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.