Frequency of TLR 2, 4, and 9 Gene Polymorphisms in Chinese Population and Their Susceptibility to Type 2 Diabetes and Coronary Artery Disease

1. Introduction

Coronary artery disease (CAD) is the leading cause of death in men and women worldwide.Type 2 diabetes mellitus, a major cause of cardi-ovascular morbidity and mortality, has increased in Chinese Han population. Although the primary cause for this increment remains unclear, the activation of innate immunity system and chronic low-grade inflammation may be plausibly involved. Recent studies have suggested the role of certain genetic variants of innate immunity system in the predisposition to the development of the disease.

Toll-like receptors (TLRs) are the family of genetically conserved transmembrane receptors involved in the innate immunity and pathogen recognition. Recognition of pathogen-associated molecular patterns by TLRs activates signaling events that induce the expression of e ector molecules, such as cyfftokines and chemokines, controlling theadaptive immune responses.

Genetic variations within genes encoding these receptors have an important influence on the pathogenesis of inflammatory diseas-es. Variations within genes of the family of innate immune receptors may account, in part, for the inherited di erences in the susc- ffeptibility to autoimmune diseases or inflamm-atory disease. The ability of certain individua-ls to respond properly to TLR ligands may be impaired by single nucleotide polymorphisms (SNPs) within TLR genes, resulting in an alter-ed susceptibility to the disease.

Considering the potential role of TLRs pathway in the overall immune reconstitu-tion, we examined whether the altered im-mune response caused by TLRs gene var- iation was associated with type 2 diabetes and/or its macrovascular complications.We were particularly interested in compa-ring the role of TLR variations in subgrou-ps of CAD patients with and without type 2 diabetes.

2.Materials and Methods

Genotyping. Blood samples from all subj-ects were collected in EDTA vials and stored at −80◦C until required. Genomic DNA was is-olated from frozen whole blood using the EZ-10 Spin Column Whole Blood Genomic DNA MiniPreps Kit (Sangon, Canada) according to the manufacturer’s instructions.The alleles of TLR gene polymorphisms were detected using polymerase chain restriction-restriction fragm-ent length polymorphism (PCR-RFLP) proced-ure.

PCR reactions were set up in a 25 μLreactionvolumecontaining 1.5μL10 μMforwardprimer,1.5 μL10 μMreverse primer, 1.5 μL DNA extract, 12.5 μLGoTaqGreenMaster Mix (Promega, USA), and 8.0 μL sterilized ddH2O.Reactions were run on a PTC-200 DNA Engine PCR (BIO-RAD, USA) using the following conditions: initial denatura-tion at 95◦C for 5min followed by 36 cycles of denaturationat 94◦C for 40 seconds, annealing at X◦C for 40 seconds,and extention at 72◦C for 1 minute. A final extension stepwas at 72◦Cfor10minute.ThePCRproductswereheldat4◦C until analysis. The primers and PCR conditions used todetect TLR variants were listed in Table 2.PCRproductswereelectrophoresed in an agarose gel and visualized by ethidium bromide staining. TLR9 gene PCR products were shown in Figure 1.

The PCR products (10 μL) were digested overnight or for 12–14 h at 37◦C with 5U of restriction endonucleases:ciI for TLR2 Arg677Trp and Arg753Gln polymorphisms,NcoI for TLR4 Arg299Gly and HinfIfor TLR4 Arg399Ile polymorphisms, and BstNI for TLR9-1237T/C and AflII for TLR9-1486T/C polymorphisms. Digested PCR productswere separated by electrophoresis through 1%–2.5% agarosegel. After digestion, the wild-type allele sizes of TLR2 were 55 bp, 147 bp, and 228 bp; the wild-type allele sizes of TLR4 did not change and they were 249 bp for the Asp299 (A allele) and 406 bp for the Thr399 (C allele); the wild-type allele sizes of TLR9-1237T/C polym-orphism were 108 bp and 27 bp; the wild-type allele sizes of TLR9-1486T/C polymorphism were 172 bp and 327 bp. The sizes for poly-morphic alleles were 283 bp and 147 bp for TLR2 Arg677Trp; 375 bp and 55 bp for TLR2 Arg753Gln; 223 bp and 26 bp for TLR4 299Gly(G allele) and 377 bp for TLR4 399Ile (T allele); 60 bp,48 bp, and 27 bp for TLR9-1237T/C and 499 bp for TLR9-1486T/C. Electrophoretic separation of TLR9 gene -1486T/C polymorphism was shown in Figure 2.

3. ResultsIn T2DM group, 14 of the 33 patients were heterozy-gotes for TLR9-1486T/C polymorphism and 6 were Mutant homozygotes. In CAD group, 76 of the 173 patients were heterozygous for TLR9-1486T/C poly-morphism and 28 were mutant homozygous. In T2DM and CAD group, 71 of the 160 patients were heteroz-ygous for TLR9-1486T/C polymorphism and 23 were mutant homozygous. In control group, 37 of the 66 patients were heterozygotes for TLR9-1486T/C poly-morphism and 6 were mutant homozygotes. The frequencies of TLR-1486T/C genotypes and alleleswere not significantly di erent between groups, respffectively(P = 0.642, P = 0.962, Table 3).

4. DiscussionOur findings showed that there were three geno-types in TLR9 promoter-1486T/C position in ChineseHan population. The frequency of the C allele was 37.5%.The genotype frequencies of the TLR9-1486T/C in Chinese Han population were similar to those of Koreans. But exploratory analyses did not support the association between TLR9-1486T/C polymorphism and the prevalence of T2DM or angiographic coronary artery disease. Although no significant association was found, the CC genotype of TLR9-1486T/C tended to be overrepresented in patients with T2DM compared with controls.However, the frequency of C allele in controlsis not in line with the finding from Japanese population (Table 4).

It was reported that Korea population had low frequencyof TLR9-1237T/C. No TLR9-1237T/C poly-morphism was present in 183 patients with SLE and 198 controls in a Japanese population. But high frequency of the variant allele was reported in the Caucasian population. The genetic variation at position-1237 is associated with an increased risk of asthma in European American popu-lations. However, we did not detect any SNP at position-1237 in our study, and Korean and Japanese populations and other Chinese population also have much less variations at position-1237. It would be very interesting to examine whether distinct TLR9-1237T/C genotype variations worldwide may be related to the disease patterns in these countries, especially consideringthe relatively low incident rate of heart diseases in theOriental populations.

Many studies in Caucasians suggested that TLR4polymorphisms were associated with innate immunity-related diseases, such as chronic inflammatory diseaseand atherosclerosis. One study showed that TLR4Asp299Gly polymorphism was associated with reductions in vascular inflammation, angiographic coronary arterydisease, and clinical diabetes in Caucasian populations.A strong association between the TLR4 Asp299Gly/Thr399Ilepolymorphism and diabetic neuropathy was showed inRudofsky’s study.

In contrast, TLR4 Asp299Gly andThr399Ile polymorphisms were reported to be very rare inseveral studies of Asian ethic groups. Hang et al. failed todetect any homozygous or heterozygous variant genotypes ofTLR4 Asp299Gly and Thr399Ile polymorphisms in 491 HanChinese subjects, consisting of cotton and silk textile workerswho was exposed to endotoxins. In addition, almostno Asp299Gly were detected in ethnic Chinese patients in astudy that analyzed the association of ischemic stroke withthe TLR4 gene polymorphism.

In our study subjects, TLR2 Arg677Trp and Arg753Glnpolymorphisms, TLR4 Asp299Gly and Thr399Ile polym-orphisms, and TLR9-1237T/C mutation were all absent,In a complete agreement with studies in Japanese andKorean population. It is not clear whether the very low frequency of these TLR variants, as reported in thisstudy, would be related to the low incident rates of diseases in the Orientals, such as diabetes and coron-ary artery disease compared with the western popula-tion. A large international study covering both develo-ped countries and Asian populations that have varied TLR variations should be investigated to address this hypothesis.

In conclusion, the present study suggests that TLR9-1486T/C polymorphism may not be appropriate to predict the susceptibility to T2DM or CAD in Chinese Shanghai Han population. Like other Asian populations, Shanghai Han population has very low occurrence of other TLR SNPs, including TLR2 Arg677Trp and Arg753Gln polymorphisms, TLR4 Asp299Gly and Thr399Ile polymorphisms, and TLR9 promoter-1237T/C mutation, which is unlike western countries. Whether these unusually rare TLR variations are also related to distinct disease patterns in di erent racial population awaits further invesfftigation.