BioMed Research International
Volume 2016 (2016), Article ID 5675084, 11 pages
http://dx.doi.org/10.1155/2016/5675084

Research Article

Identification of ITGA2B and ITGB3 Single-Nucleotide Polymorphisms and Their Influences on the Platelet Function

Qian Xiang,¹ Shun-Dong Ji,2,3 Zhuo Zhang,¹ Xia Zhao,¹ and Yi-Min Cui¹

¹Department of Pharmacy, Base for Clinical Trial, Peking University First Hospital, Beijing 100034, China
²Jiangsu Institute of Hematology, Key Laboratory of Thrombosis and Hemostasis of Ministry of Health, The First Affiliated Hospital of Soochow University, Suzhou 215006, China
³Collaborative Innovation Center of Hematology, Soochow University, Suzhou 215006, China

Received 3 February 2016; Accepted 18 April 2016

Academic Editor: Robert Baiocchi

Copyright © 2016 Qian Xiang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The aim of the study was to investigate ITGA2B and ITGB3 genetic polymorphisms and to evaluate the variability in the platelet function in healthy Chinese subjects. The genetic sequence of the entire coding region of the ITGA2B and ITGB3 genes was investigated. Adenosine diphosphate-induced platelet aggregation, glycoprotein IIb/IIIa content, bleeding time, and coagulation indexes were detected. Thirteen variants in the ITGA2B locus and 29 variants in the ITGB3 locus were identified in the Chinese population. The rs1009312 and rs2015049 were associated with the mean platelet volume. The rs70940817 was significantly correlated with the prothrombin time. The rs70940817 and rs112188890 were related with the activated partial thromboplastin time, and ITGB3 rs4642 was correlated with the thrombin time and fibrinogen. The minor alleles of rs56197296 and rs5919 were associated with decreased ADP-induced platelet aggregation, and rs55827077 was related with decreased GPIIb/IIIa per platelet. The rs1009312, rs2015049, rs3760364, rs567581451, rs7208170, and rs117052258 were related with bleeding time. Further studies are needed to explore the clinical importance of ITGA2B and ITGB3 SNPs in the platelet function.

1. Introduction

Platelet aggregation plays a central role in the pathogenesis of acute thrombosis in coronary heart disease, stroke, and peripheral arterial disease. The cellular events leading to platelet aggregation are mediated by the binding of fibrinogen to the glycoprotein (GP)IIb/IIIa receptor of platelets as a final common pathway. GPIIb/IIIa is a platelet-specific, surface membrane receptor and also called alpha IIb beta 3 (aIIb β3) in the integrin nomenclature and thus plays a primary role in both platelet adhesion and thrombus formation at the vascular injury site [1]. A large interindividual number variability for GPIIb/IIIa receptors expressed on the platelet surface is commonly observed [2, 3]. Moreover, a defect in the GPIIb/IIIa complex or a qualitative abnormality of this complex is seen in Glanzmann’s thrombasthenia patients with impaired platelet aggregation and increased bleeding [4].

The ITGA2B gene encodes the aIIb subunit (GPIIb), whereas the ITGB3 gene encodes β3 (GPIIIa). The ITGA2B spanning 17 kb has 30 exons, whereas the ITGB3 spanning 46 kb has 15 exons; they are closely located on chromosome 17q21.32 without evidence for coordinated expression [5]. A few studies have linked single-nucleotide polymorphisms (SNPs) in ITGA2B and ITGB3 with increased or decreased platelet responses to various agonists and the risk of acute coronary syndrome and atherosclerosis [6–8].

A common polymorphism in the ITGB3, known as the human platelet antigen 1 (HPA-1b, PlA2, or rs5918), arises from a single-nucleotide change at position 1565 in Exon2 of ITGB3, resulting in a leucine (PlA1) to proline (PlA2) substitution at residue 33 [9]. The SNP has been extensively studied as an inherited risk factor for acute coronary syndrome and for its effect on the platelet function [6–8]. The HPA-3 (rs5910) polymorphism results from a thymine to guanine base change that leads to the replacement of isoleucine (HPA-3a) by serine (HPA-3b) at codon 843 of GPIIb (ITGA2B). This polymorphism may potentially influence the activity of the GPIIb/IIIa complex and associate with thrombosis [10].

According to the aforementioned studies, GPIIb/IIIa was believed to be a platelet-platelet contact receptor playing an important role in platelet aggregation, and its SNPs were associated with platelet hyperreactivity and have an effect on the pharmacodynamics of antiplatelet drugs. However, limited information was available on other genetic polymorphisms of ITGA2B and ITGB3 in Asian populations or their association with the platelet function [11, 12]. Moreover, the prevalence of the PlA2 allele (rs5918) is dependent on ethnicity, with a frequency of approximately 15/100 in Caucasian populations [13] falling to less than 1/100 in Oriental populations [12, 14].

In this study, regions of the exons of ITGA2B and ITGB3 genes were sequenced in 86 unrelated healthy Chinese. In addition, the association between genetic variants of ITGA2B and ITGB3 exons and the adenosine diphosphate- (ADP-) induced platelet aggregation, GPIIb/IIIa content, bleeding time, and coagulation indexes was investigated in 55 of the 86 subjects.

2. Materials and Methods

2.1. Study Design

The research was conducted in compliance with the Declaration of Helsinki. The study protocol was approved by the Ethical Review Board of the Peking University First Hospital. All subjects gave their written informed consent prior to participation in the study. Healthy native Chinese subjects () between 18 and 45 years of age with a body mass index (BMI) of 19–24 kg/m² were included in the study, and their genotypes were unknown.

All the subjects were considered healthy on the basis of their medical history, physical examination, vital signs (blood pressure, pulse rate, and temperature), safety laboratory tests (blood chemistry, hematological tests, and urinalysis), and 12-lead electrocardiography.

The ADP-induced platelet aggregation (transmission, max), GPIIb/IIIa content (GPIIb/IIIa per platelet), bleeding time, and coagulation indexes, including the mean platelet volume (MPV), platelet count (PLT), prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen (FIB), and thrombin time (TT) were detected in 55 of the 86 subjects. None of the donors had taken any medication for 2 weeks before blood collection.

2.2. ADP-Induced Platelet Aggregation

Blood was collected in 3.8% sodium citrate tubes, and platelet-rich plasma (PRP) was obtained by centrifuging blood at 1000 revolutions per minute (rpm) for 10 minutes at room temperature. The PRP was collected in a fresh tube and platelet was counted by Platelet Counter PL100 (Sysmex, Kobe, Japan). Platelet-poor plasma (PPP) was obtained by centrifuging the remaining blood at 3000 rpm for 10 minutes at room temperature, and platelet numbering PRP was adjusted to 250 × 10⁹/L by PPP. Detection was completed within 1 hour after sampling.

Platelet aggregation was determined by the turbidimetric method using 20 umol/L ADP as the agonist. After zero setting with the PPP, assays were performed in platelet-rich plasma in a Chrono-Log aggregometer. Platelet aggregation was quantified as the maximum change in light transmission occurring within 5 minutes of addition of agonist.

2.3. GPIIb/IIIa Content

GPIIb/IIIa on the platelet surface was evaluated in the PRP as the maximal binding of a ¹²⁵I-labeled GPIIb/IIIa integrin antiplatelet antibody F(ab)₂ [15]. The PRP was fixed with equal volume of anticoagulant-fixative solution (10 mmol/L EDTA-Na₂, 0.2% glutaraldehyde, and 0.02% sodium azide dissolved in PBS, pH 7.4). After stored at 4°C, overnight, platelet was washed by Tyrode’s solution twice and resuspended in Tyrode solution, containing 0.35% bovine serum albumin (concentration adjusted to 1 × 10¹¹ platelets/L), and sodium azide was added at final concentration of 0.02% (V/V) to preserve the platelet at 4°C for a week-long before assay. For detection, the platelet suspension (100 μL) was added to a 0.5 mL Eppendorf tube and then incubated with 100 μL of antibody (containing 20,000 cpm of labeled monoclonal antibody (McAb) and 0.8 μg of unlabeled McAb) at 37°C for 1 hour, after washed with 0.35% bovine serum albumin/Tyrode’s solution for three times. The radioactivity count of the precipitate in the tube was measured. Assuming that one monoclonal antibody would only bind one GP molecule on the platelet membrane, the number of GP molecules on the platelet membrane was calculated as number of GP molecules/platelet = (binding rate × amount of antibody (g) × Avogadro’s number)/(molecular weight of antibody × platelet count).

2.4. Bleeding Time

The skin bleeding time was carried out using the Simplate-II device (General Diagnostics, NJ, USA). A sphygmomanometer cuff was inflated on the patient’s arm to 40 mmHg. The arm was supported at the level of the heart, and a muscular area on the volar aspect distal to the antecubital area was identified and swabbed with alcohol. The Simplate-II device was used to perform the incision perpendicular to the antecubital fossa. Blood was blotted with sterile filter paper every 30 seconds until blood no longer stained the paper. The time from incision to stopping of bleeding was recorded.

2.5. Genetic Analysis

Genomic DNA was extracted from peripheral whole blood samples of each subject using a DNA Purification Kit (Wizard; Promega, WI, USA). After the polymerase chain reaction (PCR) products were obtained, all samples were directly sequenced to determine the SNPs in ITGA2B and ITGB3 (Life Technologies Biotechnology Co., Ltd., China).

Primers required for PCR amplification and sequencing were designed according to the wild-type ITGA2B and ITGB3 sequences reported in the GenBank (NG_008331.1 and NG_008332.1, resp.). Tables 1 and 2 describe the primer pairs used to amplify the promoters, the 5′- and 3′-untranslated regions (UTRs), the entire coding regions and the intron-exon junctions of the ITGA2B and ITGB3 genes.

Table 1: Summary of GPIIb (ITGA2B) variations detected in this study.

Sequence number obtained in this study
dbSNP
Location
NC_000017.11
NM_000419.3
Nucleotide change
NP_000410.2 amino acid change
MA(F)
H-W

ITGA2B-01
rs3760364
5′ upstream end
44390436
-963
ctcccaaggg A/T ctcatttaca

T(0.052)
0.609

ITGA2B-02
New
5′ upstream end
44390152
-679
tagaccaagg T/C ccattcacca

C(0.006)
0.957

ITGA2B-03
New
5′ upstream end
44390081
-608
caagacggag G/A aggagtgagg

A(0.006)
0.957

ITGA2B-04
New
Exon3
44385910
354
tgatgagacc C/T gaaatgtagg
Arg108Stop
T(0.006)
0.957

ITGA2B-05
New
Exon13
44380960
1344
ctcccaggtc C/A tggacagccc
Leu438Met
A(0.006)
0.957

ITGA2B-06
rs201355504
Intron13
44380821
1393+58
cttggcactt C/T cagcgaatgt

A(0.006)
0.957

ITGA2B-07
New
Exon14
44380638
1401
tagacctgat C/G gtgggagctt
Ile467Met
G(0.006)
0.957

ITGA2B-08
rs850730
Intron21
44377095
2188-7C>G
ccctcctcat C/G tcccagatag

G(0.477)
0.289

ITGA2B-09
New
Exon23
44376336
2320
cgtgccggtc C/T gggcagaggc
Arg774Trp
T(0.006)
0.957

ITGA2B-10
rs117870452
Exon23
44376322
2334
gcagctccac C/T tgggcctctg
Gln778=
G(0.012)
0.913

ITGA2B-11
rs5911
Exon26
44375697
2621T>G
ggggctgggg A/C tgggcagccc
Ile874Ser
G(0.477)
0.289

ITGA2B-12
rs5910
Exon30
44372421
3063C>T
acccccaggt C/T ggcttcttca
Val1021=
T(0.465)
0.289

ITGA2B-13
New
3′-UTR
44372213
151C>A
gctacccccc C/A tcctgctgcc

A(0.017)
0.869

dbSNP, single nucleotide polymorphism database; H-W , Hardy–Weinberg equilibrium value; MA(F), minor allele (frequency); GP, glycoprotein.

SNPs which related with bleeding time in this study.

Table 2: Primer sequences used in this study.

DNA sequence number
Amplified or sequenced region
Forward primer (5′ to 3′)
Reverse primer (5′ to 3′)
Amplified region NC_000017.11
Length (bp)

ITGA2B-1

TCCTCCTCTTCCGCTTACCG
TACTACCACCGTGCTAGTCC
44389728–44390630
848

ITGA2B-2
Exon1
CCAATATGGCTGGTTGAG
AACTTCCCTTACGGCTCA
44389267–44390059
792

ITGA2B-3
Exon1
CCAGTGCAGCTCACCTTCTA
GATGAGGGAAATGGAACAGA
44388253–44389368
1115

ITGA2B-4
Intron1
TATGAACCACTCCACCCT
TTGGCACTCTTGATTCTG
44388169–44389006
837

ITGA2B-5
Exon2, Exon3
ACCGCTGGTTCTTGTTGC
CCTACGGGCGTCTTCTCA
44385649-44386479
830

ITGA2B-6
Exon4–Exon6
TACAGGGCACAGGGAACAATC
AGAGGCTCTGGGAGGACACG
44384990–44385810
820

ITGA2B-7
Exon7, Exon8
TCCTGGCGGCTATTATTTCT
GCACCGACGACATATTCTGG
44384339–44385186
847

ITGA2B-8
Exon9–Exon11
ATTTGCGCCCTTGTCCTC
AGCCGAATCGCCCATAGA
44383538–44384605
1067

ITGA2B-9
Exon12
CCCTCTGTCTCCCTTTCC
CATCCAGTCTCCCACCAA
44383189–44383838
649

ITGA2B-10
Exon13, Exon14
CCTAGTCTCCTGGGATGTTC
TCACGGGTGTCTTGGTCT
44380390–44381163
773

ITGA2B-11
Exon14–Exon17
TAATCGCCAATTCTGACCC
CACATCCCACCTTCTCCTG
44379854–44380682
828

ITGA2B-12
Exon18
ACCCACTGGACTTGTTCATC
TGTGACTTGGCACTAACCC
44379610–44379957
347

ITGA2B-13
Exon19, Exon20
TGGACGACAGAGCGAGAC
GGCCATACCTCGACATTG
44378354–44378989
635

ITGA2B-14
Exon21
CATGTGACAGTCCCTTGA
AAAGTCACTCACCCAAGGA
44377551–44377933
382

ITGA2B-15
Exon22
CTTGGAGGGTGAAGACTGG
CAACTCCTGACCTCCAGTGA
44376833–44377179
346

ITGA2B-16
Exon23–Exon25
CCAGGTCTAACTTCAGTGTG
GCTCTGGCAGGAAGATCTGT
44375629–44376523
894

ITGA2B-17
Exon26
TCCGACCTGCTCTACATCC
CGGGCTTGCTCACATAGTC
44375277–44375913
636

ITGA2B-18
Exon27, Exon28
ATGACCCTCCCTGCATCTC
CACCTTGACACCTGCCTTT
44374500–44375317
817

ITGA2B-19
Exon29
GCACGCATGGTTCAACGT
CCTCCCGAGTAGCTGAGATT
44374025–44374731
706

ITGA2B-20
Exon30
AAAGGCATCCATTTGTGA
TGTTGGTAAGGCTGGTCTC
44371896–44372566
670

ITGB3-1

CAGGAGGTGGAGGATTGT
GCTGGATTCTTGGGACAC
47252637–47253474
837

ITGB3-2
Exon1
CGGTTCAGAGAAGGCATTCAG
GCTCCAAGTCCGCAACTTGA
47253373–47254015
642

ITGB3-3
Intron1
TTGGCGTAGGAGGTGAGTGA
CCGCAGGAAGCCAAGTTGAA
47253929–47254518
589

ITGB3-4
Intron1
TTGGCGTAGGAGGTGAGTGAG
GAAGTTGCAGTGAGCCGAGAA
47253929–47255063
1134

ITGB3-5
Exon2
ATTGGGAAAGTTGGGAAGG
GAAAGGGCAGCAGTGGTT
47274335–47274773
438

ITGB3-6
Exon3
AGGCTGGTCTTGAACTCTTG
CTCCACCTTGTGCTCTAT
47283116–47283612
496

ITGB3-7
Exon4
GGGCTTTCTGGTTTGCTT
CATTTCCCTCCCATTCTC
47284329–47284978
649

ITGB3-8
Exon5
TGTCTGGGTAACTGTGGT
CATCTGCCTACTTTGCTG
47286124–47286725
601

ITGB3-9
Exon6
TCCAAGGACTGGGACTGA
ATGATGCTGCTGCTATGC
47286919–47287483
564

ITGB3-10
Exon7, Exon8
AGCCCAAGCAAGATAAGT
GGAGAAGGCAGTAAGACC
47289597–47290393
796

ITGB3-11
Exon9
AAACTGGGCTCCAATAAC
TGAGGGACTGAAGGTAAAG
47290561–47291406
845

ITGB3-12
Exon10
CAGGGCAGGGAACAACTT
GGATTGGTCCTTATACTCAAAA
47292050–47292720
670

ITGB3-13
Exon11
GAGCAAGTCCTGCCATAC
TCACAGAGTGTCCTCCATAA
47299101–47299890
789

ITGB3-14
Exon12
CAGAAATGGCATAGGGTT
TCTTGCTGAGTCTGTGGG
47300168–47300824
656

ITGB3-15
Exon13
CTTGAATCTAGGCATCGT
GTATTGAACTCCTGACCC
47302581–47303050
469

ITGB3-16
Exon14
CCTCAAGTAGGTCCCAGTG
AACATGACCACCCAAAGC
47307158–47307721
563

ITGB3-17
Exon15
CTCATCTCCTCCTGTTATTT
TGACATTCTCCCAACCTAC
47309941–47310337
396

2.6. Data Analysis

The Variant Reporter v1.1 (Life Technologies Biotechnology Co., Ltd.) software suite was used for the initial analysis of the sequence, including base calling, fragment assembly, SNP, and sequence insertions/deletions detection. Polymorphisms of ITGA2B and ITGB3 genes were named according to the genomic reference sequences NG_008331.1 and NG_008332.1, respectively. Novel SNPs were named as ITGA2B-number or ITGB3-number in the present study.

2.7. Statistical Analysis

The association between two parameters was assessed by Pearson’s two-tailed test. Statistical analyses were performed using the Statistical Package for Social Sciences software program for Windows (SPSS version 16.0). A value of 0.05 was considered significant.

3. Results

3.1. ITGA2B and ITGB3 Variations

Within the Chinese sample, 13 and 29 variants in ITGA2B and ITGB3 were identified, respectively. Two novel ITGB3 SNPs with MA(F) > 0.02 were found, which were not reported in the National Center for Biotechnology Information (NCBI) dbSNP database (https://www.ncbi.nlm.nih.gov/snp/). The allele frequencies and Hardy–Weinberg equilibrium test results of the identified polymorphic sites are shown in Tables 3 and 4.

Table 3: Summary of ITGB3 variations detected in this study.

Sequence number obtained in this study
dbSNP
Location
NC_000017.11
NM_000212.2
Nucleotide change
NP_000410.2 amino acid change
MA(F)
H-W

ITGB3-01
rs147363351
5′-UTR
47253042
-820
agcttccaga G/A gttttaagtc

A(0.012)
0.913

ITGB3-02
rs3809862
5′-UTR
47253062
-800
ctggggaaga C/T ccagggactc

T(0.424)
0.822

ITGB3-03
rs7208170
5′-UTR
47253393
-469
aaggcattca G/A cagatgtttg

A(0.419)
0.680

ITGB3-04
New
5′-UTR
47253360
-502
tagtgaataa T/A aaaggactga

A(0.023)
0.913

ITGB3-05
rs7208055
5′-UTR
47253461
-401
gtgaatgtgt C/A ccaagaatcc

A(0.221)
0.273

ITGB3-06
rs55827077
5′-UTR
47253717
-145
tagagaagcc G/C gaggggagga

C(0.448)
0.494

ITGB3-07
rs567581451
5′-UTR
47253771
-91
acccaccgcg -/TCCCC tcccctcccc

insTCCCC(0.058)
0.567

ITGB3-08
rs117052258
5′-UTR
47253855
-7
cgcgggaggc G/C gacgagatgc

C(0.227)
0.771

ITGB3-09
New
Exon1
47253882
21
ggccgcggcc C/G cggccgctct
Pro7=
G(0.407)
0.567

ITGB3-10
rs11871251
Intron1
47254061
79+121
ctgggaatgc G/A cgtgtcctgg

A(0.453)
0.771

ITGB3-11
New
Intron1
47254082
79+152
tggcgcggt C/G ggagccggga

G(0.012)
0.913

ITGB3-12
rs112188890
Intron1
47254101
79+161
gagctgggga C/T cttcctggcc

T(0.116)
0.864

ITGB3-13
rs117414137
Intron1
47254192
79+252
aggctgagcg C/G cttcccggcc

G(0.116)
0.864

ITGB3-14
rs11871447
Intron1
47254252
79+312
ccgcgctcac C/G cggggctgcg

G(0.448)
0.918

ITGB3-15
New
Intron1
47254331
79+391
tggggcttcc G/A ggggttgttc

A(0.006)
0.957

ITGB3-16
rs1009312
Intron1
47254774
79+834
ggcacagccc G/A gggttgctgc

G(0.471)
0.000

ITGB3-17
rs2015049
Intron1
47254865
79+925
ggccgcctct G/A cctcagagga

A(0.529)
0.000

ITGB3-18
rs56197296
Intron5
47287025_47287029
778-45_778-41
catggctgaa TTTGT/- tttgtctcct

delTTTGT(0.169)
0.049

ITGB3-19
rs5919
Exon6
47287174
882
ttgtccagcc T/C aatgacgggc
Pro294=
C(0.262)
0.022

ITGB3-20
rs41504748
Intron7
47290145
1036-40
accaccagct T/C cctttggtaa

C(0.070)
0.334

ITGB3-21
rs15908
Exon9
47290971
1143
cttccagctc A/G/T actttagaac
Val381=
C(0.599)
0.006

ITGB3-22
New
Exon10
47292177
1299
gaggctgtcc C/T caggagaagg
Pro433=
T(0.006)
0.957

ITGB3-23
rs4642
Exon10
47292411
1533A>G
cagcaggacga A/G tgcagccccc
Glu511=
G(0.331)
0.214

ITGB3-24
rs13306487
Exon10
47292422
1544
tgcagccccc A/C/G ggagggtcag
Arg515Gln
A(0.012)
0.913

ITGB3-25
rs4634
Exon10
47292423
1545
gcagcccccg G/A gagggtcagc
Arg515=
A(0.331)
0.214

ITGB3-26
New
Exon10
47292528
1659
gcgagtgtga C/Tgacttctcct
Asp550=
T(0.006)
0.957

ITGB3-27
rs149823724
Exon11
47299519
1902
cagatgcctg C/T acctttaaga
Cys634=
T(0.006)
0.957

ITGB3-28
rs11870252
Intron11
47300459
1914-19
ccttaatcac T/C gtgtcctctc

C(0.035)
0.869

ITGB3-29
rs70940817
Exon12
47300524
1960
cctacatgac G/A aaaatacctg
Glu654Lys
A(0.076)
0.432

dbSNP, single nucleotide polymorphism database; H-W , Hardy–Weinberg equilibrium value; MA(F), minor allele (frequency).

SNPs which related with ADP induced platelets aggregation, GPIIb/IIIa content, bleeding time, or coagulation indexes in this study.

Table 4: Association between individual ITGA2B and ITGB3 SNPs and the ADP induced platelets aggregation, GPIIb/IIIa content, bleeding time, PLT, and MPV (mean ± SD).

dbSNP
Genotypes

Aggregation max
GPIIb-IIIa per platelet
Bleeding time (s)
PLT (10⁹/L)
MPV (fL)

rs3760364
AA
48

AT
7

0.148
0.433
0.038
0.512
0.911

rs7208170
GG
18

GA
24

AA
13

0.229
0.105
0.030
0.428
0.051

rs55827077
GG
18

GC
22

CC
14

0.091
0.021
0.401
0.251
0.141

rs567581451
-/-
49

-/insTCCCC
6

0.609
0.999
0.040
0.428
0.054

rs117052258
GG
29

GC
21

CC
4

0.165
0.539
0.028
0.764
0.288

GG
19

GA
22

AA
14

0.189
0.160
0.027
0.944
0.029

rs56197296
TTTGT/TTTGT
42

TTTGT/del
11

del/del
2

0.014
0.916
0.695
0.433
0.416

rs5919
TT
31

TC
16

CC
8

0.015
0.634
0.130
0.728
0.148

Note: Pearson’s two-tailed test was used to analyze correlation between genotype and parameter. rs1009312 was completely linked with rs2015049.

3.2. Linkage Disequilibrium Analysis

Using the detected polymorphisms greater than 0.01 in frequency [MA(F) > 0.02], linkage disequilibrium (LD) was analyzed for and values (Figure 1). For ITGA2B, rs5911 was completely linked with rs850730 (), and rs5910 was strongly linked with rs850730 and rs5911 (). For ITGB3, complete LD was observed between rs4642 and rs4634 (). Other LD results are shown in Figure 1. A new SNP ITGB3-09 was found for which MA(F) in this study was 0.402.

(a)

(b)

Figure 1: Linkage disequilibrium (LD) map of ITGB2A and ITGB3 SNPs along with their locations in the ITGB2A and ITGB3 genes. Variants present at >1% frequency were included in the LD analysis using the statistics and . Red depicts a significant linkage between an SNP pair. Numbers inside the square indicate . (a) ITGB2A. (b) ITGB3.

The Hardy–Weinberg equilibrium values of rs1009312 and rs2015049 were <0.001. The possible reason is that the sample in this study may have a Chinese population of other ethnic groups besides the Han population. Those two SNPs were not included in the LD analysis.

3.3. Correlation of ADP-Induced Platelet Aggregation, GPIIb/IIIa Content, Bleeding Time, and Coagulation Indexes

The GPIIb/IIIa contents, present as average numbers of GPIIb/IIIa receptor in each platelet, were associated with ADP-induced platelet aggregation (, ), PLT (, ), PT (, ), and TT (, ) (Figures 1 and 2). The relationship between GPIIb/IIIa content and APTT was not significant (, ), while the association between ADP-induced platelet aggregation and APTT was moderately significant (, ) (Figure S1). The bleeding time had no association with other parameters. It had a negative association trend with MPV but was not significant (, ). The PLT was associated with PT (, ) and TT (, ). The FIB was negatively correlated with TT (, ).

Figure 2: Correlations of the maximal level of ADP-induced platelet aggregation and GPIIb/IIIa content in healthy volunteers. , coefficient of correlation; , significance of correlation (Pearson’s test here and elsewhere).

3.4. Impact of ITGA2B and ITGB3 SNPs on ADP-Induced Platelet Aggregation, GPIIb/IIIa Content, Bleeding Time, and Coagulation Indexes

For ITGA2B, only one SNP rs3760364 was related with the bleeding time () (Table 4). No significant correlation or trend was observed between ITGA2B SNPs and other parameters.

For ITGB3, the mean values of ADP-induced platelet aggregation of homozygous mutant genotypes in rs56197296 and rs5919 were lower than those of heterozygous mutations and wild type. Moreover, the GPIIb/IIIa per platelet was associated with rs55827077. A trend of GPIIb/IIIa per platelet was observed among rs70940817 GG (45), GA (9), and AA (1) carriers (, , 61277, resp., ), although it did not reach a significant level. The bleeding time was significantly related with rs3760364, rs7208170, rs567581451, and rs117052258 (Table 4).

In the present study, SNPs related with PLT were not found. ITGB3 rs1009312, which is completely linked with rs2015049, was significantly associated with the MPV (Table 4). ITGB3 rs70940817 was correlated with the PT and APTT ( and , resp.). The coagulation indexes and their values are summarized in Table 5.

Table 5: Association between individual ITGA2B and ITGB3 SNPs and the coagulation indexes (mean ± SD).

Genotypes

PT (s)
APTT (s)
TT (s)
FIB (g/L)

CC
42

CT
12

TT
1
12.5
36.7
16.5
2.72

0.126
0.029
0.299
0.173

AA
27

AG
21

GG
7

0.770
0.088
0.015
0.029

rs70940817
GG
45

GA
9

AA
1
12.7
37.2
15.75
3.10

0.002
0.003
0.078
0.069

MPV, mean platelet volume; PLT, platelet count; PT, prothrombin time; APTT, activated partial thromboplastin time; FIB, fibrinogen; TT, thrombin time.

Note: Pearson’s two-tailed test was used to analyze correlation between genotype and parameter.

Strong LD was observed between rs112188890 and rs117414137 (); completely LD was observed between rs4642 and rs4634.

4. Discussion

In this study, 13 variants in the ITGA2B locus and 29 variants in the ITGB3 locus in the Chinese population were observed. Two of the 29 variants located in ITGB3 were novel SNPs with MA(F) > 0.02. Variants in ITGA2B and ITGB3 genes displayed significant interethnic differences in the global populations (Table 6). The C allele frequency of SNP rs5918 (T/C), located in the ITGB3 gene, was only inhomogeneously distributed at 0.7% in the Chinese population, while it is common in whites and Africans (allele frequency 13.7% versus 12.8%). The following alleles of SNPs, rs7208170A, rs55827077C, rs11871251A, rs1009312G, and rs2015049G, were found to be more common in the Han Chinese and Africans (37%~50%) than in the European ancestry (10%~20%). In the ITGA2B gene, the rs5911 was completely linked with rs850730 and strongly linked with rs5910 in the Chinese population in this study, and all the three SNPs were common in whites and Asians. However, the rs5911 was not found in Africans. According to the ethnicity difference described in the preceding text, resequencing of the ITGA2B and ITGB3 genes in the Chinese population was believed to be very important to reveal the function of SNPs.

Table 6: Comparison of ITGA2B and ITGB3 allele frequencies in different ethnic groups.

dbSNP

Number
This study Chinese

ITGA2B-01
rs3760364
T(0.052)
T(0.012)
T(0)
T(0)

ITGA2B-08
rs850730
G(0.477)
G(0.467)
G(0.297)
G(0.437)

ITGA2B-11
rs5911
G(0.477)
G(0.467)
G(0.305)
G(0)

ITGA2B-12
rs5910
T(0.465)
T(0.442)
T(0.376)
T(0.432)

ITGB3-03
rs7208170
A(0.419)
A(0.496)
A(0.194)
A(0.431)

ITGB3-05
rs7208055
A(0.221)
A(0.225)
A(0.117)
A(0.356)

ITGB3-06
rs55827077
C(0.448)
C(0.417)
C(0.158)
C(0.39)

ITGB3-08
rs117052258
C(0.227)
C(0.208)
NA
NA

ITGB3-10
rs11871251
A(0.453)
A(0.482)
A(0.199)
A(0.373)

ITGB3-12
rs12188890
T(0.116)
T(0)
T(0.023)
T(0)

ITGB3-16
rs1009312
G(0.417)
A(0.434)
A(0.125)
A(0.432)

ITGB3-17
rs2015049
G(0.471)
A(0.478)
A(0.138)
A(0.413)

NF.
rs5918
C(0)
C(0.007)
C(0.137)
C(0.128)

ITGB3-18
rs56197296
delTTTGT
(0.169)
NA
NA
NA

ITGB3-19
rs5919
C(0.262)
C(0.232)
C(0.049)
C(0.187)

ITGB3-23
rs4642
G(0.331)
G(0.31)
G(0.283)
G(0.306)

ITGB3-25
rs4634
A(0.331)
A(0.350)
A(0.283)
A(0.331)

ITGB3-29
rs70940817
A(0.076)
NA
NA
NA

dbSNP, single nucleotide polymorphism database; MA(F), minor allele (frequency); SNP, single nucleotide polymorphisms; NF, not found; NA, not available.

Resource of MP(F)s was from GenBank and HapMap, https://www.ncbi.nlm.nih.gov/snp/; Han Chinese in Beijing, China (CHB), or CHB + Japanese in Tokyo, Japan (JPT), if there is no CHB data in the SNP; Utah residents with Northern and Western European ancestry from the CEPH collection (CEU); Yoruba in Ibadan, Nigeria (YRI).

Variation in the MPV or PLT can have a profound impact on differences in the platelet function between individuals [16, 17], and these traits have a strong genetic component [18–21]. However, limited information is available for Asians. In the present study, the A alleles of rs1009312 and rs2015049, located in ITGB3, were positively associated with the MPV (). The MPV had a trend in rs7208170 alleles but did not reach a significant level (). The difference between PLT and SNPs in ITGA2B or ITGB3 was not significant.

The APTT and PT are clinical tests commonly used to indicate coagulation factor deficiencies [22, 23], activated coagulation, and risk of venous thromboembolism [24, 25]. To date, two genome-wide association studies (GWAS) of APTT and PT conducted in the European ancestry have been reported. One study identified genome-wide significant associations of APTT and variants at F12 (MIM 610619), KNG1 (MIM 612358), and HRG (MIM 142640) [26]. In the other research, the GWAS for APTT and PT was conducted and replicated genome-wide significant associations at KNG1, HRG, F11, F12, and ABO for APTT and identified significant associations at the F7 and PROCR/EDEM2 regions for PT. Eight genetic loci accounted for ~29% of the variance in APTT, and two loci accounted for ~14% of the variance in PT [27]. In this study, the association of APTT, PT, FIB, and TT with ITGA2B and ITGB3SNPs was investigated. The A allele of ITGB3 rs70940817 was found to significantly correlate with the elevated APTT and PT ( and , resp.). The T allele of ITGB3 rs112188890 was related with APTT (), and the G allele of ITGB3 rs4642 was associated with TT and FIB ( and , resp.).

The ADP-induced platelet aggregation test was often used to identify the platelet function and the efficacy of antiplatelet drugs. Jones et al. detected 1327 SNPs and investigated their correlation with ADP or collagen-related peptide-induced platelet aggregation in 500 healthy northern European subjects. This identified 17 novel associations with the platelet function () accounting for approximately 46% of the variation in response [28]. In this study, the minor allele of rs56197296 and rs5919 was found to be associated with the decreased ADP-induced platelet aggregation ( and , resp.).

GPIIb/IIIa is the central receptor of platelet aggregation. The variations of GPIIb/IIIa amount expressed on a platelet surface might affect the platelet-aggregating activity. Many studies reported that the rs5918 correlated with the GPIIb/IIIa receptor expression [29]; however, many conflict studies have also been published [3, 30]. O’Halloran et al. investigated whether three polymorphisms of the GPIIIa promoter (−468G/A, −425A/C, and −400C/A) influenced the RNA expression and receptor density in the platelets of patients with cardiovascular disease [3]. They found a threefold variation between the subjects in the number of GPIIb/IIIa receptors expressed per platelet, although no association between the receptor density and the PlA2 or the three promoter polymorphisms was demonstrated. In the present study, rs55827077, which was located at the promoter region of the GPIIIs gene at position −145, was related with GPIIb/IIIa per platelet.

The bleeding time is a test that evaluates the platelet function in vivo. A prolonged bleeding time can result from platelet abnormality, Von Willebrand factor deficiency, or vascular disorders such as Ehlers–Danlos syndrome. A disruption of platelet aggregation results in a prolongation of the bleeding time [31]. In this study, the bleeding time was related with rs3760364 of ITGA2B and rs7208170, rs567581451, and rs117052258 of ITGB3 (). No previous study reporting on the effect of SNPs on the bleeding time was found. The mechanism of the relationship needs to be further examined. However, a negative trend between the bleeding time and MPV (, ) was observed. Moreover, rs1009312 and rs2015049 were found to significantly associate with both bleeding time and MPV. Further, the minor alleles of rs7208170 and rs567581451, which were significantly related with the bleeding time, had a trend with the MPV among genotypes, although they did not reach a significant level ( and , resp.). However, no relationship was observed among SNPs, bleeding time, and MPV in rs3760364 and rs117052258.

In this study, a positive correlation of the level of ADP-induced aggregation and GPIIb/IIIa content was detected in healthy volunteers. This correlation is consistent with a previous report. Yakushkin et al. investigated the relationship between the number of GPIIb/IIIa and the level of ADP-induced aggregation in a group of 35 healthy volunteers and found positive and significant correlations between the level of platelet aggregation induced by different ADP doses (from 1.25 to 20 mmol/L) and the number of GPIIb/IIIa [32].

A strong positive correlation was observed between GPIIb/IIIa per platelet and PLT, PT, and TT (). Although the TT was strongly correlated with GPIIb/IIIa per platelet (, ), the relationship of SNPs/TT and SNPs/GP (IIb/IIIa) content is not linked. For example, ITGB3 rs4642 was significantly related with the TT (), while the value of GPIIb/IIIa per platelet had no trend among rs4642 genotypes (). The other coagulation indexes were the same. Therefore, the relationship between SNPs and GPIIb/IIIa content cannot be deduced from the correlation of coagulation indexes and SNPs.

Some of the significant correlations between SNPs and platelet function parameters in the present study were not reported previously, which may be due to the reason that SNPs with low MA(F) in the European ancestry were not selected as candidate SNPs in previous studies. For example, the GWAS-genotyping platforms lack the coverage of low frequency/rare variants [33]. Moreover, LD might be another reason, if different genetic patterns (haplotypes) are present in different populations [3].

A possible limitation of the current study is the limited number of subjects. After stratification, the number of subjects in each genotypic group was small, thereby limiting further haplotype association analysis and accession of small effects of an SNP with a small minor allele frequency.

5. Conclusion

In summary, as ethnicity difference might limit the interpretation of the function of SNPs, resequencing the ITGA2B and ITGB3 genes and investigating their functions in the Chinese population are very important. In the present study, nine SNPs were found to associate with indexes of platelet and coagulation haemostasis. Newer studies are needed, particularly, to further assess the clinical importance of the above-discussed SNPs in disease susceptibility and antiplatelet drugs pharmacodynamics. Further studies should pay more attention to the roles of ITGA2B and ITGB3 SNPs in ethnic variations.

Competing Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

This study was supported by grants from the National Natural Science Foundation of China (no. 81273592, no. 81202592, and no. 81373487).

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