Atherosclerosis 153 (2000) 261 – 262
Letter to the Editors
www.elsevier.com/locate/atherosclerosis
Role of a genetic variation in the promoter of human thromboxane synthase gene in myocardial infarction.
Thromboxane synthase (TXS) catalyzes the conver-sion of prostaglandin H2 to thromboxane A2 (TXA), a potent proaggregatory and vasoconstrictive agent [1,2]. TXA plays an important role in many pathological processes, including acute coronary syndromes [3,4]. It is therefore likely that variations in the TXS gene may contribute to increased susceptibility to myocardial in-farction. In the present study, we screened for varia-tions in the promoter region of the human TXS gene. We then investigated the physiological significance of identified variations in vitro, and examined the associa-tion between the identified variaassocia-tions and ischemic heart diseases. We identified a C to T substitution at nucleotide −822, and a T to G substitution at nucle-otide −386 (according to the numbering of the Ref. [5]). Since these two polymorphisms appear to be in tight linkage disequilibrium, the present study was lim-ited to analysing the significance of the T(−386)G polymorphism. The sequence around nucleotide −386 corresponds to the putative binding site of the GATA-1 transcriptional factor (TTATCA), and substitution of a T(−386) with a G(−386) abolishes this site (TGATCA).
To investigate the functional significance of the varia-tion in the TXS promoter region, the promoter activity of the two alleles was investigated in U937 cells using the luciferase reporter vector. The G(−386) allele was found to have promoter activity 1.5-fold higher than the T(−386) allele (PB0.001) (Fig. 1). To investigate pathophysiological significance of this polymorphism, we conducted an association study. The study popula-tion consisted of 208 patients with myocardial infarc-tion (MI) and 112 patients with angina pectoris (AP) who underwent cardiac catheterization. Two hundred and seventy-nine subjects who visited our outpatient clinic and who were identified as having no serious cardiovascular diseases and no ischemic changes on electrocardiogram (ECG) on an exercise stress test, were included as the control group, as previously re-ported [6,7]. The genotype frequencies of the T(− 386)G polymorphism were in agreement with frequencies predicted by Hardy-Weinberg equilibrium
(Table 1). The genotype frequencies of the T(−386)G polymorphism were not significantly different among the control, AP, and MI groups. The G(−386) allele frequency was significantly different (P=0.0435) among the control, AP, and MI groups.
In the control and MI groups, a multiple logistic analysis indicated that current smoking habit (PB
0.0001), diabetes mellitus (PB0.0001), hyperlipidemia (P=0.034), and the genotype of the TXS gene (TT/ TG+GG) (P=0.0184, odds ratio=1.93) were the pre-dictors of MI.
In conclusion, the G(−386) allele of the thrombox-ane A2 synthase gene, which has been associated with higher promoter activity in vitro, appears to be a risk factor for myocardial infarction in Japanese subjects. However, the present study should be repeated using a larger sample population, since the contribution of a single gene to common diseases such as hypertension, myocardial infarction, and diabetes mellitus, would ap-pear to be very small. Indeed, the significance of an-giotensin converting enzyme I/D genotype in myocardial infarction has been marginally confirmed in studies using as many as 5000 MI and 6000 control subjects [8].
Fig. 1. Comparison of the promoter activity of the two alleles. Promoter activity of the T(−386) and G(−386) allele was examined by a luciferase reporter system in U937 cells (n=6). pRL-CMV, which encodes sea pansy luciferase under the control of the CMV promoter, was used as an internal standard. Promoter activity of the G(−386) allele was 1.5-fold higher than that of the T(−386) allele.
Letter to the Editor 262
Table 1
Characteristics of the study population
AP MI P
Control
112 208
279 c
n
151/128
M/F 79/33 159/49 B0.0001
61.097.9 58.8910.2
Age 60.399.1 n.s.
23.793.7 23.193.1
22.993.3 n.s.
BMIa
11 (3.9%)
DM 37 (33.0%) 66 (31.7%) B0.0001
41 (36.6%) 66 (31.7%)
HL 86 (30.8%) n.s.
70.5% 77.9%
43.7% B0.0001
Smoking
n.s. Genotypes of 242/35/2 94/16/2 163/41/4 TXS
(TT/TG/GG)
91.1% 88.2% 0.0435 Allele T (%) 93.0%
aBMI: body mass index (kg/m2); DM and HL indicate presence of
diabetes mellitus and hyperlipidemia.
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[6] Iwai N, Shimoike H, Nakamura Y, Tamaki S, Kinoshita M. The 4G/5G polymorphism of the plasminogen activator inhibitor gene is associated with the time course of progression to acute coro-nary syndromes. Atherosclerosis 1998;136:109 – 14.
[7] Tamaki S, Iwai N, Nakamura Y, Tsujita Y, Kinoshita M. Varia-tion of the factor VII gene and ischemic heart disease in Japanese subjects. Coron Art Dis 1999;10:601 – 6.
[8] Keavney B, McKenzie C, Parish S, Palmer A, Clark S, Young-man L, Delepine M, Lathrop M, Peto R, Collins R. Large-scale test of hypothesised associations between the angiotensconvert-ing-enzyme insertion/deletion polymorphism and myocardial in-farction in about 5000 cases and 6000 controls. International Studies of Infarct Survival (ISIS) Collaborators. Lancet 2000;355:434 – 42.
Yasuyuki Tsujita, Masahiko Kinoshita, Tadashi Tanabe, Naoharu Iwai
National Cardio6ascular Center,Suita,Osaka565-8565:
Shiga Uni6ersity of Medical Science, Tsukinowa Seta
Otsu, Shiga 520-2192,Japan
E-mail: [email protected]
References
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