Sequence Variants of Toll Like Receptor 4 and Late-Onset Alzheimer's Disease

<div><h3>Background</h3><p>Toll like receptor 4 (TLR4) has been related to inflammation and beta-amyloid deposition in Alzheimer's disease (AD) brain. No study has explored the association between haplotype-tagging single nucleotide polymorphisms (htSNPs) of <em>TLR4</em> and AD risk previously and <em>ApoE e4</em> status alone showed low sensitivity in identifying late-onset AD (LOAD) patients.</p> <h3>Methods</h3><p>A total of 269 LOAD patients were recruited from three hospitals in northern Taiwan (2007–2010). Controls (n = 449) were recruited from elderly health checkup and volunteers of the hospital during the same period of time. Five common (frequency≥5%) <em>TLR4</em> htSNPs were selected to assess the association between <em>TLR4</em> polymorphisms and the risk of LOAD in the Chinese ethnic population.</p> <h3>Results</h3><p>Homozygosity of <em>TLR4</em> rs1927907 was significantly associated with an increased risk of LOAD [TT vs. CC: adjusted odds ratio (AOR) = 2.45, 95% confidence interval (CI) = 1.30–4.64]. After stratification, the association increased further in <em>ApoE e4</em> non-carriers (AOR = 3.07) and in hypertensive patients (AOR = 3.60). Haplotype GACGG was associated with a decreased risk of LOAD (1 vs. 0 copies: AOR = 0.59, 95% CI = 0.36–0.96; 2 vs. 0 copies: AOR = 0.31, 95% CI = 0.14–0.67) in <em>ApoE e4</em> non-carriers. <em>ApoE e4</em> status significantly modified this association (<em>p</em>_interaction = 0.01). These associations remained significant after correction for multiple tests.</p> <h3>Conclusions</h3><p>Sequence variants of <em>TLR4</em> were associated with an increased risk of LOAD, especially in <em>ApoE e4</em> non-carriers and in hypertensive patients. The combination of <em>TLR4</em> rs1927907 and <em>ApoE e4</em> significantly increased the screening sensitivity in identifying LOAD patients from 0.4 to 0.7.</p> </div

Characteristics of the study population.

*<p><i>p</i> value<0.05 was obtained by comparing LOAD cases and controls.</p><p>Abbreviations: LOAD, late-onset Alzheimer's disease; SD, standard deviation; BMI, body mass index; DM, diabetes mellitus; <i>ApoE e4</i>, apolipoprotein E <i>e</i>4.</p

Association between <i>TLR4</i> SNPs and LOAD risk by hypertension status.

<p>All models were adjusted for age, gender, education, and <i>ApoE e4</i> status.</p><p>Abbreviations: LOAD, late-onset Alzheimer's disease; AOR, adjusted odds ratio; CI, confidence interval; SNP, single nucleotide polymorphism.</p><p>Numbers in bold indicates statistically significant findings(p<α = 0.05).</p>a<p>0 copies, wild type; 1 copy, heterozygotes; 2 copies, homozygous variants.</p>*<p>The result remained significant (2 copies of variant SNP3 in hypertensive persons, <i>p</i> = 0.002) after controlling for type I error by using Bonferroni correction (α = 0.05/5).</p><p>Before stratification, hypertensive patients showed a decreased the risk of LOAD (AOR = 0.41, 95% CI = 0.28–0.61).</p

Association between <i>TLR4</i> haplotypes and LOAD.

<p>Abbreviations: LOAD, late-onset Alzheimer's disease; AOR, adjusted odds ratio; CI, confidence interval; DM, diabetes mellitus; HAP, haplotype; NA, not applicable; SNP, single nucleotide polymorphism; <i>ApoE e4</i>, apolipoprotein E e4.</p><p>All models were adjusted for age, gender, education, and <i>ApoE e4</i> status.</p><p>Minor alleles were underlined.</p><p>Numbers in bold indicates statistically significant findings (<i>p</i><α = 0.05).</p>a<p>0 copies, wild type; 1 copy, heterozygotes; 2 copies, homozygous variants.</p>*<p>The result remained significant (2 copies of HAP1, <i>p</i> = 0.003) after controlling for type I error by using Bonferroni correction (α = 0.05/4).</p

<i>TLR4</i> linkage disequilibrium (LD) plot.

<p>This plot was generated by Haploview program using data from this study. Five common (frequency≥0.05) htSNPs formed one block. The SNP name, e.g., SNP1, SNP2, etc., indicated five htSNPs genotyped in this study. Four common haplotypes were identified. The level of pairwise r², which indicated the association degree between two SNPs in the LD block, was shown in the cell of the LD structure in numeric. The level of pair-wise D', which indicated the strength of LD between two SNPs, was shown in the LD structure in gray scale.</p

Characteristics of <i>TLR4</i> haplotype-tagging SNPs.

<p>Abbreviations: UTR, untranslated region; CHB, Han Chinese in Beijing, China; HWE p, p value for Hardy–Weinberg equilibrium test; LOAD, late-onset Alzheimer's disease; MAF, minor allele frequency; SNP, single nucleotide polymorphism.</p

Association between <i>TLR4</i> SNPs and LOAD risk.

<p>All models were adjusted for age, gender, education, and <i>ApoE e4</i> status.</p><p>Abbreviations: LOAD, late-onset Alzheimer's disease; AOR, adjusted odds ratio; CI, confidence interval; SNP, single nucleotide polymorphism.</p>#<p>0 copies, wild type; 1 copy, heterozygotes; 2 copies, homozygous variants.</p><p>Numbers in bold indicates statistically significant findings (<i>p</i><α = 0.05).</p><p>Additive model is assessing the association between number of variant allele and LOAD.</p>*<p>The result remained significant (2 copies of variant SNP3, <i>p</i> = 0.004) after controlling for type I error by using Bonferroni correction (α = 0.05/5).</p

Postulated pathway of <i>TLR4</i> and factors involved in the pathogenesis of Alzheimer's disease.

<p>Solid lines indicated pathways that have been well documented; dotted lines indicated speculated pathways. Abbreviations: Aβ, beta amyloid; ARBs, angiotensin receptor blockers; ACEIs, angiotensin-converting enzyme inhibitors; <i>ApoE e4</i>, apolipoprotein E e4; AD, Alzheimer's disease.</p

Association between <i>TLR4</i> SNPs and LOAD risk by <i>ApoE e4</i> status.

<p>All models were adjusted for age, gender, and education.</p><p>Abbreviations: LOAD, late-onset Alzheimer's disease; AOR, adjusted odds ratio; CI, confidence interval; SNP, single nucleotide polymorphism; <i>ApoE e4</i>, apolipoprotein E e4.</p><p>Numbers in bold indicates statistically significant findings (<i>p</i><α = 0.05).</p>a<p>0 copies, wild type; 1 copy, heterozygotes; 2 copies, homozygous variants.</p>*<p>The result remained significant (2 copies of variant SNP3 in <i>AopE e4</i> non-carriers, <i>p</i> = 0.004) after controlling for type I error by using Bonferroni correction (α = 0.05/5).</p

<i>CHRNA7</i> linkage disequilibrium (LD) plot.

<p>The plot was generated by applying the Haploview program to genotype data from this study. The level of pairwise D', which indicates the degree of LD between two SNPs, is shown in the LD structure in gray scale. The level of pairwise r², which indicates the degree of correlation between two SNPs, is indicated by the number in the cell. Different numbers of common (frequency ≥5%) haplotypes were identified in each haplotype block. A modified Gabriel et al. algorithm was used to define the haplotype block <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084059#pone.0084059-Gabriel1" target="_blank">[32]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084059#pone.0084059-Chen1" target="_blank">[33]</a>.</p