Expression level of human TLR4 rather than sequence is the key determinant of LPS responsiveness.

Adeline M Hajjar,Jaehun Yi,Samuel I Miller,Robert K Ernst,Cathy S Yam,Gayle E Woloschak

doi:10.1371/journal.pone.0186308

Adeline M Hajjar, Jaehun Yi + Show 4 more

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https://doi.org/10.1371/journal.pone.0186308

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Abstract

To address the role of Toll-like receptor 4 (TLR4) single nucleotide polymorphisms (SNP) in lipopolysaccharide (LPS) recognition, we generated mice that differed only in the sequence of TLR4. We used a bacterial artificial chromosome (BAC) transgenic approach and TLR4/MD-2 knockout mice to specifically examine the role of human TLR4 variants in recognition of LPS. Using in vitro and in vivo assays we found that the expression level rather than the sequence of TLR4 played a larger role in recognition of LPS, especially hypoacylated LPS.

Highlights

Two coding human Toll-like receptor 4 (TLR4) single nucleotide polymorphisms (SNP; rs4986790 and rs4986791) resulting in Asp!Gly or Thr!Ile substitutions at amino acids 299 and 399, respectively, have been described [1]
Our comparisons were limited by the copy number of lines randomly generated, we found that the expression level of human TLR4 was the largest determinant of LPS response and that the actual sequence of human TLR4 did not reveal obvious differences in LPS recognition
Chimeric pups were identified by coat color and backcrossed to B6 mice and subsequently to TLR4/MD-2 double-KO mice, such that mice differed only in the sequence of human TLR4

Summary

Introduction

Two coding human Toll-like receptor 4 (TLR4) single nucleotide polymorphisms (SNP; rs4986790 and rs4986791) resulting in Asp!Gly or Thr!Ile substitutions at amino acids 299 and 399, respectively, have been described [1]. The earliest study on these coding TLR4 SNPs suggested that they resulted in decreased responsiveness to inhaled lipopolysaccharide (LPS) [1]. The authors proposed that the TLR4D299G variant initially arose to protect against cerebral malaria in Africa and that this allele was hyperresponsive to LPS, in contrast to the previous study. They proposed that the compensatory T399I mutation that reduced LPS responsiveness arose in Europe to protect from sepsis. Other in vitro studies demonstrated reduced responsiveness of TLR4D299G+T399I to hexa- or penta-acylated LPS [4, 5]

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