Differential interactions of bacterial lipopolysaccharides with lipid membranes: implications for TRPA1-mediated chemosensation

Justyna B Startek,Karel Talavera,Yeranddy A Alpizar,Thomas Voets

doi:10.1038/s41598-018-30534-2

Justyna B Startek, Karel Talavera + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-30534-2

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Abstract

Bacterial lipopolysaccharides (LPS) activate the TRPA1 cation channels in sensory neurons, leading to acute pain and inflammation in mice and to aversive behaviors in fruit flies. However, the precise mechanisms underlying this effect remain elusive. Here we assessed the hypothesis that TRPA1 is activated by mechanical perturbations induced upon LPS insertion in the plasma membrane. We asked whether the effects of different LPS on TRPA1 relate to their ability to induce mechanical alterations in artificial and cellular membranes. We found that LPS from E. coli, but not from S. minnesota, activates TRPA1. We then assessed the effects of these LPS on lipid membranes using dyes whose fluorescence properties change upon alteration of the local lipid environment. E. coli LPS was more effective than S. minnesota LPS in shifting Laurdan’s emission spectrum towards lower wavelengths, increasing the fluorescence anisotropy of diphenylhexatriene and reducing the fluorescence intensity of merocyanine 540. These data indicate that E. coli LPS induces stronger changes in the local lipid environment than S. minnesota LPS, paralleling its distinct ability to activate TRPA1. Our findings indicate that LPS activate TRPA1 by producing mechanical perturbations in the plasma membrane and suggest that TRPA1-mediated chemosensation may result from primary mechanosensory mechanisms.

Highlights

Lipopolysaccharides (LPS) are major components of the outer membrane of gram-negative bacteria[1,2] and are key cues for the detection of infection by the immune system[3]
We have previously shown that, at a concentration of 20 μg/ml, LPS extracted from E. coli, but not from S. minnesota, activates TRPA16
In intracellular Ca2+ imaging experiments performed in Chinese hamster ovary (CHO) cells stably transfected with mouse TRPA1 we confirm that E. coli LPS activates TRPA1, whereas S. minnesota LPS is inactive at concentrations up to 500 μg/ml (Fig. 1)

Summary

Introduction

Lipopolysaccharides (LPS) are major components of the outer membrane of gram-negative bacteria[1,2] and are key cues for the detection of infection by the immune system[3]. We showed previously that LPS with conically-shaped lipid A (such as that from E. coli) activate TRPA1 stronger than those forming symmetrical lamellar structures, such as S. minnesota LPS6 These findings suggest that LPS activate these channels by mechanically perturbing the plasma membrane. To investigate the mechanisms underlying TRPA1 activation, we tested whether the capacity of different LPS to activate this channel relates to their ability to induce mechanical alterations in artificial and cellular membranes For this we first sought to confirm the distinct action of E. coli LPS and S. minnesota LPS on TRPA1 when applied in a wide concentration range (1 to 500 μg/ml). We found that E. coli LPS was more effective than S. minnesota LPS in activating TRPA1 and in inducing changes in the arrangement of membrane lipids These results support the hypothesis that TRPA1 serves as LPS sensor by detecting mechanical alterations in the plasma membrane. This may help explaining the distinct ability of different LPS molecules to induce acute neurogenic inflammation[6]

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