AUTHOR=Chen Yu , Huang Kai , Chen Liang-Kuei , Wu Hui-Yu , Hsu Chih-Yu , Tsai Yau-Sheng , Ko Wen-Chien , Tsai Pei-Jane 

TITLE=Membrane Cholesterol Is Crucial for Clostridium difficile Surface Layer Protein Binding and Triggering Inflammasome Activation

JOURNAL=Frontiers in Immunology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2020.01675

DOI=10.3389/fimmu.2020.01675

ISSN=1664-3224

ABSTRACT=<p><italic>Clostridium difficile</italic>, an obligate anaerobic gram-positive bacillus, generates spores and is commonly found colonizing the human gut. Patients with <italic>C. difficile</italic> infection (CDI) often exhibit clinical manifestations of pseudomembranous colitis or antibiotic-associated diarrhea. Surface layer proteins (SLPs) are the most abundant proteins in the <italic>C. difficile</italic> cell wall, suggesting that they might involve in immune recognition. Our previous results demonstrated that <italic>C. difficile</italic> triggers inflammasome activation. Here, we found SLPs as well as <italic>C. difficile</italic> induced inflammasome activation, and in a dose-dependent manner. In addition, the cholesterol-rich microdomains on the cell membrane (also referred to as lipid rafts) are thought to be crucial for bacterial adhesion and signal transduction. We demonstrated that lipid rafts participated in <italic>C. difficile</italic> SLPs binding to the cell membrane. Fluorescence microscopy showed that membrane cholesterol depletion by methyl-β-cyclodextrin (MβCD) reduced the association of SLPs with the cell surface. The coalescence of SLPs in the cholesterol-rich microdomains was confirmed in <italic>C. difficile</italic>-infected cells. Furthermore, the inflammasome activations induced by SLPs or <italic>C. difficile</italic> were abrogated by MβCD. Our results demonstrate that SLPs recruit the lipid rafts, which may be a key step for <italic>C. difficile</italic> colonization and inducing inflammasome activation.</p>