Disruption of the C. elegans Intestinal Brush Border by the Fungal Lectin CCL2 Phenocopies Dietary Lectin Toxicity in Mammals

Abstract

Lectins are non-immunoglobulin carbohydrate-binding proteins without enzymatic activity towards the bound carbohydrates. Many lectins of e.g. plants or fungi have been suggested to act as toxins to defend the host against predators and parasites. We have previously shown that the Coprinopsis cinerea lectin 2 (CCL2), which binds to α1,3-fucosylated N-glycan cores, is toxic to Caenorhabditis elegans and results in developmental delay and premature death. In this study, we investigated the underlying toxicity phenotype at the cellular level by electron and confocal microscopy. We found that CCL2 directly binds to the intestinal apical surface and leads to a highly damaged brush border with loss of microvilli, actin filament depolymerization, and invaginations of the intestinal apical plasma membrane through gaps in the terminal web. We excluded several possible toxicity mechanisms such as internalization and pore-formation, suggesting that CCL2 acts directly on intestinal apical plasma membrane or glycocalyx proteins. A genetic screen for C. elegans mutants resistant to CCL2 generated over a dozen new alleles in bre 1, ger 1, and fut 1, three genes required for the synthesis of the sugar moiety recognized by CCL2. CCL2-induced intestinal brush border defects in C. elegans are similar to the damage observed previously in rats after feeding the dietary lectins wheat germ agglutinin or concanavalin A. The evolutionary conserved reaction of the brush border between mammals and nematodes might allow C. elegans to be exploited as model organism for the study of dietary lectin-induced intestinal pathology in mammals.

The intestinal intermediate filament network responds to and protects against microbial insults and toxins

“…Intestinal alterations with endotube re-organization have also been observed in naturally occurring, virally infected Caenorhabditis isolates (Félix et al, 2011). Our findings are compatible with the consequences of treating worms with the fungal Coprinopsis cinerea lectin 2 (CCL2), which is a non-immunoglobulin carbohydrate protein (Stutz et al, 2015). These animals presented brush border defects and enlarged intestinal lumina with endotube gaps and multiple small apical Fig.…”

A novel function for the MAP kinase SMA-5 in intestinal tube stability

“…The worm intestine seems to be sensitive to stress, and invaginations and luminal dilation occur in worms subjected to challenges such as microbial infection (Estes et al. , 2011) or exposure to fungal lectins (Stutz et al. , 2015) or pore-forming toxins (Los et al.…”

The C. elegans model in toxicity testing

“…Additionally, assays for motility, enzyme activity, reactive oxygen species, RNAi response and gene expression can provide information on mechanisms of action as well as relative toxicity. Other endpoints to assess chemical toxicity include intestinal morphology (Hunt et al, 2012;Stutz et al, 2015), accumulation of autofluorescence (Gerstbrein et al, 2005), gonadal morphology (Hunt et al, 2012) and internal hatching (Hunt et al, 2013).…”