Colonization-Dependent Colonic Fucosylation is Mediated by Gram Negative Bacteria via Activation of a Novel Fucosylated TLR4

Adult colonic mucosa is highly fucosylated relative to immature mucosa, and this fucosylation is dependent upon bacterial colonization. Toll-like receptor-4 (TLR4) was hypothesized to mediate this colonization-dependent fucosylation. Germ-free (GF) and bacteria-depleted (BD) mice were compared with conventional and mutant mice with regard to induction of epithelial fut2 mRNA levels and α1,2-fucosyltransferase (FUT2) activity. Induction of these activities by recolonization were compared with induction by LPS (TLR4 ligand) andmonocolonization by bacteriodes and E. coli strains. Cultured human erythroleukemia (Hel) cells were used to study fucosylated TLR4 In Vitro. Colonization-dependent induction of fucosylation occurs only in TLR2-/and wild-type mice but not in TLR4-/and MyD88-/mice, suggesting TLR4-MyD88 dependent signaling is important for fucosylation. TLR4 is fucosylated in the colonocytes of only GF and BD mice. LPS activate fut2 mRNA and FUT2 activity in the absence of bacterial colonization. Fucose-utilizing Bacteroides fragilis induce colonic fucosylation, but not a fucose-non-utilizing mutant. In Hel cells, which express fucosylated TLR4 activates fut2 mRNA and fucosylation. TLR4-specific siRNA inhibits this activation, and fucosidase treatment abolished TLR4-dependent activation of fut2 mRNA, confirming the central role of fucosylated-TLR4 in activating fut2 and cell surface fucosylation. Fucosylated-TLR4 expressed on uncolonized colonocytes mediates bacterially-induced activation of fut2 mRNA and FUT2 activity without activating inflammation, and is a necessary initial step in the communication between the colonizing bacteria and the host epithelium.