Disabled-2 negatively regulates lipopolysaccharide-stimulated Toll-like receptor 4 signaling and inflammation response in murine macrophage (INM7P.349)

Abstract

Abstract Toll-like receptor 4 (TLR4)-mediated host response to lipopolysaccharide (LPS) stimulation plays a pivotal role in host defense against from Gram-negative bacterial infection. Upon ligand binding, TLR4/MD2 complexes are internalized to form endocytic signalsomes and extend LPS response. However, the underlying mechanism of LPS-stimulated TLR4 internalization and signaling has not yet been completely understood. Here we delineated whether the endocytic adaptor protein Disabled-2 (Dab2) that is highly expressed in macrophage plays a role in TLR4 signaling and trafficking. In vivo analysis of the myeloid lineage-restricted Dab2 knockout (Dab2-/-) mice revealed that the mice were more susceptible to LPS challenge leading to an overproduction of the chemokine RANTES in serum and poor survival. The functional role of Dab2 in TLR4 signaling was investigated further using RAW264.7 macrophage with Dab2 knockdown. We found that attenuation of Dab2 expression increased the basal level of cell surface TLR4/MD2 complexes and accelerated the rate of LPS-induced down-regulation of these complexes from the cell surface. Consequently, TLR4 endocytic pathway-dependent IRF-3 activation was augmented with an increased expression for the subsets of inflammatory cytokine and IFN-inducible genes. These data indicate that Dab2 functions as a negative regulator of TLR4 endocytic pathway and signaling, supporting a novel role of Dab2 in the inflammatory response of macrophage to endotoxin.