Tu1946 Osteopontin Prevents Onset of Immune-Mediated Colitis by Inducing Tolerogenic Dendritic Cells

Abstract

Background We have previously shown that upon formation of immunogenic dendritic cell (DC) T cell contacts, autophagy is induced. This process then functions in a negative feedback loop by destabilization of the interaction. In a subset of Crohn's disease patients, this mechanism is impaired, leading to hyperstable interactions and increased immunogenicity. The correction of autophagy induction after DC-T cell contact in risk allele carriers may form a therapeutic possibilty resulting in normal interaction stability and decreased T cell activation. We therefore sought to determine the signaling events linking DCT cell interactions with the induction of autophagy. Methods Interactions were induced between human monocyte derived DC and allogeneic T cells. Activation of signalling pathways was determined byWestern Blot analysis. Inihibition of signallingmediators was achieved through siRNA and pharmacological inhibitors. Results Upon immunogenic DC-T cell interactions, phosphorylation of AMPKwas increased. AMPK is an inhibitor ofmTOR signaling, and indeed mTOR pathway activity was markedly reduced, as shown by decreased phosphorylation of mTOR itself as well as its downstream target S6. It has been shown previously that inhibition of mTOR is a strong inducer of autophagy. Conversely, HMGB1 and tissue transglutaminase 2, which are also known to influence autophagic activity, did not appear to be involved in autophagy induction under these circumstances. Interestingly, AMPK activation wasmediated through activation of LKB1, a molecule which has been shown to be involved in mediating the polarity of intestinal epithelial cells. We show that LKB1 is recruited to the site of DCT cell contact, and that inhibition of LKB1 signalling results in impaired induction of autophagy after cell-cell contact. Consequently, cell contacts formed by LKB1 deficient DC were hyperstable and resulted in increased immunogenicity, similar to the effects of autophagy deficiency. Conclusion This data shows that upon DC-T cell interaction, autophagy is induced as a regulatory mechanism and this induction is mediated through the LKB1-AMPKmTOR signaling pathway. In subsets of CD patients this regulatory mechanism is disturbed, leading to hyperstable interactions and excessive immunity. Boosting the mTOR pathway may be an interesting therapeutic option in CD patients carrying risk alleles in autophagyrelated genes.