Posttranslationally modified proteins as mediators of sustained intestinal inflammation

Oxidative and carbonyl stress leads to generation of N^ε- carboxymethyllysine-modified proteins (CML-mps), which are known to bind the receptor for advanced glycation end products (RAGE) and induce nuclear factor (NF)-κB-dependent proinflammatory gene expression. To determine the impact of CML-mps in vivo, RAGE-dependent sustained NF-κB activation was studied in resection gut specimens from patients with inflammatory bowel disease. Inflamed gut biopsy tissue demonstrated a significant up-regulation of RAGE and increased NF-κB activation. Protein extracts from the inflamed zones, but not from non-inflamed resection borders, caused perpetuated NF-κB activation in cultured endothelial cells, which was mediated by CML-mps including CML-modified S100 proteins. The resulting NF-κB activation, lasting 5 days, was primarily inhibited by either depletion of CML-mps or by the addition of sRAGE, p44/42 and p38 MAPKinase-specific inhibitors. Consistently, CML-mps isolated from inflamed gut areas and rectally applied into mice caused NF-κB activation, increased proinflammatory gene expression, and histologically detectable inflammation in wild-type mice, but not in RAGE ^-/- mice. A comparable upregulation of NF-κB and inflammation on rectal application of CML-mps was observed in IL-10^-/- mice. Thus, CML-mps generated in inflammatory lesions have the capacity to elicit a RAGE-dependent intestinal inflammatory response.