N^ε‐carboxymethyllysine‐modified proteins are unable to bind to RAGE and activate an inflammatory response

Abstract

Advanced glycation endproducts (AGEs) containing carboxymethyllysine (CML) modifications are generally thought to be ligands of the receptor for AGEs, RAGEs. It has been argued that this results in the activation of pro-inflammatory pathways and diseases. However, it has not been shown conclusively that a CML-modified protein can interact directly with RAGE. Here, we have analyzed whether beta-lactoglobulin (bLG) or human serum albumin (HSA) modified chemically to contain only CML (10-40% lysine modification) can (i) interact with RAGE in vitro and (ii) interact with and activate RAGE in lung epithelial cells. Our results show that CML-modified bLG or HSA are unable to bind to RAGE in a cell-free assay system (Biacore). Furthermore, they are unable to activate pro-inflammatory signaling in the cellular system. Thus, CML probably does not form the necessary structure(s) to interact with RAGE and activate an inflammatory signaling cascade in RAGE-expressing cells.

Structural Basis for Pattern Recognition by the Receptor for Advanced Glycation End Products (RAGE)

“…Similarly, the interplay between binding at different interaction surfaces and different chemical structures of AGE ligands may be responsible for the reported failures to detect RAGE signaling by some specific AGEs (32,77). This mechanism presents new opportunities for controlling RAGE signaling by screening for small molecules that interfere with the AGE interaction surfaces of the V domain delineated in this study.…”

Glycolaldehyde‐modified β‐lactoglobulin AGEs are unable to stimulate inflammatory signaling pathways in RAGE‐expressing human cell lines

“…We have shown previously that CML-modified bLG or HSA are unable to stimulate inflammatory signaling in the human lung epithelial cell line Beas2b [30]. Here, we first evaluated the RAGE expression in different human cell lines.…”

Evaluation of Nonenzymatic Posttranslational Modification–Derived Products as Biomarkers of Molecular Aging of Proteins

“…Evidence from several studies has suggested that the interactions of AGEs with specific receptors, especially RAGE (receptor for advanced glycation end products), and subsequent cell signaling, could play a significant role in the progression of these diseases (15 ). The role of this receptor has recently been contested, however, since most evidence of the ability of RAGE to bind AGEs has been obtained in vitro using highly glycated and aggregated proteins (31,32 ). RAGE is known as a multiligand receptor, whose most likely physiological ligands are not AGEs but peptides involved in other pathologies such as inflammation, neurodegenerative diseases, or cancer (e.g., S100/calgranulins, amyloid-␤ peptide, and amphoterin) (15 ).…”