Binding of mannose-binding lectin to fructosamines: a potential link between hyperglycaemia and complement activation in diabetes.
BACKGROUND
Complement activation via the MBL pathway has been proposed to play a role in the pathogenesis of diabetic complications. As protein glycation is increased in diabetes, we tested the possibility that the glycation product fructoselysine is a ligand for MBL and that its interaction with this protein may initiate complement activation.


METHODS
We investigated the binding of MBL to fructoselysine by chromatography of human serum on fructoselysine-Sepharose, followed by Western blot and mass spectrometry analysis. We also performed enzyme-linked immunosorbent assays using purified MBL and fructoselysine-derivatized (binding assay) or mannan-coated plates (inhibition assay). Complement activation was determined by the fixation of C3d following incubation of fructoselysine-derivatized plates with serum from subjects with different levels of MBL.


RESULTS
MBL and its associated proteases were selectively purified from serum by chromatography on fructoselysine-Sepharose. Competition experiments indicated that MBL had a similar affinity for mannose, fructose and fructoselysine. MBL bound, in a highly cooperative manner, to fructoselysine-derivatized plates. This binding was associated with complement activation and was much lower with serum from subjects with low-MBL genotypes.


CONCLUSIONS
MBL binding to fructoselysine and the ensuing complement activation may provide a physiopathological link between enhanced glycation and complement activation in diabetes. The cooperative character of this binding may explain the high sensitivity of diabetic complications to hyperglycaemia.
Fortpied
Juliette
J
Laboratory of Physiological Chemistry, de Duve Institute, Université Catholique de Louvain, Brussels, Belgium.
Vertommen
Didier
D
Van Schaftingen
Emile
E
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002846:Chromatography, Affinity; D003167:Complement Activation; D003924:Diabetes Mellitus, Type 2 / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008239:Lysine / Q000031:analogs & derivatives* / Q000378:metabolism; D037601:Mannose-Binding Lectin / Q000097:blood / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor)
D001786:Blood Glucose; D037601:Mannose-Binding Lectin; C033186:fructosyl-lysine; D017853:Phosphotransferases (Alcohol Group Acceptor); C414347:fructosamine-3-kinase; D008239:Lysine