IDENTIFICATION OF GALECTIN-3 AS A HIGH-AFFINITY BINDING-PROTEIN FOR ADVANCED GLYCATION END-PRODUCTS (AGE) - A NEW MEMBER OF THE AGE-RECEPTOR COMPLEX

Background: Advanced glycation end products (AGE), the reactive deriva tives of nonenzymatic glucose-protein condensation reactions, are impl icated in the multiorgan complications of diabetes and aging. An AGE-s pecific cellular receptor complex (AGE-R) mediating AGE removal as wel l as multiple biological responses has been identified. By screening a n expression library using antibody against a previously identified co mponent of the AGE-R complex p90, a known partial cDNA clone was isola ted with homology to galectin-3, a protein of diverse identity, and me mber of the galectin family. Materials and Methods: To explore this un expected finding, the nature of the interactions between galectin-3 an d AGE was studied using intact macrophage-like RAW 264.7 cells, membra ne-associated and recombinant galectin-1 through -4, and model AGE-lig ands (AGE-BSA, FFI-BSA). Results: Among the members of this family (ga lectin-1 through 4), recombinant rat galectin-3 was found to exhibit h igh-affinity I-125-AGE-BSA binding with saturable kinetics (kD 3.5 X 1 0(7) M(-1)) that was fully blocked by excess unlabeled naturally forme d AGE-BSA or synthetic FFI-BSA, but only weakly inhibited by several k nown galectin-3 ligands, such as lactose. In addition to the p90, immu noprecipitation with anti-galectin-3, followed by I-125-AGE-BSA ligand blot analysis of RAW 264.7 cell extracts, revealed galectin-3 (28 and 32 kD), as well as galectin-3-associated proteins (40 and 50 kD) with AGE-binding activity. Interaction of galectin-3 with AGE-BSA or FFI-B SA resulted in formation of SDS-, and beta-mercaptoethanol-insoluble, but hydroxylamine-sensitive high-molecular weight complexes between AG E-ligand, galectin-3, and other membrane components. Conclusions: The findings point toward a mechanism by which galectin-3 may serve in the assembly of AGE-R components and in the efficient cell surface attach ment and endocytosis by macrophages of a heterogenous pool of AGE moie ties with diverse affinities, thus contributing to the elimination of these pathogenic substances.