Expression of advanced glycation end products and their cellular receptor RAGE in diabetic nephropathy and nondiabetic renal disease

Advanced glycation end products (AGE) contribute to diabetic tissue injury by two major mechanisms, i.e., the alteration of extracellular matrix archi tecture through nonenzymatic glycation, with formation of protein crosslink s, and the modulation of cellular functions through interactions with speci fic cell surface receptors, the best characterized of which is the receptor for AGE (RAGE). Recent evidence suggests that the AGE-RAGE interaction may also be promoted by inflammatory processes and oxidative cellular injury. To characterize the distributions of AGE and RAGE in diabetic kidneys and t o determine their specificity for diabetic nephropathy, an immunohistochemi cal analysis of renal biopsies from patients with diabetic nephropathy (n = 26), hypertensive nephrosclerosis (n = 7), idiopathic focal segmental glom erulosclerosis (n = ii), focal sclerosis secondary to obesity (n = 7), and lupus nephritis (n = 11) and from normal control subjects (n = 2) was perfo rmed, using affinity-purified antibodies raised to RAGE and two subclasses of AGE, i.e., N-epsilon-(carboxymethyl)lysine (CML) and pentosidine (PENT). AGE were detected equally in diffuse and nodular diabetic nephropathy. CML was the major AGE detected in diabetic mesangium (96%), glomerular basemen t membranes (GBM) (42%), tubular basement membranes (85%), and vessel walls (96%). In diabetic nephropathy, PENT was preferentially located in interst itial collagen (90%) and was less consistently observed in vessel walls (54 %), mesangium (77%), GEM (4%), and tubular basement membranes (31%). RAGE w as expressed on normal podocytes and was upregulated in diabetic nephropath y. The restriction of RAGE mRNA expression to glomeruli was confirmed by re verse transcription-PCR analysis of microdissected renal tissue compartment s. The extent of mesangial and GEM immunoreactivity for CML, but not PENT, was correlated with the severity of diabetic glomerulosclerosis, as assesse d pathologically. CML and PENT were also identified in areas of glomerulosc lerosis and arteriosclerosis in idiopathic and secondary focal segmental gl omerulosclerosis, hypertensive nephrosclerosis, and lupus nephritis. In act ive lupus nephritis, CML and PENT were detected in the proliferative glomer ular tufts and crescents. In conclusion, CML is a major AGE in renal baseme nt membranes in diabetic nephropathy, and its accumulation involves upregul ation of RAGE on podocytes. AGE are also accumulated in acute inflammatory glomerulonephritis secondary to systemic lupus erythematosus, possibly via enzymatic oxidation of glomerular matrix proteins.