Abstract

Objective. To characterize glycation adducts formed both in vivo in extracellular matrix (ECM) proteins of endoneurium from streptozotocin (STZ)-induced diabetic rats, and in vitro by glycation of laminin and fibronectin with methylglyoxal (MG) and glucose. To investigate the impact of advanced glycation endproduct (AGE) residue content of ECM on neurite outgrowth from sensory neurons.

Research Design and Methods. Glycation, oxidation and nitration adducts of ECM proteins extracted from the endoneurium of control and STZ-diabetic rat sciatic nerve (3-24 weeks post-STZ), and of laminin and fibronectin that had been glycated using glucose or MG, were examined by liquid chromatography with tandem mass spectrometry. MG-glycated or unmodified ECM proteins were used as substrata for dissociated rat sensory neurons as in vitro models of regeneration.

Results. STZ-induced diabetes produced a significant increase in early glycation Nε-fructosyl-lysine (FL) and AGE residue contents of endoneurial ECM. Glycation of laminin and fibronectin by MG and glucose increased glycation adduct residue contents with MG-derived hydroimidazolone (MG-H1) and FL, respectively, of greatest quantitative importance. Glycation of laminin caused a significant decrease in both neurotrophin-stimulated and preconditioned sensory neurite-outgrowth. This decrease was prevented by aminoguanidine. Glycation of fibronectin also decreased preconditioned neurite-outgrowth, which was prevented by aminoguanidine and NGF.

Conclusions. Early glycation and AGE residue content of endoneurial ECM proteins increase markedly in STZ-induced diabetes. Glycation of laminin and fibronectin causes a reduction in neurotrophin-stimulated neurite outgrowth and preconditioned neurite-outgrowth. This may provide a mechanism for the failure of collateral sprouting and axonal regeneration in diabetic neuropathy.