Alzheimer's disease neuropathology is characterized by neuronal death,
amyloid beta-peptide deposits and neurofibrillary tangles composed of paired helical filaments of
tau protein. Although crucial for our understanding of the pathogenesis of
Alzheimer's disease, the molecular mechanisms linking
amyloid beta-peptide and paired helical filaments remain unknown. Here, we show that
amyloid beta-peptide-induced nitro-oxidative damage promotes the nitrotyrosination of the glycolytic
enzyme triosephosphate isomerase in human
neuroblastoma cells. Consequently, nitro-
triosephosphate isomerase was found to be present in brain slides from double transgenic mice overexpressing human
amyloid precursor
protein and
presenilin 1, and in
Alzheimer's disease patients. Higher levels of nitro-
triosephosphate isomerase (P < 0.05) were detected, by Western blot, in immunoprecipitates from hippocampus (9 individuals) and frontal cortex (13 individuals) of
Alzheimer's disease patients, compared with healthy subjects (4 and 9 individuals, respectively).
Triosephosphate isomerase nitrotyrosination decreases the glycolytic flow. Moreover, during its
isomerase activity, it triggers the production of the highly neurotoxic
methylglyoxal (n = 4; P < 0.05). The bioinformatics simulation of the nitration of tyrosines 164 and 208, close to the catalytic centre, fits with a reduced
isomerase activity. Human embryonic kidney (HEK) cells overexpressing double mutant
triosephosphate isomerase (Tyr164 and 208 by Phe164 and 208) showed high
methylglyoxal production. This finding correlates with the widespread glycation immunostaining in
Alzheimer's disease cortex and hippocampus from double transgenic mice overexpressing
amyloid precursor
protein and
presenilin 1. Furthermore, nitro-
triosephosphate isomerase formed large beta-sheet aggregates in vitro and in vivo, as demonstrated by turbidometric analysis and electron microscopy. Transmission electron microscopy (TEM) and atomic force microscopy studies have demonstrated that nitro-
triosephosphate isomerase binds tau monomers and induces tau aggregation to form paired helical filaments, the characteristic intracellular hallmark of
Alzheimer's disease brains. Our results link oxidative stress, the main etiopathogenic mechanism in sporadic
Alzheimer's disease, via the production of
peroxynitrite and nitrotyrosination of
triosephosphate isomerase, to
amyloid beta-peptide-induced toxicity and tau pathology.