Peroxynitrite induces Alzheimer‐like tau modifications and accumulation in rat brain and its underlying mechanisms

Abstract

To investigate the upstream effector that led to tau hyperphosphorylation, nitration, and accumulation as seen in Alzheimer's disease brain, and the underlying mechanisms, we bilaterally injected SIN-1, a recognized peroxynitrite donor, into the hippocampus of rat brain. We observed that the level of nitrated and hyperphosphorylated tau was markedly increased in rat hippocampus 24 h after drug administration, and these alterations were prevented by preinjection of uric acid, a natural scavenger of peroxynitrite. Concomitantly, we detected a significant activation in glycogen synthase kinase-3beta (GSK-3beta) and p38 MAPKs, including p38alpha, p38beta, and p38delta, but no obvious change was measured in the activity of p38gamma, ERK, and c-Jun amino-terminal kinase (JNK). Both nitrated tau and hyperphosphorylated tau were aggregated in the hippocampus, in which the activity of 20S proteasome was significantly arrested in SIN-1-injected rats. Further studies demonstrated that the hyperphosphorylated tau was degraded as efficiently as normal tau by 20S proteasome, but the nitrated tau with an unorderly secondary structure became more resistant to the proteolysis. These results provide the first in vivo evidence showing that peroxynitrite simultaneously induces tau hyperphosphorylation, nitration, and accumulation, and that activation of GSK-3beta, p38alpha, p38beta, p38delta isoforms and the inhibition of proteasome activity are respectively responsible for the peroxynitrite-induced tau hyperphosphorylation and accumulation. Our findings reveal a common upstream stimulator and a potential therapeutic target for Alzheimer-like neurodegeneration.

Cortical and Hippocampal Neurons from Truncated Tau Transgenic Rat Express Multiple Markers of Neurodegeneration

“…In contrast to wild type neurons, the viability of truncated tau bearing neurons has been decreased up to the half under the stress. This finding supports the idea that truncated tau could amplify the damage induced by oxidative stress, which was shown to impair neuronal functions (Butterfield et al 2006;Zhang et al 2006).…”

Tyrosine Nitration is a Novel Post-translational Modification Occurring on the Neural Intermediate Filament Protein Peripherin

“…More information is available on nitration of cytoskeletal proteins in pathological processes where a correlation between this post-translational modification and cytoskeletal dysfunction is strongly suggested. Actin has been found heavily nitrated in a mouse model of amyotrophic lateral sclerosis [36] and in sickle cell disease [38], nitrated tau with an unordered secondary structure is described in Alzheimer's [39], nitrotyrosine incorporated in alpha-tubulin alters microtubule assembly and organization in cellular injury [40], abnormal alphasynuclein aggregation and nitration has been found in the frontal cortex in Pick's disease [41] and effects of nitration on the structure and aggregation of alphasynuclein have been described in vitro [42]. Moreover, one of the intermediate filaments, NF-L, was found to be particularly susceptible to nitration in vivo in sporadic amyotrophic lateral sclerosis and further observations revealed that NF-L nitration is a ubiquitous occurance in neurones suggesting that NF-L might function as a sink for free reactive nitrating species [37].…”

Hyperhomocysteinemia Increases β-Amyloid by Enhancing Expression of γ-Secretase and Phosphorylation of Amyloid Precursor Protein in Rat Brain

“…37 In brief, the rat hippocampi were quickly dissected out and homogenized on ice in buffer containing 50 mmol/L TrisHCl (pH 7.5), 150 mmol/L NaCl, 1% (v/v) Triton X-100, 1% (w/v) deoxycholate, 0.1% (w/v) SDS, 10 mmol/L NaF, 1 mmol/L Na 3 VO 4 , and 2 g/ml each of aprotinin, leupeptin, and pepstatin. Then, the hippocampal extracts (about 500 g total proteins) was immunoprecipitated with antipT668-APP at 4°C and shaken overnight, and then protein G agarose (Pierce Chemical Company, Rockford, IL) was added and incubated at 4°C for 2 hours.…”