Cleavage of Tau by calpain in Alzheimer's disease: the quest for the toxic 17 kD fragment.
The amyloid cascade hypothesis of Alzheimer's disease (AD) posits that the generation of β-amyloid (Aβ) triggers Tau neurofibrillary pathology. Recently a "17 kD" calpain-induced Tau fragment, comprising residues 45-230 (molecular weight [MW], 18.7 kD), was proposed to mediate Aβ-induced toxicity. Here, we demonstrate that the "17 kD" fragment is actually much smaller, containing residues 125-230 (molecular weight, 10.7 kD). Inducing Tau phosphorylation by okadaic acid or mimicking phosphorylation by Glu mutations at the epitopes of Alzheimer-diagnostic antibodies AT100/AT8/PHF1 could not prevent the generation of this fragment. The fragment can be induced not only by Aβ oligomers, but also by other cell stressors, e.g., thapsigargin (a Ca(2+)-ATPase inhibitor) or glutamate (an excitatory neurotransmitter). However, overexpression of neither Tau(45-230) nor Tau(125-230) fragment is toxic to Chinese hamster ovary (CHO) cells, neuroblastoma cells (N2a) or primary hippocampal neurons. Finally, the calpain-induced fragment can be observed both in Alzheimer's disease brains and in control normal human brains. We conclude that the 17 kD Tau fragment is not a mediator of Aβ-induced toxicity, leaving open the possibility that upstream calpain activation might cause both Tau fragmentation and toxicity.
Garg
Sarika
S
Max-Planck-Unit for Structural Molecular Biology, Hamburg, Germany.
Timm
Thomas
T
Mandelkow
Eva-Maria
EM
Mandelkow
Eckhard
E
Wang
Yipeng
Y
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000378:metabolism* / Q000473:pathology; D016229:Amyloid beta-Peptides / Q000633:toxicity; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000494:pharmacology; D002154:Calpain / Q000494:pharmacology*; D002452:Cell Count; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D020287:In Situ Nick-End Labeling / Q000379:methods; D008970:Molecular Weight; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010446:Peptide Fragments / Q000633:toxicity; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection / Q000379:methods; D016875:tau Proteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D000099291:Adducins
D016229:Amyloid beta-Peptides; D002148:Calmodulin-Binding Proteins; D002154:Calpain; D004791:Enzyme Inhibitors; D018698:Glutamic Acid; D049452:Green Fluorescent Proteins; D010446:Peptide Fragments; D010455:Peptides; D019284:Thapsigargin; D016875:tau Proteins; C102021:ADD3 protein, human; D000099291:Adducins; C075222:amyloid beta-protein (1-42)