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Tau in Alzheimer's disease and Down's syndrome is insoluble and abnormally phosphorylated
D P Hanger1, J P Brion, J M Gallo
1Department of Neuroscience, Institute of Psychiatry, Denmark Hill, London, U.K.
Abstract:
Some investigators have described the presence in Alzheimer's disease brain extracts of several abnormal forms of the microtubule-associated protein tau, based on their unusual mobility in SDS/PAGE. It has been proposed that these abnormal forms of tau may be the result of aberrant tau phosphorylation. In this study we show that tau in extracts of Alzheimer's disease brain can be separated into two fractions based upon its solubility (100,000 g x 1 h supernatant) in non-denaturing conditions (100 mM-Mes, pH 6.5, 0.5 mM-MgCl2, 1 mM-EGTA and 1 M-NaCl). The tau isoforms with decreased mobility in SDS/PAGE are predominantly in an insoluble fraction, whereas the soluble tau is indistinguishable by its mobility in SDS/PAGE from tau in soluble extracts of control brain. Insoluble tau displaying abnormal mobility on SDS/PAGE was only found in Alzheimer and adult Down's syndrome brains and was absent from the brains of age-matched controls and from foetal and infant Down's syndrome brains. There was a good correlation between the presence of insoluble tau in brain extracts and the abundance of neurofibrillary tangles and senile neuritic plaques. The monoclonal antibody Tau. 1 stained insoluble tau on Western blots only after treatment of the nitrocellulose transfers with alkaline phosphatase, implying that this insoluble tau is in a particular state of phosphorylation. We conclude that, in Alzheimer's disease, a fraction of tau has a modified phosphorylation state and a decreased solubility; these modifications may precede formation of the neurofibrillary tangles characteristic of Alzheimer's disease and Down's syndrome in adults.
Insights
Abnormal tau protein in Alzheimer's disease brains shows decreased solubility and altered phosphorylation. This insoluble tau correlates with neurofibrillary tangles and may precede their formation.
Area of Science:
- Neuroscience
- Biochemistry
- Pathology
Background:
- Alzheimer's disease (AD) is characterized by abnormal forms of the microtubule-associated protein tau.
- Aberrant tau phosphorylation has been proposed as a cause for these abnormal tau forms.
Purpose of the Study:
- To investigate the solubility and phosphorylation state of tau in Alzheimer's disease brain extracts.
- To determine if abnormal tau is present in other neurological conditions.
Main Methods:
- Separation of tau protein into soluble and insoluble fractions from brain extracts under non-denaturing conditions.
- Analysis of tau mobility in SDS-PAGE and Western blotting using the Tau.1 antibody after alkaline phosphatase treatment.
Main Results:
- Tau with decreased SDS/PAGE mobility was predominantly insoluble in AD brain extracts.
- Insoluble tau was found in Alzheimer's and adult Down's syndrome brains, but not in controls or younger Down's syndrome brains.
- A correlation was observed between insoluble tau and the abundance of neurofibrillary tangles and senile neuritic plaques.
Conclusions:
- A fraction of tau in Alzheimer's disease exhibits altered phosphorylation and reduced solubility.
- These modifications in tau may be an early event in the development of neurofibrillary tangles in AD and adult Down's syndrome.