Elsevier

Neurobiology of Aging

Volume 19, Issue 1, January–February 1998, Pages 3-13
Neurobiology of Aging

Original Articles
Phosphorylation of Tau, Aβ-Formation, and Apoptosis After In Vivo Inhibition of PP-1 and PP-2A

https://doi.org/10.1016/S0197-4580(98)00003-7Get rights and content

Abstract

Chronic inhibition of protein phosphatases 1 and 2A in vivo was induced by infusion of okadaic acid into lateral ventricles of rat brain for up to 4 months. Cytoskeletal pathology, alterations of the amyloid precursor protein, and apoptotic cell death induced by this treatment followed a certain sequence and spatial distribution. Changes in the expression, phosphorylation, and subcellular distribution of neurofilament proteins and tau, as well as first signs of apoptotic cell death, occurred already after about 2 weeks. The distribution of apoptotic cells, however, was different from those revealing a high accumulation of hyperphosphorylated tau, indicating that those cytoskeletal pathology had no obvious sequelae for the viability of these neurones. A continuation of treatment for longer than 2 weeks induced diffuse deposits of both hyperphosphorylated tau and Aβ-amyloid-immunoreactive material in white matter areas that increased in size and number over time. Because τ-phosphorylation is a regulator of the dynamic stability of microtubules, the pathology observed in the present experimental paradigm in the white matter might be viewed as an indication of a disturbed axonal transport. It is hypothesized that perturbations of the axonal transport might also be critically involved in the formation of paired helical filaments and amyloid deposits in Alzheimer’s disease.

Section snippets

Application of Okadaic Acid (OA)

Adult Wistar rats received infusions of OA (ammonium salt, Biotrend) into lateral ventricles at a dosage of 70 ng/day via mini-osmotic pumps [4](mean pumping rate: 0.51 ± 0.02 μL/h; alzet model 2002, ALZA Cooperation, Palo Alto). Infusion cannulae (0.36 mm diameter) were stereotaxically placed under anesthesia (15 mg/kg, i.m. Rompun, Bayer, Leverkusen; 100 mg/kg, i.m. Velonarcon, Berlin-Chemie AG) at the following co-ordinates (in mm from bregma and dura, flat skull): AP-0.9; L-1.4; V-3.8. OA

Results

Okadaic acid, a specific inhibitor of protein phosphatases 1 and 2A, was continuously infused into lateral ventricles of rat brain through mini-osmotic pumps for different periods of time up to 4 months. The sequelae of a continuous inhibition of PP-1 and 2A on the expression, subcellular distribution, and phosphorylation of tau and neurofilaments, on the expression and amyloidogenic processing of the amyloid precursor protein and on neuronal viability and the induction of apoptotic cell death

Discussion

The present study extends our previous observations that chronic infusion of okadaic acid into rat brain results in an increased phosphorylation and subcellular redistribution of cytoskeletal proteins, as well as alterations in the expression and processing of the amyloid precursor protein 3, 4. The results demonstrate, furthermore, that these pathological alterations develop in a certain topographical pattern and with a characteristic time course, and show a typical relationship to apoptotic

Acknowledgements

This study was supported by the Deutsche Forschungsgemeinschaft (Ar 200/2–2) and by the Bundesministerium für Bildung, Forschung und Technologie (BMBF), Interdisciplinary Center for Clinical Research at the University of Leipzig (IZKF-C1). We thank Dr. D. Taylor for linguistic revision.

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