carbocyanines and Tauopathies

Impairment of synaptic plasticity underlies memory dysfunction in Alzheimer's disease (AD). Molecules involved in this plasticity such as PSD-95, a major postsynaptic scaffold protein at excitatory synapses, may play an important role in AD pathogenesis. We examined the distribution of PSD-95 in transgenic mice of amyloidopathy (5XFAD) and tauopathy (JNPL3) as well as in AD brains using double-labeling immunofluorescence and confocal microscopy. In wild type control mice, PSD-95 primarily labeled neuropil with distinct distribution in hippocampal apical dendrites. In 3-month-old 5XFAD mice, PSD-95 distribution was similar to that of wild type mice despite significant Aβ deposition. However, in 6-month-old 5XFAD mice, PSD-95 immunoreactivity in apical dendrites markedly decreased and prominent immunoreactivity was noted in neuronal soma in CA1 neurons. Similarly, PSD-95 immunoreactivity disappeared from apical dendrites and accumulated in neuronal soma in 14-month-old, but not in 3-month-old, JNPL3 mice. In AD brains, PSD-95 accumulated in Hirano bodies in hippocampal neurons. Our findings support the notion that either Aβ or tau can induce reduction of PSD-95 in excitatory synapses in hippocampus. Furthermore, this PSD-95 reduction is not an early event but occurs as the pathologies advance. Thus, the time-dependent PSD-95 reduction from synapses and accumulation in neuronal soma in transgenic mice and Hirano bodies in AD may mark postsynaptic degeneration that underlies long-term functional deficits.

Topics: Age Factors; Aged; Aged, 80 and over; Alzheimer Disease; Amyloid beta-Peptides; Analysis of Variance; Animals; Brain; Carbocyanines; Cell Count; Disease Models, Animal; Disks Large Homolog 4 Protein; Female; Gene Expression Regulation; Guanylate Kinases; Humans; Male; Membrane Proteins; Mice; Mice, Transgenic; Middle Aged; Synapses; tau Proteins; Tauopathies

Tau aggregation is an appealing target for therapeutic intervention. However, conformational change or aggregation needs to be targeted without inhibiting the normal biology of tau and its role in microtubule stabilization. The number of compound classes being tested at this time are very limited and include Congo red derivatives [2], anthraquinones (Pickhardt et al. 2005 [3], disputed in Crowe et al. 2007 [4]), 2,3-di(furan-2-yl)-quinoxalines , phenylthiazolyl-hydrazide (PTH) [5], polyphenols and porphyrins [6] and cyanine dyes [1, 7, 8]. Herein we have utilized a member of the cyanine dye family (C11) in an organotypic slice culture model of tangle formation. Our results demonstrate that C11 is capable of affecting tau polymerization in a biphasic, dose dependent manner. At submicromolar concentrations (0.001 microM) C11 reduced levels of aggregated tau. However, higher doses resulted in an increase in tau polymerization. These effects can also be seen at the level of individual filaments with changes in filament length and number mirroring the pattern seen via immunoblotting. In addition, this effect is achieved without altering levels of phosphorylation at disease and microtubule binding relevant epitopes.

Topics: Animals; Binding Sites; Carbocyanines; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Mice; Microtubules; Neurofibrillary Tangles; Organ Culture Techniques; Polymers; Structure-Activity Relationship; tau Proteins; Tauopathies

Tau fibrillization is a potential therapeutic target for Alzheimer's and other neurodegenerative diseases. Small molecules capable of both inhibiting aggregation and promoting filament disaggregation have been discovered, but knowledge of their mechanism of action and potential for testing in biological models is fragmentary. To clarify these issues, the interaction between a small-molecule inhibitor of tau fibrillization, 3,3'-bis(beta-hydroxyethyl)-9-ethyl-5,5'-dimethoxythiacarbocyanine iodide (N744), and full-length four-repeat tau protein was characterized in vitro using transmission electron microscopy and fluorescence spectroscopy. Analysis of reaction time courses performed in the presence of anionic fibrillization inducers revealed that increasing concentrations of N744 decreased the total filament length without modulating lag time, indicating that filament extension but not nucleation was affected by inhibitor under the conditions that were investigated. Critical concentration measurements confirmed that N744 shifted equilibria at filament ends away from the fibrillized state, resulting in endwise filament disaggregation when it was added to synthetic filaments. Both increasing bulk tau concentrations and filament stabilizing modifications such as pseudophosphorylation and glycation antagonized N744 activity. The results illustrate the importance of mechanism for the design and interpretation of pharmacological studies in biological models of tau aggregation.

Topics: Benzothiazoles; Binding, Competitive; Carbocyanines; Humans; Kinetics; Models, Chemical; Nerve Tissue Proteins; Protein Processing, Post-Translational; Solubility; tau Proteins; Tauopathies; Thiazoles