The amino terminus of tau inhibits kinesin‐dependent axonal transport: Implications for filament toxicity

Abstract

The neuropathology of Alzheimer's disease (AD) and other tauopathies is characterized by filamentous deposits of the microtubule-associated protein tau, but the relationship between tau polymerization and neurotoxicity is unknown. Here, we examined effects of filamentous tau on fast axonal transport (FAT) using isolated squid axoplasm. Monomeric and filamentous forms of recombinant human tau were perfused in axoplasm, and their effects on kinesin- and dynein-dependent FAT rates were evaluated by video microscopy. Although perfusion of monomeric tau at physiological concentrations showed no effect, tau filaments at the same concentrations selectively inhibited antero-grade (kinesin-dependent) FAT, triggering the release of conventional kinesin from axoplasmic vesicles. Pharmacological experiments indicated that the effect of tau filaments on FAT is mediated by protein phosphatase 1 (PP1) and glycogen synthase kinase-3 (GSK-3) activities. Moreover, deletion analysis suggested that these effects depend on a conserved 18-amino-acid sequence at the amino terminus of tau. Interestingly, monomeric tau isoforms lacking the C-terminal half of the molecule (including the microtubule binding region) recapitulated the effects of full-length filamentous tau. Our results suggest that pathological tau aggregation contributes to neurodegeneration by altering a regulatory pathway for FAT.

Disruption of fast axonal transport is a pathogenic mechanism for intraneuronal amyloid beta

“…The functional consequence of GSK3-mediated phosphorylation of KLC was release of kinesin-1 from its vesicle cargoes (22,23,40). Consistent with this observation, the amount of kinesin-1 on axoplasmic vesicles was substantially reduced relative to controls with both oA␤ and CK2 perfused axoplasms (Fig.…”

“…3B). Previous studies with GSK3 showed that the 63-90 epitope was also sensitive to GSK3 activity (22,23,40). Significantly, CK2 was a priming kinase for GSK3 modification of KLC and GSK3 did not phosphorylate KLC without a priming phosphorylation (22).…”

“…Phosphorylation of kinesin-1 by various kinases can regulate its activities and affect anterograde FAT (22,24,28). Previous studies on phosphorylation of KLC at the 63-90 epitope suggest that this site regulates binding of kinesin-1 to vesicle cargoes (23,40). To determine whether oA␤ leads to release of kinesin-1 from cargoes, we isolated vesicle fractions by flotation assays from axoplasms treated for 50 minutes with either uA␤ or oA␤, and evaluated the association of kinesin-1 with membrane fractions by immunoblot with the kinesin-1 KHC-specific antibody H2.…”

“…Two different mechanisms have been identified for inhibition of kinesin-based FAT. When KLCs are phosphorylated by GSK3 (22,23,40), binding of kinesin-1 to cargoes is reduced. Alternatively, phosphorylation of KHC by JNK inhibits the ability of kinesin-1 to bind microtubules (24).…”

Progression of Tau Pathology in Cholinergic Basal Forebrain Neurons in Mild Cognitive Impairment and Alzheimer's Disease

“…34 The aggregation of tau can also inhibit anterograde axonal transport. 35 Abnormalities in axonal processes appear as tau positive NTs, which might occur before tau accumulation within the soma of the neuron. 28,36 The onset of axonal/dendritic pathology within the CBF and its relation to cholinergic neuronal NFT development during the progression of AD remains unresolved.…”