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Mechanistic logic underlying the axonal transport of cytosolic proteins.

ABSTRACT: Proteins vital to presynaptic function are synthesized in the neuronal perikarya and delivered into synapses via two modes of axonal transport. While membrane-anchoring proteins are conveyed in fast axonal transport via motor-driven vesicles, cytosolic proteins travel in slow axonal transport via mechanisms that are poorly understood. We found that in cultured axons, populations of cytosolic proteins tagged to photoactivatable GFP (PAGFP) move with a slow motor-dependent anterograde bias distinct from both vesicular trafficking and diffusion of untagged PAGFP. The overall bias is likely generated by an intricate particle kinetics involving transient assembly and short-range vectorial spurts. In vivo biochemical studies reveal that cytosolic proteins are organized into higher order structures within axon-enriched fractions that are largely segregated from vesicles. Data-driven biophysical modeling best predicts a scenario where soluble molecules dynamically assemble into mobile supramolecular structures. We propose a model where cytosolic proteins are transported by dynamically assembling into multiprotein complexes that are directly/indirectly conveyed by motors.

SUBMITTER: Scott DA

PROVIDER: S-EPMC3096075 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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Mechanistic logic underlying the axonal transport of cytosolic proteins.

Scott David A DA Das Utpal U Tang Yong Y Roy Subhojit S

Neuron 20110501 3

Proteins vital to presynaptic function are synthesized in the neuronal perikarya and delivered into synapses via two modes of axonal transport. While membrane-anchoring proteins are conveyed in fast axonal transport via motor-driven vesicles, cytosolic proteins travel in slow axonal transport via mechanisms that are poorly understood. We found that in cultured axons, populations of cytosolic proteins tagged to photoactivatable GFP (PAGFP) move with a slow motor-dependent anterograde bias distinc ...[more]

PMID: 21555071

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Project description:UNLABELLED:Despite the demonstration that amyloid-? (A?) can trigger increased tau phosphorylation and neurofibrillary tangle (NFT) formation in vivo, the molecular link associating A? and tau pathologies remains ill defined. Here, we observed that exposure of cultured primary neurons to A? trimers isolated from brain tissue of subjects with Alzheimer's disease led to a specific conformational change of tau detected by the antibody Alz50. A similar association was supported by postmortem human brain analyses. To study the role of A? trimers in vivo, we created a novel bigenic Tg-A?+Tau mouse line by crossing Tg2576 (Tg-A?) and rTg4510 (Tg-Tau) mice. Before neurodegeneration and amyloidosis, apparent A? trimers were increased by ?2-fold in 3-month-old Tg-A? and Tg-A?+Tau mice compared with younger mice, whereas soluble monomeric A? levels were unchanged. Under these conditions, the expression of soluble Alz50-tau conformers rose by ?2.2-fold in the forebrains of Tg-A?+Tau mice compared with nontransgenic littermates. In parallel, APP accumulated intracellularly, suggestive of a putative dysfunction of anterograde axonal transport. We found that the protein abundance of the kinesin-1 light chain (KLC1) was reduced selectively in vivo and in vitro when soluble A? trimers/Alz50-tau were present. Importantly, the reduction in KLC1 was prevented by the intraneuronal delivery of Alz50 antibodies. Collectively, our findings reveal that specific soluble conformers of A? and tau cooperatively disrupt axonal transport independently from plaques and tangles. Finally, these results suggest that not all endogenous A? oligomers trigger the same deleterious changes and that the role of each assembly should be considered separately. SIGNIFICANCE STATEMENT:The mechanistic link between amyloid-? (A?) and tau, the two major proteins composing the neuropathological lesions detected in brain tissue of Alzheimer's disease subjects, remains unclear. Here, we report that the trimeric A? species induce a pathological modification of tau in cultured neurons and in bigenic mice expressing A? and human tau. This linkage was also observed in postmortem brain tissue from subjects with mild cognitive impairment, when A? trimers are abundant. Further, this modification of tau was associated with the intracellular accumulation of the precursor protein of A?, APP, as a result of the selective decrease in kinesin light chain 1 expression. Our findings suggest that A? trimers might cause axonal transport deficits in AD.

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Mechanistic logic underlying the axonal transport of cytosolic proteins.

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Mechanistic logic underlying the axonal transport of cytosolic proteins.

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