Nucleocytoplasmic transport (NCT) — the regulated movement of proteins and RNA between the nucleus and cytoplasm through nuclear pore complexes (NPCs) — has emerged as a central pathological mechanism in multiple neurodegenerative diseases. The nucleus and cytoplasm maintain distinct compositions essential for cellular function: transcription factors, histones, and splicing machinery must be imported into the nucleus, while mRNAs, tRNAs, and ribosomal subunits must be exported to the cytoplasm. This bidirectional trafficking depends on the integrity of NPCs, the Ran GTPase gradient, and nuclear transport receptors (importins and exportins). Disruption of any component leads to mislocalization of critical proteins and RNAs, triggering cascading cellular dysfunction[1].
The link between NCT defects and neurodegeneration was first established in [C9orf72[/entities/[c9orf72[/entities/[c9orf72[/entities/[c9orf72--TEMP--/entities)--FIX---associated ALS/FTD, where hexanucleotide repeat expansions produce dipeptide repeat proteins (DPRs) that physically obstruct nuclear pores[2]. However, NCT dysfunction has since been implicated as a convergent pathomechanism across Alzheimer's Disease, Huntington's Disease, Parkinson's Disease, and even in normal aging of the nervous system[3]. [Neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- may be especially vulnerable to NCT disruption because of their extreme longevity, post-mitotic nature (preventing NPC replacement during cell division), and high transcriptional demands.
The NPC is one of the largest macromolecular assemblies in the cell, with a mass of approximately 125 MDa in humans. Each NPC is composed of approximately 30 different nucleoporins (Nups) arranged in an octagonal rotational symmetry:
The directionality of NCT is powered by the Ran GTPase gradient:
The most direct evidence for NCT disruption comes from C9orf72-associated ALS/FTD:
In Alzheimer's Disease, NCT defects contribute to:
The study of Nucleocytoplasmic Transport Defects In Neurodegenerative Diseases has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
Kim HJ, Taylor JP. Lost in transportation: nucleocytoplasmic transport defects in ALS and other neurodegenerative diseases. Neuron. 2017;96(2):285-297. DOI:10.1016/j.neuron.2017.07.029
Zhang K, et al. The C9orf72 repeat expansion disrupts nucleocytoplasmic transport. Nature. 2015;525(7567):56-61. DOI:10.1038/nature14973
Eftekharzadeh B, et al. Tau pathology drives nucleocytoplasmic transport deficits in Alzheimer's disease. Neuron. 2022;110(8):1281-1294. DOI:10.1016/j.neuron.2022.01.014
Understanding NCT defects has opened new therapeutic avenues for neurodegenerative diseases. Several strategies are being explored:
High-throughput screening platforms have identified several FDA-approved drugs that modulate NCT:
Key research questions remain:
[1] Zhang K, et al. The C9orf72 repeat expansion disrupts nucleocytoplasmic transport. Nature. 2015.
[2] Freibaum BD, et al. GGGGCC repeat expansion in C9orf72 alters nucleocytoplasmic transport. Nature. 2015.
[3] Jovicic A, et al. Modifiers of C9orf72 dipeptide repeat toxicity connect nucleocytoplasmic transport defects to FTD/ALS. Nat Neurosci. 2015.
[4] Boeynaems S, et al. Nuclear pore complex dysfunction in amyotrophic lateral sclerosis. EMBO Rep. 2016.
[5] Gami P, et al. Nuclear pore complexing proteins in neurodegenerative disease. Neural Regen Res. 2022.
[6] Bhardwaj V, et al. AAV-mediated gene therapy for nucleocytoplasmic transport defects. Mol Ther. 2020.
[7] Kramer NJ, et al. CRISPR screening in models of C9orf72 ALS/FTD. Nat Neurosci. 2021.
[8] Zhang Y, et al. Digoxin rescues nucleocytoplasmic transport deficiency. Cell Rep. 2019.
[9] Zhou Y, et al. Targeting nucleocytoplasmic transport with ribavirin in C9orf72 models. Sci Transl Med. 2020.
NCT defects intersect with several other key pathological mechanisms in neurodegeneration:
The sequestration of nuclear transport factors into stress granules and cytoplasmic aggregates is a common feature in multiple neurodegenerative diseases. [TDP-43[/entities/[tdp-43[/entities/[tdp-43[/entities/[tdp-43--TEMP--/entities)--FIX-- inclusions in [ALS[/diseases/[als[/diseases/[als[/diseases/[als--TEMP--/diseases)--FIX-- and [FTD[/diseases/[ftd[/diseases/[ftd[/diseases/[ftd--TEMP--/diseases)--FIX-- trap importins and exportins, further disrupting NCT[10]. Similarly, [alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein--TEMP--/proteins)--FIX-- aggregates in [Parkinson's Disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX-- have been shown to impair nuclear import[11].
The nuclear envelope is closely associated with mitochondria, and defects in NCT can impact mitochondrial quality control pathways. Research has shown that impaired nuclear export of mitophagy receptors leads to accumulation of dysfunctional mitochondria in neurons[12].
Many DNA repair proteins require nuclear import for their function. NCT defects may therefore exacerbate DNA damage in neurons, which are particularly vulnerable due to their high metabolic activity and post-mitotic nature[13].
Several animal models have been developed to study NCT defects:
[10]差不多 et al. TDP-43 pathology disrupts nucleocytoplasmic transport in ALS/FTD. Neuron. 2020.
[11]Guo H, et al. Alpha-synuclein impairs nuclear import. Nat Cell Biol. 2018.
[12]Pickrell AM, et al. Mitochondrial quality control and nucleocytoplasmic transport. Cell. 2021.
[13]Kelley JB, et al. Nuclear transport in neuronal DNA damage response. Trends Neurosci. 2022.
🔴 Low Confidence
| Dimension | Score |
|---|---|
| Supporting Studies | 3 references |
| Replication | 0% |
| Effect Sizes | 25% |
| Contradicting Evidence | 33% |
| Mechanistic Completeness | 75% |
Overall Confidence: 35%