Neuronal Cell-Cycle Re-entry Defines Divergent Outcomes Through Replication-Dependent DNA Damage in ALS

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Cell-cycle dysregulation is a common factor in neurodegenerative diseases (NDs) like ALS, Alzheimer's, and Parkinson's.
• Aberrant cell-cycle signaling in post-mitotic neurons precedes degeneration, but triggers and consequences are unclear.
• Nucleocytoplasmic transport (NCT) dysfunction, common in ALS, may drive maladaptive cell-cycle activation by altering protein distribution.

Purpose of the Study:

• To investigate the role of cell-cycle activation in ALS subtypes and outcomes.
• To determine if NCT disruption mechanistically drives aberrant cell-cycle activation in motor neurons.
• To identify therapeutic targets for neuroprotection by understanding the cell-cycle's role in degeneration.

Main Methods:

• Analysis of the AnswerALS transcriptomic cohort to identify patient clusters based on cell-cycle gene expression.
• Pharmacological inhibition of importin-β in iPSC-derived human spinal motor neurons to model NCT disruption.
• Proteomic analysis to assess protein mislocalization and cell-cycle activity, including DNA replication initiation.
• Assessment of neuroprotection conferred by selective inhibition of CDK4/6 activity.

Main Results:

• A patient cluster with high cyclin B and D expression showed better functional trajectories compared to those with lower expression.
• Pharmacological NCT disruption induced TDP-43 pathology and cell-cycle activation preceding motor neuron death.
• DNA-replication initiation was identified as a key pathological event driving degeneration.
• Selective inhibition of CDK4/6 activity demonstrated neuroprotective effects.

Conclusions:

• Impaired nuclear import initiates maladaptive cell-cycle reactivation in neurons, contributing to neurodegeneration in ALS.
• Cell-cycle activation patterns correlate with disease subtypes and progression in ALS patients.
• Targeting specific cell-cycle phases, like G1/S with CDK4/6 inhibitors, offers a potential therapeutic strategy for neuroprotection.