Knockdown of Fidgetin Improves Regeneration of Injured Axons by a Microtubule-Based Mechanism

The Journal of Neuroscience, 2019 · DOI: https://doi.org/10.1523/JNEUROSCI.1888-18.2018 · Published: March 13, 2019

Regenerative Medicine Physiology Neurology

Simple Explanation

Fidgetin is a protein that cuts microtubules, which are important for axon growth. This study explores whether reducing fidgetin levels can help injured axons regenerate. The researchers used a cell culture system that mimics the inhibitory environment of a glial scar after CNS injury and an in vivo assay on rats which involves a crush injury to the central branch of the axons of the DRG. The results showed that reducing fidgetin improved axon regeneration in both the cell culture and animal models.

Study Duration

30 days in vivo

Participants

Adult rats (in vivo and in vitro DRG cultures)

Evidence Level

Level II: Experimental study using cell culture and in vivo rat model

Key Findings

1
Knockdown of fidgetin resulted in faster-growing axons on both laminin and aggrecan and enhanced crossing of axons from laminin onto aggrecan in vitro.
2
Depleting fidgetin improves axonal regeneration in vivo after a dorsal root crush in adult female rats; DRG neurons in which fidgetin was knocked down displayed enhanced regeneration of axons across the dorsal root entry zone into the spinal cord.
3
Fidgetin knockdown improved the ability of axons to grow into the aggrecan from a favorable substrate and especially increased the ability of axons to grow from within the aggrecan against the gradient to enter the favorable substrate.

Research Summary

This study establishes a workflow template from cell culture to animals in which microtubule-based treatments can be tested for their effectiveness in augmenting regeneration of injured axons relevant to spinal cord injury. The present work uses a viral transduction approach to knock down fidgetin from rat neurons, which coaxes nerve regeneration by elevating microtubule mass in their axons. Unlike previous strategies using microtubule-stabilizing drugs, fidgetin knockdown adds microtubule mass that is labile (rather than stable), thereby better recapitulating the growth status of a developing axon.

Practical Implications

Therapeutic Target

Fidgetin is identified as a novel therapeutic target to augment nerve regeneration.

Workflow Template

The study provides a workflow template for comparing microtubule-related targets in the future.

Alternative Approach

Fidgetin knockdown offers an alternative to microtubule-stabilizing drugs for promoting axon regeneration by adding labile microtubule mass.

Study Limitations

1
The knockdown alone, at least to the degree that our methods were able to achieve, did not result in obvious improvement in the animal voluntarily placing weight on its front right paw.
2
Cannot entirely dismiss the possibility of a contribution from the non-neuronal cells, which were greater in number on the aggrecan spots when fidgetin was reduced.
3
The GFP-labeled axons only represent 40% of the neurons labeled by our virus with detectable levels of GFP

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