PTEN knockout using retrogradely transported AAVs transiently restores locomotor abilities in both acute and chronic spinal cord injury

Exp Neurol, 2023 · DOI: 10.1016/j.expneurol.2023.114502 · Published: October 1, 2023

Spinal Cord Injury Regenerative Medicine Genetics

Simple Explanation

A primary cause for the loss of function experienced after a spinal cord injury (SCI) is due to the disruption of communication to and from the brain. Our project made use of a specific form of a viral vector that is commonly used for gene therapies in both humans and animals. We delivered our gene therapy in both acute and chronic SCI conditions and observed that several mice with a near-complete loss of function regained weight supporting abilities regardless of when the AAV was delivered.

Study Duration

9 weeks (acute), 9 months (chronic)

Participants

C57BL/6 PTENFloxΔ/Δ mice (male and female)

Evidence Level

Not specified

Key Findings

1
PTEN-KO using AAVrg’s improves locomotor outcomes in both acute and chronic SCI conditions, however, the effects are severity dependent.
2
PTEN-KO using AAVrg’s does increase axon growth into the lesions of acutely injured mice, demonstrating a growth effect on axons.
3
However, driving the RFP fluorescent reporter gene under the hSyn1 promoter revealed an unexpected interaction between the viral gene expression and PTEN-KO that diminished the RFP reporter.

Research Summary

First, we have replicated that delivery of AAVrg’s can exert a wide genetic influence throughout the neuroaxis when applied rostral to an SCI lesion but that transduction efficacy within the caudal Raphe nucleus and Locus Coeruleus remain limited. Even in severe and near-complete crush lesions, PTEN-KO using AAVrg’s improves locomotor outcomes in both acute and chronic SCI conditions, however, the effects are severity dependent. Specifically, we detected a loss of Fluorogold labeling within the motor cortex, an absence of normal CST labeling within the spinal cords of PTEN-KO mice, and a loss of β3-Tub labeling above the lesion within the spinal cord.

Practical Implications

AAVrg Delivery

Retrogradely transported viral particles to target a larger breadth of spinal tracts via injection directly into the spinal cord confers major advantages to both study-specific spinal tracts of interest, but also to target neuronal populations that are otherwise difficult to affect.

hSyn1 Promoter Silencing

Silencing of the hSyn1 promoter after PTEN-KO remains speculative, the implications of such findings can be extrapolated to the larger concerns with gene-therapy approaches. Future work should identify if this same interaction exists using other neuronal specific promoters.

Long-term PTEN-KO Toxicity

While using AAVrg’s to treat SCI holds significant translational promise, more work is needed to refine the approaches and tease out potential complications associated with this methodology.

Study Limitations

1
PTEN-KO may silence the hSyn1 promoter.
2
Sustaining long-term growth via PTEN-KO may potentially effect neuronal health and viability of specific populations of neurons.
3
Diminished locomotor ability is likely unrelated to neuron viability within the motor cortex.

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