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Intraneural AAV Gene Therapy Enables Focal Denervation and Functional Relief of Spasticity
Zachary Zamore
*, Jeffrey Khong, Kitae E. Park, Jared Zhang, Rachana Suresh, Sami Tuffaha
Department of Plastic and Reconstructive Surgery, Johns Hopkins University School of Medicine, Baltimore, MD
Introduction:Spasticity is a debilitating condition with limited treatment options. We hypothesized that intraneural delivery of a neuron-specific AAV vector encoding cleaved caspase-3 could induce targeted neuronal apoptosis, enabling selective denervation and functional relief of spasticity.
Methods:A recombinant AAV vector expressing cleaved caspase-3 under the neuron-specific hSyn1 promoter was injected intraneurally into the right sciatic nerve of C57BL/6J mice. Three days later, focal spasticity was induced via intramuscular injection of 0.007 ng/g tetanospasmin into the right gastrocnemius muscle, a model shown to cause transient ipsilateral plantarflexion lasting ~2 weeks. This timeline ensured full expression of the transgene prior to peak spasticity onset.
Mice were evaluated using CatWalk XT 9.1 for dynamic gait parameters every three days post-injection. The ratio of stand time between right and left hindlimbs was used to quantify asymmetric gait.
Results:Nine days following injection of the experimental vector into the sciatic nerve, cleaved caspase-3 expression was observed in numerous L3 DRG cell bodies, confirming successful transduction (Figure 1A). Three weeks after sciatic nerve injection, CD68+ macrophage infiltration was significantly increased in the ipsilateral sciatic nerve (p < 0.05), consistent with Wallerian degeneration (Figure 1B)
Animals injected with the caspase-expressing vector demonstrated significant attenuation of tetanus-induced gait dysfunction. At days 5 and 8 post-tetanus injection, experimental mice showed improved right-to-left hindlimb weight-bearing ratios compared to controls (p = 0.05), suggesting effective reduction in focal spasticity.
Conclusion:Intraneural AAV delivery enables selective transduction and apoptosis of sensory neurons, reducing focal spasticity in a mouse model by removing the sensory arm of the stretch reflex. This represents a novel, targeted therapeutic strategy for localized spasticity, with potential applications in neuromuscular disorders where focal denervation is desired.
