PTEN deletion in spinal pathways via retrograde transduction with AAV-rg enhances forelimb motor recovery after cervical spinal cord injury; sex differences and late-onset pathophysiologies

Abstract

Spinal cord injuries (SCI) cause severe and long-lasting functional impairments due to compromised motor function and sensory signals. Regeneration of the damaged spinal cord is not possible due to intrinsic growth limitations of adult neurons and extrinsic inhibitory factors, especially at the injury site. Deletion of the phosphatase and tensin homolog (PTEN) can enable regeneration of central nervous system axons. AAV-retro is a retrogradely transported AAV variant that can deliver gene modifying cargos to the cells of origin of multiple pathways. In this study, we used AAV-retro to delete PTEN in multiple pathways after cervical SCI to promote regeneration of descending tracts and recovery of motor function. We injected different titers of AAV-retro/Cre into the cervical spinal cord at C5 in PTENf/f;RosatdTomatomice and control RosatdTomatomice at the time of a C5 dorsal hemisection injury. Our results revealed that PTENf/f;RosatdTomatomice injected with high and mid AAV-retro/Cre doses exhibited transient improvements in forelimb gripping ability in comparison to controls. There were major sex differences, with male mice exhibiting greater recovery than females. The values for male mice largely account for the overall differences between PTEN-deleted and controls. However, some PTEN-deleted mice began to exhibit pathophysiologies involving excessive scratching and hindlimb dystonia with persistent extension, which increased over time. Overall, although intra-spinal injections of AAV-retro/Cre in PTENf/f;RosatdTomatomice can lead to initial improvements in forelimb motor recovery after SCI, there are late-developing functional abnormalities with the experimental conditions used here. The mechanisms underlying these late-developing pathophysiologies remain to be defined.