Pten Deletion Promotes Regrowth of Corticospinal Tract Axons 1 Year after Spinal Cord Injury

Chronic spinal cord injury (SCI) is a formidable hurdle that prevents a large number of injured axons from crossing the lesion, particularly the corticospinal tract (CST). This study shows that Pten deletion in the adult mouse cortex enhances compensatory sprouting of uninjured CST axons. Furthermore, forced upregulation of mammalian target of rapamycin (mTOR) initiated either 1 month or 1 year after injury promoted regeneration of CST axons. Our results indicate that both developmental and injury-induced mTOR downregulation in corticospinal motor neurons can be reversed in adults. Modulating neuronal mTOR activity is a potential strategy for axon regeneration after chronic SCI. SIGNIFICANCE STATEMENT As one of the long descending tracts controlling voluntary movement, the corticospinal tract (CST) plays an important role for functional recovery after spinal cord injury. The regeneration of CST has been a major challenge in the field, especially after chronic injuries. Here we developed a strategy to modulate Pten/mammalian target of rapamycin signaling in adult corticospinal motor neurons in the postinjury paradigm. It not only promoted the sprouting of uninjured CST axons, but also enabled the regeneration of injured axons past the lesion in a mouse model of spinal cord injury, even when treatment was delayed up to 1 year after the original injury. The results considerably extend the window of opportunity for regenerating CST axons severed in spinal cord injuries.