Alpha 9 integrin expression enables reconstruction of the spinal cord sensory pathway

Full recovery from spinal cord injury can only occur if the axon pathways connecting the brain and spinal cord regenerate and restore motor and sensory connections. Neither sensory nor motor axons can regenerate spontaneously in the spinal cord in mammals. This failure is partly due to the lack of suitable adhesion molecules on the sensory axons that allows them to interact with the environment of the damaged spinal cord. In this rat study, an integrin adhesion molecule along with its activator was expressed in sensory neurons using an adeno-associated viral (AAV) vector. Expression of these adhesion molecules allowed sensory axons to regenerate through the spinal cord injury and all the way back to the brainstem, restoring the sensory pathway. Treated animals regained touch sensation and sensory behaviours. The integrin ligands in the injured spinal cord are tenascin-C and osteopontin, but adult PNS and CNS neurons lack receptors to them. Sensory neurons were transduced with α9 integrin, which combines with endogenous β1 as α9β1 (which is a tenascin/osteopontin receptor) together with the integrin activator kindlin-1. Regeneration from sensory neurons transduced with α9integrin and kindlin-1 was examined after C4 and after T10 dorsal column lesions with C6,7 and L4.5 sensory ganglia injected with AAV1 vectors. In animals treated with α9 integrin and kindlin-1, sensory axons regenerated through tenascin-C-expressing connective tissue strands and bridges across the lesion and then re-entered the CNS tissue. Many axons regenerated rostrally to the level of the medulla. Regenerated axons were particularly visible at the border between white and grey matter in the dorsal cord. Stimulation of the median/sciatic nerve caused many neurons rostral to the injury to activate and express cFos. VGLUT1/2 staining indicated newly formed functional synapses above the lesion. Behavioural recovery was seen in heat, mechanical sensation and tape removal tests. Many axons regenerated from the thoracic lesions to the brainstem, a distance of 4-5 cm, equivalent to the length of 1 or 2 spinal segments in humans.