Systemic administration of PEP-1–SOD1 fusion protein improves functional recovery by inhibition of neuronal cell death after spinal cord injury

Spinal cord injury (SCI) produces excessive levels of reactive oxygen species (ROS) that induce apoptosis of neurons. Cu,Zn-superoxide dismutase (SOD1) is a key antioxidant enzyme that detoxifies intracellular ROS, thereby protecting cells from oxidative damage. PEP-1 is a peptide carrier capable of delivering full-length native peptides or proteins into cells. In the study described here, we fused a human SOD1 gene with PEP-1 in a bacterial expression vector to produce a genetic in-frame PEP-1–SOD1 fusion protein; we then investigated the neuroprotective effect of the fusion protein after SCI. The expressed and purified PEP-1–SOD1 was efficiently delivered into cultured cells and spinal cords in vivo, and the delivered fusion protein was biologically active. Systemic administration of PEP-1–SOD1 significantly decreased levels of ROS and protein carbonylation and nitration in spinal motor neurons after injury. PEP-1–SOD1 treatment also significantly inhibited mitochondrial cytochrome c release and activation of caspase-9 and caspase-3 in spinal cords after injury. Furthermore, PEP-1–SOD1 treatment significantly reduced ROS-induced apoptosis of motor neurons and improved functional recovery after SCI. These results suggest that PEP-1–SOD1 may provide a novel strategy for the therapeutic delivery of antioxidant enzymes that protect neurons from ROS after SCI.