Emerging evidence suggests that
tissue plasminogen activator (tPA), currently the only FDA-approved medication for
ischemic stroke, exerts important biological actions on the CNS besides its well-known thrombolytic effect. In this study, we investigated the role of tPA on primary neurons in culture and on brain recovery and plasticity after
ischemic stroke in mice. Treatment with recombinant tPA stimulated axonal growth in culture, an effect independent of its
protease activity and achieved through
epidermal growth factor receptor (EGFR) signaling. After permanent focal
cerebral ischemia, tPA knockout mice developed more severe sensorimotor and cognitive deficits and greater axonal and myelin injury than wild-type mice, suggesting that endogenously expressed tPA promotes long-term neurological recovery after
stroke. In tPA knockout mice,
intranasal administration of recombinant tPA
protein 6 hours poststroke and 7 more times at 2 d intervals mitigated white matter injury, improved axonal conduction, and enhanced neurological recovery. Consistent with the proaxonal growth effects observed in vitro, exogenous tPA delivery increased poststroke axonal sprouting of corticobulbar and corticospinal tracts, which might have contributed to restoration of neurological functions. Notably, recombinant mutant tPA-S478A lacking
protease activity (but retaining the
EGF-like domain) was as effective as wild-type tPA in rescuing neurological functions in tPA knockout
stroke mice. These findings demonstrate that tPA improves long-term functional outcomes in a clinically relevant
stroke model, likely by promoting brain plasticity through EGFR signaling. Therefore, treatment with the
protease-dead recombinant tPA-S478A holds particular promise as a neurorestorative
therapy, as the risk for triggering
intracranial hemorrhage is eliminated and tPA-S478A can be delivered intranasally hours after
stroke.