Objectives: Stroke is the leading cause of long term neurological disability with limited therapeutic options. Human recombinant tissue plasminogen activator (tPA) is currently the only FDA approved drug for the thrombolytic treatment of ischemic stroke. Emerging evidence suggests that the effects of tPA in ischemic brain may extend beyond its thrombolytic activity. In this study, we investigated the role of tPA in long term stroke recovery.
Methods: Cortical infarct was induced by distal middle cerebral artery occlusion (dMCAO) in tPA knockout (KO) and wild type (WT) mice. Sensorimotor functions were evaluated at 3-35 days after dMCAO. White matter integrity was assessed by luxol fast blue staining, immunohistochemistry for SMI-32, and diffusion tensor imaging (DTI). The neuronal tracer biotinylated dextran amine (BDA) was used to label the corticorubral tract and the corticospinal tract. For rescue experiment, tPA (2mg/kg) was delivered intranasally to tPA KO mice once a day for 14 days starting 6h after dMCAO.
Results: Infarct volume was comparable between tPA KO and WT mice after dMCAO. Sensorimotor deficits after dMCAO were exacerbated in tPA KO mice than WT mice. tPA KO mice also showed more severe demyelination in post-stroke white matter and reduced axonal sprouting at 35 days after dMCAO compared to WT mice. DTI studies revealed deteriorated white matter integrity in tPA KO mice, as manifested by decreased fractional anisotropy. Intranasal delivery of tPA after dMCAO rescued the neurological phenotype shown by tPA KO mice.
Conclusion: Endogenous tPA promotes white matter integrity and is essential for functional recovery after ischemic stroke. tPA may be a novel neurorestorative therapy for stroke recovery.