Recovery of Motor Function Impaired by Cortical Injury: An Exploratory Comparison of the Influences of Four Different Post-injury Treatments on Processes Affecting Neuroplasticity

Boston University Medical Campus, Boston MA

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Abstract

ABSTRACT: Injury to the brain due to stroke or trauma is a leading cause of disability. While research has focused on reducing stroke related brain damage by neuroprotection such as immediate treatment with tissue plasminogen activator (tPA), the benefits are limited. As an alternative, neurorestorative therapies facilitate plasticity and recovery of function but have been less extensively investigated. Over the past 5 years with NIH and industry funding we have used our monkey model of cortical injury that impairs fine motor function of one hand to test four neurorestorative treatments. We found that all four significantly enhance recovery of function following injury. These were: 1) Cell Therapy with human umbilical tissue-derived cells (hUTC) which do not differentiate into new neurons but instead release a variety of growth factors that stimulate endogenous plasticity; 2) Treatment using exosomes derived from bone marrow mesenchymal stem cells that provide an enriched and modifiable source of the same growth factors as the hUTCs; 3) Purine Nucleoside Treatment with inosine which stimulates axonal growth in culture and promotes corticospinal tract sprouting; 4) Treatment with Glial Growth Factor 2 (GGF2), a neuregulin which increases axonal sprouting and synaptic density and may stimulate myelination. While untreated monkeys developed compensatory movements similar to that observed in human stroke patients, our treated monkeys returned to pre-injury levels of fine motor function. Interestingly, while each treatment resulted in a greater recovery than typically observed in other animal models of injury or stroke, the extent and timing of recovery differed across treatments suggesting different mechanisms. Pilot work suggests that recovery may be the result of reduction of post-injury inflammation and oxidative damage, thereby limiting the evolution of the lesion. Another process may be axonal and synaptic reorganization in surviving motor cortices or spinal cord. There is also evidence of remyelination and increased density of mature oligodendrocytes in peri-infarct regions of recovered subjects. Here we propose to investigate these issues using a unique resource of archived cryopreserved tissue sections from cortex and spinal cord of 29 monkeys that had cortical damage followed 24 hours later by one of the treatments or vehicle control. In cortex and spinal cord gray and white matter we will use c-fos immunohistochemistry to identify in treated subjects compared to controls cortical areas differentially activated during a final behavioral testing session of the impaired hand. Second, in adjacent sections we will quantify markers of axonal and synaptic plasticity (GAP43 & synaptophysin). Third, we will also quantify markers of inflammation and oxidative damage (4HNE, 8OHG) as well as activated microglia and astrocytes. Fourth, we will quantify myelination and both proliferating oligodendroglia precursor cells and myelinating oligodendroglia. This offers a unique opportunity to conduct a comprehensive investigation of the loci in cortex and spinal cord that are associated with recovery and to identify the underlying neurobiological processes modulated by 4 distinct neurorestorative treatments.