Abstract
Traumatic brain injury (TBI) represents a serious public health problem as there are no clinically-available treatments to mitigate the functional complications and societal burdens endured by patients and their caregivers. In addition to the primary mechanical insult, deleterious secondary injuries contribute to the progressive atrophy and long-term histopathological changes that impair functional and cognitive outcomes. The studies carried out in this dissertation project assessed two treatment strategies designed to engage and enhance endogenous neurorestorative responses in the injured brain. We postulated that the protection of vulnerable cortical neurons and perilesional parenchyma together with the promotion of endogenous hippocampal neurogenesis would confer histological and behavioral improvement after brain injury. The first series of experiments evaluated the effects of transplanting syngeneic neural progenitor cells (NPCs) with or without genetic modification to secrete a synthetic multineurotrophin (MNTS1) with multifunctional, multitargeting, neurotrophic capacity. NPCs were obtained from Sprague Dawley fetuses at embryonic stage E15 and transduced with either MNTS1 and GFP constructs (MNTS1-NPCs) or with GFP and blue fluorescent protein (BFP) constructs (control GFP-NPCs). Adult Sprague Dawley rats received a moderate fluid percussion-induced insult over the right parietal cortex or underwent sham surgery. Animals were transplanted pericontusionally 1 week later with either control GFP-NPCs, MNTS1-NPCs, or injected with saline (vehicle). Five weeks after surgery, groups were evaluated for hippocampal-dependent spatial memory and then sacrificed for immunohistochemical analyses. Six weeks after TBI (5 weeks after transplantation), there was significant survival and neuronal differentiation of MNTS1-transduced NPCs, as well as injury-activated targeted migration towards contused brain regions. NPCs displayed long processes with spine-like formations that extended into many cortical and subcortical brain structures, including the hippocampus and contralateral hemisphere. All transplanted NPCs, irrespective of transduction profile, conferred significant preservation of pericontusional host tissues and enhanced hippocampal neurogenesis in the posttraumatic brain. Furthermore, NPC transplantation significantly improved spatial memory capacity on the hippocampal-dependent Morris water maze (MWM) cognitive task. Transplant recipients exhibited escape latencies approximately half that of injured vehicle controls, performing on par with sham uninjured animals. The second set of experiments was conducted to assess histological and functional outcomes with administration of a recently-discovered proneurogenic compound, the highly-active aminopropyl carbazole, P7C3-A20. Sprague Dawley rats were subjected to moderate fluid percussion brain injury or sham surgery. Treatment with 10 mg/kg of P7C3-A20 or vehicle was initiated intraperitoneally 30 min post surgery, and twice per day everyday thereafter for 7 days. Administration of P7C3-A20 significantly reduced overall contusion volume, preserved vulnerable NeuN-positive pericontusional cortical neurons, and improved sensorimotor function 1 week after trauma. P7C3-A20 treatment also significantly increased both 5-bromo-2'-deoxyuridine (BrdU)-positive and doublecortin (DCX)-positive cells within the subgranular zone of the ipsilateral hippocampus 1 week after TBI. Five weeks after TBI, animals treated with P7C3-A20 showed significantly increased BrdU/neuronal nuclei (NeuN) double-labeled neurons in the ipsilateral dentate gyrus and improved cognitive function in the MWM compared to TBI-vehicle animals. These results suggest that P7C3-A20 is neuroprotective and promotes endogenous reparative strategies, such as hippocampal neurogenesis, after brain trauma. The chemical scaffold represented by P7C3-A20 may provide a basis for developing new pharmacological agents for protecting patients against the early and chronic consequences of TBI. Neural progenitor cell transplantation and treatment with a highly-active proneurogenic compound both resulted in significant neuroprotection, enhanced hippocampal neurogenesis, and preservation of cognitive capacity in an experimental model of TBI. Collectively, the experiments carried out in this dissertation project suggest that exogenous interventions that target and strengthen endogenous reparative processes, such as NPC-mediated trophic support and enhanced hippocampal neurogenesis, may be effective at restoring and protecting histological and functional outcomes after traumatic brain injury.