abstract: Of the 2.87 million traumatic brain injuries (TBI) sustained yearly in the United States, 75% are diffuse injuries. A single TBI can have acute and chronic influences on the neuroendocrine system leading to hypothalamic-pituitary-adrenal axis (HPA) dysregulation and increased affective disorders. Preliminary data indicate TBI causes neuroinflammation in the hippocampus, likely due to axonal damage, and in the paraventricular nucleus of the hypothalamus (PVN), where no axonal damage is apparent. Mechanisms regulating neuroinflammation in the PVN are unknown. Furthermore, chronic stress causes HPA dysregulation and glucocorticoid receptor (GR)-mediated neuroinflammation in the PVN. The goal of this project was to evaluate neuroinflammation in the HPA axis and determine if GR levels change at 7 days post-injury (DPI). Adult male and female Sprague Dawley rats were subjected to midline fluid percussion injury. At 7 DPI, half of each brain was post-fixed for immunohistochemistry (IBA-1) and half biopsied for gene/protein analysis. IBA-1 staining was analyzed for microglia activation via skeleton analysis in the hypothalamus and hippocampus. Extracted RNA and protein were used to quantify mRNA expression and protein levels for GRs. Data indicate increased microglia cell number and decreased endpoints/cell and process length in the PVN of males, but not females. In the dentate gyrus, both males and females have an increased microglia cell number after TBI, but there is also an interaction between sex and injury in microglia presentation, where males exhibit a more robust effect than females. Both sexes have significant decreases of endpoints/cell and process length. In both regions, GR protein levels decreased for injured males, but in the hippocampus, GR levels increased for injured females. Data indicate that diffuse TBI causes alterations in microglia morphology and GR levels in the hypothalamus and hippocampus at 7 DPI, providing a potential mechanism for HPA axis dysregulation at a sub-acute time point. / Dissertation/Thesis / Masters Thesis Biology 2019

abstract: Traumatic brain injury (TBI) is a leading cause of disability worldwide with 1.7 million TBIs reported annually in the United States. Broadly, TBI can be classified into focal injury, associated with cerebral contusion, and diffuse injury, a widespread injury pathology. TBI results in a host of pathological alterations and may lead to a transient blood-brain-barrier (BBB) breakdown. Although the BBB dysfunction after TBI may provide a window for therapeutic delivery, the current drug delivery approaches remains largely inefficient due to rapid clearance, inactivation and degradation. One potential strategy to address the current therapeutic limitations is to employ nanoparticle (NP)-based technology to archive greater efficacy and reduced clearance compared to standard drug administration. However, NP application for TBI is challenging not only due to the transient temporal resolution of the BBB breakdown, but also due to the heterogeneous (focal/diffuse) aspect of the disease itself. Furthermore, recent literature suggests sex of the animal influences neuroinflammation/outcome after TBI; yet, the influence of sex on BBB integrity following TBI and subsequent NP delivery has not been previously investigated. The overarching hypothesis for this thesis is that TBI-induced compromised BBB and leaky vasculature will enable delivery of systemically injected NPs to the injury penumbra. This study specifically explored the feasibility and the temporal accumulation of NPs in preclinical mouse models of focal and diffuse TBI. Key findings from these studies include the following. (1) After focal TBI, NPs ranging from 20-500nm exhibited peak accumulation within the injury penumbra acutely (1h) post-injury. (2) A smaller delayed peak of NP accumulation (40nm) was observed sub-acutely (3d) after focal brain injury. (3) Mild diffuse TBI simulated with a mild closed head injury model did not display any measurable NP accumulation after 1h post-injury. (4) In contrast, a moderate diffuse model (fluid percussion injury) demonstrated peak accumulation at 3h post-injury with up to 500 nm size NPs accumulating in cortical tissue. (5) Robust NP accumulation (40nm) was found in female mice compared to the males at 24h and 3d following focal brain injury. Taken together, these results demonstrate the potential for NP delivery at acute and sub-acute time points after TBI by exploiting the compromised BBB. Results also reveal a potential sex dependent component of BBB disruption leading to altered NP accumulation. The applications of this research are far-reaching ranging from theranostic delivery to personalized NP delivery for effective therapeutic outcome. / Dissertation/Thesis / Doctoral Dissertation Biomedical Engineering 2018

Un dysfonctionnement du métabolisme cérébral est observé au décours d'un traumatisme crânien (TC). L’œdème cérébral et l’hypoxie cérébrale post-traumatiques sont des acteurs principaux de l’apparition des lésions ischémiques secondaires responsables en partie de la défaillance énergétique. Cette hypoxie tissulaire résulte de troubles macrocirculatoires, de troubles de la microcirculation et/ou de troubles de la diffusion de l’oxygène des capillaires sanguins aux tissus. La baisse de la consommation en oxygène est également liée à une dysfonction mitochondriale post traumatique de la chaine respiratoire. Ces phénomènes ischémiques ou hypoxiques aboutissent ainsi à une élévation de lactate endogène en condition anaérobie. Cependant, l'élévation de lactate endogène post traumatique est liée majoritairement à une crise métabolique conduisant à une hyperglycolyse en dehors de tout phénomène hypoxique ou ischémique. L'objectif de notre étude était donc d’étudier l'œdème cérébral, l'oxygénation cérébrale, la défaillance mitochondriale post traumatique et le métabolisme cérébral dans un modèle expérimental de traumatisme crânien diffus par impact accélération chez l'animal. Nous avons étudié les effets de différents neuroprotecteurs sur le métabolisme cérébral à l'aide d'un monitorage multimodal. Les effets de la rhEpo (5000UI/Kg), du mannitol (1g/kg) et du lactate de sodium molaire (1.5 ml/Kg soit 3mOsm/kg) ont été étudiés sur l'œdème cérébral (IRM, microscopie électronique), sur l'hypoxie cérébrale tissulaire (IRM BOLD, mesure de la pression tissulaire en O2, saturation veineuse en O2 du sinus longitudinal supérieur), sur le métabolisme cérébral (spectroRMN) et sur la mitochondrie (analyse de la capacité de rétention calcique, de la chaine respiratoire, microscopie électronique et mesure du calcium intramitochondrial) chez des rats wistar mâles. Notre hypothèse était que l’injection de différents neuroprotecteurs permettrait d’améliorer le métabolisme cérébral post traumatique par des effets bénéfiques sur l’hémodynamique cérébrale et l'œdème cérébral, sur l'hypoxie tissulaire ou sur la dysfonction mitochondriale post TC. Nos résultats ont démontré que la rhEpo avait un effet bénéfique sur l'hypoxie cérébrale post traumatique par le biais d'une diminution de l'œdème cérébral péri capillaire en phase aigue associée à une diminution de la dysfonction mitochondriale proapoptotique. Le mannitol améliore l'hypoxie cérébrale post traumatique en jouant sur la microvascularisation cérébrale perturbée par l'œdème astrocytaire péri capillaire. Enfin, le lactate de sodium molaire avait des effets bénéfiques anti œdémateux et sur la dysfonction mitochondriale post TC améliorant ainsi la crise métabolique post traumatique. Ces résultats permettent d'améliorer la compréhension de la physiopathologie des lésions survenant au décours du traumatisme crânien ainsi que les mécanismes d'action de différentes molécules neuroprotectrices. / Cerebral metabolism is impaired after a Traumatic Brain Injury (TBI). Post traumatic cerebral edema and hypoxia are mainly responsible of the development of secondary ischemic lesions after TBI leading to metabolic impairment. Tissular hypoxia can result from disorders in macro and microcirculation and/or disturbance in the diffusion of oxygen from the blood capillaries to tissue. The decrease in oxygen consumption observed after brain injury is also related to a post traumatic dysfunction of the mitochondrial respiratory chain. These ischemic or hypoxic phenomena may be responsible for metabolic disorders leading to elevated level of endogenous lactate under anaerobic conditions. However, the elevation of endogenous lactate is mainly the consequence of a metabolic crisis that led to a state of hyperglycolysis without cerebral hypoxia or ischemia after TBI. The aim of our study was to investigate cerebral edema, cerebral oxygenation, mitochondrial and metabolic impairment post TBI in an experimental model of impact acceleration diffuse brain injury in rats. We also analyzed the effects of various neuroprotective agents on cerebral metabolism using a multimodal monitoring. The effects of rhEpo (5000UI/Kg), mannitol (1g/Kg) and of molar sodium lactate (1.5 ml/Kg or 3mOsm/kg) were investigated on brain edema (MRI, electronic microscopy), on brain tissue hypoxia (BOLD MRI, measurement of the tissular pressure of O2, venous O2 saturation of the upper longitudinal sinus), on brain metabolism (Magnetic Resonance Spectroscopy) and on mitochondria (study of the calcium retention capacity, of the respiratory chain, morphological analysis with electronic microscopy and measurement of intramitochondrial calcium) in male wistar rats. We hypothesized that the injection of various neuroprotective agents would improve posttraumatic cerebral metabolism by restoring a better cerebral hemodynamic status, by improving cerebral edema, tissular oxygenation and/or mitochondrial function. On the early phase of TBI, we demonstrated that rhEpo had a beneficial effect on post traumatic cerebral hypoxia by decreasing post-traumatic cerebral capillaries collapse due to astrocytic end-foot swelling. This effect was associated with an improvement in cellular apoptosis induced by mitochondrial pathways. Mannitol improved brain hypoxia by decreasing peri vascular astrocytic edema. Sodium lactate had benefic effects on cerebral hypoxia by decreasing cerebral edema and improved mitochondrial and metabolic impairments after TBI. These results help understanding physiopathological events after TBI and the various effects of neuroprotective agents that can be used in future clinical research.