Active and passive transport of substances between the microcirculation in the brain and the central nervous system is regulated by the Blood-Brain Barrier (BBB). This barrier allows for chronic and acute modulation of the CNS microenvironment, and protects the brain from potentially noxious compounds carried in the circulatory system. In-vitro modeling of the BBB has become the target of much research over the past decade, as there are many unanswered questions regarding modulations in the permeability of this barrier. Additionally, the development of a practical and inexpensive model of the BBB would facilitate a much more efficient drug development process. The goal of this project is to investigate the formation of the BBB through assessment of tight junction formation and endothelial cell monolayer permeability. Accomplishment of this goal will include completion of the two primary aims of this thesis, which are 1) development of an immunohistochemical staining protocol for the labeling of tight junctional proteins, and 2) characterization of permeability across a porous membrane co-cultured with bovine aortic endothelial cells (BAECs) and C6 glioma cells. Both of these aims were met, as a reliable IF protocol for tight junctional staining was developed, and permeability values across a permeable membrane seeded with BAECs and C6s were collected. The completion of these aims has helped to accomplish the goal of investigating the formation of tight junctions in an in-vitro model of the BBB. The IF protocol that has been developed, along with the collected permeability data will aid the development of a more dynamic in-vitro model of the BBB to aid in research surrounding acute modulation of the BBB, along with facilitating a timelier drug development process.

Astrocytes comprise the most abundant cell population in human brain (1). First described by Virchow as being 'glue' of the brain (2), modern research has truly extended our knowledge and understanding regarding the vast array of roles these cells execute under normal physiological conditions. Examples include neurotransmitter reuptake at the synapse (3), the regulation of blood flow at capillaries to meet neuronal energy demand (4), and maintenance/repair of the blood-brain barrier (BBB) (5), which is comprised, in part, of tight junction proteins such zonula-occludens-1 (ZO1) (6) and Claudin-5 (7). Underlying the execution of these processes is the morphological and spatial arrangement of astrocytes between neurons and endothelial cells comprising blood vessels, where comprehensively speaking, these cells form what is known as the gliovascular unit (8). Astrocytes extend large processes called endfeet that intimately associate with and enwrap up to 99% of the cerebrovascular surface (9). Disruptions to this association can occur in the form of retracted endfeet, and this has been characterized in several disease states such as major depressive disorder (10-12), ischemia (13-15), and normal biological aging (16-18). Disruption can also take the form of cellular/protein aggregate intercalation, which our lab previously characterized in a human-derived glioma model (19) and vascular amyloidosis human Amyloid Precursor Protein J20 (hAPPJ20) animal model (20). In both models, focal astrocyte-vascular disruptions coincided with perturbations to astrocyte control of blood flow, with deficits in BBB integrity present in the glioma model as well. These findings lead to the preliminary work in this dissertation where we aimed to extend BBB findings in the glioma model to the hAPPJ20 vascular amyloidosis model. Immunohistochemical analysis in two-year old hAPPJ20 animal arterioles revealed that indeed in locations of vascular amyloid buildup and endfoot separation, there was a significant reduction in a tight junction protein critical for BBB maintenance, ZO1. This reduction in ZO1 expression was accompanied by extravasation of 70kDa FITC and the ~1kDa Cadaverine, suggesting that BBB integrity was compromised. These findings led to the objective of this dissertation, which was to determine if focal ablation of an astrocyte is sufficient to disrupt BBB integrity. By utilizing the in vivo 2Phatal single-cell apoptosis induction method (21), we found that 1) focal loss of astrocyte-vascular coverage does not result in barrier deficits, but rather induces a plasticity response whereby surrounding astrocytes extend processes to reinnervate vascular vacancies no longer occupied by previously ablated astrocytes. 2) Replacement astrocytes are capable of inducing vasocontractile responses in blood vessels, and that 3) aging significantly attenuates the kinetics of this process. We then tested the hypothesis that focal loss of astrocyte-vascular coverage leads to a gliovascular structural plasticity response, in part, through the phosphorylation of signal transducer and activator of transcription 3 (STAT3) by Janus Kinase 2 (JAK2). This dissertation found that 4), this was indeed the case, and finally, 5) we determined that gliovascular structural plasticity occurs after reperfusion post-focal photothrombotic stroke. Together, the work presented in this dissertation sheds light on a novel plasticity response whereby astrocytes maintain continual cerebrovascular coverage and therefore physiological control. Future studies should aim to determine if 1) astrocytes also replace the synaptic contacts with neighboring neurons once held by a previous astrocyte, and 2) what therapeutic opportunity gliovascular structural plasticity may present regarding BBB repair following stroke. / Doctor of Philosophy / Astrocytes are the most abundant cell type in the brain. Their anatomical relationship to neurons and endothelial cells allows them to execute many vital brain functions, and comprehensively speaking, these cells form what is known as the gliovascular unit. Important for maintaining the expression of proteins preventing vascular leakage in the brain are molecules released from astrocytes processes called endfeet. These endfeet intimately enwrap blood vessels, and disruptions to endfeet-vascular coverage often coincide with vascular leakage in the brain. This dissertation therefore aimed to determine if astrocyte-vascular coverage is necessary in preventing vascular leakage. State-of-the art imaging in live animals determined this not to be the case, and rather found that focal loss of astrocyte-vascular coverage induces a plasticity response wherein neighboring astrocytes extend new endfeet to reinnervate vascular vacancies. Furthermore, we found that the kinetics of endfoot replacement are significantly reduced in aging, and that the phosphorylation of signal transducer and activator of transcription 3 (STAT3) is a critical arbiter underlying this response. Finally, given that we found endfoot replacement to occur in locations of lost astrocyte-vascular contact following reperfusion post-focal photothrombotic stroke, these findings may have implications regarding repair of the blood-brain barrier following CNS insults such as stroke.

The immune response is a complex series of cell-mediated reactions by which an organism combats infection, responds to injury, external stresses, or disease. In both Drosophila melanogaster and vertebrates, aging is associated with progressive declines in physiological functions as well as susceptibility to stress and disease. Naturally, the immune activity is increased with age, yet the efficacy of this response is reduced with age. Conversely, when the immune activation is artificially-induced by Lipopolysaccharide, aging is accelerated. Like aging, neurodegeneration is also associated with increased immune activity. The Blood-Brain barrier (BBB) is a physical barrier with highly selective permeability that isolates the brain from the rest of the body. This barrier is essential for ion homeostasis, and exclusion or efflux of exogenous chemicals. The exclusion properties of the Dm BBB are facilitated by paracellular septate junctions of subperineural glia (SPG), which prevent diffusion into or out of the brain. Using the GAL/UAS system in Drosophila, we found that activation of a glial-specific immune response in either immunodeficiency (IMD) or Toll pathways led to reductions in lifespan and age-dependent negative geotaxis. These reductions were also correlated with an early sensitivity towards oxidative and thermal stresses. Furthermore, we found that a SPG-specific immune response of the Toll pathway or disruption of the paracellular BBB itself was sufficient to show the same reductions as pan-glial activation. In short, we found that flies with CNS-specific immune activation showed an inability to cope with long-term and acute forms of stress, and that SPG-specific Toll Activation was sufficient to show these effects. This implicates chronic immune response as a negative factor during aging, neurodegenerative disease, and brain homeostasis. / Thesis / Master of Science (MSc)

In addition to protecting the brain from circulating pathogens and neurotoxins, the blood-brain barrier (BBB) limits both the delivery of drugs to the brain and the migration of neurological disease biomarkers from the brain into the blood. Focused-ultrasound blood-brain barrier opening (FUS-BBBO) addresses both of these transport limitations by transiently and noninvasively opening the BBB. Although originally designed as a drug delivery method, FUS-BBBO has also been shown to be an effective neuroimmunotherapy and method of improving liquid biopsy specificity for neurological disease. Prior to the work presented herein, the mechanism of FUS-BBBO neuroimmunotherapy remained poorly characterized and FUS-BBBO liquid biopsy remained poorly optimized. Initially, we present the temporal response of brain macrophages to FUS-BBBO. Due totheir role as the main phagocyte in the brain and the well-documented association between their dysfunction and neurodegenerative disease progression, we hypothesized that FUS-BBBO affects brain macrophage population composition and phenotype. Utilizing temporal single-cell RNA sequencing, we establish that treatment remodels the immune landscape via a number of processes including microglia proliferation, disease-associated microglia population size increase, and central-nervous-system associated macrophage recruitment. To further elucidate the functional role of the brain macrophage response to FUS-BBBO, we find that their depletion is associated with significantly decelerated BBB restoration. Secondly, we compare FUS-BBBO with two other methods of focused ultrasound neuroimmunotherapy, focused ultrasound neuromodulation (FUS-N) and focused ultrasound with microbubbles without BBBO (FUS+MB). FUS-N utilizes FUS parameters that alter neuronal connectivity via a combination of mechanosensitive receptor interactions and transient hypothermia without the injection of microbubbles (MB). FUS+MB is the combination of MB and FUS below the pressure threshold for BBBO (FUS+MB). FUS+MB has been shown to trigger morphological activation of brain macrophages and has proven efficacious as a method of immunotherapy within the peripheral nervous system. Due to the findings of brain macrophage modulation in response to FUS-BBBO, we compare brain macrophage modulation between all three paradigms both in the presence and absence of Alzheimer’s Disease (AD) pathology. We identify FUS-BBBO as the paradigm which maximizes brain macrophage modulation including an increase in the population of neuroprotective, disease-associated microglia and direct correlation between FUS cavitation dose and brain macrophage phagocytosis. Next, we combine spatial and single-cell transcriptomics with immunohistochemical validation to characterize the effect of FUS-BBBO on brain macrophage distribution in both wild-type and Alzheimer’s disease animals. Given their relevance within neurodegeneration and perturbation response, we emphasize the distribution of three brain macrophage populations - disease- and interferon-associated microglia and central-nervous-system-associated macrophages. We find a genotype-specific redistribution of each population, with an overall trend towards increased interaction with the brain-cerebrospinal fluid barrier after FUS-BBBO, an effect that is found to be more pronounced in the presence of disease pathology. Finally, we investigate the role of extracellular vesicles (EVs) in both the mechanism ofFUS-BBBO neuroimmunotherapy and as a method of improving FUS-BBBO liquid biopsy. EVs are lipid vesicles that are responsible for the transport and exchange of diverse cargo between cells and have been reported to modulate the immune system. Isolation of EVs has emerged as a method of improving biomarker detection. Prior to this study, the effect of FUS-BBBO neuroimmunotherapy on EV concentration and content remained unexplored. We investigate the concentration and content of isolated EVs from the serum of mice and Alzheimer’s Disease patients prior to and after treatment with FUS-BBBO. We illustrate a 100% increase in EV concentration one hour after treatment in both mice and patients. Furthermore, we illustrate an increase in murine EV RNA that is associated with the previously reported neuroimmunotherapeutic responses to FUS-BBBO including synaptic remodeling and neurogenesis. Finally, we illustrate an increase in AD biomarker concentration within the patient EVs three days after treatment that is proportional to the volume of blood-brain barrier opening. Overall, we establish that FUS-BBBO drug-free neuroimmunotherapy triggers complex brain macrophage modulation in a manner incomparable by other FUS neuroimmunotherapy paradigms. Furthermore, we illustrate the effect of FUS-BBBO on EV concentration and content in both preclinical and clinical experiments, indicating the role of EVs in FUS-BBBO neuroimmunotherapy and their utility as a method of improving liquid biopsy specificity. The results presented herein support the potential of FUS-BBBO as both a method of neuroimmunotherapy and a method of amplifying liquid biopsy specificity in Alzheimer’s Disease.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental toxicants found in anthropogenic mixtures such as crude oil, air pollution, vehicle exhaust, and in some natural combustion reactions. Single PAHs such as benzo[a]pyrene (BaP) also impact fish behavior when animals are exposed in early life stages and for short periods of time. Aquatic animals such as fish may encounter BaP through road runoff and oil spills, but few studies have examined the impact of aqueous exposure on adult fish, and fewer have examined the resulting fitness-relevant behavioral consequences of BaP and PAH mixtures and their long-term persistence. This dissertation targets this gap in the literature by examining how aqueous exposure to BaP influences anxiety-like behavior, learning, and memory in adult zebrafish, and how parental exposure to the PAH mixture, crude oil, combined with hypoxia affects social and exploratory behavior in unexposed larval zebrafish. We found that learning and memory were not affected by 24 hour exposure to BaP, that anxiety-like behavior was minimally affected, and that locomotor parameters such as distance moved and times spent in darting and immobile states were significantly altered by exposure to BaP. Additionally, we found that parental exposure to crude oil and hypoxia decreased larval velocity. Additionally, we examined how crude oil, BaP, and the detergent COREXIT influence a monolayer of mouse and fish endothelial cells, as an in vitro blood-brain barrier (BBB) model. We found that exposure to BaP in particular caused significant damage to both fish and mammal in vitro BBB models, and damage to the BBB is one potential mechanism by which neural integrity and behavior may be influenced. Understanding how these toxicants influence fish brains and behavior will give insight into how fish populations explore and interact with their environment and with predators, and how these interactions persist even when toxicants are no longer present.

Since the discovery of quantum dots in the 1980s, there has been significant interest in their potential biomedical applications. Caffeine is known to readily be able to cross the blood brain barrier, a highly selective barrier in the cerebrovascular endothelium. Creating drug delivery systems that are able to cross the blood brain barrier while maintaining its integrity are also in need. Experiments were conducted to determine if caffeine is able to successfully adsorb on the surface of synthesized manganese (Mn2+) doped zinc sulfide quantum dots. Caffeine adsorption on the surface of quantum dots is hypothesized to enhance uptake by cells and facilitate the delivery of small nanoparticle cargos. In this study, quantum dots were synthesized with and without the addition of caffeine and the nanoparticles were characterized by infrared spectroscopy (FTIR) in order to determine successful binding.

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