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Alzheimer’s Disease (AD) is a progressive neurodegenerative disease that accounts for 60-70% of the 55 million worldwide dementia cases. The blood-brain barrier (BBB) acts as a mediator between the brain and cerebral vasculature, preventing the passage of deleterious substances, albeit significantly reducing drug delivery efficiency to the brain. The BBB is comprised of specialized cells that both maintain brain homeostasis and respond to pathological stress. Focused ultrasound-induced blood-brain barrier opening (FUS-BBBO) presents a noninvasive, transient, and targeted method to enhance drug delivery by locally increasing BBB permeability, in addition to modulating the neuroimmune landscape. This technique offers countless therapeutic opportunities for diseases of the brain, especially neurodegenerative disorders and AD. Previous studies have demonstrated effective pathological amelioration and cognitive improvement by applying FUS-BBBO in severely progressed murine models of AD. However, growing interest in clinical translation of FUS-BBBO and in alternative, early intervention therapeutic paradigms necessitates a more thorough characterization of the role of FUS-BBBO in AD therapeutics, particularly at early disease states. This thesis focuses on characterizing three key elements of FUS-BBBO treatment for applications to AD therapy. First, the physical effects of age and AD on the brain’s response to a single session of FUS-BBBO will be characterized. Next, the extent of cognitive and pathological improvement resulting from early intervention in male and female AD mice with repeated FUS-BBBO alone, then in combination with an amyloid-targeting therapeutic will be evaluated. Finally, the cell-specific response of astrocytes, oligodendrocytes, neurons and endothelial cells to FUS-BBBO will be characterized to elucidate the contribution of these cell types to previously observed cognitive and pathological improvements in male and female, young and aged, wild-type and AD mice. Broadly, the findings of the work described herein will elucidate the role of FUS-BBBO in AD therapeutics. By defining the most important considerations for applying FUS-BBBO in aged and AD populations, characterizing the expected cognitive and pathological outcomes from early FUS-BBBO intervention, and characterizing a time course of cell-specific responses to elucidate the mechanisms that underlie these observations, these aims collectively seek to improve our understanding and optimize our use of FUS-BBBO for AD therapeutics.

The placenta plays a vital role in a healthy pregnancy by supporting the intricacies of fetal development. Over 10% of pregnancies experience impaired placental function, resulting in the loss of critical neuroactive steroids the fetal brain cannot yet make, thus leaving them vulnerable to perinatal brain injury and abnormal neurodevelopment. However, this vulnerability is not always equal. Many neurodevelopmental disorders exhibit a sex bias in incidence and severity. I hypothesize that loss of placental support during pregnancy results in sex differences in both behavioral presentation as well as on the cellular and transcriptomic levels. Utilizing the akr1c14cyp19aKO (plKO) mouse model, which features placenta-specific allopregnanolone (ALLO) knockdown, I investigated the sex specific impact of placental hormones on cerebellar development. Here I show that placental ALLO is essential for cerebellar white matter development and inflammatory regulation via microglial function. Male mice without placental ALLO exhibit signs of placental inflammation, accelerated postnatal myelination, and defects in microglial phagocytosis of excess myelin. Alternatively, females seem to be more resilient with a progressive anti-inflammatory profile across development and reduced myelination. Additionally male plKO show autism-like behaviors such as deficits in social behavior and increased stereotyped behavior. The females do not exhibit this phenotype. My main goals were threefold; to investigate how male and female inflammatory profiles differ and where this difference originates, to investigate how this inflammation impacts microglia and thereby oligodendrocytes, and how I can alter microglial function in a way to improve plKO outcomes. Mechanistically, these changes appear to be in part due to baseline sex differences in response to inflammatory stimuli which prime microglia to differentially support the surrounding white matter. Together, this work supports a novel link between placental ALLO loss, microglial function, and sex specific presentation of neurodevelopmental disorders.

Oligodendrocytes derived in the laboratory from stem cells have been proposed as a treatment for acute and chronic injury to the central nervous system (CNS). Platelet-derived growth factor-receptor alpha (PDGFRÑ)w signaling is known to play an important role for regulation of oligodendrocyte progenitor cell numbers both during development and adulthood. Here, we analyze the effect of PDGFRÑ signaling on CNS stem cells derived from embryonic day 13.5 murine cortex and cultured in monolayer. Fetal and adult CNS stem cells express PDGFRÑ, and PDGF-AA treatment increases viability and proliferation of these cells. In the absence of insulin, this effect of PDGF-AA is very clear. Consistent with this result, PDGF-AA strongly stimulates glycolytic rate. PDGF-AA treatment rapidly induces morphological changes in the cells although the cells maintain expression of a wide range of precursor markers. We show that a brief exposure to PDGF-AA rapidly and efficiently induces oligodendrocytes from CNS stem cells. Our data suggest that phosphoinositide kinase-3 (PI3K)/Akt, mitogen-activated protein/extracellular signal-regulated kinase kinase/extracellular signal-related kinase (MEK/Erk), mammalian target of rapamycin (mTOR) regulate survival, proliferation, glycolytic rate, and oligodendrogliogenesis induced by PDGF-AA. By treating with PDGF-AA, progenitor cells directly from embryonic cortex can be expanded and differentiated into oligodendrocytes with high efficiency. Our results show that PDGF-AA promotes oligodendrocyte progenitor generation from CNS stem cells and supports their survival and proliferation. The derivation of oligodendrocytes demonstrated here may support the safe and effective use of stem cells in the development of new therapies targeting this cell type.

Glial cells represent the most abundant cell population in the central nervous system (CNS), and yet, have historically been thought of as merely support cells for neurons. Over the past few decades, however, the number of identified roles that glial cells play in the CNS has expanded at an exponential rate, revealing new and exciting functions in neuron-glial communication. At synapses, astrocytes are now recognized as part of a "tripartite" complex with pre- and postsynaptic structures and can modulate synaptic transmission and plasticity. Accumulating evidence has also revealed new roles for oligodendrocytes in regulating axon diameter and integrity, and ion channel clustering. Despite our knowledge of the physiological connections between neurons and glia, relatively little is known about the morphological interplay of these cells during development and in the mature brain. The results presented in this thesis reveal the extent and time-course of rapid remodelling of astrocytes and oligodendrocytes in close proximity to dendritic spines and axons respectively. These findings provide further evidence that glia play an important role in regulating the structural plasticity of the brain. The methodology developed also provides a powerful system for the study of neuron-glial structural dynamics and may contribute to the development of novel therapeutic strategies for diseases affecting the central nervous system.

Oligodendrocyte progenitors are highly sensitive to oxidative insults. Among the factors postulated to contribute to this susceptibility are high levels of intracellular iron and low antioxidant content. During ischemia, the neurotransmitter dopamine (DA) is released and may contribute to oxidative stress and oligodendrocyte injury in the hypomyelinating disorder, periventricular leucomalacia (PVL). In this thesis, I investigated the role of iron in DA-induced toxicity in primary cultures of oligodendrocyte progenitors, and assessed the contribution of the antioxidant defenses (glutathione (GSH), glutathione peroxidase (GPx) and superoxide dismutase (SOD)) and other survival factors (heat shock proteins and the protein kinase Akt) in determining the response of the cells to DA. / Addition of iron to cultures increased DA-induced expression of the stress protein heme oxygenase-1 (HO-1), and toxicity as assessed by mitochondrial activity, cellular release of lactate dehydrogenase, nuclear condensation and caspase-3 activation. In contrast, an iron chelator reduced these events. Furthermore, DA induced accumulation of superoxide, which was also reduced by the iron chelator. Surprisingly, a mimetic of the superoxide detoxifying enzyme, SOD potentiated DA toxicity, suggesting that generation of hydrogen peroxide via superoxide dismutation may be contributing to toxicity. Both a mimetic of the peroxide-scavenging enzyme, GPx and a GSH analog blocked DA-induced superoxide accumulation, HO-1 expression and caspase-3 activation. In addition, the GPx mimetic blocked caspase-3 activation induced by the combination of DA with iron. In contrast, an inhibitor of glutathione synthesis potentiated DA-induced HO-1 expression and cell death. / Finally, in further examining the cellular defense mechanisms, I found that various heat shock proteins increased in expression levels during oligodendroglial differentiation, however only heat shock protein-90 (HSP-90) was detected in oligodendrocyte progenitors. An HSP-90 inhibitor decreased activated Akt levels, induced caspase-3 activation, increased nuclear condensation, reduced oligodendrocyte progenitor viability, and potentiated DA-induced apoptosis. In addition, an Akt inhibitor alone exacerbated DA toxicity and in combination with the HSP-90 inhibitor caused synergistic potentiation of DA toxicity by enhancing caspase-3 activation. / In conclusion, elevated levels of iron, superoxide, deficient detoxification of peroxides by glutathione peroxidase and inadequate defense by glutathione contribute to the susceptibility of oligodendrocyte progenitors to DA-induced toxicity. On the other hand, HSP-90 alone or in concert with Akt play important roles in oligodendrocyte progenitors survival following an insult that produces oxidative stress.

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During differentiation stem cells are exposed to a range of microenvironmental chemical and physical cues. In this study, human multipotent progenitor cells (hMLPCs) were differentiated from umbilical cord into oligodendrocytes and astrocytes. Chemical cues were represented by a novel defined differentiation medium containing the neurotransmitter norepinephrine (NE). In traditional 2 dimensional (2D) conditions, the hMLPCs differentiated into oligodendrocyte precursors, but did not progress further. However, in a constructed 3 dimensional (3D) environment, the hMLPCs differentiated into committed oligodendrocytes that expressed MBP. When co-cultured with rat embryonic hippocampal neurons (EHNs), hMLPCs developed in astrocytes or oligodendrocytes, based on presence of growth factors in the differentiation medium. In co-culture, physical cues provided by axons were essential for complete differentiation of both astrocytes and oligodendrocytes. This study presents a novel method of obtaining glia from human MLPCs that could eliminate many of the difficulties associated with their differentiation from embryonic stem cells. In addition, it reveals the complex interplay between physical cues and biomolecules on stem cell differentiation.

Primary cilia are nonmotile, hair-shaped organelles that extend from the basal body in the centrosome. The present study is the first investigation of this organelle in the oligodendrocyte lineage in vivo. I used immunohistochemical approaches in normal and cilia-deficient mutant mice to study cilia in relation to oligodendrogenesis and myelination. Primary cilia immunoreactive for Arl13b and ACIII were commonly present in NG2+ oligodendrocyte progenitor cells (OPCs), in which cilia-associated pathways control proliferation, differentiation, and migration. The loss of primary cilia is generally associated with enhanced Wnt/β-catenin signaling, and Wnt/β-catenin signaling has been shown to promote myelin gene expression. I examined whether the lack of cilia in the oligodendrocyte lineage is associated with elevated Wnt/β-catenin activity. I found that absence of a primary cilium was associated with with higher levels of TCF3, and with β-galactosidase in Axin2-lacZ Wnt reporter mice. This evidence supports the proposal that cilia loss in oligodendrocytes leads to enhanced Wnt/β-catenin activity, which promotes myelination. Cilia are dependent on the centrosome, which assembles microtubules for the cilium, the cytoskeleton, and the mitotic spindle. Centrosomes are the organizing center for microtubule assembly in OPCs, but this function is decentralized in oligodendrocytes. I found that the intensity of centrosomal pericentrin was reduced in oligodendrocytes relative to OPCs, and γ-tubulin was evident in centrosomes of OPCs but not in mature oligodendrocytes. These decreases in centrosomal proteins might contribute to functional differences between OPCs and oligodendrocytes. The importance of cilia in the oligodendrocyte lineage was examined in Tg737orpk mice, which have a hypomorphic IFT88 mutation resulting in decreased cilia numbers and lengths. These mice showed marked, differential decreases in numbers of oligodendrocytes and myelin, yet little or no change in OPC populations. It appears that sufficient cells were available for maturation, but lineage progression was stalled. There were no evident effects of the mutation on Wnt/β-catenin. Factors that might contribute to the abnormalities in the oligodendrocyte lineage of Tg737orpk mice include decreased cilia-dependent Shh mitogenic signaling and dysregulation in cilia-associated pathways such as Notch and Wnt/β-catenin.

No description available.