Polyglutamine (polyQ) diseases are progressive fatal neurodegenerative movement disorders. Although many cellular processes are perturbed in polyQ disease, recent studies highlight the importance of protein misfolding as a central event in polyQ toxicity. Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease, is a particularly interesting polyQ disease because of the special qualities of the disease protein ataxin-3, which normally participates in cellular protein quality control. Here I use multiple mouse models of disease to explore toxic protein species and the role of protein homeostasis in SCA3 pathogenesis. In Chapter 1, I review the key features of polyQ disease, and outline the background and rationale behind our strategy for identifying toxic protein species in SCA3. In Chapter 2, I examine the role of the protein quality control ubiquitin ligase, CHIP (C-terminus of Hsp70 interacting protein), in regulating the toxicity of expanded ataxin-3 in vivo. Genetic reduction or removal of CHIP increases formation of detergent-resistant ataxin-3 microaggregates specifically in the brain. Concomitant with this, reduction or removal of CHIP exacerbates the phenotype of SCA3 mice, revealing a correlation between high levels of microaggregates and phenotypic severity. Additional cell-based studies confirm that CHIP may not directly mediate ataxin-3 degradation, suggesting that CHIP reduces expanded ataxin-3 toxicity in the brain primarily by enhancing ataxin-3 solubility. In Chapter 3, I use various biochemical techniques to reveal the presence of brain-specific ataxin-3 microaggregates in two genetically distinct mouse models of SCA3. Selective neuropathological evaluation of SCA3 mice reveals that major neuronal loss and reactive glial proliferation are not shared features of phenotypically-manifesting SCA3 mice. Additional studies fail to provide evidence for loss-of-function of endogenous ataxin-3 in SCA3 mice. Our results suggest that neuronal dysfunction in SCA3 is mediated through a toxic gain-of-function mechanism by ataxin-3 microaggregates in the CNS. In Chapter 4, I discuss important areas for future research in polyQ disease. I describe studies that would help elucidate the structural nature of toxic soluble microaggregates, and their effects on other cellular proteins. I also consider how the results described in this thesis inform potential treatment strategies.

Alzheimer’s disease (AD) is a devastating neurodegenerative disease that affects millions of peoples’ lives worldwide. While the consequences of AD are recognizable, the etiology is unclear. Gene-environment interactions have been implicated in the development of the disease, and exposure to organophosphorus (OPs) compounds is one of the environmental factors associated with AD. Evidence links exposure to levels of OPs encountered in agriculture, horticulture, and other work places with neurodegenerative disease, psychiatric illness, and sensorimotor deficits. Unfortunately, the mechanisms underlying these effects have yet to be established. Here, we set out to examine the long-term consequences of exposure to a commonly applied OP insecticide, chlorpyrifos (CPF), in an attempt to identify a causal link between occupational exposures and chronic illnesses. We exposed a transgenic rodent model of AD, TgF344-AD, to levels of CPF representing occupational exposures and examined ensuing behaviors and neuropathologies. We observed a sex-specific, biphasic response in CPF-exposed animals, including acute neurotoxicities, followed by intermediate recovery, and finally, chronic cognitive impairments. CPF exposure exacerbated neuronal damage in brain regions critical to the impaired behaviors, and neuroinflammatory pathways were identified as facilitators of this damage. This work emphasizes the long-term consequences of early life repeated exposures to OPs and identifies dysregulated microglia as a potential deleterious modifier of disease. Additionally, we investigated the efficacy of a neuroprotective compound, (-)-P7C3-S243 in TgF344-AD rats. P7C3 compounds exert protection by preventing young hippocampal neurons from dying prematurely and also enhancing flux of nicotinamide adenine dinucleotide (NAD), thereby aiding in neuron survival under conditions that normally cause axon degeneration and cell death. These compounds have proven effective in preclinical models of Parkinson’s disease, amyotrophic lateral sclerosis, and traumatic brain injury. Thus, we sought to investigate the neuroprotective efficacy of P7C3 compounds in AD, as well. (-)-P7C3-S243 was administered to wild-type and transgenic male and female rats daily for 9 and 18 months, and classic hallmarks of the disease were assessed. Transgenic rats developed a spectrum of AD pathologies and behaviors, as expected, and (-)-P7C3-S243 ameliorated early depression-like behaviors, late learning and memory deficits, and progressive neuronal damage in this model, without influencing amyloid plaque deposition, tauopathies, or neuroinflammation. This data suggests that targeting neuronal cell death pathways is a promising treatment strategy in AD. Taken together, the research presented here expands our current understanding of pathways of regulation in Alzheimer’s disease—organophosphates are capable of exacerbating the severity of AD, while P7C3 compounds are promising therapeutic candidates for neuronal death in the disease. Given the overlapping molecular pathways of modulation in CPF-induced toxicity and (-)-P7C3-S243 neuroprotection in AD, future studies will investigate the efficacy of (-)-P7C3-S243 in cognitive deficits induced by CPF exposure. Ultimately, this body of work highlights the plasticity of neuronal cell death and cognitive impairment in AD, thus indicating a better understanding of these pathways could facilitate vastly improved intervention strategies in Alzheimer’s disease.

Proper control of movements is critical for an animal’s survival, and requires the robust function of a number of genetic, molecular, neuronal and biomechanical processes. This dissertation describes a body of inter-related studies utilizing a diverse collection of Drosophila mutants to probe the roles individual genes play in shaping motor pattern generation. A particular emphasis is placed on describing the consequences of genetic perturbations of voltage-gated sodium, calcium and potassium ion channels (NaV, CaV, and KV respectively) on the function of neuronal circuits that drive motor behavior. Here, I describe the development of several quantitative protocols to study alterations in of walking (IowaFLI Tracker) and flight motor program activity and behavior in Drosophila mutants. These approaches were utilized to analyze the highly-stereotypic aberrant motor program associated with electroconvulsive stimulation (ECS)-induced seizure discharge activity in each hyperexcitable mutant. Several quantitative and mechanistic similarities between flight motor program activity and ECS-evoked discharges were identified, and the distinct aberrant ECS-evoked activity disclosed an electrophysiological signature of each mutation. Ion channel mutants display a diverse spectrum of neuronal excitability phenotypes that was highlighted in a novel hyperexcitable mutant, Shaker wings down (Swd), characterized by ether-induced leg shaking reminiscent of certain KV channel mutants (e.g. Shaker, KV1) is presented. Detailed analyses revealed disrupted walking and flight, correlated with neuronal hyperexcitability and aberrant action potential generation. Surprisingly, the Swd mutation site was mapped to a single amino acid in the voltage sensor region in paralytic (para, encoding the only NaV gene in Drosophila). Genetic analysis of intra-genic heteroallelic interactions amongst Swd and other identified para alleles further revealed a number of complex mechanisms underlying a wide phenotypic spectrum of altered neuronal excitability and motor pattern generation. The effects of perturbed ion channel function on motor program generation are compared with progressive alterations associated normal aging as well as neurodegeneration. A number of age-resilient and age-vulnerable circuits were identified along with circuit-function biomarkers of aging. Throughout this study, an integrative framework utilizing non-linear dimensional reduction approaches unraveled a broader perspective to visualize and quantify similarities and distinctions between discharge phenotypes across a large collection of Drosophila mutants.

Alzheimer’s disease (AD), identified over 100 years ago and intensively studied since the 1970s, has no effective treatments or mechanistic understanding of the underlying neurodegenerative process. Most investigators believe accumulation or aggregation of amyloid beta (Ab) proteins plays a causative role. Aβ peptides (~39-43 residues) are generated by proteolysis of the transmembrane protein APP. One reason we know so little about AD is an incomplete understanding of the cellular mechanisms responsible for Ab proteotoxicity. Human ES and iPSC models of AD are recent additions to many other models used to investigate these mechanisms. AD, however is a chronic progressive condition of old age and cultured neurons may not live long enough to model what goes wrong in neurons from AD patients. In my research, I used hESCs which directly express Ab peptides thus avoiding the time it takes to process APP. One App allele in H9 hESCs was previously edited using TALEN. A homologous recombination cassette coding directly for a secretory form of either Ab1-42 or Ab1-40 and containing a stop codon, was inserted into the first exon of App upstream of the normal translational start site. I used multiple independently isolated clones of edited cells with 3 genotypes: App/App (unedited), App/Aβ1-40 and App/Aβ1-42. Expression of Ab from edited alleles was confirmed by qRT-PCR using primers specific for the edit. I first sought to establish if editing changed any aspects of neuronal differentiation in culture. All 3 genotypes have similar embryoid body (EB) development, and similar numbers and sizes of neuronal clusters (NC) up to 34 days after EB dissociation and neural differentiation. Immunostaining of neuronal markers, NeuN and DCX (doublecortin), likewise revealed no difference among edited and unedited cells, suggesting that the edits do not affect the ability of my stem cells to differentiate into neurons. I next measured accumulation of aggregated Ab using an aggregate specific antibody, 7A1a. Data at 34-days post EB dissociation indicates NCs in the Aβ1-42 edited cells accumulate significantly more aggregates relative to either unedited or Ab1-40 edited lines, a result consistent with the increased ability for Ab1-42 to form aggregates. Aβ aggregates also appear to be concentrated around fragmented nuclei within neuronal clusters suggesting that intracellular accumulation may play a key role in proteotoxicity. Additionally, I observed a significant decrease in the number of synapsin1 puncta, a marker of synapses, another feature of AD. I documented a nearly 3-fold greater neuronal cell death in both the Aβ1-40 and Aβ1-42 neurons at 70 days after differentiation. RNA sequencing data also shows independently isolated clones group together and show differential expression of genes related to memory and neuronal cell death. The early presence of Aβaggregation and subsequent cell death is in line with the chronic and progressive nature of AD and this is the first known model to exhibit a neurodegenerative phenotype. These isogenic cell lines thus appear to be useful to screen for therapeutics that may prevent or slow Ab1-42 dependent neurodegeneration and a tool to investigate Ab-dependent mechanisms with relevance to AD.

Mon projet de thèse a été dédié à l’étude des synucléinopathies. Ces maladies neurodégénératives sont caractérisées par la présence d’inclusions intracytoplasmiques positives pour l’alpha-synucléine et contenues dans les neurones pour la maladie de Parkinson (i.e. les corps de Lewy) ou dans les oligodendrocytes pour l’atrophie multisystématisée (i.e. les inclusions cytoplasmiques oligodendrogliales). L’objectif de mon travail de thèse fut de proposer une approche multifactorielle et translationnelle en développant les aspects de modélisation, de mécanistiques et de thérapeutiques associées aux synucléinopathies. Nous nous sommes tout d’abord intéressés à disséquer les mécanismes sous-jacents à la neurodégénérescence induits par la protéine alpha-synucléine dans un modèle primate non-humain de la maladie de Parkinson. Nous avons ainsi souligné le rôle toxique de la protéine alpha-synucléine et mis en lumière de nouveaux processus cellulaires impliqués dans le phénomène de neurodégénérescence. Dans ce même modèle animal, nous avons étudié l’hypothèse d’une propagation de la pathologie induite par l’alpha-synucléine entre les systèmes nerveux centraux et périphériques. Nous avons ainsi pu démontrer l’existence d’une route bidirectionnelle de propagation et de neurodégénérescence de la protéine entre les deux systèmes nerveux, pouvant corroborer la présence de symptômes non moteurs précoces au cours de la pathologie. Enfin, nous nous sommes concentrés sur le rétablissement de la fonction autophagique comme cible thérapeutique commune aux synucléinopathies. Nous avons ainsi pu démontrer qu’une restauration de la machinerie de dégradation de la voie autophagie était suffisante pour rétablir les taux physiologiques de la protéine alpha-synucléine et induire une neuroprotection dans un modèle rongeur de la maladie de Parkinson et d’atrophie multi-systématisée. Ces travaux corroborent le rôle clé de la protéine alpha-synucléine dans l’étiologie des synucléinopathies et proposent de nouvelles stratégies thérapeutiques communes à toutes les synucléinopathies afin de rétablir les niveaux physiologiques cellulaires de la protéine et une neuroprotection au sein du système nerveux central. / My thesis project was dedicated to the study of synucleinopathies. Synucleinopathies are neurodegenerative diseases characterized by the presence of alpha-synuclein positive intracytoplasmic inclusions which are present either in neurons for Parkinson’s disease (i.e. Lewy Bodies) or in oligodendrocytes for Multiple system atrophy (i.e. Glial Cytoplasmic Inclusions). The aim of my work was to establish a multifactorial and translational approach through modeling, mechanistic and therapeutic aspects associated with synucleinopathies. First, we focused on dissecting the underlying alpha-synuclein-mediated mechanisms of neurodegeneration using a non-human primate model of Parkinson’s disease. We confirmed the toxic role of alpha-synuclein in the pathology and highlighted unpredictable cellular processes involved in neurodegeneration. Using the same Parkinson’s disease model, we studied the hypothesis of a pathological propagation between the central and peripheric nervous systems in an attempt to decipher the initiation point and the direction of propagation of the associated pathology. We thus demonstrated a bidirectional route of propagation of alpha-synuclein between the CNS and the ENS and within the ENS. Finally, we focused on the restoration of the autophagic function as a potential common therapeutic target for all synucleinopathies. We demonstrated through a gene-based restoration of the autophagy, we efficiently reestablish alpha-synuclein physiological protein levels, while inducing neuroprotection in a Parkinson’s disease and Multiple system atrophy rodent models. Thus, this work corroborates the key role of alpha-synuclein in the etiology of synucleinopathy and offers new common therapeutic strategies for all synucleinopathies to decrease alpha-synuclein-induced toxicity into the central nervous system.

Parkinson’s disease is the second common neurodegenerative disease and is most frequently diagnosed in individuals over 60. There are no available medications that can prevent or restore the loss of neurons that correspond to motor impairments in patients. Identifying novel therapeutic compounds that are capable of slowing and reversing the extensive neurodegeneration that occurs in PD remains an important goal of the field. While basic research has identified potential therapeutic agents, studies often use young model organisms to demonstrate efficacy of the target compound. This approach ignores the impact of the aged CNS on the disease process, and likely contributes to high failure rates of translation in clinical trials. Here we investigate the capacity for astaxanthin (AXT), a xanthophyll carotenoid, to attenuate the neurotoxicity to MPTP, a toxin routinely used to establish parkinsonian symptoms in mice. We show that AXT reduces MPTP induced neurotoxicity in young, but less effective in the aged animals. While AXT is an interesting neuroprotective capacity, there are also multiple reports that indicate AXT may preserve cognitive function in the context of neurodegeneration and neural injury, the impact of AXT under physiological conditions and in the aged CNS has been largely uninvestigated. We also evaluate the effect of AXT on cognitive function in young and aged mice. Here, we show that AXT supplementation can modulate neural plasticity is associated with improved performance in cognitive behavioral tasks. This diet effect was observed in both young and aged mice, suggesting a novel and direct mechanism of action in synaptic function.

The neurodegenerative disorders Alzheimer??s Disease (AD) and Parkinson??s Disease (PD) are characterised by the accumulation of misfolded amyloid beta 1-42 peptide (Aβ1-42) or α-synuclein, respectively. In both cases, there is extensive evidence to support a central role for these aggregation-prone molecules in the progression of disease pathology. However, the precise mechanisms through which Aβ1-42 and α-synuclein contribute to neurodegeneration remain unclear. Organismal, cellular and in vitro models are under development to allow elucidation of these mechanisms. A cellular system for the study of intracellular Aβ1-42 misfolding and localisation was developed, based on expression of an Aβ1-42-GFP fusion protein in the model eukaryote Saccharomyces cerevisiae. This system relies on the known inverse relationship between GFP fluorescence, and the propensity to misfold of an N-terminal fusion domain. To discover cellular processes that may affect the misfolding and localisation of intracellular Aβ1-42, the Aβ1-42-GFP reporter was transformed into the S. cerevisiae genome deletion mutant collection and screened for fluorescence. 94 deletion mutants exhibited increased Aβ1-42-GFP fluorescence, indicative of altered Aβ1-42 misfolding. These mutants were involved in a number of cellular processes with suspected relationships to AD, including the tricarboxylic acid cycle, chromatin remodelling and phospholipid metabolism. Detailed examination of mutants involved in phosphatidylcholine synthesis revealed the potential for phospholipid composition to influence the intracellular aggregation and localisation of Aβ1-42. In addition, an existing S. cerevisiae model of α-synuclein pathobiology was extended to study the effects of compounds that have been hypothesized to be environmental risk factors leading to increased risk of developing PD. Exposure of cells to aluminium, dieldrin and compounds generating reactive oxygen species enhanced the toxicity of α- synuclein expression, supporting suggested roles for these agents in the onset and development of PD. Expression of α-synuclein-GFP in phosphatidylcholine synthesis mutants identified in the Aβ1-42-GFP fluorescence screen resulted in dramatic alteration of α-synuclein localisation, indicating a common involvement of phospholipid metabolism and composition in modulating the behaviours of these two aggregation-prone proteins.

Degree awarded (2004): PhDBmS, Neuroscience Program, George Washington University / Glutamate is critically important as an excitatory neurotransmitter in the central nervous system. Increasing evidence suggests additional signaling roles for glutamate in cell proliferation and migration in normal and oncogenic states. Recently, glutamate release from glioma cells has been shown to increase tumor growth in vivo. To investigate the mechanism of glutamate enhancement of tumor growth, we investigated the effect of glutamate on tumor cell proliferation, invasion, and glioma-induced cell death. Here we demonstrate that glutamate enhances tumor growth via increasing tumor cell proliferation and inducing excitotoxic death of cells surrounding the solid tumor mass, thereby facilitating tumor expansion. The evidence that glutamate enhances tumor growth suggests that regulating extracellular levels of glutamate may restrict tumor growth. In the normal brain, extracellular glutamate levels are maintained by a family of glutamate transporters. To investigate the therapeutic potential of regulating extracellular glutamate concentrations on tumor growth, we utilized a transgenic mouse model of EAAT2 glutamate transporter overexpression. In this report, we demonstrate that increased glutamate transport limits tumor growth in vivo and provides protection against glioma-associated neuronal cell death. In addition, seizure activity, often associated with the presence of a CNS tumor, is attenuated in transgenic mice overexpressing the glutamate transporter, EAAT2. These findings suggest that glutamate transporters may provide a new therapeutic target for limiting tumor expansion and secondary epileptogenesis. / Advisory Committee: Dr. Margaret Sutherland (Chair), Dr. Steven Patierno (Chair), Dr. Tim Hales, Dr. Vincent Chiappinelli, Dr. Linda Werling, Dr. Frances Noonan

The lithium/pilocarpine model of epilepsy mimics mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) in humans. Systemic injection of pilocarpine in lithium chloride (LiCL) pretreated adult rats results in an acute episode of severe continuous seizure activity (status epilepticus, SE). SE causes a latent period, whereby the animal appears neurologically normal, with subsequent development of spontaneous recurrent seizures (SRSs). Neuropathological changes that occur during the latent period are believed to contribute to the epileptic condition. The present thesis characterized the development of neuronal death and behavioural alterations in rats after SE induced by the repeated low-dose pilocarpine procedure (RLDP), and investigated the causal relationship between these two processes. Our data demonstrated that the RLDP procedure for the induction of SE results in widespread neurodegeneration and behavioural alterations comparable to the pilocarpine and low-dose pilocarpine (LDP) procedures. However, the advantage to using this protocol was strain-dependent as it reduced mortality in Wistar, but not in Long Evans Hooded (LEH), rats. Stereological analysis of neurons (stained for the neuronal specific marker [NeuN]) at various times (1 hr to 3 months) following SE showed that different brain regions within the hippocampus, amygdala, thalamus and piriform cortex exhibited differential rates of neuronal loss, with the majority of SE-induced neuronal death present by 24 hours. SE resulted in decreased exploratory behavior as assessed in the open field test, increased aggression to handling, increased hyperreactivity as assessed in the touch-response test, and anxiolytic effects as measured in the elevated-plus maze. Furthermore, deficits in search strategies used, as well as impaired spatial learning and memory, contributed to poor Morris water maze (MWM) performance. Partial neuroprotection within the hippocampus (by tat-NR2B9c) had no effect on the number of rats developing SRSs or on behavioural alterations; this argues against a causal relationship between neurodegeneration within this region, genesis of SRSs, and behavioural morbidity.

This thesis focuses on the regulation of the ubiquitous second messenger Ca2+ in neuronal physiology and disease. Ca2+ signalling in neurons is regulated by ion channels located in the plasma membrane, as well as in the endoplasmic reticulum (ER) and mitochondrial membranes. Ca2+ signalling is essential for numerous cellular processes, including neuronal excitability, neurotransmitter release, synaptic plasticity, and induction of cell death. Age-related disruptions in Ca2+ signalling may contribute to decline of cognitive function and motor control associated with aging. Furthermore, disruption in neuronal Ca2+ signalling is implicated in several neurodegenerative disorders including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and Amyotrophic Lateral Sclerosis (ALS). In this thesis, I studied neuronal Ca2+ signalling and how it is affected in neurodegenerative disease. First, I examined the role of the ER Ca2+ binding protein Calreticulin (CRT) in AD. CRT is involved in regulation of ER Ca2+ signalling and modulation of susceptibility to cell death. I found that there was an increase in the expression of CRT in in vitro and in vivo models of AD. However, increased levels of CRT did not alter susceptibility of neuronal cells to death induced by AD-related stressors. Second, I examined the role of X-Linked Inhibitor of Apoptosis Protein (XIAP) in the modulation of neuronal Ca2+ signalling. I found that overexpression of XIAP in neuronal cells modified Ca2+ signalling by decreasing Ca2+ flux through multiple plasma membrane and ER channels. These effects appear to be independent of caspase inhibition, which is one of the ways that XIAP can inhibit apoptosis. Third, I examined a compound found in green tea, L-theanine, a glutamate receptor antagonist that is protective in models of excitotoxic neuronal injury. I found that 24 hour L-theanine treatment reduces the amount of Ca2+ released from neuronal intracellular stores in response to both glutamate stimulation and passive leak through ER channels. An acute 30 minute L-theanine treatment had similar effects. In conclusion, these observations further the understanding of the regulation of Ca2+ signalling in neurons and may lead to novel therapeutic strategies in neurodegenerative disease. / October 2008