Tobacco dependence dramatically increases health burdens and financial costs. Limitations of current smoking cessation therapies indicate the need for improved molecular targets. Nicotine, the main addictive component of tobacco, exerts its dependency effects via nicotinic acetylcholine receptors (nAChRs). The homomeric α7 nAChR is one of the most abundant receptors found in the brain and has unique features in comparison to other nAChR subtypes such as high calcium permeability, low probability of channel opening, and a rapid desensitization rate. α7 nAChR agonists reduce nicotine's rewarding properties in the conditioned place preference (CPP) test and i.v. self-administration. Recently, the peroxisome proliferator-activated receptor type-α (PPARα) has been implicated as a downstream signaling target of the α7 nAChR in ventral tegmental area dopamine cells. It is unknown whether the intrinsic characteristics of the α7 nAChR and PPARα are involved in its attenuation of nicotine reward. Therefore, this dissertation sought to investigate the role of α7 nAChRs in a mouse model of nicotine CPP and nicotine withdrawal by 1) investigating the impact of pharmacological modulation of α7 nAChR function in nicotine dependence and 2) evaluating a possible role for PPARα as a downstream mediator of α7 nAChRs in nicotine dependence. Positive allosteric modulators (PAMs) and a silent agonist were used to investigate the role of α7 nAChR conformations. The utilization of the α7 nAChR Type I PAM NS1738, Type II PAM PNU120596, and silent agonist NS6740 provided insight about the probability of channel opening (NS1738, PNU120596), desensitization (PNU120596, NS6740), and modulation of the endogenous acetylcholine/ choline tone (NS1738, PNU120596) as it relates to the α7 nAChR in nicotine CPP and withdrawal. In addition, this dissertation sought to elucidate the role of the α7 nAChR and PPARα in nicotine dependence using pharmacological interventions. The results suggest that the role of the α7 nAChR in nicotine dependence is conformation-dependent and PPARα-mediated. This dissertation is the first to report PPARα-mediation of the effects of α7 nAChR in nicotine reward and attenuation of nicotine withdrawal signs by PPARα activation. This data supports the development of α7 nAChR agonists and PPARα activators as possible smoking cessation aids.

<p>Gliomas are the most common tumors of the central nervous system. Our lab recently identified mutations in <italic>IDH1</italic> and <italic>IDH2</italic> as occurring frequently in progressive gliomas. We applied a series of biochemical and genetic approaches to explore the roles of the mutations in tumors and generate models for study. </p><p><italic>IDH1/2</italic> mutations have the potential to impact a number of metabolic pathways. IDH1/2 convert isocitrate to &#945;-ketoglutarate while simultaneously converting NADP+ to NADPH. To assess changes in metabolism, we completed metabolic profiling and complementary studies in cell lines with and without mutant <italic>IDH1</italic> or mutant <italic>IDH2</italic>. We identified a decrease in hypoxia signaling and a decrease in global 5-hydroxymethylcytosine in cell lines with mutant <italic>IDH1/2</italic> .</p><p>Having observed mutations in <italic>IDH1/2</italic> in a large fraction of progressive gliomas, we asked if the mutations were either 1) advantageous for growth in brain parenchyma, or 2) advantageous in a particular cell-of-origin. Sequencing of a series of metastases to the brain from non-central nervous system tumors identified no mutations in <italic>IDH1/2</italic>, lending less credence to the first hypothesis. To elucidate whether mutations in <italic>IDH1/2</italic> can initiate glioma progression and explore the potential cell-of-origin for progressive gliomas, we generated mice in which we induced expression of mutant <italic>IDH2</italic> in different populations of cells in the brain, either alone or in combination with <italic>TP53</italic> deletion, another frequently altered gene in progressive gliomas. Mice with broad expression of mutant <italic>IDH2</italic> developed hydrocephalus and encephalomalacia early in life, but did not develop tumors. Therefore, we restricted expression, and two brain tumors were identified in mice with both <italic>IDH2</italic> mutation and <italic>TP53</italic> deletion. While this suggests that both mutations might be required for the development of tumors, this is too small a number to draw significant conclusions. Further research with an expanded cohort of mice, utilization of additional drivers of expression, and further characterization of identified tumors will help in elucidating the role of mutant <italic>IDH2</italic> and the cell-of-origin for progressive gliomas.</p> / Dissertation

No description available.

Glioblastoma Multiforme (GBM) is the most common and lethal of human primary central nervous system tumours, with a median survival of 14-16 months despite surgery, radiation and chemotherapy. A reason for this dismal prognosis is insufficient understanding of the ontogeny of GBMs, which are highly heterogeneous at a pathological level. This pathological diversity, between and within GBMs as well as varying grades of gliomas, is not fully explained on the grounds of an oncogenic stimulus. Interaction with the tumour microenvironment, as well as inherent characteristics of the tumour cell of origin are likely a source of this heterogeneity. In this thesis we describe the use of a novel mouse model which integrates Cre-Lox mediated and Tet-regulated gene expression. This system in combination with germline and somatic strategies has enabled us to interrogate how the state in glial development and the region in the brain where transformation occurs influence the process of gliomagenesis. The findings of this thesis suggest that the state of glial development at which a mutation is introduced is an important determinant of gliomagenesis. In support of this, we showed that early progenitors in the radial glial lineage are more susceptible to transformation than those, which have committed to a gliogenic lineage and are presumably further along in the process of differentiation. Highlighting the interplay between genetic alterations and the molecular changes that accompany the process of differentiation. Despite findings that suggest that neurogenic regions of the adult brain are more susceptible to transformation, we show that this is not always the case and instead, transformation is dependent on an interaction between specific combinations of genetic mutations and susceptible cell types regardless of the region of origin. Results from this thesis highlight the need to view the tumourigenic process of gliomas in the context of normal brain development as the cell context of oncogene expression may determine the phenotype and biologic aggressiveness of the tumour. Thus, the results of genetic or epigenetic alterations leading to brain tumours may be quite different in different cells of the hierarchy, suggesting unique treatment targets and strategies depending on the cell of origin.

Glioblastoma Multiforme (GBM) is the most common and lethal of human primary central nervous system tumours, with a median survival of 14-16 months despite surgery, radiation and chemotherapy. A reason for this dismal prognosis is insufficient understanding of the ontogeny of GBMs, which are highly heterogeneous at a pathological level. This pathological diversity, between and within GBMs as well as varying grades of gliomas, is not fully explained on the grounds of an oncogenic stimulus. Interaction with the tumour microenvironment, as well as inherent characteristics of the tumour cell of origin are likely a source of this heterogeneity. In this thesis we describe the use of a novel mouse model which integrates Cre-Lox mediated and Tet-regulated gene expression. This system in combination with germline and somatic strategies has enabled us to interrogate how the state in glial development and the region in the brain where transformation occurs influence the process of gliomagenesis. The findings of this thesis suggest that the state of glial development at which a mutation is introduced is an important determinant of gliomagenesis. In support of this, we showed that early progenitors in the radial glial lineage are more susceptible to transformation than those, which have committed to a gliogenic lineage and are presumably further along in the process of differentiation. Highlighting the interplay between genetic alterations and the molecular changes that accompany the process of differentiation. Despite findings that suggest that neurogenic regions of the adult brain are more susceptible to transformation, we show that this is not always the case and instead, transformation is dependent on an interaction between specific combinations of genetic mutations and susceptible cell types regardless of the region of origin. Results from this thesis highlight the need to view the tumourigenic process of gliomas in the context of normal brain development as the cell context of oncogene expression may determine the phenotype and biologic aggressiveness of the tumour. Thus, the results of genetic or epigenetic alterations leading to brain tumours may be quite different in different cells of the hierarchy, suggesting unique treatment targets and strategies depending on the cell of origin.

Neurodevelopmental disorders encompass a spectrum of different conditions with both genetic and environmental etiologies. Although rapid progress has been made in deciphering the genetic landscape of these disorders, in most cases, it remains unclear how mutations undermine neurodevelopmental mechanisms. However, increasing identification of risk genes suggests chromatin remodelling is frequently impacted. For instance, de novo variants encoding the chromatin remodeller CHD4 causes Sifrim-Hitz-Weiss syndrome, which manifests as an overgrowth-intellectual disability syndrome. To further understand Chd4’s role during cortical development, we excised the ATPase domain of Chd4 in the germline or specifically in the developing telencephalon, creating three mouse models. Germline heterozygotes presented a slight decrease in brain weight, cortex area and Ctip2+ cells, with females displaying more overt impairments in learning and memory. Telencephalon-specific conditional heterozygotes exhibited slight changes in white matter, increased repetitive movements and altered social behaviours. Telencephalon-specific conditional knockouts presented with decreased brain size, brain weight, and cortex thickness due to decreased upper layer neurons, and anxiety phenotypes. These data reveal an unexpected complexity in the impacts of Chd4 mutations on neurodevelopmental processes and behaviour.

No description available.

Parkinson’s Disease (PD), the second most common neurodegenerative disease worldwide, pathologically presents with the inclusion of Lewy bodies and dopaminergic cell loss in the brain. Lewy bodies are composed of aggregated a-synuclein protein, and although essential to our understanding of PD, not much is known about the native, pre-synaptic state of a-synuclein (a-syn). Due to its mostly synaptic local, immunostaining results in diffuse signal, ultimately providing little insight into the types of a-syn-resident cells. As a result, insight into a-syn expression driven cellular vulnerability has been difficult to ascertain. Using a knockin mouse model that localizes a-syn to the nucleus of cells by insertion of a nuclear localization signal into the a-syn gene locus (SncaNLS), we overcome visualization issues and map out the topography and cells-of-origin of a-syn in mice. I performed immunohistochemistry on SncaNLS mouse tissue to map out the endogenous distribution of a-synuclein in the brain. Using ilastik machine learning analysis, I determined regions with high a-syn expression, which were subsequently co- stained with cell-type specific markers to gain further topographical granularity. a-syn showed high expression in the olfactory bulb, hippocampus, cerebral cortex, substantia nigra and cerebellum. Within these structures, there was a high level of expression of a-syn in granule cells, pyramidal cells, mitral cells, and dopaminergic neurons. Taken together, the SncaNLS mouse serves as a tool to define an atlas of a-syn topography, potentially providing insight into cellular vulnerability in PD.

Warburg Micro syndrome is a severe autosomal recessive condition characterised by abnormalities affecting the ocular, neurological and endocrine systems. Previous studies have identified causative loss-of-function mutations in four members of the RAB protein network; RAB3GAP1, RAB3GAP2, RAB18 and TBC1D20, causing clinically indistinguishable phenotypes. RAB3GAP1 and RAB3GAP2 form a heterodimeric complex specifically regulating the RAB3 family of proteins in calcium mediated exocytosis of hormones and neurotransmitters. Rab3gap1 deficient mice have previously been generated and showed altered short term plasticity in the hippocampus and inhibition of Ca2+ mediated exocytosis of glutamate from cortical synaptosomes, but failed to recapitulate the characteristic ocular or neurological features of Warburg Micro syndrome. Mutations in TBC1D20, a GTPase activating protein (GAP) for the RAB1 family, have recently been identified in Warburg Micro syndrome patients and the bs (blind sterile) mouse model; although this model recapitulated many ocular and endocrine abnormalities of the disease any neurological abnormalities have yet to be reported. The function and localisation of RAB18 remains to be fully elucidated and its role in disease pathogenesis is still unclear. Initially, I have confirmed previous reports co-localising RAB18 with the cis-Golgi, ER and lipid droplets in mouse embryonic fibroblasts and identified a novel localisation in neuronal processes of primary hippocampal neurons. To examine the role of RAB18 in vivo a novel Rab18 genetrap mouse was generated by MRC Harwell as part of the EUMODIC screen. In this study I describe detailed histopathological and neurological characterisation of the Rab18-/- mouse model. Rab18-/- mice were viable and fertile. At eye opening they presented with dense nuclear congenital cataracts and atonic pupils recapitulating major ocular features of Warburg Micro syndrome. Analysis of embryonic eye development revealed a delay in lens development in Rab18-/- mice as early as embryonic day 12.5. From three weeks of age Rab18-/- mice developed progressive hind limb weakness indicative of neurological dysfunction. I have undertaken detailed neuropathological analysis of the observed hind limb weakness and identified no abnormalities in synaptic vesicle recycling and no atrophy of peripheral muscles or aberrant development or stability of neuromuscular connectivity. However, loss of RAB18 resulted in gross accumulations of neurofilament and microtubule proteins at the neuromuscular junction and disorganisation of the cytoskeleton in peripheral nerves. Investigation of global proteomic profiling in peripheral nerve of Rab18-/- mice identified alterations in core pathways regulating the axonal cytoskeleton in neurons. In summary this thesis describes a novel Rab18-/- mouse model recapitulating the characteristic ocular and neurological features of Warburg Micro syndrome. I highlight a novel mechanistic insight into Warburg Micro syndrome disease pathogenesis and a role for RAB18 in regulating cytoskeletal dynamics in neurons.

Parkinson's disease is a progressive neurodegenerative disorder of the central nervous system, manifesting with both motor and non-motor symptoms. Autosomal recessive mutations in the FBXO7 gene have been identified to cause a rapidly progressing early-onset form of PD. Canonically, FBXO7 functions as a substrate-recruiting subunit of the SCF-type E3 ubiquitin ligase. However, it also has a variety of other atypical functions, such as cell cycle regulation, proteasome regulation, and mitophagy. The overall aim of this research was to characterise the functional role of FBXO7 in various in vitro and in vivo PD models. The models examined included FBXO7 shRNA knockdown SH-SY5Y cell lines, FBXO7 CRISPR knockout SH-SY5Y cell lines, primary patient fibroblasts with a FBXO7 mutation, and MEFs and tissues from a Fbxo7 KO mouse. My analysis of fibroblasts from a patient without FBXO7 expression revealed several interesting phenotypes. Briefly, the patient fibroblasts proliferated slower due to increased apoptosis and lower CDK6 and cyclin D1 expression, which led to fewer cells progressing through the G1 phase of the cell cycle. My experiments showed that these cells also had mitochondrial respiration defects, exhibiting lower basal respiration, ATP production, maximal respiration and spare capacity, in addition to complex I, III and IV deficiencies. Patient fibroblasts also had significantly lower levels of 12S and 16S ribosomal mRNA transcripts, which are necessary for the translation of mitochondrially encoded subunits of complexes I, III, and IV. Similar phenotypes were also observed in MEFs from a Fbxo7 KO mouse model, indicating conservation between human and mouse FBXO7 in regulating mitochondria, cell death and proliferation. In a tissue-specific KO mouse model of PD, where FBXO7 expression was ablated in the dopaminergic neurons, I analysed proteins regulated by FBXO7 which might be responsible for cell loss in the substantia nigra. I discovered that RPL23, a regulator of MDM2, was ubiquitinated by SCFFbxo7 using K48 chain linkages, promoting its degradation by the proteasome. This suggests that misregulation of the MDM2:p53 axis may underlie the cell loss observed in this conditional Fbxo7 KO mouse model. In conclusion, these results elaborate on the role of FBXO7 in mitochondrial biology, and identify a new ubiquitination substrate of FBXO7 in a mouse model of PD. It is hoped that by elucidating the potential pathogenic mechanisms of FBXO7 in rare familial forms of the disease, it will be possible to translate findings to the more prevalent sporadic forms of Parkinson's disease as well.