Prader-Willi syndrome (PWS) is a rare, neurodevelopmental disorder with multiple features caused by hypothalamic deficiency, including infantile failure to thrive, hyperphagia leading to obesity, growth hormone deficiency, hypogonadism, and central adrenal insufficiency. Other features of PWS including global developmental delay, hypotonia, pain insensitivity, gastrointestinal dysfunction, and psychiatric disorders are caused by deficits in other regions of the nervous system. PWS is caused by the loss of a subset of paternally-expressed genes on chromosome 15, which includes NDN and MAGEL2. Necdin and Magel2 are both members of the melanoma antigen (MAGE) family of proteins and are expressed throughout development, particularly in the nervous system. This thesis describes experiments that examine the loss of function of necdin and Magel2 in mice and their potential roles in the pathogenesis of PWS. Targeted inactivation of Ndn and Magel2 in mice has aided in determining how loss of function of these proteins affects the development and function of the nervous system. Loss of necdin causes reduced axonal outgrowth and neuronal differentiation in the central and peripheral sensory nervous systems. I examined the autonomic nervous system in Ndn-null embryos and identified a defect in the migration of the most rostral sympathetic chain ganglion and consequently increased neuronal cell death and reduced innervation of target tissues supplied by this ganglion. Reduced axonal outgrowth was observed throughout the sympathetic nervous system in Ndn-null embryos although no gross deficits in the parasympathetic and enteric nervous systems were identified. Loss of Magel2 causes reduced fertility and abnormal circadian rhythm patterns in mice. I further identified an altered response to stress, a delayed response to insulin-induced hypoglycemia, a reduced stimulated growth hormone response, and lower thyroid hormone levels in Magel2-null mice, indicative of deficits in multiple hypothalamic-pituitary axes. The findings presented in this thesis support a role for necdin and Magel2 in the development and function of the nervous system. The data also indicates that these MAGE proteins play a key role in multiple features of PWS, including endocrine deficiencies and autonomic dysfunction

Of the thousands of dividing progenitor cells (PCs) generated daily in the adult brain only a very small proportion survive to become mature neurons through the process of neurogenesis. Identification of the mechanisms that regulate cell death associated with neurogenesis would aid in harnessing the potential therapeutic value of PCs. Apoptosis, or programmed cell death, is suggested to regulate death of PCs in the adult brain as overexpression of B-cell lymphoma 2 (Bcl-2), an anti-apoptotic protein, enhances the survival of new neurons. To directly assess if Bcl-2 is a regulator of apoptosis in PCs, this study examined the outcome of removal of Bcl-2 from the developing PCs in the adult mouse brain. Retroviral mediated gene transfer of Cre into adult floxed Bcl-2 mice eliminated Bcl-2 from developing PCs and resulted in the complete absence of new neurons at 30 days post viral injection. Similarly, Bcl-2 removal through the use of nestin-induced conditional knockout mice resulted in reduced number of mature neurons. The function of Bcl-2 in the PCs was also dependent on Bcl-2-associated X (BAX) protein, as demonstrated by an increase in new neurons formed following viral-mediated removal of Bcl-2 in BAX knockout mice. Together these findings demonstrate that Bcl-2 is an essential regulator of neurogenesis in the adult hippocampus.

Quetiapine, an atypical antipsychotic drug, is effective in treating the behavioural and the psychological symptoms of dementia (BPSD). The objective of this study was to examine the effects of quetiapine on anxiety-like behaviour in the amyloid precursor protein (APP)/ presenilin 1 (PS1) double transgenic mouse model of Alzheimers disease (AD). The mice were treated with quetiapine (0, 2.5, or 5 mg/kg/day) orally in drinking water for 7 or 10 months starting from 2 months of age. Conditioned anxiety was measured using the elevated T-maze (ETM). To measure memory, the Y-maze and the Morris Water maze were employed. After behavioural testing, â-amyloid (Aâ) plaques in the hippocampus and cortex of transgenic mice were stained using Congo Red. Brain-derived neurotrophic factor (BDNF) in the basolateral amygdala (BLA) and the hippocampus of mice was examined using immunohistochemical methods. The statistics revealed an interaction between quetiapine and APP/PS1 double transgenic mice in the avoidance phase of the ETM. Quetiapine modulates anxiety-like behaviours in the ETM. The anxiety-like behaviours were associated with reductions in BDNF levels in the BLA and hippocampus of the transgenic mice. This was reversed by treatment with quetiapine. Furthermore, chronic administration of quetiapine attenuated the memory impairment and decreased the Aâ plaque load in the brain. This study demonstrates that quetiapine normalizes anxiety-like behaviour and up-regulates cerebral BDNF levels in the APP/PS1 mice, suggesting that quetiapine may function as a neuroprotectant as well as an antipsychotic in treating the BPSD associated with AD.

Quetiapine, an atypical antipsychotic drug, is effective in treating the behavioural and the psychological symptoms of dementia (BPSD). The objective of this study was to examine the effects of quetiapine on anxiety-like behaviour in the amyloid precursor protein (APP)/ presenilin 1 (PS1) double transgenic mouse model of Alzheimers disease (AD). The mice were treated with quetiapine (0, 2.5, or 5 mg/kg/day) orally in drinking water for 7 or 10 months starting from 2 months of age. Conditioned anxiety was measured using the elevated T-maze (ETM). To measure memory, the Y-maze and the Morris Water maze were employed. After behavioural testing, â-amyloid (Aâ) plaques in the hippocampus and cortex of transgenic mice were stained using Congo Red. Brain-derived neurotrophic factor (BDNF) in the basolateral amygdala (BLA) and the hippocampus of mice was examined using immunohistochemical methods. The statistics revealed an interaction between quetiapine and APP/PS1 double transgenic mice in the avoidance phase of the ETM. Quetiapine modulates anxiety-like behaviours in the ETM. The anxiety-like behaviours were associated with reductions in BDNF levels in the BLA and hippocampus of the transgenic mice. This was reversed by treatment with quetiapine. Furthermore, chronic administration of quetiapine attenuated the memory impairment and decreased the Aâ plaque load in the brain. This study demonstrates that quetiapine normalizes anxiety-like behaviour and up-regulates cerebral BDNF levels in the APP/PS1 mice, suggesting that quetiapine may function as a neuroprotectant as well as an antipsychotic in treating the BPSD associated with AD.

Besides age, inheritance of the apoE-E4 allele is the main risk factor for late-onset AD. To determine the role of apoE in amyloid deposition, we studied mice expressing both mutant human amyloid [beta]-protein precursor (APP) and presenilin 1 (PS1) that were either normal or knocked-out for apoE. By 7 months, amorphous A[beta] deposition developed equally in both lines, indicating that A[beta] alone is sufficient for deposition to occur. In contrast, filamentous amyloid deposition was catalyzed at least 3000 fold by apoE. Electron micrographs further illustrate the filamentous nature of these plaques. These results and other, behavioral, data indicate that the primary function of apoE in AD is to promote the polymerization of A[beta] into mature, neurotoxic, amyloid. ApoE is also synthesized in the liver and is crucial in cholesterol metabolism, for mice lacking apoE exhibit hypercholesterolemia. We investigated neuropathology in mice using an uncommon technique, parabiosis, to determine whether apoE in the peripheral circulation influences brain amyloid formation. This surgical procedure allows exchange of proteins via peripheral circulation. We show that plasma apoE is found in parabiosed PS/APP/apoE-KO mice, rescuing their hypercholesterolemia. Unexpectedly, amyloid deposition is reduced in parabiosed PS/APP/apoE-KO mice compared to PS/APP controls. ApoE in the periphery seems to slightly reduce amyloid burden, by likely promoting efflux of A[beta];from the brain. These findings reinforce that the mechanisms whereby apoE affects A[beta] metabolism are complex, and the modulation of peripheral apoE metabolism is not likely to impact AD neuropathology. Since cognitive stimulation is associated with lower risk of AD, we sought to investigate the preventative potential of environmental enrichment (EE) using our mouse model.

Podocytes are specialized epithelial cells which wrap glomerular capillaries with numerous interdigitating foot processes (FP). Between adjacent FPs a unique junction, the slit diaphragm (SD), functions as the final blood filtration barrier. Actin organization is critical for maintaining FP structure and SD function, and the adaptor protein Nck can bind an intracellular SD component to couple it with actin regulators. Podocyte-specific deletion of Nck in mice results in proteinuria and FP effacement. To better understand FP remodelling, we have pursued a transgenic mouse model utilizing an inducible and reversible dominant negative Nck (DN-Nck) to prevent signalling to actin regulators, exclusively in podocytes. Effects of DN-Nck were first confirmed in vitro, and transgenic mice were then generated and induced to express DN-Nck. Despite obtaining several mice which exhibited a mild renal phenotype, transgene expression appeared to be lost in successive generations. Full in vivo analysis awaits generation of additional transgenic founders.

No description available.

Of the thousands of dividing progenitor cells (PCs) generated daily in the adult brain only a very small proportion survive to become mature neurons through the process of neurogenesis. Identification of the mechanisms that regulate cell death associated with neurogenesis would aid in harnessing the potential therapeutic value of PCs. Apoptosis, or programmed cell death, is suggested to regulate death of PCs in the adult brain as overexpression of B-cell lymphoma 2 (Bcl-2), an anti-apoptotic protein, enhances the survival of new neurons. To directly assess if Bcl-2 is a regulator of apoptosis in PCs, this study examined the outcome of removal of Bcl-2 from the developing PCs in the adult mouse brain. Retroviral mediated gene transfer of Cre into adult floxed Bcl-2 mice eliminated Bcl-2 from developing PCs and resulted in the complete absence of new neurons at 30 days post viral injection. Similarly, Bcl-2 removal through the use of nestin-induced conditional knockout mice resulted in reduced number of mature neurons. The function of Bcl-2 in the PCs was also dependent on Bcl-2-associated X (BAX) protein, as demonstrated by an increase in new neurons formed following viral-mediated removal of Bcl-2 in BAX knockout mice. Together these findings demonstrate that Bcl-2 is an essential regulator of neurogenesis in the adult hippocampus.

Alzheimer’s disease (AD) is a neurodegenerative disorder, characterised by severe memory loss and the accumulation of amyloid-beta (Aβ) and tau pathology within neocortex and medial temporal lobe (MTL) structures. Episodic memory impairment is a defining feature of early AD. The hippocampal formation (HF), a major network involved in both memory formation and retrieval is one of the first areas affected by AD pathology. However, the aetiology of AD is unknown; specifically how Aβ and tau pathologies cause memory impairment and how the physiological function of HF is affected. In this thesis, the 3xTgAD mouse was used as a high fidelity model of human AD pathological progression to study the function of HF during early (intracellular Aβ) and more progressive (extracellular plaque and hyperphosphorylated tau pathology) AD stages, referred to as ‘young’ and ‘old’ respectively. Specifically we: i) applied the hippocampal-dependent What-Where-Which (WWWhich) task to study the onset and progression of episodic-like memory decline (previously uncharacterised in the 3xTgAD mouse); ii) examined allocentric spatial memory in radial arm water maze (RAWM) and spontaneous alternation (SA) behaviour in T-Maze to discern whether cognitive differences exist between spontaneous and negatively reinforced tasks (the latter could be influenced by an exaggerated stress response); and iii) performed electrophysiological recordings in vivo from the HF of urethane-anaesthetised 3xTgAD and control mice to study basic synaptic connectivity, short-term synaptic plasticity and neuronal reverberation across the CA1-DG axis using a multi-site electrode. Our results showed an early and specific deficit for WWWhich episodic-like memory in the 3xTgAD model, with a decline in performance witnessed in mice as young as 3 months. In contrast, 3xTgAD component memory comprising single or dual associations of ‘What’, ‘Where’, ‘Which’ and ‘When’ remained intact suggesting the episodic impairment was due to dysfunction during the association of three component information streams within hippocampus (Chapters 3 and 4). 3xTgAD mice were equally impaired for allocentric spatial memory in RAWM and in their SA behaviour, suggesting no inherent advantage of examining cognition in paradigms which elicit behavioural distress (Chapter 5). We witnessed the development of subtle synaptic abnormalities in young 3xTgAD mice in the form of enhanced short-term paired pulse facilitation in CA1 and DG, however, a paucity of response facilitation in CA1 in response to train stimulation. In contrast, we saw intact basic synaptic function (fibre integrity and synaptic connectivity) in 3xTgAD mice of both young and old ages, suggesting gross hippocampal circuitry remained in place (Chapter 6). Finally, we saw an effect of normal ageing on cognition in the WWWhich and spatial tasks (Chapters 4 and 5), and a decline in neuronal reverberation with age in control and 3xTgAD mice. Dysfunction in these two parameters (behavioural and electrophysiological) coincided with the onset of intracellular Aβ accumulation within HF in 3xTgAD mice. This suggests a role of intracellular Aβ in impairing the physiological function of HF in AD which translates as cognitive decline in hippocampal-dependent forms of memory. Episodic memory was found to be especially sensitive to AD-related pathology and impairment, thus the WWWhich task may be applied to faithfully study the onset of cognitive decline in other AD mouse models. Further examination of the relative contribution of Aβ to hippocampal dysfunction in the 3xTgAD model is required.

Missense single-nucleotide polymorphisms (mSNPs) in titin are emerging as a main causative factor of heart failure. However, distinguishing between benign and disease-causing mSNPs is a substantial challenge. Here, we research the question of whether a single mSNP in a generic domain of titin can affect heart function as a whole and, if so, how. For this, we studied the mSNP T2850I, seemingly linked to arrhythmogenic right ventricular cardiomyopathy (ARVC). We used structural biology, computational simulations and transgenic muscle in vivo methods to track the effect of the mutation from the molecular to the organismal level. The data show that the T2850I exchange is compatible with the domain three-dimensional fold, but that it strongly destabilizes it. Further, it induces a change in the conformational dynamics of the titin chain that alters its reactivity, causing the formation of aberrant interactions in the sarcomere. Echocardiography of knock-in mice indicated a mild diastolic dysfunction arising from increased myocardial stiffness. In conclusion, our data provide evidence that single mSNPs in titin's I-band can alter overall muscle behaviour. Our suggested mechanisms of disease are the development of non-native sarcomeric interactions and titin instability leading to a reduced I-band compliance. However, understanding the T2850I-induced ARVC pathology mechanistically remains a complex problem and will require a deeper understanding of the sarcomeric context of the titin region affected.