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<strong>Background:</strong> Malignant transformation of cells is typically characterised by aerobic glycolysis, resulting in supressed mitochondrial function, a state that helps resistance to apoptosis. This characteristic has been widely accepted as a hallmark of cancer and has been shown to be of critical importance in tumour development. The bioenergetic differences between normal and malignant cells are being exploited to identify potential cancer specific therapeutics. Improved in-vitro models are required to aid the identification and assessment of candidate drugs. In this project, we investigated the bioenergetic phenotypes of a panel of adult and paediatric cancer cell lines and evaluated the potential of 3D models as a platform for testing drugs that target cancer metabolism. We also investigated a novel method to assess mitochondrial function that enables the quantification of the level of oxygenation within the cell. <strong>Results:</strong> The results presented in this thesis show that not all cancers display this aerobic glycolytic phenotype. We found that while some cell lines displayed the Warburg phenotype others displayed high levels of oxidative metabolism. These bioenergetic profiles need to be considered when deciding which anti-cancer drugs to use in a chemotherapeutic regime. If a bioenergetic pattern can be identified it may one day form the basis of a screening strategy for tumours. Dichloroacetate (DCA) is a small molecule PDK inhibitor that was investigated in this study. It was found to be relatively non-toxic to cells cultured in 2D but had improved toxicity when the cells were cultured in a 3D environment. Lastly, we evaluated a new oxygen sensing nanoprobe, Mito-Xpress Intra, and the results demonstrate its potential as a non-invasive means of measuring oxygen concentrations within the cell in real time as well as highlighting some striking differences between applied ambient and measured intracellular oxygen concentrations. <strong>Conclusion:</strong> The findings suggest that not all cancers display the characteristic glycolytic phenotype. They also highlight the importance of controlling oxygen and glucose levels when evaluating metabolism and when drug testing.

Extraction and quantitation of myosin light chain two coupled with myograph recordings from Ascaris muscle perfused with calmodulin inhibitors and neurotransmitters in conjunction with their respective agonists and antagonists have been used to establish the regulation of contraction in this muscle. Densitometric tracings of isolectric focusing gels separating the regulatory light chain were used to quantitate phosphorylation in resting, contracted and flaccid muscle. These studies indicated that inhibitory neurostimulation is mediated by a true GABA receptor. Myosin-mediated contraction is responsible for maintaining the level of tension observed in resting actin-mediated muscle. Actin-mediated contraction is responsible for the rapid rise in tension following excitatory stimuli. Both systems function simultaneously and are independant.

ABSTRACT Phosphorylation is a post-translational modification important for regulating protein activity and protein binding capacity. It is used in many different signaling pathways within the cell. Src Family Kinases and Protein Kinase A (PKA) are two prototyptical non-receptor tyrosine and serine/ threonine kinases, respectively, which are found in canonical signaling pathways. These two kinases are critical for signaling in essentially every cell of a multicellular organism, and are particularly important in development, cell migration and proliferation. Although both proteins have been intensely studied for many decades, an understanding of the molecular mechanisms which govern their regulation and the regulation that they effect on other proteins are still being elucidated. Fyn, like its related Src Family Kinase members, has previously been shown to be regulated by two tyrosine phosphorylation events at residues Y420 and Y531. Y420 is located in the kinase (Src Homology 1(SH1)) domain and it is a highly-characterized intermolecular autophosphorylation site that increases the activity of the kinase. Y531 is located near the C-terminus and is phosphorylated by C-terminal Src kinase (Csk). Phosphorylation of Y531 allows it to bind to R176 in the SH2 domain in an intramolecular fashion. In this conformation Fyn has only basal activity. Since these sites are essential for regulating the activity of the kinase, we hypothesized that four novel sites of tyrosine phosphorylation in Fyn could also importantly regulate the protein. Three of the novel sites lie in the SH2 domain, and one is located in the kinase domain. Mass spectrometry, in vitro kinase assays, as well as western blot analysis aided in uncovering that these novel Fyn phosphorylation sites fine tune the activity and substrate binding of the protein. PKA has been implicated in a multitude of signaling pathways and is particularly important in cell growth, proliferation, and migration. Fyn and PKA have classically been considered to be in separate signaling pathways. However, research over the past several decades has provided evidence that there is crosstalk that exists between the two pathways. The SFK Fyn and PKA can phosphorylate each other, thereby regulating each other's activity. Based on these data, we hypothesized the existence of downstream effectors of this relatively uncharacterized pathway. It was hypothesized that the presence of Fyn could lead to PKA activation and to differences in PKA binding partners. Through the use of co-immunoprecipitations, Stable Isotope Labeling of Amino Acids in Cell Culture (SILAC) and quantitative mass spectrometry, many proteins were found to increase their binding to PKA in the presence of Fyn. Several proteins were selected and further biochemically validated. These data suggest that the presence of Fyn could allow for PKA to more importantly interact with discrete pools of proteins within the cell to effectuate its signal transduction. Together these studies provide understanding on critical and fundamental processes by which all cells function.

Tau est une protéine associée aux microtubules enrichie dans l’axone. Dans la maladie d’Alzheimer, Tau devient anormalement hyperphosphorylée, s’accumule dans le compartiment somato-dendritique et s’agrège pour former des enchevêtrements neurofibrillaires (NFTs). Ces NFTs se propagent dans le cerveau dans un ordre bien précis. Ils apparaissent d’abord dans le cortex transenthorinal pour ensuite se propager là où ces neurones projettent, c’est-à-dire au cortex entorhinal. Les NFTs s’étendent ensuite à l’hippocampe puis à différentes régions du cortex et néocortex. De plus, des études récentes ont démontré que la protéine Tau peut être sécrétée par des lignées neuronales et que lorsqu’on injecte des agrégats de Tau dans un cerveau de souris, ceux-ci peuvent pénétrer dans les neurones et induire la pathologie de Tau dans le cerveau. Ces observations ont mené à l’hypothèse que la protéine Tau pathologique pourrait être sécrétée par les neurones, pour ensuite être endocytée par les cellules avoisinantes et ainsi propager la maladie. L’objectif de la présente étude était donc de prouver la sécrétion de la protéine Tau par les neurones et d’identifier par quelle voie elle est secrétée. Nos résultats ont permis de démontrer que la protéine Tau est sécrétée par des neurones corticaux de souris de type sauvage ainsi que dans un modèle de surexpression dans des cellules HeLa et PC12. Nos résultats indiquent que la sécrétion de Tau se ferait par les autophagosomes. Finalement, nous avons démontré que la protéine Tau sécrétée est déphosphorylée et clivée par rapport à la protéine Tau intracellulaire non sécrétée. / Tau, a microtubule-associated protein, is enriched in the axon. In Alzheimer’s disease, Tau becomes hyperphosphorylated, redistributes to the somato-dendritic compartment and forms aggregates called neurofibrillary tangles (NFTs). The NFTs propagates in a predictable manner in particular neuronal networks. Indeed, they appear in the trans-entorhinal region and then propagate to the entorhinal cortex where the trans-entorhinal cortex projects. Then, the NFTs propagate to the hippocampus and to different regions of the cortex and neocortex. Recent studies have reported that Tau can be secreted by neuronal cell lines. Besides, when aggregates of Tau protein were injected in mouse brain, they could enter neurons and induced Tau pathology. Based on those observations, it was speculated that Tau could be secreted by neurons and then captured by neighbouring cells to propagate Tau pathology in the brain. The goal of the present study was to prove that Tau can be secreted by neurons and to find the secretory pathway involved in Tau secretion. Moreover, the phosphorylation state of Tau protein was examined and compared to intracellular non-secreted Tau. Our results showed that Tau is secreted by cortical neurons isolated from wild-type mice and by HeLa and PC12 cells overexpressing human Tau. Our results also indicated that autophagosomes would be involved in Tau secretion. Finally, we found that secreted Tau was dephosphorylated and cleaved compared to the non-secreted intracellular Tau.

Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) hold great promise in the fields of drug development and regenerative medicine. If iPSCs reprogrammed from patient cells replicate what is seen in vivo they may be used as a model of disease. A process that is disrupted in many neurodegenerative diseases is mitochondrial biogenesis. One of these diseases is amyotrophic lateral sclerosis (ALS), which is characterized by loss of motor neurons in the brain and spinal cord. Differentiation of hPSCs into motor neurons offers a way to study a previous unavailable cell type and may further our understanding of human motor neuron biology. The aims of the present study were to differentiate motor neurons from hESCs and iPSCs in low oxygen conditions and to explore mitochondrial biogenesis and electrical maturation during this process. After three weeks of treatment with retinoic acid and purmorphamine, a sonic hedgehog agonist, cells increased expression of post mitotic spinal motor neuron markers. One week later electrophysiological analysis revealed voltage-gated currents and action potential generation. Mitochondrial biogenesis signaling and expression of respiratory chain proteins increased with motor neuron differentiation. Respiration analysis revealed a decrease in glycolysis in motor neurons compared to neural stem cells. Interestingly, this was not accompanied by an increase in basal respiration or mitochondrial mass. These findings enhance our understanding of motor neuron mitochondrial biogenesis, a process impaired in ALS.

Tonic arterial smooth muscle can produce strong contractions indefinitely by formation of slowly cycling crossbridges (latchbridges) that maintain force at a high energy economy. To fully understand the uniqueness of mechanisms regulating tonic arterial contraction, comparisons have been made to phasic visceral smooth muscles that do not sustain high forces. This study explored mechanisms of force maintenance in a phasic artery by comparing KCl-induced contractions in the tonic, femoral artery (FA) and its primary branch, the phasic saphenous artery (SA). KCl rapidly (5 N/m2) and [ca2+]i (250 nM) in FA and SA. By 10 min, [ca2+]i declined to 175 nM in both tissues but stress was sustained in FA (1.3 x 105N/m2) and reduced by 40% in SA (0.8 x l05 N/m2). Reduced tonic stress correlated with reduced myosin light chain (MLC) phosphorylation in SA (28% vs. 42% in FA). SA expressed more MLC phosphatase than FA, and permeabilized (β-escin) SA relaxed more rapidly than FA in the presence of MLC kinase blockade, suggesting that MLC phosphatase activity in SA was greater than that in FA. The reduction in MLC phosphorylation in SA was insufficient to account for reduced tonic force (latchbridge model), and SA expressed more "fast" myosin isoforms than did FA. Cytochalasin-D reduced force-maintenance more in FA than SA. These data support the hypothesis that strong force-maintenance is absent in SA because expressed motor proteins do not support latchbridge formation, and because actin polymerization is not stimulated.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.