Combining the nematode Caenorhabditis elegans with novel microfluidic technology has produced a phenotypic movement assay that is at once rapid, sensitive, and low-cost. The method is based on the neurophysiologic phenomenon of worms exhibiting robust, continuous, directed locomotion in response to mild electric fields inside a microchannel. As we demonstrate with the studies reported herein, our microfluidic electrotaxis platform is a unique tool for studying the effects of environmental and genetic manipulations on C. elegans’ movement behaviour, which in turn indicates the state of the organism’s neuronal and muscular systems. In one initiative to develop an inexpensive biosensor, we use the setup to measure the response of worms to common environmental pollutants. Results indicate that worms’ electrotactic swimming behaviour is particularly susceptible to metal salts. A comparison with traditional assays measuring fecundity, growth, and lifespan reveals that electrotactic speed shows a comparable level of sensitivity as a toxicity endpoint. Another study demonstrates that worms expressing a mutant form of α-synuclein, a familial Parkinson’s disease-related protein, show deficits in electrotactic swimming speed that coincide with dopaminergic neuron damage. We further show that both the electrotaxis and neuronal phenotypes can be ameliorated by treatment with curcumin, a putative neuroprotective agent. We have also used the platform to investigate the effects of other environmental and genetic stresses on electrotactic behaviour. Our findings indicate that the response can withstand many different insults but is affected by stresses that induce the mitochondrial and ER unfolded protein responses, which themselves play roles in preserving electrotactic swimming behaviour alongside the heat shock response. These data expand our knowledge of how the motor output component of C. elegans’ electrotactic response is perturbed by environmental and genetic manipulations, and also support the utility of microfluidic electrotaxis as a functional output of nematode locomotory circuits in a multitude of contexts. / Thesis / Doctor of Science (PhD)

Cholera toxin (CT) is a bacterial protein toxin responsible for the gastrointestinal disease known as cholera. CT stimulates its own entry into intestinal cells after binding to cell surface receptors. Once internalized, CT is delivered via vesicle-mediated transport to the endoplasmic reticulum (ER), where the CTA1 subunit dissociates from the rest of the toxin and is exported (or translocated) into the cytosol. CTA1 translocates from the ER lumen into the host cytosol by exploiting a host quality control mechanism called ER-associated degradation (ERAD) that facilitates the translocation of misfolded proteins into the cytosol for degradation. Cytosolic CTA1, however, escapes this fate and is then free to activate its target, heterotrimeric G-protein subunit alpha (Gsα), leading to adenlyate cyclase (AC) hyperactivation and increased cAMP concentrations. This causes the secretion of chloride ions and water into the intestinal lumen. The result is severe diarrhea and dehydration which are the major symptoms of cholera. CTA1’s ability to exploit vesicle-mediated transport and ERAD for cytosolic entry demonstrates a potential link between cholera intoxication and a separate quality control mechanism called the unfolded protein response (UPR), which up-regulates vesicle-mediated transport and ERAD during ER stress. Other toxins in the same family such as ricin and Shiga toxin were shown to regulate the UPR, resulting in enhanced intoxication. Here, we show UPR activation by CT, which coincides with a marked increase in cytosolic CTA1 after 4 hours of toxin exposure. Drug induced-UPR activation also increases CTA1 delivery to the cytosol and increases cAMP concentrations during intoxication. We investigated whether CT stimulated UPR activation through Gsα or AC. Chemical activation of Gsα induced the UPR and increased CTA1 delivery to the cytosol. However, AC activation did iv not increase cytosolic CTA1 nor did it activate the UPR. These data provide further insight into the molecular mechanisms that cause cholera intoxication and suggest a novel role for Gsα during intoxication, which is UPR activation via an AC-independent mechanism

<p> Cellular cholesterol homeostasis is a fundamental and highly regulated process. Transcription factors known as sterol regulatory element binding proteins (SREBP) are responsible for the expression of many genes involved in the uptake and biosynthesis of cholesterol. SREBP activation and lipid dysregulation has been associated with cellular endoplasmic reticulum (ER) stress and the activation of the unfolded protein response (UPR). Our lab has previously reported a relationship between ER stress and SREBP activation causing lipid dysregulation and hepatic steatosis. This project was designed to elucidate the mechanism of ER stress-induced SREBP activation and determine its relationship with cellular pathologies associated with ER stress and lipid accumulation. My research has examined the mechanism by which ER stress activates SREBP-2 in various cell lines, including epithelial and macrophage cells. This research revealed that (1) ER stress-induced SREBP-2 activation is not dependent on caspases and occurs through the conventional sterol-mediated proteolytic pathway; (2) the mechanism of ER stress-induced SREBP-2 activation is sensitive to changes in ER calcium; (3) ER stress is associated with SREBP-2 activation and lipid dysregulation in a model of renal injury; and ( 4) ER stress-induced SREBP activation in vitro is not associated with lipid accumulation in macrophage foam cells. </P> <p> This project has also offered me the opportunity to further enhance our understanding of the mechanism by which ER stress causes SREBP activation in a sterolindependent manner. </P> / Thesis / Doctor of Philosophy (PhD)

<p>Atherosclerosis is a chronic inflammatory disease of the arterial wall and is the primary cause of coronary artery disease, the most common cause of death in western societies. Risk factors for cardiovascular disease include dyslipidemia, diabetes, smoking, and obesity. These risk factors have also been shown to promote vascular endoplasmic reticulum (ER) stress; a cellular response characterized by the accumulation of misfolded proteins in the ER. Thickening and decreased stability of arterial plaque can lead to thrombosis and subsequent clinical complications of myocardial infarction and stroke. However, the exact mechanisms that lead to the development of atherosclerosis remain unclear. Here we show that inhibition, as well as a deficiency of glycogen synthase kinase (GSK)-3α, can protect against accelerated atherosclerosis in a low-density lipoprotein receptor (LDLR) knockout mouse model. Compared to LDLR^-/- controls, mice deficient in GSK-3α showed a decrease in lesion volume in the aortic root as well as protection against diet-induced hepatic steatosis. In addition, necrotic core volume was significantly reduced in LDLR^-/-GSK-3α^-/- mice compared to controls, a characteristic indicative of advanced plaque formation. Furthermore, hepatic and vascular ER stress levels were unaffected by the deletion of GSK-3α, a result that is consistent with the hypothesis that GSK-3α functions downstream of ER stress. Macrophages isolated from GSK-3α deficient mice had a reduction in unesterified cholesterol accumulation as well as a significant increase in the expression of the anti-inflammatory cytokine IL-10. Finally, BMT experiments showed a significant decrease in plaque size in the aortic sinus of LDLR^-/-GSK-3α^+/+ mice transplanted with GSK-3α deficient bone marrow. These results demonstrate a possible link between ER stress-induced activation of GSK-3α and the downstream effects leading to atherogenic initiation and progression.</p> / Master of Science (MSc)

<p>Introduction: Mitochondrial dysfunction and oxidative stress increase with aging and may contribute to age-associated muscle atrophy (sarcopenia). Resistance exercise (RE) can promote the accretion of muscle mass, increase strength, and ultimately improve function in the elderly. Such beneficial effects are thought to be mitigated solely by increased muscle mass and strength; however, the contribution of the mitochondria to the beneficial effects of RE in aging have not been thoroughly characterized. While mitochondrial benefits have been established separately in both young and aged adults following chronic RE, the acute effects have not been well characterized. Methods: Sedentary young and aged adult males completed either an acute bout of fatiguing RE or endurance exercise (EE), and muscle biopsies were obtained at 3, 24 and 48 h post- exercise depending on the study. Results: Despite equivalent lean-body mass, increased age was associated with elevated mtDNA deletions, indicating potential for mitochondrial dysfunction. RE was associated with reduced mitochondrial content (transcripts, protein, and mtDNA copy number) at 48 h post-exercise, a response that did not differ with increasing age. Paradoxically, reduced mitochondrial content occurred alongside elevated total peroxisome proliferator-activated receptor γ coactivator one α (PGC-1α) mRNA; however, RE altered only the PGC-1α4 isoform post-exercise, a transcript that regulates myostatin and insulin-like growth factor one (IGF1) signalling and ultimately muscle hypertrophy and not mitochondrial adaptations. In addition, PGC-1α modulates the unfolded protein response (UPR), and RE was subsequently shown to elevate endoplasmic reticulum stress and elicit the UPR. Conclusion: PGC-1α mRNA increases regardless of exercise mode; however, differential expression or regulation of alternate PGC-1α isoforms or transcriptional binding partners co-activated by PGC-1α may dictate the specific phenotypic adaptations that occur following divergent modes of exercise. Furthermore, RE acutely decreases mitochondrial content despite elevated PGC-1α mRNA, and this response is not influenced by age.</p> / Doctor of Philosophy (Medical Science)

Tissue fibrosis occurs in the advanced stages of various chronic diseases and can account for 45% of all deaths related to chronic diseases worldwide. The extracellular matrix (ECM) components comprising the fibrotic scar are primarily derived from myofibroblasts, which are contractile fibroblasts arising from the trans-differentiation of several cellular progenitors. Disturbances in immune cell infiltration and function could lead to the uncontrolled production of pro/anti-inflammatory mediators, which may alter the phenotype, state, and function of myofibroblasts progenitors, leading to aberrant wound repair and pathological fibrosis. A great deal of knowledge has implicated macrophages in the pathogenesis and exacerbation of the fibrotic process. Nonetheless, much remains to be elucidated on the potential mechanisms regulating macrophage accumulation and pro-fibrotic polarization, and whether these mechanisms can be further investigated to modulate tissue repair. The Endoplasmic reticulum (ER) stress has recently been implicated as a key mechanism that propagates the pathogenesis of the fibrotic process. How ER stress precisely impacts the fibrotic process is still unclear. This thesis partly explored how modulating the outcome of ER stress – the unfolded protein response (UPR), would affect the severity of lung fibrosis and addressed the role of IL-6 signalling in macrophages during fibrosis. The data demonstrated that UPR activation in pro-fibrotic macrophages and partial deficiency of Grp78, the master regulator of the UPR, abrogated pulmonary fibrotic changes and reduced the accumulation of pro-fibrotic (M2-like) macrophages. These findings were later associated with high TUNEL levels, 7AAD positive cells, Chop and cleaved caspase 3 levels, which are suggestive of GRP78 mediated apoptosis in this population. On the contrary, mice lacking a terminal UPR mediator of apoptosis, called Chop, had increased ECM deposition and greater persistence of non-apoptotic macrophages. These findings suggest that UPR-mediated macrophage polarization and apoptosis may alter lung wound repair processes. As IL-6 synergized the effect of IL-4 to promote a hyper M2 macrophage state, it provided a unique and compelling model to study the dynamics of macrophage alternative programming, which has set the stage to investigate whether the UPR was implicated in the generation of a hyper pro-fibrotic macrophage phenotype. This hyper M2 macrophage model led to the identification of ER expansion program and the IRE1-XBP1 arm of the UPR in pro-fibrotic macrophage polarization, and suggested an unprecedented in vivo role of IL-6 in priming macrophages in the injured lungs to possibly potentiate pathological wound repair. Looking forward, many questions remain to be answered in order to precisely identify the vital UPR axis regulating ER expansion in macrophages during pathological wound repair and to get closer to the understanding of whether the UPR modulates the pro-fibrotic/pro-resolving capacity of macrophages. Insights on these mechanisms may facilitate the development of therapeutics that better manage chronic fibrotic diseases which pose fatal consequences and increase public concern. / Thesis / Doctor of Philosophy (PhD)

The unfolded protein response (UPR) is composed of three highly conserved pathways (ATF6, IRE1, PERK). Cellular stressors induce protein misfolding and aggregation in the endoplasmic reticulum (ER). This signaling pathway maintains protein homeostasis when there is stress in the ER. When the UPR is activated, the eukaryotic initiation factor 2 alpha (eIF2α) becomes phosphorylated, which inhibits global mRNA translation. If ER stress remains chronically unmitigated, the UPR induces apoptosis. GADD34 and CReP shift in expression when the UPR is activated and work as phosphatases and dephosphorylate eIF2α in a feedback loop, allowing protein synthesis to resume. Several human diseases, including fatty liver disease (FLD) are affected by cell stress from improper protein folding and accumulation, making the UPR a therapeutic target. Previous studies have indicated the UPR to both cause or become activated by FLD, depending on the duration of cellular stress. At least 25% of humans worldwide have steatosis, and zebrafish are a powerful model organism for FLD studies. Their embryos are easily obtained, and the liver develops quickly in their transparent larvae, which allows us to visualize the development of fat in the liver. It is unknown how exactly the UPR is involved in inducing lipogenesis in hepatocytes. We sought to better understand the link between UPR activation and steatosis. Pharmacological treatments with various drugs, some of which induce ER stress, were administered over different durations in zebrafish embryos and subsequently the expression of UPR network and lipogenesis genes were quantified through RT-qPCR. To visualize whether these drugs induced steatosis, zebrafish livers were stained with Oil Red O and imaged. Our results indicate that all chronic durations of pharmacological treatments resulted in fatty liver, and the expression of atf6 decreased in response to treatment that prevents the dephosphorylation of eIF2α. This data provides insight pertaining to the activity of the UPR network during FLD in zebrafish models.

Le stress du Réticulum Endoplasmique (RE) est impliqué dans la physiopathologie des maladies rénales, et la réponse UPR (Unfolded Protein Response), qui est activée en réponse à ce stress, joue un rôle important dans l'homéostasie des cellules tubulaires rénales et des podocytes. L’étude des mécanismes moléculaires et des conséquences de l'activation de cette voie est donc importante dans la compréhension de la physiopathologie des maladies rénales et dans la caractérisation de biomarqueurs de lésions évolutives. L’Angiogénine (ANG, appelée également RNase 5) est une ribonucléase secrétée, qui est impliquée dans la réponse à certains stress cellulaires, et permet une adaptation cellulaire et tissulaire.
L'objectif de ce travail a été de mettre en évidence les mécanismes de régulation et les fonctions biologiques de l'ANG en réponse au stress du RE. A partir d'un modèle de cellules tubulaires rénales humaines en culture, nous avons montré que le stress du RE induisait l’expression de l’Angiogénine ainsi que sa sécrétion. Cette observation a été également faite sur différents modèles murins de lésions rénales. Le facteur transcriptionel sXBP1, activé par le transducteur de la réponse UPR, IRE1a, est directement impliqué dans la régulation de l'expression de l'Angiogénine.
Nous avons mis en évidence que l'Angiogénine participait à l’inhibition de la traduction protéique en réponse au stress du RE en produisant des fragments d'ARN de transfert appelés tiRNAs (stress-induced tRNA fragments) qui répriment la traduction des protéines en interférant avec le complexe initiateur de la traduction. L'Angiogénine favorise la survie cellulaire en réduisant l'apoptose induite par le stress du RE, et des souris invalidées pour le gène codant l'Angiogénine sont plus sensibles aux lésions de nécrose tubulaire aigues induites par la Tunicamycine. Outre les propriétés cellulaires "intrinsèques" de l'Angiogénine, nous avons également caractérisé les mécanismes de sécrétion de l'Angiogénine par l'épithélium rénal en situation de stress du RE. La sécrétion épithéliale de l'Angiogénine est sous le contrôle des facteurs transcriptionnels NF-κB et sXBP1, et se produit sous un mode conventionnel, c’est-à-dire dépendant du transit par l'appareil de Golgi. A ce titre, la régulation de l'Angiogénine est similaire à celle de l'Interleukine 6. L'Angiogénine induit une polarisation des macrophages vers un phénotype pro-inflammatoire. Enfin, considérant que l'Angiogénine est secrétée par l'épithélium rénal en situation de stress, nous avons montré que l’Angiogénine peut être un marqueur non invasif de souffrance rénale. L'Angiogénine peut être quantifiée dans les urines de patients porteurs de maladies rénales, et sa concentration est corrélée à la concentration urinaire de Retinol Binding Protein (une protéine de petit poids moléculaire, marqueur de dysfonction tubulaire), mais pas avec celle de l'Albumine. En outre, la concentration urinaire d'Angiogénine est significativement plus élevée dans les urines de patients transplantés rénaux dont la biopsie rénale met en évidence des lésions de tubulite (rejet aigu cellulaire et néphropathie associée au BK virus) que dans les urines de patients indemnes de lésions tubulaires (rejet humoral, ou absence de lésions histologiques). Nous avons mis en évidence par immuno-histochimie un marquage nucléaire du facteur transcriptionnel sXBP1 dans les tubules de reins porteurs de lésions de tubulite, suggérant un lien potentiel entre sécrétion d'Angiogénine et activation du facteur transcriptionnel sXBP1 dans un environnement inflammatoire. En conclusion, nous avons intégré la régulation l'Angiogénine dans la réponse épithéliale rénale au stress du RE, et caractérisé ses fonctions biologiques intracellulaires et paracrines. Notre travail a identifié l'Angiogénine urinaire en étant que potentiel marqueur de lésions rénales tubulaires. / The Endoplasmic Reticulum (ER) stress is involved in the pathophysiology of renal diseases ; the UPR (Unfolded Protein Response), which is activated in response to that stress plays an important role in renal tubular cells and podocytes homeostasis and consequently in tissu homeostasis. Understanding the molecular mechanisms and the consequences of the activation of this pathway is important to characterize the pathophysiology of renal diseases and identification of biomarkers of ongoing lesions. Angiogenin (ANG, also known as RNase 5) is a secreted ribonuclease, which is involved in the cellular stress response, it allows cell and tissue adaptation. The goal of this work was to clarify and identify the mechanisms regulating Angiogenin’s expression and its biological functions during ER stress. Using a human renal tubular cell line, we have shown that ER stress induces the expression of angiogenin and its secretion. This observation was also made on several murine models of renal injury. The transcriptional factor sXBP1 activated by the UPR transducer, IRE1α, is directly involved in regulating the expression of angiogenin. We have shown that angiogenin participates in the inhibition of protein translation in response to ER stress by cleaving transfer RNA and generating tiRNAs (stress-induced tRNA fragments) that suppress protein translation by interfering with the translation initiation complex. Angiogenin promotes cell survival by reducing ER stress-induced apoptosis, ANG knockout mice are more sensitive to acute tubular necrotic lesions induced by tunicamycin. In addition to the cell-autonomous effects of angiogenin, we also characterized the mechanisms by which Angiogenin is secreted by the renal epithelium under ER stress. Angiogenin is secreted in a conventional manner under the control of the transcriptional factors NF-kB and sXBP1. As such, the regulation of angiogenin is similar to Interleukin-6. We also demonstrated that Angiogenin induces macrophage polarization to a pro-inflammatory phenotype. Finally, considering that angiogenin is secreted by the renal epithelium under stress, we have shown that angiogenin may be a noninvasive marker of kidney injury. Angiogenin can be quantified in the urine of patients with kidney disease, its urinary concentration is correlated to the urinary concentration of Retinol Binding Protein (a low molecular weight protein marker of tubular dysfunction), but not with that of Albumin . In addition, the urinary concentration of angiogenin is significantly higher in the urine of renal transplant patients whose renal biopsy highlights tubulitis lesions (cell acute rejection and BK virus associated nephropathy) than in the urine of patients without histological tubular damage (antibody-mediated rejection, or no visible histological lesions). We have demonstrated by immuno-histochemistry a tubular nuclear localization of the activated transcriptional factor sXBP1 in the biopsies of patients with high tubulitis score, suggesting a potential relationship between the secretion of Angiogenin and the activation of transcriptional factor sXBP1 within an inflammatory environment. To conclude, we have described Angiogenin as a new mediator of the integrated ER stress response, and characterized its cell- and non-cell-autonomous biological functions. Our study have identified urinary angiogenin as a potential marker of ongoing kidney tubular injuries.

Les connaissances actuelles en pathologie hépatique suggèrent que HCV n'est pas directement oncogénique mais expose les patients au risque de cancer du foie dans un contexte inflammatoire associé à une réponse UPR (Unfolded Protein Response) et une régénération hépatique. La nétrine-1, le ligand canonique de la famille des DRs (Récepteurs à dépendance), est une protéine anti-apoptotique impliquée dans le développement, l'inflammation et la tumorigenèse. Les DRs induisent l'apoptose en absence de leurs ligands. A ce jour, il n'existe aucune donnée reliant le concept de DR et les virus oncogènes. Au cours de ma thèse, j'ai contribué à démontrer que la fonctionnalité des DRs était altérée au cours de l'infection par HCV in vitro et in vivo. Nous avons montré que la surexpression de la nétrine-1 augmente l'infectivité des virions et promeut leur entrée via l'activation et la diminution du recyclage de l'EGFR. De son coté, HCV augmente l'expression de la nétrine-1 suite à l'activation de l'épissage de son ARN pré-messager. Nous avons aussi montré que l'expression du récepteur à la nétrine-1, UNC5A, était diminuée au cours de l'infection suite à des diminutions transcriptionnelle et traductionnelle. Dans ce cadre, la nétrine-1 joue le rôle de facteur proviral en inhibant une potentielle voie de signalisation antivirale induite par le récepteur UNC5A non lié. Nous avons ensuite voulu savoir quelles conséquences cette surexpression de nétrine-1 pourrait avoir en physiopathologie hépatique en contexte non infectieux. Un stress du RE (Réticulum Endoplasmique) est observé au cours de l'infection par HCV. Le stress du RE entraîne l'activation de la réponse UPR qui induit l'apoptose médiée par la DAPK1 en cas de stress prolongé. Le fait que le récepteur UNC5B active aussi l'apoptose via l'activation de la DAPK1 nous a conduit à étudier l'implication de la nétrine-1 dans la survie cellulaire au cours de la réponse UPR en contexte hépatique. Nous avons démontré à la fois in vitro et in vivo que l'expression de la nétrine-1 pourrait protéger les cellules contre l'apoptose induite par la réponse UPR suite à sa liaison aux récepteurs UNC5A et C qui entraîne l'inhibition de la DAPK1. De nombreuses études ont également reporté des rôles de la nétrine-1 dans l'inflammation et la néoangiogenèse. Nous avons montré que la nétrine-1 inhibe la migration transendothéliale hépatique des PBMCs (Peripheral Blood Mononucleated Cells) et accélère la tubulogenèse des cellules endothéliales intrasinusoïdales hépatiques. Dans leur ensemble, mes travaux de thèse suggèrent que la nétrine-1 via ses récepteurs UNC5s joue des rôles délétères en pathophysiologie hépatique favorables à la persistance virale et à la résistance à la mort cellulaire / Current knowledge in hepatic pathology suggests that HCV is not directly oncogenic but puts patients at risk for liver cancer in a context associated with a chronic inflammation, UPR (Unfolded Protein Response) and liver regeneration. Netrin-1, the canonical ligand of the DR (Dependence Receptor) family, is an antiapoptotic secreted factor implicated in development, cancer and cancer-associated inflammatory diseases. DRs induce cell death when unbound. No data linking the DR system to oncogenic viruses are available to date. During the first part of my PhD, I contributed to demonstrate that HCV infection alters DR functionality both in vitro and in vivo. We found that Netrin-1 conditions HCV virion infectivity and promotes virion entry by increasing the activation and decreasing the recycling of the EGFR. In turn, HCV increases Netrin-1 expression through enhanced Netrin-1 pre-mRNA splicing. The Netrin-1 UNC5A receptor expression was decreased upon HCV infection through diminished transcription and translation. In this setting, Netrin-1 acts as a proviral factor by inhibiting a putative antiviral signaling pathway conveyed by the unbound UNC5A receptor. In this context, we wanted to determine what consequences such Netrin-1 up-regulation could induce in non-infectious hepatic pathophysiology. Chronic ER (endoplasmic reticulum) stress is observed during HCV infection. ER stress leads to UPR activation which triggers apoptosis via DAPK1 activation upon prolonged stress. The fact that the UNC5B receptor induces apoptosis through DAPK1 activation led us to investigate Netrin-1 implication in cell survival upon UPR in the liver. During the second part of my PhD, I have demonstrated both in vitro and in vivo in mice that Netrin-1 translation during UPR could protect cells against UPR-related cell death after binding to UNC5A and C, in a DAPK1-mediated fashion. Several studies have also identified Netrin-1 roles in inflammation and neo-angiogenesis. We found that Netrin-1 inhibits hepatic transendothelial migration of PBMCs (Peripheral Blood Mononucleated Cells) and accelerates tubulogenesis of liver sinusoidal endothelial cells. Netrin-1’s role in a hepatic inflammation and neoangiogenesis, both events being tightly associated with viral hepatitis, remains to be thoroughly elucidated. Altogether, our results suggest that Netrin-1 plays UNC5-dependent deleterious roles in hepatic pathophysiology, leading to viral persistence as well as resistance to cell death

Pancreatic beta-cells are responsible for secreting insulin into the circulation to maintain whole body glucose homeostasis. While pancreatic beta-cells have a large capacity to secrete insulin, their function progressively deteriorates during the pathogenesis of type 2 diabetes as a result of both genetic predisposition and environmental factors. Obesity is the largest risk factor for developing type 2 diabetes and is associated with various conditions that can impair normal beta-cell function, including excess free fatty acids, inflammation and insulin resistance. Accumulating evidence in the literature suggests that endoplasmic reticulum (ER) stress contributes to the molecular mechanism of pancreatic beta-cell failure during the progression of type 2 diabetes. In this thesis, I have examined the role of the ER stress sensor ATF6-alpha and also the ER-resident chaperone GRP78 in pancreatic beta-cell homeostasis and function. Work presented in Chapter 2 examined the function of naturally occurring ATF6-alpha protein variants associated with type 2 diabetes. I also examined the role of endogenous ATF6-alpha in pancreatic beta-cells, which is described in Chapter 3. Results from these analyses suggest that the ATF6-alpha gene is not a type 2 diabetes susceptibility gene; however, ATF6-alpha protein expression is important to beta-cell function and survival. Finally, ER stress markers have been detected in pancreatic beta-cells and insulin sensitive tissues (such as adipose and liver), which promote beta-cell dysfunction and insulin resistance, respectively. In Chapter 4, I examined the contribution of ER stress in beta-cell dysfunction specifically by generating transgenic mice over-expressing GRP78. The mice were subsequently challenged by high fat diet to determine their susceptibility to developing symptoms of type 2 diabetes. Indeed increased chaperone capacity in pancreatic beta-cells protected against obesity-induced glucose intolerance and insulin resistance. Overall, these data support the hypothesis that ER stress contributes to beta-cell dysfunction in type 2 diabetes progression.