Mondialement, le cancer du sein est celui le plus fréquent et mortel chez les femmes. Malgré un programme de dépistage national et de nouveaux traitements, le taux de rechute demeure haut. Ceci illustre le besoin de nouvelles thérapies. Même dans un pays industrialisé comme le Canada, ce cancer est toujours le deuxième plus mortel chez les femmes. Nos travaux précédents ont identifié PACE4, un membre de la famille des proprotéines convertases (PCs), comme étant une nouvelle cible thérapeutique dans le cancer de la prostate. Dans cette étude, nous avons vérifié si PACE4 pourrait aussi être une cible dans le cancer du sein. À l’aide d’échantillons clinique de cancer du sein, nous avons premièrement démontré que PACE4 est spécifiquement surexprimé dans le sous-type moléculaire positif aux récepteurs hormonaux. Par la suite, nous avons sélectionné une lignée cellulaire pour poursuivre nos expériences. Nous avons choisi la lignée de cancer du sein ZR-75-1 parce qu’elle provient du sous-type positif aux récepteurs hormonaux et qu’elle exprime PACE4. En culture cellulaire, nous avons comparé la croissance de cellules ZR-75-1 modifiées qui sous-exprimaient furine, PACE4 ou PC7. Lors de ces expériences, PACE4 était la seule PC importante pour la prolifération cellulaire. L’importance de PACE4 pour la croissance tumorale a aussi été confirmée in vivo à l’aide d’un modèle de xénogreffes de cellules ZR-75-1 chez des souris immunosupprimées. Les inhibiteurs peptidiques spécifiques à PACE4 C23 et Multi-Leu (ML) ont aussi été testés en culture cellulaire où ils étaient en mesure de diminuer la prolifération des cellules ZR-75-1 et MCF-7. Nous avons aussi démontré, à l’aide d’un peptide ML radiomarqué, que l’expression de PACE4 est nécessaire pour que les peptides inhibiteurs pénètrent dans la cellule. De plus, le peptide C23, lorsqu’administré systémiquement à des souris immunosupprimées portant des tumeurs de cancer du sein, était en mesure de diminuer la croissance tumorale. De manière intéressante, les tumeurs sous-exprimant PACE4 et celles traitées avec le peptide C23 démontraient un ralentissement de la croissance tumorale similaire. De plus, lorsque ces tumeurs ont été analysées en immunohistochimie, elles possédaient une diminution du marqueur de prolifération Ki67 et une augmentation de cellules positives aux marqueurs d’arrêt du cycle cellulaire p27KIP1 et p21Waf1/Cip1 comparativement aux tumeurs contrôles. Pour conclure, la sous-expression de PACE4 et l’administration systémique d’un inhibiteur de PACE4 en culture cellulaire ainsi que dans un modèle de xénogreffe résultent en une diminution de la prolifération néoplasique. Nos résultats suggèrent que PACE4 est une cible intéressante dans le cancer du sein positif aux récepteurs hormonaux. / Abstract: Breast cancer is the most frequent and deadly malignancy in women worldwide. Despite national screening prog rams combined with new treatments relapse rate remain high and new therapies are needed. Even in industrialized country like Canada, it is still the second most deadly cancer in women. From previous work, we identified PACE4, a member of the proprotein convertases (PCs) family of endoproteases, as a novel therapeutic target in prostate cancer. In the present study, we examined whether PACE4 could also be a potential target in breast cancer. In clinical samples of breast adenocarcinoma, we observed a specific overexpression of PACE4 in the estrogen-receptor-positive (ER+) subtype. We therefore looked for a breast cancer cell line model which would be representative and thus focused on ZR-75-1 since it both expresses PACE4 and is estrogen-receptor-positive. We compared stable knockdowns of furin, PACE4 and PC7 in the estrogen-receptor-positive cell line ZR-75-1 to evaluate their respective contribution to cell growth and tumor progression. PACE4 was found to be the only PC displaying a decrease in cell growth. The impact of PACE4 on tumor growth was also confirmed in vivo with xenograft of the ZR-75-1 cell line in athymic nude mice. PACE4 specific peptide-based inhibitors (C23 and Multi-Leu) were tested and shown to decrease prolife ration of ZR-75-1 cells in cell-based assays. We also confirmed that PACE4 expression was necessary for its specific peptide-based inhibitors to penetrates in the cell using a radiolabeled Multi-Leu peptide. Moreover, the systemic administration of C23 had a potent effect on tumor growth on xenografts of the ZR-75-1 cell line. Interestingly, PACE4-silencing and systemic administration of the PACE4 inhibitor C23 resulted in similar slowed tumor growth in vivo. Furthermore, these tumors demonstrated lower Ki67 proliferative indices with increased cell quiescence assessed with p27 KIP1 and p21 Waf1/Cip1 biomarkers. To conclude, PACE4-silencing and systemic administration of a PACE4 inhibitor result in hindered tumor progression and slower cellular proliferation. Our results suggest that PACE4 is a promising target for estrogen-receptor-positive breast cancer.

Le cancer du poumon est la principale cause de mortalité par cancer au Canada et entraîne un taux de mortalité important chez les patients. En effet, l’Organisation Mondiale de la Santé (OMS) indique que le cancer du poumon est la principale cause de décès liés au cancer dans le monde, avec 2.21 millions de diagnostics par année qui conduisent en moyenne à 1.8 millions de décès par an. Initialement asymptomatique, ce cancer évolue rapidement, devenant très invasif et métastatique, et est alors responsable de plus de morts par an que ces quatre cancers meurtriers combinés : côlon, sein, prostate et pancréas. Les Proprotéines Convertases (PCs) sont une famille de 9 sérines protéases qui jouent un rôle dans la maturation des précurseurs de protéines. Les PCs activent/désactivent ces précurseurs en les clivant à un unique ou une paire de résidus d’acides aminés et sont ainsi essentiels pour divers processus biologiques, tels que l’activation de facteurs de croissance qui jouent un rôle vital dans la transformation cellulaire et les risques de formation de tumeurs. Parmi les neufs membres des sérines protéases identifiées, les rôles physiologiques du septième membre de la famille, PC7, restent encore largement méconnus à ce jour. Afin d'identifier davantage de substrats de PC7, un criblage protéomique quantitatif a été réalisé pour l'enrichissement sélectif de polypeptides Nglycosylés, sécrétés par les cellules hépatiques HuH7. Deux protéines transmembranaires de type II clivées par PC7/Furine, et sécrétées sous forme soluble, ont alors été identifiées : CAncer Susceptibility Candidate 4 (CASC4) and Golgi PhosphoProtein de 130 kDa (GPP130). Des études ultérieures menées sur CASC4 par iii notre laboratoire ont mis en évidence son rôle protecteur contre la migration et l'invasion du Cancer du Sein Triple Négatif. GPP130 est une protéine transmembranaire de type II avec un domaine luminal contenant des déterminants endosomaux et de récupération du Golgi, lui offrant une voie de trafic cellulaire unique. Jusqu'à présent, le rôle de GPP130 a principalement été étudié dans la liaison et le trafic rétrograde des Shiga-toxines. Un récent rapport a cependant aussi montré son implication dans la progression du cycle cellulaire et dans la prolifération des cellules du cancer de la tête et du cou. Ainsi, notre analyse du cBioPortal pour Cancer Genomics a révélé que GPP130 est amplifié jusqu'à 35% chez les patients atteints de cancer du poumon. Le travail présenté ici montre les implications du clivage de GPP130 par PC7 et Furine dans la progression du cancer du poumon, en identifiant la région de GPP130 responsable de la croissance cellulaire. Ce projet dévoile ainsi des stratégies thérapeutiques potentielles ciblant la prolifération cellulaire induite par GPP130. / Lung Cancer is the leading cause of cancer death in Canada and causes significant morbidity in patients. Globally, World Health Organization (WHO) reports lung cancer as the leading cause of cancer-related deaths, with 2.21 million diagnoses/year, resulting in approximately 1.8 million deaths/year. Initially asymptomatic, it progresses to a highly invasive and quickly metastasizing cancer. It is responsible for more deaths per year than the combined death of the four deadly cancers: colon, breast, prostate, and pancreas. Proprotein Convertases (PCs) are a family of nine serine proteases that play a role in the maturation of secretory precursor proteins. Basic amino acid-specific PCs activate/inactivate precursor proteins by cleaving them at single or paired basic aminoacid residues. They are crucial for various biological processes, including the activation of growth factors that play a vital role in cellular transformation and the likelihood of tumor formation. Of the nine serine proteases identified, the physiological functions of the seventh member of the family, PC7, currently remain mostly unidentified. To further identify novel PC7 substrates, a quantitative proteomics screen for selective enrichment of N-glycosylated polypeptides, secreted from hepatic HuH7 cells, was performed. This identified two type-II transmembrane proteins, which were shed into soluble secreted forms by PC7/Furin: CAncer Susceptibility Candidate 4 (CASC4) and Golgi PhosphoProtein of 130 kDa (GPP130). Subsequent studies on CASC4 by our laboratory reported the protective role that CASC4 plays against migration and invasion in Triple Negative Breast Cancer. v GPP130 is a type-II transmembrane protein with a luminal domain containing endosomal and Golgi-retrieval determinants enabling a unique subcellular trafficking route. So far, the role of GPP130 has only been extensively studied in the binding and retrograde trafficking of Shiga toxin. However, recent reports have shown its implication in cell-cycle progression and cellular proliferation of head and neck cancer cells. Our analysis from cBioPortal for Cancer Genomics revealed that GPP130 is amplified in up to 35% of patients with lung cancer. The work presented here shows the implications of shedding GPP130 by PC7 and Furin in lung cancer progression by identifying the region of GPP130 responsible for cellular growth and unravelling potential therapeutic strategies for GPP130-induced cellular proliferation.

Amyloid is defined as extracellular protein aggregates with a characteristic fibrillar ultra-structure, Congo red affinity and a unique x-ray diffraction pattern. At present, 25 different human amyloid fibril proteins have been identified, and amyloid aggregation is associated with pathological manifestations such as Alzheimer’s disease, spongiform encephalopathy and type 2 diabetes. Amyloid aggregation triggers apoptosis by incorporation of early oligomers in cellular membranes, causing influx of ions. Amyloid is the only visible pathological islet alteration in subjects with type 2 diabetes, and islet amyloid polypeptide (IAPP) is the major islet amyloid fibril component. IAPP is produced by beta-cells and co-localized with insulin in the secretory granules. Both peptides are synthesised as pro-molecules and undergo proteolytic cleavage by the prohormone convertase 1/3 and 2. Although IAPP is the main amyloid constituent, both proIAPP and proIAPP processing intermediates have been identified in islet amyloid. The aim of this thesis was to study the role of impaired processing of human proIAPP in early islet amyloidogenesis. Five cell lines with individual processing properties were transfected with human proIAPP and expression, aggregation and viability were studied. Cells unable to process proIAPP into IAPP or to process proIAPP at the N-terminal processing site accumulated intracellular amyloid-like aggregates and underwent apoptosis. Further, proIAPP immunoreactivity was detected in intracellular amyloid-like aggregates in betacells from transgenic mice expressing human IAPP and in transplanted human beta-cells. ProIAPP was hypothesized to act as a nidus for further islet amyloid deposition, and to investigate this theory, amyloid-like fibrils produced from recombinant IAPP, proIAPP and insulin C-peptide/A-chain were injected in the tail vein of transgenic mice expressing the gene for human IAPP. Pancreata were recovered after 10 months and analysed for the presence of amyloid. Both IAPP and proIAPP fibrils but not des-31,32 proinsulin fibrils, caused an increase in affected islets and also an increase of the amyloid amount. This finding demonstrates a seeding capacity of proIAPP on IAPP fibrillogenesis. IAPP has been known for some time to trigger apoptosis in cultured cells, and a novel method for real time detection of apoptosis in beta-cells was developed. Aggregation of recombinant proIAPP and proIAPP processing intermediates were concluded to be inducers of apoptosis as potent as IAPP fibril formation. From the results of this study, a scenario for initial islet amyloidogenesis is proposed. Initial amyloid formation occurs intracellularly as a result of alterations in beta-cell processing capacity. When the host cell undergoes apoptosis intracellular proIAPP amyloid becomes extracellular and can act as seed for further islet amyloid deposition.

The liver regulates inflammation during sepsis, and most liver functions are carried out by hepatocytes. Bacterial lipids, including lipopolysaccharide (LPS) and lipoteichoic acid (LTA), can be cleared by hepatocytes, but the underlying mechanisms are uncertain. Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates uptake of LPS by hepatocytes, but it is unknown whether LTA uptake is similarly regulated. Therefore, our objectives were to characterize the PCSK9-regulated pathway of bacterial lipid uptake by hepatocytes by identifying whether low-density lipoprotein (LDL) receptor (LDLR) and LDLR-related protein 1 (LRP1) are the target receptors, and by determining which lipoproteins are involved. To study this pathway, we assessed the uptake of fluorescently-labeled LPS or LTA by human HepG2 hepatocytes using flow cytometry. We pre-treated HepG2 cells with PCSK9, alone or in combination with anti-LDLR or anti-LRP1 antibodies, in order to identify the PCSK9-regulated receptors that are involved, and utilized media containing normal serum or lipoprotein-deficient serum to investigate the lipoprotein- dependence of this pathway. We also determined the roles of LDL and HDL in bacterial lipid uptake through a series of add-back experiments to lipoprotein-deficient serum, and blocked LDLR to confirm that LDLR mediates LDL-dependent uptake. The HepG2 cell response to variable degrees of bacterial lipid uptake was also assessed in a subset of experiments by measuring several cytokines and extracellular alanine aminotransferase (ALT) activity in the cell culture supernatant. We found that PCSK9 regulates LDLR-mediated uptake of both LPS and LTA through an LDL-dependent mechanism, while LRP1 is not involved. Increased bacterial lipid uptake did not result in any hepatocellular injury or cytokine production, as measured by ALT activity and interleukin (IL)-6, IL-8, IL-10, and IL-17 concentrations. In conclusion, we completed our objective of characterizing the PCSK9-regulated pathway of bacterial lipid uptake, and provide supporting evidence for targeting PCSK9 as a novel therapeutic avenue in sepsis. / Thesis / Master of Science (MSc) / Bacterial compounds stimulate inflammation that can be overwhelming during sepsis. Understanding the processes behind uptake and clearance of these compounds may lead to better sepsis treatments. Therefore, our goal was to understand how uptake of two bacterial compounds, lipopolysaccharide and lipoteichoic acid, occurs by liver cells called hepatocytes. Hepatocytes are naturally equipped to clear foreign compounds, so understanding their role in clearing bacterial compounds is important. Another goal was to identify the role of the protein PCSK9 in this uptake process, as treatments targeting PCSK9 could be applied to sepsis once we understand its role in this disease. Our research demonstrates the negative role of PCSK9 in regulating uptake of lipopolysaccharide and lipoteichoic acid through a lipoprotein receptor called LDLR, and identifies the role of lipoproteins in this process. These findings further our understanding of the hepatocyte response to bacterial compounds in relation to sepsis, and identify PCSK9 as a potential target for new sepsis therapies.

Les proprotéines convertases (PCs) sont des enzymes impliquées de nombreux processus pathologiques. Nous avons étudié deux substrats des PCs: l'apeline et la glycoprotéine B (gB) du virus d'Epstein Barr (EBV), et le rôle de cette maturation protéolytique dans la médiation de leurs fonctions. L'apeline est surexprimée dans plusieurs cancers dont le cancer colorectal (CCR), et nous avons montré que la furine, un membre des PCs, clive l’apeline. Pour déterminer le rôle de ce clivage dans le CCR métastatique, nous avons généré un mutant non clivable (apeline-DM). In vitro, ce mutant inhibe la croissance de cellules cancéreuses du côlonet ne les protège pas de l'apoptose, contrairement à l'apeline sauvage. In vivo, l'apeline-DM diminue drastiquement la croissance tumorale et la formation de métastases hépatiques chez la souris. Les mêmes résultats sont obtenus dans des modèles de souris déficientes pour l’apeline, démontrant l'intérêt d'utiliser l'apeline-DM ou des dérivés comme potentiels agents anticancéreux dans le traitement des CCR métastatiques. La gB du virus EBV, virus impliqué dans certains cancers lymphoïdes et épithéliaux chez l'homme, permet l'entrée du virus dans la cellule lors de l'infection. Nous avons montré que les PCs, et notamment la furine, clivent la gB. In vitro, l'induction de la protéine virale LMP1 augmente l'expression de la furine, qui se traduit par une augmentation de l'infection par EBV. Ces résultats suggèrent l'existence d'une boucle de régulation entre la furine et LMP1 permettant d'améliorer la propagation cellulaire du virus. L'utilisation d'inhibiteurs de l'activité des PCs permettrait donc de bloquer l'infection par EBV. / Proprotein convertases (PCs) are enzymes involved in many pathological processes. We have identified two novel substrates of the PCs: apelin and glycoprotein B (gB) of Epstein Barr Virus (EBV), and studied the role of PC-mediated proteolytic maturation in their functions. Apelin is overexpressed in some cancers including colorectal cancer (CRC), and we demonstrated that furin, one of the PCs member, cleaves apelin in two peptides. To determine the role of apelin cleavage by furin in the metastatic CRC, we generated a non-cleavable mutant (apelin-DM). This mutant inhibited the growth of colon cancer cells in vitro and could not protect against apoptosis, unlike the wild-type apelin. In vivo, apelin-DM drastically reduces tumor growth and the formation of hepatic metastases in mice. These results were confirmed in apelin deficient mouse models thus demonstrating the potential interest of using apelin-DM, or its derivatives, as anticancer agents in the treatment of metastatic CRC. The gB of EBV, a virus involved in some lymphoid and epithelial cancers in humans, is involved in the entry of the virus into the cell during infection. We have shown that PCs, especially furin, cleave gB. In vitro,induction of the LMP1 viral protein increases furin expression, which results in an increase in EBV infection. These results suggest the existence of a regulatory loop between furin and LMP1 to improve the cellular propagation of the virus. The use of inhibitors of PCs activity would thus block EBV infection, a virus against which there is no treatment nowadays.

Magister Pharmaceuticae - MPharm / Cardiovascular diseases (CVDs) such as ischaemic heart diseases, heart failure and stroke remain a major cause of death globally. Various deep-rooted factors influence CVD development; these include but are not limited to elevated blood lipids, high blood pressure, obesity and diabetes. A considerable number of proteins are involved directly and indirectly in the transport, maintenance and elimination of plasma lipids, including high and low-density lipoprotein cholesterol (HDL-C and LDL-C). There are several mechanisms involved in the removal of LDL particles from systemic circulation. One such mechanism is associated with the gene that encodes proprotein convertase subtilisin/kexin type 9 (PCSK9), which has become an exciting therapeutic target for the reduction of residual risk of CVDs. Currently, statins are the mainstay treatment to reduce LDL-C, and a need exists to further develop more effective LDL-C-lowering drugs that might supplement statins. This study was aimed at contributing to the generation of knowledge regarding the effect of niacin in reducing LDL levels through PCSK9 interaction. The aims/objectives of this study were achieved by utilizing two approaches, which included animal intervention with niacin followed by genetic screening of five prioritized genes involved in cholesterol synthesis and regulation. For animal intervention, 16 vervet monkeys were divided into two groups of eight animals consisting of a control and an experimental (niacin) group. The control group was given a normal standard diet of pre-cooked maize meal throughout the study, while the experimental group received the same diet supplemented with 100 mg/kg of niacin (SR) for 12 weeks. During the niacin intervention, blood was collected at baseline, every four weeks during the treatment period and the end of the washout period. The collected blood was used for biochemical analysis (total cholesterol, triglycerides, LDL-C, and HDL-C) and downstream genetic applications. The second phase included the screening of PCSK9, LDLR, SREBP-2, CETP and APOB-100 using genotyping and gene expression. Niacin administration produced statistically significant increases in plasma HDL-C at fourtime points (T1, T2, T3 and T4), which resulted in an overall increase in plasma HDL-C. Additionally, niacin administration resulted in a slight reduction in LDL-C and total cholesterol levels. Furthermore, the genotyping analysis revealed 13 sequence variants identified in PCSK9, LDLR, SREBP-2, CETP and APOB-100 genes. Five of these variants were predicted to be disease-causing and correlated with gene expression patterns. Three identified PCSK9 variants (H177N, R148S, G635G) were categorized as LOF mutations, and this was supported by a decline in gene expression in animals harbouring these variants. The LDLR also had LOF variants that were the reason for its decreased mRNA expression. Additionally, SREBP-2 proved to be a key mediator of cholesterol pathways. Therefore, the findings of the study conclusively suggest that niacin does increase HDL-C and decrease LDL-C and total cholesterol. Moreover, an interaction between niacin administration and PCSK9 was observed which resulted in decreased gene expression.

Oxidative stress is a cellular condition where cells are challenged by elevated levels of reactive oxygen species (ROS) that are produced endogenously or exogenously. ROS can damage vital cellular components, including lipid, protein, DNA and RNA. Oxidative damage to DNA often leads to cell death or mutagenesis, the underlying cause of various human disease states. Previously our laboratory discovered that human PC4 gene can prevent oxidative mutagenesis in the bacterium Escherichia coli and that the yeast homolog SUB1 has a conserved function in oxidation protection. In this thesis I examined the underlying mechanisms of PC4’s oxidation protection function. My initial efforts to examine the predicted role of SUB1 in transcription-coupled DNA repair essentially negated this hypothesis. Instead, results from our experiments suggest that PC4 and yeast SUB1 can directly protect genomic DNA from oxidative damage. While testing SUB1’s role in double strand DNA break (DSB) repair, I found the sub1Δ mutant resects DSB ends rapidly but still ligates chromosomal breaks effectively, suggesting that DSB resection is not inhibitory to nonhomologous end-joining, an important DSB repair pathway. Finally, in the course of studying transcription recovery after UV damage, I found UV induces a longer form of RPB2 mRNA and demonstrated that this is caused by alternative polyadenylation of the RPB2 mRNA and that alternative polyadenylation contributes to UV resistance. Based on results of preliminary experiments, I propose that UV activates an alternative RNA polymerase to transcribe RNA POL II mRNA, a novel mechanism to facilitate recovery from inhibition of transcription resulting from UV damage. The hypothetical polymerase switch may account for the UV-induced alternative polyadenylation of the RPB2 mRNA.

No description available.

Les maladies cardiovasculaires (MCV) demeurent au tournant de ce siècle la principale cause de mortalité dans le monde. Parmi les facteurs de risque, l’hypercholestérolémie et l’obésité abdominale sont directement liées au développement précoce de l’athérosclérose. L’hypercholestérolémie familiale, communément associée à une déficience des récepteurs des lipoprotéines de basse densité (LDLR), est connue comme cause de maladie précoce d’athérosclérose et de calcification aortique chez l’humain. La subtilisine convertase proprotéine/kexine du type 9 (PCSK9), membre de la famille des proprotéines convertases, est trouvée indirectement associée aux MCV par son implication dans la dégradation du LDLR. Chez l'humain, des mutations du gène PCSK9 conduisent soit à une hypercholestérolémie familiale, soit à une hypocholestérolémie, selon que la mutation entraîne un gain ou une perte de fonction, respectivement. Il demeure incertain si les individus porteurs de mutations causant un gain de fonction de la PCSK9 développeront une calcification aortique ou si des mutations entraînant une perte de fonction provoqueront une obésité abdominale. Dans cette étude, nous avons examiné : 1) l’effet d’une surexpression de PCSK9 dans le foie de souris sur la calcification aortique ; 2) les conséquences d’une déficience en PCSK9 (Pcsk9 KO), mimant une inhibition pharmacologique, sur le tissu graisseux. Nous avons utilisé un modèle de souris transgénique (Tg) surexprimant le cDNA de PCSK9 de souris dans les hépatocytes de souris et démontrons par tomographie calculée qu’une calcification survient de façon moins étendue chez les souris PCSK9 Tg que chez les souris déficientes en LDLR. Alors que le PCSK9 Tg et la déficience en LDLR causaient tous deux une hypercholestérolémie familiale, les niveaux seuls de cholestérol circulant ne parvenaient pas à prédire le degré de calcification aortique. Dans une seconde étude, nous utilisions des souris génétiquement manipulées dépourvues de PSCK9 et démontrons que l’accumulation de graisses viscérales (adipogenèse) apparaît régulée par la PCSK9 circulante. Ainsi, en l’absence de PCSK9, l’adipogenèse viscérale augmente vraisemblablement par régulation post-traductionnelle des récepteurs à lipoprotéines de très basse densité (VLDLR) dans le tissu adipeux. Ces deux modèles mettent en évidence un équilibre dynamique de la PCSK9 dans des voies métaboliques différentes, réalisant un élément clé dans la santé cardiovasculaire. Par conséquent, les essais d’investigations et d’altérations biologiques de la PCSK9 devraient être pris en compte dans un modèle animal valide utilisant une méthode sensible et en portant une attention prudente aux effets secondaires de toute intervention. / Cardiovascular disease (CVD) is the leading cause of death in the 21st century. Among risk factors, hypercholesterolemia and abdominal obesity are directly linked to premature development of atherosclerosis. Familial hypercholesterolemia, commonly due to low-density lipoprotein receptor (LDLR) deficiency, is known to cause premature atherosclerosis and aortic calcification in humans. Proprotein convertase subtilisin/kexin 9 (PCSK9), a member of the proprotein convertase family, is indirectly associated with CVD through enhanced LDLR degradation. Mutations in the human PCSK9 gene lead to either familial hypercholesterolemia or hypocholesterolemia, depending on whether the mutation causes a gain or a loss of function, respectively. It is uncertain if individuals carrying mutations causing a gain-of-function of PCSK9 will develop aortic calcification or whether loss-of-function mutations will lead to abdominal obesity. In this thesis, we investigated: 1) the effect of PCSK9 overexpression on aortic calcification; 2) the consequences of PSCK9 deficiency, mimicking pharmacological inhibition of PCSK9 on fat tissue. We employed a transgenic (Tg) mouse model overexpressing mouse PCSK9 and illustrated by micro-computerized tomography that calcification occurs to a lesser extent in PCSK9 Tg mice than in LDLR-deficient mice. While both PCSK9 Tg and LDLR deficiency caused familial hypercholesterolemia, circulating cholesterol levels alone could not dictate the degree of aortic calcification. In another study, we used genetically modified mice lacking PCSK9 and demonstrated that visceral fat accumulation (adipogenesis) is regulated by circulating PCSK9. Thus in the absence of PCSK9, visceral adipogenesis increases likely via post-translational regulation of very-low-density lipoproteins receptors (VLDLR) in the adipose tissue. In conclusion, these two studies highlight the dynamic balance of PCSK9 in different metabolic pathways, making it a key element in cardiovascular health. Consequently, attempts to survey and/or alter PCSK9 biology should be performed in a valid animal model using sensitive methods and with careful attention to side effects of any given intervention.

Les dynorphines sont des neuropeptides importants avec un rôle central dans la nociception et l’atténuation de la douleur. De nombreux mécanismes régulent les concentrations de dynorphine endogènes, y compris la protéolyse. Les Proprotéines convertases (PC) sont largement exprimées dans le système nerveux central et clivent spécifiquement le C-terminale de couple acides aminés basiques, ou un résidu basique unique. Le contrôle protéolytique des concentrations endogènes de Big Dynorphine (BDyn) et dynorphine A (Dyn A) a un effet important sur la perception de la douleur et le rôle de PC reste à être déterminée. L'objectif de cette étude était de décrypter le rôle de PC1 et PC2 dans le contrôle protéolytique de BDyn et Dyn A avec l'aide de fractions cellulaires de la moelle épinière de type sauvage (WT), PC1 -/+ et PC2 -/+ de souris et par la spectrométrie de masse. Nos résultats démontrent clairement que PC1 et PC2 sont impliquées dans la protéolyse de BDyn et Dyn A avec un rôle plus significatif pour PC1. Le traitement en C-terminal de BDyn génère des fragments peptidiques spécifiques incluant dynorphine 1-19, dynorphine 1-13, dynorphine 1-11 et dynorphine 1-7 et Dyn A génère les fragments dynorphine 1-13, dynorphine 1-11 et dynorphine 1-7. Ils sont tous des fragments de peptides associés à PC1 ou PC2. En plus, la protéolyse de BDyn conduit à la formation de Dyn A et Leu-Enk, deux peptides opioïdes importants. La vitesse de formation des deux est réduite de manière significative dans les fractions cellulaires de la moelle épinière de souris mutantes. En conséquence, l'inhibition même partielle de PC1 ou PC2 peut altérer le système opioïde endogène. / Dynorphins are important neuropeptides with a central role in nociception and pain alleviation. Many mechanisms regulate endogenous dynorphin concentrations, including proteolysis. Proprotein convertases (PCs) are widely expressed in the central nervous system and specifically cleave at C-terminal of either a pair of basic amino acids, or a single basic residue. The proteolysis control of endogenous Big Dynorphin (BDyn) and Dynorphin A (Dyn A) levels has a profound impact on pain perception and the role of PCs remain unclear. The objective of this study was to decipher the role of PC1 and PC2 in the proteolysis control of BDyn and Dyn A levels using cellular fractions of spinal cords from wild type (WT), PC1-/+ and PC2-/+ animals and mass spectrometry. Our results clearly demonstrate that both PC1 and PC2 are involved in the proteolysis regulation of BDyn and Dyn A with a more important role for PC1. C-terminal processing of BDyn generates specific peptide fragments Dynorphin 1-19, Dynorphin 1-13, Dynorphin 1-11 and Dynorphin 1-7 and C-terminal processing of Dyn A generates Dynorphin 1-13, Dynorphin 1-11 and Dynorphin 1-7, all these peptide fragments are associated with PC1 or PC2 processing. Moreover, proteolysis of BDyn leads to the formation of Dyn A and Leu-Enk, two important opioid peptides. The rate of formation of both is significantly reduced in cellular fractions of spinal cord mutant mice. As a consequence, even partial inhibition of PC1 or PC2 may impair the endogenous opioid system.