Le diabète de type I est la maladie chronique la plus grave de l'enfance. L'alimentation saine et équilibrée constitue la pierre angulaire du traitement de cette maladie (Delamater, 2000). Or, au quotidien, plus de 60 % des adolescents diabétiques ne parviennent pas à suivre leur plan alimentaire (Rapoff & Barnard, 1991). Devant la gravité des conséquences physiques et psychologiques qu'entraîne la mauvaise gestion alimentaire, la présente thèse a pour objectif général de décrire et de comprendre les facteurs contextuels et motivationnels qui contribuent à l'observance. S'appuyant sur un cadre théorique reconnu, la théorie de l'autodétermination (Deci & Ryan, 1985, 2002), cette thèse vise la validation d'un modèle motivationnel de l'observance chez les adolescents diabétiques. Le modèle propose que le soutien des parents et des professionnels de la santé favorise chez les adolescents des facteurs motivationnels optimaux, c'est-à-dire une motivation autonome et une perception d'efficacité personnelle élevée, lesquels facilitent leur observance du plan alimentaire. Trois articles découlent de cette thèse. Un premier présente les statistiques descriptives de l'ensemble des variables proposées dans le modèle, et ce, en accordant une attention particulière à la description des recommandations médicales reçues et observées par les adolescents, de même qu'à la qualité de leur motivation et de leur équilibre glycémique. Un deuxième article teste l'ensemble des liens postulés dans le modèle à l'aide d'un devis transversal. Précisément, il examine dans quelle mesure les facteurs contextuels (soutien à l'autonomie de la part des parents et des professionnels de la santé) et motivationnels (qualité de la motivation et perception d'efficacité personnelle) expliquent les relations observées entre les facteurs immuables (genre, âge, durée de vie avec le diabète) et l'observance. Un troisième article examine, sur une période de 24 mois, la direction des liens postulés dans le modèle motivationnel. Les résultats découlant de ces articles offrent un soutien satisfaisant au modèle proposé. La discussion générale de la thèse se centre sur les apports méthodologiques, pratiques et théoriques de ces résultats. Des pistes de recherches futures y sont également proposées, et ce, afin d'améliorer l'avancement des connaissances sur l'observance du plan alimentaire chez les adolescents diabétiques de type I.

The endoplasmic reticulum (ER) is the organelle responsible for synthesis and folding of secreted and membranous protein and lipid biosynthesis. It also functions as one of the main cellular calcium stores. Pancreatic beta-cells evolved to produce and secrete insulin upon demand in order to regulate blood glucose homeostasis. In response to increases in serum glucose, insulin synthesis represents nearly 50% of the total protein biosynthesis by beta-cells. This poses an enormous burden on the ER, rendering beta-cells vulnerable to agents that perturb ER function. Alterations of ER homeostasis lead to accumulation of misfolded proteins and activation of an adaptive response named the unfolded protein response (UPR). The UPR is transduced via 3 ER transmembrane proteins, namely PERK, IRE-1 and ATF6. The signaling cascades activated downstream of these proteins: a) induce expression of ER resident chaperones and protein foldases. Increasing the protein folding capacity of the ER; b) attenuate general protein translations which avoids overloading the stressed ER with new proteins; c) upregulate ER-associated degradation (ERAD) genes, which decreases the unfolded protein load of the ER. In severe cases, failure by the UPR to solve the ER stress leads to apoptosis. The mechanisms linking ER stress to apoptosis are still poorly understood, but potential mediators include the transcription factors Chop and ATF3, pro-apoptotic members of the Bcl-2 familly, the caspase 12 and the kinase JNK. <p>Accumulating evidence suggest that ER stress contributes to beta-cell apoptosis in both type 1 and type 2 diabetes. Type 1 diabetes is characterized by a severe insulin deficiency resulting from chronic and progressive destruction of pancreatic beta-cells by the immune system. During this autoimmune assault, beta-cells are exposed to cytokines secreted by the immune cells infiltrating the pancreatic islets. Our group has previously shown that the pro-inflamatory cytokines interleukin-1beta (IL1-beta and interferon-gamma (IFN-gamma), via nitric oxide (NO) formation, downregulate expression and function of the ER Ca2+ pump SERCA2. This depletes beta-cell ER Ca2+ stores, leading to ER stress and apoptosis. Of note, IL1-beta alone triggers ER stress but does not induce beta-cell death, while IFN-gamma neither causes ER stress nor induces beta-cell death. Together, these cytokines cause beta-cell apoptosis but the mechanisms behind this synergistic effect were unknown.<p>Type 2 diabetes is characterized by both peripheral resistance to insulin, usually as a result of obesity, and deficient insulin secretion secondary to beta cell failure. Obese patients have high levels of circulating free fatty acids (FFA) and several studies have shown that the FFA palmitate induces ER stress and beta-cell apoptosis.<p>In the present work we initially established an experimental model to specifically activate the ER stress response in pancreatic beta-cells. For this purpose, insulinoma cells (INS-1E) or primary rat beta-cells were exposed to the reversible chemical SERCA pump blocker cyclopiazonic acid (CPA). Dose-response and time course experiments determined the best conditions to induce a marked ER stress without excessive cell death (<25%).<p>The first goal of the work was to understand the synergistic effects of IL1-beta and IFN-gamma leading to pancreatic beta-cell apoptosis. Our group previously observed, by microarray analysis of primary beta-cells, that IFN-gamma down-regulates mRNAs encoding for some ER chaperones. Against this background, our hypothesis was that IFN-gamma aggravates beta-cell ER stress by decreasing the ability of these cells to mount an adequate UPR. To test this hypothesis, we investigated whether IFN-gamma pre-treatment augments CPA-induced ER stress and beta cell death. The results obtained indicated that IFN-gamma pre-treatment potentiates CPA-induced apoptosis in INS-1E and primary beta-cells. This effect was specific for IFN-gamma since neither IL1-beta nor a low dose CPA pre-treatment potentiated CPA-induced apoptosis in INS-1E cells. These effects of IFN-gamma were mediated via the down regulation of genes involved in beta cell defense against ER stress, including the ER chaperones BiP, Orp150 and Grp94 as well as Sec61, a component of the ERAD pathway. This had functional consequences as evidenced by a decreased basal and CPA-induced activity of a reporter construct for the unfolded protein response element (UPRE) and augmented expression of the pro-apoptotic transcription factor Chop. <p>We next investigated the molecular regulation of the Chop gene in INS-1E cells in response to several pro-apoptotic and ER stress inducing agents, namely cytokines (IL1-beta and IFN-gamma), palmitate, or CPA. Detailed mutagenesis studies of the Chop promoter showed differential regulation of Chop transcription by these compounds. While cytokines (via NO production)- and palmitate-induced Chop expression was mediated via a C/EBP-ATF composite and AP-1 binding sites, CPA induction required the C/EBP-ATF site and the ER stress response element (ERSE). Cytokines, palmitate and CPA induced ATF4 protein expression and further binding to the C/EBP-ATF composite site, as shown by Western blot and EMSA experiments. There was also formation of distinct AP-1 dimers and binding to the AP-1 site after exposure to cytokines or palmitate. <p>\ / Doctorat en Sciences biomédicales et pharmaceutiques / info:eu-repo/semantics/nonPublished

Doctorat en Sciences médicales / info:eu-repo/semantics/nonPublished