Type 2 diabetes (T2D) is characterized by impaired beta cell function. The generation of various types of cellular stresses, including oxidative stress and ER stress, and the induction of cellular senescence can contribute to beta cell dysfunction. Recent studies have demonstrated associations between petrochemical exposure and beta cell dysfunction, particularly through induction of cellular stress. One class of compounds, commonly found in crude oil, are sulphur-containing heterocyclic aromatic compounds (S-HACs). S-HACs have been previously demonstrated to induce cellular stress in mammalian cells. This thesis aims to determine if S-HACs can induce cellular stress in beta cells and, consequently, impair beta cell function, particularly insulin production. Rat pancreatic beta cells, INS-1Es, were treated with two commonly occurring S-HACs, BNT(2,3D) and DBT, at doses which reflect non-occupational exposure levels. Upon treatment, various functional assays and qPCR experiments were performed for examining glucose uptake, ROS production, cellular senescence, ER stress and intracellular insulin production. It was observed that both BNT(2,3D) and DBT significantly increased glucose uptake and ROS production in the beta cells and upregulated the mRNA expression of various ER stress markers. In addition, BNT(2,3D) also induced cellular senescence, likely through a p53-independent pathway. This suggests that S-HACs may induce oxidative stress and ER stress in exposed beta cells, and some S-HACs may cause irreversible cell cycle arrest in response to these cellular stresses. However, intracellular insulin content in the INS-1Es was not altered by exposure to either S-HAC, suggesting that S-HACs may not impair insulin production. Nevertheless, the significant accumulation of ROS in S-HAC-exposed beta cells and the subsequent induction of cellular senescence by some S-HACs may alter other important beta cell functions, including mitochondrial function and insulin secretion, which could lead to the development of T2D; suggesting the potential for S-HACs to be novel beta cell toxicants. / Thesis / Master of Science (MSc)

Aspergillus niger souche G131 est un champignon qui produit en quantité des métabolites secondaires appartenant à la famille des naphtho-gamma-pyrones (NγPs). Ces NγPs sont des pigments qui présentent des intérêts industriels de par leurs importants potentiels antiradicalaires. L’objectif de ce doctorat est la production à l’échelle pilote et en continu de NγPs à travers la culture du champignon sur milieu solide. Le choix de la fermentation en milieu solide (FMS) comme processus de culture repose sur des aspects d’ordre qualitatif et quantitatif de production, ainsi que sur des raisons économiques et éthiques, relatives à la protection de l’environnement avec notamment la possibilité de valoriser des coproduits agricoles comme milieu de culture pour le champignon. Dans un premier temps, ce travail s’intéresse à la caractérisation de la composition et des potentialités associées aux molécules produites par la souche. Ces potentialités incluent les activités anti-radicalaires et les mesures de cytotoxicité. La thèse porte également sur la caractérisation de la physiologie de croissance de la souche en FMS et sur l’optimisation des conditions de culture par la méthodologie des plans d’expériences pour l’augmentation de la production de NγPs. Une stratégie originale d’optimisation adaptée aux contraintes posées par la FMS est d’ailleurs proposée. Finalement, un transfert d’échelle de production est réalisé au moyen d’un bioréacteur prototype innovant permettant la production à l’échelle pilote de milieu fermenté en continu. Dans son dernier chapitre, ce travail s’intéresse donc à la mise au point des paramètres opératifs qui entourent la production continue de NγPs par FMS. / Aspergillus niger strain G131 is a non-ochratoxigenic filamentous fungus producing high quantities of secondary metabolites known as naphtha-gamma-pyrones (NγPs). NγPs are pigments of industrial interest in reason of their high antioxidant properties. The aim of this dissertation is the continuous, pilote-scaled production of these NγPs through the cultivation of the fungus on solid medium. The choice of solid state fermentation (SSF) as cultivation method is not only driven by quantitative and qualitative considerations, but also by economical and ethical concerns related to environmental protection. SSF allows, in fact, a direct valorization of agricultural byproducts as the solid medium for the fungal growth. First, this work deals with the characterization of the composition and potentialities associated with the molecules produced by the strain, which include antioxidant and cytotoxic activities. Second, the dissertation focuses on the characterization of the fungal growth’s physiology on solid medium and on the optimization of the culture conditions using experimental methodology in order to increase NγPs production. For this purpose, an original optimization strategy is proposed to overcome specific constraints connected to SSF. Finally, a scale transfer of the production is advanced by means of an innovative prototype bioreactor continuously producing fermented material. The final chapter of this work addresses the development of parameters regarding the continuous NγPs production using SSF.