Date of Award
Spring 2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Public Health
First Advisor
Vasiliou, Vasilis
Abstract
Currently, over 537 million people worldwide have diabetes, a disease characterized by impaired insulin synthesis, and/or utilization. Of diabetics, roughly 90% have type 2 diabetes and develop high blood glucose caused by pancreatic islet dysfunction. The islet is composed of five different endocrine cell types. Sixty - 80% (varies by species) of islet cells are insulin-producing β cells. A hallmark characteristic of dysfunctional β cells is impaired insulin secretion. Among the many factors implicated in islet cell dysfunction is oxidative stress. Oxidative stress is defined as the imbalance between reactive oxygen species (ROS) and cellular antioxidant capacity. During oxidative stress, the cellular antioxidant capacity is overwhelmed, and ROS-mediated cellular damage is induced. The low expression and activity of antioxidant enzymes may increase the sensitivity of islet cells to oxidative stress. Islet cells have relatively higher expression and activity of the heterodimeric enzyme, γ-glutamate-cysteine ligase (GCL) particularly, the catalytic subunit (GCLC). GCLC catalyzes the rate-limiting step in glutathione (GSH) biosynthesis. GSH is the most abundant cellular antioxidant and is essential for preventing oxidative stress. GSH is associated with many physiological functions, including insulin secretion, wherein glucose stimulated insulin secretion requires an increased GSH pool. Additionally, islets derived from type 2 diabetic patients show decreased GSH and GCLC expression. As such, understanding the role of GSH biosynthesis in the development and progression of diabetes is of great clinical interest. In this thesis, I describe work that directly demonstrates the essentiality of GSH biosynthesis for pancreatic islet development and function. First, I show that the deletion of the Gclc gene in islet progenitor cells causes impaired GSH biosynthesis and an overt diabetes phenotype, later in life. Further, I establish that, overt diabetes is predated by structural and functional changes to the islet and provide initial mechanistic evidence suggesting that these changes are promoted by an oxidative DNA damage-associated senescence-like phenotype. Second, I describe generation of an inducible mouse model for the β cell-specific deletion of Gclc, in adulthood. I demonstrate that reduced GCLC expression promotes a uniquely heterogenous diabetic phenotype with mild hyperinsulinemia predating transient hyperglycemia, which may be promoted by islet adaptation. Lastly, I employ the rat insulinoma β cell line, INS-1 (832/13), for mechanistic studies and demonstrate that cellular GSH content is essential for controlled basal insulin secretion. The worked presented in this dissertation has provided the field of diabetes with three novel models. Through creating these models, I have contributed new insights regarding the consequences of perturbed intrinsic GSH biosynthesis on islet development and function. As such, these insights are poised to improve collective understanding of the antioxidant capacity of the islet.
Recommended Citation
Davidson, Emily Ann, "Models For Interrogating The Role Of Glutathione Biosynthesis In Pancreatic Islet Development And Function" (2024). Yale Graduate School of Arts and Sciences Dissertations. 1377.
https://elischolar.library.yale.edu/gsas_dissertations/1377
