In vivo regulation of pancreatic beta cell function

Abstract

Pancreatic beta cells within the islets of Langerhans contribute to the regulation of glucose homeostasis by secretion of insulin, a hormone that stimulates the uptake of glucose by liver, muscle and fat tissue. In response to variations in insulin demand, the beta cell population can adapt by (1) changing the total beta cell mass, and (2) modulating the functional capacity of individual beta cells. A failure of this mechanism will lead to disturbances in glucose homeostasis and the development of diabetes mellitus. A better understanding of the mechanisms underlying the regulation of a functional beta cell mass can help comprehend how diabetes develops and facilitate efforts to advance therapeutic strategies. Since quite some research has been performed on the regulation of beta cell mass, this thesis focused on elucidating mechanisms behind the functional adaptation of beta cells.

The first part of the thesis describes the development of several tools to be able to study the beta cells in the context of the islet in vitro, and in vivo following transplantation into the anterior chamber of the mouse eye (ACE). Exploiting confocal microscopy and the intrinsic light scattering properties of islet cells, a label-free methodology was developed to describe the morphology and secretory status of the islets. This approach was utilised to quantify the islet volume and study islet mass kinetics in different mouse models of diabetes. Taking advantage of pseudoislets, a novel procedure was established to genetically engineer islets pretransplantation. It was shown that the synthetic modulation of an amplifying pathway in the beta cell could be used to regulate islet graft function, indicating that this technique is suitable to assess the role of specific proteins in beta cell function in vivo.

In the second part, we researched how murine beta cells naturally regulate their function in vivo using a model of reduced beta cell mass. First, pancreatic beta cells were removed, leading to hyperglycaemia. Subsequently, glycaemia was normalised by transplanting a minimal number of islets into the ACE. This model enabled us to study the consequences of an increased workload on beta cells. It was found that long-term exposure to high workload leads to several functional adaptations in vivo as well as changes in the islet gene expression profile, thus indicating that beta cells can display functional plasticity under normoglycaemic and non-obese conditions.

Our newly developed tools have broadened the possibilities to assess and enhance beta cell function in vivo, and helped to gain insights into the mechanisms regulating functional beta cell mass. Collectively, the technical advances and findings presented in this thesis could be used to improve diagnostics and therapeutics for diabetes.