Longitudinal imaging of pancreatic islets transplanted into the anterior chamber of the eye

Abstract

Diabetes is a growing health problem associated with substantial health and socioeconomic costs. Current medications address hyperglycaemia and related complications, but a definitive cure for diabetes remains elusive. Pharmacotherapy with the potential to restore β-cell function is urgently needed. To this end, it is vital that we achieve a better understanding of islet function in both health and disease states. While major breakthroughs in diabetes research have traditionally resulted from in vitro experimentation, the crucial role of the pancreatic internal milieu is being increasingly recognised. The islet in the eye imaging platform is the first experimental tool which allows for the longitudinal and direct investigation of β-cell function in a non-invasive manner. This thesis describes the application of this imaging platform to three divergent areas of islet research. Firstly the physiology of co-ordinated insulin secretion is examined. Pulsatile insulin secretion is physiologically relevant and is impaired in diabetes. The imaging platform is used to establish, for the first time in vivo, that the calcium waves that underlie insulin secretion arise from the co-ordinated activity of a heterogeneous group of β-cells. Obesity is the greatest risk factor for developing Type 2 diabetes. The effects of high fat diet on islet calcium dynamics are incompletely understood. Hyperglucagonaemia is traditionally thought of as a contributing factor to diabetes disease progression. Emerging evidence however suggests that glucagon signalling has beneficial effects on food intake and energy expenditure. More recently, the insulin potentiating effects of intra-islet glucagon has been suggested. The imaging platform is developed to investigate the longitudinal effects of high fat diet and the subsequent weight-loss independent effects of a synthetic glucagon analogue on islet function. Together, these two studies investigate the utility of the islet in the eye imaging platform to better our understanding of intercellular β-cell calcium dynamics in the acute and in a more chronic setting. Islet transplantation has not provided a reliable cure for patients with Type 1 diabetes, due to a relative lack of suitable donors but, more importantly, because the majority of patients fail to achieve long term insulin independence. The reasons for transplant failure are manifold and poorly 9 understood, although engraftment failure is a major issue. There is a clear need to improve transplant success rates, especially if this can be achieved in line with a more reliable supply of β-cells/islets (for example stem-cell derived therapies). The last experimental chapter aims to investigate the effects of epidermal growth factor receptor (EGFR) overexpression in β-cells and whether this treatment improves islet engraftment. In particular, this chapter focuses on the angiogenesis of newly transplanted islets and whether the islet in eye platform is capable of longitudinally monitoring this process.