ABSTRACT

This PhD dissertation is based on studies carried out during my stay at Steno Diabetes Center, Gentofte, Denmark, and consists of a review, four published papers and one manuscript.

Development of type 1 diabetes (T1D) is characterised by selective destruction of the insulin producing β -cells in the islets of Langerhans due to a complex interplay between the β -cell, the immune system and the environment in genetically susceptible individuals. Cytokines, e.g. interleukin-1 β (IL-1 β ), are present in the islets during β -cell destruction. We hypothesise that the β -cell, when exposed to IL-1ß, initiates a race between protective and deleterious events, and that the deleterious events prevail. Proteins are involved in most cellular processes, and their cumulative expression pattern reflects the cellular activity. Examination of protein expression profiles (proteome analysis) may be useful in describing the diabetic phenotype.

We have previously demonstrated by proteome analysis that IL-1 β induces changes in the expression of 82 out of 1815 protein spots in diabetes-prone Bio Breeding (BB-DP) rat islets in vitro. In the present work, we have identified the proteins in these 82 spots by mass spectrometry. The identified proteins are involved in pathways, such as DNA and RNA synthesis, chaperoning, signal transduction and cellular defence. We have followed these 82 protein spots during development of diabetes and protection from diabetes in syngeneic islet transplants in BB-DP rats. During spontaneous diabetes development, the 82 proteins changed expression in a rather complex pattern. At onset of diabetes, the highest number of changes, similar to expression changes seen in IL-1 β exposed islets in vitro are seen (25 out of 32). Prophylactic insulin treatment of pre-diabetic BB-DP rats decreases the incidence of diabetes and alters the expression profile of the 82 protein spots in transplanted islets. Furthermore, we have shown that intrauterine exposure to a low protein (LP) diet changes the protein expression profile in fetal rat islets in ways explaining the observed long-lasting increased apoptotic rate and vulnerability to cytokines seen in such islets.

In conclusion, we have produced a rather detailed picture of protein expression in IL-1 β exposed BB-DP rat islets in vitro and shown that protein expression changes seen in vitro also occur in islets in vivo. Furthermore, we have shown that the islet protein expression can be changed by environmental factors, i.e. LP diet and prophylactic insulin treatment. No single protein alone seems to be responsible for the development of diabetes. Rather the cumulative pattern of changes seems to be what favours a transition from a dynamic stability in the unperturbed β -cell to dynamic instability and potentially β -cell destruction.