ABSTRACT

The PhD dissertation was carried out at Steno Diabetes Center in Gentofte. Type 1 diabetes mellitus (T1D) is caused by an autoimmune destruction of the insulin-producing β -cells in the islets of Langerhans in the pancreas. Infiltration of the islets with macrophages and lymphocytes results in the release of cytokines, such as interleukin-1 β (IL-1 β ), to which β -cells are particularly sensitive. The pancreatic endocrine cells ( α , β , γ and PP) all arise from a common stem cell and, dependent upon sequential activation of different transcription-factors, the stem cells will mature into single-hormone expressing cells.

The aims of the thesis are 1) to establish the value of the NHI-cell system as a model for acquired IL-1 β sensitivity during β -cell maturation, 2) to characterize the pathways leading to the acquired sensitivity to IL-1 β and their importance for β -cell toxicity and 3) to reveal, by functional characterization, whether this acquired IL-1 β sensitivity is dependent upon induction of the transcription factor Pdx-1 and/or Nkx6.1 expression.

We demonstrated by using a glucagon-producing pre- β -cell phenotype (NHI-glu), which matures to an insulin-producing β -cell phenotype (NHI-ins), that β -cell maturation was associated with the acquired sensitivity to IL-1 β . Furthermore, this was substantiated in our proteome and transcriptome analyses, since we identified proteins/transcripts involved in pathways important for β -cell maturation, and many of these were further affected by IL-1 β . In addition, transcriptome analyses revealed that several toxic pathways were modulated that could explain the increased sensitivity to the toxic effects of IL-1 β in the β -cell phenotype compared to the pre- β -cell phenotype. Furthermore, an induced Pdx-1 expression and in particular a stable expression of Nkx6.1 were associated with increased IL-1 β sensitivity.

These results support our hypothesis that β -cells acquire IL-1 β sensitivity as a consequence of their maturation. Further analyses are necessary to identify genes regulated by Pdx-1 and in particular Nkx6.1, thereby narrowing the important pathways involved in cytokine-mediated β -cell destruction. Such knowledge may provide useful information to design preventive and/or curative strategies in T1D.