Abstract
Considering the globally increasing rate of incidence, Type 2 diabetes mellitus belongs to the
most frequent endocrine metabolic disorders today. In addition to insulin resistance of
peripheral tissues, this disease is the result of dysfunction of the endocrine pancreas and in
particular of the functional failure of β-cells. The progress of therapeutical strategies is based
on the research of the underlying mechanisms. The aim of the present dissertation was the
analysis of new molecular regulators which might improve our underdstanding of the
differentiation of pancreatic islets and the functional maintenance of adult β-cells.
The first part of this work concerned the role of the transcription factor Pax6 and especially
the role of its transactivation domain (TA) and of its two DNA binding domains, the paired
domain (PD) and the homeodomain (HD), in differentiation of pancreatic endocrine cells. By
analyzing four different mouse lines with specific mutations in one of these three domains,
we found that the PD of Pax6 is essential for differentiation of glucagon producing α-cells.
Inactivation of this domain resulted in a phenotype similar to that of Pax6 knockout mice
(Pax6-/-) with a near complete absence of glucagon positive α-cells, a markedly reduced
number of insulin producing β-cells, and a disorganized islet structure. Mutations of HD or TA
showed a less severe pancreatic phenotype. Islets either exhibited no morphological
changes or they showed a reduction of α- and β-cells. Intraperitoneal glucose tolerance tests
demonstrated the utmost importance of the transcription factor Pax6 for maintenance of
normal pancreatic endocrine function in adult animals.
In the second part of this study we identified new genes and proteins, respectively, which
could play a regulatory role in normal function of β-cells. In particular it was possible to show
that Eny2, hitherto a protein only described in yeast or invertebrates like drosophila, is
involved in the regulation of insulin secreting vertebrate cells. si-RNA mediated knockdown of
Eny2 resulted in markedly increased glucose and incretin-induced insulin secretion. This
could be at least in part attributed to a higher glucose-dependent cellular metabolism and an
enhanced signal transduction via protein kinase A and is accompanied by elevated levels of
intracellular calcium. Taken together, these results indicate that Eny2 functions as a negative
regulator of glucose-stimulated and incretin-mediated insulin secretion, at least in vitro.
However, a gap of knowledge still remains between the established nuclear functions of
Eny2 and the cellular phenotype we observed upon its suppression. Nevertheless, the
effects of an Eny2-knockdown are glucose dependent and additive to the incretin signaling.
This feature makes this model attractive to obtain new insights in how insulin secretion of β-
cells proceeds and how to find new therapeutical strategies to treat type 2 diabetes mellitus