Six monogenic forms of
maturity-onset diabetes of the young (
MODY) have been identified to date. Except for
MODY2 (
glucokinase), all other
MODY subtypes have been linked to
transcription factors. We have established a
MODY3 transgenic model through the beta-cell-targeted expression of dominant-negative
HNF-1alpha either constitutively (rat
insulin II promoter) or conditionally (Tet-On system). The animals display either overt diabetes or
glucose intolerance. Decreased insulin secretion and reduced pancreatic
insulin content contribute to the hyperglycemic state. The conditional approach in INS-1 cells helped to define new molecular targets of
hepatocyte nuclear factor (HNF)-1alpha. In the cellular system, nutrient-induced insulin secretion was abolished because of impaired
glucose metabolism. Conditional suppression of HNF-4alpha, the
MODY1 gene, showed a similar phenotype in INS-1 cells to
HNF-1alpha. The existence of a regulatory circuit between HNF-4alpha and
HNF-1alpha is confirmed in these cell models. The
MODY4 gene, IPF-1 (
insulin promoter factor-1)/PDX-1 (pancreas duodenum homeobox-1), controls not only the transcription of
insulin but also expression of
enzymes involved in its processing. Suppression of Pdx-1 function in INS-1 cells does not alter
glucose metabolism but rather inhibits
insulin release by impairing steps distal to the generation of mitochondrial coupling factors. The presented experimental models are important tools for the elucidation of the beta-cell pathogenesis in
MODY syndromes.