Characterisation of human amylin transgenic mice

Abstract

Type 2 diabetes has become an enormous health concern and effective therapies are urgently needed. Pancreatic islet amyloid deposits are observed in >90% type 2 diabetics and consist of human amylin (hA) polypeptide. These amyloid deposits are toxic to pancreatic insulin producing β-cells. [25,28,29Pro]hA is a non-toxic non-fibril forming analogue of hA with three proline residue substitutions at positions 25, 28 and 29 of the amyloidogenic region of the molecule. hA transgenic mouse models serve as important instruments for researchers to understand the intricate mechanisms involved in diabetes disease development. In this thesis I characterised the diabetic phenotype of hA transgenic females and investigated the changes in pancreatic morphology of both hA transgenic males and females pre- and post- weaning. I determined that therapeutic intervention could be attempted just prior to weaning, since pancreatic β-cell loss occurs after weaning concurrent with the onset of hyperglycaemia. These mice develop severe diabetes at a very young age with hyperglycaemia, glucose intolerance, pancreatic β-ceil loss and insulin deficiency. I also characterised the diabetic phenotype of [25,28,29Pro]hA transgenic mice. Transgenic males exhibit transient hyperglycaemia, glucose intolerance, pancreas hyperplasia and insulin resistance. [25,28,29Pro]hA transgenic females did not demonstrate clear signs of diabetes. I investigated the lipid profiles of hA transgenic females at 150 days of age and [25,28,29Pro]hA transgenic animals at 60 and 150 days of age. [25,28,29Pro]hA transgenic males showed increased plasma free fatty acids, which is consistent with their observed hyperinsulinaemia and insulin resistant phenotype. Sexual dimorphism is common in hA transgenic mouse models that develop diabetic phenotypes and both hA and [25,28,29Pro]hA transgenic mouse models demonstrated this phenomenon. The two transgenic mouse models display very different diabetic phenotypes. hA transgenic animals serves as a good model to study fibrillogenesis as well as the toxic effects of hA on the development of type 2 diabetes. Unfortunately this model does not allow for the investigation into the peripheral effects of hA, because the phenotype generated is too severe and animals die early in life. [25,28,29Pro]hA transgenic animals do not develop pancreatic lesions that result in β-cell loss, but instead present pancreatic hyperplasia. Instead of advanced pancreatic dysfunction these animals demonstrated signs of insulin resistance. The characterization of these two transgenic mouse models shed light on the multi-faceted process of diabetic disease progression. I hope that my characterisation of the [25,28,29Pro]hA transgenic mice will assist in the future unravelling of the mechanisms underlying hA’s involvement in peripheral insulin resistance.