Human islet amyloid polypeptide transgenic mice: in vivo and ex vivo models for the role of hIAPP in type 2 diabetes mellitus

Abstract

Human islet amyloid polypeptide (hIAPP), a pancreatic islet protein of 37 amino acids, is the main component of islet amyloid, seen at autopsy in patients with type 2 diabetes mellitus (DM2). To investigate the roles of hIAPP and islet amyloid in DM2, we generated transgenic mice expressing hIAPP in their islet beta cells. In this study, we found that after a long-term, high-fat diet challenge islet amyloid was observed in only 4 of 19 hIAPP transgenic mice. hIAPP transgenic females exhibited severe glucose intolerance, which was associated with a downregulation of GLUT-2 mRNA expression. In isolated islets from hIAPP males cultured for 3 weeks on high-glucose medium, the percentage of amyloid containing islets increased from 5.5% to 70%. This ex vivo system will allow a more rapid, convenient, and specific study of factors influencing islet amyloidosis as well as of therapeutic strategies to interfere with this pathological process.

Figure 1

Plasma insulin and glucose levels immediately before and at different timepoints after an intraperitoneal injection of glucose (1 g/kg body weight) in anaesthetized, nonfasted nontransgenic (NT, dotted line), and hIAPP transgenic mice (solid line) on a high-fat diet for 14 months. Mean values and SEM are shown; n = 5–11 per group of mice; statistically significant changes between hIAPP and NT mice are indicated by *(P < .05) and **(P < .01).

Figure 2

In situ mRNA hybridization (using radiolabeled oligoprobes) for hIAPP (a), (b), and GLUT-2 (c), (d) in islets of nontransgenic (a), (c), and hIAPP transgenic (b), (d) female mice after 14 months on high-fat diet. Note that hIAPP mRNA expression is absent in the nontransgenic islet, and that GLUT-2 mRNA expression is reduced in the transgenic islet. Scale bar = 30 μm.

Figure 3

Comparison of the average labeling density of GLUT-2 mRNA in situ hybridization in pancreatic islets from nontransgenic (NT) and hIAPP transgenic (hIAPP) mice (P = .02). For both groups 4 mice were analysed, 2 males, and 2 females. The 4 transgenic mice did not have amyloid.

Figure 4

Detection of islet amyloid in islet of Langerhans isolated from an hIAPP transgenic mouse, and cultured in medium with a high glucose concentration. Frozen section of a gelatine-embedded islet was stained with the amyloid-specific dye Congo red and visualized with light microscopy (a) and fluorescence microscopy (b), respectively.