1730-P: In Vitro and In Vivo Effects of Increased IAPP Expression on Human Islet Function

Introduction & Objective: Islet amyloid composed of islet amyloid polypeptide (IAPP) is often present in the pancreas in type 2 diabetes. Cell culture and transgenic rodent models have been used to study islet amyloid toxicity, but less is known about the effects of endogenously-produced IAPP on human islet function and health. Methods: To evaluate acute and chronic effects of amyloid formation, we established a pseudoislet platform with adenoviral delivery of constructs expressing human IAPP (huIAPP) or mouse IAPP (moIAPP), which is not amyloidogenic. After 7 days in culture +/- exposure to the fatty acid palmitate, pseudoislets were evaluated for secretory function, islet structure and amyloid formation by ThioS staining. Pseudoislets were also transplanted into the anterior chamber of the eye of immunodeficient mice for assessment of secretory function for up to 3 months. Results: After 7 days in culture, transduced pseudoislets had 6.3 fold greater cellular IAPP content than untransduced pseudoislets. HuIAPP expression resulted in greater amyloid formation (0.49 ± 0.12 vs 0.17 ± 0.07 % islet area), but no changes in insulin or glucagon secretion or cellular toxicity, compared with moIAPP pseudoislets. High resolution microscopy showed ThioS+ fibrils in the ER of huIAPP-expressing beta cells. No extracellular amyloid was seen. Exposure to 0.5mM palmitate for 3 days further increased amyloid deposition and impaired insulin secretion by huIAPP pseudoislets, but not moIAPP. HuIAPP pseudoislets transplanted into immunodeficient mice had normal insulin secretion after 4 and 8 weeks, but impaired secretion after 12 weeks, compared to moIAPP pseudoislets. Conclusion: In vitro overexpression of IAPP in human pseudoislets induces intracellular amyloid formation, and in combination with lipotoxic stress, impairs insulin secretion. In vivo, human IAPP overexpression impairs insulin secretion after three months. This model will be valuable to elucidate mechanisms of islet dysfunction in type 2 diabetes.