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siRNA-Mediated Suppression of Pro-Islet Amyloid Polypeptide Expression Inhibits Islet Amyloid Formation and Enhances Survival of Human Islets in Culture

Departments of¹ Pathology & Laboratory Medicine & and
²Surgery, Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada
³Department of Genetic Medicine and Development, University of Geneva Medical Center, Geneva, Switzerland
⁴Department of Medicine, Duke University, Durham, NC, USA
⁵Department of Surgery, McGill University, Montreal, QC, Canada
⁶Department of Surgery, University of Illinois at Chicago, Chicago, IL, USA
⁷Department of Medical Biophysics, University of Toronto, Toronto ON, Canada

OBJECTIVE: Islet amyloid, formed by aggregation of the β-cell peptide islet amyloid polypeptide (IAPP, amylin), is a pathologic characteristic of pancreatic islets in type 2 diabetes. Toxic IAPP aggregates likely contribute to the progressive loss of β-cells in this disease. We used cultured human islets as an ex vivo model of amyloid formation to investigate whether suppression of proIAPP expression would inhibit islet amyloid formation and enhance β-cell survival and function.

RESEARCH DESIGN AND METHODS: Islets from cadaveric organ donors were transduced with a recombinant adenovirus expressing a short interfering RNA (siRNA) designed to suppress human proIAPP (Ad-hProIAPP-siRNA), cultured for 10 days, and then assessed for the presence of islet amyloid, β-cell apoptosis, and β-cell function.

RESULTS: Thioflavine S-positive amyloid deposits were clearly present after 10 days culture. Transduction with Ad-hProIAPP-siRNA reduced (pro)IAPP expression by 75% compared to non-transduced islets as assessed by Western blot analysis of islet lysates 4 days post-transduction. siRNA-mediated inhibition of IAPP expression decreased islet amyloid area by 63% compared to non-transduced cultured islets. Cell death assessed by TUNEL staining was decreased by 50% in transduced cultured human islets, associated with a significant increase in islet insulin content (Cont: 100 ± 4% vs. +Ad-siRNA: 153 ± 22%, P<0.01) and glucose-stimulated insulin secretion (Cont: 222 ± 33% vs. +Ad-siRNA: 285 ± 21 (% basal, P<0.05).

CONCLUSIONS/INTERPRETATION: These findings demonstrate that inhibition of IAPP synthesis prevents both amyloid formation and β-cell death in cultured human islets. Inhibitors of IAPP synthesis may have therapeutic value in type 2 diabetes.

Correspondence: verchere{at}interchange.ubc.ca

Key Words: Amyloid • islet amyloid polypeptide • amylin • β-cell apoptosis • type 2 diabetes • IAPP gene silencing

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