DC2420 - Amyloid Formation in Cultured Human Islets is Associated with a Shift in Macrophage Phenotype – Implications in Type 2 Diabetes

Blinded Abstract:

Background: In type 2 diabetes (T2D), formation of toxic protein aggregates named amyloid in pancreatic islets contributes to islet inflammation, and beta-cell dysfunction and death, by promoting IL-1beta production and activation of the Fas-mediated apoptotic pathway. Islet macrophages are the main source of amyloid-induced IL-1beta production. We examined the effects of amyloid formation on pro-inflammatory (M1) and anti-inflammatory (M2) islet macrophages.

Methods: Human islets (n=4 cadaveric donors) were cultured in normal glucose as control (5.5 mM; no or minimal amyloid) or elevated glucose (11.1 mM; islets form amyloid) for 7 days. Quantitative immunolabelling was performed on paraffin-embedded human islet sections for insulin and each CD68 (general macrophage marker), iNOS (M1 marker), CD163 (M2 marker), IL-1beta, Fas, thioflavins S (amyloid), or TUNEL (apoptosis). Also, IL-1beta release from islets was assessed.

Results: Human islets progressively formed amyloid during 7-day culture in elevated glucose (but not normal glucose), leading to increased beta-cell apoptosis. Amyloid formation was associated with increased islet IL-1beta levels, beta-cell Fas upregulation, and a shift in macrophage phenotype, manifested as elevated iNOS-positive (M1) and reduced CD163-positive (M2) macrophages. The mean of total macrophages per islet was comparable in pre-culture and 7-day cultured islets at both glucose levels.

Conclusion: Amyloid formation in human islets led to a shift in macrophage phenotype towards pro-inflammatory (M1), thereby promoting IL-1beta production and IL-1bteta/Fas-mediated beta-cell apoptosis. Thus, modulation of islet macrophage phenotype may provide a therapeutic strategy to improve beta-cell survival in patients with T2D by reducing amyloid-induced beta-cell death.