Amyloid Formation Reduces Phospho-PKB Levels in Islet β-Cells Which is Restored by Blocking IL-1β Signalling

Abstract

Islet transplantation provides a feasible approach for treatment of type 1 diabetes (T1D) but is currently limited by insufficient donors and islet loss during pre-transplant culture and in islet grafts. Aggregation of human islet amyloid polypeptide (hIAPP), a hallmark of pancreas in T2D, also occurs during islet culture and transplantation. Amyloid formation contributes to β-cell death in all 3 conditions. Protein kinase B (PKB) signalling pathway plays a key role in the regulation of β-cell survival, function and proliferation. In this study, we examined if: 1. hIAPP aggregates can reduce PKB phosphorylation via inducing islet IL-1β production; 2. blocking amyloid or IL-1β can restore reduced PKB phosphorylation associated with amyloid formation. hIAPP-treated INS-1 β-cells had markedly lower phospho-PKB levels, reduced proliferation and higher apoptosis than non-fibrillogenic rat IAPP-treated or untreated cells, all of which were restored by the amyloid inhibitor Congo red. Human islets and transgenic hIAPP-expressing mouse islets formed amyloid during culture associated with elevated IL-1β and reduced β-cell phospho-PKB levels, both of which were prevented by Congo red. Prevention of amyloid formation during islet culture by collagen matrix reduced islet IL-1β and restored β-cell phospho-PKB levels. Blocking IL-1 receptor (anakinra) or treatment with GLP-1 agonist (exenatide) restored β-cell phospho-PKB levels in amyloid forming islets. These data suggest that amyloid formation reduces phospho-PKB in islet β-cells likely via IL-1β signalling. Blocking amyloid or amyloid-induced IL-1β production may enhance β-cell survival by restoring phosphorylation of PKB during pre-transplant culture and in islet grafts.