The pathophysiologic mechanism of glycated albumin-induced pancreatic islets dysfunction

Abstract

The purpose of this study was to investigate whether glycated albumin (GA), an early precursor of Advanced Glycation End-product (AGEs), would induce dysfunction in pancreatic ß-cells and to determine which kinds of cellular mechanisms are activated in GA-induced-cell apoptosis. Decreased viability and increased apoptosis were induced in INS-1 cells treated with 2.5 mg/mL GA under 16.7 mM high-glucose conditions. Insulin content and glucose-stimulated secretion from isolated rat islets were reduced in 2.5 mg/mL GA-treated cells. In response to 2.5 mg/mL GA in INS-1 cells, autophagy induction and flux decreased as assessed by green fluorescent protein– microtubule-associated protein 1 light chain 3 dots, microtubule - associated protein 1 light chain 3-II conversion, and sequestosome1(SQSTM1)/p62 in the presence and absence of bafilomycin A1. Accumulated SQSTM1/p62 through deficient autophagy activated the nuclear factor-B (p65)-inducible nitric oxide synthase(NOS)-caspase-3 cascade, which was restored by treatment with small interfering RNA against p62. Small interfering RNA treatment against autophagy-related protein 5 significantly inhibited the autophagy machinery resulting in a significant increase in iNOS-cleaved caspase-3 expression. Treatment with 500 μM 4-phenyl butyric acid significantly alleviated the expression of endoplasmic reticulum stress markers and iNOS in parallel with upregulated autophagy induction. However, in the presence of bafilomycin A1, the decreased viability of INS-1 cells was not recovered. Glycated albumin, an early precursor of AGE, caused pancreatic-ß cell death by inhibiting autophagy induction and flux, resulting in nuclear factor-B (p65)-iNOS-caspase-3 cascade activation as well as by increasing susceptibility to endoplasmic reticulum stress and oxidative stress.