Endoplasmic reticulum stress induced by lipopolysaccharide is involved in the association between inflammation and autophagy in INS­1 cells.

ABSTRACT

Type 2 diabetes is a chronic inflammatory disease. Autophagy, the dynamic process of lysosomal degradation of damaged organelles and proteins, may protect ß­cells from destruction by inflammation in type 2 diabetes. The present study investigated the role of autophagy, inflammation and endoplasmic reticulum (ER) stress in type 2 diabetes. INS­1 cells were incubated with lipopolysaccharide. The chemical chaperone 4­phenylbutyric acid was used to inhibit ER stress, and 3­methyadenine (3­MA) was used to inhibit autophagy. Apoptosis was detected by flow cytometry and cell proliferation using Cell Counting kit­8 solution. Light chain­3B, interleukin (IL) 1ß, caspase­1 and C/EBP homologous protein production were assessed by western blotting, and rat activating transcription factor 4 and rat binding immunoglobulin heavy chain protein gene expression were determined by real­time reverse transcription­polymerase chain reaction. The results showed that inhibiting autophagy with 3­MA unexpectedly contributed to cell death in ß­cells. This response was associated with an increase in inflammatory cytokines, including IL1ß and caspase­1. Inhibiting ER stress with 4­phenylbutyric acid led to a decrease in cell apoptosis. These results showed that autophagy may have a protective effect by reducing inflammatory cytokines in ß­cells. In addition, the inositol­requiring enzyme 1 pathway mediated the ER stress associated with autophagy and inflammatory cytokines (IL1ß and caspase­1). Therefore, inflammatory cytokines may be critical signalling nodes, which are associated with ER stress­mediated ß­cell death.