Interleukin-6 treatment induces beta-cell apoptosis via STAT-3-mediated nitric oxide production

Type 2 diabetes is characterized by progressive beta-cell failure and apoptosis is probably the main form of beta-cell death in this disease. It was reported that circulating levels of interleukin-6 are elevated in type 2 diabetic patients, but whether this is involved in the pathogenesis of type 2 diabetes is still debated. In this study, we examined whether interleukin-6 can induce beta-cell damage in vitro and elucidated its mechanisms.

To examine the effect of interleukin-6 on beta cells, glucose-stimulated insulin secretion (GSIS) by enzyme immunoassay (EIA) method and cell apoptosis by propidium iodide and annexin-V staining were measured in a rat beta-cell line (INS-1 or INS-832/13) after treatment with interleukin-6. The expression of apoptosis-related molecules was measured using western blotting and nitric oxide (NO) production was measured using Griess assay. AG490 and N-monomethyl-L-arginine were used to inhibit Janus kinase-mediated signal transducers and activators of transcription signalling and NO production, respectively.

Exposure (48 h) of INS-1 cells to 20 ng/mL interleukin-6 significantly decreased GSIS as well as cell viability. We found that sub-G1/G0 population was increased as compared with untreated cells and expression of cleaved caspase-3, cleaved poly(ADP-ribose) polymerase, phosphorylated p38 mitogen-activated protein kinase and phosphorylated nuclear factor-κB was increased in interleukin-6-treated INS-1 cells. Interleukin-6 increased the amount of early apoptotic cells; this increase was blocked by AG490 or N-monomethyl-L-arginine treatment. Moreover, NO production, which is known to induce apoptosis, was increased by interleukin-6 treatment but abrogated in AG490-treated cells.

Our results show that exposure to interleukin-6 for 48 h can induce beta-cell death, in part via signal transducers and activators of transcription-3-mediated NO production.