Inflammatory Oxidative Stress Compounds Inhibit Insulin Secretion through Rapid Protein Carbonylation

Pancreatic β-cells in pre-type 1 diabetes (T1D) experience stress due to islet inflammation, which accompanies early defects in insulin secretion that precede autoimmune destruction. One product of inflammatory stress is protein carbonylation (PC), brought on by reactive oxygen species (ROS) combining with lipids to produce reactive aldehydes such as 4-hydroxynonenal (4-HNE) that irreversibly modify Cys, His, and Lys sidechains. In this study, we used proteomics to measure patterns of PC in pancreatic islets from 10-week-old pre-diabetic NOD mice and in cultured insulin-secreting cells treated with either 4-HNE or pro-inflammatory cytokines. All three stress conditions increased carbonylation of proteins central to β-cell function including Rab GTPases and other proteins that are essential for vesicle trafficking. Gene ontology analysis indicates that the affected proteins and pathways in pre-diabetic NOD islets reflect a combination of those impacted by 4-HNE and cytokine treatment. Furthermore, both 4-HNE and cytokines significantly inhibited insulin secretion by ~50% in cultured MIN6 and INS-1-GRINCH cells. In particular, exposure to 4-HNE for as little as 5 minutes suppressed insulin secretion and increased the carbonylation of over 1000 proteins. Overall, the observed PC pattern in pre-T1D islets is consistent with a model in which β-cells experience multiple sources of oxidative stress, including ROS generation within β-cells themselves and reactive compounds released by infiltrating immune cells. The latter exogenous source may represent a novel rapid mechanism for inhibiting insulin secretion.