Inflammatory Oxidative Stress Compounds Inhibit Insulin Secretion through Rapid Protein Carbonylation.

Area of Science:

• * Endocrinology and Immunology
• * Molecular Biology and Proteomics

Background:

• * Pancreatic beta cells in pre-type 1 diabetes (T1D) face inflammation, leading to early insulin secretion defects preceding autoimmune destruction.
• * Protein carbonylation (PC), induced by reactive oxygen species (ROS) and reactive aldehydes like 4-hydroxynonenal (4-HNE), is a marker of inflammatory stress.
• * PC involves irreversible modification of amino acid sidechains (Cys, His, Lys) in proteins.

Purpose of the Study:

• * To investigate protein carbonylation patterns in pancreatic islets of pre-diabetic NOD mice.
• * To analyze the impact of 4-hydroxynonenal (4-HNE) and pro-inflammatory cytokines on protein carbonylation and insulin secretion in cultured beta cells.
• * To elucidate the role of oxidative stress in beta cell dysfunction during the pre-diabetic phase of T1D.

Main Methods:

• * Proteomic analysis of pancreatic islets from 10-week-old pre-diabetic NOD mice.
• * Treatment of cultured insulin-secreting cells (MIN6 and INS-1-GRINCH) with 4-HNE or pro-inflammatory cytokines.
• * Measurement of protein carbonylation and insulin secretion levels.

Main Results:

• * All three stress conditions (pre-diabetic islets, 4-HNE, cytokines) elevated protein carbonylation, particularly affecting Rab GTPases and vesicle trafficking proteins.
• * Gene ontology analysis revealed that affected pathways in pre-diabetic islets mirrored those impacted by 4-HNE and cytokine treatments.
• * Both 4-HNE and cytokines significantly reduced insulin secretion by approximately 50% in cultured cells, with 4-HNE causing rapid inhibition and extensive carbonylation.

Conclusions:

• * The observed protein carbonylation pattern in pre-T1D islets suggests beta cells experience multifaceted oxidative stress from both internal ROS generation and external inflammatory sources.
• * Exogenous reactive compounds from infiltrating immune cells may represent a novel, rapid mechanism for inhibiting insulin secretion in pre-diabetic conditions.
• * Protein carbonylation is a significant consequence of inflammatory stress in pre-T1D, contributing to beta cell dysfunction and impaired insulin secretion.