Proinsulin C-peptide interferes with insulin fibril formation

Area of Science:

• Biochemistry
• Molecular Biology
• Diabetes Research

Background:

• Insulin aggregation is a concern in type-1 diabetes treatment, potentially causing localized amyloidosis and hindering insulin uptake.
• Understanding factors influencing insulin fibrillation is crucial for improving diabetes management and therapeutic strategies.

Purpose of the Study:

• To investigate the effect of C-peptide on insulin fibrillation under conditions optimal for fibril formation (low pH, high concentration).
• To determine if C-peptide interacts with and is incorporated into insulin aggregates.
• To explore the implications of C-peptide's interaction with insulin for pancreatic beta-cell function and diabetes treatment.

Main Methods:

• Studied insulin fibrillation at low pH and high concentration.
• Utilized Thioflavine T fluorescence to assess fibril formation.
• Employed electrospray ionization mass spectrometry to detect C-peptide-insulin interactions.
• Applied hydrogen/deuterium exchange mass spectrometry to analyze structural changes in insulin aggregates.

Main Results:

• C-peptide significantly altered insulin aggregation kinetics, changing the lag time.
• Insulin fibrils formed in the presence of C-peptide appeared as rounded clumps of short fibrils, distinct from typical extended fibrils.
• Thioflavine T positivity confirmed the amyloid nature of the altered fibrils.
• Mass spectrometry confirmed C-peptide interaction with and incorporation into insulin aggregates.
• Hydrogen/deuterium exchange revealed reduced backbone accessibility in insulin aggregates formed with C-peptide.

Conclusions:

• C-peptide modulates insulin fibrillation, affecting aggregation dynamics and fibril morphology.
• C-peptide interacts with and is incorporated into insulin aggregates, influencing their structure.
• These findings suggest C-peptide has a general capacity to interact with amyloidogenic proteins found in pancreatic beta-cell granules.
• The observed interactions are relevant to physiological insulin secretion and in vivo conditions related to insulin treatment.