Degradative processing of internalized insulin in isolated adipocytes

Area of Science:

• Cell biology
• Endocrinology
• Biochemistry

Background:

• Insulin signaling is crucial for glucose homeostasis.
• Understanding insulin internalization and degradation pathways is key to metabolic research.

Purpose of the Study:

• To elucidate the kinetics of insulin binding, internalization, and degradation.
• To determine the temperature sensitivity of insulin processing.
• To identify the cellular compartments and mechanisms involved in insulin degradation.

Main Methods:

• Utilized 125I-insulin to track insulin binding, internalization, and release.
• Assessed insulin processing at different temperatures (37°C and 16°C).
• Employed trichloroacetic acid precipitability and column chromatography for composition analysis.
• Investigated the role of lysosomes and energy dependence using chloroquine and dinitrophenol.

Main Results:

• Insulin binds rapidly to cell surface receptors (t 1/2 = 0.4 min) and accumulates intracellularly (t 1/2 = 3.5 min) at 37°C.
• Internalization is more temperature-sensitive than intracellular processing.
• 75% of internalized insulin is degraded, with degradation products released within 4-5 min post-uptake.
• Insulin enters lysosomes by 2.5-3 min and degradation products are released via diffusion.

Conclusions:

• Insulin internalization and degradation are dynamic processes influenced by temperature.
• Degradation is the predominant fate of internalized insulin.
• Insulin degradation involves lysosomal processing followed by diffusion-based release of products.