Characterization of GLUT4-containing vesicles in 3T3-L1 adipocytes by total internal reflection fluorescence...

Area of Science:

• Cell biology
• Molecular biology
• Metabolic regulation

Background:

• Insulin-responsive glucose transporter 4 (GLUT4) translocation regulates glucose uptake in adipose tissue and muscle.
• The existence and dynamics of specialized GLUT4 storage vesicles (GSVs) and their translocation to the plasma membrane (PM) upon insulin stimulation remain debated.

Purpose of the Study:

• To investigate the dynamics of single GLUT4-containing vesicles in 3T3-L1 adipocytes.
• To determine if a specialized secretory GSV pool exists and how it translocates to the PM under insulin stimulation.

Main Methods:

• Systematic analysis of single GLUT4-containing vesicle dynamics using total internal reflection fluorescence microscopy (TIRFM).
• Classification of vesicles based on mobility patterns (vertical, stable, lateral).
• Analysis of vesicle composition, specifically the presence of transferrin receptors.

Main Results:

• GLUT4-containing vesicles were classified into three mobility groups: vertical, stable, and lateral.
• Vertical GLUT4-containing vesicles excluded transferrin receptors and exhibited insulin-responsive movement towards the PM.
• Stable and lateral vesicles contained transferrin receptors and were not insulin-responsive.

Conclusions:

• Vertical GLUT4-containing vesicles represent specialized secretory GSVs.
• These specialized GSVs directly approach the PM, bypassing the constitutive recycling pathway.
• The findings clarify the mechanism of insulin-stimulated GLUT4 translocation for glucose uptake.