Dynamic glucose uptake, storage, and release by human microvascular endothelial cells

Area of Science:

• Cell biology
• Physiology
• Biochemistry

Background:

• Endothelial cells are crucial for solute transport between blood and tissues.
• The precise mechanisms of glucose transport across endothelia remain incompletely understood.
• Understanding endothelial glucose handling is vital for tissue metabolic regulation.

Purpose of the Study:

• To elucidate the mechanisms of glucose transport in human adipose-tissue microvascular endothelial cells.
• To differentiate between transporter-mediated and non-transporter-mediated glucose uptake.
• To investigate the fate and release of transported glucose within endothelial cells.

Main Methods:

• Utilized radioactive [3H]-2-deoxyglucose (2-DG) to track glucose uptake and intracellular processing.
• Employed fluorescent 2-NBD-glucose (2-NBDG) to study endocytosis and recycling pathways.
• Investigated the role of glucose transporters (GLUT1, GLUT3) and other cellular mechanisms.

Main Results:

• 2-DG uptake was primarily mediated by GLUT1 and GLUT3, with rapid intracellular phosphorylation and glycogen incorporation.
• A fraction of intracellular 2-DG was released, largely unphosphorylated, involving endoplasmic reticulum components and stimulated by adrenaline.
• 2-NBDG entered cells via fluid phase endocytosis, insensitive to GLUT inhibitors, and exited through recycling sensitive to N-ethylmaleimide.

Conclusions:

• Endothelial cells possess two distinct glucose entry routes: transporter-mediated uptake into the cytosol and endocytosis.
• Glucose handling involves complex intracellular processing, including phosphorylation, glycogen synthesis, and regulated release.
• These findings highlight the intricate mechanisms of endothelial glucose transport, impacting tissue solute delivery.