Schwann cell glycogen selectively supports myelinated axon function

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Axon loss can result from interrupted energy supply.
• Glycogen's role in peripheral nerve energy metabolism was previously unclear.

Purpose of the Study:

• To determine if glycogen is present in mammalian peripheral nerve.
• To investigate if glycogen supports axon conduction during aglycemia (glucose deprivation).

Main Methods:

• Biochemical assays and electron microscopy to detect glycogen.
• Electrophysiology to assess axon function (compound action potential - CAP).

Main Results:

• Glycogen was found in sciatic nerve, mainly in Schwann cells, and its levels correlated with ambient glucose.
• During aglycemia, large myelinated axon (A fiber) conduction failure paralleled glycogen depletion.
• Glycogen content predicted CAP failure latency in A fibers; glycogen did not benefit unmyelinated C fibers.

Conclusions:

• Peripheral nerve glycogen, primarily in Schwann cells, exclusively supports large myelinated axon conduction during aglycemia.
• Glycogen breakdown likely provides lactate to myelinated axons for energy.
• Unmyelinated axons lack glycogen protection and are vulnerable during hypoglycemia.