Schwann cell metabolism

Several aspects of Schwann cell metabolism emerge as potential points of vulnerability to toxicants. The Schwann cell perikaryon (cell body) supports an enormous peripheral structure, the myelin sheath, which, if unwrapped, would dwarf the body of the Schwann cell (see Figure 30.4). Thus, as in the case of axonal transport in neurons, there may be specialized processes involved in supporting the topologically distant myelin. Furthermore, myelin has a specialized lipid and protein composition and a relatively rigid and ordered structure as compared to other membranes. Metabolic perturbations that potentially cause alterations in the composition of lipids and proteins assembled to form this membrane may cause destabilization and collapse of the myelin membrane. In this context, myelin might be much more vulnerable than plasma membranes of other cells. 

The neuregulins also act on Schwann cells to stimulate motility and migratory activity. It is postulated that this interaction provides a mechanism by which neurons can influence glial metabolism and behavior, which are important both in development and for peripheral nerve regeneration. 

Oligodendrocytes are present in the CNS as well and wrap around axons to form a myelin sheath. Myelin wraps into concentric layers that spiral around the axon. Gaps in the oligodendrocytes are the nodes of Ranvier, where the membrane maintains contact with extracellular fluid. The nodes serve to propagate the action potential in myelinated axons. Schwann cells perform an analogous function, myelinating axons in the peripheral nervous system. Not all neurons are myelinated, but myelination increases the metabolic efficiency of action potentials. Demyelination of neurons produces deficits in neuronal conduction, as is seen in multiple sclerosis. 

Neuroglia include (1) ependymal cells lining the ventricles of the brain and the central canal of the spinal cord, (2) cells of the PNS (Schwann cell) and CNS (oligodendrocyte) that wrap around axons to form compacted plasma membranes (myelin) that provide electrical insulation to speed nerve conduction, (3) cells (astrocytes) that interface between nerve cells and capillaries in the CNS, regulate interstitial water content, concentration, remove and metabolize certain NT molecules, and proliferate following injury. 

Miinea C, Eichberg J. Altered arachidonic acid metabolism and diminished antioxidant production is induced in cultured Schwann cells by elevated glucose, Diabetes 2000 49(Suppl 1) A166. 

Diabetics are also damaged by another consequence of hyperglycemia increased metabolism by the sorbitol pathway. In some cells that do not require insulin for glucose uptake (e.g., Schwann cells in... 

Not only may this relationship confer a special susceptibility to metabolic derangements but so may also the endowment of certain axons with myelin sheaths. The intimate myelin investment of axons in segmented fashion by the specially differentiated cell membranes of Schwann cells serves to allow an increased rate of transmission of electrical impulses by virtue of saltatory conduction at the nodes of Ranvier. Since the rate of conduction of impulses in the absence of this segmental sheath is much slower, myelinated fibre function can be... 

Although in the conditions now to be discussed little is known of the precise mechanism of cell damage, it seems reasonable to conclude in each case that it is due to disruption of the normal metabolic activities of either neurones or Schwann cells, resulting in one or other of the above-mentioned types of degeneration. 

---