Remyelination

Key takeaways

Remyelination belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Remyelination to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Remyelination from memory before moving on to harder problems.

Reference excerpt

Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the Central nervous system (CNS). This is a process naturally regulated in the body and tends to be very efficient in a healthy CNS. The process creates a thinner myelin sheath than normal, but it helps to protect the axon from further damage, from overall degeneration, and proves to increase conductance once again. The processes underlying remyelination are under investigation in the hope of finding treatments for demyelinating diseases, such as multiple sclerosis. As of 2022 the status of possible remyelination acceleration is of trials only, with side effects of possible drugs one limiting issue.

Function Remyelination is activated and regulated by a variety of factors surrounding lesion sites that control the migration and differentiation of Oligodendrocyte Precursor Cells. Remyelination looks different from developmental myelination in the structure of the myelin formed. Reasons for this are unclear, but proper function of the axon is restored regardless. Perhaps of most interest are the inhibition and promotion factors of this physiological process. One way this process can be traced is by following different protein activation sequences which have shown just how quickly remyelination begins after injury (within a few of days).

Characteristics of remyelinated axons The most notable evidence that remyelination has taken place on an axon is its thin myelin sheath created by an oligodendrocyte, though the reason why the new myelin sheath is thinner remains unclear. This can be quantified in the g-ratio, the ratio between the diameter of the axon itself to the outer diameter of the myelinated fiber. Remyelinated axons tend to have values closer to 1, indicating a thinner myelin sheath than those myelinated naturally. The g-ratio differences are less apparent on smaller axons.

The thinner myelin not only restores protection of the axon from degradation, but also restores a faster conduction velocity. The conduction velocity, however, is not as strong as naturally myelinated axons and the Nodes of Ranvier are inclined to be wider which results in less coverage in the axon by myelin than what is natural.

OPC involvement Oligodendrocyte Precursor Cells, or OPC's, are the main cells responsible for the remyelination of demyelinated axons. There are two physiological changes that must occur to OPC's for remyelination to occur. Once a signal is sent that remyelination is needed, OPC's will first migrate to the damaged axon. This process may be signaled or enhanced by microglia or astrocytes at the injured axon site that stimulate migratory OPC pathways From there the cells must differentiate from being progenitors to being pre-oligodendrocytes, then premyelinating oligodendrocytes, and finally mature oligodendrocytes. These oligodendrocytes can then wrap damaged axons with new myelin sheaths. This process of differentiation through several phases has many involved and direct pathways and factors necessary for the completion of this process. It is easy to completely stop remyelination with the failure of a number of pathways.

Propagation factors One of the difficulties of studying remyelination is the variety of factors that play a role in differentiating oligodendrocyte progenitors. While some factors promote and others inhibit, still some factors that are known to be involved are yet not understood enough to know whether it promotes, inhibits, or does both. Many factors are poorly understood and subject to much change as research is done.

Cytokines and chemokines Cytokines mediate inflammatory responses that promote pathogen and debris clearance so that further tissue damage is avoided. Too much can mean cell death but failure to propagate cytokines at all in remyelination results in a lack of debris clearance at a damaged axon site; this buildup of myelin and oligodendrocyte debris has been shown to inhibit the differentiation of Oligodendrocyte Precursor Cells. Specifically, cytokines promote TNFR2 and eventually TNF-alpha which plays a key role in OPC differentiation. It has also been shown that chemokines are involved in guiding immune cells to sites of axon lesions to facilitate inflammation and debris clearance as well as possibly guiding OPCs migration to lesion sites. So then, chemokines are directly involved with both migration and differentiation of OPCs. The specific chemokines involved with each of these two processes is known: CXCL12 is related to migration and differentiation is increased with an increase in CXCR7 and a decrease in CXCR4. In certain demyelinating diseases CXCL12 has been shown to be decreased, possibly playing a role in demyelination failure. Still much is to be researched in this field, as certain chemokines like CXCR2 plays a role in inflammation and repair but in an unknown manner over much controversy.

Signaling pathways LINGO1, a cell receptor, has been proposed to be involved in the regulation of remyelination. It is thought to inhibit not only axon regeneration but also regulate oligodendrocyte maturation by inhibiting OPC differentiation. Animal studies suggest that when a LINGO1 is inhibited, OPC differentiation and thus remyelination can be promoted at demyelinated sites. LINGO1 gene expression is also known to activate RhoA which may also play a part in inhibition. Myelin debris build up might be responsible for the promotion of the LINGO1 signalling and overall inhibition. The Notch-1 receptor pathway is another pathway that inhibits the differentiation of OPCs. When the ligands Jagged1 and Delta, produced by axons, neurons, and astrocytes, are stimulated and bind to the membrane, oligodendrocyte maturation is inhibited. This pathway may also be facilitating migration despite its differentiation inhibition. In some experiments, altering the pathway so that differentiation is increased caused a decrease in the proliferation of OPCs. There may be other ligands that have either promoting or inhibiting effects when attached to the Notch-1 receptor. The Wnt-β-Catelin pathway has been shown to also inhibit remyelination when it is dysregulated in the body. Demyelinating diseases have been shown to cause this dysregulation. Possible genes involved inside this pathway are TCF4 and OLIG2 which are both expressed in high amounts in areas where remyelination has failed from demyelinating diseases.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Remyelination

Start with the simplest possible case. Write down what Remyelination claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Remyelination before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Remyelination ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Remyelination

In research: Remyelination appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Remyelination in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Remyelination is common in secondary-school and first-year university syllabi. It links to neighbouring topics Neurology, so understanding it makes those chapters shorter.
In everyday life: Look for Remyelination outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Remyelination in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Remyelination means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Remyelination out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Remyelination in simple terms?

Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the Central nervous system (CNS). This is a process naturally regulated in the body and tends to be very efficient in a healthy CNS.

Why does Remyelination matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Remyelination?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Remyelination.