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What is involved in the spontaneous regeneration of
the myelin sheath surrounding nerve fibres?
Researchers have discovered, in mice, the unexpected
regenerative role of testosterone in this process.
Transmission electron micrograph of a myelinated
axon. The myelin layer (concentric) surrounds the
axon of a neurone, showing cytoplasmathic organs
inside. Generated and deposited into the public
domain by the Electron Microscopy Facility at
Trinity College.
This could be a factor in the progression of
demyelinating diseases, such as multiple sclerosis,
which can present differently in women and men, and
heralds new therapeutic opportunities.
The myelin sheath allows the rapid transmission of
information between the brain or spinal cord and the
rest of the body.
Myelin may be targeted by conditions known as
demyelinating diseases, such as multiple sclerosis
or injuries that lead to its destruction.
These diseases disrupt neurotransmission, leading to
various symptoms including paralysis.
Repair mechanisms then come into play, and bring
about myelin regeneration and resolution of
symptoms.
This regenerative process is erratic, for reasons
that are still largely unknown. This question was
analysed by the research team “Myelination and
Myelin Repair” in Unit 1195, “Neuroprotective,
Neuroregenerative and Remyelinating Small Molecules”
(Inserm/Paris-Sud University).
In this study, the researchers present evidence of
the unexpected central role of the well-known male
sex hormone, testosterone, and of its receptor, the
androgen receptor, in spontaneous myelin repair.
“Testosterone promotes the production of myelin by
the cells that synthesise it in the central nervous
system, in order to repair the sheath, which is
essential to the transmission of nerve impulses,”
explains Elisabeth Traiffort, Inserm Research
Director.
In the absence of testes and hence of the hormone,
testosterone, that these organs produce, the
spontaneous myelin repair process is disrupted in
mice.
Indeed, the maturation of cells specialised in
myelin synthesis, known as oligodendrocytes, is
defective. The researchers also showed that control
of this maturation, provided by astrocytes, another
type of cell with an important role in repair, is
what is compromised.
But why testosterone? Returning to the origins of
this hormone, it turns out, surprisingly, that the
androgen receptor that enables testosterone to act
appeared at the same time as myelin, very late in
the evolution of gnathostomes (vertebrates with
jaws). According to the researchers, this would
explain their very strong association in the
myelination process.
For more information
PNAS
Unexpected central role of the androgen receptor in
the spontaneous regeneration of myelin
Link...
Inserm
Institut national de la santé et de la recherche
médicale
Link...
MDN |