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Satellite cells and apoptotic signaling in aging muscle.
Satellite cells are normally quiescent nuclei or muscle stem cells,
that sit between the basement membrane and the sarcolemma of a muscle fiber.
When these cells are activated they proliferate,
and are essential to the repair or regeneration of muscle
after injury or in response to even exercise or other loading stimuli.
In aging, satellite cell proliferation is suppressed
as there is differentiation capacity that is limited,
and that means that muscle repair is inhibited.
Satellite cells and apoptotic signaling, TUNEL labeling,
identifies DNA nicks and are DNA fragments that occur in the nuclei.
It turns out that apoptotic signaling is elevated in
satellite cells and muscles from old subjects as compared to young subjects,
and fully at all.
If isolated satellite cells,
culture them for four to 72 hours,
and then they imaged them after incubation with
the TUNEL substrate to identify apoptotic nuclei.
Fulle reported that there was a marked increase in the TUNEL labeling
as indication of apoptosis from these cells isolated from older subjects,
and they were much higher than them as compared to the younger subjects.
So, Fulle and co-workers have described more completely
the apoptotic signaling cascade that
occurred in satellite cells from young and old muscles,
from averaging age subjects that were
71 years old and they compared them to subjects that were 27 years old.
In the TUNEL labeling was evaluated as an apoptotic index along with annexin V,
which was another indicator of apoptotic nuclei.
Their data suggest that humans satellite cells are indeed susceptible to a apoptosis.
The interesting and important note,
is that satellite cells are in fact eliminated,
then this will result in a reduction in
the ability for muscles to repair in the aging environment.