All stem cells have active telomerase right?
Stem cells and telomerase
#1
Posted 10 June 2005 - 08:29 AM
All stem cells have active telomerase right?
#2
Posted 10 June 2005 - 10:48 AM
Well, there is one, namely ALT, which is active in some cancers. But it confers genomic instability and is not known to be active without cancer. So if you count cancer-stem cells, there might be some telomerase-negative, but ALT positive ones.
(I just posted some related points in the journal club.)
#3
Posted 11 June 2005 - 03:58 AM
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#4
Posted 11 June 2005 - 04:14 PM
If stem cells have telomerase they could replace old telomere short cells with new ones.
I rather suspect that stem cell mutations are important.
#5
Posted 11 June 2005 - 10:57 PM
#6
Posted 12 June 2005 - 11:12 PM
#7
Posted 12 June 2005 - 11:55 PM
#8
Posted 13 June 2005 - 01:45 AM
Transplantations with stem/progenitor cells derived from embryonic stem cells (which is also a form of young to old transplantation) are more frequent and easily found on pubmed. But in many tissues, the teratoma problem has not been resolved.
#9
Posted 15 June 2005 - 08:54 PM
#10
Posted 15 June 2005 - 10:58 PM
Plus:During aging, telomerase levels and telomere lengths decline in many stem cells, which is thought to contribute to their age-related exhaustion.
There may be other causes (other mutations, hormone signalling, extracellular matrix changes, niche cell dysfunction), that also contribute to the decline of stem cell numbers with age. This of course puts more stress on non-stem somatic cells, because they get less frequently renewed (and stress can shorten telomeres).
All in all, the idea that the same telomere gets progressively shorter over the life-span seems pretty wrong. It's all a highly dynamical thing.
#11
Posted 16 June 2005 - 11:28 AM
#12
Posted 16 June 2005 - 11:59 PM
#13
Posted 17 June 2005 - 02:13 PM
#14
Posted 17 June 2005 - 05:29 PM
Where I live scientist including human geneticist and cancer specialists seem to "know" that aging is caused by telomere shortening.
I too have heard this from scientists who don't study aging. Unfortunately, this misconception is very widespread and well entrenched.
#15
Posted 18 June 2005 - 12:02 AM
That would mean that telomere shortening has no effect on aging invivo.
Whilst this is apparently the case in 1st - 3rd generation mice one would want to be very cautious about applying this line of reasoning towards a longer lived mammal where the number of stem cell divisions is greater during the span of lifetime and where the interactions and effects of telomerase may be more complex.
#16
Posted 22 July 2005 - 05:00 PM
This experiment has been done, but not quite in the way you wanted it to be done (I guess). In one paper [Dressler et al., 2005 ] they claimed to have frozen stem cells of a rabbit and injected them back into the same old animal (into the tendon) and measured the repair. The old stem cells are supposed to regenerate the tendon as good as the young stem cells. But they did not look for engraftment of the young stem cells in the old animal as control.
Not all stem cells have active telomerase. The expression in some stem cells is still under discussion.
In addition, some stem cells seem only to have active telomerase for short period of times (see haematopoetic stem cells). And even when telomerase is active, this does not mean that not telomere shortening can occur. In blood stem cells it was shown that despite them being sometimes telomerase positive they loose telomeres. Some studies have also shown that oxidative stress can increase telomere shortening by introducing single/ double strand breaks, which shortens the telomeres with the next round of replication even faster. Telomerase activity under high stress might not be sufficient to stabilise telomeres
To the discussion about aging researcher. Sure they say they know why aging occurs and how it occurs, as only then they will get many. It is either my theory (my money) or your theory (your money).
Greetings
Edited by Mondey, 03 August 2005 - 08:42 PM.
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