44 replies to this topic

[manofsan]

I have some questions on telomeres.

Are the telomeres in the various cells of your body all the same length?
What is the average telomere length, when you are born? How many units? How many cell generations does the average person have in them?

Do all human beings have the same telomere length at birth? Or does it vary from person to person?

Can conventional genome sequencing methods measure the telomere length?

What mechanism causes the telomere to decrement its length by a single unit, during replication?
Can that mechanism be overridden/suppressed, and if so, how?

[olaf.larsson]

Now create a libary on your computer go to www.pubmed.org search for "telomeres" AND "telomerase". Dowload interesting files in pdf-format, after some a some days of reading you will know alot more about the subject. Then search for "mitochondria AND mutations" soon you will know pretty much about all areas discussed here.

A average person has 50-60 cell replication left about the time he/she is born. Telomere length is limiting for human lifespan but the importence of telomere shorting for normal aging is very over estimated according to me. Mouse have longer telomers and telomerase ON all the time but I dont think you would like to change your lifespan with a mouse. What is your profesion manofson.. have I asked this before is it chemist?

[manofsan]

Hi, I work in IT, but my schooling was in chemical engineering. I hear what you're saying, but if mouse cells are dividing sufficiently faster than human cells, this could overcome the fact of longer telomeres.

I'd like to compare a longer-telomere person with a shorter-telomere person. Because at some point, comparing mice to humans is like comparing apples to oranges.

Are all humans born with the same telomere lengths? Is there any correlation between telomere length and longevity within humans?

[John Schloendorn]

Telomerase knock-out mice propagate for like 6 generations, 8 if they get p53 knocked out, while human telomeres would not be long enough to allow for a single generation without elongation, though of course no experiments have been done to validate this in humans.
Mean telomere length is highly variable between chromosomes, cells and cell types and somewhat variable between individuals.
There is a correlation between telomere length, longevity and even vitality. The type of comparison youre thinking of between short- and long telomered persons is currently underway somewhere. I think I picked that up in one of the sens talks, though I cant find it right now, sorry.

As for the shortening mechanism, yep, do pick up a textbook. They're no black magic and pretty fascinating to read I bet you'll get stuck for hours :-)

It is possible that ALT+ cancers bypass the shortening mechanisms by creating DNA loops rather than linear telomeres. But do I hope no one catches me posting this, since it is heavily debated right now.

[olaf.larsson]

If ALT would create loops it would be known since long time wouldn´t it?
The mechansim for ALT is not known but is now under investigation.

[John Schloendorn]

I hope no one catches me posting this

geez, i did get caught :-) the loops structures are
known, but not the mechanism that's right.

[olaf.larsson]

As I know the telomeres are normaly aranged in loops with various protein
sticked to them.

[John Schloendorn]

Yes, sorry I was oversimplifying. The finding of that paper I cited was that in the ALT line studied there exist free, as in not chromosome bound, circular DNA structures with telomeric repeats on them, plus the normal telomeric loops (t-loops) at the end of the chromosomes.
Now the idea is that telomeric DNA replication might, and that is a big MIGHT of course, happen on the free circles, where it obviously does not run into an end-replication problem. The daughter DNA might then integrate into the genomic telomeres via homologous recombination, drawing on the homology between the TTAGGG repeats themselves. This supported by the observation that genomic t-loops are unusually short in the ALT line, so that some genomic TTAGGG repeats sit outside the loop, where they are not shielded by telomere associated proteins, or tertiary structure and thus should be especially prone to recombination.

Now this is significant for a reason. Similar free circular TTAGGG containing DNA structures have been observed in vertebrate early embryonic development, where they might, if I may engage in some more wild speculation, be responsible for non-pathogenic ALT that could cooperate with telomerase to maintain telomere length in times of rapid cell division, such as in the early phase of xenopus development. Cancerous ALT then, may be nothing more than another developmental mechanism gone awry, which is very common in cancer after all. Furthermore, distinct enzymatic machinery may exist to get the job done, which can be knocked down, or out, supporting the feasibility of whole body interdiction of lengthening of telomeres (WILT) as a cancer-prevention strategy.

[John Schloendorn]

Manfosan, as for your initial question of telomere length correlation with longevity, look, I found one:

http://www.ncbi.nlm....t_uids=12573379

[John Schloendorn]

Prometheus, sure WILT is pure science fiction. We'd need the technology to regenerate all stem cells periodically from ex vivo. Even then, undergoing the repetitious treatments and probably the accelerated aging in between will suck. Only if it should turn out to be perfect cancer prevention, and other therapies continue to fail, it may be a consideration.

[ddhewitt]

Just a note on WILT:

Stem cells are as telomerase positive as cancer cells.
What can you foresee would be the effects of impairing stem cell lifespan?

Something that may be of even greater concern to some people would be the effect on germ cells.

I guess the way to work around this is to defer treatment until childbearing is done or perhaps bank sperm and eggs early on for later fertilization.

[macdog]

Part of my stack includes Carnosine, which purportedly can extend the extend the Hayflick limit by ~10%. If you figure that the limit is 50 times, in an average lifespan of 80 years that means each cell divides every ~1.5 years. The increase in the limit would then mean about 7.5 extra years. Of course, this is a radical oversimplification. Still, if you can extend the Hayflick limit, and slow down the rate of division through calorie restriction or mimics, that should lead to a life extension, or at least more healthy years later in life.

I'd like to note that I doubt any single theory of aging is the end all answer. The free radical theory, the membrane theory, declining mitochondrial populations, and I think especially the decline in the function of the liver and kidneys all have an input in lifespan. None of which matters of course, if you get hit by a bus.

[John Schloendorn]

Telomere elongation is the only thing I can think of that happens in each and every tumor cell on earth, with at least some rudimentary specificity. That is, if you abolish it, you can live for a short while, but you are absolutely postivie to kill every tumor. If you want something ultimately effective that would be a choice. But of course, I could not agree more with you that WILT is highly controversial for a reason. You might just not need something ultimately effective.
Especially when we already have the technology to regenerate each and every stem cell from ex vivo, it might as well be used to rescue the patient after overdose traditional chemotherapy, which abolishes all cell division more quickly and is much easier to apply than WILT.

[marcus]

John,

This is my first post on this site, but I have had an active interest in aging biology for a couple of years now. My personal goal is to learn as much as I can about the many different aspects of aging biology so as to paint an ever increasingly clearer picture of how to best go about defeating the aging process. I am very interested in the work of Aubrey de Grey and much of what he has written has me thinking in new directions.

Currently, I see stem cell therapy as probably the most likely route toward real rejuvenation. I am also very interested in what sort of ex-vivo gene therapy manipulations that could be utilized on to-be-transplanted stem cells to help confer greater health benefits.

Back to your post about WILT, have you taken a look at some of the work being done at Geron? Their telomerase inhibitors could play a major role in helping reduce the incidence of cancer. All it takes is a major intervention preventing cancer from aquiring the 6 superpowers that makes them deadly and the advance of the disease could be broken. Inhibiting telomerase would help dramatically lower the chances that pre-malignant cells would be able to live long enough to acquire the ability to metastisize. It's an interesting approach I am following the development of.

Even though I have been following the development of aging research over the past couple of years this is the first time I've gotten time to really explore this site and see what is going on here. This looks like a good forum for quickly gaining insight into current developments and also in getting some analysis on the reports. Do you have any suggestions to help me best utilize this site? I appreciate your time in a response.

Marcus

[John Schloendorn]

Marcus,
Welcome to Imminst, good to have you here. I agree with your strategy. I think, cell therapy with appropriately ex vivo engineered cells, in conjunction with tissue engineering and maybe a bit of classical gene therapy for postmitotic tissues that prove resistant to either (brain?) will be the way to go.

Haven't been to Geron's web site for a while, but from what you tell me I see they have not lost much of their initial promise. When do you think we'll se the first approved therapies from them?

The best way to make use of imminst is certainly to check around and get involved where you think it's productive or fun. Make a post in the intro forum, tell us a few things about yourself and get in touch with people. Everyone here is grateful about a new colleague, especially when you're into biomed.

Btw, Aubrey is always happy to receive fan mail from young biomed people. Have you checked out his new Conference in September? Registration just opened. Costs a whole sack of money but should be well worth it.

[marcus]

John,

I appreciate your reply. As I look further around up and down the different threads I see I was mistaken in not looking deeper into this site when I initally discovered it.

I think a re-visit to Gerons site is worth the time. They have their hands on some interesting telomerase based technologies as well as a nice stem cell research program. Here are the highlights though, as this may save you a little time.

We have designed and synthesized a special class of short-chain nucleic acid molecules, known as oligonucleotides, that target the template region, or active site, of telomerase. These oligonucleotides, called GRN163 and GRN163L, have demonstrated highly potent telomerase inhibitory activity at very low concentrations in biochemical assays, various cellular systems, and animal studies.

Comment: These drugs could be potent anti-cancer drugs that specificaly target cancer cells(as well as stem cells albeit). The preclinical data is considered quite strong and extremely efficacious. Human trials will begin shortly

I was going to attempt to summarize their stem cell research but really it requires a detailed reading. They are doing some cool stuff. Check out the link.

http://www.geron.com...asp?code=prodst

I have been in touch with Aubrey a few times over the past couple of years. I find his work very interesting and I am actually looking to expand on it and help formulate the broad ideas into a more concrete plan. I believe that by coming to a solid understanding of the current approaches/technologies and following recent developments in important fields such as stem cell therapy, gene therapy, cancer, basic research into the aging process itself etc. etc. we will be able to formulate an evermore realistic concrete research agenda. I actually like to think of it as a battle plan. First thing you do in a battle is gather as much information as you can about the enemy(in this case aging) and only then can you begin to formulate the best battle plan that has the best odds of defeating your enemy. I know it's a strange way of looking at things, but systems analysis can apply just about anywhere.

I'm still in the fun learning process, though, and I still have much to learn as there are dozens of companies and labs that are working on one aspect or another that could potentially apply to the development of a real cure for aging. But everyday I try and learn something to help paint a clearer picture of what the techology will look like that finally thwarts aging. I really feel pretty strongly that right now the end vision of using stem cells to re-seed various tissues on a mass scale in a directed manner holds a lot of promise toward being able to regenerate tissues that are on a cellular level phenotypically younger, on a tissue level phenotypically younger, on the organ level theyare phenotyically younger, and so on up to the level of the organism being phenotypically younger. These cells could be manipulated ex-vivo and primed for optimal health. Early work on stem cells holds great promise with their ability to integrate with existing tissue. Multipy this effect in a controlled way on a large scale and you may have solved aging on a cellular level.

There would still be the problem of cleaning up the junk/aggregates, and further downstream problems that would surely develop, but having young cells would be a huge step toward having young tissues. Alteon has a drug in development that could begin to address the problem of 1 class of cellular aggreagates. I think this field in general is one of the more underfunded, overlooked aspects towards developing solid aging therapies. Cleaning up some of the mess whether through genetic modulation allowing for production of new enzymes or drugs which facillitate the breakdown of currently undegradeable aggregates needs WAY more attention in my opinion. I think this aspect is especially overlooked when you look at it from a commercial development standpoint. Research in this field could not only help one day lead to reversing aging, but along the way attacking the molecular basis of these aggregates which are linked in everything from heart disease to arthereosclerosis to wrinkles would likely have huge commercial benefit.

Thank you for the welcome. I will post a message on the intro. forum and look forward to spending a lot more time on these threads. I would love the opportunity to go to the SENS conference. Howeverm I probably will be unable to attend. With a little work this thread could help to communicate what some of the big thinkers in the field are saying and working on. I firmly believe that sites like this could help in the all important dissemination of relevant information that can only help spur progress in the field. The more we all learn the closer we get to a cure. I also welcome all debate and challenges to anything I post and would look forward to anyone correcting anything I may have mis-statesd as it will only help spur discussion that can help us all.

Marcus

Edited by marcus, 02 January 2005 - 06:40 AM.

[John Schloendorn]

I was not aware Geron's stem cell program had grown into something that impressive. Thanks for showing me. I see that we have much strategic thinking in common so if you seek heavy criticism, look elsewhere!
By the way, I'm also a big fan of something like Aubrey's IBG idea. Such a centralized institution, where everyone personally meets everyday, would allow us to merge all our individual 'battle plans' into a more coherent picture, more than this online forum can do. (This is at least so for biotech people. Lab rats need a lab to hang out in.)

As for AGE-breakers and their commercial value, I have my doubts, mainly due to their demonstrable utility for cosmetic skin treatment. Today's pharma companies have become extremely successful at selling skin rejuvenation products that don't work. By making one that does work and has to be applied as rarely as an AGE breaker would likely have to be, they would deprive themselves of their most profitable income. Anyways, I hope I'm wrong.

What do you think of the following idea for a small skirmish in our battle:
I'd love to take nearly any of the SENS ideas, package them on a huge artificial chromosome, make a transgenic mouse with it, regularly smear some ALT-711 on top of it and see how it goes.

[John Schloendorn]

And I might add that I also feel that elaboration and expansion of SENS is a high priority of our time. If you are working on anything concrete, and could use a hand, be sure to let me know.

[LifeMirage]

New Study:


Biochem Biophys Res Commun. 2004 Nov 12;324(2):931-6. Related Articles, Links
L-carnosine reduces telomere damage and shortening rate in cultured normal fibroblasts.

Shao L, Li QH, Tan Z. Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, PR China.

Telomere is the repetitive DNA sequence at the end of chromosomes, which shortens progressively with cell division and limits the replicative potential of normal human somatic cells. L-carnosine, a naturally occurring dipeptide, has been reported to delay the replicative senescence, and extend the lifespan of cultured human diploid fibroblasts. In this work, we studied the effect of carnosine on the telomeric DNA of cultured human fetal lung fibroblast cells. Cells continuously grown in 20 mM carnosine exhibited a slower telomere shortening rate and extended lifespan in population doublings. When kept in a long-term nonproliferating state, they accumulated much less damages in the telomeric DNA when cultured in the presence of carnosine. We suggest that the reduction in telomere shortening rate and damages in telomeric DNA made an important contribution to the life-extension effect of carnosine.

[John Schloendorn]

Prometheus: Thats right, on every single tumor there is plenty of specific target molecules. But which one is essential to each and every tumor? As you target one surface marker, you often enough get relapse from the few cells that had learned to do without it due to genomic instability. Don't get me wrong, I still think we may learn to perfect this present approach to a degree where it is sufficient, which would be just another point against WILT.

LifeMirage:
Nootropics people did their homework? That's good :-)

[marcus]

John,

I haven't looked into artificial chromosomes since they were intially developed here in my hometown at Case Western. I've visited the company that owns those intial rights(Athersys) on a couple of occasions. They are right down the road from me. They appear to be applying minimal resources towards further developing the artificial chromosomes and are puting most of their effort into the development of their RAGE expression vector. Are you aware of further developments in the past 3-4 years? I should probably do a literature search and see where AC development stands today...I'm under the assumption though that ACs may be made somewhat obsolete by the reality of whole cell(stem) therapy. I think it would be easier to alter the genome of cells before implantation using more traditional ex-vivo gene therapy vectors versus using an entire artificial chromosome. I could be wrong though.

On an unrelated note, I have been working on compiling a list of leading companies and labs that are either directly or indirectly working on research that could lend a hand in making SENS a reality. I was thinking of posting my list and then others could add to it and the relative importance of the different labs work could be debated. I think I'll work on compiling my notes over the next couple of days and come up with something to post for everyone. I'm very curious to hear what others on this forum see as key developments and areas to keep a close eye on.

Marcus

[ddhewitt]

What could be designed to respond to a high concentration of a specific protein?

Priming a T-cell based immune response against the protein of interest.

Even if the protein is expressed internally there will probably be some display of it on the cell surface by MHC molecules.

Duane

[ddhewitt]

To address manosfan's original questions:

Are the telomeres in the various cells of your body all the same length?

No because different cell types and even different cells of the same type have different replication histories.
Highly proliferative tissues will tend to have shorter telomeres while tissues that do not replicate very often will tend to have longer telomeres. Cancer cells often have short telomeres even though telomerase has been activated.

What is the average telomere length, when you are born? How many units? How many cell generations does the average person have in them?

I believe in humans the average telomere length is 10 kilobases. In mice it is 50 kilobases. The Hayflick limit is about 80 divisions.

Do all human beings have the same telomere length at birth? Or does it vary from person to person?

Good question. I am not aware of any studies into this.

Can conventional genome sequencing methods measure the telomere length?

No but there is a kit available from Roche to measure telomere length called the TeloTAGGG Telomere Length Assay.

What mechanism causes the telomere to decrement its length by a single unit, during replication?
Can that mechanism be overridden/suppressed, and if so, how?

The telomere is by definition the end of the chromosome. By virtue of how DNA polymerase works each time the DNA of a chromosome is replicated part of the end fails to replicate. Telomerase overcomes this by using an RNA template to synthesize a DNA repeat that extends the end of the chromosome.

Hope this helps.

Duane

[John Schloendorn]

Marcus: I'd be happy to save you some work in turn. Since I'm currently working with that stuff I have some references at hand (that is I could send you full text if need be). State of the art MAC engineering is here, the use of MACs to engineer stem cells ex vivo is here and the creation of transgenic animals using MACs is here.

And that researchers list thing, funny, I've been doing the same in the course of my study going on here. By the way, feel free to participate and/or comment on that project. I want to send an invitation to the list of research groups in the coming days, but it may be worth to line up our lists first. Mine was compiled also with the researchers personal awareness/disposition in mind to extend human life, not just their work. I sent you a copy by email.
Discussing the groups' work is an excellent idea. I'm sure we will all learn a lot from such an extensive discussion. Go for it. Though you might have to ask Bruce for an extra forum to fit it in ;-)

Prometheus:
I'm not into cancer treatment at all, but I think Duane's suggestion is being heavily pursued at this time. Knock-down by local administration of siRNA also showed some promise. Doing such things for most gene expression changes we see in different cancers is a way to go. At this time clinical success is modest, but we may see considerable improvement as the network of knowledge is growing. Let's hope this happens before cancer becomes the one thing that a mature regenerative medicine can't heal.

[John Schloendorn]

A caspase? Other suicide gene? Sounds promising. Any unduly proliferating cells might shut down before they get a chance do clonal expansion and microevolution to silence your system.
But what would be the mechanism for your inducible system? Some cancer markers are transcription factors (e2f, ect), but I can't think of any that would not again be active in every dividing cell. So what are you up to? Any concrete ideas which genes/promoters to use? Out with it!