Telomere Length and Mitochondrial DNA Copy Number Over the Mouse Lifespan

The science of intervention in aging has reached the point at which the research community should be undertaking a great deal more of the sort of work exhibited here. The authors of this open access paper have done the public service of producing reference data on telomere length and mitochondrial DNA copy number in multiple tissues over the mouse life span. Telomere length is a terrible metric for aging when measured in the immune cells taken from a blood sample; it varies widely between individuals, is dynamic for a given individual, dependent on day to day environmental and health factors, and trends with age only show up in statistical analyses carried out across sizable study populations - and sometimes not even then. Mitochondrial DNA copy number is more interesting, and a reference work here might be quite useful.

Both of these metrics, regardless of their quality or lack of same, are downstream consequences of lower-level forms of damage in aging. Average telomere length is a loose measure of stem cell activity, a proxy for the replacement rate for cells in a tissue. Stem cell activity declines with age, and thus so does the supply of new cells with long telomeres. Mitochondrial DNA copy number is generally thought to fall with age (though see the results below), and lower copy number counts correlate with poor health outcomes. Mitochondria, the power plants of the cell, undergo a general malaise with age, their function faltering, and this contributes to many age-related conditions, particularly in energy-hungry tissues like muscles and the brain. These processes have underlying causes, and go on to cause further issues themselves. A good fraction of the research community involved in aging seeks to override these evident declines without trying to address the root causes - an approach that may well produce some benefits, but will not solve the problem of aging in and of itself.

Our study aimed to provide chronological aging standard curves and slopes of telomere length and mitochondrial DNA copy number (mtDNAcn), which can help researchers objectively assess the degree of aging in target tissues in various studies using C57BL/6 male mice. C57BL/6 is one of the commonly used rodent models. To evaluate telomere length by qPCR, we used the telomere primer set telg and telc. Unlike previously suggested primers that generate PCR products of various lengths, the telg and telc set produced PCR products of constant length, resulting in stable amplification and clear chronological standard curves.

The telomere qPCR conditions proposed in this study resulted in reproducible and discriminating amplification outcomes, and the fidelity of the qPCR result was further confirmed by telomere restriction fragment (TRF) analysis. The telomere standard curves also showed significant changes with aging. To the best of our knowledge, this is the first report of the aging standard curves of mouse telomeres using the telg and telc set and integrating various tissues across the body.

All 12 tissues showed age-dependent changes in telomere length or mtDNAcn, indicating that we can estimate tissue-specific aging status using at least one of these aging markers. A variety of studies have indicated that telomere erosion occurs in aged human or animal subjects. In our study, all tissues showed telomere length decline with aging. However, the mtDNAcn showed a tendency to increase or decrease with aging depending on the tissue. We found increments in mtDNAcn in the retina, thoracic aorta, and spleen, but the other tissues showed a decreasing tendency with aging.

In addition to mitochondrial dysfunction due to a decreased mitochondrial genome, increased mtDNAcn has also been suggested to be detrimental to cells and eventually induces cellular senescence or apoptosis. Accumulation of mtDNA mutations induces high mtDNAcn in nucleoids (mtDNA-protein complexes), and results in nucleoid enlargement and subsequent mitochondria functional deficiency. Excessive mtDNA replication could be triggered by the activation of twinkle mtDNA helicase and mitochondrial transcription factor A. These previous studies support the notion that an increase in mtDNAcn is a normal phenomenon in aging, although the mechanism of tissue-specific increase or decrease with aging remains to be elucidated.

It is known that telomerase activity in adult tissues differs between human and rodents. Telomerase is constitutively expressed in various tissues of laboratory mice, whereas it is tightly regulated in human somatic cells. Therefore, the results of mouse experiments cannot be directly applied to humans. Nevertheless, animal model experiments are indispensable to understanding human diseases, and the results have to be compared with human data to infer the clinical symptoms of the human body.

Link: https://doi.org/10.3390/cells8030247

Comments

Finally someone is looking at telomere lengths in different tissues, and low and behold, even in mice with active telomerase, lengths decline.

Posted by: Mark at March 22nd, 2019 7:05 AM

Hi Mark ! Just a 2 cents. Telomerase is negative pleiotropic element, it's meant for 'fitness'/survival/improvement of health - but at cost of IEAA/EEAA (Intrinsic Epigenetic Age Acceleration/Extrinsic Epigenetic Age Acceleration..telomerase activates IEAA/EEAA in methylome by creating epigenetic drifting/activation of CpG-rich genes (the ones cancer hijack/cancers hijack telomerase)) - hydras jelly fish are imm*tal...we think. They have continious telomerase (they go back to 'juvenile state' do di 'loop di loop' old-young-old-young-old-y...never dying of age/never advancing to last stage/death), bristle cone pines live 5000 years - they telomerase bouts in meristem cells in trunk and roots (mostly roots), red lobsters live 130 years or so, they have continuous telomerase and don't stop growing (until exoskeletal problems jamming them in them),

then..mouse...continous telomerase, dies in 3 years. Telomerase does not stop anything and is not the element that stop aging - at all (I used to think so until I saw it increases aging in DNA epiclock), it might make a replicative senescene post-poned a lil bit, but it does not stop intrinsic aging. That's the epigenome domain. It's interesting, because hydras (living eternally (supposedly) or least..a few thousand years if undisturbed in natural habitat, alone like hermits)) can revert their 'state'...I would guess even their Very Identity of their cells - hence, go back to a young cell identity (like fetal stemcells whom have epiage of 0). Humans, living 120 years or so, have telomerase, but a very small activity of it; telomerase does not make human live 120; it simply allows 'health' to be maintained - until you reach 120. Because, it is a fitness evolution mechanism/antagonistic pleiotropic element. Bowhead whales live up to 211 years old, they are big; no cancer even if high cellularity - naked mole rats NMR, very small, lives 10 times longer than mouse (35 years), bowhead whale (211) vs human (120) vs NMR (35) vs mouse (3), paradoxal much? Although, the size 'rises' with the longevity, stil NMR lives long for such small thing. And, one that lives Even much longer
hydra (eternal) vs iceland quahog (500) vs greenland shark (500) vs blue parrot (111) vs pigeon (35) ...demonstrating, there are outliers and many of them 'have telomerase' just like a 'safe guard' for their health, but not much more, but they keep pristine health (telomerase can reduce damage, muddying the 'damage' responsible of aging, damage can be inconsequential to 'clock aging/time passing' altering 'identity' of cell; because health and aging are uncouplable/diassociatable/independent, yet dependent (at same time)). If humans live 120 with lil telomerase and a mouse lives 3 years with high telomerase/has long telomeres but still lose some...it means telomeres are antagonistic safeguard for health/cell cycling/replication breaks (as they lower) to stop cancer formation (since cancers will hijack telomerase and lenghten telomeres or use ALT).

''Excessive mtDNA replication could be triggered by the activation of twinkle mtDNA helicase and mitochondrial transcription* factor A.''

Transcription. Telomerase hTERT (human Telomerase Transcript), transcriptome/splice-osome -> epigenetic/DNA methyl clock...transcriptional/epigenenomic 'drifting' with age -> cell identity change, one step close to cell death when it acquires cell identity 'death' on its epiclock tab.

Just a 2 cents.

Posted by: CANanonymity at March 24th, 2019 6:11 AM

@CANanonymity,

Telomerase means you always have another replacement cell if required when cells die from oxidative stress, for example. So a mouse has more replacement cells, but oxidative stress is too high even so, hence telomere lengths decline - plus apoptosis falls behind so you accummulate senescent cells.

Of course keeping a cell line going forever with telomerase would inevitably lead to epigenetic drift; to reset this we'll need to take a leaf out of your favourite jellyfish's book and press some de-differentiation buttons. But it's not clear to me that we'll need to do that in the first round of anti-aging treatments.

Posted by: Mark at March 25th, 2019 5:05 AM

Hi Mark! Thanks for that. Just 2 cents. I so hope that jellyfish ends up being the answer...the last studies where they did the whole epigenetic reversal and the epiclock was set back to 0...except the cell identity did not change/there was no potency (like pluripotency/totipotency iPSCs) created since that would be reversal...dedifferentiation. When I look at CEO Bioviva Mrs.Parrish (Elizabeth Parish), I think to myself, so she looks so young, in her 40s, thanks to her hTERT telomerase self-done therapy...yet, Telomerase is antagonistic element (leading to epigenetic advacnement of epiclock, at least the internal one), it's where I'm wondering..so many studies demonstrated telomeres shrinking as cancer prevention for accelerated damage/heahlth loss and slowly but surely, death..now, aging, is mostly in the epiclock; telomeres are part of aging, and why progeria people lose 500 bp/year while healthy humans lose 50 bp/year (HGPS live 15 years...dogs...same thing, 500 basepairs nucleotide loss/year in telomeric DNA...they live 10-15 years...it' not coincidence). If a human can live 120 losing 50 or so bs..and another live 15 years losing 500..then..
telomeres are either causal or correlative (I don't that there is still much ambiguity),

If telomerase makes you have replacement cells, always handy, to stave off the rising oxidative stress..that's great - but I think it thus means, that telomerase, is indeed, an antagonistic pleiotropic element - it's meant to stave off oxidative stress - And - in doing so, it Accelerate epipgenetic drifting (as a negative effect of requiring telomerase - antagonist pleiotropy).

I could no believe it when the study said that telomerase/hTERT increases IEAA/EEAA - but they showed it, I await a study proving contrary; telomerase is just a health guard.
I think that humans really 'push' to maximum...they live to 120 max - but that's The MAX or near max...
If you are Unhealthy and have progeria for example...you Drastically Accelerate Damage accumulation and Oxidative Stress - thus you Succomb of damage not of epigenetic aging by time passing (where as you said, at a certain point replicative senescence 'Hayflick Limit end replication' signals end as time passes and multiple division rounds, otherwise transformation to cancer (oncoscenence/immortalization).

In the sense, that a cell can die 'prematurely' and 'exit' frmo the main program (epigenetic) and have 'Spontaneous Scenescence' (caused by rising oxidative stress/causing health threshold homeostatis loss)...it's ambiguous,I know, but there seems to be two layers/two folds..a main epigenetic one (clock tab) - and health layer one (senescence/damage) on top of it. aNywaY! You are right, we need to work on both telomeres and epiclock to make sure telomeres are lengthned (or at least frozen still/no shrinking), and reversing epiclock age - the finnicky thing is the cell identity/potency (to not make teratoma cancer if using Yamanaka facotrs Oct Sox Nanog c-MYC (c-MYC is 100% involved in cancer and metastasis because improves cell division/cycling/proliferation 'stem-cell'ish' (like iPSCs) quality that cancers harbor by hijacking it)). It's tricky, telomerese are cancer inhibitors, we lose them, we increases chromosome dysfuction (uncapped short telomers/creating health compromised) again with the paradoxs/double-edged swords. The way I see it it will take more than SENS, only a very combination of so much therapy cover the whole thing (damage, clock, health, aging, like each needing something); it's why I dose my optimism of LEV possible/or eve 20 years boost of life, by therapies coming in next 20 years.

Just a 2 cents.

Posted by: CANanonymity at March 25th, 2019 7:49 PM

@ CANanoymity - Horvath has published more studies on the telomerase-epigenetic age link since, and it turns out that telomerase does not accelarate the epigenetic aging rate; the effect is purely a result of a cell line surviving for longer, so having longer to accumulate epigenetic alterations.

https://www.ncbi.nlm.nih.gov/pubmed/30332397

As with anything, once you understand it, the complex becomes simple. If you bypass senescence, you will accumulate more epigenetic changes. Whether or not this is harmful is an open question, as in humans telomere attrition and 'independent' epigenetic changes are both occurring simultaneously, so we are unable to separate the two. It will be interesting to see how Liz Parrish fares long term. I suspect she'll age very well (i.e. slowly), though I'd be suprised if her therapy reached as many cells as you'd need to cause significant rejuvenation.

Posted by: Mark at March 26th, 2019 10:19 AM

RE

''In the AD-affected brain samples, the team detected roughly 323,000 H4K16ac peaks by ChIP-seq - slightly fewer than the 349,000 or so peaks in the brain samples from older, unaffected individuals. Consistent with the histone mark's ties to aging, the young brain samples had just 239,000 H4K16ac peaks.''

"[T]he negative correlation between aging and disease clarifies an important question in the field, that is, whether AD is a simple exacerbation of aging or rather a dysregulation of aging," the authors explained. "Our results reveal the more complex latter scenario, where there is a clear component of dysregulation of aging in the pathology of AD."

https://www.genomeweb.com/sequencing/postmortem-analyses-point-distinct-epigenetic-features-aging-alzheimers-brains#.XJqxhkxFzRY

This demonstrates what I was saying, aging and health are two different things. AD (Azleimer's diseases) is a pathology, a health problem - which can kill you hen below health threshold necessary for function/brain function (my uncle died of Alz and his functions were slowly witting away as AD progressed). It is independent of aging/epigenetic aging - but it manifests as 'different epigenetic signature' (as they say : 'dysregulation of aging') - that do not correlate to Healthy chronogical aging 'regular epigenetic program/signature' of people who do not have Alzheimer's/are healthy until death.
This comes down to the old 'healthy aging' thing...healthy aging means 'undysregulated aging'..undistubved until the end, in other words, healthy until death (sustaining (health above) health threshold of 'dysregulation' (showing up increases Histone peaks in epigenome, or, as you epigenetic alterations. The young people have much less epigenetic alterations for - they are younger/haven'T had time 'to change anything yet'..and..less dysregulation, thus less peaks/alterations..while old people show much more alterations - but Old People With Alzheimers' and Same Age as Other Old People (that are healthy) show Even Moer Alterations..a sign of dysregulation in the main normal process of acquiring 'epi-alterations' with age).

Dysregulated aging, is health compromised, which hastens death - no of 'age', by of dysregulation of the Normal 'healthy aging' program. From this study it is clear we accumulate epialterations/epimutations with age..it's most likely adaptation etc...and the program 'running its course'..until death 'of age/time passing'. I think what this shows us is that there is Threshold of Maximal Alterations (per se), or let's say, at a certain point, it's just Not Viable anymore; and this would cause death, so it would be the stocastic accumulation of epialterations that would lead to a point of dysfunction 'jamming' - the difference between This (healthy aging till death) and a Disease like Azhleimers is that the pathology (much more likely to happen in old age) will Cause Dysregulation of 'healthy aging' program - to a 'unhealthy aging prograM (hence die quicker - suddnely of whatever disease).

Thus, as I sspecified, 'exit' from main program (healthy aging) and enter dysregulated aging program (which is basically a 'disease'/unhealthy aging).

If we bypass senescence (replicative senescen Hayflick)...and telomerase keeps on 'keepin' the telomeres tall enough - and DNA epiclock = roughlt telomere size...than

Indeed, it would be true, that Telomerase does Not increase epigenetic aging...if it so (and I hope it is) than it would correspond a true rejuvenation effect - but, as you said, we don't know what are the consequence of accumulating so many epialterations..with age, if we Go Above Replicative Senescence.

Maybe (and it's a big maybe), maybe it's possible that clock can continue infinitely to accumulate epialterations - as long as the replications continue of cells - then it would be inconsequential on health - only a Tab, that's it..like saying : I am 956 years old..so what...you are still alive, you have 956 years old and accumulated 956-years old of epigenetic alterations..you never died and yes You Aged for 956 years and still continuing livig. Thus, death not coming because you keep on aging on the epiclock, but as said, inconsequential on health.

IT's the 'death' parth that I have difficulty with - cells that go above hayflick/replicatve turn cancerous generally speaking - it's unallowed by epigenetic program - it manifests as 'different epigentic signatuer - in cancers. So, it's like almost we are unallowed to live 956 years, because if we go above replicative senescence -we create mutations/replication crisis/immortalization of cells - acquiring cancerous properties. I could be wrong and it could be possible to extend the cells indefinitely - and never creating immortalization or senescence for that matter. Just by making sure they avoid hayflick and they can keep on acquiring epialterations forever...but must not stop dividing/replicating.

Anyway, it's complicated, indeed. Yes, I hope that she gets a big boost out of it..you're right I am not sure how much of a systemic/all cells effect of hTERT this is doing in her to be of relevance for her aging/longevity. When you seem to rejuvenate in the face by 20 years..it's a good sign...but maybe not the entire story..it might be just the skin rejuvenated, a lil bit organs..not that much..

Posted by: CANanonymity at March 26th, 2019 6:40 PM

I don't disagree with anything you're saying CANanonymity - we just don't know the effect of continued epigenetic changes. I suspect eventually it would be a problem if it influenced gene expression, but I think that might be at a point considerably above current Max life span. Rejuvenation of skin is an extremely good sign as it's an important organ; as is the lining of the intestine and gut - two areas with extremely high cell turnover.

Posted by: Mark at March 28th, 2019 6:00 AM

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