From the Salk Institute in La Jolla, CA came an announcement last week that the four factors previously identified to turn ordinary cells into stem cells (in cell cultures) was successfully used as a rejuvenation procedure in live mice. The results provide important new evidence for the hypothesis that aging is under epigenetic control, and a proof of principle that we might slow aging by modifying the chromosome markers and attachments that determine gene expression. But the way in which this was done involved genetic engineering before birth, and there is no obvious way to translate the results quickly into an anti-aging teatment for living humans.
Ten years ago, Shinya Yamanaka’s Kyoto University laboratory announced that just four proteins could turn an ordinary, differentiated cell back into the stem cell from whence it came. The four were transcription factors, high level switches that turn whole systems of genes on and off with one signal, and the “Yamanaka factors” became known by their initials, OSKM.
Last week, Izpisua Delmonte’s laboratory at the Salk Institute announced a success in rejuvenating whole animals, live mice, using the same OSKM.
Whether this is the germ of a potent new rejuvenation treatment remains to be seen; but the immediate message is a dramatic affirmation of the new paradigm in anti-aging medicine: aging can be reversed by signaling, without artificially-engineered repair of damage. A bold form of this paradigm is the epigenetic hypothesis—now just 4 years old—which says that aging is controlled by gene expression. It is the set of genes that are turned on and off, and the genes’ levels of expression that determine the state of the body’s age. (This idea does not deny that tissues and biomolecules suffer damage with age; but the hypothesis says that the body knew how to repair this damage at one time, and is capable of repairing the damage again, when the signal molecules engage repair mechanisms appropriately for a young individual.)
Gene expression is controlled, in turn, by markers on the chromosome and on the histone spool around which the DNA is wrapped like thread on a spool. These markers are known to change with age in a characteristic pattern. Shifting epigenetic markers program all the stages of development, and (according to the hypothesis), the program continues, and causes the body to pass through the stages of aging.
But in nature this clock never goes backward. The epigenetic clock is reset to zero as the genome is wiped clean and reprogrammed. This happens twice: once in the creation of germ cells, the sperm and egg; and a second time after sperm and egg join to make a zygote. (This is a simplification; some traits are epigenetically inherited, implying that some genome markers are retained and pass across generations.)
If we buy the epigenetic hypothesis, then the holy grail of anti-aging medicine would be to reset all the epigenetic markers, say from age 60 to age 20, but not all the way back to zero. This must be “possible” in some sense of the word; but if it depends on us to read (for example) the methylation of a 20-year-old’s chromosomes and write the results onto the chromosomes of a 60-year-old, in every cell of the body, without otherwise disrupting the living organism, then the task is daunting. And methylation is just one of about 100 known epigenetic modifications of the chromatin.
Nature knows how to reset the epigenetic clock all the way to age 0, but there is no precedent for a partial reset. All tissue differentiation is lost, and the growth rate is pedal-to-the-metal high. It should be no surprise that previous attempts to rejuvenate the living mouse by resetting the clock with OSKM have led to cancer disasters [ref, ref]. In this new report, the Salk researchers used short, intermittent exposure to OSKM to “partially reset” the epigenome. If this really works, and if the epigenetic hypothesis continues to pan out, then this is indeed a week to celebrate.
The experiment
The procedure was first tested in human cell cultures, demonstrating “partial de-differentiation”, where functional cells were rejuvenated without returning them completely to stem cell status. This was an important proof of concept. The authors cite previous experiments suggesting that OSKM re-setting is a multi-step process, so it is possible in principle to halt the process after partial re-programming, and hope for a somewhat younger state.
Next, the procedure was tested on mice with genetically short life spans, living an average of just 18 weeks. Mice with the OSKM treatment lived 24 weeks. Impressively, the treatment was tuned so that it did not increase cancer rates. The particular life-shortening gene was defective LMNA (Lamin A). Lamin A is important for structure and function in the cell nucleus (details hazy), and there is no way to distinguish from this experiment whether the OSKM treatment merely counteracts the deficiency of Lamin A or whether it slows aging generally. Finally, the procedure was tested in normal, aged mice. They showed signs of improved healing, nerve regrowth, and mitochondrial chemistry typical of younger mice. But the mice were sacrificed to determine these things, so there was no demonstration of increased lifespan for genetically normal mice. Sometimes “publish or perish” pressure leads researchers to kill the goose that lays the golden egg…
But the big asterisk on this new result is that the delivery system was through a gene added to the mice at the egg stage. It is easy to modify genes at the egg stage, when there is just one cell, and then the modification is copied in every cell of the adult; but to do gene therapy for adult humans is still at an early experimental stage. Every cell in their bodies had an extra copy of each of the 4 genes for the OSKM factors, and these genes were so configured that they could be turned on and off with a drug (doxycycline). Administration of the drug was arranged to be just right to reprogram the cells, but not all the way. Optimum was found to be a low dose, just two days a week.
Theoretical hedging
Bench scientists have learned to adopt the epigenetic hypothesis in practice, but some are still bound to the obsolete theoretical ideas, inherited from sclerotic thinking about “selfish genes”. Belmonte was quoted as saying the epigenome becomes “damaged” late in life “At the end of life there are many marks and it is difficult for the cell to read them.”
But studies of aging epigenomics show that in addition to random changes in the epigenetic state, there are definite, programmed changes—enough to make an accurate epigenetic clock—and that some of these changes turn down cell repair functions and turn up inflammation. Aging involves a loss of order (“damage”), but it also entails a set of programmed changes. It is the latter that we may hope to address through a streamlined, signaling approach to anti-aging medicine, and, if we are lucky, the body may take up the ball from here and undo part or all of the damage.
The bottom line
This is an important new confirmation of the epigenetic hypothesis. Previous confirmations were
- in parabiosis experiments, but the experiment could not be continued long enough to be sure that lifespan was extended
- in “methylation clock” measurements, but there has been no way to distinguish whether epigenetic changes were a cause or a result of aging.
This new experiment shows that epigenetic changes can extend lifespan. But the experiment offers no clear extrapolation to life extension for humans. The treatment depends on four large molecules that need to be delivered to every cell nucleus in the body. These molecules cannot be taken orally because they will not survive digestion, and even intravenous delivery will not get the molecules to cell nuclei where they are needed.
In cell cultures with the OSKM factors applied externally, stem cell yields are still just a few percent, even after ten years of experience.
The Salk researchers got around this by inserting the OSKM genes into the cell, but for already-living humans this is not a possibility. The best we know how to do is to modify some of the body’s cells with gene therapy; CRISPR in living humans is itself a new technique in its experimental phase.
So for the foreseeable future, I see a two-pronged approach to cell-level rejuvenation. One is to remove senescent cells (senolytics); and the other is stem cell removal, rejuvenation, multiplication in vitro, and return to the body. OSKM may be useful in this second step, rejuvenation of stem cells in vivo.
Discussion
32 reader comments
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Publish or perish, yes. Plus, it seems that Belmonte was in a race with another Spaniard, Maria Blasco, who was testing the very same OSKM approach on 4F mice but with a focus on telomeres, her claim to fame. In 2012 Blasco showed that telomerase gene therapy prolongs murine lifespan. No doubt, her work was the inspiration behind Liz Parrish’s decision to self-experiment with hTERT.
Now Blasco has shown that cellular reprogramming with Yamanaka factors not only elongates telomeres, but also loosens DNA on its histones, which is also a signature of younger cells.
So that’s probably why Belmonte chose not to wait another 20+ months to test OSKM gene therapy on normally ageing mice.
But a careful reading of his paper leads me to believe that Belmonte is currently undertaking a study on OSKM effects on normally aging mice. What makes me think that? The fact that he has 12-months old “wildtype 4F” mice at his disposal to test some aspects of his approach. Those are actually transgenic mice with the 4F gene cassette – genes for OSKM factors whose expressions gets triggered by doxycycline. I am quite sure they bred a lot of those WT 4F mice themselves and used surplus mice “left over” from their longevity study for those add-on experiments in the 2016 paper. Thus, I would expect them to publish their results of OSKM therapy on WT 4F murine lifespan sometime in early 2018.
Btw, gene therapy is already a 20+ year old technology, and has already been used in humans. Follistatin gene therapy already passed Phase 2 for patients with muscular dystrophy, IIRC.
So I think, if we can demonstrate the viability of OSKM gene therapy in normally aging animals (we can start with nematodes or flies to save time), we could see this approach tried in humans within 4-5 years. Or maybe Liz will test it on herself sooner. :)
After all, the lentiviral OSKM vehicle is already up for sale for as low as $400 at multiple sites - just google "OSKM lentivirus".
Hi Josh,
I believe both Belmonte's name and the link to the OSKM induced rejuvenation paper are broken.
Regards
Gabor
Publish or perish, yes. Plus, it seems that Belmonte was in a race with another Spaniard, Maria Blasco, who was testing the very same OSKM approach on 4F mice but with a focus on telomeres, her claim to fame. In 2012 Blasco showed that telomerase gene therapy prolongs murine lifespan. No doubt, her work was the inspiration behind Liz Parrish’s decision to self-experiment with hTERT.
Now Blasco has shown that cellular reprogramming with Yamanaka factors not only elongates telomeres, but also loosens DNA on its histones, which is also a signature of younger cells.
So that’s probably why Belmonte chose not to wait another 20+ months to test OSKM gene therapy on normally ageing mice.
But a careful reading of his paper leads me to believe that Belmonte is currently undertaking a study on OSKM effects on normally aging mice. What makes me think that? The fact that he has 12-months old “wildtype 4F” mice at his disposal to test some aspects of his approach. Those are actually transgenic mice with the 4F gene cassette – genes for OSKM factors whose expressions gets triggered by doxycycline. I am quite sure they bred a lot of those WT 4F mice themselves and used surplus mice “left over” from their longevity study for those add-on experiments in the 2016 paper. Thus, I would expect them to publish their results of OSKM therapy on WT 4F murine lifespan sometime in early 2018.
Btw, gene therapy is already a 20+ year old technology, and has already been used in humans. Follistatin gene therapy already passed Phase 2 for patients with muscular dystrophy, IIRC.
So I think, if we can demonstrate the viability of OSKM gene therapy in normally aging animals (we can start with nematodes or flies to save time), we could see this approach tried in humans within 4-5 years. Or maybe Liz will test it on herself sooner. :) After all, the lentiviral OSKM vehicle is already up for sale for as low as $400:
http://www.cellomicstech.com/p-45-cmv-oskm-lentivirus-puro.aspx
https://www.kerafast.com/product/1676/oskm-cmv-lentivirus
http://invivogen.cn/PDF/LENTI-Smart_OSKM_TD.pdf
PS: Here’s Blasco’s 2017 OSKM paper:
http://www.cell.com/stem-cell-reports/abstract/S2213-6711(17)30001-2
Is anyone aware if Geron or some other antiaging company has picked up the news and the search for Yamanaka factors activators has begun? Or activating all those genes at once pharmacologically seems unfeasible?
Hi Josh,
Thanks for providing your perspective and analysis of this important work, myself and I am sure many others appreciate your explanations of these important advancements as many of these papers are of limited access due to pay walling.
Purhaps you can shed some further light on this question, do we really know that epigenetic markers can be passed from parents to offspring , or is the epigenetic status always reset to a baseline state at fertilization and then the epigenetic clock is just being quickly reestablished by the hormonal and general signaling environment in which the embryo is developing?
Thanks Josh,
Jeff said: "In sum, there is little doubt that DNA methylation levels and aging are strongly linked. The general trend seems to be the establishment of global hypomethylation and regions of CpG-island hypermethylation with age. Speculatively, this overall decrease in 5mC content could lead to less efficient gene regulation, and the CpG island hypermethylation could cause inappropriate silencing of specific genes. Such methylomic changes may render the genome unstable and contribute to aging phenotypes (Fig. 1). Additional studies are required to illuminate the finer details of epigenetic aging and the precise role DNA methylation plays in senescence and longevity."
Gabor B said: "My idea is that DNA methylation serves only as a kind of lock to mask the part of the genome that is not needed in the actual cellular context but it is histone modification that really controls the active part of the genome. Where histone modifications pull back, DNA methylation freezes the genome. But the cellular process controlling DNA meth also weakens as we age thus the hypomethylation."
I have been interested in reading about epigenetics and aging including histones et cetera.
But, in spite of all said above and all published, anyone knows how epigenetics can explain why different mammalian species have so different longevities and aging rates? (35 fold from mice to humans9. For me this is the key question to be answered.
And if methylation et cetera "goes wrong" with age, then this is the opposite of an aging program (if it is "wrong" for me this is not what drives aging, because aging is adaptive. Aging is not something wrong. Aging it is not like a car breaking down, not at all. An AP is "on purpose". So, the rate of aging of each species (or DR vs. AL animal) is designed (DR is surely gene expression controlled) to be the value it has. So, not going wrong but the reverse. It is RIGHT for mice to age fast and it is also RIGHT for humans to age much more slowly.
I look at the aging program as the continuation of the development program. The aging program kind of piggybacks on the development program. Aging serves a different purpose than development, it defines the "learning rate" of the genome looking for infinite multiplication in a competitive and hostile environment. Because the genome can discover a new set of parameters only with a new conception. New conceptions require the death of old instances. Does not really matter if we think about individual gene, chromosome, genome, or species genome. The more crossovers, the more mutations, the more conceptions the better.
So lets look at the development program. Mice gets fertile about 10 weeks after conception. HS gets fertile ~14 years after conception. Here the difference is even larger than with maximal lifespan. (4 years vs 120 years).
How is puberty regulated?
HI there
Good question Gabor- That question always bothered me until recently I learned of the Greenland Shark that can live 400 years and takes 150 years to reach sexual maturity. Upon considering this it finally dawned on me that the linkage amongst species of increasing maximum lifespan, with increased gestation period, declining litter size, and increasing age at puberty are all linked so as the aging rate slows and life span increases, the amount of reproduction an individual can engage in is reduced to preserve the diversity of the gene pool. I call it the reproduction limiting mechanism and discuss it in the last chaper of my new book.
The cycles of upto the peak of 25 yrs in humans and then a very slow decline till 40-50yrs and then a rapid decline till death seems to be patterned for optimum reproduction and survival of species. By 25 assumed multiple mating and birth cycles - then the parents are kept around in reasonable health to look after their progeny till they reach their peak - as children across species are vulnerable till then - that is why the maternal hormones and animals do not end up eating their children even when hungry. Once the children turn to adults to start their own reproductive and child raising cycle nature does not see much utility of the parents and their decline moves up 3 gears. Since recorded time if we see the human lifespan it was almost half of where we are today. So we have already influenced nature's AP and doubled our given lifespan by making the most of natures cheat codes (nature rewards those that are more active - meaning higher utility - higher hunting gathering for children - and those that reproduce more often by slowing the rate of their decline) and invention of modern medicine. Similar cycles can be seen in most species based on when the baby reaches peak maturity including the 400 year living whales.
Despite epigenetic and genetic interventions seeming incredibly risky today it looks like being one of the fastest moving branches of anti aging research thanks brilliant scientists like George Church. Developing tools like FISSEQ and repair intervention like TFAM are exciting steps moving towards the holy grail - reversal of aging.
http://www.nextbigfuture.com/2016/06/first-phase-1-human-aging-reversal.html?m=1
The great thing about Church is that he has seeded multiple teams each working from a different approach, technology and tools. In my books if there is anyone who can the impossible possible it may be him.
More things of interest>>Hormonal control of Yamanaka factors?
1.
Cell Biol Int. 2014 Aug;38(8):924-32. doi: 10.1002/cbin.10286. Epub 2014 May 12.
Stem cell and extracellular matrix-related molecules increase following melatonin treatment in the skin of postmenopausal rats.
Uslu S1, Oktem G, Uysal A, Soner BC, Arbak S, Ince U.
AND
Cell Biol Int. 2011 Oct;35(10):1037-41. doi: 10.1042/CBI20100927.
The neurosteroid dehydroepiandrosterone could improve somatic cell reprogramming.
Shoae-Hassani A1, Sharif S, Verdi J.
Author information
Abstract
Expression of four major reprogramming transgenes, including Oct4, Sox2, Klf4 and c-myc, in somatic cells enables them to have pluripotency. These cells are iPSC (induced pluripotent stem cell) that currently show the greatest potential for differentiation into cells of the three germ lineages. One of the issues facing the successful reprogramming and clinical translation of iPSC technology is the high rate of apoptosis after the reprogramming process. Reprogramming is a stressful process, and the p53 apoptotic pathway plays a negative role in cell growth and self-renewal. Apoptosis via the p53 pathway serves as a major barrier in nuclear somatic cell reprogramming during iPSC generation. DHEA (dehydroepiandrosterone) is an abundant steroid that is produced at high levels in the adrenal cells, and withdrawal of DHEA increases the levels of p53 in the epithelial and stromal cells, resulting in increased levels of apoptotic cells; meanwhile, DHEA decreases cellular apoptosis. DHEA could improve the efficacy of reprogramming yield due to a decrease in apoptosis via the p53 pathway and an increase in cell viability.
PMID: 21355850 DOI: 10.1042/CBI20100927
This idea requires a lot more research!!
I was trying to find a recent study I saw where it was reported that in aged cellls that the DNA methyltransferase starts to malfunction causing reduced methylation of the last to be transcribed genes on the DNA, kibnd of like the cell was running out of DNMT>>>Could not find the study but found this and thought it was interesting enough to share>>>
DNMT modulation and longevity
DNA methylation in Drosophila melanogaster is carried out by the sole methyltransferase gene dDnmt2. Lin et al. ubiquitously expressed the UAS-dDnmt2 transgene driven by daughterless-GAL4 in Drosophila. Flies with this overexpressed gene (two- to four-fold increase as confirmed by RT-PCR) enjoyed a boost of up to 58% in mean life span compared to controls. In contrast, creation of flies with approximately 50% less dDnmt2 resulted in a 27% reduction in mean life span. Feeding Drosophila the free radical generator paraquat revealed that dDnmt2-overexpressing flies were more resistant to oxidative stress. Multiple small heat shock protein–encoding (sHsp) genes (Hsp22, Hsp23, and Hsp26) were also upregulated approximately three-fold in flies overexpressing dDnmt2. Conversely, sHsp-encoding genes were downregulated two- to three-fold in flies with diminished levels of dDnmt2.65 This study demonstrates that, in Drosophila, dDnmt2 is a regulator of life span and stress resistance. Further studies are warranted to determine if these changes in dDnmt2 expression correspond to changes in 5mC content.
In social insects such as honeybees, there exist different castes. Despite having identical genomes, female larvae diverge into two classes of bees—infertile worker bees and fertile queens. The queens are behaviorally dominant, physically larger, and substantially longer-lived compared to their worker sisters. The difference in development is thought to lie in differential feeding. Larvae fed a diet of royal jelly emerge as queen bees. This diet is thought to influence the methylome and, concordant with this, queens have significantly different 5mC content compared with workers.66 Interestingly, treating larvae with siRNAs directed against Dnmt3a engendered adult bees with queen characteristics, including fully developed ovaries. Knockdown of Dnmt3a was accompanied by decreased levels of 5mC content.67 While longevity has to our knowledge not been studied in this context, these studies suggest that differing levels of Dnmt expression and 5mC content may also account for the life span difference between the two castes.
Apart from a few in vivo studies in mice, fruit flies, and potentially honeybees, very little evidence attests to the ability of DNMTs to regulate organismal life span. Additional studies attempting to modulate longevity by modifying 5mC content and associated partners in model organisms are imperative to determine whether or not DNA methylation is simply correlated with aging or if it is indeed a modulator of aging.
In sum, there is little doubt that DNA methylation levels and aging are strongly linked. The general trend seems to be the establishment of global hypomethylation and regions of CpG-island hypermethylation with age. Speculatively, this overall decrease in 5mC content could lead to less efficient gene regulation, and the CpG island hypermethylation could cause inappropriate silencing of specific genes. Such methylomic changes may render the genome unstable and contribute to aging phenotypes (Fig. 1). Additional studies are required to illuminate the finer details of epigenetic aging and the precise role DNA methylation plays in senescence and longevity.
At the epigenetic level, widespread remodeling of certain histone modifications, but not of DNA methylation patterns, was seen within the first few cell divisions of iPSC induction (Koche et al., 2011).
http://www.cell.com/cell/fulltext/S0092-8674(12)01424-9
My idea originlly was that histone modifications are upstream to DNA methylation. The above reference seems to confirm this. My idea is that there are many enzymes and possible even more regulators involved in histone modifications, but for DNA methylation there are only 3 enzymes - quite blunt.
My idea is that DNA methylation serves only as a kind of lock to mask the part of the genome that is not needed in the actual cellular context but it is histone modification that really controls the active part of the genome. Where histone modifications pull back, DNA methylation freezes the genome. But the cellular process controlling DNA meth also weakens as we age thus the hypomethylation.
Interesting idea.
yes how all these epigenetic mechansims all fit together and interrelate is I believe understudied and a ripe area for theoretical breakthroughs.There are a growing number of things that bind to DNA to control gene expression that relate to aging
such as Lamin A proteins (defective in progeria) , WRN protein which when 6 of the come together form a DNA helicase, but single WRN proteins bind to DNA to control gene expression in stem cells (I believe). When WRN is defective you get the rapid aging disease of Werner's syndrome,
then you have the chromatin proteins,
and of course DNA methylation,
and also telomeres which fold over and cover up coding DNA after DNA replication is complete-this is responsible for 'the position effect" on genes near telomeres...I'm sure they will find a few more.
I have originally proposed that rather them all being controlled in coordiation, that they might all be redundant aging systems each one designed to kill you. The aging system with the "shortest fuse" is the one that kills you, and if you defeat this aging system with a beneficial mutation, there is another one waiting to get you next. I think this is a good possibility as it seems like evolution would always be trying to rid the genome of aging systems to allow the relentless march of the selfish gene. Having multiple aging systems is one way to fight off this push by the selfish gene, if aging is otherwise good for the species.
Jeff I agree that death has been given special attention as we are yet to see any single mutation creating prolonged lifespans beyond a certain limit. Multiple instructions/mechanisms/pathways have been incorporated to ensure death. Having said that how would a biological being die unless something fails? What if we are able to counter the loss of efficiency of every repair mechanism and are able to maintain youthful peak homeostasis? It would be interesting to see what happens then. A young healthy human at peak systemic efficiencies can not just fall over and die. Something has to fail to die.
Akshay said: "Jeff I agree that death has been given special attention as we are yet to see any single mutation creating prolonged lifespans beyond a certain limit".
Yes, I noticed many years ago (e.g. Barja, Gene Cluster of Aging, Biogerontology 2008) that the long-lived mutant mice live (AT BEST) around 1.4 fold compared to controls (similar to best results with DR rodents), but no more. I think that the reason is that most of those mutants (e.g. insulinIGF-1like ones) impact on the same Pre-nuclear cytosolic pathways signaling DR to the nuclear AP (the Gene Clusters of Aging). That is why they increase longevity only by 1.4. Because this is the "convenient" (for the rodent species) life extension for a DR animal. That "convenience" is programmed in the AP (which responds to the DR signals modifying the activity of the Post-nuclear aging effectors like mitROSp, or perhaps autophagy and others).
If we want to increase maximum longevity by much more than 1.4 fold (by 3, 4, 10 fold, 10 fold is eanogh for humans to get negligible senescence) we need to modify the MASTER GENES of the AP (of the "Gene Clusters of Aging"). That is what mother nature does each time it changes the longevity from one species to the next one during evolution (mothe nature does it frequently, relatively easily and quickly, and by 10 fold, 30 fold, 100, 1000 fold et cetera).
So, we should look inside the nucleus at the AP, instead of continuing mutating genes that codify for the pre-nuclear cytoplasmic signaling of DR to the nucleus. We should identify the AP and especially the master genes of the AP.
In summary, especially those of you good at molecular genetics and interested in longevity:
PLEASE LOOK AT THE NUCLEUS (inside it, look at the AP, at the GENE CLUSTERS OF AGING AND LONGEVITY) :
https://www.ncbi.nlm.nih.gov/pubmed/?term=barja+biogerontology+2008+gene+cluster+of+aging
I think group selection and the increased diversity is much more important than selfish gene. Thus, there is no need of many killing genes designed to oppose selfish gene
Hello Gustavo
If you get to the last chapters of my most recent book (which is free for download on amazon today and tomorrow-Merry Xmas!) titled-What Darwin Could Not See-The Missing Half of The Theory. I make the case that it is not group selection that is selecting for aging, because it is too weak a force and differences can be instantly destroyed by interbreeding. I suggest a force similar to group selection but operating at one level above group selection is where the evolution of aging and sex is selected for- it is known as species selection. And there are only about 15 papers in al of Pub Med that even mention this term. So if it sounds unfamiliar , it should. But I explain species selectionthat operates at the local ecosystem level everywhere all the time, driven by evolving predators. The other people theorizing on species selection (like Steven Jay Gould and George Williams)generally incorrectly look at it as a planet wide simultaneous phenomenon.
Anyway, a very interesting fact is that mice have telomeres 4 times longer than humans, and they do shorten each time a mouse cell replicates, Telomeres have epigenetic functions such as folding over and covering genes on sub telomereic DNA/ preventing transcription. What is amazing is if you knock out the telomerase gene you get mice with telomeres that continulally shorten genreation after generation. The shortening telomeres have no effect on the mice until about the 4th generation when they start to get gray hair. start getting bald patches, and become infertile.
I just present this example to suggest that there may be multiple aging systems in various species and in some cases the aging systems have been overcome by evolution and something else will have to kill the individual. So the bottom line is how epigentics kills the mammalian host appears to vary amongst species, but can probably be narrowed down to one of a number of epigenitc aging sytems.
From an evolutionary perspective what is interesting is that the longest living mammals based on body size/life span ratio are human and bats. The two mammalian species with highly effective defenses to predation>> flight/isolation and extreme intelligence.
Gustavo, I believe that the current maximum life extension for mice is 1.6 fold. Actually subjecting GH receptor mutants to DR, so I guess both activate slightly different pathways
http://www.nature.com/nature/journal/v414/n6862/full/414412a0.html
This makes a lot of sense. The studies on Sirtuin (although there is no clear evidence of longevity benefit by activating Sirt 1 or other Sirts in mammals) the there are 100+ publications (some of good quality) which demonstrate some improvement in health status, perhaps even healthspan, of mice. Sirt 1 is best known as a histone deacetylase (although it deacetylates 50+ other proteins) and thus intimately involved in epigenetic modulation of gene expression. So as Gabor says, the primary control point for epigenetic modulation of gene expression may be histones and DNA methylation may be a more permanent and secondary lock.
I woudl like to point out that the "ep[igentic hypothesis is not "just 4 years old". It was first "hypothesized in detail at least in 1998 paper on the Evolution of Aging which would make it 18 years old. And that paper didn't just sit their unread, I got hundreds of reprint requests from scientists all over the wolrd at all the best institution.Anyone who has read my 1998 paper should clearly see it is the "epigenetic hypothesis" that was just lacking the word epigenetic which did not start coming into much use until around 2005>>> And it might be said that before me a one Al Mazin almost got it right as he proposed that DNA methylation was lost over time via to C to T mutations which altered gene expression. (He's been at it since 1973 at least , and he nailed the DNA methylation- loss and aging connection WAY BACK IN 1993).Here are his various publications:
Suicidal function of DNA methylation in age-related genome disintegration.
Mazin AL.
Ageing Res Rev. 2009 Oct;8(4):314-27. doi: 10.1016/j.arr.2009.04.005. Review.
PMID: 19464391
Similar articles
Select item 8557095
2.
Life span prediction from the rate of age-related DNA demethylation in normal and cancer cell lines.
Mazin AL.
Exp Gerontol. 1995 Sep-Oct;30(5):475-84.
PMID: 8557095
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Select item 7723765
3.
[Methylation of the factor IX gene--a basic reason for the mutation causing hemophilia B].
Mazin AL.
Mol Biol (Mosk). 1995 Jan-Feb;29(1):71-90. Russian.
PMID: 7723765
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Select item 8145751
4.
[Enzymatic DNA methylation as an aging mechanism].
Mazin AL.
Mol Biol (Mosk). 1994 Jan-Feb;28(1):21-51. Review. Russian.
PMID: 8145751
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Select item 8246940
5.
[The mechanism of replicative and post-replicative DNA methylation as a generator of mutations in a cell].
Mazin AL.
Mol Biol (Mosk). 1993 Sep-Oct;27(5):965-79. Review. Russian.
PMID: 8246940
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Select item 8361495
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[Loss of total 5-methylcytosine from the genome during cell culture aging coincides with the Hayflick limit].
Mazin AL.
Mol Biol (Mosk). 1993 Jul-Aug;27(4):895-907. Russian.
PMID: 8361495
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Select item 8483468
7.
[Genome loses all 5-methylcytosine a life span. How is this connected with accumulation of mutations during aging?].
Mazin AL.
Mol Biol (Mosk). 1993 Jan-Feb;27(1):160-73. Russian.
PMID: 8483468
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Select item 1339947
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[Enzymatic methylation of regulatory elements in controlling the activity of genes from various groups of organisms].
Mazin AL.
Mol Biol (Mosk). 1992 Mar-Apr;26(2):244-63. Review. Russian.
PMID: 1339947
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Select item 2348823
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[Possible origin and evolution of enzymatic methylation of eukaryotic DNA. Methylation of cytosine residues in 3 palindromic families: RYRY, YYRR, and YYRYRR].
Mazin AL, Vaniushin BF.
Mol Biol (Mosk). 1990 Jan-Feb;24(1):23-43. Russian.
PMID: 2348823
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Select item 3252156
10.
[Loss of CpG dinucleotides from DNA. VI. Methylation of mitochondrial and chloroplast genes].
Mazin AL, Boĭko LM, Ogarkova OA, Vaniushin BF.
Mol Biol (Mosk). 1988 Nov-Dec;22(6):1688-96. Russian.
PMID: 3252156
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Select item 3657781
11.
[The loss of dinucleotides CpG from DNA. IV. Methylation and divergence of genes and pseudogenes of small nuclear RNA].
Mazin AL, Vaniushin BF.
Mol Biol (Mosk). 1987 Jul-Aug;21(4):1099-109. Russian.
PMID: 3657781
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Select item 3657769
12.
[The loss of CpG dinucleotides from DNA. III. Methylation and evolution of histone genes].
Mazin AL, Vaniushin BF.
Mol Biol (Mosk). 1987 May-Jun;21(3):678-87. Russian.
PMID: 3657769
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Select item 3600628
13.
[The loss of CpC dinucleotides from DNA. II. Methylated and non-methylated genes of vertebrates].
Mazin AL, Vaniushin BF.
Mol Biol (Mosk). 1987 Mar-Apr;21(2):552-62. Russian.
PMID: 3600628
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Select item 3600627
14.
[The loss of CpG dinucleotides from DNA. I. Methylated and non-methylated genome compartments in eukaryotes with different levels of 5-methylcytosine in DNA].
Mazin AL, Vaniushin BF.
Mol Biol (Mosk). 1987 Mar-Apr;21(2):543-51. Russian.
PMID: 3600627
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Select item 3081615
15.
[Cytokinin (6-benzylaminopurine) incorporation into DNA of the protozoan Tetrahymena pyriformis].
Mazin AL, Vaniushin BF.
Izv Akad Nauk SSSR Biol. 1986 Jan-Feb;(1):122-5. Russian. No abstract available.
PMID: 3081615
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Select item 4047038
16.
[Non-enzymatic DNA methylation by S-adenosylmethionine results in the formation of minor thymine residues and 5-methylcytosine from cytosine].
Mazin AL, Gimadutdinov OA, Turkin SI, Burtseva NN, Vaniushin BF.
Mol Biol (Mosk). 1985 Jul-Aug;19(4):903-14. Russian.
PMID: 4047038
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Select item 6432506
17.
[5-methylcytosine is lacking in the DNA of Drosophila melanogaster and Drosophila virilis].
Mazin AL, Mukhovatova LM, Shuppe NG, Vaniushin BF.
Dokl Akad Nauk SSSR. 1984;276(3):760-2. Russian. No abstract available.
PMID: 6432506
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Select item 4735514
18.
The content of 5-methylcytosine in animal DNA: the species and tissue specificity.
Vanyushin BF, Mazin AL, Vasilyev VK, Belozersky AN.
Biochim Biophys Acta. 1973 Mar 28;299(3):397-403. No abstract available.
Josh you said:
"Finally, the procedure was tested in normal, aged mice. They showed signs of improved healing, nerve regrowth, and mitochondrial chemistry typical of younger mice. But the mice were sacrificed to determine these things, so there was no demonstration of increased lifespan for genetically normal mice."
Before reading your blog, a couple of days ago I looked at Izpitsua´s paper and saw that there was no data of mouse life span (longer than normal controls) so I was "not interested" in the paper from the point of view of longevity extension.
You said that they killed the animals instead of continuing. ¿? I do not understand why. Without demonstarting increases in life span over that of normal mice, without mice of more than 4 years of age, there is no advance concerning (maximum) longevity. The publish or perish argument is nonsense to me.
On the other hand I listened a talk given by Manuel Esteller, a scientist expert on epigenetics and aging, on December 1 at Madrid at the National Academy of Pharmacy. He told us on his talk that, on his opinion, epigenetics can improve going towards 122 years (mean life span only) but will never be useful to overcome the 122 limit (maximum life span in humans). To accomplish that, he said, it is the hardware (genome) what must be "touched", not just the epigenome.
Gustavo, could you expand a bit on what kind of genes should be tweaked to overcome the epigenetic maximum lifespan? As long as I know we have already pretty much all the genes we need for indefinite lifespans. I believe we only miss the genes to fix some crosslinks like those due to glucosepane
1-As I said an updated review from myself is coming. Concerning target genes directly controlling the aging effectors of the AP, I can advance (in addition to many others already mentioned on my Biogerontology 2008 Aging Gene Cluster paper) that at least the following ones must be part of them: delta-5 and delta-6 desaturase genes (important for control of the membrane fatty acids DBI), genes of some of the -likely accessory- polypeptides of the hydrophilic domain of complex I (participating in the control of the mitROS production rate), and, at least in the genetic response to the different DRs, ATG genes (controlling autophagy activity). But the most important ones to finally modify longevity 2 fold, 4 fold et cetera are not these but the master genes upstream of these target genes in the AP.
2-Concerning reprogramming, stem cells et cetera, about which there is much excitement, I do not deny their possible relevance. But I want to remind everybody that the aging problem mainly concerns tissue cells that do not divide or do it only rarely. That is another reason why factors like mitROSp, DBI or autophagy are most important for longevity, because, taken together, they can help to explain why tissues made up mainly or most importantly of postmitotic cells (heart, muscle, brain) can last for 100 years in humans and only 3,5-4 years in mice. The 3 factors above can help to explain that, which is the most important thing in longevity, not age-related changes in a single species. There is already evidence that they can explain longevity across species, especially concerning the first two mentioned parameters), whereas any factor linked to cell division (telomers, stem cells et cetera) can not.
Hi Gustavo,
the epigenetic clock is not specific to dividing cells, it is uniform across many tissue types from blood to brain.
http://escholarship.org/uc/item/3q3151v9.pdf
Wow that's then a game changer for what I considered the final rejuvenation therapy. But after giving it some thought it makes sense that nature can get away creating a fresh individual at conception resetting the epigenetic clock and doing some exhaustive cellular repair in the egg but for an adult individual full of postmitotic cells the same trick may not be enough.
So then would you agree that the final rejuvenation technique would be comprised of these 3 steps?
- Clear major existing cellular and structural damage
- Reset the epigenetic clock to that of a young adult and lock it in that state
- Add the necessary genes so postmitotic cells can have an indefinite lifespan
Actually in a paper I can't seem to get a hold of, a fellow named Ludwig (Ludwig FC, Elashoff RM. Mortality in syngeneic rat parabionts of different chronological age. Trans N Y Acad Sci. 1972;34:582–7. [PubMed]) showed that the older parabionts in a heterochronic parabiosis experiment lived 20% longer than expected. And remember, as Michael Conboy noted that the younger parabionts were no longer young by the time the elders died. Whether that was simply the effect of the younger body taking on the added functions of the older one, or true rejuvenation was revealed by the 2005 experiment, where aged stem and progenitor cells were shown to display youthful characteristics.
I managed to track that paper down at this link:
http://onlinelibrary.wiley.com/doi/10.1111/j.2164-0947.1972.tb02712.x/pdf
Relevant part:
"The older member of the male heterochronic pairs did not differ significantly from the single control groups (p 0.15). However, the older member of the female heterochronic pair follows a survival curve that is significantly at the right side of the single females as was the parabiosed controls (p < 0.05). Furthermore, the curve of the homochronic male control parabionts is significantly at the left side of that of the single male controls."
PS: Yes, Sci-Hub has it.