30. July 2009 by admin.

About four years ago I suffered an accident that resulted in significant loss of nerve sensation in two fingers.  I was carrying a bottle of wine by the neck to a friend’s house, slipped on a wet slimy board, fell down and smashed the bottle on the board.  I suffered a slash from the broken glass that nearly caused me to lose two fingers.  The surgeon was very skilled.  He sewed the tendons and the severed nerves together as best he could.   After several surgeries and a long period of recovery the two fingers were saved but the tendon in one finger and the nerve sensation in both fingers were left compromised, a situation that persists to this day.  The fingers constantly feel like I am starting to recover from a Novocain shot in them.  During my final appointment with the surgeon I asked him “How about injecting a nerve growth factor in my two fingers to restore full sensation in them?”  He knew of no such thing and looked at me as if I came from Mars.  He said absolutely nothing further could be done. 

I look at research related to nerve regeneration in this post, still anticipating the day when the nerves in these fingers can be fully restored.  First of all, I need mention that peripheral nerve regrowth can occur naturally after an accident .  “Human axon growth rates can reach 2 mm/day in small nerves and 5 mm/day in large nerves(ref).”  There is increasing understanding of the factors that impact on nerve growth, such as the role of Schwann cells.  “Regeneration of peripheral nerve involves an essential contribution by Schwann cells (SCs) in collaboration with regrowing axons. — Reforming peripheral nerve trucks involves a very close and intimate relationship between axons and Schwann cells that must proliferate and migrate, facilitated by laminin(ref).” 

“Schwann cells (also referred to as neurolemnocytes) are a variety of glial cell that keep peripheral nerve fibres (both myelinated and unmyelinated) alive. In myelinated axons, Schwann cells form the myelin sheath(ref)”  “During peripheral nerve development the Schwann cell population is expanded so that adequate numbers are available for ensheathment of both nonmyelinated and myelinated nerve fibres. As ensheathment of these fibres progresses each axon–Schwann cell unit becomes surrounded by a basal lamina, providing a unique microtubular framework within the peripheral nerve trunk(ref).”   

A plentiful supply of Schwann cells is therefore important to support repair of severed peripheral nerves.  So adequate differentiation of stem cells into Schwann cells is required for nerve regeneration, bringing us back to the discussion of the Decline in Adult Stem Cell Differentiation theory of aging.  Hair follicle stem cells can be induced to differentiate into Schwann cells and such induction might be an approach to improving nerve regeneration(ref).  You might want to read the recent post Hair stem cells and hair growth if you have not already done so.

The process of nerve regrowth can be facilitated or inhibited by various glycoproteins..  For example “Myelin-associated glycoprotein (MAG), a carbohydrate-binding protein on the myelin sheaths that coat nerve cells, inhibits regeneration of damaged neurons by binding to gangliosides on axon surfaces. This interaction causes gangliosides to cluster together, generating a signal that inhibits axon regrowth(ref).”  Another nerve growth-inhibiting substance can be “chondroitin sulphate proteoglycans (CSPGs). CSPGs are inhibitory to axon growth in vitro, and regenerating axons stop at CSPG-rich regions in vivo. Removing CSPG glycosaminoglycan (GAG) chains attenuates CSPG inhibitory activity.”  – “To test the functional effects of degrading chondroitin sulphate (CS)-GAG after spinal cord injury, we delivered chondroitinase ABC (ChABC) to the lesioned dorsal columns of adult rats. We show that intrathecal treatment with ChABC degraded CS-GAG at the injury site, upregulated a regeneration-associated protein in injured neurons, and promoted regeneration of both ascending sensory projections and descending corticospinal tract axons(ref).”

One important thread of current research involves the use of spinal chord stem cells (ependymal stem cells) to repair spinal chord injuries, a major challenge of nerve regeneration.  From a 2007 report of work:  “We know that stem cells are present within the spinal cord, but it was not known why they could not function to repair the damage. Surprisingly, we discovered that they actually migrate away from the lesion and the question became why - what signal is telling the stem cells to move.” “The researchers then tested numerous proteins and identified netrin-1 as the key molecule responsible for this migratory pattern of stem cells following injury. In the developing nervous system, netrin-1 acts as a repulsive or attractive signal, guiding nerve cells to their proper targets. In the adult spinal cord, the researchers found that netrin-1 specifically repels stem cells away from the injury site, thereby preventing stem cells from replenishing nerve cells. “When we block netrin-1 function, the adult stem cells remain at the injury site(ref).”

A December 2007 report indicates “A study carried out by researchers at the Kyoto University School of Medicine has shown that when transplanted bone marrow cells (BMCs) containing adult stem cells are protected by a 15mm silicon tube and nourished with bio-engineered materials, they successfully help regenerate damaged nerves(ref).”   Another experiment with laboratory animals reported in January of 2009 “found that transplantation of stem cells from the lining of the spinal cord, called ependymal stem cells, reverses paralysis associated with spinal cord injuries(ref).”  Finally, I mention that in January 2009, the Geron company got FDA approval for a clinical trial of its embryonic stem cell product GRNOPC1 in patients with acute spinal cord injury(ref).

There are reports also of non stem-cell approaches for dealing with spinal chord injuries, ones that might come under a broad heading of “tissue engineering.”  For example, “Northwestern University researchers have shown that a new nano-engineered gel inhibits the formation of scar tissue at the injury site and enables the severed spinal cord fibers to regenerate and grow. The gel is injected as a liquid into the spinal cord and self -assembles into a scaffold that supports the new nerve fibers as they grow up and down the spinal cord, penetrating the site of the injury.  When the gel was injected into mice with a spinal cord injury, after six weeks the animals had a greatly enhanced ability to use their hind legs and walk(ref).”  Another approach to nerve regeneration reported in March of this year involves engineered transplantable living nerve tissue.  ““We have created a three-dimensional neural network, a living conduit in culture, which can be transplanted en masse to an injury site,” explains senior author Douglas H. Smith, MD, Professor, Department of Neurosurgery and Director of the Center for Brain Injury and Repair at Penn. Smith and colleagues have successfully grown, transplanted, and integrated axon bundles that act as ‘jumper cables’ to the host tissue in order to bridge a damaged section of nerve(ref).”

My fantasy is still going back to visit my hand surgeon who will this time give me an injection in each of my semi-numb fingers and assure me that in a couple of months the nerves will have completely grown back.  I don’t know when that day will be but I think we are getting closer to it.

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29. July 2009 by admin.

Experiments extending the lives of mice up to about 35% have been reported, and that is about it.  However, last year an experiment was reported that extended the life span of baker’s yeast by a factor of 10.  Certain genes and genetic pathways involved in longevity of primitive species like yeast are conserved by evolution in higher species including humans.  “Genes that modulate aging have been conserved not only in sequence, but also in function, over a billion years of evolution(ref).”  Studies of longevity-promoting genetic interventions are relatively easy in yeast because its life span is very short, and the hope is that insights can be realized through such studies that can eventually be applied to higher species including our own.    

The latest research involved ”knocking out two genes, known as RAS2 and SCH9, which promote ageing in yeast and cancer in humans, and putting the microbes on a diet low in calories(ref).”  The researchers reported “The deletion of both RAS2 and the Akt and S6 kinase homolog SCH9 in combination with calorie restriction caused a remarkable 10-fold life span extension, which, surprisingly, was only partially reversed by the lack of Rim15. These results indicate that the Ras/cAMP/PKA/Rim15/Msn2/4 and the Tor/Sch9/Rim15/Gis1 pathways are major mediators of the calorie restriction-dependent stress resistance and life span extension, although additional mediators are involved. Notably, the anti-aging effect caused by the inactivation of both pathways is much more potent than that caused by CR.” — “Our study also showed that by combining the genetic manipulation and calorie restriction intervention, yeast can reach a life span ten times that of those grown under standard conditions. This extreme longevity requires Rim15 and also depends on other yet-to-be identified mechanisms. Our findings provided new leads that may help to elucidate the mechanisms underlying the anti-aging effect of calorie restriction in mammals(ref).”    

There is a long history of longevity-related experiments on yeast.  Back in 2005 some of the same researchers looked at the role of SIR2 in aging in yeast.  “Rather than adding copies of SIR2 to yeast, Longo’s research group deleted the gene altogether. –The result was a dramatically extended life span - up to six times longer than normal - when the SIR2 deletion was combined with caloric restriction and/or a mutation in one or two genes, RAS2 and SCH9, that control the storage of nutrients and resistance to cell damage. — Human cells with reduced SIR2 activity also appear to confirm that SIR2 has a pro-aging effect, Longo said, although those results are not included in the Cell paper(ref).”  

A 10-fold increase in longevity in humans would bring our average life spans up to about 800 years, more than enough to satisfy any contemporary anti-aging zealot.   But, will the life-extending interventions used on the yeast also work for more advanced species?  My answer is that the knowledge gained in the yeast experiments has been valuable though the anti-aging interventions used on yeast may not work or be inappropriate.  I wrote about one of the two pathways involved in the cited experiment in an earlier blog post Longevity genes, mTOR and lifespan.  I wrote that “With respect to humans, much of the machinery of TOR signaling found in more primitive species is conserved.”  “The longevity function of SIR2 is conserved in at least one multicellular organism, Caenorhabditis elegans(ref)” and SIR1 appears to play a similar role in mammals.  SIR2 and its mammalian  counterpart SIR1 are involved in the calorie-restriction anti-aging pathway and have been the subject of much recent research(ref)(ref)(ref).  

The cited yeast research studies are interesting because they are  based on simultaneously altering two longevity-related genetic pathways to achieve extraordinary longevity, something not yet systematically studied in higher animals.   So the yeast research might ultimately prove to be very valuable for us. 

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27. July 2009 by admin.

We will be hearing more and more about chimeras.  In genetics, a chimera is an animal that has two or more different populations of genetically distinct cells that originated in different zygotes(ref).    The word was adopted from Greek mythology where the description is more colorful and gets down to the nitty-gritty.  According to Wikipedia  “the Chimera (Greek Χίμαιρα (Chímaira); Latin Chimaera) was a monstrous fire-breathing creature of Lycia in Asia Minor, composed of the parts of multiple animals: upon the body of a lion with a tail that terminated in a snake’s head, the head of a goat arose on its back at the center of its spine. The Chimera was one of the offspring of Typhon and Echidna and a sibling of such monsters as Cerberus and the Lernaean Hydra.”  Get the idea?

The news this week was two reports from Chinese researchers of making chimeric mice using induced pluripotent stem cells (iPSCs).  The mice were made by taking skin cells from mice, reverting these cells to iPSC status where they become virtually identical to embryonic stem cells (see the blog post Rebooting cells and longevity), and injecting them back into into eary-stage mouse embryos.  On of the reasons this work is important is that it established the true pluripotency of the iPSCs used.  After all, if you can make a whole living mouse out of them, they must be capable of differentiating into any mouse tissue.  “The generally accepted “gold standard” for determining whether a mouse iPSC line has been fully reprogrammed is to show that when injected into an early embryo (or blastocyst), the iPSCs can contribute to many different tissues in the resulting chimeric mouse, including the germline(ref).”  One of the chimeric mice made this way is reported to have mated with a normal mouse resulting in the birth of a normal mouse pup. Of course this is all on the level of the mouse.  Ethical and legal considerations are in the way of making chimeric “designer people,” but the results still give hope that iPSCs can be used for any purpose embryonic stem cells (eSCs) could be used for.

However, other stem cell research reported earlier this month indicates that the gene expression profiles of iPSCs and eSCs are different.  The study compared eSCs and iPSCs made by reprogramming skin cells. “The data from the study suggest that embryonic stem cells and the reprogrammed cells, known as induced pluripotent stem (iPS) cells, have overlapping but still distinct gene expression signatures. The differing signatures were evident regardless of where the cell lines were generated, the methods by which they were derived or the species from which they were isolated(ref).”  The researchers do not know what the practical implications of this finding are.  Whatever they are, they seem to be not enough to get in the way of making whole living chimeric mice. 

Chimeras, hybrid animals, have been around for some time and are interesting curiosities. According to Wikipedia “Chimeras are formed from four parent cells (two fertilized eggs or early embryos fused together) or from three parent cells (a fertilized egg is fused with an unfertilized egg or a fertilized egg is fused with an extra sperm). Each population of cells keeps its own character and the resulting animal is a mixture of tissues.”  Moreover people may be chimeras and not know it.  “As the organism develops, the resulting chimera can come to possess organs that have different sets of chromosomes. For example, the chimera may have a liver composed of cells with one set of chromosomes and have a kidney composed of cells with a second set of chromosomes. This has occurred in humans, and at one time was thought to be extremely rare, though more recent evidence suggests that it is not as rare as previously believed. Most will go through life without realizing they are chimeras. The difference in phenotypes may be subtle (e.g., having a hitchhiker’s thumb and a straight thumb, eyes of slightly different colors, differential hair growth on opposite sides of the body, etc) or completely undetectable . Another telltale of a person being a chimera is visible Blaschko’s lines(ref).”

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26. July 2009 by admin.

A study published in the latest issue of the online journal Cell Stem Cell provides additional research evidence supporting the Decline in Adult Stem Cell Differentiation theory of aging, the 14^th theory treated in my treatise.  This theory holds that aging is due to a slowing rate of organ regeneration due to declining somatic cell differentiation activity.  This theory states that in addition to or perhaps instead of being concerned that aging is due to cells being damaged or reaching their reproductive  limit (such as according to the Oxidative Damage or the Telomere Shortening and Damage theories  of aging), we should be concerned that cells are not being replaced by freshly minted cells created by differentiating stem cells. 

The new study report TAp63 Prevents Premature Aging by Promoting Adult Stem Cell Maintenance  indicates that “that the p53 family member, TAp63, is essential for maintenance of epidermal and dermal precursors and that, in its absence, these precursors senesce and skin ages prematurely.” “TAp63 / mice (mice with TAp63 knocked out) age prematurely and develop blisters, skin ulcerations, senescence of hair follicle-associated dermal and epidermal cells, and decreased hair morphogenesis.” – “These data indicate that TAp63 serves to maintain adult skin stem cells by regulating cellular senescence and genomic stability, thereby preventing premature tissue aging(ref).” 

Again the message is that if you are worried about aging, be concerned with the supply chain for new somatic cells.  Start focusing on what is happening to adult stem cells. 

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25. July 2009 by admin.

Some readers of this blog have expressed interest in my new hair growth which I have tentatively attributed to telomerase activation resulting from taking an astragaloside IV supplement.  This has led me to look into what recent research tells us about hair stem cells and what the implications are for impeding or reversing baldness.  I found out a lot more on the subject than I anticipated.  Here are some of the highlights.

Hair follicles

To start with, a little background on hair follicles and hair growth.  A good general source of information can be found at hairfolliclecells.com.  Basically, a hair follicle is tiny bulb-like organ that , if it remains healthy “ –keeps on producing hair throughout an individual’s life.”  Growth of a hair takes place in a cycle of the follicle in three stages: anagen - the hair growing phase which may last 2-6 years; catagen - the intermediate phase lasting 2-3 weeks where “the hair stops growing and the hair follicle shrinks and part of it starts to die(ref),” and telogen – a resting phase that lasts about three months when the hair follicle is inactive and the old hair may be shed.  Then the follicle starts the cycle over again with a new hair, pushing out the remains of the old hair if it is still there. A follicle may be reborn 10-20 times and produce that many hairs over a lifetime.

Hair follicle stem cells

Hair follicle stem cells are epithelial stem cells that divide and produce new hair follicle cells in each growth cycle.  They are found in a part of the follicle known as the bulge, though stem cells capable of generating new hair follicles may also exist elsewhere on the skin. “Interfollicular epidermal cells also retain some capacity to generate new hair follicles(ref).”  Research has shown that at least some hair stem cells are pluripotent, that is, a single stem cell can differentiate into all the multiple cell types found in a follicle.  “The rat whisker stem cells participated again in forming all the cell types needed to form the hair follicle and sebaceous glands, resulting in hair bulbs that underwent repeated normal phases of growth, rest and regeneration. The fact that the transplanted cells participate in the hair cycle over long periods of time shows that they are true multipotent stem cells and not progeniture cells(ref).” 

Actually, some hair follicle stem cells are sufficiently pluripotent that they can be induced to differentiate into multiple types of somatic cells.  “– the researchers isolated and grew a new type of multipotent adult stem cell from scalp tissue obtained from the National Institute of Health’s Cooperative Human Tissue Network.” – “The mutipotent stem cells grow as masses the investigators call hair spheres. After growing the “raw” cells from the hair spheres in different types of growth factors, the investigators were able to differentiate the stem cells into multiple lineages, including nerve cells, smooth muscle cells, and melanocytes (skin pigment cells).” –“The differentiated cells acquired lineage-specific markers and demonstrated appropriate functions in tissue culture, according to each cell type(ref).”  In fact, neural crest stem cells that live in hair follicles could possibly be used for stem cell therapy purposes in lieu of embryonic or other stem cell types(ref).  “The neural crest is a population of stem cells that migrate extensively during development and give rise to many derivatives, including most of the bone and cartilage of the head skeleton, pigment cells of the skin, and cells of the peripheral nervous system (ref).”

“Overall then, it seems that stem cells are very flexible. Stems cells form other parts of the body can form hair follicles thus triggering hair regrowth if given the correct signals. Equally, stem cells in hair follicles can also form other tissues if given the appropriate signals(ref). The implications of using hair stem cells for tissue regeneration are widespread.  “

“Engineering blood vessels for bypass surgery, promoting the formation of new blood vessels or regenerating new skin tissue using stem cells obtained from the most accessible source — hair follicles — is a real possibility,” – “The group recently produced data showing that stem cells from human hair follicles also differentiate into contractile smooth muscle cells.  “We have demonstrated that engineered blood vessels prepared with smooth muscle progenitor cells from hair follicles are capable of dilating and constricting, critical properties that make them ideal for engineering cardiovascular tissue regeneration.” – “Since smooth muscle cells comprise the muscle of numerous tissues and organs, including the bladder, abdominal cavity and gastrointestinal and respiratory tracts, this new, accessible source of cells may make possible future treatments that allow for the regeneration of these damaged organs as well(ref).”

Hair stem cells and hair growth

Stem cell division and differentiation enable a hair follicle to renew itself at the start of each growth cycle and are essential for hair growth. According to a recent report “For a new round of hair growth to begin, stem cells in the hair follicle must receive a signal to divide. In response to this signal, the hair follicle regenerates first by growing downward through the skin’s middle layer, the dermis, and then producing the specialized cells that form the hair. After a period during which the hair grows longer, stem cells stop dividing, and the hair follicle gradually retracts again. There is then a period of rest and the cycle repeats(ref).”  A small compartment at the bottom of the bulge known as the hair germ plays a role in transmitting the signal for a hair follicle to renew itself and start making a new hair. “The researchers believe, however, that toward the end of the resting phase, the hair germ gets activated to proliferate before the bulge. Moreover, the team showed that the activating signal comes from a structure known as the dermal papilla(ref).”  What are the signals? “We think that FGF7 might contribute, along with the Wnts and BMP inhibitory signals, to coax the hair germ to divide and proliferate(ref).”  In case you are wondering, FGF7 is a growth factor made by the dermal papilla; Wnts is an important protein signaling pathway; BMP is bone morphogenic protein. Wnt and BMP signaling are important for neural crest stem cell maintenance(ref), bringing us back to the probable importance of these pluripotent cells in hair follicles.

Another study reports “We’ve found that we can influence wound healing with wnts or other proteins that allow the skin to heal in a way that has less scarring and includes all the normal structures of the skin, such as hair follicles and oil glands, rather than just a scar,” explains Cotsarelis.” – “By introducing more wnt proteins to the wound, the researchers found that they could take advantage of the embryonic genes to promote hair-follicle growth, thus making skin regenerate instead of just repair. Conversely by blocking wnt proteins, they also found that they could stop the production of hair follicles in healed skin. — Increased wnt signaling doubled the number of new hair follicles(ref).”

Recent research unveiled another important property of hair follicle stem cells.  They “can divide actively and transport themselves through the skin tissue(ref).”  That means that once dividing, they are not necessarily confined to a follicle of origin. “Here we show that Lgr5+ cells comprise an actively proliferating and multipotent stem cell population able to give rise to new hair follicles and maintain all cell lineages of the hair follicle over long periods of time. Lgr5+ progeny repopulate other stem cell compartments in the hair follicle, supporting the existence of a stem or progenitor cell hierarchy. By marking Lgr5+ cells during trafficking through the lower outer root sheath, we show that these cells retain stem cell properties and contribute to hair follicle growth during the next anagen(ref).”

Finally, I found a piece of research published this month that shows a direct link between telomerase activation, Wnt signaling and epidermal (including hair) stem cell differentiation. “Either stimulation of Wnt/ -catenin signalling or overexpression of telomerase is sufficient to activate quiescent epidermal stem cells in vivo,” — “These data reveal an unanticipated role for telomerase as a transcriptional modulator of the Wnt/ -catenin signalling pathway(ref).”

All of this is to say that:

IF telomerase activation promotes the differentiation of hair stem cells (and the last citation and other research I have cited previously says it does; see the recent post Extra-telomeric benefits of telomerase -  good news for telomerase activators)

AND activated hair stem cells can wander across the skin and start new hair follicles (which the above-cited research says happens)

THEN there is a plausible basis that telomerase activation will over time lead to more and more new hair follicles and hairs appearing on the head of a previously-bald guy like me (which is happening).  Besides, my often-cited shaggy mouse story shows it works in mice.  So, why not in me?  Given that hair follicles go into renewal phase only every 2-6 years I have to be reconciled that getting a full head of hair back may take some time.

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24. July 2009 by admin.

When a salamander is faced with a predator, it may simply cause its tail to fall off, which flops around distracting the predator while the salamander scampers away.  It will grow a new tail.  It can also grow an entire new limb if it needs one.  The salamander is not unique in its capability to grow new appendages.  Tadpoles, newts and other amphibian species can regenerate limbs and fish caudal fins can regenerate after amputation(ref).  I thought I would look a bit into how these animals go about doing that and the implications for human limb regeneration. 

This recent citation outlines the general process.  “When a salamander loses an appendage, such as a limb, a remarkable series of events unfolds: a clump of cells forms at the site of the injury, and this deceptively simple structure, known as a blastema, regenerates the missing body parts. Skin, muscle, bone, blood vessels and neurons all arise from this collection of nondescript cells through patterning and self-assembly.”    According to another study report “Axolotl (salamander) limb regeneration is considered by many to be divided in two main phases [2], [7], [8]. The first phase is referred to as the preparation phase and begins immediately following amputation with the formation of a wound epithelium (WE) over the amputation plane. Cellular dedifferentiation and migration, which will eventually lead to the formation of a regeneration blastema, also take place in this phase. In the second phase of limb regeneration, referred to as the redevelopment phase, blastema cells stop proliferating and start to redifferentiate to regenerate the lost part [1], [8](ref).”

Another recent publication  looks at the cells in the blastema.  “During limb regeneration adult tissue is converted into a zone of undifferentiated progenitors called the blastema that reforms the diverse tissues of the limb.” – “Surprisingly, we find that each tissue produces progenitor cells with restricted potential. Therefore, the blastema is a heterogeneous collection of restricted progenitor cells. On the basis of these findings, we further demonstrate that positional identity is a cell-type-specific property of blastema cells, in which cartilage-derived blastema cells harbour positional identity but Schwann-derived cells do not. Our results show that the complex phenomenon of limb regeneration can be achieved without complete dedifferentiation to a pluripotent state, a conclusion with important implications for regenerative medicine(ref).”  This work relates to the salamander Ambystoma mexicanum (the axolotl).  As I understand it, this says that the blastema consists of progenitor cells for the various tissues that will be in the final limb but not fully pluripotent stem cells that can differentiate into anything. 

But how is the blastema formed?  It appears that de-differentiation of stump tissue is involved(ref).  In other words, if you tear off a salamander’s leg, cells in the tissue left in the stump responds by de-differentiating from their initially highly specific types into progenitor cells in the blastema. 

Put yet another way “Epimorphic regeneration following limb amputation involves wound healing, followed shortly by a phase of dedifferentiation that leads to the formation of a regeneration blastema. Up to the point of blastema formation, dedifferentiation is guided by unique regenerative pathways, but the overall developmental controls underlying limb formation from the blastema generally recapitulate those of embryonic limb development(ref).”  Again it is a two-phase process, first of de-differentiation to form the blastema, and then of limb formation which is similar to that of embryonic limb development.  It works that way in salamanders but generally not in mammals who do not form a blastema when a limb is lost.  “Epimorphic regeneration usually produces an exact replica of the structure that was lost, but in mammalian tissue regeneration the form of the regenerate is largely determined by the mechanical environment acting on the regenerating tissue, and it is normally an imperfect replica of the original(ref).”

Nontheless, research on salamander limb regeneration may turn out to be quite relevant to humans since some of the underlying mechanisms of tissue regeneration may be similar.  Mammals have a very limited capability to regenerate appendages compared to salamanders but still can do so to a limited extent.  For example, mice and men can regenerate ends of fingertips. “–genetic studies on mouse digit tip regeneration have identified signaling pathways required for the regeneration response that parallel those known to be important for regeneration in lower vertebrates. In addition, recent studies establish that digit tip regeneration involves the formation of a blastema that shares similarities with the amphibian blastema, thus establishing a conceptual bridge between clinical application and basic research in regeneration. In this review we discuss how the study of endogenous regenerating mammalian systems is enhancing our understanding of regenerative mechanisms and helping to shed light on the development of therapeutic strategies in regenerative medicine(ref).”

The hope for limb regeneration is worthy of science fiction.  After amputating your brother’s arm that was completely crushed in an auto accident, the doctor tells him “We will get your body to form a blastema that will turn into a new new arm during your visit next week.  But then you will need patience.  It will take several years before the arm grows to full size and links completely up to your body nerve and vascular systems.  During that time the new arm will most likely be awkward.”

Researchers are developing insights that may lead to realization of that hope.  For example, de-differentiation of stump tissue in salamanders may result from the activation of skeletal muscle multipotent satellite cells(ref).  “We describe a multipotent Pax7+ satellite cell population located within the skeletal muscle of the salamander limb. We demonstrate that skeletal muscle dedifferentiation involves satellite cell activation and that these cells can contribute to new limb tissues. Activation of salamander satellite cells occurs in an analogous manner to how the mammalian myofiber mobilizes stem cells during skeletal muscle tissue repair. Thus, limb regeneration and mammalian tissue repair share common cellular and molecular programs. Our findings also identify satellite cells as potential targets in promoting mammalian blastema formation(ref).” 

Another stream of similarity between human wound healing and salamander limb regeneration involves TGFβ, transforming growth factor beta. “Multiple authors have recently highlighted the similarities between the early phases of mammalian wound healing and urodele (amphibians of the order Caudata, including salamanders and newts) limb regeneration. In mammals, one very important family of growth factors implicated in the control of almost all aspects of wound healing is the transforming growth factor-beta family (TGF-β).” – “Our results also demonstrate the presence of multiple components of the TGF-β signaling machinery in axolotl (salamander) cells. By using a specific pharmacological inhibitor of TGF-β type I receptor, SB-431542, we show that TGF-β signaling is required for axolotl limb regeneration(ref).”

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22. July 2009 by admin.

I am concerned that the popular view of telomerase activation is too simplistic and misses many the main benefits.  The popular view is that exogenously-activated telomerase extends telomeres (the endcaps of chromosomes) thus allowing cells to reproduce beyond the normal “Hayflick” limit of 50-70 reproductions  Therefore, by activating telomerase it may be possible to extend the lives of cell lines, and therefore the lives of organs, and therefore also the lives of animals including people.  This story is the one that got me into anti-aging science 15 years ago, still may be valid, and still inspires me.  However, it completely misses characterizing other recently-discovered health and longevity-producing benefits of telomerase, benefits that could turn out in the long run to be as or more important than telomere extension.  I review some of those benefits here. 

1.   Telomerase expression does not always lengthen telomeres.  When a cell is under stress, telomerase (actually its catalytic subunit TERT) migrates into the mitochondria.  There TERT plays a DNA-protective role and improves mitochondrial functioning. 

“While TERT maintains telomere length under standard conditions, telomeres under increased stress shorten as fast as in cells without active telomerase. This is because TERT is reversibly excluded from the nucleus under stress in a dose- and time-dependent manner. Extranuclear telomerase colocalises with mitochondria. In TERT-overexpressing cells, mtDNA is protected, mitochondrial membrane potential is increased and mitochondrial superoxide production and cell peroxide levels are decreased, all indicating improved mitochondrial function and diminished retrograde response. We propose protection of mitochondria under mild stress as a novel function of TERT(ref).”  Several other recent research reports supports this finding.  For example, see the June 2009 publication Mitochondrial telomerase reverse transcriptase binds to and protects mitochondrial DNA and function from damage.  Here is a May 2009 review study on the same issue. 

2.   Over- expression of telomerase can extend the lives as well as proliferation capability of adult of stem cells . 

“We have recently demonstrated that overexpression of human telomerase reverse transcriptase (hTERT) in hMSC (human mesenchymal stem cells) reconstitutes telomerase activity and extends life span of the cells.” – “Thus, telomerization of hMSC (by hTERT overexpression maintains the stem cell phenotype of hMSC and it may be a useful tool for obtaining enough number of cells with a stable phenotype for mechanistic studies of cell differentiation and for tissue engineering protocols(ref).”  As I said in my treatise “Loss of adult stem cells via telomere attrition provides strong selection for senescent, cycle-arrested, abnormal and malignant somatic cells, producing vulnerability to the diseases of old age.”  So keeping up expression of  telomerase in adult stem cells via telomerase activation could be very important for longevity.

3.   Telomerase promotes the differentiation of stem cells through a mechanism independent of telomere extension. 

Again, TERT does the job independently of telomere extension.   “We show that TERT(ci) retains the full activities of wild-type TERT in enhancing keratinocyte proliferation in skin and in activating resting hair follicle stem cells, which triggers initiation of a new hair follicle growth phase and promotes hair synthesis(ref). “  And I am continuing to get more hair on top of my head as a result of telomerase activation as previously mentioned in this blog. And I can’t help but mention the shaggy mouse story yet again.  I have no doubt that telomerase promotes the differentiation of other kinds of stem and progeniotor cells as well, but the research literature related to this is just starting to appear.   

One tantalizing study I just ran across says that transduction with human telomerase has opposite effects on healthy and cancerous nerve stem cells(ref).  On the one hand “Neural progenitor cells (NPCs) transduced with human telomerase reverse transcriptase (hTERT), the catalytic component of telomerase, have the potential both to proliferate indefinitely in vitro and to respond to differentiation signals necessary for generating appropriate cells for transplantation.”  And on the other hand,  for the cancerous NT2 cell line,  “– following hTERT transduction. RT-PCR and telomerase activity data demonstrated that persistent exogenous hTERT expression significantly inhibited the differentiation of neurons from NT2 cells. Following retinoic acid induced differentiation, hTERT-NT2 cells produced only one fourth of the neurons generated by parental and vector-control cells.”   

Not only does exogenous telomerase support the proliferation and differentiation of  healthy stem cells, but it also inhibits the differentiation of cancer stem cells.  NT2 is a neuronally committed human teratocarcinoma cell line.  I have to say this finding partially puts to rest a concern I have expressed in this blog – that telomerase activation may activate cancer stem cells.  We will have to see how telomerase activation works in the case of other cancer stem cell types.   

I have mentioned the role of telomerase in promoting stem cell differentiation before, both in my treatise and in blog posts, though it seems not to have been taken up in other anti-aging blogs.  It is important because longevity of organisms, people in particular may in fact more depend more on continuing differentiation of adult stem cells than on the number of times mature adult somatic cells reproduce.  See the 14^th theory of aging in my treatise Decline in Adult Stem Cell Differentiation.   

To editorialize a bit I feel strongly that it if we want to understand aging we have to go beyond looking at it only through the filter of a single theory like Telomere Shortening and Damage.  “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”  (words of Shakespeare spoken by Hamlet).  The Decline in Adult Stem Cell Differentiation theory provides a new and refreshing view of aging, one synergistic with the Telomere Shortening and Damage theory. 

4.   When considering telomeres. Not only lengths but absence of DNA damage is important for healthy cell reproduction and avoidance of cellular senescence. 

Cellular senescence can be triggered by either too-short telomeres or by unrepaired nuclear DNA damage .  Mitochondrial health and telomeric health seem to be bound up with each other.  “Firstly, it has been established that telomere shortening, which is the major contributor to telomere uncapping, is stress dependent and largely caused by a telomere-specific DNA single-strand break repair inefficiency. Secondly, mitochondrial DNA (mtDNA) damage is closely interrelated with mitochondrial ROS production, and this might also play a causal role for cellular senescence.” – “Together, these data suggest a self-amplifying cycle between mitochondrial and telomeric DNA damage during cellular senescence(ref).”  Going back to the first point above, TERT that has migrated to the mitochondria under conditions of cellular stress can protect the DNA there averting signaling that results in telomere shortening. Activated telomerase works indirectly to keep telomeres from shortening under conditions of stress.  This demonstrates an inter- relationship between four of the theories of aging in my treatise Oxidative Damage, Cell DNA Damage, Mitochondrial Damage , and Telomere Shortening and Damage. 

In the light of the above, I am not excessively concerned about whether telomere lengthening is happening in me as a result of my taking the astragaloside IV telomerase activator.  The other benefits are likely to be worthwhile by themselves.

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21. July 2009 by admin.

In this post I dip into some recent developments in the rapidly evolving field of stem cell research, this time focusing on embryonic stem (ES) cells.Today a news item appeared that reports a Spanish researcher has discovered a genetic circuit that regulates the differentiation behavior of embryonic stem cells(ref).  As explained in the original article, “There is evidence that pluripotency of mouse embryonic stem (ES) cells is associated with the activity of a network of transcription factors with Sox2, Oct4, and Nanog at the core.”  Apparently the degree of expression of Nanog is in constant flux and only when this level is low is an ESC ready for differentiation.  At any given time this is the case in only a small percentage (5% - 20%) of the available ESCs.  “Our results show that a population of ES cells represents a dynamic distribution of related states fluctuating between a stable state of high Nanog expression (HN) and an unstable state of low Nanog expression (LN). We also observe that LN cells are prone to differentiate, and exhibit an increased variability in gene expression as well as low-level expression of differentiation markers(ref).” Previously it was thought that the differentiation availability of ESCs was homogeneous, all cells being in the same state of pluripotency, and it was thought that the cells that differentiated were those that received external differentiation signals,  This is very interesting because the same three protein transcription factors (Sox2, Oct4, and Nanog) plus Lin28 can be used to cause any normal somatic cell to revert to IPSC (induced pluripotent stem cell) status.  See the post on this blog Update on induced pluripotent stem cells.  Apparently these same proteins are involved in a two-way street between pluripotent and differentiated cell status.

A related 2007 finding involves the self-renewal of ESCs.  “The researchers found that Jmjd1a and Jmjd2c, which encode enzymes that demethylate histone H3 lysine 9, regulate self-renewal in mouse ES cells: Depletion of Jmjd1a and Jmjd2c promoted differentiation, at the expense of self-renewal. Thus, these two histone modifying enzymes are required for maintaining pluripotency of ES cells(ref).”  Self-renewal vs differentiation of ES cells thus appears to be a matter of epigenetics.  As long as Jmjd1a and Jmjd2c are around, histone methylation is nipped in the bud and the cell acquires no epigenetic history due to such methylation.  Once methylation starts to take place the cell starts acquiring history and is prone to differentiation. See the blog entries Epigenetics, Epigenomics and Aging, DNA methylation, personalized medicine and longevity and Epigenomic complexity.  Also, you can check the discussion of the Programmed epigenomic changes theory of aging in my Anti-Aging Firewalls treatise. 

Whether we are concerned with embryonic stem cells or induced pluripotent stem cells, a key issue is how to get such pluripotent cells to differentiate into desired cell types including adult stem cells like hematopoietic stem cells or astrocytes or mesenchymal stem cells and then how to get these further to differentiate into the somatic cell types ultimately wanted.   My impression is that there is a lot of work going on studying aspects of this issue.  For example, this report is on work looking at the elacticity of a stem cell’s environment as a determinant of what type of somatic cell that stem cell becomes.  “In laboratory tests, Dennis Discher and Adam Engler *researchers at the University of Pennsylvania) grew mesenchymal stem cells (derived from adult bone marrow) in polymer hydrogels with either soft, medium or rigid elasticity.  Based on resulting cell shapes as well as messenger RNA and protein markers, stem cells grown in softer environments — such as brain tissue — tended to produce nerve-like cells; those grown in environments with medium elasticity — similar to muscle — produced muscle-like cells.  – The stem cells grown in more rigid environments — like bone — produced bone-like cells(ref) .”   There have been several successful attempts to get embryonic stem cells to differentiate into tissue-specific cells.  For example, a research team in Sweeden “ has managed to establish and isolate the tissue-specific stem cell that produces blood cells (blood stem cell) by using genetically modified embryonic stem cells(ref).”   

Another report is about using human ESCs to generate “natural killer” immune system cells that can can combat  cancers.  “This is the first published research to show the ability to make cells from human embryonic stem cells that are able to treat and fight cancer, especially leukemias and lymphomas,”  – “We hear a lot about the potential of stem cells to treat conditions such as Parkinson’s disease, diabetes, and Alzheimer’s disease. This research suggests it is possible that we could use human embryonic stem cells as a source for immune cells that could better target and destroy cancer cells and potentially treat infections(ref).”  Also see the blog post  Dendritic  cell cancer immunotherapy on Geron’s work producing dendritic cells on a large scale from ESCs for immunotherapy purposes. Besides research related to embryonic stem cells there is much research going on related to induced pluripotent stem cells and to adult somatic stem cells.  I will continue to report selectively on important developments.

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20. July 2009 by admin.

One of the headlines this week describing a population study in Denmark reads:  “Men’s key to longevity: have sex with younger women: Study.”  Another headline reporting on the same study reads “Daily sex with woman 15 yrs younger cuts death risk by 20%.”   “The study reveals that a man’s chances of dying an untimely death are cut by one-fifth if his bedpartner is 15 to 17 years younger to him.”  – “Men who took care of children and put food on the table lived longer, found the study that examined deaths between 1990 and 2005 for the entire population of Denmark.  The higher life expectancy in case of men having sex with younger women was attributed possibly not to having the sex itself, but rather to having a younger woman around to take care of you as you grow old and have increasing problems.   Hmm. 

But is having sex really irrelevant?  There is the Caerphilly Cohort Study which relates frequency of sexual orgasims to mortality, a 10-year cohert study of 918 men living in Caerphilly, South Wales and adjacent villages aged 45-59 at time of enrollment in the study.  “RESULTS: Mortality risk was 50% lower in the group with high orgasmic frequency than in the group with low orgasmic frequency, with evidence of a dose-response relation across the groups(ref).” 

Living with and having frequent sex with a female probably adds to longevity in other species in addition to humans.  Back some time ago in this blog posting I reported research that indicates that living and mating with a female adds up to 20% in the longevity of fertility of male mice.  See also the post Polygamy helps men live longer  and the post Use it or lose it and sexual intercourse.  Hmm again.  Seems like having women around, younger ones and perhaps more than one, and having frequent sex contribute to male longevity. 

Another study casts light on the issue from an evolutionary point of view. “It turns out that older men chasing younger women contributes to human longevity and the survival of the species, according to new findings by researchers at Stanford and the University of California-Santa Barbara(ref).  The study looked at contemporary primitive societies, investigating “ longevity and fertility data from two hunter-gatherer groups, the Dobe !Kung of the Kalahari and the Ache of Paraguay, one of the most isolated populations in the world. They also looked at the forager-farmer Yanomamo of Brazil and Venezuela, and the Tsimane, an indigenous group in Bolivia. “They’re living a lifestyle that our ancestors lived and their fertility patterns are probably most consistent with our ancestors.” – “In the less developed, traditional societies, males were as much as 5-to-15 years older than their female partners. In the United States and Europe, the age spread was about two years. “It’s a universal pattern that in typical marriages men are older than women,” Puleston said. “The age gaps vary by culture, but in every group we looked at men start [being sexually reproductive] later.”  – “The paper noted that the age gap is most pronounced in societies that favor polygyny, where a man takes several wives, and in gerontocracies, where older men monopolize access to reproductive women. The authors also cite genetic and anthropological evidence that early humans were probably polygynous as well(ref).”The researchers argue that older males mating with younger women provides an evolutionary advantage because it enables safer pregnancies of women in stable marriages before menopause and because: “the fatherhood of a small number of older men is enough to postpone the date with death because natural selection fights life-shortening mutations until the species is finished reproducing(ref).”  So, an old man fathering a child with a younger woman may not personally receive any longevity benefit, but his offsprings might. 

As a personal note, I have fathered five children with four different women.  One of these wonderful women, one wife back, is 16 years younger than me and another, my current wife, is 17 years younger than me.

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18. July 2009 by admin.

According to a news release yesterday; “TOKYO — Japanese people are living longer than ever, with the average life expectancy now 86.05 years for women and 79.29 years for men, the health ministry said Thursday.  Japanese women extended their life expectancy by almost 22 days in 2008 from the previous year, while men added another 37 days, the ministry said.”   

It seems like an immense increase in lifespan to happen in just one year. It is interesting to ask how could this happen.   The usual theories are related to improvements in public health and nutrition: changes that happened 70-90 years ago that affected the survival rate of infants, public sanitation systems, less air and water pollution, better balanced diets, improvements in the Japanese health care system and more public awareness about health.  I speculate here that something else more profound could also be involved – physical evolution of our species.

First I want to comment that the trend to longer life expectancy has been going on for many centuries now and has been happening in all developed countries. This table provides government statistics for “Life expectancy at birth, at 65 years of age, and at 75 years of age, by race and sex: United States, selected years 1900–2005.”  All the numbers have been going up every year.  A woman born in 1900 could expect to live 48.3 years; a woman born in 2005 can expect to live 80.4 years – a 66% increase.  In Germany life expectancy at birth increased from 78.42 years in 2003 to 79.1 years in 2008(ref).  The trend of increasing expectancy has been a very long one.  This Table suggest that average life expectancy at birth in Medieval Britain was 20-30 years, in the early 20^th century 30-40 years. This Table from the CIA World Factbook lists 2008 life expectancy at birth for 191 countries.  At the top of the list is Macau with 84.38 combined male-female life expectancy at birth and at the bottom is Swaziland with 39.6 years combined life expectancy.  The US ranks 45^th on the list with 78.06 years.  At the same time as life expectancy has increased there have been other shifts in average human body characteristics, such a towards greater height, particularly in advanced countries(ref).

My speculation is that human cultural evolution is leading to species evolution via epigenomic modifications in inheritable DNA that makes for longer longevity, and that this process is ongoing right now..  Specifically:

·        As human industrial and post-industrial societies become more and more complex it takes longer and longer for young people to achieve the education and skills for them to become fully-functioning members of society.  In Neolithic societies, at the age of about 15 children could start taking full adult responsibilities for hunting and gathering, bearing children and taking on the roles required for society to work.  Nowadays, if a young person is pursuing a professional path, about twice as many years are required before that person is a fully-functioning doctor, lawyer, or other skilled professional.  Instead of starting to have children at 15-16, the tendency in advanced countries now is for childbearing to be postponed until women are in their 30s or 40s(ref). 

·        While there are clearly class differences, the individual and societal investment required to bring young people up to speed has been growing and in the US may be nearing a half-million dollars for advanced professionals like doctors, lawyers, scientists and diplomats.  While few finished high school a century ago, yesterday President Obama advocated that everyone should be provided at least a 2-year college education.  Everything connected with full social maturation takes longer, is more complex and is more expensive

·        From a viewpoint of simple cultural economics, it makes sense that this greatly expanded investment in initial maturation of individuals be accompanied by a much longer productive lifespan over which that investment is amortized. 

In other words, arguing purely from an evolutionary viewpoint, it would make excellent sense for cultural evolution to induce species evolution so that people live longer.  That is exactly what has been happening, but the exact mechanisms involved are unclear.  There are probably several mechanisms at work including advances in public health knowledge and developments such as decline in cigarette smoking.   Another mechanism may be greater dissemination of knowledge as to what makes for health and longevity, this blog playing a tiny part. 

My speculation is that, in addition, inheritable epigenomic changes are happening in our DNA that are leading to greater longevity.  That is, our genes themselves are not being changed but that there are modifications in our histone acetylation and DNA methylation patterns and other chromatin changes that on the whole help us live longer. 

The general process of epigenomic modification is described in my February blog entry Epigenetics, Epigenomics and Aging.  My speculation is feasible, given what we know about epigenomics.  In fact, as I have speculated before, aging itself may largely be an epigenomic phenomenon.  However, my speculation remains a speculation for now because I cannot say how and when longevity-promoting epigenomic reprogramming is taking place.  For a possible hint, see also my previous blog post Longevity Genes and Two Fantasies.  See also this reference for how hormonal mechanisms may affect longevity genes via epigenomic modifications. 

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