New Findings in the Control of Stem Cell Differentiation

Nodal Activin Pathways Image Source
Researchers from the Genome Institute of Singapore have helped to untangle how stem cells might be controlled with a single signaling pathway -- the nodal activin pathway.

Morphogens are secreted signaling molecules that orchestrate the spatial distribution and sequence of cellular differentiation events throughout embryonic development. The specific cell types, their localization and order of induction from recipient stem cell populations are determined by the concentration gradient of morphogens diffusing from the source of secretion. Previous studies have proposed some of the models by which morphogen gradients are initiated, established and stabilized including the level of receptor occupancy, positive/negative feedback and feed forward mechanisms [1]–[3]. However, little is understood about the transcriptional mechanisms responding to variable receptor activation and how they permit pluripotent stem cells to interpret signaling levels and direct the appropriate differentiation programs during mammalian development....

Nodal and Activin are morphogens of the TGFbeta superfamily of signaling molecules that direct differential cell fate decisions in a dose- and distance-dependent manner. During early embryonic development the Nodal/Activin pathway is responsible for the specification of mesoderm, endoderm, node, and mesendoderm. In contradiction to this drive towards cellular differentiation, the pathway also plays important roles in the maintenance of self-renewal and pluripotency in embryonic and epiblast stem cells. The molecular basis behind stem cell interpretation of Nodal/Activin signaling gradients and the undertaking of disparate cell fate decisions remains poorly understood. Here, we show that any perturbation of endogenous signaling levels in mouse embryonic stem cells leads to their exit from self-renewal towards divergent differentiation programs. Increasing Nodal signals above basal levels by direct stimulation with Activin promotes differentiation towards the mesendodermal lineages while repression of signaling with the specific Nodal/Activin receptor inhibitor SB431542 induces trophectodermal differentiation. To address how quantitative Nodal/Activin signals are translated qualitatively into distinct cell fates decisions, we performed chromatin immunoprecipitation of phospho-Smad2, the primary downstream transcriptional factor of the Nodal/Activin pathway, followed by massively parallel sequencing, and show that phospho-Smad2 binds to and regulates distinct subsets of target genes in a dose-dependent manner. Crucially, Nodal/Activin signaling directly controls the Oct4 master regulator of pluripotency by graded phospho-Smad2 binding in the promoter region. Hence stem cells interpret and carry out differential Nodal/Activin signaling instructions via a corresponding gradient of Smad2 phosphorylation that selectively titrates self-renewal against alternative differentiation programs by direct regulation of distinct target gene subsets and Oct4 expression. _PLoS Genetics

This finding has profound implications for experimental approaches to guided stem cell differentiation and / or stem cell self renewal. The ability to control multiple distinct sets of genes by titrating the dose of signaling molecules is likely to prove a very powerful tool for geneticists, stem cell researchers, and bio-developmental scientists.

In other longevity news, a team of scientists from multiple universities has helped elucidate how cryoprotectant molecules protect proteins from freezing. Future research should enlarge the scope of study to discover optimal cryoprotectants for cells, tissues, organs -- and eventually for entire organisms.

It is quite possible that different types and levels of cryoprotectant will prove optimal for different organs and tissues, so that in order to viably freeze and thaw an entire organism -- say, a human being -- a complex process of multiple simultaneous organ infusion with several cryoprotectants would be necessary.

Are We Closer to Viable Long-Term Freezing for Organs and People?

Once we are able to viably freeze and thaw living organs and whole animals, without damage or injury, we will be able to plan for the targeted freezing and thawing of living humans for purposes of extended survival.

A technology that has come from the frozen sushi industry in Japan is being studied for possible application to living animals and human organs such as hearts, livers, lungs, and kidneys.

A technology used to freeze sushi is solving a dilemma for organ storage. By borrowing tech used to preserve high-end food delicacies, a Hiroshima University research group proved it possible to safely freeze whole teeth and their delicate attaching tissues. As long as the freezer stays cold, the folks at Hiroshima U. think your teeth could be stored for 40 years, no problem.

But the sushi-storage system isn’t a one trick pony: internal organs could be next thanks to the magic of supercooling. In typical cryo-storage, fast freezing of organs requires poisonous levels of anti-freeze, and let’s face it, no one wants a poisoned kidney transplanted into their body. But slower freezing causes cell popping ice crystals to form.

So, what do you do to prevent ice crystals during slow freezing? Use magnets. ABI is the Japanese company producing the freezer system. ABI’s “Cells Alive System” (CAS) vibrates water with magnetic fields, preventing freezing, even at supercool temperatures of -10 degrees Celsius (According to the Patent.) When the field is turned off, the water in the food instantly freezes. No time for ice growth means no Freddy Krueger action on frozen organs.

...The transition of this tech from food to longevity science is slowly evolving, but the steps forward are real. You can, right now, pay to store your teeth. Hiroshima University tested the cooling technology for teeth, and uses ABI CAS freezer tech at The Teeth Bank, the world’s first commercial tooth bank. Dr. Toshitsugu Kawata, a Hiroshima University professor who has done extensive research at the Teeth Bank, helped prove that CAS is a viable technology to preserve teeth. Spare teeth used to be worthless medical waste. Now, removed wisdom teeth aren’t garbage, they can be frozen and re-implanted at any point during your life.

...The founder of the ABI Corporation and its CAS freezer, Norio Owada (known internationally as “Mr. Freeze,”) is actively pursuing medical advances. There’s a hodgepodge of reports out there about what’s being done. According to various sources, Mr. Freeze is collaborating with 40 researchers to translate their work with teeth and sushi to hearts, nerves, and other organs. Transplant medicine could benefit tremendously. With further research, this technology could supercool, or even freeze internal organs, putting an end to the dangerously brief time frame for organ transplants. In a 2008 Forbes article, Mr. Freeze speculated on where his technology may lead. “If you could preserve a heart for three days, you could fly it anywhere.” On the late-night Japanese TV show, World Business Satellite, there was discussion of research towards using ABI’s CAS freezers to store ovaries during cancer treatment, allowing women to keep their fertility. On the ABI company webpage, photos of a rat heart transplant and undamaged cell walls of frozen wasabi are a reminder of the unusual coupling of frozen food and medicine. _SingularityHub_via_NextBigFuture

One further step is needed: a vitrification agent which can be added to the supercooled organs which would allow the electromagnetic field to be turned off without the risk of freezing. One step at a time.

Brain - Cooling Techniques

Scientists and physicians are developing new brain - cooling techniques to reduce morbidity after heart attacks (and presumably strokes) and to aid successful resuscitation after heart attacks. One device, like a reverse hair drying hood, cools the scalp and its blood vessels, achieving about 1 degree C cooling of the brain per hour. Another device sprays a refrigerant deep into the nose to indirectly cool arteries passing nearby, heading for the brain. The nasal device cools the brain by 2.4 degrees C per hour. A third device uses an icy slurry lavage into lung airways, to cool blood passing into the carotid arteries to the brain.

For some time, doctors have observed that cooling patients following a heart attack can reduce brain damage. Although they are not yet sure of the mechanism behind this effect, researchers suspect that cooling the brain by 4 °C, to around 33 °C, reduces the metabolism of brain cells, reducing their hunger for oxygen for the crucial moments during which blood is in short supply. Damage seems to be reduced even if the brain is only cooled once the heart has been restarted, suggesting that cooling may also slow the release of toxic chemicals from neurons and glial cells - a process called the ischaemic cascade, which triggers further brain-cell death up to 24 hours after a cardiac arrest or stroke.

Previously, doctors have induced "therapeutic hypothermia" by applying ice packs or cooling blankets to the whole body, or injecting cold saline solution into the veins. However, cooling the whole body can increase the risk of infection and pneumonia, so researchers are now building targeted devices that chill the brain directly.

...The ice slurry can cool the brain by 4 °C - the safe limit before damage is risked - in less than 15 minutes, says Kasza, who has so far tested the technique on pigs. His team is investigating whether their icy slurry could also be applied to the kidneys (see picture) and the heart during invasive surgery, to prevent damage to the organs when blood flow is suspended for the operation.

One of the main advantages of all the new techniques is that they are simple enough to apply before or immediately after resuscitation following a heart attack - minimising the delay between the heart malfunction and cooling the brain. "A paramedic could deliver the slurry," says Kasza.

What's more, a recent study in pigs suggests that immediate cooling with the RhinoChill device, besides reducing brain damage, could also improve the chances of success of the resuscitation itself, although it is not yet certain why this is. Sixteen pigs were given a heart attack, and then left for 15 minutes before CPR was applied to start their hearts again. Of the eight pigs cooled using the RhinoChill system during CPR, six survived, compared with just two of the eight who were left unchilled (Resuscitation, DOI: 10.1016/j.resuscitation.2008.03.087).

Rapid application of such techniques could be particularly good news for stroke victims. "Clot-busting drugs can only be administered after diagnosis and brain scans in the hospital," says Andrews. "But applying therapeutic cooling at the scene of the stroke could lengthen the time window in which the drugs are effective - before too much damage has occurred," he says. _NewScientist

These techniques are a far cry from the advanced cryonics and vitrification methods needed for long - term organismic storage or hibernation. But experiments with them, and experience using them should add to the knowledge needed to develop the longer - term methods.

Alcor Cryonics Video

This 28 minute video from Alcor looks at the history of life extension technology--specifically the cryonic approach to making "death" reversible indefinitely.

Exploring Life Extension--A Film by the Immortality Institute

This one hour and 45 minute film explores cryonics (cryogenics), caloric restriction, transhumanism, and other scientific pursuits of extreme life extension. Related websites: http://www.Mprize.org http://www.ImmInst.org http://www.sens.org