June 08, 2005
Gene Activation Makes Adult Stem Cells Divide Rapidly
Adult stem cells are hard to grow. But MIT Whitehead Institute researchers have discovered that turning on a gene that is active in the early embryo causes adult stem cells to grow rapidly.
While research on human embryonic stem cells gets most of the press, scientists are also investigating the potential therapeutic uses of adult stem cells. Although less controversial, this research faces other difficulties. Adult stem cells are extremely difficult to isolate and multiply in the lab.
Now, as reported in the May 6 issue of Cell, researchers led by Rudolf Jaenisch of the Whitehead Institute have discovered a mechanism that might enable scientists to multiply adult stem cells quickly and efficiently.
"These findings provide us with a new way of looking at adult stem cells and for possibly exploiting their therapeutic potential," says Jaenisch, who also is a professor of biology at MIT.
I have repeatedly argued that it is just a matter of time before scientists find ways to turn adult stem cells into cells that can become any other cell type. This latest research from MIT is certainly a step in that direction. Note that these scientists used existing knowledge that the gene Oct4 is known to be active in embryonic stem cells. They turned that same gene on in adult stem cells. So this research is a clear step in the direction of making adult stem cells more like embryonic stem cells.
This research focuses on a gene called Oct4, a molecule that is known to be active in the early embryonic stage of an organism. Oct4's primary function is to keep an embryo in an immature state. It acts as a gatekeeper, preventing the cells in the embryo from differentiating into tissue-specific cells. While Oct4 is operating, all the cells in the embryo remain identical, but when Oct4 shuts off, the cells begin growing into, say, heart or liver tissue.
Konrad Hochedlinger, a postdoctoral researcher in Jaenisch's lab, was experimenting with the Oct4 gene, curious to see what would happen in laboratory mice when the gene was reactivated in adult tissue in which it had long been dormant. Hochedlinger found that when he switched the gene on, the mice immediately formed tumors in the gut and in the skin where the gene was active. When he switched the gene off, the tumors subsided, demonstrating that the process is reversible.
Discovering that simply flipping a single gene on and off had such an immediate effect on a tumor was unexpected, even though Oct4 is known to be active in certain forms of testicular and ovarian cancer. Still, the most provocative finding was that "Oct4 causes tumors by preventing adult stem cells in these tissues from differentiating," says Hochedlinger. In other words, with Oct4 active, the stem cells could replicate themselves indefinitely, but could not produce mature tissue.
One of the main obstacles with adult stem cell research is that,
This experiment showed that when Oct4 was reactivated, the adult stem cells in those tissues continued to replicate without forming mature tissue. In a mammal's body, this type of cell behavior causes tumors. But under the right laboratory conditions, it could be a powerful tool.
"This may allow you to expand adult stem cells for therapy," Hochedlinger said. "For instance, you could remove a person's skin tissue, put it in a dish, isolate the skin stem cells, then subject it to an environment that activates Oct4. This would cause the cells to multiply yet remain in their stem cell state. And because this process is reversible, after you have a critical mass of these cells, you can then place them back into the person where they would grow into healthy tissue."
"This could be very beneficial for burn victims," Jaenisch said.
The difference between adult and embryonic stem cells is just that they are in different regulatory states. Think of the genome of a cell as having a big set of switches on it with the pattern of which switches are set On and Off being one way in embryonic cells and other ways in other cell types. One reason I haven't been pessimistic about limitations on human embryonic stem research is that I expect scientists working with adult stem cells to find ways to change their regulatory state (i.e. their pattern of On and Off for their genetic switches) into the same states as is found in embryonic stem cells.
The irony of religious opposition to human embryonic stem cell research is that it logically leads scientists to look harder for ways to make adult stem cells act more like embryonic stem cells. The inevitable outcome of this search will be development of techniqes that convert adult stem cells into cells that can be turned into all other cell types - just as embryonic stem cells can. The ability of embryonic stem cells to turn into all other cell types is called pluripotency. Once non-embryonic stem cells can be made pluripotent then the religious opponents of human embryonic stem cell research are going to have to decide whether they believe all pluripotent stem cells are mini-humans or not.
Even if work with all human pluripotent stem cells is outlawed regardless of what cell type is converted into the pluripotent state or how it is turned into the pluripotent state that still won't stop scientists from manipulating adult stem cels into all other cell types. Such a ban would be just another regulatory barrier that could be programmed around with genetic engineering. Scientists could respond to that ban by fiding some difference between fully pluripotent cells and slightly differentiated cells and convert cells into slightly differentiated (i.e. slightly specialized) states rather into the fully pluripotent state.
So far the acrimonious debate about human embryonic stem cells has caused a big increase in adult stem cell funding by the US federal government (over $500 million per year in total stem cell research funding) and the passage of an initiative in California to spend $300 million per year on stem cells without a restriction on human embryonic funding. So obviously funding levels have risen greatly. The rate of advance is accelerating. But I'd like to see even greater acrimonious debate so that we can get total funding over $1 billion. Come on, get mad at each other. We need more funding!
Yes, hopefully we will get to the point when every cell is considered scared and any one who murders even a single human cell will be punished to the fullest extent of the law. I will finally get back at my brother for knocking out one of my teeth when we were younger. He must have killed billions (trillions?) of human cells that day .
From all of my reading on the subject, I am yet to encounter anyone who has a religious opposition to stem cell research because of a confusion of a cell culture and an embryo, and the religious right has been quite consistent in supporting research on adult stem cells. Confusion seems more prevalent among some on the left who confuse gametes with embryos and who come up with straw man arguments that the religious people are concerned with the preservation of every sperm. The preceding comment indicates another kind of straw man argument.
I was being sarcastic, (although I was singing Monty Python's Every Sperm is Sacred when I was typing my first post.)
But there is an interesting issue on what kind of legal standing (if any) human cells should have. I would argue that no individual nor small group of human cells should have any legal rights.
I say that it is time we ignored the people who object to stem cell research and do the research anyway, even if stupid laws have to be broken or else do the research "underground" in secret (it is unbelievable how the world has got itself into this state where progress is stopped by fanatics who like to live with their fairy tails of devine creator etc. These people should get their noses out of science's business and go live with the iatolas in the middle east if they can't handle the progress of science in the 21st century and would preffer to live in the dark ages like those relgious fanatics that blew up the world trade center.
If you are growing replacement organs from stem cells, obviously your own cells are the best place to start. No need for anti-rejection treatments for either you or the donor cells that way. Adult cell derived stem cells will require the greatest advances in cell biology knowledge and will give the greatest benefit.
Embryo derived stem cells are great for basic research, but fixating on them to the exclusion of the more important goal of adult cell derived stem cells is a mistake that too many short-sighted and politically skewed persons are making.
But progress has not been stopped by fanatics. California is providing a few hundred million a year for adult and embryonic stem cells. South Korea's government provides $100 million per year (and I'd have a URL for that amount if my computer didn't crash after I'd typed up a longer post on this). Chinese scientists are working on embryonic stem cells.
But Somatic Cell Nuclear Transfer (SCNT) allows creation of embryonic stem cells which have the same nuclear DNA as your own cells. So adult stem cells are not the only way to avoid the immune problems or to otherwise make cells extremely similar to your own.
Though I have to say SCNT is going to be limited by the number of eggs that can be acquired. Also, you have to be careful about choosing an egg donor since you will get their mitochondrial DNA.
I think most are missing the point. This is exactly what those agains embryonic stem cell research were hoping for, a way to achieve the same result without involving embryos.
Good point about the SCNT technique, RP. The nuclear DNA would indeed all come from the donor somatic cell nucleus. So far that process is incredibly inefficient and requires creation of a cloned embryo to get the pluripotent stem cells. Even so no one knows what potential problems remain from cytoplasmic components in the enucleated egg, including the mitochondria.
How much more elegant to grow the specific stem cells that you need directly from adult cells. That is the dream of organ transplant scientists and surgeons.
Please note that this result does not yet produce pluripotent cells. Yes, it is a step in that direction. But it does not get us all the way there.
As for whether "embryos" are the issue: I see it as more complex than that. Suppose cells that are effectively embryonic stem cells (i.e. they are pluripotent) are created without first using an egg either for fertilization or SCNT. Well, SCNT already avoids the fertilization step and yet hESC opponents still oppose SCNT. Why won't at least some of them judge what the pluripotent stems are capable of and say that pluripotent stem cells created from adult cells are mini-humans? After all, they that for the pluripotent cells created from SCNT.
The other point about SCNT worth keeping in mind is that most SCNT attempts fail. The reason is that the egg cytoplasmic has to, in effect, reprogram the adult nucleus and this reprogramming has a high rate of failure. So if the goal is to use each person's own cells to make pluripotent cells customized to their DNA then SCNT might be a transitory technology until more precise and controlled ways to do it are found.
> Though I have to say SCNT is going to be limited by the number of eggs that can be acquired.
this is unlikely to remain a problem for long IMO. Several research groups have demonstrated that it is possible to obtain unfertilized eggs not through egg donation, but from embryonic stem cells as well as cultures of ovarian surface cells. These techniques will enable medical researchers to lab produce eggs in unlimited quantities, and probably even before stem-cell cloning becomes a practical therapeutic option. Egg donation is destined to turn into a non-issue.
Important note, without embryonic stem cell research, how could they have found this way to enhance adult stem cells?
Obviously stem cell therapies would be cheaper and easier using adult stem cells than embryonic ones, but research into embryonic stem cells will probably provide key information on the use of adult ones.
My guess is that the Oct4 gene was first found in a mouse model. I could be wrong. But keep in mind that most stem cell research, whether adult or embryonic, is still done in other species for the same list of reasons that most biomedical research is done in other species. They are a cheaper, easier to work with, faster to work with, more controllable, less restricted by ethical considerations, more consistent because they are inbred and live in controlled environments, etc.
Also see what stem cell researcher Evan Snyder said about federal restrictions on human embryonic stem cell research a couple of years ago.
A pluripotent stem cell is not equivalent to an embryo. The embryo derives certain patterning signals from protein gradients established in the egg from the ambient ovary. Without these the pluripotent stem cell will tend to differentiate in an organized manner, resulting in a teratoma, an unorganized mass of differentiated tissue that is not integrated into a viable organism. Thus, those who are concerned that human embryos be respected do not have the same concern about pluripotent stem cells, at least not those familiar with developmental biology. Note that the Kass committee looked favorably on a proposal to make the result of SCNT unable to respond to the egg's patterning signals by temporarily disabling a critical gene within the nucleus, thus avoiding forming a cell that could be considered an embryo.
Yes, a pluripotent stem cell does not equate with an embryo. There is a larger structure too. However, some of the religious folks might not see it that way.
As for disabling a gene: I've been thinking about writing a post about how one could permanently disable some key developmental gene in an egg (say turning off the gene only disabled neural development), have the egg meet a sperm, and create an embryo. Because of the disabled gene that embryo would not have the ability to develop into a baby. Yet it might be useful for, say, growing a liver . Would religious folks object to use of such an embryo to grow livers? After all, it would be an embryo. But it couldn't produce a human.
Ah yes, the Kass committee proposal. Knock out a gene so that the embryo won't form a placenta and stops dividing even if implanted in a womb...
...and yet fundies cried foul, calling these pre-teratomas "disabled embryos". Who's to say they're wrong? Their judgement aims at ethics, not science. Isn't every skin cell a potential embryo and, by extension, a "potential person" if we find out which chemical substances can reverse the epigenetics of adult stem cells back to 'embryonic'? Is a group of pluripotent cells which would have to be bathed in just one more chemical solution in order to turn totipotent a non-embryo or a starved embryo?
My point being, of course, that it shouldn't matter either way. Embryos have no capacity for suffering, conscious experience and anticipating the future whether they're engineered for disorganized development or not. The upcoming tattles over what is an embryo and what isn't could be avoided if only lawmakers chose to protect people rather than cellular masses.
On the other hand, if this teratoma thing can navigate the research around legal obstacles then by all means try it, and fast!:)
I don't see the benefit of what you propose, as the resulting liver would be subject to rejection. I suspect that what you have in mind would have to derive from SCNT so that it would match the intended recipient. However, how much would you have to disable the embryo in order that it not be considered worthy of respect? Do you regard the thalidomide children, born without arms, to be less than human?
Whatever you deprived the embryo of would probably make it more difficult to raise to a size that its parts could be usefully harvested, so there would be the temptation to leave it entire for convenience. This would pose no problem to those who see nothing wrong with late term abortions. Indeed there are some who believe that our humanity derives entirely from socialization, so by the simple expedient of depriving the organism of that it could be raised to adult size without giving those who so believe any pause; it would be kind of like raising veal. Note that this can all be done with existing knowledge. No further research would be required, but it would require a considerable hardening of our own hearts, a stage that those able to dismiss the organism as a "cellular mass" would seem to have almost reached.
Now I don't know just what you think on some of these points, although from your last post it would appear that you think that something would have to be done to avoid ethical errors. My hope is that it will be possible to breed some animal that does not reject human tissue and that such things as livers and kidneys can be grown in them.
Some hESC researchers think optimistically that the immunocompatibility problem will be solved. However, I put forth the problem more as an exercise to ask what the religious opponents to hESCs would think. The creation of an embryo from egg and sperm is more "natural" or "the way the lord meant it to happen" and hence that scenario most directly elicits their moral reaction.
There is a reason to want the immunocompatibility: emergency organs. Just got in a car accident and toasted your liver? There's no time for SCNT to produce a new one.
Yes, SCNT makes more sense for growing new organs. Yes, the same sort of disablement of key genes could be done.
I'm talking selective disablement far more severe than what thalidomide causes. There'd be no birth of a baby that could survive outside the womb. Whole subsystems could not develop. I specifically mentioned prevention of the development of the nervous system. Take away the brain and most people would say it is not a human.
Lots of genes are expressed only in subsets of organ types. I'm sure that genes could be found to disable that would prevent full development but allow differentiation into, say, a liver or pancreas.
I expect methods to develop pluripotent cells from adult stem cells will be found. We might get replacement organs grown more rapidly using SCNT-derived cells. But we will get them one way or another. I think the bigger challenge will be in the tissue engineering to control development of just a single organ. Managing its environment will be hard.
Maybe xenotransplantation can be solved. But getting a pig that is already an adult to, say, grow a new kidney strikes me as being about as hard as having a human adult grow a new kidney. Genetically engineering pigs to grow up with kidneys that humans could use poses a different set of problems. Strikes me as requiring transplantation of lots of human genes into pigs to make it work and lots of immune system fiddling in the pigs and in humans who'd get the organs.
The June issue of Wired magazine has an article about the proposal to create stem cells using methods of the type discussed by toot and Zoeific above. The article is called "How to Farm Stem Cells Without Losing Your Soul". Here is an excerpt:
In a bit of diplomacy that may satisfy both the scientists and the theologians, Hurlbut advocates genetically altering cloned embryos so, like a teratoma, they wouldn't have the DNA necessary to become viable humans. For the first few days of existence, they would grow normally and produce stem cells, but then die when a critical embryonic component - say, a placenta - failed to emerge.
Here is a link to the Wired article
. I do not think that many religious groups will oppose the creation of multipotent or pluripotent cells. If stem cell technology continues to progress then in the future each cell will be manipulatable into a pluripotent cell. Any religious group that maintains that every living skin cell that is shed from the body is "sacred" and most be preserved will probably have difficulty attracting adherents.
The Washington Post also has a recent article on this topic titled "Stem Cell Advances May Make Moral Issue Moot". It discusses a variety of strategies for creating stem cells. Here is an excerpt:
Yet the gathering consensus among biologists is that embryonic stem cells are made, not born -- and that embryos are not an essential ingredient. That means that today's heated debates over embryo rights could fade in the aftermath of technical advances allowing scientists to convert ordinary cells into embryonic stem cells.
The article is here
Yes, I am aware of Hurlbut's suggestion; it was what I was referring to at the end of my first comment, but his name had slipped my mind. I agree with you that most religious groups would make the distinction and not confuse stem cells and an embryo. Of course, I would be reluctant to make the same claim for all religious individuals, as people will be quite diverse in their understanding and attitudes, and some of the distinctions to be made are rather fine.
If they find a way to promote the growth of a new organ within the individual who needs it, that would certainly be a better solution than attempting to grow the organ in an animal. Here the problem would be to keep the patient alive long enough for the organ to develop, e.g., by dialysis, but that would be necessary in any case. It would probably be what would be required to replace portions of a damaged nervous system.
I get an impression you misread my previous post, so let me clarify: I wasn't advocating growing blastocytes into feeling conscious entities to harvest their tissues, but what Randall said: growing organs without a central nervous system attached. I take it that with "cellular mass" the essay I linked to meant the embryo before cell differentiation even sets in, not fetuses with a functional brain or something along that line.
On a vaguely related note, the media sometimes seems to be having fun associating the future of replacement medicine with glaring visions of headless clones-in-vats plopping out of pod-like artificial wombs. While most people don't consider a body without a brain to be a person, it is quite clear that, apart from a slew of feasibility problems, this would elicit a good deal of yuck-reactions from the general public. Thankfully tissue engineering offers lots of more low-key (as well as faster and less expensive) approaches. This article sums up some developments in the field. While artificial blood supply to larger organs keeps being a problem for now, other promising ideas seek to make use of the recipient's own bodily environment to order a soup of stem cells into an organ. The latter approach has its own limitations, of course. An entire new heart muscle with valves and all would arguably be more difficult to grow inside the patient's body than a lowly jaw bone.
At any rate, the more research is done, the sooner the ethical issues around organ replacement will be overcome and rendered obsolete.
"On a vaguely related note, the media sometimes seems to be having fun associating the future of replacement medicine with glaring visions of headless clones-in-vats plopping out of pod-like artificial wombs. While most people don't consider a body without a brain to be a person, it is quite clear that, apart from a slew of feasibility problems, this would elicit a good deal of yuck-reactions from the general public. "
Until they need one of their own. The problem comes when those bastards that call themselves the "general public" stop me from getting one.
(And a headless clone wouldn't be as much good as a brainless clone.) Forget turning off placentas and nonsense like that, just keep the thing from growing its own brain.
With brainless clones and a full body transplant, we've licked the aging process everywhere except inside the brain.
"Thankfully tissue engineering offers lots of more low-key (as well as faster and less expensive) approaches. "
And thankfully, foreign countries offer a way that the "general public" can be circumvented and techniques that are not so low-key can be developed and obtained.
It seems to me not a little of the demand for stem-cell-derived fixes comes from those like Christopher Reeve who needed to repair or replace a portion of his nervous system. Consider the commonly made claim that stem cell research will lead to a cure for Alzheimer's disease. It seems that creating organisms without nervous systems is not going to be the answer.
I also question the extent to which researchers and spare parts providing companies are going to jump through hoops in order to keep their developing products from becoming too human. They will tend to assume that humanness derives from socialization, and they will adopt the methods of the veal industry. Yes, you can bet that the cures will come earliest from those foreign countries where the concern for human rights is minimal. After all, once one has the attitudes of a slave trader, little stands in the way of becoming a dealer in human parts.
"Consider the commonly made claim that stem cell research will lead to a cure for Alzheimer's disease. It seems that creating organisms without nervous systems is not going to be the answer. "
That would be the time to grow organs, or in this case nerves, rather than a complete organism. The other tack, of course, is to grow an organism without a brain, not without a nervous system. You want to have something to hook the brain up to when you do the transfer, after all.
"I also question the extent to which researchers and spare parts providing companies are going to jump through hoops in order to keep their developing products from becoming too human."
Once techniques are developed to switch the growth of individual parts on and off, which is what you need for any of this to become a reality, omitting a brain shouldn't be too much of a hoop.
"They will tend to assume that humanness derives from socialization, and they will adopt the methods of the veal industry. Yes, you can bet that the cures will come earliest from those foreign countries where the concern for human rights is minimal. After all, once one has the attitudes of a slave trader, little stands in the way of becoming a dealer in human parts."
A dealer in human parts is a useful profession. A dealer in stolen human parts, however, is a criminal. Once we recognize that the human brain is the person, and thus any brain grown becomes the owner of the associated parts, all civilized people can make the required distinctions quite easily.
In the meantime, research into viable hibernation techniques would be useful, so that old people can simply stall for time rather than take physical or moral risks with early technology...
I see you have an answer for everything. However, keep in mind that you are advocating an unrealized ideal, and that being unrealized, it can be made to accommodate to any situation and to solve any problem. Give some thought to what reality might become.
Before we can reliably create knockout-clones (with anencaphaly) with an _artificial_ human-host-uterus, it will be irrelevant to do so.
Using the techniques of Rapid-Prototyping (3D plastic+metal printing AKA primitive-Star-Trek replicators) has printed a _working_ mouse kidney from mouse-kidney-cells.
So ... now we need a vast supply of the patient's cells of a particular type, lets say Liver since everyone is using that as an example. Take bone-marrow or nasal-lining stem-cells (easy to get) and convert to Liver stem cells (recently reported as done for both types), bathe in Oct4-proteins (no need to change the genetics, just provide whatever Oct4 would code for) and grow several multiples of the amount needed to fill the printer's tanks of each differentiated cell type relevant.
Then print the liver based on a CAD/CAM layout, laying down the same absorbable mesh endostructure as the mouse-kidney used. Also lay down hollow-mesh/plastic areas to become the arteries/veins/etc and let the new liver stabilize for a while in a nutrient/collagen bath. Then transplant.
I read all these comments, amazed how any discussion of stem cells immediately diverges into a mix of name-calling about whether ESCs are life or not, imagining of far-off tissue engineering scenarios involving ESCs, and discussion about whether ESCs qualify for legal protection. Correct me if I'm wrong, but wasn't the original article about Oct4 in adult stem cells?
Why is everyone obsessed with ESCs? There are more therapeutic applications for adult stem cells than ESCs at the moment, mainly because you can't administer ESCs to people. They form teratomas, they're contaminated with mouse antigens, and they're essentially a in vitro culture artifact to begin with.
Oct4 is interesting, but what's the point? The last thing you'd want to do is make adult stem cells more like ESCs. Adult stem cells such as MSCs can already be expanded greatly in vitro, without loss of their differentiation potential. If we find that adult stem cells are restricted to the tissue type they come from(and we may still find that; Making cells express a couple liver genes and actually making liver cells are two different things) and you want to make astrocytes or neurons or something, maybe you'd need to do something like this, but the statement that adult stem cells are difficult to culture in vitro is most certainly not true.