Adult Stem Cells: Potent Stuff!
Why all this fuss over embryonic stem cells when we have perfectly good adult stem cells in our bodies?
I think that’s a great question. Many researchers asked the same one. The short answer is “potency.” Potency in stem cell terms refers to the ability of a specific stem cell to make different mature cell types. The going theory (and I really haven’t seen much in the literature to change my mind) is that the older a person is, the less potent their stem cells are. Here’s a quick breakdown of stem cell potency, from super potent to “not-so-much”:
1- Totipotency: This refers to the very earliest embryo, where all the cells have the ability to make not only all the cells in the body, but also the cells of important things like placental tissue.
2- Pluripotency: This is what ES cells are: Pluripotent. That means they have lost the ability to make extraembryonic tissue, but still have the ability to make all the cells in the adult body.
3- Multipotency: This is what the lion’s share of our adult stem cells are: Multipotent. This is a more restricted type of stem cells and they reside in stem cell niches all over the body. Examples include the brain, bone marrow, intestines, muscles, and liver. These stem cells can be considered committed to certain lineages: The stem cells in your brain will make more brain cells, the stem cell in your bone marrow will make more blood cells, etc…..
4- Unipotency: This is the runt of the potency litter. This is the true committed progenitor cell. It will only make one specific cell. For example, a stem cell in your brain can make, say, a neuron or an astrocyte, 2 very different types of brain cells. However, once that stem cell makes a decision either way, it commits to that cell type to become the committed progenitor (insert jokes here about how all committed progenitors must not be male, blah blah…..). It may still be able to divide, but it will only make of those two cells types.
OK back to the original question. In my opinion (and really, it is just that: my opinion), multipotent stem cells are absolutely perfect for the organs in which they are intended to help. In other words, if I have leukemia, I want hematopoietic stem cells to repopulate my bone marrow after radiation therapy. If I have some god-awful surgery to take out portions of my colon, I want intestinal stem cells to do their work and repopulate the intestinal lining. You get the idea. So here’s where adult stem cells lose their luster in the “what’s sexy now in the clinic” arena. A hematopoietic stem cell, which is a stem cell that makes all your blood cells so we don’t run out of blood over our long lives, does not have the ability to make more intestinal lining. Nor does it have the ability to help the Alzheimer’s patient repopulate lost brain tissue. ES cells, on the other hand, have the ability to make all those cell types. They can also make pancreatic tissue for diabetics, so they can stop jabbing themselves with needles. They can make cells of the retina to help those of us with awful eyesight see better into our Golden Years. Though personally, I may want to see the world in a hazy state. Why be able to see my receding hairline, wrinkles, varicose veins and liver spots? Best to simply deny they’re even there, right? It’s working for me, so far.
And there we have a stem cell tutorial. We can all enjoy summer now that class is over, I’ve stepped off my soapbox, and am already on the hunt for next month’s topics. I’m thinking “Scientists: The existence of very real names of genes that suggest they ought to get out more often.”
Until then, enjoy the weather, wear your sunscreen, and please, don’t make the cell culture hood your only means of enjoying UV light!