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'Tis only a flesh wound!



We have all witnessed first-hand the magical power of healing that our skin possesses. Even a deep cut can fix itself up with almost no help from special medical procedures. My favorite personal example involves my fourth toe being half torn from my foot after a freak accident at a friend’s sleepover. Cringe-worthy stories aside, I learned a lot more about the mysterious workings of our largest organ at a talk by Elaine Fuchs during UCLA’s Mautner Lecture Series earlier this year.

Part of what makes skin special is the pool of stem cells that hang out down inside our hair follicles. “Ooooh, stem cells!” you say. I couldn’t agree more! And for good reason: stem cells are powerful. They are different from the other cells in your body in a couple of ways. Most tissues in your body are made up of cells that can essentially clone themselves. These cells undergo mitosis – an exact copy of the genetic material of the cell is made, then it splits itself in half, forming two completely identical cells. This means that a muscle cell can only divide into more muscle cells and a fat cell can only make more fat cells. Stem cells on the other hand, have the power of multipotency. That is, when a stem cell divides it has the capacity to specialize, becoming a cell of any number of tissue types. If stem cells divide to become other types of cells, wouldn’t we run out of stem cells pretty fast? Yes however, the solution to this problem lies in the stem cells’ second power – self-renewal. Some of a stem cell’s progeny are more stem cells. So when a stem cell divides, it can divide into 2 new stem cells or one stem cell and one “fated” cell. The “fated” cell then goes on to become a new fat cell, or a muscle cell. There are lots of factors that govern when a stem cell divides and where the “fated” cells end up – this is where the hair follicle comes in.

Stem cells exist in what are termed “niches”. The niche basically refers to the area where the stem cells hang out and the immediate environment. In this case, the hair follicle acts as a niche for a specific type of stem cell that is found there. The most important thing for us to know is that the “decision” a stem cell makes about dividing is a direct result of changes in the niche environment. Now, when I say changes in the niche environment, I don’t mean global-niche-warming or emissions of greenhouse niche gases. The types of signals that stem cells care about are for example, the presence or lack of a certain protein in the area or the switching-on of a chemical pathway within the cell itself.

Dr. Fuchs describes one of these types of signals in her hair follicle research. The pathway is known as the Wnt-signalling pathway and it is known to play a role in stem cell differentiation in mammals (along with some other important cell responses). When a Wnt-protein bumps into a cell with a special receptor molecule that recognizes Wnt-proteins, a chemical chain reaction starts inside that cell. In the case of stem cells, the message that the chain reaction sends to the cell is “differentiate!” The cool thing about this type of cell-cell communication is that it is directional. In the hair follicle niche, if a Wnt-signal comes from below a stem cell, it will trigger the growth of a new hair. However, if a Wnt-signal comes from above a stem cell, it will know that it needs to focus on repairing a wound to the skin. That just blows my mind.

This is only the tip of the hair follicle iceberg, and if you’re keen to see what else Dr. Fuchs and colleagues have discovered about our largest organ, you should check out a few of the papers listed below. I would also like to acknowledge my grandmother, Dr. Emily F Maverick who made it possible for me to attend Dr. Fuchs’ lecture at UCLA. Thanks!



Sources and further reading:


Fuchs E, Chen T (2013) A matter of life and death: self-renewal in stem cells. EMBO Reports 14: 39-48.

Hsu Y, Pasolli HA, Fuchs E (2011) Dynamics between Stem Cells, Niche, and Progeny in the Hair Follicle. Cell 144: 92-105.

Tumbar T, et al. (2004) Defining the Epithelial Stem Cell Niche in Skin. Science 303: 359-363.
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Comments

  1. Anne MMay 17, 2013 at 6:00 PM

    So, no hair, no healing? Anne M.

    ReplyDelete
  2. UnknownMay 22, 2013 at 9:30 PM

    Or, one may ask, is it the follicle or the hair that counts? Some of us have more hair than others; do some of us have better healing of skin wounds than others? Emily says the stem cells react to signals from "above" the follicle. So maybe it's having enough follicles that is important.

    ReplyDelete

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