One of the big myths going around right now, started by clinics using dead umbilical cord and amniotic tissue, is that you’re too old to have useful stem cells. All of that is, of course, completely false. If you’re alive, your body has huge populations of stem cells helping you stay that way. This morning, we’ll explore one of those that’s actually one of several stem cell fail-safe mechanisms. Let me explain.
Hematopoietic Stem Cells in the Bone Marrow
Our hematopoietic stem cells (HSCs), which live in the bone marrow, are the production center for all of the body’s blood cells (white blood cells, red blood cells, platelets). Quite simply, if we didn’t have HSCs, we wouldn’t have blood. Why? Many of our circulating blood cells are extremely short lived and only last about 120 days. Hence, our HSCs pump out about 2 million new blood cells every second. So our bones aren’t just a support framework for the body, they are also critical living cell production factories.
The blood-cell production process accomplished by our HSCs is known as hematopoiesis, which literally translated means “blood producing.”
Mesenchymal Stem Cells in the Bone Marrow
Mesenchymal stem cells (MSCs) also live primarily in the bone marrow (though they can also be found in many other tissues, such as adipose, or fat, tissue). Our MSCs are multipotent adult stem cells, which means they can differentiate into, or become, other specialized cells in the body. We know that in order for HSCs to survive, you need MSCs around. Now, a new study suggests there may be an even more intimate connection between our HSCs and MSCs…Our MSCs may serve as the protectors, the guardians if you will, of a hidden subpopulation of critical HSCs in our bone marrow. Let me explain.
What Happens When Our Active HSCs Are Destroyed? Seems We Have Reserve HSCs That Take Over
The purpose of the new study was to determine how the bone marrow manages to continue to produce blood cells when the blood-producing hematopoietic stem cells have been depleted, for example, from chemotherapy or radiation therapy. They discovered there are actually two types of HSCs in the bone marrow: primed HSCs and reserve HSCs.
Primed HSCs are the active cells in the bone marrow that are constantly producing new blood cells (e.g., white blood cells, red blood cells, platelets, etc.). In addition to these blood cells, primed HSCs also produce reserve HSCs that hide out under the protection of mesenchymal stem cells (MSCs) in the inner lining of the bone until they are needed. So when chemotherapy or some other catalyst depletes the primed HSCs, the reserve HSCs take over.
Interestingly, the active primed HSCs are sensitive and easily destroyed by chemotherapy, but the study found that the reserve HSCs were resistant to chemo as they are protected and supported by the MSCs in the bone lining. When researchers depleted these supporting MSCs in mice, the resistant HSCs then became sensitive to chemotherapy and did not survive.
What exactly does all of this mean? The protective and chemo-resistant MSCs seem to be the key to having a steady supply of HSCs in backup should the active blood-producing HSCs be destroyed. And when this happens, those protected reserve HSCs then move into production to assure we keeping pumping out new blood cells. Isn’t it fascinating how the human body comes prepared with a second-line backup for such a critical function?
Another Stem Cell Back-up System: MUSE Cells
As I discussed above, your body has multiple stem cell back-up systems. Another cell type that acts this way is called MUSE for MUlti-lineage differentiating Stress Enduring cell. These cells can produce more cell types than MSCs, and as the name implies, they can endure stress. Meaning, under conditions that would normally kill other cells, your MUSE cells survive. They can also detect damage and spontaneously differentiate into the type of stem cells needed in that type of tissue. They also live in the bone marrow as well as in the skin and fat.
The upshot? As you can see, your body is a stem cell machine. Without an active and healthy stem cell population, you wouldn’t be able to produce new blood cells or repair the wear and tear that your body encounters every day. In fact, your body has so many stem cells and these are so critical to life that you have multiple stem cell back-up systems. This is why it’s easy for us to find stem cells in one part of your body and transplant via precise injection to another damaged part in need of repair.