One of the things that makes placing stem cells in the exact right spot so critical is that they take clues from their environment about which cells to become. Those can be chemical or physical. This morning I’d like to go over what happens when you remove the stimulus normally provided by gravity. Meaning, you take stem cells into space.
What Are Mesenchymal Stem Cells?
Mesenchymal stem cells (MSCs), or often referred to as “adult stem cells (though they are present in anyone past embryo age), are pluripotent. This means they can differentiate into, or become, many different cell types (e.g., bone cells, muscle cells, tendon cells, cartilage cells, fat cells etc.). MSCs are found in the bone marrow but can also be found in other tissues, such as fat and the umbilical cord (though this would not be a viable source of MSCs for real-world orthopedic treatments as current products manufactured from birth tissues contain no living stem cells).
If you were to take a peek at MSCs under a microscope, the cells are spindle-shaped, with a tapering segment and a fatter segment of the cell housing the nucleus. Using scientific terminology, MSCs are linear and elongated and have a fibroblastic morphology.
Let’s take a look at what happens to stem cells in outer space, in this case bone marrow MSCs that are cultured in outer space.
Without Gravity, Mesenchymal Stem Cells from Bone Marrow Become Fat
The new study investigated the impact of microgravity (little to no gravity) on human mesenchymal stem cells (from bone marrow) in culture. The study was literally set on a satellite orbiting outer space. Researchers accomplished this by mounting the MSC experiments to the satellite before launch. On return to earth, the researchers found that the bone marrow-derived MSCs, after their 12 days in microgravity while traveling through space, had differentiated into fat. In normal gravity conditions, these bone marrow-derived MSCs would typically differentiate, or develop, into bone.
What caused microgravity to have this effect on the bone marrow MSCs? The study reports the answer may lie in the decrease in 10 gene expressions associated with osteogenesis (bone development) and the increase in 4 gene expressions associated with adipogenesis (fat development). Little to no gravity seems to cause the shift in gene expression in the cells to activate fat development.
The Forces on Your Stem Cells Determine What They Will Be
In our bodies, the local microenvironment where stem cells reside helps those stem cells figure out what to be. So for bone, that stems from gravity pushing on the bone. No gravity and the bone marrow-derived stem cells become fat as this study shows. The body is quite efficient!
The take-home lesson here for everyone is that loading your body matters to your stem cells. This same thing happens right here on earth as women age. Between a chemical switch after menopause and less pressure on cells due to inactivity, their bone marrow stem cells switch from making new bone to becoming fat cells. This is one of the causes of osteoporosis.
Other types of forces similarly force stem cells to become different tissues. For example, stretching causes cells to become muscle or tendon. Lower compressive forces push cells toward cartilage, and high loads push cells towards bone.
The upshot? The forces that your stem cells experience determine what they will become. Hence, it’s critical that you load the part that’s healing so that your stem cells will turn into the right type of tissue. In addition, it’s use it or lose it as you age, as the body doesn’t waste resources on making strong tissues when they’re not being used!