When most people think about stem cells they generally think that there are only two types in existence: embryonic stem cells and adult stem cells
However, the term “embryonic” or “adult” refers more to where the stem cells come from than what they are. In reality, there are many different kinds of stem cells, each with their own set of capabilities and limitations.
Preface
It was plastic surgeons that first noticed fat’s ability to increase vascular activity at an injection site.
Who knew liposuction would prove to be so useful?
Before dermal fillers became all the rage, wrinkles were treated by injecting them with a person’s own fat cells. While the effects were only temporary, plastic surgeons noticed that, even once the wrinkle had returned, the skin at the injection site appeared healthier and had an obvious lack of signs of aging such as discoloration and age spots.
Further investigation revealed that the skin had increased vascular activity wherever the fat was injected!
Up to that point, the primary role of stem cells was thought to be differentiation; that is, it was believed that they worked by differentiating into other cell types and regenerating tissue in the affected areas.
Stem cells are the conductors of regeneration
But we now know is that this is only a small part of a much bigger picture.
What the liposuction process taught us was that mesenchymal stem cells work not only by regeneration but also by releasing specific chemicals that communicate with other cells in the area.
Think of stem cells like conductors in an orchestra: Not only are they able to play an instrument, but they also tell other musicians what to do.
What do stem cells do?
Most of the time, adult stem cells are in a dormant state, pretty much waiting around for something to happen. As cells die off through normal cellular aging they release chemicals that stimulate the dormant stem cells into action. The adult stem cells then direct the surrounding cells to ensure the right type of cell is created and ends up where it needs to be.
In this way, stem cells are not just blank slates that can morph into different cell types; they are also responsible for orchestrating the response of the surrounding tissue.
And you thought fat was just something to whittle away at the gym!
Stem cell therapy basics
In the beginning, there is a sperm and there is an egg.
Once joined, this fertilized egg, now known as a zygote, begins a two-week period of rapid cell division in which each cell doubles by dividing into two cells in a process known as mitosis.
This two-week stage, known as the germinal period of development, is closely followed by the embryonic phase where the newly divided cells begin to differentiate into three distinct (germ) layers:
- endoderm
- mesoderm
- ectoderm
The endoderm layer will eventually form the internal organs including the stomach, pancreas, liver, lungs, and intestines. The ectoderm layer will develop into parts of the central nervous system, the epidermis, hair, and mammary glands.
And the mesoderm layer will develop into skeletal muscle, bones, connective tissue, the heart, and blood (lymph cells).
It is here, in the mesoderm, where the current stem cell story begins.
What’s potency got to do with it?
The potency of a cell specifies its potential to differentiate into different cell types
There are three types of cell potency:
- totipotency
- pluripotency
- multipotency.
The zygote is an example of a totipotent cell.
The problem with these types of stem cells is that they are meant to develop into whole beings and when taken out of this environment they have a tendency to form teratomas, an encapsulated tumor that contains components of all three germ layers.
Pluripotency refers to a stem cell that has the ability to differentiate into any of the three germ layers.
They can develop into any fetal or adult cell type; however, they cannot develop into a fetal or adult animal due to a lack of potential to contribute to extraembryonic tissue such as the placenta.
Multipotent stem cells have the potential to differentiate as well, but only into a limited number of lineages.
For example, a hematopoietic cell is a blood stem cell that can differentiate into several types of blood cells but cannot develop into brain cells or other types of cells.
Mesenchym-Who?
Mesenchymal stem cells, also known as MSCs, are multipotent cells that have the ability to differentiate into a variety of cell types including bone and tendon.
It is these types of stem cells that reside in adipose tissue and that are responsible for all the positive press fat has been getting these days.
A mesenchymal stem cell is just a cell that is derived from the mesoderm.
While these stem cells are capable of differentiation, they can only differentiate into cells that the mesoderm is meant to develop into. They cannot develop into tissue such as nerves or internal organs because these tissues originate from a different embryonic germ layer.
Putting stem cells to work
It is because of their multipotency that adipose-derived stem cells are perfect for treating diseased muscle, bone, and tendons but cannot be used to generate other tissue types.
While scientists have successfully manipulated stem cells to turn multipotent cells into pluripotent cells, this type of stem cell therapy is still in its infancy and studies on the effects of the manipulated cells are underway.
As you can see, stem cells are a varied group of cells that exhibit a wide range of characteristics and therefore have great potential and application in current veterinary medical therapy.
We are just starting out on this stem cell journey and we have so much to learn but one thing is clear: stem cell therapy offers the medical world a unique way to use the body’s own cells to heal itself.
And that’s a wonderful thing.
Do you have a dog or cat that suffers from a musculoskeletal issue? Would you consider stem cell therapy if your veterinarian offered it?
Related articles:
Veterinary Regenerative Medicine: My Interview with Dr. Robert J. Harman, D.V.M., M.P.V.M. – CEO and founder of Vet-Stem, Regenerative Veterinary Medicine
Platelet Therapy for Dogs: Regenerative Veterinary Medicine
Further reading:
What is VetStem Regenerative Medicine?