Stem Cells is a hot topic nowadays. We all have heard some fascinating stories and potential uses of Stem Cells, but what they exactly are, what wonders they can do, and what is the secret behind this superpower? There are several things, most people might not be aware of.
Figure 1: This image shows the Human Embryonic Stem Cells. (Image Credit: http://thedishonscience.stanford.edu/posts/from-bombs-to-blood)
In this article, we will discuss the notion of Stem Cell, what potential it holds in medical treatments and further research and how could it be a game changer. Then we will talk about where does Stem Cell get its power from.
First, I begin by defining stem cells.
What Is A Stem Cell?
Our body is made of more than 200 different cell types e.g. blood cells, heart cells, neurons. These cells are developed from a single type of cell i.e. zygote (a cell made by fusion of sperm and egg). This zygote differentiates further into all kinds of different cell types and makes the whole organism.
Therefore, Stem Cells are the undifferentiated cells which have potential to differentiate into various cell types keeping the self-renewal property (means they differentiate as well as keep the pool of stem cells maintained).
Figure 2: The definition of Stem Cells. (Image Credit: http://stemcellgeneticmed.com)
We can categorize Stem Cells depending (1) on the basis of the source (from where we harvest it from) or (2) on the basis potency (the ability to differentiate). On the basis of source, we have mainly three types of cells; Embryonic Stem Cells (ESCs), Adult Stem Cells (ASCs) and Induced Pluripotent Stem Cells (IPSCs or ISCs). On the other hand, we can categorize stem cells as Totipotent, Pluripotent, Multipotent Stem Cells on the basis of their ability to differentiate.
It is known that the Stem Cells differentiate into various types of specialized cells depending on the mechanical and biochemical cues they get from their environment.
Potential Applications Of Stem Cells In Therapy:
As we learned above that Stem Cell can become any kind of cell, it immediately tells us that it can replace any kind of cell. This gives us endless possibilities for medical uses. The list is exhaustive and I am only giving only a few of the therapeutic uses here.
Stem Cells can be used to replace damaged cells e.g. in case of any kind of skin damage (due to severe burn or wound), the damaged skin cells can be replaced by stem cells and these will differentiate into the skin cells.
The Stem Cells can also be used for organ replacement. As of now, organ from some other person is transplanted to the patient and there are chances that body will reject that organ due to mismatch. Stem Cell gives a way out of this. If we harvest the Stem Cells from the same person and grow a full organ, the transplantation of such organ will not have the complication of rejection as it is from the same body.
Stem Cells are successfully used to restore the vision by replacing damaged retinal cells to the corneal stem cells.
There are many cosmetic uses of the stem cell too e.g. growing teeth, hair regrowth. To name a few more, Stem Cells can be used to treat brain and spinal cord injury, cardiovascular diseases, orthopedic diseases, infertility and a lot more. Possibilities are endless and we are still exploring.
Where Does The Stem Cell Get Its Power From?
Enough about the uses of stem cells. Now we discuss that why stem cell can differentiate into so many different types of specialized stem cells. How can it achieve all the cell fates?
The genome in the Stem Cell state is very loose (figure 2) and pliable. It is in the hyperdynamic state, means that the chromatin is constantly exchanging the histones with the pool of loose histone proteins and a big part of the genome is accessible to the cell. It can express almost any gene it wants, hence can achieve any fate, resulting in various cell types.
On the other hand, the specialized cells have much more compact and condensed genome (figure 3) and not every gene is accessible to the cell, hence cannot be expressed. This is how Stem Cell gets its power. It is the dilute chromatin that is responsible for such an amazing power.
We can tune these differentiated cells into Stem Cells by introducing some reprogramming factors but that will be topic for another day.
Figure 3: Left-hand side shows a stem cell with the open chromatin while the right-hand side figure shows the differentiated cell which has much more concentrated and less accessible chromatin.
Summary:
The Stem Cell's chromatin is much more dilute and almost every gene is accessible while in the differentiated cells, the chromatin is much more condensed. Hence Stem Cell can differentiate into any kind of specialized cell.
In this article, I have left many important points. There is a lot more to cover and probably, I will do that in future articles. Please share your thoughts and feedback in the comment section.
Thanks for reading,
Kamal Tripathi.
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