Biology of Stem Cells

 There are many different types of cells in the human body, 220 to be more accurate. All of them have a specific function, but there is one exception – stem cells. Stem cells are unique cells because they are undifferentiated and can reproduce indefinitely as long as an organism is alive. That’s why they have many uses in the human body, and lots of scientific research is being done on stem cells, hoping to use them in various treatments.

The first unique point of the stem cells is that they can divide indefinitely as long as an organism is alive. They can do so even after long periods of inactivity, in places like heart muscles, where they are used only in certain events and can divide only at a certain condition. In places like bone marrow, they are used to replace old cells, so they divide constantly. The second unique point is that they are unspecialised, so they don’t have any specific organelles or structures for a specific tissue cell until they differentiate. Last but not least, they can become tissue-specific cells. This means, that whenever the body needs to replace cells in certain tissues, they can be used. Gut tissue is an example. However, there are several types of stem cells, each one having a different potential to become specialised cells.

Stem cells are broken down into the types by their potency to differentiate into specialised cells, and these are: totipotent, pluripotent, multipotent, oligopotent, unipotent. Totipotent cells can differentiate into any type of specific cells, and usually found in zygote. Pluripotent cells can differentiate into almost any type of specific cells, and usually found in the embryo. Multipotent cells can differentiate only into a small number of specialised cells related to their place. Oligopotent cells can differentiate only in a few specialised cells. Unipotent cells can differentiate into cells of only one kind, which is their own. Interesting fact: embryotic stem cells are pluripotent because they can’t differentiate into the placenta cells, whereas totipotent ones can. However, to perform experiments on stem cells, they need to be extracted from somewhere, and not all types of stem cells are eligible to be used in experiments. 

There are two varieties of stem cells that are used in research: human embryotic and human adult stem cells. Embryotic stem cells are taken from embryos that have been fertilised in vitro, from donated eggs. After derivation from the embryo, they are placed into the dish that has culture medium which allows stem cells to reproduce. There is a feeder layer of mouse embryotic stem cells, that are kept from dividing using special conditions, serving as nutrients for human embryotic stem cells to reproduce. But cells derived from embryo don’t always survive, but if they do and multiply to form a crowd in a dish plate, some of them will be taken to the other dishes where they will continue to multiply, and eventually, embryotic stem line will be established. After that, some dishes can be frozen and sent to other institutions to perform experiments or continue multiplication. The process of subculturing stem cells is done for a long period of time, ensuring that cells are capable of long-term self-renewal, as well as many checks are made, including watching chromosomes under microscope and test to reassure the presence of special cell surface cover. The method is slow and inefficient, because not all of the cells survive after being derived from the embryo, and it takes a long time to establish a reliable embryotic stem cell line. But what about an adult stem cell? 

Adult stem cells are more specific than embryotic stem cells, but they have their uses as well. These stem cells are found in organs like: blood vessels, brain, skin, teeth, etc., and they are thought to be crowded in specialised niche. However, there are a few stem cells in each organ, and after extraction, their capacity to reproduce is limited, so culturing them in large quantities can be very difficult. The problem with adult cells is that they need to be proved to be the right kind of cells, and that’s done by allowing them to differentiate and see which tissue cells they will differentiate too. The other problem with adult stem cells is that they are hard to find in human body because they can stay inactive for a long period of time, until the body needs them. So, there are some similar problems to embryotic stem cells, with long periods of time taken to grown stem cells, and some of the cells dying shortly after being derived.

As well as that, there are other types of stem cells worth noting. Mesenchymal stem cells, come from connective tissue surrounding organs in the body, and were used to grow organ tissues, and have a potential of being used in various treatments. Induced pluripotent stem cells behave similarly to embryotic stem cells and have similar ways of extraction to them. Generally, they are easier to get and easier to establish a stem cell line, so there are lots of potential uses, but more investigation needs to be accomplished. So, after looking at ways of harvesting stem cells, a question can be asked – what are the uses? 

Stem cells are undifferentiated as mentioned above, and can become any type of specialised cell, including red blood cells. Leukaemia is a disease where bone marrow produces excessive number of abnormal leukocytes, causing a flaw in production of normal blood cells, which can result anaemia and other blood-related syndromes. This condition, however, can be treated with stem cells. The treatment is done using stem cells transplant, which is done via giving them to a recipient intravenously, which takes about an hour. After that, stem cells travel to the bone marrow and start to differentiate into the normal red blood cells. This process is called engraftment. But, before receiving a transplant, as much leukaemia cells as possible need to be destroyed. This can be accomplished by chemotherapy or radiation therapy. Another case where stem cells can be used is Stargardt’s disease. This is an inherited disease, affecting one in 9000 people. The light-sensitive layer in muscular region degenerates, causing detailed vision loss. This disease usually starts to develop before the age of 20. To treat Stargardt’s disease, limbal stem cells are taken from the patient’s eye and artificially reproduced in the lab and after that put back into the patient’s eye to restore the sight. However, to have a successful transplantation, limbal stem cells in patients eye need to be undamaged.

However, with all those possibilities for treating various diseases, stem cells are a big ethical dilemma, and for quite a long time. The problem is, some people consider blastula, which is a hundred molecules bolus that is going to be implanted into the wall of uterus, a human being, whereas other people don’t consider it as a human being. Blastula is used as the main source of embryotic stem cells, and it is usually artificially grown in the petri dish, and after stem cells are taken out it is usually killed. This what causes the concern of ‘pro-life’ members, who think that it is a human being. Scientist, who perform the research, usually disagree with statement that blastula is a human being, as well as many other people, who don’t consider an embryo a human until it is born. Also, some people hold middle ground, saying that only certain types of research should proceed, and only if there is a good scientific justification.

To conclude, stem cells are the unique tool for understanding human nature better and perfecting our ways of treating various diseases. However, we are far from fully understanding the nature of stem cells and the ways of using them, so more research and experiments are to be done in order to succeed in those areas.

Bibliography

Bethesda. (n.d.). Stem Cell Basics. Retrieved 11 1, 2018, from Stem Cell Information: http://stemcells.nih.gov/info/basics/pages/basics1.aspx

Lo, B., & Parham, L. (2009). Ethical Issues in Stem Cell Research. Endocrine Reviews, 30(3), 204-213. Retrieved 11 1, 2018, from https://ncbi.nlm.nih.gov/pmc/articles/pmc2726839

“Eurostemcell.” Edited by Jan Barfoot, Stem Cell Therapy & Treatment – Diseases and Conditions, 17 Nov. 2016, www.eurostemcell.org/what-diseases-and-conditions-can-be-treated-stem-cells.

Lo, Bernard, and Lindsay Parham. “Ethical Issues in Stem Cell Research.” Endocrine Reviews, The Endocrine Society, May 2009, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2726839/.

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