Stem Cells

You have probably heard of stem cells before. From curing deadly diseases to replacing damaged cells, they could become the future of transplant and regenerative medicine. So what exactly are stem cells?

Stem cells are cells with the potential to develop into many different cells in the body. They serve as a repair system for the body, with the ability to divide and renew themselves over a long period of time. They are also unspecialized, meaning they can do specific functions in the body and have the potential to become specialized cells, such as muscle cells, blood cells, and brain cells. In other words, they have the capabilities of self renewal, which means they can divide for much longer periods of time than normal cells, and have the ability to self differentiate into other types of cells depending on the  body’s needs. There are four main types of stem cells: embryonic stem cells, adult stem cells, cancerous stem cells, and induced pluripotent stem cells.

An early embryo contains stem cells that give rise to the developing cells of the tissue of the fetus as well as the support tissue such as the placenta. Embryonic stem cells are pluripotent, meaning they have the ability to differentiate into any type of cell in the body. Stem cells removed from the embryo are called human embryonic stem cells or hESCs. However, in order to extract these cells, you have to destroy the embryo, a method that is politically and ethically controversial.

The second type of stem cells are adult stem cells. These cells, also called somatic stem cells, exist in small numbers in most human tissues, but are not controversial in comparison to the embryonic stem cells because they do not require the destruction of an embryo. Adult stem cells are currently being used in medicine and healthcare and are the standard of stem cell therapy. These stem cells are currently being used for tissue maintenance and wound healing. For example when you get a scab, it is the adult stem cells that are used to restore the layer of skin over the wound. However, there is a key difference between adult and embryonic stem cells that hinder the use of them for more medical purposes. Adult stem cells are multipotent which means that they can differentiate only into certain types of cells, in contrast to pluripotent stem cells. For example, hematopoietic stem cells can differentiate into various types of blood cells, while neural stem cells can only differentiate into neurons. 

Cancer stem cells are malignant stem cells that give rise to tumors. Some cancer stem cells are believed to arise from adult stem cells that acquire mutations and become tumorigenic. Cancer stem cells are a small subpopulation of cells within tumors with capabilities of self renewal, differentiation, and tumorigenicity when transplanted into an animal host. A number of cell surface markers such as cd44, cd24, and cd133 are often used to identify and enrich cancer stem cells. The clinical relevance of cancer stem cells has been strengthened by emerging evidence demonstrating that cancer stem cells are resistant to conventional chemotherapy and radiation therapy and that cancer stem cells are very likely to be the origin of cancer metastasis. Cancer stem cells are believed to be an important target for novel anticancer drug discovery.

Lastly, we have induced pluripotent stem cells, abbreviated as iPSCs. These are created artificially in the lab and have the property of pluripotency. However, unlike embryonic stem cells, iPSCs do not have to be extracted from embryos, meaning they could be the future of stem cell research. These iPSCs are engineered from skin cells called fibroblasts. iPSCs have many unique characteristics. Aside from being pluripotent, they are immortal, which means that the iPSCs grow forever in the lab unlike most other types of stem cells which die after a short period of time. They are also karyotypically normal, which means they have the correct number of chromosomes without any major mutations. Lastly they are personalized, so they can be generated from any person for studying or treating that person's specific diseases. 

Comprehension Questions

1. What are the four types of stem cells?

The four main types of stem cells are embryonic stem cells, adult stem cells, cancer stem cells, and induced pluripotent stem cells.

1. Why are iPSCs so revolutionary, and what characteristics do they exhibit?

iPSCs exhibit pluripotency but in contrast to hESCs they do not need to be harvested from embryos. iPSCs also are immortal, karyotypically normal, and are personalized.

Citations

https://www.mayoclinic.org/tests-procedures/bone-marrow-transplant/in-depth/stem-cells/art-20048117

https://stemcellres.biomedcentral.com/articles/10.1186/s13287-019-1165-5

https://www.stanfordchildrens.org/en/topic/default?id=what-are-stem-cells-160-38

https://www.medicalnewstoday.com/articles/323343

Image Credit:

https://www.lifecell.in/blog/stem-cells/what-are-stem-cells