Introduction

Stem cells are unspecialized human cells, able to differentiate – or undergo maturation – and become a variety of specialized cell types, including neurons (nerve cells), hematocytes (blood cells), and myocytes (muscle cells) [1]. Unlike regular somatic cells in the body, stem cells undergo mitotic division an unlimited number of times.

The term “stem cell” was first coined in the late 19th century by German biologist Ernst Haeckel and American epidemiologist William Thompson Sedgwick [1]. However, it was not until the mid-1990s that stem cell research seriously took flight and the self-renewing properties and behaviour of stem cells were uncovered. Ernest McCulloch and James Till incited the stem cell revolution with their 1960s research at the University of Toronto, where they found that specific cells in the bone marrow of mice had the ability to generate new colonies of the same type once transplanted into other mice [2]. Drawing on the work of Drs. McCulloch and Till, other scientists and clinicians went on to isolate stem cells (1981), perform innovative bone marrow transplants (1957, 1968), and discover a link between stem cells and human diseases such as cancer (1997) [1]. Today, stem cell research remains a vast field of cell biology, heralding the arrival of a new era of personalized medicine.

Types of Stem Cells

Stem cells are categorized as either embryonic stem cells (ESCs) or adult stem cells (ASCs) [3]. Embryonic stem cells (ESCs) are derived from the inner cell mass of an embryo that has undergone an in vitro fertilization procedure (IVF) [4]. Before implantation and about 3-5 days after fertilization, the blastocyst (embryo at this stage) has an inner cell mass that has the ability to give rise to all the specialized tissues in the human body. [5] When used for research purposes, the inner cell mass is extracted and grown in specific laboratory conditions, where they retain their properties of being ESCs. Adding on, ESCs are pluripotent, meaning they can turn into almost any type of cell in the body or divide into more stem cells [6].

Stem Cell Properties

Stem cells are characterized by their ability to divide indefinitely and differentiate into different adult cell types [3]. 

Differentiation of stem cells relies heavily on the presence of growth factors from surrounding cells, epigenetic changes to the cells’ own genome, cytokine activity, and transcription factors that promote the expression of some genes but inhibit the expression of others [4]. Epigenetic changes include the silencing of pluripotent genes, which limits the cell’s differentiation ability [5].

The ability of stem cells to divide indefinitely is partly due to the fact that stem cells express the enzyme telomerase [6]. Telomeres are non-coding, repetitive sequences of DNA located at the ends of chromosomes. The purpose of telomeres is to protect the genetic content of chromosomes from being damaged each time the cell divides [6]. A typical eukaryotic cell (e.g. somatic cell) that doesn’t express telomerase will experience a shortening of telomeres each time it divides [6]. Since telomeres are not regenerated in these cells, they become shorter and shorter with each cell division until the telomeres reach a critically low length, and the cell will no longer divide [6]. In stem cells, telomeres are regenerated with each cell division because they express telomerase, which allows them to divide indefinitely [6].

Stem Cell Differentiation

Multicellular organisms have different types of specialized cells (e.g. skin cells, stomach cells, muscle cells, etc.) that originate from undifferentiated stem cells. Stem cells are undifferentiated cells that are capable of continually dividing and becoming specialized. A stem cell potency refers to the number of differentiated cell types that a stem cell can give rise to; this potency diminishes with time [7]. 

There are several types of stem cells, each with its own differentiation abilities. A totipotent stem cell, for example, can divide and differentiate into any type of cell [6]. Zygote cells in animals are examples of totipotent stem cells. Pluripotent stem cells can differentiate into almost any type of cell. Early embryos contain pluripotent stem cells. Compared to previous stem cells, multipotent stem cells have a lower differentiation potential and fewer differentiation options. Multipotent stem cells can be found in the adult bone marrow. Additionally, we have unipotent/bipotent stem cells with only one or two options for differentiation. Therapeutic stem cells can be used to repair damaged organs, but this approach comes with many ethical implications.

Applications of Stem Cells

There are numerous applications of stem cells, including:

Tissue regeneration

 This is one of the most important and common applications of stem cells. It includes growing new cells in order to replace damaged organs or tissues. For example, using existing skin stem cells to make new skin tissue [8].       

Stem cell therapy for curing diseases

Cardiovascular and vascular diseases can be treated with the help of stem cells [9]. Other diseases like diabetes can also be treated by stem cell therapies [10]. Many other brain diseases, genetic defects, and blood diseases can be cured with stem cells [9]. 

Drug development

Stem cells are extensively used in testing and developing new drugs. For this purpose special types of stem cells are used: induced pluripotent stem cells. These are a type of pluripotent stem cells which are derived from adult somatic cells and pluripotency is induced in them [8,11].

Main Takeaways – Dr. YuFei Chen (Ph.D.) 

YouthConnect led a webinar with Dr. Chen to have an opportunity to learn about the cutting edge stem cell research that he and his research team are conducting.  Key things to know about stem cells are that they are the body’s raw materials and possess specific characteristics which differentiate them from other cells. For instance, they have to be able to adhere to plastic surfaces, be able to express certain surface antigen markers, and have to show multipotent differentiation potential. The experiment in his research lab was conducted using animals and there was evidence of wound closure due to the regeneration assisted by the BD-MSCs(burn-derived mesenchymal stromal/stem cells). In his lab, they observed the wound closure and saw the level of epidermis restoration and fibrosis of the local tissue to indicate whether regenerative skin is effective. His research gave an efficient finding that MSCs that are isolated from the burned skin have efficient regeneration for the skin. The low dose of MSCs also demonstrated much better skin regeneration.  

References

1. Stem Cells History [Internet]. Boston Children’s Hospital. Available from: http://stemcell.childrenshospital.org/about-stem-cells/history/
2. Sharkis SJ. Canadian stem cell scientists take the prize. Cell. 2005Sep23;122(6):817–9. 
3. Types of stem cell: Stem Cells: University of Nebraska Medical Center [Internet]. UNMC. 2022. Available from: https://www.unmc.edu/stemcells/educational-resources/types.html 
4. Answers to your questions about Stem Cell Research [Internet]. Mayo Clinic. Mayo Foundation for Medical Education and Research; 2022. Available from: https://www.mayoclinic.org/tests-procedures/bone-marrow-transplant/in-depth/stem-cells/art-20048117  
5. Stem Cells: Sources, types, and uses [Internet]. Medical News Today. MediLexicon International; 2022. Available from: https://www.medicalnewstoday.com/articles/323343#sources
6. Default – Stanford Children’s health [Internet]. Stanford Children’s Health – Lucile Packard Children’s Hospital Stanford. 2022. Available from: https://www.stanfordchildrens.org/en/topic/default?id=what-are-stem-cells-160-38  
7. Cell potency: Totipotent vs pluripotent vs Multipotent Stem Cells [Internet]. Cell Science from Technology Networks. [cited 2022 Feb23]. Available from: https://www.technologynetworks.com/cell-science/articles/cell-potency-totipotent-vs-pluripotent-vs-multipotent-stem-cells-303218 
8. What are stem cells, and what do they do? [Internet]. Medical News Today. [cited 2022April2]. Available from:                                                              https://www.medicalnewstoday.com/articles/323343
9. Cardiopoietic stem cell therapy in ischaemic heart failure: long-term clinical outcomes [Internet]. Willey Online Library. [cited 2022April2]. Available from: https://onlinelibrary.wiley.com/doi/full/10.1002/ehf2.13031
10. Generation of stem cell-derived β-cells from patients with type 1 diabetes [Internet]. National Library of Medicine. [cited 2022April2]. Available from: https://pubmed.ncbi.nlm.nih.gov/27163171/
11. Induced Pluripotent Stem Cells and Their Potential for Basic and Clinical Sciences [Internet]. Natural Library of Medicine. [cited 2022April2].Available from:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3584308/#:~:text=Abstract,ES)%20cells%20in%20many%20aspects.