Stem Cells for Dummies

Transcription

1 Stem Cells for Dummies Moira Wood Professor Johnson Immunology 31 October 2011

2 Dear Reader: One of the most wonderful things about St Olaf is that as a student, you know people in almost every major, from physics to philosophy. We attempt to gain a breadth of knowledge through our extensive general education requirements, but with just one lab science required, some of our humanities majors still come up short in the sciences. I fully acknowledge that stem cells are a tricky and sticky topic, not only scientifically confusing, but medically complicated, and ethically convoluted. It is for St Olaf s intelligent study body that I am writing this paper, in the humble attempt to educate my peers on Stem Cells, and in the vein that maybe someone will explain quantum mechanics to me Yours truly, Moira Wood 13 Stem Cells is a title that everyone seems to recognize, but that very few seem to understand. As stigmatized through media and political propaganda, opinions on stem cells, their use, and research, tend to run hot, so it is my ambition to give unbiased insight into the science of stem cells and their medical application. Stem cells are exceptional because they are able to self-regenerate and differentiate. Selfregeneration gives stem cells a nearly infinite life span, and can divide repeatedly to produce numerous, identical stem cells. With their ability to differentiate, these self-renewing stem cells can also specialize in to all diverse forms of tissues, that are organ specific tissues with special 2

3 functions, such as muscle, blood, bone, nerve, and all other tissues found in the body. It is through these two defining characteristics that it becomes obvious why stem cells are so critical in medicinal therapies and treatment, known as regenerative medicine. Stem cells have an intrinsic hierarchy, due to the fact that as they differentiate they reduce their ability to develop into any tissue, and their cell-path becomes more restricted. Totipotent stem cells are the head of the lineage as they are able to differentiate into an entire organism, seen in the fusion of an egg and sperm, which forms a zygote with infinite cellular possibilities. After the first few cellular divisions, the zygote differentiates into a pluripotent blastocyst, which can give rise to almost all cells in the body, although they are unable to form an entire organism or yield a placenta. Pluripotent, or embryonic, stem cells can then differentiate into multipotent stem cells, also known as adult or somatic stem cells, which have the ability to give rise to a limited number of cell types, usually within a specific family of cells, as seen in hematopoietic stem cells, which differentiate into all the types of blood cells. Oligopotent stem cells, also described as progenitor cells, can give rise to just a select few cells lines and are most commonly seen in the The image displayed to the above gives a visual representation of the line of differentiation for stem cells. am.png 3

4 lymphoid and myeloid system. Finally, unipotent stem cells are not capable of any further differentiation and can only self-regenerate, critical in the repair of damaged tissue. It is embryonic stem cells that are so coveted due to their primitive nature, that have also, unrightfully received such strong opposition. People often think that those who support embryonic stem cell research also support killing babies, and that is just not the case. Most often in today s research, pluripotent stem cell lines are derived from mouse models. And even so, any scientists who desired to culture human embryonic stem cells would obtain them by consenting patients using in vitro fertilization to donate their abundant, unused zygotes that would have otherwise have been medical waste. To avoid any and all opposition, a most research has moved toward using induced pluripotent stem cells, or ipsc s, instead of embryonic stem cells. ipsc s are artificially derived from multipotent adult stem cells by forcing certain gene expression. This allows for the uses of The Image displayed above is the differentiation of an adult hematopoietic stem cell. 4

5 a cell without the stigmatized association with embryonic, and with all of the advantages of potency and differentiability. IPSC s have some not-yet-fully identified or understood limitations that are not present in authentic pluriopotent stem cells, but they also have the possible therapeutic advantage of deriving a patients ipsc s from their own somatic tissue and therefore avoiding possible immunogenic complications from the treatment, such as the patient rejecting the transplant tissue. Adult stem cells are also much less controversial as they can be found in mature adult tissues, such as bone, skeletal muscle, liver, and many other sources throughout the body. While they are slightly less desirable than pluripotent stem cells due to the multipotency, but they remain quiescent, that is non-dividing, until they are activated to divide and multiply by disease or injury. Bone marrow transplants are an example of adult stem cell therapy, and are currently the only stem cell treatment in use in today s medicine. With this single type of hematopoietic stem cells transplant, you are able to restore a faulty hematopoietic system, or replace a defective system by providing a functional one. The promise and possibilities of these and all other types of stem cells treatments are literally limitless. The demand for tissue and organ transplant is always high, and with stem cells, you could force genetic expression to yield the desired tissue type for implantation. With their ability to differentiate into a variety of tissues, they could be used in the brain to treat damage from stroke, or cure Alzheimer s and Parkinson s. Or yield healthy insulin producing cells for diabetes patients. They could repair damaged muscle, such as the heart, or amend spinal cord injuries; the list goes on. Their ability to self renew, allows stem cells to not just be temporary treatment for alleviation of symptoms, but an actual cure as they could be introduced into the body and remain there producing healthy tissue. This idea is held in 5

6 gene therapy, where the patient replace a defective gene that is causing a specific disorder, with a functional one by reinjecting the now engineered functional stem cells into the donor, inducing a self renewing cure for an originally untreatable disease. It is not to say that stem call therapy is the cure for all of medical issues, as the use of stem cells involves it s own unique set of complications. With a transplant of any kind, there is the fear that the patient s immune system will see the transplanted tissue as a threat and attack it. Suppressing the patient s immune system before therapy reduces this threat, but the immunosuppressive drugs also can have harmful side effects. The greatest chance of a successful transplant is with a genetically identical donor, but often those are difficult to find. That is why using somatic stem cells from your own tissue, as is done to derive ipsc s, holds so much promise for stem cells transplantation as the cells would be completely identical as they would actually be your own. Even with these hurdles, the continuous research proves that stem cells are an excellent therapy and could lead to incredible gains in medicine. Due to stem cells unique capabilities of self-regeneration and differentiation, they have proven to be fascinating components of the human body, but even more significantly, critical tools to curing some of the world s most devastating diseases. 6