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As printed in Hearing Health, volume 20:4,
Winter 2004
By C. Eduardo Corrales, M.D. and Karen F. Watters,
M.D.
A stem cell is a special kind of cell that has the
unique capacity to replicate or “self-renew”
over a long period of time, often throughout the life
of an organism. Under the right conditions or given
the right signals, stem cells have the potential to
develop into the specialized cells that make up the
tissues and organs of the body, such as heart cells,
nerve cells and even inner ear hair cells.
We commonly hear about two different types of stem
cells – embryonic and adult stem cells. Embryonic
stem cells are derived from a group of cells called
the inner cell mass, which is part of the blastocyst,
a lump of cells that forms four-five days after fertilization
of an egg by a sperm. Once the cells from the inner
cell mass are removed from the blastocyst they can be
cultured in petri dishes into embryonic stem cells (see
figure). Embryonic stem cells are pluripotent, which
means that they can develop into all cell types of the
body, when they are appropriately stimulated. Thus,
embryonic stem cells have the potential to generate
replacement cells for many organs such as the brain,
the heart, the liver, the ear and the pancreas, among
others. They hold the promise of being able to repair
or replace tissues or cells that have been damaged or
destroyed by disease.
Adult stem cells are undifferentiated or unspecialized
cells that are found embedded in specialized tissue.
Adult stem cells are capable of making identical copies
of themselves for the lifetime of the organism. They
can form themselves into specialized cells that match
the tissues from which they originate, thereby regenerating
from within. For example, stem cells taken from bone
marrow can give rise to new blood cells even after they
are transplanted elsewhere. There is evidence that adult
stem cells have even greater potential than this and
that they may be used to generate many more cell types
than just the cells of the organ from which they were
removed. This raises the hope that in the future, for
example, stem cells isolated from a patient’s
bone marrow could be used to repair other organs such
as the heart or the inner ear. Recently, stem cells
have been found in the adult inner ear and it remains
to be seen whether stimulation of such internal stem
cells could be an option to restore hearing in patients.
The potential of stem cell research is enormous. At
a basic level, stem cells can help us further understand
the development and mechanisms of the human body. Beyond
this is the field of drug research and pharmacology,
in which drugs can be applied directly to cells generated
from human stem cells thus eliminating the need for
years of testing before a potentially useful drug can
be introduced on the market.
At a more visionary level, the ability to restore
any type of cell could be the ultimate panacea. Stem
cells may be vital to help us generate cell types or
tissues that have been destroyed by disease or trauma.
By transplanting specialized cells generated from stem
cells we could restore vital body parts and functions.
In the next decades, we expect that stem cells will
be used for treating a large number of diseases, including
chronic heart failure, diabetes, end-stage kidney disease,
liver failure and neurological disorders such as Parkinson’s
disease, multiple sclerosis, hearing and vision loss
and spinal cord injury.
Related Articles:
Stem Cells and Gene
Therapy—Are We Expecting Too Much Too Soon
What Causes
Hearing Loss?
Getting
the Solution to the Problem Area
Gene Therapy
Already a Reality
I Would
Choose Deafness Before a Cure from Embryonic Stem Cells
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