Stem Cell Basics
Research on stem cells is advancing
knowledge about how an organism develops from a single cell and how healthy
cells replace damaged cells in adult organisms. This promising area of science
is also leading scientists to investigate the possibility of cell-based
therapies to treat disease, which is often referred to as regenerative or
Stem cells are one of the most
fascinating areas of biology today. But like many expanding fields of scientific
inquiry, research on stem cells raises scientific questions as rapidly as it
generates new discoveries.
The NIH developed this primer to help
readers understand the answers to questions such as: What are stem cells? What
different types of stem cells are there and where do they come from? What is the
potential for new medical treatments using stem cells? What research is needed
to make such treatments a reality?
A. What are stem cells and why are
|Stem Cells for the Future
Treatment of Parkinson's Disease
Parkinson's disease (PD) is a very common neurodegenerative disorder that affects more than 2% of the population over 65 years of age. PD is caused by a progressive degeneration and loss of dopamine (DA)-producing neurons, which leads to tremor, rigidity, and hypokinesia (abnormally decreased mobility). It is thought that PD may be the first disease to be amenable to treatment using stem cell transplantation. Factors that support this notion include the knowledge of the specific cell type (DA neurons) needed to relieve the symptoms of the disease. In addition, several laboratories have been successful in developing methods to induce embryonic stem cells to differentiate into cells with many of the functions of DA neurons.
In a recent study, scientists directed mouse embryonic stem cells to differentiate into DA neurons by introducing the gene Nurr1. When transplanted into the brains of a rat model of PD, these stem cell-derived DA neurons
re-enervated the brains of the rat Parkinson model, released dopamine and improved motor function.
Regarding human stem cell therapy, scientists are developing a number of strategies for producing dopamine neurons from human stem cells in the laboratory for transplantation into humans with Parkinson's disease. The successful generation of an unlimited supply of dopamine neurons could make neurotrans plantation widely available for Parkinson's patients at some point in the future.
Stem cells have two important
characteristics that distinguish them from other types of cells. First, they are
unspecialized cells that renew themselves for long periods through cell
division. The second is that under certain physiologic or experimental
conditions, they can be induced to become cells with special functions such as
the beating cells of the heart muscle or the insulin-producing cells of the
Scientists primarily work with two kinds
of stem cells from animals and humans: embryonic stem cells and adult stem
cells, which have different functions and characteristics that will be explained
in this document. Scientists discovered ways to obtain or derive stem cells from
early mouse embryos more than 20 years ago. Many years of detailed study
of the biology of mouse stem cells led to the discovery, in 1998, of how to
isolate stem cells from human embryos and grow the cells in the
laboratory. These are called human embryonic stem cells. The embryos used in
these studies were created for infertility purposes through in vitro
fertilization procedures and when they were no longer needed for that purpose,
they were donated for research with the informed consent of the donor.
Stem cells are important for living
organisms for many reasons. In the 3 to 5 day old embryo, called a blastocyst, a
small group of about 30 cells called the inner cell mass gives rise to the
hundreds of highly specialized cells needed to make up an adult organism. In the
developing fetus, stem cells in developing tissues give rise to the multiple
specialized cell types that make up the heart, lung, skin, and other tissues. In
some adult tissues, such as bone marrow, muscle, and brain, discrete populations
of adult stem cells generate replacements for cells that are lost through normal
wear and tear, injury, or disease.
It has been hypothesized by scientists
that stem cells may, at some point in the future, become the basis for treating
diseases such as Parkinson's disease, diabetes, and heart disease.
Scientists want to study stem
cells in the laboratory so they can learn about their essential
properties and what makes them different from specialized cell types. As
scientists learn more about stem cells, it may become possible to use
the cells not just in cell-based therapies, but also for screening new
drugs and toxins and understanding birth defects. However, as mentioned
above, human embryonic stem cells have only been studied since 1998.
Therefore, in order to develop such treatments scientists are
intensively studying the fundamental properties of stem cells, which
1) determining precisely how stem cells remain unspecialized and self
renewing for many years; and 2) identifying the signals that cause stem
cells to become specialized cells.
B. Scope of this document
This primer on stem cells is
intended for anyone who wishes to learn more about the biological
properties of stem cells, the important questions about stem cells that
are the focus of scientific research, and the potential use of stem
cells in research and in treating disease. The primer includes
information about stem cells derived from the embryo and adult. Much of
the information included here is about stem cells derived from human
tissues, but some studies of animal-derived stem cells are also
Stem cells differ from other
kinds of cells in the body. All stem cells — regardless of their
source — have three general properties: they are capable of dividing
and renewing themselves for long periods; they are unspecialized; and
they can give rise to specialized cell types.
Scientists are trying to understand two
fundamental properties of stem cells that relate to their long-term
self-renewal: 1) why can embryonic stem cells proliferate for a year or
more in the laboratory without differentiating, but most adult stem cells
cannot; and 2) what are the factors in living organisms that normally regulate
stem cell proliferation and self-renewal? Discovering the answers to these
questions may make it possible to understand how cell proliferation is regulated
during normal embryonic development or during the abnormal cell division that
leads to cancer. Importantly, such information would enable scientists to grow
embryonic and adult stem cells more efficiently in the laboratory.
-- From the National Health Institute:
Back to Medical Matters
Disclaimer: The material in this site is provided for personal, non-commercial, educational and informational purposes only and does not constitute a recommendation or endorsement with respect to any company or product. Guiding Light Foundation makes no representations and specifically disclaims all warranties, express, implied or statutory, regarding the accuracy, timeliness, completeness, merchantability or fitness for any particular purpose of any material contained in this site. You should seek the advice of a professional regarding your particular situation.
© 2003, The Guiding Light Foundation