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Senior Citizen Health & Medicine
Discovery Could Lead to Treatment of Age-Related
Macular Degeneration
Bone Marrow may restore eye cell damage that
causes AMD
June 9, 2006 - University of Florida scientists
conducting experiments with mice have found evidence that the body
naturally replenishes small amounts of cells in the eye essential for
healthy vision. The finding may shatter the belief that a cell
layer vital for eyesight called the retinal pigment epithelium, or RPE,
is a nonrenewable resource. It is damaged RPE that causes age-related
macular degeneration (AMD), the leading cause of blindness in senior citizens.
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RPE plays a vital role in our visual health by
forming the outer barrier of the retina and supporting the function of
cells that receive light. Damage to RPE is present in many diseases of
the retina, including AMD, which affects
more than 1.75 million people in the United States.
With evidence that the body does indeed regenerate
these cells in small amounts, scientists can focus on ways to accelerate
natural healing processes to treat sight-robbing injuries or diseases.
"What this tells us is for problems such as
age-related macular degeneration, we should be able to harvest stem
cells to help repair the damage," said senior author Edward Scott,
Ph.D., a professor of molecular genetics at the UF Shands Cancer Center
and director of the Program in Stem Cell Biology and Regenerative
Medicine at UF's College of Medicine.
"The question is whether we can do it in a
patient," he added.
Scientists widely believe that RPE is a finite
resource. The same belief used to be held about brain cells - people who
suffered from trauma, stroke or disease formerly faced no hope of
growing new cells to replace dead ones.
Then, in the late 1990s, when scientists began to
report findings of brain cell growth in humans and monkeys later in
life, focus turned toward understanding the mechanisms to regenerate
cells in the brain.
Now, UF researchers believe it may be possible to
also grow new cells in the retina to replace cells lost to injury or
disease.
"In people, retinal pigment epithelium can become
damaged with age," said Jeffrey Harris, a graduate student in the
department of molecular cell biology in UF's College of Medicine and
first author of the paper.
"Factors like smoking and diet also come into play.
The problem is without these cells, the rods and cones - our primary
cells for vision - die. If we can regenerate the retinal pigment
epithelium, it could make a big difference in our visual health."
Scientists were able to detect that RPE cells
indeed appear to be naturally replenished in the test animals by
transplanting bone marrow cells from normal male mice into albino
females with two different types of acute RPE injury.
Bone marrow contains stem cells, which have the
extraordinary abilities to home in on injuries and possibly regenerate
other cell types in the body. In this case, the cells were transplanted
to confirm that bone marrow does regenerate the injured RPE. It was
easier to track male, pigment-producing cells in female, albino
recipients, Harris said.
Chemical and microscopic analysis showed the cells
that traveled to the injury site and transformed into RPE indeed had
male genetic characteristics. Furthermore, these cells were capable of
producing pigment - a colorful indication that the RPE could only have
arisen from the donor bone marrow stem cells.
"We did not use a direct model of age-related
macular degeneration," Scott said. "But we now know that when RPE is
injured, it can be replaced in certain situations. It gives us growth
factors, cell pathways and other different places to look at to find
reasons why the disease is occurring."
Researchers want to discover ways to mobilize an
elderly patient's own cells to travel to the injury site to make
repairs.
"The dogma has been that we're born with a fixed
amount of RPE, but there is growing evidence retinal progenitor cells
exist in the adult," said Lawrence Rizzolo, Ph.D., a Yale University
associate professor of anatomy and experimental surgery and of
ophthalmology and visual science who was not involved in the research.
"To derive cells of neuronal lineage from cells of
bone-marrow lineage is significant, if the finding stands up to the test
of time. Compared to RPE transplantation, there are a lot of advantages
if someone's own bone marrow could supply the cells, because it's a
ready source and the cells would not be rejected by the patient.
Further, if bone-marrow progenitors circulating in the blood could be
attracted to sites of disease, surgery could be avoided," Rizzolo said.
The research appears in Investigative Ophthalmology
& Visual Science.
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