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Scientists discover unique source of postnatal stem cells
April 22, 2003
Scientists report for the first time that "baby" teeth, the
temporary teeth that children begin losing around their
sixth birthday, contain a rich supply of stem cells in
their dental pulp. The researchers say this unexpected
discovery could have important implications because the
stem cells remain alive inside the tooth for a short time
after it falls out of a child's mouth, suggesting the cells
could be readily harvested for research.
According to the scientists, who published their findings
online today in the Proceedings of the National Academy of
Sciences, the stem cells are unique compared to many
"adult" stem cells in the body. They are long lived, grow
rapidly in culture, and, with careful prompting in the
laboratory, have the potential to induce the formation of
specialized dentin, bone, and neuronal cells. If followup
studies extend these initial findings, the scientists
speculate they may have identified an important and easily
accessible source of stem cells that possibly could be
manipulated to repair damaged teeth, induce the
regeneration of bone, and treat neural injury or disease.
"Doctors have successfully harvested stem cells from
umbilical cord blood for years," said Dr. Songtao Shi, a
scientist at NIH's National Institute of Dental and
Craniofacial Research (NIDCR) and the senior author on the
paper. "Our finding is similar in some ways, in that the
stem cells in the tooth are likely latent remnants of an
early developmental process."
Shi and colleagues named the cells SHED, which stands for
Stem cells from Human Exfoliated Deciduous teeth. The term
"deciduous teeth" is the formal name for what most people
call colloquially "baby teeth." Children normally develop a
set of 20 deciduous teeth, which appear after six months of
life and generally are replaced, one tooth at a time,
between age 6 and 12.
Shi said the unique acronym was needed to differentiate
SHED from stem cells in adult tissues, such as bone or
brain. "Stem cell research has exploded during the past
seven or eight years, yet people still talk in general
terms of postnatal and adult stem cells as though they are
one and the same. Postnatal cells from children may act
totally differently than adult stem cells, and we felt the
inherent difference needed to be emphasized," said Shi.
Today's finding, as so often happens in science, stems from
a chance interaction. As Shi recounts, it happened one
evening when his then-six-year-old daughter, Julia, asked
for help in pulling out a loose baby tooth. "Once it was
out, we sat and looked carefully at the tooth," recalled
Shi, a pediatric dentist. "I said, 'Wait a minute, there is
some red colored tissue inside of the tooth,' so I took the
tooth to my laboratory the next day and examined it. Sure
enough, it had beautiful pulp tissue left over."
A few days later, when another of Julia's teeth came out,
Shi said he was better prepared. He placed the tooth into a
liquid medium used to culture cells, drove it to the
laboratory, and extracted the dental pulp. Soon thereafter,
he succeeded in isolating living stem cells from the
tissue, a discovery that would lead to the collection of
more exfoliated teeth from Julia and other children.
The group launched an initial round of studies to determine
whether the cells would grow well in culture. Using dental
pulp extracted from the children's exfoliated incisors,
they discovered that about 12 to 20 stem cells from each
tooth reproducibly had the ability to colonize and grow in
culture.
"We also found the SHED behaved much differently than
dental pulp stem cells from permanent teeth, which our
group studied previously," said Dr. Masako Miura, an NIDCR
scientist and a lead author on the study. "They exhibited
an ability to grow much faster and doubled their
populations in culture at a greater rate, suggesting SHED
may be in a more immature state than adult stem cells."
Interestingly, Muria said she and her colleagues soon found
these cells could be prompted to express proteins on their
surface indicative of stem cells that were in the process
of switching into bone and dental pulp cells. This
discovery led to additional followup experiments, led by
Dr. Bai Lu of NIH's National Institute of Child Health and
Human Development (NICHD), to determine whether SHED also
possessed the potential to switch into neural and fat
cells. The groups found, under specific cell culture
conditions, the cells responded accordingly, expressing a
variety of proteins indicative of neural and fat cells.
"These data are just the start," said Shi. "We're trying to
characterize more fully which cell types can be generated
from these stem cells. Can they be switched into nerve
cells only? We need to find this out. We're also interested
in determining the difference between adult dental pulp s-
tem cells and those in deciduous teeth."
The NIDCR and NICHD are research components of the federal
National Institutes of Health (NIH), part of the U.S.
Department of Health and Human Services.
National Institutes of Health
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