Women's Breast Tissue Ages Faster Than Rest of Body
Everyone grows older, but scientists
don't really understand why. Now a UCLA study has uncovered a biological clock
embedded in our genomes that may shed light on why our bodies age and how we
can slow the process. Published in the Oct. 21 edition of Genome
Biology, the findings could offer valuable insights into cancer and stem
cell research.
While earlier clocks have been linked
to saliva, hormones and telomeres, the new research is the first to identify an
internal timepiece able to accurately gauge the age of diverse human organs,
tissues and cell types. Unexpectedly, the clock also found that some parts of
the anatomy, like a woman's breast tissue, age faster than the rest of the
body.
To create the clock, Horvath focused
on methylation, a naturally occurring process that chemically alters DNA.
Horvath sifted through 121 sets of data collected previously by researchers who
had studied methylation in both healthy and cancerous human tissue.
Gleaning information from nearly
8,000 samples of 51 types of tissue and cells taken from throughout the body,
Horvath charted how age affects DNA methylation levels from pre-birth through
101 years. To create the clock, he zeroed in on 353 markers that change with
age and are present throughout the body.
Horvath tested the clock's
effectiveness by comparing a tissue's biological age to its chronological age.
When the clock repeatedly proved accurate, he was thrilled -- and a little
stunned.
"It's surprising that one could
develop a clock that reliably keeps time across the human anatomy," he
admitted. "My approach really compared apples and oranges, or in this
case, very different parts of the body: the brain, heart, lungs, liver, kidney
and cartilage."
While most samples' biological ages
matched their chronological ages, others diverged significantly. For example,
Horvath discovered that a woman's breast tissue ages faster than the rest of
her body.
"Healthy breast tissue is about
two to three years older than the rest of a woman's body," said Horvath.
"If a woman has breast cancer, the healthy tissue next to the tumor is an
average of 12 years older than the rest of her body."
The results may explain why breast
cancer is the most common cancer in women. Given that the clock ranked tumor
tissue an average of 36 years older than healthy tissue, it could also explain
why age is a major risk factor for many cancers in both genders.
Horvath next looked at pluripotent
stem cells, adult cells that have been reprogrammed to an embryonic stem
cell-like state, enabling them to form any type of cell in the body and
continue dividing indefinitely.
"My research shows that all
stem cells are newborns," he said. "More importantly, the process of
transforming a person's cells into pluripotent stem cells resets the cells'
clock to zero."
In principle, the discovery proves
that scientists can rewind the body's biological clock and restore it to zero.
"The big question is whether
the biological clock controls a process that leads to aging," Horvath
said. "If so, the clock will become an important biomarker for studying
new therapeutic approaches to keeping us young."
Finally, Horvath discovered that the
clock's rate speeds up or slows down depending on a person's age.
"The clock's ticking rate isn't
constant," he explained. "It ticks much faster when we're born and
growing from children into teenagers, then slows to a constant rate when we
reach 20."
In an unexpected finding, the cells
of children with progeria, a genetic disorder that causes premature aging,
appeared normal and reflected their true chronological age.
UCLA has filed a provisional patent
on Horvath's clock. His next studies will examine whether stopping the body's
aging clock halts the aging process--or increases cancer risk. He'll also
explore whether a similar clock exists in mice.
Story Source:
The above story is based on materials provided byUniversity of California, Los Angeles
(UCLA), Health Sciences.
Note: Materials may be edited for
content and length. For further information, please contact the source cited
above.
Journal Reference:
1.
Steve Horvath. DNA
methylation age of human tissues and cell types. Genome Biology,
2013; 14 (10): R115 DOI:10.1186/gb-2013-14-10-r115
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University
of California, Los Angeles (UCLA), Health Sciences (2013, October 20).
Scientist uncovers internal clock able to measure age of most human tissues;
Women's breast tissue ages faster than rest of body. ScienceDaily.
Retrieved October 21, 2013, from http://www.sciencedaily.com/releases/2013/10/131020203006.htm
