Subodh
Varma, TNN | Oct 21, 2013, 11.57 AM IST
Theoretically, it is possible to reverse aging if one
understands how it is taking place.
NEW DELHI: In a step towards
unraveling the mystery of aging, a US scientist has discovered a human body
clock tucked away in body's DNA. It measures the age of cells, tissues and
organs.
Steve Hovarth of the University of California, Los Angeles found that different parts of the body were aging at different speeds - some faster, others slower. Significantly, diseased organs showed ages many years in ahead of the rest of the normal body. Hovarth's study is reported in the scientific journal Genome Biology on Monday.
"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."
Theoretically, it is possible to reverse aging if one understands how it is taking place. Horvath's work is a clear identification of a biochemical process linked to aging. By understanding how Hovarth's clock works, it may be possible to get the key to aging, and perhaps develop ways of stopping or slowing it down.
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. Analysing 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. He tested the clock's effectiveness by comparing a tissue's biological age to its chronological age. Repeated tests showed that the clock was accurate.
"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."
Horvath also found that the clock's rate speeds up or slows down depending on a person's age. At birth, the clock is faster and continues like that till adolescence. But after about 20 years age it slows down to a constant rate for the rest of the life.
Steve Hovarth of the University of California, Los Angeles found that different parts of the body were aging at different speeds - some faster, others slower. Significantly, diseased organs showed ages many years in ahead of the rest of the normal body. Hovarth's study is reported in the scientific journal Genome Biology on Monday.
"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."
Theoretically, it is possible to reverse aging if one understands how it is taking place. Horvath's work is a clear identification of a biochemical process linked to aging. By understanding how Hovarth's clock works, it may be possible to get the key to aging, and perhaps develop ways of stopping or slowing it down.
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. Analysing 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. He tested the clock's effectiveness by comparing a tissue's biological age to its chronological age. Repeated tests showed that the clock was accurate.
"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."
Horvath also found that the clock's rate speeds up or slows down depending on a person's age. At birth, the clock is faster and continues like that till adolescence. But after about 20 years age it slows down to a constant rate for the rest of the life.
Posted by:
Rajni Jaiswal
Faculty of Bioinformatics
BII,Noida
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