October 21, 2013
New Biological Clock Shows Body Parts Age At Different Rates
Brett Smith for redOrbit.com - Your Universe Online
According to a UCLA researcher’s newly developed way of measuring a person’s biological clock, a woman’s breasts age faster than the rest of her body.The novel method developed by Steve Horvath, a professor of human genetics and biostatistics at UCLA, was created by studying methylation, a naturally occurring genetic progression that chemically changes DNA.
"To fight aging, we first need an objective way of measuring it. Pinpointing a set of biomarkers that keeps time throughout the body has been a four-year challenge," Horvath explained. "My goal in inventing this clock is to help scientists improve their understanding of what speeds up and slows down the human aging process."
According to Horvath’s report in Genome Biology, the geneticist examined over 120 sets of genomic data previously collected by researchers who had looked at the methylation process in both healthy and cancerous human tissue.
Using nearly 8,000 samples of 51 tissue and cell types, Horvath tracked the relationship between age and methylation levels from gestation through 101 years of age. To create his clock, Horvath focused on over 350 genetic markers that vary with age and are found throughout the body.
The UCLA scientist tested the clock's efficacy by contrasting various tissues' biological age to their chronological age. When his method was shown to be accurate, Horvath said was ecstatic—and a little astonished.
"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."
Using the new clock as a guide, most of the cell and tissue samples' biological ages matched their chronological ages. However, a few diverged significantly – most notably women's breast tissue was found to age faster than the rest of the body.
"Healthy breast tissue is about two to three years older than the rest of a woman's body," Horvath said. "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 geneticist speculated that his results could explain why breast cancer is the most common form of the disease in women. Horvath’s clock found that cancerous tissues are 36 years older, on average, than healthy tissue. The results could also explain why age is a key risk factor for many cancers in both genders.
In the study, Horvath also looked at the relative age of pluripotent stem cells, mature cells that have been reprogrammed to an embryonic stem cell-like state that can transition into any type of cell in the body and continue dividing ad infinitum.
"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."
"The big question is whether the biological clock controls a process that leads to aging," Horvath added. "If so, the clock will become an important biomarker for studying new therapeutic approaches to keeping us young."
The UCLA researcher’s new method also indicated that the rate of human aging isn’t constant.
"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."