Every cell in your body has a little clock ticking away in it, researchers reported on Sunday. And while most of you is aging in a coordinated way, odd anomalies that have the researchers curious: Your heart may be “younger” than the rest of your tissues, and a woman’s breasts are older.
Tumors are the oldest of all, a finding reported in the journal Genome Biology that might help scientists better understand cancer, explain why breast cancer is so common and help researchers find better ways to prevent it.
Less surprising, but intriguing: embryonic stem cells, the body’s master cells, look just like newborns with a biological age of zero.
The new measurements might be useful in the search for drugs or other treatments that can turn back the clock on aging tissue and perhaps treating or preventing diseases of aging, such as heart disease and cancer, says Steve Horvath, a professor of genetics at the David Geffen School of Medicine at UCLA.
“The big question is whether the biological clock controls a process that leads to aging,” Horvath said.
Horvath looked at a genetic process called methylation. It’s a kind of chemical reaction that turns on or off stretches of DNA. All cells have the entire genetic map inside; methylation helps determine which bits of the map the cells use to perform specific functions.
He found a pattern of specific methylation events that could be associated with cellular aging. “Methylation levels either increase with age or they decrease with age,” He says. “I identified 353 of these markers that are located on our DNA. I managed to aggregate their information so they arrive at a very accurate clock."
He’s not sure what each methylation marker does on its own.
“It’s really the aggregate that is making the difference,” Horvath said in a telephone interview. "The whole is more than the sum of its parts.”
He looked at blood and tissue samples from hundreds of people, from unborn babies to someone 101 years old. He looked at tumors from people with 20 different types of cancer, samples of non-cancerous tissue from the same patients and perfectly healthy people.
On average, tumors were 36 years older than the rest of the body, a finding that supports the idea that cancer is a disease in which the biological clock runs amok.
Surprisingly, most people’s hearts look younger than the rest of their bodies, the researchers found. ”That looked one average nine years younger,” Horvath says. “It’s really striking. I don’t know why, but it looks younger.”
And some cells looked older. “The tissue that looked oldest was female breast tissue,” Horvath says. Normal, healthy female breast tissue looked about two to three years older on average. Non-cancerous tissue taken from breast cancer patients – samples from right next to a tumor – looked about 12 years older.
Horvath believes the findings suggest there may be ways to reverse the aging of tissue that leads to disease. There’s a way that scientists make embryonic-like stem cells from ordinary cells. These new stem cells are called induced pluripotent stem cells, and they are genetically altered to look like the baby cells that are created soon after conception.
Even though they’re made using old cells, Horvath says that, measured using his process, they look like they’ve truly been converted back into brand-new cells.