生物钟为你提供老去的线索

 　　If you’re searching for the fountain of youth, you might find it in your DNA 1. That’s according to a new study that sheds light on the biological clock ticking in our genomes, why our bodies age and how we can slow down the process.

　　University of California genetics professor Steve Horvath has created a new tool that can accurately 3 measure the aging body.
　　“Basically I developed a way of predicting age based on DNA," Horvath said. "To achieve this goal I identified 353 markers on the DNA which measure DNA methylation levels.”
　　Methylation is a naturally occurring epigenetic - or gene 2 altering - process that chemically modifies the DNA and is critical in the development of every organism. Horvath and his colleagues gleaned 4 information from 8,000 samples to chart methylation in healthy and diseased organs, tissues and cells, from fetuses 5 to centenarians.
　　“For one thing, I find that this epigenetic clock ticks fastest during development, and after age 20 it slows down to a constant ticking rate," he said. "But also I find that cancer tissue is on average 36 years older than healthy tissue and I observed that effect in all 20 cancer types that I studied.”
　　In other words, some cells age faster than others.
　　Horvath notes that while most biological samples matched their chronological 6 age, some diverged 7 significantly. The average human heart, for example, appears to be 12 years younger than its chronological age, and a woman’s healthy breast tissue ages faster than the rest of her body.
　　“So it is possible that the cancer that is adjacent to this tissue accelerates the age," he said. "Having said this, I had one data set that was composed of truly healthy breast tissue and even there I observed a significant age acceleration 8.”
　　The results may explain why breast cancer is the most common cancer in women.
　　Remarkably 9, Horvath says the clock kept reliable time across the human anatomy 10, irrespective of where the DNA came from.
　　“This new epigenetic clock really frees us up from focusing on one tissue at a time because it really works in most tissues and organs and cell types, and the great advantage is that we now can compare the ages of different tissues and organs from the same individual,” he said.
　　Horvath says the work holds promise for studying human development, aging and disease, but also shows potential for rejuvenating 11 tissues.
　　"Of course it has been a long-standing hope to find therapies or compounds that keep us young, and if this epigenetic clock measures a process that causes aging, then we will have a tool that allows us to evaluate compounds that keep us young,” he said
　　So has Horvath found the Fountain of Youth?
　　"I have unfortunately no data that would support that,” he said with a laugh.