They could measure the length of telomeres—protective caps at the end of our DNA that wear away with time. But doing so is hard and expensive, and telomere length naturally varies between people of the same age.
Sharpless's team has focused on one particular aspect of aging—a process called senescence, in which cells permanently stop dividing. Senescent cells accumulate as we get older, and they contain ten times the usual levels of a protein called p16.
Glowing Mice
The team has developed a strain of mice that produce a protein that glows whenever they make p16. "When they get older and have lots of senescent cells, they glow like crazy," says Sharpless. "When you expose them to gerontogens, they'll glow at a younger age than you expect."
The team members are using their mice to test potential gerontogens, and they've sent the animals to around 50 different labs that are doing the same. They're also working with a company called HealthSpan Diagnostics to create a version of their p16 test that could measure biological age in people.
"One marker isn't going to do it. You need a panel," says Sharpless. "The perfect test doesn't exist, but I'm certain that within my lifetime we'll have the ability to measure someone's physiological age with precision."
Sharpless expects the research to change perceptions. "If you did what we've done for carcinogens, where we've tested millions of compounds, you'd find stuff that you'd be really surprised were gerontogens," he says.