Aging is as much about the physical processes of repair and regeneration – and their slow–motion failure – as it is the passage of time. And scientists studying stem cell and regenerative biology are making progress understanding those processes, developing treatments for the many diseases whose risks increase as we get older, while at times seeming to draw close to a broader anti–aging breakthrough.

If stem cells offer potential solutions, they’re also part of the problem. Stem cells, which can differentiate into many cell types, are important parts of the body’s repair system, but lose regenerative potency as we age. In addition, their self–renewing ability allows the mutations that affect every cell to accumulate across cellular generations, and some of those mutations lead to disease.

“We do think that stem cells are a key player in at least some of the manifestations of age,” said Professor of Stem Cell and Regenerative Biology David Scadden, co–director of the Harvard Stem Cell Institute. “The hypothesis is that stem cell function deteriorates with age, driving events we know occur with aging, like our limited ability to fully repair or regenerate healthy tissue following injury.”

“The process of aging involves all tissues in your body and, while different things go wrong in each tissue, they go wrong at basically the same rate,” Rubin said. “We can think of it as a process that is somehow coordinated, or there are fundamental processes in each tissue that play out.”

In addition to key tissues, certain chemical pathways – like insulin signaling – seem to be able to control aging, said Rubin, whose work has received backing from the National Institute of Neurological Disorders and Stroke, as well as private foundations. The insulin signaling pathway is a chemical chain reaction in which the hormone insulin helps the body metabolize glucose. Reducing it has been shown to greatly extend life span in flies and worms, Rubin said. Also, signaling doesn’t have to be reduced in all tissues.

“If you just reduce it in neurons, the whole fly or worm lives longer,” Rubin said. “Certain key tissues in those organisms, if you selectively manipulate those tissues, have a positive effect on a number of processes in other tissues.”

Because it circulates throughout the body, blood is an obvious place to look for controlling or signaling molecules that prompt or coordinate aging. A key carrier of oxygen and nutrients, blood is also rich with other compounds, some of which appear to play a role in decline linked to age.

Rubin said the experiments suggest that blood contains both positive and negative factors that influence aging. It may be, he said, that both are always present, but that positive factors outweigh negative in the young and that negative factors increase as we age.