"Young blood" keeps old mice alive longer

What's the news: "Young blood" extends mouse longevity by (at least) 10%.

Why should we believe it? This news is based on a study published last week by scientists at Duke University and Harvard Medical School. The scientists took mice and then performed a gruesome medical procedure on them, called "heterochronic parabiosis."

In heterochronic parabiosis, scientists surgically sew together two mice of different ages (heterochronic) so their cardiovascular systems function as one (parabiosis). In other words, the blood of the old mouse goes into the young mouse, the blood of the young mouse into the old one, and it all gets mixed up.

Why are scientists doing this? This might sound like a truly perverse experiment, but it has been performed a number of times over the past few years, and by reputable scientists at top institutions. Studies published last year showed heterochronic parabiosis rejuvenates blood stem cells as well as liver cells. A study earlier this year showed that heterochronic parabiosis rejuvenates the brain.

The point of this gruesome research is to show that there's something in the young blood that can actually trigger rejuvenation. Perhaps that something is a kind of stem cell. Perhaps it's other, simpler signalling factors — some protein or metabolite.

Why this news is a big deal: The duration of the current study. Previous experiments typically kept the two mice surgically joined for two weeks. In the present study, the mouse were kept joined for 12 weeks, roughly 10% of a mouse's lifespan.

The result was bodywide rejuvenation and a 10% longer lifespan for the older mice. It's possible that a still longer treatment would produce still greater lifespan effects.

So what’s next? Once scientists identify what those rejuvenating factors are, they might be able to trigger rejuvenation — first in mice, then in humans — without having to sew two unfortunate creatures together. Let’s hope that day comes soon, both for the mice and for ourselves.