What’s the deal with lifespan?

Posted by Benjamin Buller on

A lot of attention has been paid recently to the life-lengthening capabilities of blood and bone marrow collected from young mice, when injected to older mice. For example, a recent study from Marina Kovina and colleagues in Moscow (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3736046/) reported that when they introduced bone marrow from 6 week old mice into the veins of 21.5 month old mice (average lifespan for a laboratory mouse is normally about two years) that the mice experienced a whopping 39% increase in lifespan after introduction of the young, healthy bone marrow cells!

What does this mean for humans? It’s difficult to say, exactly. The work does come with some caveats. Firstly, that 39% increase in lifespan was a 39% increase in the average amount of life the mice in the experimental group lived after treatment, which, in this case, was about 5 months, compared to 3.5 months for control animals. When looked at in those terms, the increase looks more modest, since 1.5 extra months is a 6% increase in lifespan when the whole 24 month life of the mouse is considered. We don’t know whether the increase in life would have been longer were the mice treated earlier or later than 21.5 months. Earlier work from Gerald de Haan’s laboratory at the University of Groningen has shown that the older a mouse is, the more likely it is to engraft newly introduced bone marrow cells. This leads one to speculate that were young bone marrow cells to be introduced at a younger age, that they might not have such a great (or at least no greater) effect on the mice’s lifespan.

Other biological differences exist between mice and humans that might be confounding factors. The one that occurs most obviously to me is that mice and humans have vastly different development schedules. A mouse reaches sexual maturity at about 4 weeks, or 1/24th of its total life. To put in perspective how accelerated this is, that would be like a human maturing at age 3! So the mouse spends virtually its entire life as an adult. We don’t know what this does to its bone marrow, but we do know that both mice’s and humans’ marrow cells become fewer and less viable as they approach the end of their natural lives. Therefore, despite the differences, it is entirely conceivable that the similarities are more significant. So in the end, it’s difficult to assess the analogy between this study and what might happen in humans. However, when we look at the totality of the organism, there are far more similarities than differences between us. This study is about as exciting as I’ve seen in bone marrow science!

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