What’s the Deal with Lifespan?
A lot of attention has been paid recently to the life-lengthening capabilities of blood and bone marrow collected from young mice when injected into older mice. For example, a recent study from Marina Kovina and colleagues in Moscow reported significant results regarding this intervention. They introduced bone marrow from 6-week-old mice into the veins of 21.5-month-old mice, noting that the average lifespan for a laboratory mouse is normally about two years.
The results were striking: the mice experienced a whopping 39% increase in lifespan after the introduction of the young, healthy bone marrow cells. This discovery has sparked significant interest in the field of gerontology and regenerative medicine.
What Does This Mean for Humans?
It’s difficult to say exactly what these findings mean for humans, as the work comes with several important caveats. The 39% increase refers specifically to the average amount of life the mice lived after treatment. In this study, that amounted to about 5 months for the experimental group compared to 3.5 months for control animals.
When viewed in the context of the animal's entire life, the increase looks more modest. An extra 1.5 months represents a 6% increase in total lifespan when the full 24-month life of the mouse is considered. Furthermore, several variables remain unknown:
Whether the increase would be longer if mice were treated earlier or later than 21.5 months.
The impact of engraftment rates, as research from Gerald de Haan’s laboratory suggests older mice engraft new cells more easily.
Whether introducing cells at a younger age would result in a diminished effect on overall lifespan.
Biological Differences and Confounding Factors
Other biological differences between species might serve as confounding factors. Most notably, 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 this in perspective, that would be equivalent to a human maturing at age 3.
Because mice spend virtually their entire lives as adults, we don't fully understand the specific impact on their bone marrow. However, we do know that in both species, marrow cells become fewer and less viable as they approach the end of their natural lives. While it is difficult to assess the direct analogy to humans, the similarities between the organisms may be more significant than the differences. This remains some of the most exciting research currently seen in bone marrow science.
