Age Appropriate

Pancreas cells are a mix of older (yellow-pink) and younger (blue-green).

Salk Institute

Scientists have long thought that organ and tissue cells—with the exception of neurons in the brain and muscle cells in the heart—are forever young, constantly replacing themselves over the course of a lifespan. A new study shows, however, that in mice (and presumably in humans), the liver and pancreas are also full of old cells, mixed in with the expectedly younger cells. Learning more about this blend of young and old cells, known as age mosaicism, could help in understanding many disease states and the aging process.

A research team led by Martin Hetzer of the Salk Institute in La Jolla, California, relied on a recently developed microscopy technique to date cells by determining the amount of certain forms of nitrogen in cellular proteins. They applied this analysis to various tissue types in a mouse model. Neurons, as expected, were indeed made of ancient cells and served as an age baseline for identifying old cells. Unexpectedly, the endothelial cells that line blood vessels were just as ancient, and cells as old as their organs were also found in the liver and pancreas.

Further investigation showed that these old cells, which never divide into fresh cells in order to renew themselves, age differently from cells constantly undergoing replenishment. The researchers want to delve deeper into how these non-dividing cells perform over the course of an organism’s lifetime. Compared to young cells, older cells seem likelier to lose control over the quality and integrity of their constituent proteins and key cellular structures. That loss of control contributes to aging and diminishing function.

Preventing that degradation by keeping organs sprightly could prove a powerful new therapeutic strategy. “The ultimate goal,” said Hetzer, is to “delay age-related decline of organs with limited cell renewal, such as the brain, pancreas and heart—all of which are associated with age-related ailments, such as Alzheimer’s, Type 2 diabetes, and cardiovascular [disease]. . . If we understand how we can change the ratio of young and old cells working in an organ, we could have a positive effect on health maintenance.” (Cell Metabolism)