Cells in many organs are found to live as long as brain cells.

Scientists have known that brain cells –– neurons –– generally have life spans the same as the organism itself. It was thought, however, that cells in most other organs generate new cells on a regular basis and then die, leaving the younger cells behind.

Researchers at the Salk Institute decided to determine if that was true and found some surprising results.

To do so, they determined the age of cells in different mouse tissues, including the brain, liver and pancreas. First, however, they had to develop new microscopy methods that would allow them to determine the age of imaged cells, which were achieved in collaboration with scientists at the University of California, San Diego.

Advanced imaging and electron isotope labeling were used to quantify turnover among cells and proteins. Neurons from the brain were evaluated first, and then compared with the results for cells from the liver and pancreas.

The researchers were surprised to find that, in the liver, despite its ability to regenerate fresh tissue, many of the cells were as old as neurons. Long-lived cells were also observed in blood vessels and in the pancreas. In fact, they concluded that most of the cells in the liver and pancreas were as old as cells in the brain.

The age of the proteins within the older cells varied. Some neurons and beta cells from the pancreas had both very young and very old proteins, while the liver cells had no long-lived proteins.

Understanding why some cells persist and others continue to replicate and be replaced could provide insight into disease mechanisms and lead to the development of new drugs. One example is insulin-producing beta cells in the pancreas –– some continue to divide and others are as old as neurons. The cause of the different behavior could provide information about type 2 diabetes.

Next for the team is determination of the age of the nucleic acids and lipids in different types of cells important to type 2 diabetes, followed by seeking more information on cells involved in cardiovascular disease and dementia. Ultimately, they hope to learn how long-lived cells age, what changes they undergo and what causes them to transition into diseased states.