Cell Stem Cell paper describes results from study in flies showing a decrease in older specimens because of changes in niche environment.!--h2>
During the aging process, the level of support for stem cells drops off, which diminishes the their ability to self-renew indefinitely, report scientists at the Salk Institute for Biological Studies.
“You can manipulate stem cells and propagate them in a dish, but many recipients of stem cell replacement therapies will be older individuals,” points out Leanne Jones, Ph.D., an assistant professor in the laboratory of genetics who led the study. “If the stem cell niche has aged, it might not be capable of supporting the transplanted stem cells.”
In an earlier study, Dr. Jones had shown that the hub cells, a cluster of somatic cells surrounded by stem cells, secrete the self-renewal factor, upd. This signals neighboring stem cells to maintain their identity, making hub cells an essential component of the stem cell niche environment. This investigation also found that artificially increasing the levels of upd results in tumor-like masses of stem cells.
The current analysis compared the number of stem cells in young, middle-aged, and old Drosophila flies. The investigators found that over time stem cell numbers fell from an average of 8.3 in young flies to 5.1 in old flies, explaining the observed decrease in spermatogenesis in aged males.
The number of hub cells, on the other, hand remained unchanged. When the team measured the levels of upd in the testes of aging males, they found a sharp decline in the self-renewal factor. In contrast, forced expression of upd within niche cells delayed the loss of germline stem cells in older males.
The article will be published in the October 11 issue of Cell Stem Cell.