Ageing leads to a decrease in the functioning of stem cells in tissues, such as adult neural stem cells and muscle satellite cells (which participate in regeneration in mouse skeletal muscle). Adult neural stem cells lie in close contact with endothelial cells, which provide signals modulating stem cell proliferation and differentiation, and which also deteriorate with ageing. Previous studies have shown that systemic factors from the circulation of a young mouse placed in parabiosis with an older animal can rescue the function of satellite cells. Two studies (Science 344, 630–634, 649–652; 2014) have identified a specific factor that alone restores satellite cell function in aged muscle and improves neural stem cell and endothelial cell function in the aged brain.

Wagers and colleagues showed that aged satellite cells display DNA damage and regeneration defects in response to irradiation. Injection of GDF11 (growth differentiation factor 11), which is known to reverse age-related hypertrophy and whose systemic levels decline with age, restored genomic integrity and improved satellite cell muscle regeneration capacity in old mice. Likewise, Rubin and colleagues found that young blood from parabiotic animals increased the proliferation and differentiation of neural stem cells and their progenitors. They also described remodelling events in the vasculature and, in particular, an increase in endothelial cell proliferation. They too found that GDF11 injection can have effects similar to those of exposure to young blood in parabiotic animals, ultimately resulting in a functional improvement of neurogenesis, as measured by improved olfactory functions.