There has been a great deal of interest in the idea of using stem cells to reverse age-associated declines in organ function. However, recent studies have shown that ageing tissues often have plenty of stem cells; nonetheless, the stem cells lose their ability to differentiate and to repopulate tissues with healthy cells. Now, in recent issues of SCIENCE (1) and NATURE MEDICINE (2), several research reports have shown that factors in the blood of young mice can reverse age-related declines in stem cell and tissue function. Some of these studies used parabiosis, that is joining the circulatory systems of old and young animals. Another study focused on GDF11, a TGF-beta type growth factor whose expression declines in older animals. Injections of this protein improved both muscle function and (in another report) growth of brain blood vessels and olfactory neurons. Perhaps the most exciting study (2) demonstrated that blood from young mice could reverse age-related declines in hippocampal cells and associated cognitive impairments.
There has always been tremendous interest in seeking means to slow the declines associated with ageing. However, the work discussed here, as well as other recent studies, suggest that an actual reversal (at least in part) of the ageing process may be possible. While this is all still far away from use in humans, it offers a tantalizing prospect that could have enormous implications both medically and in terms of impacts on society.