Two studies published in Cell by scientists from the Institute for Research in Biomedicine (IRB Barcelona) at the Barcelona Science Park, the Pompeu Fabra University (UPF) and the University of California, Irvine (UCI) reject the scientific dogma associating ageing with the loss of stem cell circadian rhythm. Their results reveal that stem cell functions continue to be governed by day and night cycles (circadian rhythms) during ageing, but their rhythms become devoted to tissue repair and not to the maintenance of tissue tone.

It is widely believed that, with the passage of time, stem cells cease to differentiate between day and night cycles, in other words they lose their circadian rhythm, and that this loss promotes ageing. However, this has been found not to be the case. Scientists from the IRB, UPF and UCi has discovered that stem cells continue to show rhythmic activity but reprogram their circadian functions during ageing.

“Aged stem cells conserve circadian rhythm but now perform another set of functions to tackle the problems that arise with age,” explains ICREA researcher Salvador Aznar Benitah, head of the Stem Cells and Cancer group and leader of the two studies. The scientists do not know how such reprogramming comes about. Aznar Benitah adds, “the problem is that as they age, stem cells lose the rhythmic functions necessary for tissue protection and maintenance, which become replaced by functions aimed at coping with stress. Loss of the previous circadian functions of stem cells during natural ageing contributes in some way to greater damage and greater ageing”.
 

A low-calorie diet keeps the circadian rhythm young  

According to the researchers, their studies would explain why a calorie restriction diet slows down ageing. “The low-calorie diet greatly contributes to preventing the effects of physiological ageing. Keeping the rhythm of stem cells “young” is important because in the end these cells serve to renew and preserve very pronounced day-night cycles in tissues. Eating less appears to prevent tissue ageing and therefore prevents stem cells from reprogramming their circadian activities,” explains Aznar Benitah.

According to the researchers, their studies would explain why a calorie restriction diet slows down ageing. What is not clear is whether low-calorie diets would keep ageing at bay in humans. “Such diets are unlike to become widely followed because they entail constant hunger and so require a lot of willpower; also, such eating regimes provide the body with the minimum energy to perform its basic functions, which in the long term may have negative effects on people’s everyday lives,” stresses Aznar Benitah. The scientist explains that, in this regard, it is important to further examine why metabolism has such a dominant effect on the stem cell ageing process and, once the link that promotes or delays ageing has been identified, to develop treatments that can regulate this link.
 

► For further information: IRB Barcelona website [+]

► Reference articles:
Solanas, Guiomar et al. “Aged Stem Cells Reprogram Their Daily Rhythmic Functions to Adapt to Tissue-Specific Stress“. Cell (2017). Doi: 10.1016/j.cell.2017.07.035

Sato, Shogo et al. “Circadian Reprogramming in the Liver Identifies Metabolic Pathways of Aging“. Cell (2017). Doi: 10.1016/j.cell.2017.07.042