Biologists discover how yeast cells reverse ageing

Human cells have a finite lifespan: They can only divide a certain number of times before they die. However, that lifespan is reset when reproductive cells are formed, which is why the children of a 20-year-old man have the same life expectancy as those of an 80-year-old man.

How that resetting occurs in human cells is not known, but MIT biologists have now found a gene that appears to control this process in yeast. Furthermore, by turning on that gene in aged yeast cells, they were able to double their usual lifespan.

If the human cell lifespan is controlled in a similar way, it could offer a new approach to rejuvenating human cells or creating pluripotent stem cells, says Angelika Amon, professor of biology and senior author of a paper describing the work in the June 24 issue of the journal Science.

''If we can identify which genes reverse aging, we can start engineering ways to express them in normal cells,'' says Amon, who is also a member of the David H. Koch Institute for Integrative Cancer Research. Lead author of the paper is Koch Institute postdoc Elçin Ünal.

Rejuvenation
Scientists already knew that aged yeast cells look different from younger cells. (Yeast have a normal lifespan of about 30 cell divisions) Those age-related changes include accumulation of extra pieces of DNA, clumping of cellular proteins and abnormal structures of the nucleolus (a cluster of proteins and nucleic acids found in the cell nucleus that produce all other proteins in the cell).

However, they weren't sure which of these physical markers were actually important to the ageing process. ''Nobody really knows what ageing is,'' Amon says. ''We know all these things happen, but we don't know what will eventually kill a cell or make it sick.''