Vacuole Changes as a Contributing Cause of Yeast Cell Aging
The type of vacuole found in yeast cells is somewhat analogous to the lysosome that we animals possess in that it is involved in breaking down waste products and recycling broken cellular components (via the process of autophagy) that would otherwise harm the cell. It is an agent of cellular housekeeping, in other words. There the similarities end, however, as the vacuole performs many other vital tasks that the more specialized lysosome does not.
So here, researchers show that they can extend life in yeast by reversing a change that occurs in the vacuole. Because the vacuole has many more tasks than the lysosome, it's not immediately clear that this has any application to our biology of aging, however. It is still worth keeping an eye on this research as we know that decline in lysosomal function (and thus of cellular housekeeping) is important in animal aging. You might recall, for example, that researchers managed to reverse the age-related loss of liver function in mice by finding a way to keep lysosomal function running at youthful rates. Similarly, reversing the root causes of lysosomal decline is on the SENS agenda - to be achieved by breaking down the build up of metabolic waste products that accumulate in lysosomes and cause them to malfunction.
Normally, mitochondria [in yeast] are beautiful, long tubes, but as cells get older, the mitochondria become fragmented and chunky. The changes in shape seen in aging yeast cells are also observed in certain human cells, such as neurons and pancreatic cells, and those changes have been associated with a number of age-related diseases in humans.The vacuole - and its counterpart in humans and other organisms, the lysosome - has two main jobs: degrading proteins and storing molecular building blocks for the cell. To perform those jobs, the interior of the vacuole must be highly acidic. [Researchers] found that the vacuole becomes less acidic relatively early in the yeast cell's lifespan and, critically, that the drop in acidity hinders the vacuole's ability to store certain nutrients. This, in turn, disrupts the mitochondria's energy source, causing them to break down. Conversely, when [researchers] prevented the drop in vacuolar acidity, the mitochondria's function and shape were preserved and the yeast cells lived longer.
Until now, the vacuole's role in breaking down proteins was thought to be of primary importance. We were surprised to learn it was the storage function, not protein degradation, that appears to cause mitochondrial dysfunction in aging yeast cells. ... The unexpected discovery prompted [the researchers] to investigate the effects of calorie restriction, which is known to extend the lifespan of yeast, worms, flies and mammals, on vacuolar acidity. They found that calorie restriction - that is, limiting the raw material cells need - delays aging at least in part by boosting the acidity of the vacuole.