One inevitable fact of life is that we age. As we get older, our skin gets less elastic, our hair colour begins to grey and our bodies don't function as well as they used to. Our cells can only divide a certain number of times, after which, they die. If I placed a photo of a 50 year old male and a 20 year old male, you'd no doubt be able to distinguish the two individuals. Yet a baby from a 50 year old man looks the same age as a baby from a 20 year old man. Somehow the characteristics we associate with aging aren't conveyed to our offspring. So somewhere in the process of creating a baby, aging is reset.
Yeast cells also age, with several hallmarks of aging visible under a microscope. Like humans, as cells age, proteins begin to form clumps in the cells, which can impede cellular function. Accumulation of proteins is one of the major symptoms in neurodegenerative diseases like Alzheimer's or Parkinson's Disease. In addition, aged yeast cells accumulate extrachromosomal ribosomal DNA circles (ERCs) in their body. The nucleolus – the part of the cell that produces factories for making proteins – begins to look abnormal as cells age. Moreover, older yeast cells contain more bud scars (a consequence of cell division) than daughter cells; talk about a traumatic birth!
Elçin Ünal from the Amon lab at MIT set out to investigate this phenomenon in yeast: why is it that aging characteristics aren't conveyed to the next generation? She found that that yeast reset their age during the process of forming spores, which are the yeast equivalent of sperm or egg. Before forming spores, he saw those hallmarks of aging in yeast cells yet subsequent to sporulation, many of those hallmarks were gone. Those protein blobs were eliminated, likely due to autophagy, a cellular process that degrades the cell's own components. In addition, the ERCs were now eliminated from spores.
They found a gene, Ndt80, was activated as the aging reset was occurring. In fact, when they forced the gene to turn on in old yeast cells, it could significantly extend the old yeast-cells lifespan! What is Ndt80? Ndt80 is something called a transcription factor; it functions as a switch to turn on many other genes in the cell. Strangely, turning on this gene in old cells only causes the abnormal nucleolar structure to be fixed, yet this is enough to cause the cells to live twice as long. This could mean that one major cause of aging is nucleolar damage.
In summary, the Amon lab found a gene linked with resetting aging during the formation of children. Turning on Ndt80 in old cells was enough to make them live longer. The next steps would be to see whether this process holds for mice and humans. Humans do have a gene related to Ndt80. Interestingly, this gene is turned on in a cell-type that doesn't age, cancer cells, which further suggests that the anti-aging process may hold true in humans. If it is true, one can envision that turning on Ndt80 in humans may prevent aging.
Unal, E., Kinde, B., and Amon, A. (2011). Gametogenesis Eliminates Age-Induced Cellular Damage and Resets Life Span in Yeast. Science. 332, 1554-7. Paper
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