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Mitochondrial Mutations Associated with Aging. |
The October 22nd issue of Science reports that
specific changes in the mitochondria DNA (mtDNA) are associated with
aging.
There are several reasons to believe that the mitochondria may be
important in aging. The mitochondria are the generators that power our
cells. In performing this function they generate free radicals. Therefore
changes in
the mitochondria that occur with aging are of practical interest for those
who would like
to extend the human life span.
Mitochondria
are unique components of a cell because they possess DNA of their own and
replicate
in a manner
similar to the cells in which they are found. This DNA is a remnant of the
ancient
forerunner of the mitochondria which was a free-living bacterium. This
study, which was
conducted at the California Institute of
Technology focused on mutations in the region of mtDNA that controlled
the
replication of the mtDNA itself . It was found that specific mutations in
the control region
would appear and proliferate within individuals as they age. This
complements prior work that demonstrated that the amount of
active mtDNA declines as an individual ages. It may be that the
accumulation of
the mutations
such as those detected in this study are the underlying cause of this
phenomenon.
This study involved meticulous and laborious bench work and data analysis. Samples from over twenty individuals were assayed for multiple mutations. In some cases two samples from the same individual at different ages were processed. Certain mutations were common (57%) in older individuals (above 65 years) but absent in samples from younger individuals. In the samples taken from the same individual at different ages (longitudinal studies) the same frequency of mutations was also observed. This data indicates that specific mutations in mtDNA become more frequent with age. However, these results do not prove that these mutations are involved in aging. Further studies will be required to determine if these mutations are related to impaired function of the mitochondria.
One concern that arises with these experiments comes from the fact that the region being examined is involved in mitochondrial DNA replication. This means that it is possible that mutations in this region may impair or increase the efficiency of replication of the mutated mtDNA. Therefore it is quite possible that the mutations observed in this study give rise to mitochondria that are more efficient at self-replication. (For an excellent explanation of self-replication see Dawkins) This would explain the accumulation of mtDNA with these mutations with the passage of time (i.e. in older individuals) without any role in the phenomenon of aging.
Created November 14th, 1999. Copyright 1999 by Duane Hewitt
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