DNA damage, mutations and aging 2

Published on July 31, 2017   28 min

Other Talks in the Series: Aging

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So the next question for us was, how can we, first of all, escape the limits of that reporter and really look at the genome overall? There are so many interesting features in a genome and we really want to see where the mutations are because maybe the reporter is not such a great measure for the genome overall, and there are all sorts of differences maybe between genes and regulatory sequences. And second, how can we expand our studies, or in general how can we expand studies of somatic mutations to humans, from experimental animals to humans? The first thing we tried is basically try to hitchhike on data that were available, that were collected by others. And it's a student in the lab, another student Brandon Milholland, who started to do this.
Brandon began to use what we called the Cancer Genome Atlas after the emergence of next generation sequencing, so the capacity to really sequence the genome or a substantial part of the genome at low cost and very quickly and efficiently. That was used, that technology, for sequencing tumors because a tumor obviously originates from one cell, it's essentially a clone. So you can take that tumor and basically sequence the genome and they have all the mutations that vary in that original cell when it was still normal, but also that started to accumulate in the tumor itself once it was already a tumor. That's all put together in the Cancer Genome Atlas so others have collected the data, we didn't collect it. But Brandon could access it, because it is free, you can look at it.
This, sort of, summarizes his studies which have been published recently. I think it's really important to some extent it confirms what was already known or suspected in a number of papers on individual cancers. We had already noticed that when it was a cancer, like a juvenile tumor in young patients, they generally didn't contain that many mutations. The way you looked at tumors from older people there were many more mutations. And Brandon sort of confirmed that and studied this in a large number of patients, so you see about 7000. And he really showed proofs, I think without a doubt, that you see mutations in these tumors increasing as a function of age, and it increases exponentially. So it's pretty dramatic, actually. So the argument here is of course that yes, maybe so now and then a tumor will begin to accumulate many mutations after it stopped being normal. That's true, but probably in virtually all cases most of the mutations in the tumor were actually already there in a normal cell, and there's also other evidence that that's exactly the case. So clearly that is another piece of convincing evidence but now in humans that yes, mutations do accumulate as a function of age in different cell types. Obviously that's really not what we were ultimately interested in. We really want to look at normal tissues, normal cells, and check if mutations accumulate in these normal tissues.