How do humans age? While we are “programmed to die,” there doesn’t seem to be one thing that causes our death by “old age.” For example, one way we carry out our own deaths is found on the cellular level, where we accumulate mutations in the DNA repair process and the cells themselves die, or the enter senescence (non-replicating state) as they age. These processes occur at several different times, overlapping and alternating. Therefore, what appears to be the best time to intervene in order to promote healthy aging? No one knows, but they do know what DNA becomes extremely damaged as time goes on and has an incredible impact on our aging process. The cells have sooner suicide dates where they undergo apoptosis more rapidly than normal, and the loss of too many cells can cause tissue atrophy and dysfunction. In addition to creating a lack of cells, the damaged DNA can even shift epigenetic markers.
Typically, epigenetic marks shift in tumor cells, which can lead to cancerous cells. However, in the early 1990s at Johns Hopkins University, Jean-Pierre Issa was studying changes in DNA methylation in colon cancer cells when he observed shifts in epigenetic markers over time, but not only in tumor cells; he found that (to a lesser degree) these shifts were occurring in healthy cells as well. After mapping DNA methylation in human cells, we know that some areas of the genome become hypermethylated with age while others exhibit reduced methylation. These changes typically occur through DNA replication or DNA damage repair because the histone modifications are not always perfectly reproduced and in order to repair damaged DNA, repair proteins must remove the epigenetic marks to access the damaged genetic material to repair it, and once completed, the epigenetic marks can be omitted or misplaced. These epigenetic alterations have been linked to a reduced regenerative capacity of stem cells with age, and bring up a valuable question:
“Is this an epiphenomenon that happens just because we age, or is it actually causing symptoms or diseases of aging and limiting life span?”
Article source: http://www.the-scientist.com/?articles.view/articleNo/42280/title/How-We-Age/