Damage and Cellular Signaling
Our cells talk to one another constantly, and much of the damage of aging involves harmful changes to those signals - cells instructed to behave in ways that cause further detrimental effects. For example: "When cells experiencing DNA damage fail to repair themselves, they send a signal to their neighbors letting them know they're in trouble. The discovery, which shows that a process dubbed the DDR (DNA Damage Response) also controls communication from cell to cell, has implications for both cancer and aging. ... . The discovery of the extracellular signaling mechanism, which sets off an inflammatory response, explains how unsuccessful DNA repair at the cellular level impacts tissues ... With regard to cancer, we found that if there is a mutant and potentially cancerous cell in the vicinity of the damaged cell, the signals from the damaged cell can encourage that mutant cell to behave more aggressively cancerous. With regard to aging, we think the inflammatory signals from damaged cells propagate an aging 'field' whereby damage builds up over time, impacting not only the individual damaged cells, but the function of the tissue itself. ... Damaged cells that survive the activity of the immune system are sending out continuous danger signals to surrounding cells. That constant alarm drives inflammation, which helps drive aging."
Link: http://www.eurekalert.org/pub_releases/2009-07/bifa-ddc070709.php