Stem Cells, Tissue Environments, Aging
From Ouroboros: "These papers add to the growing body of evidence that stem cells don't fare well in aged niches. In other words, the stable introduction of stem cells into patients will become more difficult as a function of the recipients' age; since it's a question of capacity rather than efficiency, the problem can't be solved by adding more stem cells. Clinically, this means that [we] may need to engineer the niche itself in order to cajole aged tissues into accepting a new batch of stem cells - and this will be very hard. We are much better at manipulating cells outside the body and re-introducing them than we are at making genetic changes to particular cells inside a specific tissue architecture while they remain inside the body - and by 'much better' I mean that at present we can do the former sometimes and the latter not at all. Perhaps a better approach would be to make the stem cells less sensitive to the cues they receive from the niche? Yes, that would be nice: immortal cells, freed from requirements for context-specific pro-growth and anti-apoptotic factors, free in the body to do as they pleased ... oh, wait." There's an evolutionary reason for many of the declines of aging - it's called cancer. The body is a finely tuned device; fixing problem A is often going to require fixing problems B and C as well. This is one of the reasons a general strategy of repairing all age-related changes is needed.