I notice that two good review papers on the topic of stem cells, stem cell niches and aging are presently freely available in the latest Aging Cell. Journal publishers tend to put out these free full text promotions for a limited time, so take a look while the looking is there.
Declining stem cell function during aging contributes to impaired tissue function. Muscle-specific stem cells ('satellite cells') are responsible for generating new muscle in response to injury in the adult. However, aged muscle displays a significant reduction in regenerative abilities and an increased susceptibility to age-related pathologies. This review describes components of the satellite cell niche and addresses how age-related changes in these components impinge on satellite cell function.
Significant advances in the past decade have revealed that a large number of highly plastic stem cells are maintained in humans through adulthood and are present even in older adults. These findings are notable in light of the reduced capacity for repair and regeneration in older tissues. The apparent dichotomy can be reconciled through an appreciation of the age-associated changes in the microenvironmental pathways that govern adult stem cell plasticity and differentiation patterns.
As this second paper illustrates, the weight of evidence is shifting to the view that we are packed full of functional stem cells even as we age. These stem cell populations are shut down by changes in biochemical signals and systems, possibly due to accumulated damage that causes aging and malfunction, possibly as an evolved defense against the increasing likelihood of cancer in old tissue. As cancer medicine becomes increasingly sophisticated, safe and effective, learning the signals to set our stem cells back to work begins to look like a plausible near term strategy for enhancing longevity.