Lab Notes looks at how to go about making aged stem cells work once more: "The regenerative properties of organs are tied to the behavior of stem cells. So I focus on what happens to those cells with aging. Why don't they work anymore and can we fix them? ... The problem is that as the body ages, the molecules that regulate stem cells eventually change and inhibit their regenerative properties. Simply adding a new supply of stem cells to a damaged muscle, for instance, won't work because the foreign environment will interfere with the cells' behavior. ... They'll quickly stop repairing the muscle. But if you can supplement them with regulatory factors and also protect them somewhat from the aged environment, they'll behave better."