I just went to a talk by Amy Wagers, who is a researcher at Harvard now but used to be at Stanford. She talked about work that she did with Stanford’s Tom Rando, putting young and old mice together so that they share blood circulation. It turns out that when old mice are exposed to young blood their aging stem cells in the muscle and brain start acting young again. They heal quicker and create more new cells. There seems to be some soluble factor in the blood that causes this, and researchers are now looking for that factor or factors.
What is really interesting is that they have found some gene candidates, and these genes are connected to the pathways that extend life in calorie restricted animals.