Part 4 of the Howard Hughes Medical Institute's 2006 Holiday Lectures on Science series. Dr. Nadia Rosenthal discusses the role stem cells play in aging.

A family of proteins called PPARs (peroxisome proliferator-activator receptors) controls how the body uses sugar and fat. PPAR-gamma drives the formation of fat cells and regulates the storage of fat. It encourages muscles to burn sugar and maintains insulin sensitivity. PPAR-delta regulates how muscles burn fat by stimulating cellular ...