Leptin: brains and bones

Leptin, is a 16 kDa protein derived mainly, though not entirely, from white fat cells. It regulates the size of the body's fat load (i.e., energy rese rves) and has a growing list of other functions. The latest addition is bon e growth. The evidence so far indicates that leptin controls bone growth in two ways. It stimulates the release of an undefined hypothalamic osteoblas t-inhibiting factor(s), which limits the amount of bone matrix that osteobl asts can make. interestingly, it is itself a bone anabolic factor that dire ctly stimulates bone growth by inducing osteoblasts to make IGF-I (insulin- like growth factor-I) and inhibiting osteoclast generation.