The osteoblast: A sophisticated fibroblast under central surveillance

The study of the biology of osteoblasts, or bone-forming cells, illustrates how mammalian genetics has profoundly modified our understanding of cell d ifferentiation and physiologic processes. Indeed, genetic-based studies ove r the past 5 years have revealed how osteoblast differentiation is controll ed through growth and transcription factors. Likewise, the recent identific ation, using mutant mouse models, of a central component in the regulation of bone formation expands our understanding of the control of bone remodeli ng. This regulatory Loop, which involves the hormone Leptin, may help to ex plain the protective effect of obesity on bone mass in humans. In addition, it provides a novel physiologic concept that may shed Light on the etiolog y of osteoporosis and help to identify new therapeutic targets.