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 differentiation and physiologic processes. Indeed, genetic-based studies over the past 5 years have revealed how osteoblast differentiation is controlled through growth and transcription factors. Likewise, the recent identification, using mutant mouse models, of a central component in the regulation of bone formation expands our understanding of the control of bone remodeling. This regulatory loop, which involves the hormone leptin, may help to explain the protective effect of obesity on bone mass in humans. In addition, it provides a novel physiologic concept that may shed light on the etiology of osteoporosis and help to identify new therapeutic targets.