The heterogeneity of the osteoblast phenotype

Developmentally, anatomically and histologically, bones are not all the sam e. A number of studies over several years has raised the issue of osteoblas t heterogeneity. These include observations on the diverse behavior of clon al cell lines from both tumor and normal osteogenic tissue, on the heteroge neous occurrence of disease in different parts of the skeleton, and on the response of different parts of the skeleton to therapeutic interventions. M ore recent observations on the biochemical make up of different bones and d ifferent regions of bones and on the molecular profiles of osteoblasts asso ciated with different skeletal sites are giving new insights. The accumulat ing evidence indicates that osteoblasts in different maturational states, i n different environments, and in different microenvironments, express diver se gene repertoires. The diversity extends to expression of bone matrix mol ecules, transcription factors, hormones and cytokines, and their receptors. The data support the view that there is not a single unique phenotype char acterizing all osteoblasts, but rather that different expressed gene repert oires are associated with distinct osteoblast subpopulations and that this molecular diversity may reflect a need for functional diversity in osteobla sts engaged in different activities.