In vitro differentiation potential of a new human osteosarcoma cell line (HOS 58)

Cultured rodent osteoblastic cells reiterate the phenotypic maturation of osteoblasts seen in vivo. Under appropriate culture conditions this maturation is a stepwise sequence of phenotypic changes culminating in the production of a mineralised matrix. Although individual components of the osteoblast phenotype are apparent in transformed osteosarcoma cell lines, the co-ordination of the maturation sequence appears to be compromised. Because to date no comparable human cell differentiation system has been developed we investigated the recently introduced HOS 58 osteosarcoma cell line up to 3 months in culture. Proliferation, the secretion of osteoblast specific proteins, gene expression and mineralisation were analysed at different time points. Low-density HOS 58 cultures exhibit rapid proliferation and high levels of c-myc, collagen type I and osteopontin mRNAs. This phenotypic stage was maximum between the 4th and 5th days of culture. As cell density increased expression of these genes declined and by day 14 the predominant mRNAs was alkaline phosphatase. Osteocalcin secretion was detected after confluence at an increasing level. In the presence of ascorbate and beta-glycerophosphate the production of alkaline phosphatase and collagen type I increased coincident with the elaboration of a Von Kossa staining matrix. Nevertheless no proper mineralisation of the collagenous matrix was detectable by electron microscopy. Hence, the human osteosarcoma cell line HOS 58 expressed a rather differentiated phenotype with further maturation during a culture period of 21 days. We conclude that the developmental sequence exhibited by the HOS 58 human osteosarcoma cell line is comparable to that described for primary rat osteoblasts. However, in detailed analysis considerable differences to other species are evident. Further evaluation of the HOS 58 system and comparison to other human osteoblast cell lines will be necessary to establish the most appropriate differentiation model for human bone cell cultures.