MARROW STROMA-DERIVED OSTEOGENIC CLONAL CELL-LINES - PUTATIVE STAGES IN OSTEOBLASTIC DIFFERENTIATION

This report documents characterization of five osteogenic cell subpopu lations of bone marrow stroma. The clonally derived cell lines were is olated from the parental line MBA-15 known to express osteoblastic-ass ociated features in vitro and to form bone in vivo. The latter, presum ably ''arrested'' at a particular stage along the osteogenic lineage, are useful models to study the processes involved in the differentiati on of bone forming cells. The clones differ in their morphology, proli feration rate, quantities and distribution of extracellular matrix pro teins, levels of alkaline phosphatase activity and activation of adeny late cyclase by parathyroid hormone and/or prostaglandin E. These prop erties have been retained during prolonged growth and subculturing thr ough many passages. MBA-1 5.4 is a presumptive preosteoblast with a fi broblast-like appearance; it proliferates rapidly, synthesizes equal a mounts of collagen and noncollagenous proteins, and produces constitut ively low levels of alkaline phosphatase. This clone has PGE2-stimulat ed adenylate cyclase activity and a very low constitutive response to PTH. On the other hand, MBA-15.6 has a large polygonal morphology with limited proliferative potential, synthesizes twice as much noncollage nous proteins as collagen, has high alkaline phosphatase activity, and responds strongly to PTH. The characteristics of the other clones pla ce them between these two categories. The effects of 10(-7) M dexameth asone or 10(-12)-10(-8) M 1,25 dihydroxyvitamin D3 on growth and diffe rentiation further strengthen the variance between these clones. The d ifferent in vitro characteristics of the various clones were directly reflected in their bone formation ability in vivo. When transplanted u nder the renal capsule, MBA-1 5.33 formed a thick fibrous tissue, MBA- 1 5.4 formed small foci of bone, and MBA-15.6 formed massive woven bon e at the same period of time.