Different Behavior of Human Osteoblast-Like Cells Isolated from Normal and Heterotopic Bone In Vitro

Abstract

In this study, a characterization of human bone-forming cells responsible for heterotopic ossification was carried out in vitro. The biological and biochemical cell characteristics of the heterotopic osteoblast-like (HOB) cells were compared with those of orthotopic osteoblast-like (OB) cells from normal bone and stromal bone marrow cells believed to contain a subpopulation of osteogenic precursor cells. We found that HOB's from the spongiosa of heterotopic ossification required less time until the beginning of migration and the achievement of confluence in vitro compared with OBs from femoral shaft spongiosa. The fraction of mitotically active cells assessed by a clonogenic assay was higher as well in HOB cells. The in vitro studies of mitogenesis and the efficiency of colony formation of osteogenic cells indicate that with increasing differentiation and relative age they become more dependent on growth factors in the medium, otherwise the morphology of osteoblast-like cells changes and they pass irreversibly into the postmitotic stage of the cell cycle. The activity of the alkaline phosphatase is distinctly higher in the HOB than in the OB cells, HOB cells exhibit a lower level of osteocalcin expression compared with OB cells. No significant difference was found between OB and HOB cells in the amount of procollagen of type I sequestered by the cells. After 30 days, HOB and OB cells formed a mineralized matrix on exposure to 2 mM beta-glycerophosphate. Since HOBs were isolated from heterotopic bone that had developed within 3-6 months after hip surgery, the differences in cellular behavior compared with OBs may be attributed to the relatively young age of HOB cells.

A comparative analysis of phenotype expression in human osteoblasts from heterotopic ossification and normal bone

“…In the present study, we have demonstrated that bone cells originating from HO express the osteoblast phenotypes type I collagen and alkaline phosphatase to a similar extent as osteoblasts originating from normal bone, relating these cells to the osteoblast phenotype. In accordance to this result, other studies have also found collagen expression and alkaline phosphatase expression to be similar in both cell culture types [11,12]. Mature osteoblasts exclusively produce type I collagen and only rudimentary amounts of other collagen types [11], indicating that cells from HO express the proteins characteristic of the osteoblast phenotype.…”

Combined Radiotherapy and Indomethacin for the Prevention of Heterotopic Ossification after Total Hip Arthroplasty

“…The action of RT lies in the suppression of the proliferation of mesenchymal cells and therefore prevents pluripotent mesenchymal cell differentiation into osteogenic progenitors [5,11,24]. In vitro studies have shown that there is almost no effect on mineralization and osteoinductivity in irradiated cells [38]. On the other hand, the inhibition of HO by indomethacin is probably due to a nonspecific suppression of the prostaglandin-induced inflammatory response which is present in the postoperative period [17], by inhibiting the prostaglandin synthesis mechanism [16,40] and a synchronous direct inhibition of the differentiation of mesenchymal cells into osteogenic cells [39,42].…”

Osteogenic Gene Expression Correlates With Development of Heterotopic Ossification in War Wounds

“…Studies suggest the rate of ectopic bone formation in combat-related injuries is substantially higher than prior estimates reported in civilian trauma populations [16,39]. Despite several studies investigating systemic factors and the in vitro measurement of osteoblastic activity of cells from heterotopic bone [2,27,45], the biological mechanisms responsible for HO as a result of traumatic injury have not been defined.…”