[Study of bone remodeling mechanism induced by mechanical stress. Differentiation of osteoclasts induced by compressive force in newborn rat cultured long bone].

Abstract

The purpose of this investigation was to reveal the mechanism of differentiation of osteoclast (OC) induced by mechanical stress in long bone cultivation of new born rats. A long bone was loaded with 30 gf of continuous compressive force and cultured for 5 days in CO2 incubator. Numbers of OC increased in the long bone were counted after H-E staining and compared with the control. The study was dealt with the effects of recombinant tumor necrosis factor alpha (rTNF alpha), recombinant interleukin-1 beta (rIL-1 beta), prostaglandin E2 (PGE2) and the co-cultivation of osteoblast (OB) originated from new born rat calvariae, as to differentiation of OC. Since the bone remodeling was interacted with OB and bone marrow (BM) cells, the activity of alkaline phosphatase (ALPase) was also investigated for OB in co-cultivation with BM cells originated from new born rat long bones. In the region of diaphysis of a long bone loaded with compressive force, the bend of trabecular bones was noticed after 3 days incubation. Also, the enrichment of monocyte-macrophage (Mo-M phi) lineage cells was noticed along the trabecular bones. After 5 days incubation, the increase of the number of OC was specifically recognized. The increase of the number of OC was shown in medullary cavity of the long bone by addition of rTNF alpha to the culture medium, but any synergistic effect was not shown with the treatment of rTNF alpha and compressive force to the increase of the number of OC. Furthermore, the increase of the number of OC induced by compressive force did not suppressed by addition of anti-TNF serum. Under the treatment of rIL-1 beta or PGE2, OC slightly increased in the long bone when loaded by compressive force, but the treatment of indomethacin did not suppress it completely. However, the increase of OC in the long bone loaded by compressive force was clearly inhibited in co-cultivation with OB. On the other hand, the activity of ALPase of OB was markedly abated in co-cultivation with BM cells. These results indicated that the mechanism of differentiation of OC induced by mechanical stress was different from that induced by the general inflammation. Results also indicated that it was controlled mainly by the factor(s) or interaction between BM cells and OB and was associated with Mo-M phi lineage cells.(ABSTRACT TRUNCATED AT 400 WORDS)