Effects of mechanical strain magnitude on formation and differentiation of osteoclasts

Abstract

Objective To study the effects of early mechanical strain magnitude on formation and differentiation of osteoclasts. Methods RAW 264.7 cells induced by macrophage colony-stimulating factors and osteoclast differentiation factors were subjected to 0, 1 000, 1 500, 2 000, 2 500 and 5 000 μe mechanical straining for three days. The morphological changes, number of osteoclasts and proliferation of precursor cells were determined at day 7. The activity of the tartrate-reaistant acid phosphatase (TRAP) in the culture medium was detected at days 4 and 7. Results The number of osteoclasts was decreased in 2 500 μe group, while it was increased in 5 000 μe group. The proliferation of precursor cells was increased in 2 000 and 2 500 μe group, while it was decreased significantly in 5 000 μe group. There was no significant difference in the number of osteoclasts and proliferation of precursor cells among 1 000 μe group, 1 500 μe group and 0 μe group. The activity of TRAP was decreased in 1 000, 1 500, 2 000, 2500 and 5 000 μe groups at days 4 and 7 when compared with μe group. Conclusions Early mechanical straining plays a direct role in formation and differentiation of osteoclasts. The high strain magnitude within physiological load inhibits osteoclast formation, while high strain magnitude beyond physiological load stimulates osteoclast formation. Low strain magnitude has nearly no impact on formation of osteoclasts. Early mechanical straining may inhibit differentiation of osteoclasts. Key words: Osteoporosis; Osteoclasts; Mechanical strain