Slight changes in the mechanical stimulation affects osteoblast- and osteoclast-like cells in co-culture.
BACKGROUND
Osteoblast- and osteoclast-like cells are responsible for coordinated bone maintenance, illustrated by a balanced formation and resorption. Both parameters appear to be influenced by mechanical constrains acting on each of these cell types individually. We hypothesized that the interactions between both cell types are also influenced by mechanical stimulation.


METHODS
Co-cultures of osteoblast- and osteoclast-like cells were stimulated with 1,100 µstrain, 0.1 or 0.3 Hz for 1-5 min/day over 5 days. Two different setups depending on the differentiation of the osteoclast-like cells were used: i) differentiation assay for the fusion of pre-osteoclasts to osteoclasts, ii) resorption assay to determine the activity level of osteoclast-like cells.


RESULTS
In the differentiation assay (co-culture of osteoblasts with unfused osteoclast precursor cells) the mechanical stimulation resulted in a significant decrease of collagen-1 and osteocalcin produced by osteoblast-like cells. Significantly more TRAP-iso5b was measured after stimulation for 3 min with 0.1 Hz, indicating enhanced osteoclastogenesis. In the resorption assay (co-culture of osteoblasts with fused osteoclasts) the stimulation for 3 min with 0.3 Hz significantly increased the resorption activity of osteoclasts measured by the pit formation and the collagen resorption. The same mechanical stimulation resulted in an increased collagen-1 production by the osteoblast-like cells. The ratio of RANKL/OPG was not different between the groups.


CONCLUSIONS
These findings demonstrate that already small changes in duration or frequency of mechanical stimulation had significant consequences for the behavior of osteoblast- and osteoclast-like cells in co-culture, which partially depend on the differentiation status of the osteoclast-like cells.
Julius Wolff Institute, Berlin-Brandenburg Center for Regenerative Therapies, Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin, Germany.
Anke
A
Kadow-Romacker
Julius Wolff Institute, Berlin-Brandenburg Center for Regenerative Therapies, Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin, Germany.
Georg N
GN
Duda
Julius Wolff Institute, Berlin-Brandenburg Center for Regenerative Therapies, Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin, Germany.
Nicole
N
Bormann
Department of Orthopedic and Trauma Surgery, University of Heidelberg, Germany.
Gerhard
G
Schmidmaier
Julius Wolff Institute, Berlin-Brandenburg Center for Regenerative Therapies, Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin, Germany.
Britt
B
Wildemann
Co-culture; Differentiation; Mechanical stimulation; Osteoblast-like cells; Osteoclast-like cells