Promoting bone growth by endocrine factors and mechanostimulation.

Abstract

Regulation of bone mass is a complex process, involving many factors. It has earlier been proposed by Frost that mechanical load influences bone cells, and can enhace formation of bone mass. In this study we wanted to see which effect load has on osteoblasts, and whether different endocrine factors can influence these cells when applied alone or in combination with mechanical loading. NHO-4 cells were studied both undifferentiated and differentiated for 10 days. The cells were divided in tree groups and treated with adiponectin, leptin and serotonin respectively. Then the cells were loaded at 1G, 6G, 22G and 50G. Futher, cell medium was analysed using ELISA to measure ALP, OPG, OC, CD44, leptin, resistin, IL-6. Analysis of gene expression was also performed. Considering loading alone, our findings suggest that in undifferentiated cells there is an increase in bone markers when a moderate loading is applied, while the secretion of factors known to affect surrounding cells slightly decrease with increasing load. We also observed an increase in secretion of proteins (ALP, OC, OPG, CD44) and factors (resistin, IL-6) from undifferentiated cells when high mechanical loading was combined with leptin treatment. Combination of load and adiponectin gave also increase in IL-6, resistin, leptin, OPG in both differentiated and undifferentiated cells, and in addition on OC in the latter group, when treatments were combined with high mechanical loading. As far as we can conclude, leptin in combination with increased mechanical load has a positive effect on the secretion and expression of most of the bone parameters and adipokines we have measured in undifferentiated human osteoblasts. Resistin and adiponectin might also be important, but further studies are necessary to clarify their role.