Is There an Influence of Electrically Stimulated Osteoblasts on the Induction of Osteoclastogenesis?

Bone is a highly dynamic tissue characterized mainly by the interactions of osteoblasts and osteoclasts. When the healing ability of bone regeneration is disturbed, targeted biophysical stimulations such as electrical stimulation are applied. In this study the indirect effects of electrically stimulated human osteoblasts on osteoclastogenesis were investigated to better understand detailed cellular interactions. Therefore, two different cell developmental stages were examined: peripheral blood mononuclear cells (PBMCs) as precursors and pre-osteoclasts as differentiated cells. Previously, over a 21-day period, human osteoblasts were stimulated with a low-frequency alternating electric field. The supernatants were collected and used for an indirect co-culture of PBMCs and pre-osteoclasts. The cellular viability and the induction of differentiation and activity were analyzed. Further, the secretion of relevant osteoclastic markers was examined. Supernatants of 7 d and 14 d stimulated osteoblasts led to a decrease in the viability of PBMCs and an increased number of cells containing actin ring structures. Supernatants from osteoblasts stimulated over 7 d induced PBMC differentiation and pre-osteoclastic activation. Furthermore, pre-osteoclasts showed varying mRNA transcripts of MCP-1, ACP5, CA2, and CASP8 when cultivated with media from osteoblasts. Supernatants from day 21 did not influence PBMCs at all but increased the viability of pre-osteoclasts. We could show that different time points of stimulated osteoblasts have varying effects on the cells and that changes can be observed due to the differentiation stages of the cells. Through the effects of the indirect stimulation, it was possible to underline the importance of studying not only osteoblastic differentiation and mineralization behavior under electric stimulation but also analyzing changes in osteoclastogenesis and the activity of osteoclasts