A 635-nm light-emitting diode (LED) therapy inhibits bone resorptive osteoclast formation by regulating the actin cytoskeleton.

Bone diseases such as osteoporosis are mainly caused by upregulated activity of osteoclasts. The present study was designed to examine the effects of light-emitting diode (LED) irradiation on the formation and activity of multinucleated osteoclasts, specifically "round-shaped" osteoclast cells (ROC) in different cell types derived from mouse. After 635-nm LED irradiation, the cell viability was evaluated by MTT assay. The amount of total tartrate-resistant acid phosphatase (TRAP) + osteoclast and the number of ROC cells were also estimated by TRAP solution assay and TRAP staining, respectively. Actin rings were stained with rhodamine-conjugated phalloidin, and resorption assay was performed by dentin slices. In addition, gene expression levels between the control and irradiation groups were evaluated by RT-PCR. In a morphological analysis, the formation of ROC was significantly inhibited by 635-nm LED irradiation in the different cell types. Actin rings were seen at cell peripheries in most ROC cells of the control group, but patches containing disorganized actin were found in the irradiation group. Both the number of ROCs and bone resorption activity were much lower in the irradiation group than in the control group. Also, the gene expression levels involved in actin ring formation such as integrin β3 and c-Src decreased in RT-PCR analysis. Overall, 635-nm LED therapy may play a pivotal role in regulating bone remodeling, and it may prove to be a valuable tool to prevent bone loss in osteoporosis and other resorptive bone diseases.