The osteoclastogenesis is regulated by a complex signaling system between the pro-apoptotic factors (Bax-Cyclin E2-Cdk2) and the tumor necrosis factor family (RANKL-RANK-OPG). Extracorporeal Shock Waves Therapy (ESWT) have recently been used in orthopaedic treatments to induce bone repair, but their mechanisms of action are not sufficiently investigated. So we studied the effect of shock-waves on murine osteoblastic cells. Osteoblast cultures were subjected to a single shock-wave with combinations of low energy intensities (0.05mJ/mm2) and 500 number of shocks (impulses), whereas control cells received no treatment. We valued the cell viability quantifying the expressions of Bax and Opg by PCR. We found an immediate negative effect on cell viability, that occurs with an increase of Bax protein expression after 3 hours of treatment. After a longer time lapse a stimulatory effect on cell proliferation, as reflected by the increase of a G(1)-S phase marker, was observed. In fact, in the following 24, 48 and 72 hours after ESW treatment, we found a stronger association of Cyclin E2 and Cdk2, forming active cyclin E-Cdk2 kinase, compared to untreated cells at the same times. We further explored the molecular mechanism for the ESW induction of osteogenesis: by Real Time PCR an enhancement of Runx2 mRNA, evident 48 hours after the treatment, was found. A link between physical ESW and Runx2 activation has been already demonstrated. ESW-induced O2- production, followed by tyrosine kinase mediated ERK activation and Runx2 activation, resulted in osteogenic cell growth and maturation. Moreover, we analyzed the cytokines RANK-L and OPG osteoblast expression, involved in regulation of osteoclastogenesis. A decrease in RANK-L/OPG ratio was found, perhaps leading to a reduced osteoclastogenesis. The Shock waves have a repair action on bone and it can been explained by the regulation on osteoclastogenesis by the apoptoic pathway of BAX and OPG.
