Inhibition of osteoclast bone resorption activity through osteoprotegerin-induced damage of the sealing zone

Abstract

Bone remodeling is dependent on the dynamic equilibrium between osteoclast-mediated bone resorption and osteoblast-mediated osteogenesis. The sealing zone is an osteoclast-specific cytoskeletal structure, the integrity of which is critical for osteoclast-mediated bone resorption. To date, studies have focused mainly on the osteoprotegerin (OPG)‑induced inhibition of osteoclast differentiation through the OPG/receptor activator of the nuclear factor kappa-B ligand (RANKL)/RANK system, which affects the bone resorption of osteoclasts. However, the effects of OPG on the sealing zone have not been reported to date. In this study, the formation of the sealing zone was observed by Hoffman modulation contrast (HMC) microscopy and confocal laser scanning microscopy. The effects of OPG on the existing sealing zone and osteoclast-mediated bone resorption activity, as well as the regulatory role of genes involved in the formation of the sealing zone were examined by immunofluorescence staining, HMC microscopy, quantitative reverse transcription polymerase chain reaction (RT-qPCR), western blot analysis and scanning electron microscopy. The sealing zone was formed on day 5, with belt-like protuberances at the cell edge and scattered distribution of cell nuclei, but no filopodia. The sealing zone was intact in the untreated control group. However, defects in the sealing zone were observed in the OPG-treated group (20 ng/ml) and the structure was absent in the groups treated with 40 and 80 ng/ml OPG. The podosomes showed a scattered or clustered distribution between the basal surface of the osteoclasts and the well surface. Furthermore, resorption lacunae were not detected in the 20 ng/ml OPG-treated group, indicating the loss of osteoclast-mediated bone resorption activity. Treatment with OPG resulted in a significant decrease in the expression of Arhgef8/Net1 and DOCK5 Rho guanine nucleotide exchange factors (RhoGEFs), 10 of 18 RhoGTPases (RhoA, RhoB, cdc42v1, cdc42v2, RhoU/Wrch1, RhoF/Rif, Rac2, RhoG, Rnd1 and RhoBTB1), ROCK1 and ROCK2. In conclusion, podosome distribution was affected by the OPG-induced inhibition of the expression of genes in the RhoGTPase signaling pathway. This resulted in damage to or destruction of the sealing zone, thus inhibiting osteoclast-mediated bone resorption activity.

Psoriatic cutaneous inflammation promotes human monocyte differentiation into active osteoclasts, facilitating bone damage

“…To date, studies have focused mainly on the OPG-induced inhibition of osteoclastogenesis through the RANKL/RANK system [37]. However, recently, Song et al [38] have demonstrated that OPG had directly affect osteoclastogenesis inhibiting the expression of critical genes involved in osteoclast maturation. Hence, we speculate that in our experiment in the absence of its ligand, OPG could explain its direct inhibitory function, acting in supplementation to OPG levels in IFN-γ stimulated-OC supernatant.…”

RhoV mediates apoptosis of RAW264.7 macrophages caused by osteoclast differentiation

“…OPG is also produced by cells of osteoblastic lineage, and is able to inhibit the differentiation of macrophages into osteoclasts (9,11). To verify the hypothesis that the differentiation of RAW264.7 macrophages caused their apoptosis, OPG was added into the RANKL+M-CSF induction treatment group in order to inhibit the differentiation of RAW264.7 macrophages.…”

“…Previous studies indicated that in the presence of receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF), osteoclasts are able to be formed by the differentiation of several monocyte/macrophage precursors (1,(6)(7)(8). Osteoclast differentiation and bone resorption is mainly regulated by osteoprotegerin (OPG)/RANKL/receptor activator of nuclear factor κB (RANK) system (9)(10)(11), in which RANKL and OPG are secreted by osteoblasts (4,12). RANKL binds to its receptor activator RANK in the osteoclast precursors, thereby inducing the differentiation of macrophages into osteoclasts.…”

Effects of Photobiomodulation on Root Resorption Induced by Orthodontic Tooth Movement and RANKL/OPG Expression in Rats

“…The results of OPG expression showed that PBM group had greater OPG expression on both sides of compression and tension compared to the conventional treatment group. OPG has been linked to the inhibition of osteoclastogenesis during root resorption through the OPG/RANKL/RANK pathway, damaging the sealing zone of osteoclasts or inducing apoptosis of osteoclasts and osteoclast precursor cells . However, Yu et al .…”