Continuous Compressive Force Induces Differentiation of Osteoclasts with High Levels of Inorganic Dissolution

Abstract

Background Osteoclast precursor cells are constitutively differentiated into mature osteoclasts on bone tissues. We previously reported that the continuous stimulation of RAW264.7 precursor cells with compressive force induces the formation of multinucleated giant cells via receptor activator of nuclear factor κB (RANK)-RANK ligand (RANKL) signaling. Here, we examined the bone resorptive function of multinucleated osteoclasts induced by continuous compressive force. Material/Methods Cells were continuously stimulated with 0.3, 0.6, and 1.1 g/cm 2 compressive force created by increasing the amount of the culture solution in the presence of RANKL. Actin ring organization was evaluated by fluorescence microscopy. mRNA expression of genes encoding osteoclastic bone resorption-related enzymes was examined by quantitative real-time reverse transcription-polymerase chain reaction. Mineral resorption was evaluated using calcium phosphate-coated plates. Results Multinucleated osteoclast-like cells with actin rings were observed for all three magnitudes of compressive force, and the area of actin rings increased as a function of the applied force. Carbonic anhydrase II expression as well as calcium elution from the calcium phosphate plate was markedly higher after stimulation with 0.6 and 1.1 g/cm 2 force than 0.3 g/cm 2 . Matrix metalloproteinase-9 expression decreased and cathepsin K expression increased slightly by the continuous application of compressive force. Conclusions Our study demonstrated that multinucleated osteoclast-like cells induced by the stimulation of RAW264.7 cells with continuous compressive force exhibit high dissolution of the inorganic phase of bone by upregulating carbonic anhydrase II expression and actin ring formation. These findings improve our understanding of the role of mechanical load in bone remodeling.

Effects of compressive stress combined with mechanical vibration on osteoclastogenesis in RAW 264.7 cells

“…In vitro studies of osteoclast precursor cells have shown that continuous compressive force positively affects osteclastogenesis. 16,17 In contrast, the application of tensile force to preosteoclasts stimulated with RANKL decreased the number of osteoclasts. 18 In terms of vibratory stimuli, treatment of preosteoclast cells with 0.3 g at 45 Hz for 15 min/d significantly decreased the number of RANKL-induced TRAP-positive multinucleated cells (MNCs) and inhibited osteoclast formation.…”

Effects of continuous and released compressive force on osteoclastogenesis in vitro

“…In vitro studies have demonstrated the induction of osteoclast differentiation in response to generation of various types of compressive force, varied cellular responses have been observed in these models. 8 , 9 , 10 , 11 , 12 Weight loading is simple for mechanical loading model but physical cell damage and nutrient restriction from direct contact between weight-generating materials and cells are limitations. In order to prevent direct contact and assure the constant force distribution on the cell culture, an air-pump compressor to create air pressure is suggested.…”

“…Another study exert force by increasing the amount of culture medium to osteoclast precursor cells. 9 It is possible that the increased of nutrients in the environments. In this study, to address the limitations of existing models of compressive force, we developed a novel hydrostatic pressure-generated compressive model based on pestles and cylinders.…”

Substrate stiffness regulates the differentiation profile and functions of osteoclasts via cytoskeletal arrangement

“… 9 The mechanosensitive nature of bone cells and the stimulating effects of matrix stiffness on osteoblasts, osteocytes, and chondrocytes have been extensively studied. 10 , 11 , 12 Although osteoclast differentiation has been proven to be influenced by multiple mechanical stimuli, such as tension force, 13 microgravity, 14 fluid shear stress, 15 vibration, 16 and compressive forces, 17 the activity of osteoclasts in response to different degrees of microenvironmental stiffness remains unclear.…”