Effects of mechanical vibration on cell morphology, proliferation, apoptosis, and cytokine expression/secretion in osteocyte‐like MLO‐Y4 cells exposed to high glucose

Abstract

Diabetic patients exhibit significant bone deterioration. Our recent findings demonstrate that mechanical vibration is capable of resisting diabetic bone loss, whereas the relevant mechanism remains unclear. We herein examined the effects of mechanical vibration on the activities and functions of osteocytes (the most abundant and well‐recognized mechanosensitive cells in the bone) exposed to high glucose (HG). The osteocytic MLO‐Y4 cells were incubated with 50 mM HG for 24 h, and then stimulated with 1 h/day mechanical vibration (0.5 g, 45 Hz) for 3 days. We found that mechanical vibration significantly increased the proliferation and viability of MLO‐Y4 cells under the HG environment via the MTT, BrdU, and Cell Viability Analyzer assays. The apoptosis detection showed that HG‐induced apoptosis in MLO‐Y4 cells was inhibited by mechanical vibration. Moreover, increased cellular area, microfilament density, and anisotropy in HG‐incubated MLO‐Y4 cells were observed after mechanical vibration via the F‐actin fluorescence staining. The real‐time polymerase chain reaction and western blotting results demonstrated that mechanical vibration significantly upregulated the gene and protein expression of Wnt3a, β‐catenin, and osteoprotegerin (OPG) and decreased the sclerostin, DKK1, and receptor activator for nuclear factor‐κB ligand (RANKL) expression in osteocytes exposed to HG. The enzyme‐linked immunosorbent assay assays showed that mechanical vibration promoted the secretion of prostaglandin E2 and OPG, and inhibited the secretion of tumor necrosis factor‐α and RANKL in the supernatant of HG‐treated MLO‐Y4 cells. Together, this study demonstrates that mechanical vibration improves osteocytic architecture and viability, and regulates cytokine expression and secretion in the HG environment, and implies the potential great contribution of the modulation of osteocytic activities in resisting diabetic osteopenia/osteoporosis by mechanical vibration.

Possible Mechanisms for the Effects of Sound Vibration on Human Health

“…They also noted that the anabolic effect of mechanical stimulation was enhanced with the incorporation of resting period between loadings. These findings were replicated by Sun et al (2019) who showed that MLO-Y4 osteocyte like cells stimulated by 45 Hz at 0.5 g promoted the secretion of prostaglandin E 2 and OPG, and inhibited the secretion of tumor necrosis factor-α and RANKL [ 212 ]. Tanaka et al (2003) found similar results testing osteoblasts in vitro with vibration [ 213 ].…”

Radiotherapy-induced bone deterioration is exacerbated in diabetic rats treated with streptozotocin

“…More importantly, osteocytes are found to be a powerful mechanosensor and mechanotransducer, which can orchestrate bone remodeling by the secretion of cytokines though their long dendritic processes to regulate osteoblast and osteoclast activities (e.g., sclerostin and RANKL) (37). Several previous studies have found that high glucose exposure decreases osteocyte viability and increases sclerostin expression (a negative regulator of bone formation) (38,39). Similarly, radiation has also been reported to impair osteocyte survival in rodents (40).…”

Effects of Osteocyte Shape on Fluid Flow and Fluid Shear Stress of the Loaded Bone

“…The pore pressure gradient [ 2 , 3 ], solute transport [ 4 , 5 ], and fluid shear stress generated by the fluid flow are considered to be significant biomedical signals for osteocyte mechanotransduction in situ [ 6 – 8 ]. Osteocytes are the most sensitive bone cell type that are considered as mechanosensors within bone that can sense mechanical stimulations and transduce them into biochemical signals [ 9 ], thereby regulating bone remodeling [ 10 – 12 ]; however, whether and how these factors generated by the fluid flow as a flow sensor to activate the native osteocyte remains unclear [ 13 ]. Strain amplification effect on osteocyte membrane may produce a less osteogenic than response than fluid flow [ 14 ], and some studies have suggested that the fluid flow shears the osteocyte membranes or induces cytoskeleton deformation to elicit biochemical responses [ 1 , 6 , 8 , 15 ].…”