Osteocyte physiology and response to fluid shear stress are impaired following exposure to cobalt and chromium: Implications for bone health following joint replacement

Abstract

The effects of metal ion exposure on osteocytes, the most abundant cell type in bone and responsible for coordinating bone remodeling, remain unclear. However, several studies have previously shown that exposure to cobalt (Co2+) and chromium (Cr3+), at concentrations equivalent to those found clinically, affect osteoblast and osteoclast survival and function. In this study, we tested the hypothesis that metal ions would similarly impair the normal physiology of osteocytes. The survival, dendritic morphology, and response to fluid shear stress of the mature osteocyte‐like cell‐line MLO‐Y4 following exposure to clinically relevant concentrations and combinations of Co and Cr ions were measured in 2D‐culture. Exposure of MLO‐Y4 cells to metal ions reduced cell number, increased dendrites per cell and increased dendrite length. We found that combinations of metal ions had a greater effect than the individual ions alone, and that Co2+ had a predominate effect on changes to cell numbers and dendrites. Combined metal ion exposure blunted the responses of the MLO‐Y4 cells to fluid shear stress, including reducing the intracellular calcium responses and modulation of genes for the osteocyte markers Cx43 and Gp38, and the signaling molecules RANKL and Dkk‐1. Finally, we demonstrated that in the late osteoblasts/early osteocytes cell line MLO‐A5 that Co2+ exposure had no effect on mineralization, but Cr3+ treatment inhibited mineralization in a dose‐dependent manner, without affecting cell viability. Taken together, these data indicate that metal exposure can directly affect osteocyte physiology, with potential implications for bone health including osseointegration of cementless components, and periprosthetic bone remodeling. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1716–1723, 2017.

Fluid Shear Stress Increases Osteocyte and Inhibits Osteoclasts via Downregulating Receptor-Activator of Nuclear Factor κB (RANK)/Osteoprotegerin Expression in Myeloma Microenvironment

“…These small molecules may transfer mechanical loading-induced signals via connexins, resulting in connexin upregulation, increased osteogenesis, and increased osteocyte differentiation [20]. Another possible mechanism via which fluid shear stress inhibits osteocyte apoptosis is that fluid flow may accelerate oxygen and nutrient supply to the osteocytes, increasing cell viability [21].…”

Differential Effect of Cobalt and Chromium Ions as Well as CoCr Particles on the Expression of Osteogenic Markers and Osteoblast Function

“…Cr 3+ ions, however, did not influence the gene expression and therefore most likely interact with the mineralization process directly. Shah et al showed comparable effects of cobalt and chromium on the mineralization of murine “osteoblast to osteocyte-like” cell line MLO-A5 [ 37 ]. The inhibition of mineralization by soluble Cr 3+ or on soluble CrPO 4 might be due to the binding of phosphate to Cr 3+ , thereby reducing the availability of the ionic form [ 23 ].…”

Fluid shear stress improves morphology, cytoskeleton architecture, viability, and regulates cytokine expression in a time‐dependent manner in MLO‐Y4 cells

“…Moreover, it has been shown that the gene expression in the Wnt/β‐catenin signaling pathway of MLO‐Y4 cells (e.g., Wnt3a and β‐catenin) was up‐regulated under the FSS stimulation (Santos et al, ; Huang et al, ). However, the gene expression of DKK1 (a critical negative regulator of the Wnt/β‐catenin pathway) of MLO‐Y4 cells was unaltered after FSS stimulation (Shah et al, ), although numerous in vivo studies have demonstrated that DKK1 expression of osteocytes was significantly suppressed under mechanical loading (Lara‐Castillo et al, ; Pflanz et al, ). It should be noted that most previous studies only investigated the expression of these cytokines of osteocytes in the gene level, and there is a lack of systematic study quantifying the expression of these cytokines in the protein level.…”