Role of Connexin43 in Osteoblast Response to Physical Load

Abstract

Gap junctions are hexameric transmembrane channels formed by connexins, and are responsible for direct cell-to-cell communication. The most abundant gap junction protein in bone is connexin43 (Cx43), although connexin45 (Cx45) is also expressed. In the present study, we tested the hypothesis that bone cell responses to mechanical stimulation are dependent on the type of gap junction communication provided by Cx43 in vitro and in an in vivo model of physical load. Application of cyclic stretch to calvaria osteoblasts results in a modest but detectable increase in PGE2 levels, and the amount of PGE2 produced was lower in cells isolated from Cx43 null mice. Mice with an osteoblast-specific deletion of the Cx43 gene were subjected to an in vivo four-point bending protocol on the tibia. This resulted in fast and exuberant formation of woven bone at the region directly below the loading fulcrum in both osteoblast Cx43-deleted and wild-type mice. However, indirect measurement of endosteal bone apposition suggested a less pronounced effect of physical load in Cx43-deficient than in wild-type mice. Taken together, these results indicate that deficiency of Cx43 in osteoblasts attenuates but does not abolish anabolic responses to mechanical strain.

Response of a Preosteoblastic Cell Line to Cyclic Tensile Stress Conditioning and Growth Factors for Bone Tissue Engineering

“…3,6,7 This bioreactor has applied 5%-10% elongation with 0.2-1 Hz frequency to 3D scaffolds including polyurethane nanofibrous scaffolds, 8 and fibrin, 9 and collagen gels. 10 Tensile stress of 3%-20% magnitude modulated expression of bone-related molecules such as collagen, 7,11 osteocalcin (OCN), 1,7 osteopontin (OPN), 1,7 matrix metalloproteinase-13 (MMP-13), 12 osteoprotegerin (OPG), 6 prostaglandin E 2 (PGE 2 ), 13 cyclooxygenase-2 (COX-2), 14 vascular endothelial growth factor (VEGF), 1,15 and transforming growth factor-b1 (TGF-b1). 16 Other external stimulating factors for bone regeneration are osteoinductive growth factors (GFs) such as TGF, bone morphogenetic protein (BMP), and platelet-derived GF.…”

Stem Cell-Based Tissue Engineering for Bone Repair

“…Many studies involving mesenchymal stem cells have shown that biaxial strain promoted osteogenic differentiation [51,53]. Larger strains seemed to cause differentiated cells to de-differentiate and proliferate, while guiding undifferentiated cells to an osteogenic state [51,53,54].…”

“…For the study of highly specific research questions about the healing process of bone, in-vitro models are very relevant [51,53,54]. Most of the progress in these experiments stem from examining the mechanical sensitivity of bone healing in 2D cell culture systems [51,53].…”

“…Fluid shear stress has also been applied in 2D cell culture systems [51,53,54]. Most of these experiments used parallel plate chambers to apply the mechanical stimulus [51,53].…”

“…The microtubule network in osteoblasts is also thought to be involved, where substrate deformation due to mechanical stress and fluid flow are thought to be linked to the response of osteoblasts in the healing process of bone [51,53,54]. Other in-vitro studies in 2D cell culture systems using cell poking, twisting, or pipette aspiration as the form of mechanical stimulation have provided valuable insight into the mechanical behavior of bone cells, but given the form of the mechanical stimulation, are harder to relate directly to the mechanical environment experienced by bone cells in-vivo [51,53,54].…”