TGF-beta and PKC-signaling Regulate Surface-dependent Osteoprotegerin Production by Osteoblasts

Objective: Surface roughness and surface free energy are two important factors that regulate cell responses to biomaterials. Osteoblasts grown on surfaces with rough microtopographies enhance osseointegration by producing local factors that promote osteogenesis and reduce osteoclastic bone resorption, like TGF-ß1 and osteoprotegerin (OPG). The object of this study was to examine the mechanisms involved in mediating surface dependent effects on OPG production. Methods: Titanium disks were manufactured to present three different surfaces: smooth pretreatment surfaces (PT, Ra<0.02 µm), sandblasted/acid etched surfaces (SLA, Ra=3-4µm) and SLA surfaced modified to have high surface energy (modSLA). Human osteoblast-like MG63 cells were cultured on these substrates and regulation of OPG production by via TGF-ß1 and PKC signaling pathways determined using specific inhibitors. Results: Osteoblasts grown on SLA and modSLA produced increased levels of OPG and active and latent TGF-ß1 compared to cultures grown on PT. PKC activity was also increased. Exogenous TGF-ß1 increased OPG protein on all surfaces examined and addition of blocking antibody or soluble receptor against TGF-ß1 inhibited OPG production to a similar extent on all surfaces. Inhibition of PKC reduced OPG levels, but only on the SLA and modSLA surfaces. Conclusion: These results indicate that both signaling pathways are involved in OPG production but the surface-specific increases in OPG are mediated by the PKC pathway only. These results suggest that OPG production is downstream of TGF-ß1 and that osseointegration is controlled by surface roughness through PKC-dependent production of OPG. Supported by NIH AR052102, ITI Foundation and Institut Straumann.