Osteoblast response to titanium surface roughness and 1?,25-(OH)2D3 is mediated through the mitogen-activated protein kinase (MAPK) pathway

Abstract

When osteoblasts are cultured on surfaces of increasing microroughness, they exhibit decreases in proliferation, increases in differentiation and local factor production, and enhanced response to 1α,25(OH)₂D₃. The cells interact with surfaces through integrins, which signal by the same pathways used by 1α,25(OH)₂D₃, including protein kinase C via phospholipase C and protein kinase A via phospholipase A₂. This provides opportunities for crosstalk that may contribute to the synergistic effects of surface roughness and the vitamin D metabolite. Because these pathways converge at mitogen-activated protein kinase (MAPK), we tested the hypothesis that the extracellular signal-regulated kinase (ERK1/2) subclass of MAPKs mediates the effects of surface roughness and 1α,25(OH)₂D₃. MG63 osteoblast-like osteosarcoma cells were cultured on commercially pure Ti disks with various surface roughnesses: pretreatment (PT; 0.6 μm average roughness [Ra]), coarse grit-blasted and acid-etched (SLA; 4 μm RA), and titanium plasma-sprayed (TPS; 5.2-μm R_a). At confluence, cells were treated for 24 h with control media or media containing 10⁻⁷ M 1α,25(OH)₂D₃. One-half of the cultures received 1 μM or 10 μM PD98059, a specific inhibitor of the ERK family of MAPKs. PD98059 alone did not affect proliferation, osteocalcin production, or production of transforming growth factor-β1 or nitric oxide, regardless of the surface roughness. Alkaline phosphatase was reduced by the inhibition of the ERK family kinases on all surfaces to a comparable extent. However, when PD98059 was added to the cultures with 1α,25(OH)₂D₃, the effects of the seco-steroid were blocked, including the synergistic increases seen in MG63 cells cultured on SLA or TPS. These results indicate that ERK1/2 MAPK is required for the maintenance of alkaline phosphatase at control levels and that the effects of 1α,25(OH)₂D₃ are mediated by ERK1/2. However, the effects of surface roughness are not due to the ERK family of MAPKs. This suggests that alternative pathways may be used, including those mediated by other MAPK subclasses. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 56: 417–426, 2001