Osteoblast response to titanium surface roughness and 1 alpha,25-(OH)(2)D-3 is mediated through the mitogen-activated protein kinase (MAPK) pathway

When osteoblasts are cultured on surfaces of increasing microroughness, the y exhibit decreases in proliferation, increases in differentiation and loca l factor production, and enhanced response to 1 alpha ,25(OH)(2)D-3. The ce lls interact with surfaces through integrins, which signal by the same path ways used by 1 alpha ,25(OH)(2)D-3, including protein kinase C via phosphol ipase C and protein kinase A via phospholipase A(2). This provides opportun ities for crosstalk that may contribute to the synergistic effects of surfa ce roughness and the vitamin D metabolite. Because these pathways converge at mitogen-activated protein kinase (MAPK), we tested the hypothesis that t he extracellular signal-regulated kinase (ERK1/2) subclass of MAPKs mediate s the effects of surface roughness and 1 alpha ,25(OH)(2)D-3. MG63 osteobla st-like osteosarcoma cells were cultured on commercially pure Ti disks with various surface roughnesses: pretreatment (PT; 0.6 mum average roughness [ Ra]), coarse grit-blasted and acid-etched (SLA; 4 mum RA), and titanium pla sma-sprayed (TPS; 5.2-mum R-a). At confluence, cells were treated for 24 h with control media or media containing 10(-7) M 1 alpha ,25(OH)(2)D-3. One- half of the cultures received 1 muM or 10 muM PD98059, a specific inhibitor of the ERK family of MAPKs. PD98059 alone did not affect proliferation, os teocalcin production, or production of transforming growth factor-pi or nit ric oxide, regardless of the surface roughness. Alkaline phosphatase was re duced by the inhibition of the ERK family kinases on all surfaces to a comp arable extent. However, when PD98059 was added to the cultures with 1 alpha ,25(OH)(2)D-3, the effects of the see-steroid were blocked, including the synergistic increases seen in MG63 cells cultured on SLA or TPS. These resu lts indicate that ERK1/2 MAPK is required for the maintenance of alkaline p hosphatase at control levels and that the effects of 1 alpha ,25(OH)(2)D-3 are mediated by ERK1/2. However, the effects of surface roughness are not d ue to the ERK family of MAPKs. This suggests that alternative pathways may be used, including those mediated by other MAPK subclasses. (C) 2001 John W iley & Sons, Inc.