Cowles E A, Brailey L L, Gronowicz G A
Department of Orthopaedics, MC-1110, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
J Biomed Mater Res. 2000 Dec 15;52(4):725-37. doi: 10.1002/1097-4636(20001215)52:4<725::aid-jbm18>3.0.co;2-o.
Since osteoblast proliferation is critical for bone development, the effect of bone extracellular matrix (ECM) proteins on osteoblast signaling and proliferation in serum-free medium was investigated. Proliferation was highest in primary rat calvarial osteoblasts cells grown on fibronectin but less on type I collagen; osteonectin and poly-L-lysine did not support early proliferation. Fibronectin and type I collagen binding requires integrins, whereas cell adhesion to osteonectin or poly-L-lysine does not involve integrins. Therefore, the role of integrins in osteoblast signaling, leading to the induction of AP-1 transcription factors (c-fos and c-jun) which are important in cell proliferation, was studied. c-fos and c-jun message levels were increased at 60 min in osteoblasts plated onto fibronectin or collagen, but not in cells on osteonectin or poly-L-lysine. Protein synthesis was not required for c-fos mRNA expression; however, kinase activity was necessary for c-fos induction. In cells plated onto fibronectin, c-fos mRNA levels were controlled by protein kinase C and phosphotyrosine kinase signaling pathways. In contrast, c-fos levels in collagen-adhering cells may involve protein kinase A. The signaling pathway involving the phosphorylation of focal adhesion kinase and mitogen-activated kinases was also shown to be transiently increased in osteoblasts on fibronectin and type I collagen, but not in cells on poly-L-lysine. These results demonstrate that osteoblast binding to the extracellular matrix through integrins induces c-fos and c-jun, and that both fibronectin and collagen affect these AP-1 transcription factors through protein kinase-sensitive pathways. Thus, osteoblast proliferation is modulated differentially by specific ECM components.
由于成骨细胞增殖对骨骼发育至关重要，因此研究了骨细胞外基质（ECM）蛋白在无血清培养基中对成骨细胞信号传导和增殖的影响。在纤连蛋白上生长的原代大鼠颅骨成骨细胞中增殖最高，而在I型胶原上生长的细胞增殖较少；骨连接蛋白和聚-L-赖氨酸不支持早期增殖。纤连蛋白和I型胶原的结合需要整合素，而细胞与骨连接蛋白或聚-L-赖氨酸的粘附不涉及整合素。因此，研究了整合素在成骨细胞信号传导中的作用，该信号传导导致对细胞增殖很重要的AP-1转录因子（c-fos和c-jun）的诱导。接种到纤连蛋白或胶原上的成骨细胞中，c-fos和c-jun的信息水平在60分钟时升高，但接种到骨连接蛋白或聚-L-赖氨酸上的细胞中则没有升高。c-fos mRNA表达不需要蛋白质合成；然而，激酶活性是c-fos诱导所必需的。在接种到纤连蛋白上的细胞中，c-fos mRNA水平受蛋白激酶C和磷酸酪氨酸激酶信号通路控制。相反，胶原粘附细胞中的c-fos水平可能涉及蛋白激酶A。涉及粘着斑激酶和丝裂原活化激酶磷酸化的信号通路在纤连蛋白和I型胶原上的成骨细胞中也显示短暂增加，但在聚-L-赖氨酸上的细胞中没有增加。这些结果表明，成骨细胞通过整合素与细胞外基质结合可诱导c-fos和c-jun，并且纤连蛋白和胶原都通过蛋白激酶敏感途径影响这些AP-1转录因子。因此，特定的ECM成分对成骨细胞增殖的调节存在差异。
