Background/Aims: There is an urgent need to identify the molecular factors involved in osteoblast proliferation and differentiation in order to improve bone formation and treat bone disease. Recent studies demonstrate that many ‘axon guidance’ molecules play important roles in the development and remodeling of bone through their actions regulating osteoblast or osteoclast differentiation. The expressions and roles in bone tissue of the neuron guidance molecules slit and robo have not been reported previously. The objective of the current study is to investigate the expression and the roles of slit and robo in osteoblastic cells. Methods: The mRNAs slit2 and robo were detected in primary cell lines during their osteoblastic differentiation. The role of slit2 was studied using the recombinant proteins slit2 and hemagglutinin (HA)-roboN by transfecting the 293 cells. Results: The data indicated that the mRNAs of slit2, robo1 and robo2 were expressed during the osteoblastic differentiation of rat osteoblasts (calvarial osteoblasts derived from newborn rats), the nontransformed preosteogenic cell line MC3T3-E1, rat marrow stromal cells and the murine mesenchymal progenitor cell line C3H10T1/2. The exogenous slit2 protein inhibited the differentiation of rat osteoblasts and MC3T3-E1. Furthermore, the osteoblastic differentiation was improved when the endogenous slits were antagonized by recombinant HA-roboN, which is the extracellular domain of the rat robo1 protein. The inhibition of slit2 in osteogenic differentiation was independent of the RhoA/ROCK pathway. Conclusion: Slit2 plays a role in regulating in vitro osteoblast differentiation. This has opened a new avenue to understand the molecular events involved in the osteoblastic differentiation.

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