Objective To observe the role of the Hedgehog（Hh） genes in the proliferation of osteoblasts upon mechanical tensile strains. Methods Primary osteoblasts harvested from newborn rat calvarial bone were subjected to 3% and 6% elongation of tensile stretches using Flexcell 4000TM strain unit. The cultures were also treated with either recombinant N-terminals Sonic Hedgehog（N-Shh） or cyclopamine（cy）, a Hh inhibitor or gadolinium（GdCl3 ） , an inhibitor of stretch-activated channels. The proliferation of osteoblasts was quantified by cell counting, methyl thiazolyl tetrazolium（MTT） and cell cycle detection via flow cytometry. Statistical analysis was performed using SAS 8.0 software package. Results The tensile strain, especially under 6% elongation, promoted osteoblast proliferation. Stretching force could also promote the proliferation even when the cells were treated with cy, but this effect was suppressed by GdCl3. Conclusion The induced proliferation of osteoblasts by mechanical stretched is mediated at least in part by Indian Hedgehog（Ihh） signaling.
