Abstract:

Objective　To explore the response of rat bone marrowmesenchymal stem cells (MSCs) and calvarial osteoblasts to mechanical strain and the consequent changes of cytoskeleton F-actin.Methods　Bone marrow MSCs and calvarial osteoblasts were isolated from SD rats and culturedin vitro. Mechanical stretchwas performed on passage 3 cells at 2 000μεfor 0, 2, 6 and 12 hours using four-point bending system. The response of cells and the distribution of F-actin were observed using fluorescent staining under laser scanning confocal microscope and the morphological parameters were quantified using image analysis software Laserpix.Results　Under mechanical stretch, the fluorescent staining decreased obviously at bothMSCs and osteoblasts, and F- actin filaments were rearranged and became tenuous, thinner, and abnormally distributed. The outline of nucleus became unclear and apoptotic changes were observed at some of both cells. Cellular size decreased more significantly inMSCs than in osteoblasts. Quantity analysis showed that total area of cells, total fluorescent density and green fluorescent density (F-actin) were all signifi- cantly decreased in MSCs(P<0·05 orP<0·01), and total fluorescent density, green fluorescent density and red fluorescent density (nuclei) did also in osteoblasts(P<0·05 orP<0·01).Conclusion　Mechanical stretch caused extensive response on both MSCs and osteoblasts which led to the rearrangement of F-actin filament and apoptosis in some of these cells. MSCs were more sensitive to mechanical strain than osteoblasts.

Key words: mesenchymal stem cells, osteoblasts, mechanical stretch, laser scanning confocal microscope