Cyclic stretching promotes collagen synthesis and affects F-actin distribution in rat mesenchymal stem cells

Recent studies have shown effects of mechanical environment on bone marrow mesenchymal stem cells (BMSC). In order to examine how BMSC and their cytoskeleton respond to mechanical stimulation, we investigated their collagen synthesis and F-actin expression. Rat BMSC were harvested from adult rats and cultured to passage 4. Then the cells were seeded onto a silicone membrane loaded with an uniaxial cyclic stretching (10%, 1 Hz) during 3, 6, 12, 24 and 36 h. The levels of collagen type I and III before and after stretching were analyzed by immunocytochemistry, and the F-actin in cytoplasm was observed by confocal microscopy. Immunocytochemistry results showed that the stretching enhanced the synthesis of collagen types I and III in BMSC after 24 h stimulation. However, a decrease in fluorescence density of F-actin was observed after the stretching in a time dependent manner. In addition, the F-actin filaments seemed much thinner than those of static cells. These results indicated that the cyclic stretching favored the synthesis of collagen types I and III, but decreased the amount of F-actin in the BMSC.