Effect of different frequencies of tensile strain on human dermal fibroblast proliferation and survival.

The aim of this study is to compare the effect of a high-frequency repetitive (HF) stretch or an intermittent (I) stretch on the cell proliferation and survival of human dermal fibroblasts and to determine the activation of any relevant signal pathways. Cultured human dermal fibroblasts were exposed to either HF or I stretch. Cell number was measured by counting, while DNA synthesis was assessed by 5-bromo-2'-deoxyuridine (BrdU) staining and apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. To investigate the potential mechanisms of repetitive strain on the proliferation and survival of fibroblasts, the activation of relevant transduction pathways, such as p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK)1/2, AKT, and BAD, was assessed by Western blot. In addition, the effect of inhibition of these pathways on the fibroblast response was also studied. After either HF or I stretch for 7 days, fibroblast number was significantly decreased and there were less BrdU-positive cells. The numbers of apoptotic and/or necrotic fibroblasts were not affected. p38 MAPK and ERK1/2 were significantly activated after HF stretch, but AKT and BAD were significantly activated after I stretch. The inhibitors of p38 MAPK and MAPK/ERK kinase as well as dominant-negative AKT reduced cell number after both HF and I stretch but these pathways were not critical for the stretch-induced decrease in cell number.