The effect of different frequencies of stretch on human dermal keratinocyte proliferation and survival.

The effects of cyclic stretch on mitogen-activated protein kinase (MAPK) and apoptosis in keratinocytes are not well understood. The aim of this study is to compare the effect of high frequency repetitive (HF) stretch to intermittent (I) stretch on human dermal keratinocytes proliferation and survival. Cultured human dermal keratinocytes were exposed to either repetitive HF or I stretch. Cell number was measured by coulter counter, DNA synthesis was assessed by BrdU staining, and apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. The activation of p38 MAPK, ERK 1/2, and AKT was assessed by immunoblotting. p38 MAPK, ERK 1/2, and AKT exhibited no change after HF stretch, while AKT and Homo sapiens BCL-2-antagonist of cell death (BAD) were significantly activated after I stretch. After experiencing I stretch for 2 d, keratinocyte proliferation rates were significantly decreased. This decrease was most likely not due to apoptosis as TUNEL-positive cells only increased for cells treated with an AKT inhibitor.