Mechanical stretching modulates growth direction and MMP-9 release in human keratinocyte monolayer

Cells within human skin are exposed to mechanical stretching that is considered a trigger stimulus for keratinocyte proliferation, while its effect on keratinocyte migration has been poorly investigate. In order to explore the effect of stretching on keratinocyte migration spontaneously immortalized human keratinocyte (HaCaT) monolayers seeded onto collagen I-coated silicon sheets were stimulated three times for 1 hour every 24 hours (total time = 72 hours) by mechanical stretching increasing substrate deformations (10%) applied both as static (0 Hz) and cyclic (0.17 Hz) uniaxial stretching. At the end of stimulations monolayer areas measured in both static and cyclic samples appeared reduced and strongly oriented in a direction perpendicular to the stress direction compared to unstimulated ones. Moreover during the mechanical stimulation period HaCaT monolayers strongly increased the release in the medium of matrix metalloproteinase 9 (MMP-9), a proteolytic enzyme necessary for keratinocyte migration.