Urokinase-type plasminogen activator is activated in stratum corneum after barrier disruption.

The plasminogen/plasmin system in epidermis is thought to be the major protease involved in the delay of barrier recovery. However, little is known about the mechanism through which this system is activated. In order to clarify this mechanism, we first determined the distribution of proteolytic activity by using in situ zymography. As a result, plasminogen-activator activity was found to be present in the stratum corneum (SC) after barrier disruption. Next, SC subjected to repeated barrier disruption was collected to identify the protease. The protease was identified as urokinase-type plasminogen activator, because flybrinolytic activity of the collected SC was abolished by addition of anti-urokinase antibody. Urokinase activation in SC was confirmed by means of an in vitro assay, in which the precursor of urokinase (pro-uPA) became active after incubation with the insoluble component of SC homogenate. These findings indicated that urokinase-type plasminogen activator is activated in SC after barrier disruption and this activation might trigger the plasminogen/plasmin system in the epidermis.