Activography reveals aberrant proteolysis in desquamating diseases of differing backgrounds.

The role of epidermal proteolysis in overdesquamation was revealed in Netherton syndrome, a rare ichthyosis due to genetic deficiency of the LEKTI inhibitor of serine proteases. Recently, we developed activography, a new histochemical method, to spatially localize and semiquantitatively assess proteolytic activities using activity-based probes. Activography provides specificity and versatility compared to in situ zymography, the only available method to determine enzymatic activities in tissue biopsies. Here, activography was validated in skin biopsies obtained from an array of distinct disorders and compared with in situ zymography. Activography provides a methodological advancement due to its simplicity and specificity and can be readily adapted as a routine diagnostic assay. Interestingly, the levels of epidermal proteolysis correlated with the degree of desquamation independent of skin pathology. Thus, deregulated epidermal proteolysis likely represents a universal mechanism underlying aberrant desquamation.