Corneodesmosomes degradation

The activation of enzyme precursors is likely to be of central importance. A significant fraction of the total SCCE present in the stratum corneum is in the form of inactive proenzyme.53,54 A change in the ratio of precursor to active enzyme may be expected to cause marked changes in the rate of corneodesmosomal degradation. In vitro pro-SCCE can be activated by pancreatic trypsin.39 As mentioned earlier SCTE has been suggested to act as an SCCE activator, but this remains to be elucidated. It is possible that SCCE is just one of a number of enzymes constituting a proteolytic cascade in the stratum corneum, in which one enzyme serves as activator of another enzyme. 

FIGURE 17.8 Effect of topically applied Optimase on corneodesmosome degradation in vitro. From El-Kadi, K., Rawlings, A.V., Feinberg, C., Nunn, C., Battaglia, A., Chandar, P., Richardson, N., Sabin, R., and Pocalyko, D. Arch. Dermatol. Res., 293, 500-507, 2001. 

Clearly in dry flaky skin conditions where corneodesmosome degradation is frequently and characteristically perturbed then generation of amino acid-derived intercellular humectancy will also be decreased potentially leading to a further reduction in protease activity. 

We are very far from an understanding of how and by which mechanisms desquamation is regulated. If we assume, however, that proteolytic degradation of corneodesmosomes plays a major role in desquamation, a number of possible mechanisms can be postulated on the basis of the present knowledge. These are summarized in Table 7.1. 

Enzyme diffuses towards corneodesmosomes to begin their degradation and encapsulation with barrier lipids, transformation of fragile to resilient corneocyte... 

Caubet, C. et al. Degradation of corneodesmosome proteins by two serine proteases of the kallikrein family, J. Invest. Dermatol., 122, 1235-1244, 2004. 

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