Stratum corneum cell dissociation

Stratum Corneum Cell Dissociation Involves Proteolysis. 73... 

STRATUM CORNEUM CELL DISSOCIATION INVOLVES PROTEOLYSIS... 

Experimental evidence that protein structures are involved in stratum corneum cell cohesion was presented by Bisset et al.9 They induced cell dissociation in pig and human nonpalmo-plantar stratum corneum by means of incubation of the tissue in the presence of the zwitterionic surfactant 6-octadecyldimethyl ammoniohexanoate. Cell dissociation could not be induced when the tissue had been pretreated with the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF). The fact that cell dissociation was found only in the presence of EDTA suggested a role also for calcium in stratum corneum cell cohesion. 

Egelrud T, Lundstrom A. The dependence of detergent-induced cell dissociation in non-palmo-plantar stratum corneum on endogenous proteolysis. J Invest Dermatol 1990 95 456-459. 

Lundstrom and Egelrud10 found a unipolar spontaneous cell dissociation in pieces of hypertrophic human plantar stratum corneum incubated in a simple buffer. The cell dissociation occurred only at the surface that had faced outward in vivo. The rate of cell dissociation was increased in the presence of EDTA. It was inhibited by inhibitors of serine proteases, but not by inhibitors of other groups of proteases. Since the tissue had not been heated with exogenous proteases before the experiments, it was concluded that the observed cell dissociation was mediated by an endogenous serine protease. This experimental system has been used as an in vitro model of desquamation. In addition to information about the enzyme(s) involved in the cell dissociation, it has provided information about the nature of the cohesive structures in the stratum corneum. 

There is evidence that protein structures are also responsible for cell cohesion in nonpalmo-plantar stratum corneum. When punch biopsies of normal human gluteal skin were incubated in a buffer containing a mixture of the zwitterionic surfactant /V,/V,-dimethyldodecylamine and the anionic surfactant sodium dodecyl sulfate,11 there was dissociation of cells in the stratum corneum but not in the rest of the epidermis. The cell dissociation took place only in the presence of EDTA and was inhibited by the serine protease inhibitor aprotinin.12 Suzuki et al.13,14 presented evidence that spontaneous cell dissociation in nonpalmo-plantar stratum corneum could be inhibited by a combination of inhibitors of trypsin-like and chymotrypsin-like enzymes. Thus, nonpalmo-plantar stratum corneum contains endogenous proteases that mediate cell dissociation. 

Immunoblot analyses with antibodies specific for the transmembranal desmosomal glycoprotein desmoglein I (DGI) of plantar stratum corneum undergoing spontaneous cell dissociation30 showed that although the still cohesive tissue contained only intact DG I, dissociated cells contained no... 

There are a vast number of other factors which may be expected to influence the rate of desquamation, for instance, by affecting the rate of proteolytic reactions. pH, water, and ion concentrations, and lipid composition may all be expected to be of importance. Experimental data in this area are very scarce, but some speculations can be made. For instance, the pH dependency of SCCE activity could be of importance. SCCE has optimal activity at pH 7 to 8, but close to half its maximal activity at pH 5.5.36,37 This implies that rather small variations in either direction of the pH of the extracellular space should have effects on the rate of SCCE-mediated protein degradation. In support of this, the rate of spontaneous cell dissociation observed in plantar stratum corneum in vitro showed a marked pH dependency, being highest at neutral to weakly alkaline pH and decreasing at lower pH values.10... 

---