To elucidate the precise molecular mechanisms underlying stratum corneum (SC) elasticity, we investigated the molecular dynamics of chemical residues within keratin fibers of human plantar SC under various conditions by cross polarization/magic angle spinning 13C-nuclear magnetic resonance. The intensities of nuclear magnetic resonance spectra responsible for amide carbonyl, C alpha methine, and side-chain aliphatic carbons in the intact SC decreased markedly with increasing water content of up to 30% in dry SC, and then remained constant at greater than 30%. Lipid extraction of intact SC with acetone/ether (1:1) did not induce any significant change in the nuclear magnetic resonance spectrum, whereas additional treatment with water, which released natural moisturizing factors (mainly amino acids), caused the SC to lose elasticity. The observed decrease in elasticity of the SC recovered after treatment with basic and neutral amino acids, but not after treatment with acidic amino acid. With the latter treatment, movement of amino acid molecules was significantly disturbed, suggesting a strong interaction with keratin fibers. Parallel studies of the complex elastic modulus of a pig SC sheet with a rheovibron also demonstrated that removal of natural moisturizing factor reduced the elasticity of the SC; this effect was also reversed by the application of basic and neutral amino acids, but not by the application of acidic amino acid. These findings suggest that structural keratin proteins, mainly consisting of 10-nm filaments, acquire their elasticity with the help of hydrated natural moisturizing factor via the reduction of intermolecular forces, probably through nonhelical regions between keratin fibers.

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Two cases of the Dowling-Meara type of epidermolysis bullosa simplex (EBS) are described. Both had severe blistering at birth, which improved gradually with age. Vesicles and small bullae clustering in a herpetiform fashion were seen in both cases. One showed mild pincer deformity of the nails, and in the other the nail plates were shed after subungual blistering, but regrew without deformity. Histopathology and ultrastructural study showed cytolysis of the basal cells in both cases, but ultrastructurally different forms of tonofilament clumps were present in epidermal keratinocytes. In one case there was typical round clumping of tonofilaments, and in the other a whisk-type clumping of tonofilaments. Cultured keratinocytes from the former produced round clumps of keratin filaments, but those from the latter did not. Review of previous reports of Dowling-Meara EBS revealed that cases could also be divided into two groups in terms of the type of tonofilament clumping at an ultrastructural level. The possibility of subtyping of Dowling-Meara EBS, and possible mechanisms of the blistering in this disease are discussed.

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