Effects of epidermal calcium and cytokines on the expression and function of epidermal tight junction

Abstract

[한글]

[영문]Tight junctions (TJs) are the most common component of the apical junctional complex (AJC), which are often referred to as barrier and fence functions. Epidermal calcium (Ca2+) is required to maintain permeability barrier homeostasis. The aim of this study is to identify whether the changes of epidermal Ca2+ gradient can influence a continuous network of TJs by the epidermal Ca2+ gradient change and to determine whether or not Th2 cytokines are involved in the regulation of claudin (Cldn) expression.The expression of Cldn-1 and 4 in the epidermis of mice was perturbed after acute barrier disruption and sonophoresis treatment. It then recovered progressively within six hours. The perturbation of Cldn-1 expression was restored more quickly when the barrier-disrupted skin was soaked in a high-concentration Ca2+ solution. However, the recovery of Cldn-1 expression was inhibited after the skin was occluded by a water vapor-impermeable membrane with six hours. The perturbation of Cldn-1 expression was observed when sonophoresis was used on a gel without Ca2+. However, Cldn-1 expression wasn’t perturbed when sonophoresis was used on a gel with high concentrated Ca2+. This implies that the change of epidermal Ca2+ gradient plays an important role in the regulation of epidermal TJ structure, especially Cldn-1 on mouse skin.In the permeability assay, TJs were opened and closed for approximately six hours after tape-stripping or sonophoresis treatment. In particular, the sonophoresis experiment found that the TJ function was temporarily lost by the loss of the Ca2+ gradient, even without skin barrier disruption, and restored as a result of restoring the normal Ca2+ gradient.These results suggest that the epidermis contains two important functional barriers: a stratum corneum (SC) barrier and a TJ barrier. Following acute SC permeability barrier disruption, the TJ barrier is also disrupted by changing the expression pattern or structure of TJ proteins. This allows penetration of pathogens or allergens to enter into living epidermal layers. The SC barrier disruption-induced perturbation of the TJ barrier showed rapid recovery approximately three hours after acute barrier disruption. The faster recovery of TJ barrier, as compared to the SC barrier, seems to restore the outside-to- inside barrier as well as the inside-to-outside barrier, to protect against dangerous pathogens or allergens. Following the recovery of the TJ barrier, the SC barrier is restored by increased LB secretion and production as well as the formation of corneocytes.In the clinically, normal uninvolved skin of atopic dermatitis (AD) patients, Cldn-1 was observed in the epidermis in a similar pattern to that seen in healthy controls. However, in epidermis from the acute lesions of AD patients, Cldn-1 expression was significantly reduced compared to that of non-lesional AD skin and normal, healthy skin. In contrast to the acute lesion, epidermis from the chronic lesions of AD patients showed nearly normal expression of Cldn-1. With respect to cytokines, IL-4 and IL-13, the key cytokines in the pathogenesis of acute AD lesions decreased Cldn-1 expression in keratinocytes. IL-5, which is known to be over-expressed in the chronic lesions of AD, increased Cldn-1 expression in mice epidermis. From these observations, it can be postulated that the change of epidermal Ca2+ gradient may be one of the factors influencing epidermal TJs expression. Furthermore, IL-4, IL-13, and IL-5 could modulate Cldn-1 expression and induce the different expression patterns of Cldn-1 seen between acute and chronic lesions of patients with atopic dermatitis.