Internalization of gap junctions in benign familial pemphigus (Hailey-Hailey disease) and keratosis follicularis (Darier's disease)

Hereditary mucoepithelial dysplasia: clinical, ultrastructural and genetic study of eight patients and literature review

BACKGROUND

Hereditary mucoepithelial dysplasia is a dominantly inherited disease, mainly characterized by chronic mucosal lesions associated with keratitis, non-scarring alopecia, keratosis pilaris and perineal intertrigo. Since the original report by Witkop, this condition has been considered to be a disorder of desmosome/gap junction formation, but there has been no ex vivo investigation of these components using genetic and immunolabelling techniques.

OBJECTIVES

To perform light and immunoelectron microscopic studies, and partial genetic analysis on five patients in a family and three sporadic cases and to point out similarities of this rare disorder with chronic mucocutaneous candidiasis and other follicular keratosis syndromes, i.e. ichthyosis follicularis-alopecia-photophobia (IFAP), keratitis-ichthyosis-deafness (KID) and Siemens syndromes.

METHODS

Biopsies from the involved oral mucosa and armpit skin of patient 1 were prepared for standard histopathology, electron microscopy and immunocytochemistry. Microsatellite genotyping was performed in three affected family members. Direct sequencing after polymerase chain reaction amplification of the entire coding region was performed.

RESULTS

A 14-year-old male had recurrent keratitis, widespread keratosis pilaris, perineal intertrigo, hypotrichosis and oral mucosal involvement. A similar phenotype was noted in four members of his family and in three sporadic cases. Histological examination of oral mucosa and skin samples showed a psoriasiform pattern, dyskeratotic features and cytoplasmic vacuoles. Expression of connexins (Cx), desmosomal, adherens junction and cytoskeleton proteins (Cx 26, 32 and 43, desmogleins 1 and 2, plakoglobin, desmoplakins I-II, plakophilin 1, beta-catenin, E-cadherin, keratins, beta-tubulin, vimentin and actin) was normal. Ultrastructural studies showed a reduced number of desmosomes. Dyskeratotic cells exhibited internalized gap junctions, long filamentous inclusions reactive with antikeratin antibodies, and bundles of perinuclear fibres resembling clear tonofilaments. Genetic analysis in the studied family excluded the desmosomal cadherins in chromosome 18q12 as candidate genes.

CONCLUSIONS

A diagnosis of hereditary mucoepithelial dysplasia should be strongly suggested by the triad of non-scarring alopecia, well-demarcated erythema of oral mucosa and psoriasiform perineal rash, after exclusion of the clinically related follicular keratosis syndromes. Defective expression of cytoskeleton elements and/or a modification of mechanisms regulating junction-cytoskeleton assembly may be primarily responsible for impaired epithelial cohesion.

Ultraviolet A radiation transiently disrupts gap junctional communication in human keratinocytes

Ultraviolet A (UVA) (320-400 nm) radiation is known to cause cutaneous aging and skin cancer. We studied the effect of UVA (365 nm) radiation on the human epidermis by focusing on keratinocyte gap junction-mediated intercellular communication (GJIC). We observed a dose-dependent 10-fold decrease in GJIC induced by UVA in normal human keratinocytes. This decrease in GJIC was associated with time-dependent internalization of connexin43 (Cx43). UVA radiation also damaged the actin cytoskeleton, as shown by microfilament disappearance. Importantly, the decrease in GJIC was transient when keratinocytes were irradiated with 10 J/cm(2) UVA, with a return to baseline values after 8 h. Concomitantly, Cx43 was relocalized and the actin cytoskeleton was restored. UVA irradiation and 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment activated protein kinase C and reduced GJIC. However, Cx43 localization and phosphorylation were differently regulated by the two treatments. This suggests that at least two different pathways may mediate the observed fall in GJIC. These findings identify keratinocyte GJIC as a new UVA target that might sensitize human skin to photoaging and cancer formation.