Advances in genetic dermatology. Dyskeratosis, acantholysis, and hyperkeratosis, with a note on the specific role of desmosomes and keratinosomes in the formation of the horny layer

Secretory pathway stress responses as possible mechanisms of disease involving Golgi Ca2+ pump dysfunction

In mammalian tissues, uptake of Ca(2+) and Mn(2+) by Golgi membranes is mediated by the secretory pathway Ca(2+) -ATPases, SPCA1 and SPCA2, encoded by the ATP2C1 and ATP2C2 genes. Loss of one copy of the ATP2C1 gene, which causes SPCA1 haploinsufficiency, leads to squamous cell tumors of keratinized epithelia in mice and to Hailey-Hailey disease, an acantholytic skin disease, in humans. Although the disease phenotypes resulting from SPCA1 haploinsufficiency in mice and humans are quite different, each species-specific phenotype is remarkably similar to those arising as a result of null mutations in one copy of the ATP2A2 gene, encoding SERCA2, the endoplasmic reticulum (ER) Ca(2+) pump. SERCA2 haploinsufficiency, like SPCA1 haploinsufficiency, causes squamous cell tumors in mice and Darier's disease, also an acantholytic skin disease, in humans. The phenotypic similarities between SPCA1 and SERCA2 haploinsufficiency in the two species, and the general functions of the two pumps in consecutive compartments of the secretory pathway, suggest that the underlying disease mechanisms are similar. In this review, we discuss evidence supporting the view that chronic Golgi stress and/or ER stress resulting from Ca(2+) pump haploinsufficiencies leads to activation of cellular stress responses in keratinocytes, with the predominance of proapoptotic pathways (although not necessarily apoptosis itself) leading to acantholytic skin disease in humans and the predominance of prosurvival pathways leading to tumors in mice.

Transepithelial electrical resistance and tight junctions of human gingival keratinocytes

Human gingival keratinocytes (HGKs) were studied by means of freeze-fracture technique, conventional electron microscopy and the transepithelial electrical resistance for the investigation of intercellular contacts. For the purpose of comparison, MDCK cells and HaCat cells were also included. An unexpected finding was the presence of tight junctions in the HGKs. In vivo the tight junctions, which were of low complexity and P-face-associated, were co-distributed with desmosomes; in one case, the strands ran directly through desmosomal plaques. Where tight junctions and desmosomes occurred together, no gap junctions were seen. In contrast, where no tight junctions were present, gap junctions and desmosomes were co-localized. However, the unfavourable fracture planes through the tissue did not allow a clearcut allocation of gap junction/tight junction occurrence to certain strata. In vitro, HGKs also expressed tight junctions which formed networks of low complexity and high P-face association. Whereas desmosomes were highly expressed, gap junctions were not observed in cultured keratinocytes. Transepithelial electrical resistances (TEER) of cultured HGKs were higher than the values in low resistance-MDCK cells and HaCat cells but considerably lower than the values in high resistance MDCK cells, supporting the fundamental correlation between tight junction morphology and TEER. The results with this cell culture model of the human gingiva provide some valuable information about in vitro differentation and concommittent changes in cellular contacts of human gingival keratinocytes.

Confluent and reticulated papillomatosis: clinical, light and electron microscopic studies

A case of a 17-year-old Japanese-Canadian boy with a 2-year history of skin lesions relevant to confluent and reticulated papillomatosis (CRP) is reported with electron microscopic findings. He had scattered skin lesions of brownish-colored, rough-surfaced, fine-scaled patches and plaques distributed on the nape, shoulders, and both flanks, extending to the chest and back. Importantly, they showed reticular or confluent arrangement. There was no family history of the same skin lesions. The histology showed epidermal papillomatosis and mild acanthosis with a marked hyperkeratosis. Electron microscopically, the skin lesions consisted of the following abnormal findings: (1) a marked alteration of cornified cell structures showing snake coil-like, or triangle-like stacks, (2) a marked increase in the number of lamellar granules in the granular layer, (3) an increased number of melanosomes in the horny layers, and (4) no significant fine structural changes of epidermal melanocytes. This is the first electron microscopic report on CRP suggesting that the pathophysiology of this disease is related to abnormal keratinocyte differentiation.

Keratin expression in equine normal epidermis and cutaneous papillomas using monoclonal antibodies

Keratin expressions in normal equine epidermis and experimentally induced equine papillomas were studied by immunohistochemical methods with three different human cytokeratin monoclonal antibodies, 34 beta B4 (directed against component 1), 34 beta E12 (directed against components 1, 5, 10, 11) and 35 beta H11 (directed against component 8). Staining patterns with 34 beta B4 and 34 beta E12 in the normal equine epidermis did not differ from those in the normal human epidermis. In the early developing papilloma, keratinocytes showed an abnormal suprabasal staining pattern and expressed an additional 56 kD keratin protein detected by 34 beta E12. In the advanced papilloma, cytolytic cells in the outer spinous and the granular layers did not stain positively with any of the three antibodies used. In both early and advanced papillomas, the expression of high molecular weight keratin proteins, as detected by 34 beta B4 and 34 beta E12, did not correlate with the degree of keratinization. By electron microscopy, keratinocytes in the advanced papilloma showed a marked decrease of tonofibrils and desmosome-tonofilament complex. These alterations may result from an abnormality in both proliferation and functional terminal differentiation of keratinocytes in the papilloma. There were obvious differences in staining patterns with 35 beta H11 between the normal human and equine epidermis; 54 kD keratin protein was expressed in suprabasal layers of the equine normal and papillomatous epidermis. Thus, this keratin protein may be regarded as a "permanent" marker for the equine epidermis.

Dyskeratosis congenita in two male cousins

Dyskeratosis congenita is reported in two male Singaporean Chinese cousins. The family pedigree is presented. Lichen planus or lichenoid lesions, instead of leukoplakia, was the manifestation in the oral cavity. The mode of inheritance and the differential diagnosis of Fanconi's anaemia are discussed. Dental findings are emphasised as such information is lacking in previously reported cases. One of the subjects expired of aplastic anaemia, which together with oral malignancy, is one fatal complication of this disease.

Ultrastructure of dyskeratosis in morbus Darier

Biospy specimens from three patients with morbus Darier were studied by electron microscopy: Grains appeared in groups in the midst of dyskeratotic lesions and were recognized as being the result of more advanced acantholysis and precocious keratinization. Corps ronds were formed individually in the regions lateral to that of grains, where hypergranulosis was prominent in contrast to a mild dyskeratosis. Therefore, the formation of grains and corps ronds seem to be independent of each other. While in the literature acantholysis has mainly been ascribed to the separat;on of desmosones into two segments, another initial process seems to be the primary disappearance of the attachment plaque along with the connecting tonofilaments. From the existence of the other contact complexes, it seems likely that a restoration of desmosomes between acantholytic cells should take place. In early stages of dyskeratotic cells, keratinosomes were increased in number and some of them persisted inside the plasma membrane without a release into the intercellular spaces, and thus they were present in grains and corps ronds. The dyskeratosis in morbus Darier is characterized by a premature, incomplete and individual keratinization as evidenced by the existence of keratohyalin granules and keratinosomes as early as at the level of the 3rd epidermal layer and the absence of a keratin pattern in the dyskeratotic horny cells.