Plasma membranes in psoriatic cells. A freeze-fracture study

Upregulation of connexin 26 is a feature of keratinocyte differentiation in hyperproliferative epidermis, vaginal epithelium, and buccal epithelium

In epidermis, it has been suggested, intercellular communication through gap junctions is important in coordinating cell behavior. The connexins, may facilitate selective assembly or permeability of gap junctions, influencing the distribution of metabolites between cells. Using immunohistochemistry, we have compared the distribution of connexins 26 and 43 with that of proliferating cells (Ki67 labeling) in normal epidermis, hyperplastic epidermis (tape-stripped epidermis, psoriatic lesions, and viral warts), and vaginal and buccal epithelia. Connexin 43 was abundant in spinous layers of all epidermal specimens and in vaginal and buccal epithelia. Connexin 26 was absent from the interfollicular and interductal epidermis of normal hair-bearing skin, and nonlesional psoriatic epidermis but present at very low levels in plantar epidermis. Connexin 26 was prominent in lesional psoriatic epidermis and viral warts and in vaginal and buccal epithelia. In three independent experiments connexin 26 appeared in a patchy intercellular distribution in the basal epidermis within 24 h of tape stripping, proceeding to more extensive distribution in basal and suprabasal layers by 48 h. The increase in connexin 26 preceded that in cell proliferation. In vaginal epithelium, buccal epithelium, and viral warts connexin 26 was restricted mainly to suprabasal, nonproliferating cells. In psoriatic lesional epidermis connexin 26 was also located mainly in suprabasal, nonproliferating cells. Connexin 26 was present in a patchy distribution in the basal layer of psoriatic lesional epidermis, but double labeling for connexin 26 and Ki67 showed that many connexin 26 positive basal cells were nonproliferative, suggesting that connexin 26 may be related to differentiation rather than to proliferation. These observations would be consistent with a role for connexin 26 containing gap junctions during both early and later stages of keratinocyte differentiation in hyperplastic epidermis and in vaginal and buccal epithelia.

Upregulation of connexin 26 between keratinocytes of psoriatic lesions

To assess whether the expression of connexins (Cx) by keratinocytes is altered under conditions of abnormal epidermal differentiation, we have compared Cx26, Cx32, Cx37, Cx40, and Cx43 in the epidermis of 11 psoriatic patients who had not been treated for at least 1 mo and of seven healthy individuals. In all samples of fully mature psoriatic plaques, we have observed a massive expression of Cx26, as judged at both the transcript level (northern blot) and the protein level (immunofluorescence). This protein became consistently detected between keratinocytes of the basal and granular layers at the periphery of psoriatic plaques and in all layers of fully developed psoriatic epidermis, except in regions of parakeratosis. None or a minimal amount of Cx26 was observed in both control and nonlesional regions of psoriatic epidermis. Psoriatic plaques also contained Cx43, the prominent gap junction protein in the interfollicular epidermis of normal human skin. The levels of this protein appeared to be slightly higher in psoriatic than in control skin, as judged at both the transcript level (northern blot) and the protein level (immunofluorescence). Three other connexins (Cx32, Cx37, and Cx40), which are not observed in control interfollicular epidermis, were not induced in either nonlesional or lesional regions of psoriatic skin. The data indicate that selective changes in the normal expression of connexins by keratinocytes are associated with the changes in the proliferation and differentiation program that these cells undergo in psoriasis.

Ultrastructural localization of gap junction protein connexin 43 in normal human skin, basal cell carcinoma, and squamous cell carcinoma

The expression and localization of connexin 43 (Cx43) were investigated in normal human epidermis, pilosebaceous apparatus, basal cell carcinoma, and squamous cell carcinoma by immunofluorescence as well as by immunoelectron microscopy. In the normal epidermis the immunofluorescence was weak in the basal layer, increased in spinous layer and negative in the horny layer. In the sebaceous gland, peripheral lobular cells showed weak cell membrane dotted pattern. Cell membrane and cytoplasmic fluorescence was strong in the central lobular cells. In the lower hair follicle, the cortex, inner and outer root sheath cells showed cell membrane fluorescence. As cortical cells underwent keratinization, they lost Cx43 epitopes. Basal cell carcinoma and squamous cell carcinoma were poorly stained, and eccrine and apocrine glands were unstained. In immunoelectron microscopy, close membrane appositions of typical gap junctions were often observed in the spinous layers of the epidermis and the immunolabeling for Cx43 was seen along the gap junction structures. Circular and long gap junctions often were found in follicular root sheaths and sebaceous glands. Gold particles labeling Cx43 in these gap junctions were found on the gap junctions or localized in the cytoplasm near the gap junction membranes. Basal cell carcinoma and squamous cell carcinoma had a small number of small gap junctions, and gold particles were not only localized to gap junctions but scattered in the cytoplasm. No gap junctions were labeled in eccrine and apocrine glands. These findings confirmed that 1) long, curved or circular membrane appositions found in hair follicle and sebaceous gland are true gap junctions, 2) immature cells such as epidermal basal cells, peripheral germinative cells of sebaceous gland and basal and squamous cell carcinoma cells do not have fully developed gap junctions, and 3) Cx43 or its precursors are present in the cytoplasm as well as on poorly developed gap junctions in these immature cells. Immunofluorescence findings generally corresponded to ultrastructural distribution and structural maturity of gap junctions.

Identification of aberrantly regulated genes in diseased skin using the cDNA differential display technique

It is hypothesized that psoriasis may be caused by aberrant gene expression. In an effort to identify and clone psoriasis-specific genes, we compared gene expression in normal, tape-stripped (wounded), and psoriatic skin using the cDNA differential display technique. Four genes not previously described in psoriasis--connexin 26, a gap junction protein; squamous cell carcinoma antigen-1 (SCCA1), a serine protease inhibitor; and mitochondrial NAD subunits 5 and 6--were identified as having very high expression levels in psoriatic skin. In situ hybridizations showed that connexin 26 mRNA was expressed 10-fold higher in psoriatic and 4-fold higher in tape-stripped epidermis than in controls. SCCA1 showed a 40-fold increase in mRNA expression, whereas mitochondrial NAD5 and NAD6 expression was increased 10- and 20-fold, respectively, in psoriatic skin. Northern blots confirmed the increased expression of connexin 26, SCCA1, and NAD6 genes in psoriatic skin. Immunohistochemistry showed that connexin 26 protein was strongly expressed in spinous keratinocytes from psoriatic skin and chronic wounds, but was absent in normal epidermis. These studies demonstrate the usefulness of this approach for identifying genes that are conditionally expressed in growth-activated human skin.

Harlequin ichthyosis: an ultrastructural study

The clinical, electron microscopic, and freeze-fracture features of the skin of a harlequin fetus are described. Ultrastructural findings included large, concentric lamellar bodies, focal absence of intercellular stratum corneum lipid, and an increase in the size of desmosomes and the number of tight junctions. Although the cause of this genodermatosis is unknown, these features may partially explain the marked thickening of stratum corneum that characterizes this disorder.

Cell-to-cell communication within intact human skin

We have characterized cell-to-cell communication (coupling) within intact human skin by microinjecting single keratinocytes with a gap junction-permeant tracer (Lucifer Yellow). 25-50 keratinocytes from different layers of the epidermis were seen to be coupled after most injections (n = 31). A few noncommunicating cells were also microinjected (n = 3) or observed within large territories of coupled keratinocytes. Microinjections of dermal fibroblasts demonstrated an extensive coupling (greater than 100 fibroblasts); however, none of the keratinocyte (n = 34) or fibroblast (n = 3) injections revealed coupling between the epidermal and dermal compartments. Cell coupling was found to be more extensive in epidermal ridges than in suprapapillary plates and, in both regions, was less extensive after injection of the basal layer of the epidermis than after that of the suprabasal layers. This study shows that junctional cell-to-cell communications take place in normal and fully differentiated human tissue. The quantitative data gathered also indicate a regional heterogeneity of keratinocyte-to-keratinocyte communication within intact adult skin and the lack of effect of retinoids on this pattern.

Red blood cell sodium and potassium fluxes in psoriatic patients

Psoriasis might be a widespread membrane disorder. Therefore, the red blood cell sodium, potassium and lithium outward fluxes (through Na-K-ATPase, Na-K-Cl co-transport, Li-Na countertransport and passive permeability), as well as the Na and K content, were studied in 31 psoriatic patients and 23 normal controls. A significant increase in intracellular potassium content, in the maximal velocity of the Na-K ATPase and of Na-K-Cl co-transport as well as in the outward passive permeability for Na were found in the psoriatic patients compared with controls. On the contrary, no differences were observed in sodium content, Li-Na countertransport and passive potassium permeability between the two groups. These results are compatible with a selective increase in inward, as well as outward, membrane permeability to sodium, which is compensated for by increased activity of the Na-K pump, and of the outward Na-K-Cl cotransport with a secondarily increased erythrocyte potassium content. They indicate that the red blood cell might be a useful model for the study of membrane transport in psoriatics.

Membrane characterization of cultured human keratinocytes by freeze-fracture electron microscopy

Human skin explants obtained from 2 to 5-year-old patients with harelips were cultured in NCTC 168 medium at 37 degrees C, in a humidified atmosphere of 5% CO2 in air. After a 2-week incubation period, plasma membranes of the newly grown cells were characterized by freeze-fracture electron microscopy. Desmosomal diameter in cultured keratinocytes was much smaller, ranging from 0.08 to 0.19 micron, than that in vivo, where it ranged from 0.3 to 0.7 micron in diameter. On the E-face of the plasma membranes, attached to the bottom of the culture dish, small particle aggregations were observed. These were thought to be half-desmosomes, each consisting of 10 to 30 particles. Small gap junctions were also observed. These ranged in size from 0.05 to 0.1 micron in diameter. Membranous structures were found adhering to the plasma membrane from the intercellular spaces. These membranous structures may be lipid vesicles, since they are similar in freeze-fracture electron-microscopic features to lamellar lipid structures seen in the intercellular spaces of horny cells in vivo.

Freeze-fracture replication technique of human skin

The freeze-fracture replication technique represents one of the most advanced methods for studying the ultrastructure of biological tissues and has given a new dimension to the ultrastructure research. This technique makes it possible to obtain a cast of a fracture surface of frozen preparations. Apart from allowing samples to be examined without being dehydrated, i.e. under conditions very close to those of living state, it has proved especially useful for the analysis of many tissue functions concerned with membrane activity and exchanges between cells and their disturbance in specific disease conditions. Even through good quality replicas had already been obtained back in 1961 (Moor et al. 1961), only after 1970, mainly thanks to the contribution made by Breathnach and his collaborators (Breathnach et al. 1972, Breathnach 1973, Breathnach et al. 1973) was the freeze-fracture replication technique successfully used in the study of the skin, since this tissue had proved especially difficult to process. In this review paper, technical principles will be summarized and the most important findings so far obtained in the study of normal and pathologic skin will be illustrated.

Light and electron microscopy of psoriatic skin before and during retinoid (Ro 10-9359) and retinoid-PUVA treatment

Eight patients with psoriasis (pustular, erythrodermic or severe plaque type) were treated successfully with retinoid (Ro 10-9359) or with retinoid followed by PUVA (RePUVA). The histological changes in recovering skin were examined during 14 weeks. Treatment resulted in normalization of keratinocyte differentiation with fine structural changes suggesting decreased metabolic activity and a reduction of mitoses. There was an increase in the number of keratohyalin granules and of tonofilaments and desmosomes and a decrease in leukocytes in the epidermis. The different cell organelles were studied in detail, but the exact mechanism of retinoid action remains unsolved. Although the treatments were clinically highly effective, total normalization of the histological and electron microscopical picture was not achieved.

A freeze-fracture study of the human nail plate

This study of freeze-fracture replicas of human nail plate fragments demonstrates that keratin filaments have a width of about 100 A. The 'marginal band' is probably formed by a row of particles, 50 A in diameter, arranged along the inner surface of the plasma membrane. These particles are often masked by keratin filaments. In nonjunctional areas, the plasma membranes are devoid of membrane-associated particles. The only type of junction observed is the desmosome. Even though the modes of keratinization are different, the structures of the keratin pattern, of cell membranes, and of the desmosomes are identical in replicas of wholly keratinized nail and human stratum corneum cells. The ultrastructural differences observed appear to be related to the barrier function carried out by the epidermis and by its desquamation process.

Ultrastructural characterization of the extramammary Paget cell plasma membrane: a freeze-fracture study

The plasma membrane ultrastructure of the extramammary Paget cells was characterized by freeze-fracture electron microscopy, which was first employed for the study of Paget cells. The Paget cell plasma membrane revealed a flat fractured plane with much fewer and smaller desmosome-particle aggregations than those of the keratinocyte. No gap junctions were detected. Many intramembranous particle-free vesicles were seen in the intercellular spaces. Particle-free blebs projecting from the plasma membranes were seen on some cell surfaces. These features greatly differed from those of keratinocytes. On the other hand, an increase of gap junctions was noticed o the keratinocytes around or in the Paget's disease lesions.

GAp junctions in skin tumors of molluscum contagiosum

Thin section, tracer, and freeze-fracture experiments demonstrate that the infection caused by molluscum contagiosum virus implies alterations of cellular contacts in the epidermis, never before observed in cutaneous viroses. These changes are basically represented by a distinctive variation in particle packing of gap junctions, a greater proliferation of these junctions and the presence of a high amount of intracytoplasmic gap junctions. Skin tumors caused by molluscum contagiosum virus appear to be a convenient model to study the morphological and topological variations as well as the turnover of gap junctions in the epidermis.