The plasma unit membrane. Membrane mediated growth control and its failure in psoriasis

Domain structure of erythrocyte membranes in psoriasis: an EPR study

Membrane fluidity of erythrocytes from psoriatic patients in active and inactive period of the disease was studied by electron paramagnetic resonance (EPR). Comparison of simulated and experimental EPR spectra of erythrocyte membranes from controls and psoriatics showed that they are essentially superimposition of three components; two regions with a high degree of order of the lipid acyl chains and one region with poor alignments of hydrocarbon chains (with a small order parameter). In psoriatic erythrocytes not only the portion of the most rigid domain was enlarged, but also the order parameter of this domain was increased, while the order parameters of two other domains were the same than in normal erythrocytes. Results obtained in this article showed that the portion of the most rigid domain (W(A)) better correlated with polymorphonuclear elastase (PMN elastase) than with PASI score. Additionally, correlation between PMN elastase and W(A) in the active period of the disease was observed to be higher than in the inactive period. Therefore, portion of the most ordered domain (W(A)) seems to be a good marker for evaluation of the disease activity in psoriatic patients.

Erythrocyte membrane fluidity changes in psoriasis: an EPR study

The aim of the study was to find the cause of membrane fluidity decrease in psoriasis, observed by other authors, in different types of cells and its clinical consequences. To this end, we have examined the influence of different clinical and biochemical factors on erythrocyte membrane fluidity changes in psoriatic patients. Membrane fluidity was studied by the electron paramagnetic resonance spin-labeling method. The data revealed that the decrease of membrane fluidity corresponded with exacerbation of skin lesions. The results clearly indicate that the increased lipid peroxidation may be the essential mechanism of membrane fluidity decrease in psoriasis.

In vivo and in vitro influence of etretinate on erythrocyte membrane fluidity

The molecular mechanisms underlying the action of synthetic retinoids have been studied intensively, but they are not fully understood yet. It is well known that retinoids exert their effects on gene expression via the retinoic acid receptor. Some observations suggest that the main aromatic retinoid etretinate (Tigason) exerts its therapeutic effect in psoriasis also through an action on the cell membrane. In this paper, we present the results of previously unreleased experiments (when Tigason was still in use) concerning the in vivo and in vitro influence of etretinate on erythrocyte membrane fluidity in psoriatic patients. Erythrocytes from healthy subjects and topically treated psoriatics were chosen as control groups. Membrane fluidity was measured by the electron paramagnetic resonance (EPR) spin-labelling technique. Erythrocytes from psoriatic patients had lower membrane fluidity, a lower antioxidant activity and a greater susceptibility to peroxidation than those from healthy subjects. After treatment with etretinate, a significant increase in erythrocyte membrane fluidity and in antioxidant activity as well as a decrease in lipid peroxidation were observed in erythrocytes from patients. Local therapy of psoriatic lesions had no influence on the improvement in membrane fluidity and antioxidant activity of erythrocytes. Incubation of erythrocytes from healthy controls and topically treated psoriatics with etretinate in vitro confirmed its fluidizing effect on erythrocyte membranes. These data may indicate that two mechanisms lead to an increase in erythrocyte membrane fluidity in psoriatic patients treated with Tigason: the first one, indirect, by improvement of the antioxidant defence system and cell protection against lipid peroxidation, and the second one, by a direct fluidizing effect of etretinate on the erythrocyte membrane.

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.

Cell surface carbohydrates in psoriasis. Defective cytoplasmic transport by glycoconjugates carrying fucose residues suggested by lectin staining

Eleven biopsy specimens of normal skin and twenty-four biopsy specimens of psoriatic lesions were examined histochemically by using several lectins (Ulex europaeus, UEA-1; Dolichos biflorus, DBA; Bandeirea simplicifolia, BS-I; Concanvalia ensiformis, Con A; Triticum vulgaris, WGA; Ricinus communis, RCA; Arachis hypogoea, PNA) in order to evaluate the presence and distribution of various carbohydrates in normal and psoriatic keratinocytes. The findings revealed that keratinocytes from psoriatic lesions are distinguished by a different composition of carbohydrate residues incorporated in their plasma membranes. In particular, the intracellular transport of alpha-L-fucose, alpha-D-mannose, and alpha-D-glucose to the plasma cell membrane is impeded, whereas their synthesis in the cytoplasm of the psoriatic keratinocytes is largely unaltered. In addition, due to the lack of terminal alpha-L-fucose, the alpha-D-N-acetyl-galactosamine and alpha-D-galactose residues cannot be transferred to the plasma membranes and, therefore, the antigens for blood groups A and B remain incomplete in psoriatic epidermis. On the basis of these findings and in comparison with previous findings of our group on hyperproliferative, malignant keratinocytes, it is concluded that particularly the disordered cytoplasmic transport of alpha-L-fucose-carrying glycoconjugates may represent a specific defect in psoriasis, possibly linked with the pathogenesis of this disease.

Surface glycoproteins of cultured human keratinocytes from normal and uninvolved psoriatic epidermis

Surface glycoproteins of cultured human keratinocytes from normal skin and uninvolved psoriatic epidermis, isolated by the suction blister method, were studied by two different methods. Cells were cultured on collagen-coated culture dishes and showed a fibrillar keratin-specific staining by immunofluorescence. Surface labelling experiments using the neuraminidase/galactose oxidase/sodium borohydride method (which labels the penultimate galactose moieties of glycoproteins) revealed one major glycoprotein with Mr 53 kD (kilodaltons) both in normal keratinocytes and in keratinocytes from uninvolved psoriatic skin. The periodate/sodium borohydride method (which labels the terminal sialic acids in glycoproteins) by contrast revealed three major glycoproteins, with Mr 53 kD to 63 kD, in normal keratinocytes but only a single major glycoprotein, with Mr 53 kD, in keratinocytes from uninvolved psoriatic skin. Treatment of cultured keratinocytes with etretinate appeared to restore the normal pattern of surface glycoproteins in uninvolved psoriatic keratinocytes.

Altered binding of Ulex europaeus I lectin to psoriatic epidermis

We have used Ulex europaeus I (UEA I) lectin, specific for alpha-L-fucose-containing glycoconjugates, in fluorescence microscopy to stain cryostat sections of human skin from normal persons and patients with psoriasis and lichen simplex. In normal skin the upper layers of the stratum spinosum and the stratum granulosum were strongly reactive with UEA I, whereas the lower layers of the epidermis did not react. The staining intensity of the upper epidermis was similar to that of the endothelium of dermal blood vessels. Biopsies of the lesional skin of lichen simplex showed an intense UEA I-specific staining throughout the whole epidermis, similar in intensity to that seen in the upper epidermis of normal skin. In psoriatic lesions positive UEA I-specific fluorescence was seen throughout the whole epidermis, but the fluorescence was more faint and often granular. In uninvolved skin of psoriatic patients the whole epidermis showed a diffuse UEA I-specific fluorescence, differing in this respect from normal skin. In normal skin UEA I binds to epidermal cells which are at a certain state of differentiation. The results with psoriatic epidermis confirm that both uninvolved and lesional epidermis have a defect in epidermal maturation, as shown by the altered binding of UEA I lectin.

Erythrocyte membrane phosphorylation in untreated and in etretinate-treated psoriatic patients

Levels of phosphorylation were decreased in bands 2 to 2.1, 2.9 to 3 and 4.5 to 4.8 of erythrocyte membranes from psoriatic patients compared with control values. In addition, higher than control levels of 32P were incorporated into a new polypeptide band (mol.wt. 18-20,000 daltons) of red cell membranes from patients. Uptake of 32P by these bands returned towards normal after the patients received oral etretinate treatment. These results suggest there is a generalized plasma membrane defect in psoriasis and that etretinate may affect the metabolism of red cell membrane proteins.

Altered erythrocyte membrane phosphorylation in psoriasis

Autophosphorylation by [gamma-32P]ATP of erythrocyte membranes from controls, psoriatic patients and patients with skin disorders other than psoriasis was compared by polyacrylamide gel electrophoresis. Compared with controls, membranes from psoriatic patients showed significantly less 32P incorporation in the band 2 region (nomenclature of Fairbanks et al., 1971). In addition, psoriasis and some of the other skin diseases examined displayed decreased phosphorylation in the region of bands 2.9-3 and 4.5-4.8. A new polypeptide band in the 18-20,000 dalton region was also observed in the diseases examined. Altered epidermal plasma membranes have been implicated in the pathogenesis of psoriasis, and our findings suggest the defective plasma membranes may be a generalized phenomenon in this disorder.

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.

Studies on the plasma membrane of normal and psoriatic keratinocytes. 3. Uptake of labelled sugars and their incorporation into glycoconjugates

We report the uptake of four labelled sugars by keratinocytes isolated from normal epidermis, psoriatic 'uninvolved' skin and psoriatic lesions. Our findings include the following: (1) The rate of uptake of all sugars by the psoriatic lesion is increased. (2) This abnormally high uptake diminishes dramatically during 22 h incubation in vitro. (3) There is a striking abnormality in the metabolism of fucose by psoriatic keratinocytes; our data suggest an increased rate of incorporation of fucose into glycoconjugates.

Incorporation of 14C-linoleic acid in cerebrosides of psoriatic and normal human skin

Psoriasis is marked by loss of glycoalyx. Glycocalyx is composed of glycoproteins and glycolipids such as cerebrosides. It was shown that the incorporation of 14C-linoleic acid in cerebrosides of normal and psoriatic human skin is different. In psoriatic epidermis and corium the turnover of this fatty acid is significantly elevated. It is suggested that in psoriasis the epidermal cell is not able to build up a regular carbohydrate sequences of lipids because the false carbohydrate chain activates the degradation of glycolipids and in compensating for the increased degradation raises the synthesis rate of glycolipids.

The presence of beta2 microglobulin on the membrane of the keratinocyte in premalignant skin disorders

Beta2 Microglobulin, the invariable light chain of the histocompatibility antigen, has proved to be absent on the cell surface of basal cell carcinoma. In actinically damaged skin and in patients with a past history of arsenic ingestion changes can be observed on the epidermal cell membrane which can predict malignancy before cell dysregulation is visible. The epidermis in the basal cell naevus syndrome behaves in this respect as normal epidermis and the spontaneous tumour growth cannot be explained by a predisposing defect in the HLA-antigens of the epidermal cell surface.

Incorporation of D-(3H)glucosamine into normal and psoriatic epidermal glycoconjugates

Samples of normal, uninvolved and involved psoriatic skin were maintained for 18 h in organ culture in the presence of D-(6-3H) glucosamine which is a precursor of cell-surface associated carbohydrates in the epidermis. The total incorporation into involved psoriatic epidermis (solubilized with 8 mol/l urea, 5% sodium dodecyl sulphate, 10 mmol 2-mercaptoethanol) was less than into normal or uninvolved epidermis. This decrease was found whether specific radioactivities were expressed in terms or area, wet weight or protein content of the epidermis. Electrophoresis revealed that the major labelled component in normal and uninvolved epidermis had a high molecular weight. The labelling of this material was significantly reduced in involved psoriatic epidermis. Using pig epidermis we have shown previously that this material represents mainly extracellular glycosaminoglycans and proteoglycans. The decrease labelling (and presumable synthesis) of these extracellular carbohydrates may be related to the failure of mechanisms controlling cell proliferation and to the altered cell interactions which are found in psoriatic epidermis. Electrophoresis also showed that a non-glycosylated protein, molecular weight approximately 50,000, which was present as a singly band in both normal and uninvolved epidermis was always present as a doublet band in the involved psoriatic epidermis.

The dermis is required for the synthesis of extracellular glycosaminoglycans in cultured pig epidermis

1. Slices of pig ear skin were cultured in the presence of D-[3H]glucosamine and the epidermis solubilised in 8 M urea/5% sodium dodecyl sulphate was analysed by polyacrylamide gel electrophoresis. A high molecular weight peak, previously shown to contain glycosaminoglycans, was a major labelled component of epidermis separated from dermis using either CaCl2, dispase or trypsin. This material was unlikely to represent dermal contamination of the epidermis since (a) it was present mainly in epidermis rather than dermis, and (b) both histology and comparison of protein compositions showed the epidermis to be essentially free of dermal components. 2. When the epidermis was separated from dermis before rather than after culture (using CaCl2, dispase, trypsin or suction) the labelled glycosaminoglycan peak was never observed. The labelling of other epidermal glycoconjugates was unaffected. Thus the dermis was necessary specifically for the synthesis of epidermal glycosaminoglycans. 3. All-trans-retinoic acid (1 x 10(-5) M) had a marked effect on the labelling of the epidermal but not the dermal glycosaminoglycan peak, indicating that the epidermal glycosaminoglycans were not synthesised in the dermis. 4. The results suggest that dermal influences in the epidermis could be mediated via dermal control of epidermal glycosaminoglycan synthesis.

Plasma membranes in psoriatic cells. A freeze-fracture study

A freeze-fracture study of affected and unaffected psoriatic skin has demonstrated the presence of marked modification of the plasma membrane in the psoriatic lesion. In the lower layers of the epidermis, an increase of membrane associated particles was observed in many keratinocytes, possibly representing the morphological intramembranous equivalent of changes in the outer cell membrane demonstrated with cytochemical techniques. Furthermore, in the malphighian layer, numerous gap junctions have been found, which may be interpreted as a phenomenon compensating the uncontrolled proliferation, and may represent a point of differentiation between cell proliferation in psoriasis and neoplasia. This technique confirmed the poor tendency to adhesion of keratinocytes in extrajunctional areas, which had already been shown by other morphological techniques.

Histochemistry of the intercellular substance of the normal and psoriatic human epidermis

The intercellular substance of skin samples obtained from normal subjects and from psoriatic patients has been studied with histochemical methods for carbohydrate containing substances and checked with enzymatic extractions. The surface coat which makes up most of the intercellular substance was stained with colloidal iron and with Alcian Blue solutions containing up to 0.20 M magnesium chloride; the stainings were heavily affected by the previous treatment of the sections with testicular hyaluronidase, but not with neuraminidase. The staining of the intercellular substance with Alcian Blue solutions containing up to 0.20 M magnesium chloride and the action of the hyaluronidase gives strength to the hypothesis that hyaluronic acid is contained in the substance. In the skin of psoriatic patients intercellular spaces wider than in normal skin and a reduced surface coat, particularly in the higher layers, has been observed.

Demonstration of giant and anular nexus in the psoriatic epidermis

In the psoriatic skin, nexus were most prominent in the upper layers of the viable epidermis, using the Alcian blue-Lanthanum technique. There, they reached double and manifold the length (giant nexus) of those in normal epidermis. According to the villous transformation of the epidermal cell surface in psoriasis, the nexus showed a great variation in their shape. Undulating nexus were seen beside invagination--and anular nexus. On ther other hand, nexus were lacking in the deepest layers of the psoriatic epidermis in contrast to normal epidermis. From these findings it seems that the intercellular communication by specialized low resistant junctions is reduced in the deepest layers of the psoriatic epidermis. In the upper epidermal layers, however, the extensive formation and the variable configuration of the nexus express a high synthetic activity and a well developed intercellular information in these areas of the psoriatic epidermis.

Intramembraneous particles and transmembraneous ionic channels in the epidermal cell membrane. A cytochemical study with the alcian blue-lanthanum technique

Normal skin was investigated with the Alcian blue-lanthanum technique. Nexus (gap junctions) were found in the stratum Malpighii. They were less numerous in the basal layer, increasing to the upper layers of the epidermis and lacking in the stratum corneum. They were five-layered, about 20 nm thick and showed a 5-7 nm broad lanthanum positive intercellular dense line. Transitional forms between the narrow intercellular space and the real nexus were observed. These "nearly nexus" were broader, the intercellular dense line measured 6-15 nm, and sometimes they were seven-layered. Both, nexus and "nearly nexus" revealed a specific distribution of lanthanum in their membranes. Lanthanum ions seemed to penetrate the membranes forming electron-dense transversal channels branching off from the central dense line with a periodicity of 3 nm. The tangential sections suggested that this distribution was based on the aggregation of intramembraneous particles 1.5-2.0 nm in diameter, which in some areas may be gathered to greater subunits. The nexus may play a role in the control of epidermal proliferation.