Caveolin-1 Expression in Different Types of Psoriatic Lesions: Analysis of 66 Cases

Abstract

Background:

Caveolin-1 is a key structural and functional protein. Caveolin-1 is known to modulate multiple signal-transducing pathways involved in cell differentiation and proliferation. Psoriasis is viewed as a multifactorial pathology characterized by keratinocyte hyperproliferation and abnormal cell maturation.

Objectives:

To examine the expression of caveolin-1 in skin biopsies from normal subjects, patients, and subjects with the three respective isoforms of psoriasis (psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis). The expression level of caveolin-1 was compared among psoriasis vulgaris, localized pustular psoriasis, erythrodermic psoriasis, and normal subjects.

Materials and Methods:

Using immunohistochemical methods, caveolin-1 protein expression was assayed in four groups. An analysis was conducted on skin samples obtained from 22 normal subjects and 28 patients with psoriasis vulgaris, 22 patients with localized pustular psoriasis, and 16 patients with erythrodermic psoriasis. The statistical analysis of the scoring criteria reflecting the level of Caveolin-1 immunostaining between different groups was determined using the Mann–Whitney U-test.

Results:

In the normal skin, intense and consistent caveolin-1 staining was present in 22 cases. The Caveolin-1 protein was significantly reduced and showed very weak or absent staining within the tissues of psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis (respective P < 0.001). Caveolin-1 protein expression in psoriasis vulgaris was higher than that in localized pustular psoriasis and erythrodermic psoriasis (respective P < 0.05). Caveolin-1 protein expression was no different in localized pustular psoriasis and erythrodermic psoriasis (P > 0.05).

Conclusion:

The finding of this study was consistent with a downregulation of Caveolin-1, which might serve as an etiological factor in the development of psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis. Further mechanistic investigations are required to prove that Caveolin-1 protein has the potential and may be a novel target for therapy of psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis.

Background

What was known?

Caveolin-1 is a key structural and functional protein for plasmalemmal invaginations termed ‘caveolae’. Caveolin-1 is known to modulate multiple signal-transducing pathways involved in cell differentiation and proliferation. Previous studies indicate that Caveolin-1 reduction induces cell proliferation not only in tumor cells, but also in non-tumor cells. In 2002, Campbell and Laidler demonstrated the downregulation and altered spatial expression patterns of Caveolin-1 in chronic plaque psoriasis, but only demonstrated the downregulation expression of Caveolin-1 in chronic plaque psoriasis. The expression of Caveolin-1 in other types is still not clear. The expression difference of Caveolin-1 among psoriasis vulgaris, localized pustular psoriasis, erythrodermic psoriasis, and normal subjects is not known.

Caveolae are small bulb- or flask-shaped, scrotiform or tubiform invaginations located at the cell surface.[1] They represent a microdomain of the plasma membrane.[1,2] Caveolae are predominantly present in the endothelial cells, adipocytes, and muscle cells. Caveolin, a 21-24 kDa integral membrane protein,[3,4] is a major structural scaffold and regulatory component of the caveolae in the membranes.[3,5,6,7] Three isoforms of Caveolin have been detected in mammals; Caveolin-1, Caveolin-2, and Caveolin-3. Caveolin 1 has two further splice variants: Caveolin-1α and Caveolin-1ß. Caveolin-1 and Caveolin-2 are generally distributed in tissues, such as the epithelial, endothelial, and smooth muscle cells. The functions of Caveolin-1 and the caveolae membrane system are not fully elucidated. The caveolae are involved in regulation of signal-transduction cascades.[8,9] Caveolae have also been implicated in several aspects of calcium cellular signaling,[10] and in transcytosis and potocytosis of nutrients, growth factors, hormones, antibodies, and chemokines. They are also involved in the transport of molecules to the target sites, in cell development, and in other important physiological functions. In addition, studies have shown that caveolae regulate cellular cholesterol transportation and play an important physiological role in maintaining cholesterol equilibrium in vivo.[11] Caveolin-1 has been shown to directly modulate the activity of select signaling cascades, generally playing a negative regulatory role, and in particular exerting an inhibitory effect on the kinase activities associated with the promotion of cell proliferation and oncogenic transformation.[12,13,14,15,16] Consistent with its cell growth restrictive properties, Caveolin-1 has also been reported to sensitize cells to proapoptotic signals.[17]

Psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis are viewed as components of a multifactorial pathology, characterized by keratinocyte hyperproliferation, abnormal cell maturation, increased cellular activity of the epidermis, and dermal alterations. An accelerated proliferation of the epidermal basal cells is one of the pathophysiological characteristics, with a cell mitotic cycle duration as short as 37.5 h, and an epidermal turnover time of three to four days (normal: >28 days). The pathology involves benign and not malignant hyperproliferation.

Several studies have implicated Caveolin-1 in the pathophysiology of psoriasis. A study by Campbell and Gumbleton, in 2000, demonstrated aberrant (downregulated) Caveolin-1 expression in ordinary psoriasis.[18] In 2002, Campbell and Laidler demonstrated downregulation and altered spatial expression patterns of Caveolin-1 in psoriasis vulgaris.[19,20] These studies investigated Caveolin-1 expression in psoriasis vulgaris by using immunohistochemical approaches, but did not find Caveolin-1 expression in other forms of psoriasis.

In the present study, using immunohistochemical methods, we have analyzed the expression of Caveolin-1 in tissues from three types of psoriasis — psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis — as compared to the expression in normal tissue. We have investigated differences in Caveolin-1 expression in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis, and analyzed the effect of these differences on the development of psoriasis vulgaris.

Materials and Methods

Patients and sample preparation

All the patients gave written informed consent. Experiments were approved by the Ethics Committee of the First Affiliated Hospital of Harbin Medical University. Skin punch biopsies were obtained from the four groups, from May, 2009 to November, 2011. The first set included 28 patients with psoriasis vulgaris; 16 men and 12 women; mean age 31.65 years (range 21-59 years). The second set included 22 patients with localized pustular psoriasis; three men and 19 women; mean age of 43.55 years (range 20-68 years). The third set included 16 patients with erythrodermic psoriasis; 13 men and three women; mean age 44.50 years (range 35-68 years). None of these patients had received systemic medication or phototherapy before entering the study, and all topical therapies, except for emollients, were discontinued two weeks prior to their entry into the study. The fourth set included 22 controls; three men and 19 women; mean age of 34.58 years (range of 23-49 years). They underwent surgical skin flap excision at the Department of Cosmetology and Plastic Surgery, who did not have any skin disease and who demonstrated normal epidermal morphology.

Reagent sources

Phosphate buffered saline (PBS) was purchased from Hyclone Reagent Co, Ltd, Beijing, China. Anti-rabbit/mouse polymer, Fresh DAB (3,3-diaminobenzidine) was purchased from Zhongshan Golden Bridge Reagent Co, Ltd, Beijing, China. Primary rabbit polyclonal antibody to caveolin-1 was purchased from Santa Cruz Biotechnology, Inc, USA.

Immunohistochemistry

Tissue sections (4 μm) were prepared from formalin-fixed paraffin-embedded blocks. Immunostaining was done according to our laboratory method.[21] Briefly, the deparaffinised section was quenched with 3% H₂O₂ for 10 min. After washing with phosphate buffered saline (PBS), the sections were incubated in 5% bovine serum albumin for 20 min, followed by incubation with primary rabbit polyclonal antibody to caveolin-1 (1:50) (Santa Cruz Biotechnology, Inc, USA.) for 60 min at 37^° C and secondary antibodies for 30 min at room temperature. The localisation of caveolin-1 was visualised by 3,3 diaminobenzidine (DAB) solution for 3-5 min. Finally, the slides were washed with water before being counterstained with haematoxylin. PBS was substituted for primary antibody as a negative control.

Scoring of stained specimens

The Caveolin-1-staining status was identified as either negative or positive. Immunohistochemistry positive staining was defined as the presence of pigmentosus chromogen detection on the cell membrane. Immunohistochemistry positive staining for scoring of sections was performed independently by four investigators (1 dermatologist, and 3 pathologists). The sections were scored using a double-headed light microscope in a blinded fashion. A scoring system for Caveolin-1 immunoreactivity was adapted from what was previously reported[22], and was as follows:

1. 0 = almost complete absence of staining throughout the full-thickness of the epidermis.

2. 1 = sporadic or weak staining that was confined to the basal epidermis.

3. 2 = moderate noncontinuous staining in the basal layers of the epidermis.

4. 3 = strong consecutively staining in the basal and nearly all the layers of the epidermis.

In each case there was an initial difference in scoring between the independent investigators, and a general consensus was reached. Each experimental group set up negative control.

Statistics

The statistical analysis of the scoring criteria reflecting the level of Caveolin-1 immunostaining between different groups was determined using the Mann–Whitney U-test. The statistical significance was defined as P < 0.05 (two-sided test).

Results

The expression of Caveolin-1 was decreased markedly in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis, compared to the level in normal tissues (P < 0.001 respectively). The expression levels of Caveolin-1 were higher in psoriasis vulgaris than in localized pustular psoriasis and erythrodermic psoriasis (P < 0.05 respectively). However, there was no difference between the expression levels of Caveolin-1 in localized pustular psoriasis and erythrodermic psoriasis [Tables 1 and 2, Figures 1–5]. Results of negative control antibody are shown in Figure 6.

Table 1.

The mean score difference of Caveolin-1 expression in psoriasis vulgaris, localized pustular psoriasis and erythrodermic psoriasis

Table 2.

The mean and standard deviation difference of caveolin-1 expression in psoriasis vulgaris, localized pustular psoriasis and erythrodermic psoriasis

Figure 1.

The mean score difference of Caveolin-1 expression in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis. The mean score of Caveolin-1 protein was signficantly reduced in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis (respective P < 0.001)

Figure 5.

Immunohistochemical expression in the erythrodermic psoriasis psoriasis epidermis tissue, Caveolin-1 staining was absent. (a) Elivision Super/HRP immunohistochemistry, ×100. b) Elivision Super/HRP immunohistochemistry, ×100

Figure 6.

Negative control antibody (a) normal, Elivision Super/HRP immunohistochemistry, ×400. (b) psoriasis vulgaris, Elivision Super/HRP immunohistochemistry, ×200. c) localized pustular psoriasis, Elivision Super/HRP immunohistochemistry, ×100. d) erythrodermic psoriasis, Elivision Super/HRP immunohistochemistry, ×100

Figure 2.

Immunohistochemical expression in normal skin specification, Caveolin-1 (brown) was observed the continuous expression in the basal layer, almost throughout the entire epidermis. a) Elivision Super/horseradish peroxidase immunohistochemistry, ×400. b) Elivision Super/HRP immunohistochemistry, ×400

Figure 3.

Immunohistochemical expression in the psoriasis vulgaris epidermis tissue, (a) Caveolin-1 staining (brown) was very weak only in basal layer. Elivision Super/HRP immunohistochemistry, ×200. b) Caveolin-1 staining was absent. Elivision Super/HRP immunohistochemistry, ×200

Figure 4.

Immunohistochemical expression in the localized pustular psoriasis epidermis tissue, Caveolin-1 staining was absent. a) Elivision Super/HRP immunohistochemistry, ×100. b) Elivision Super/HRP immunohistochemistry, ×40

Discussion

There are differences in the clinical manifestation and pathology in the three type psoriasis. The clinical effects of psoriasis vulgaris are seen as well-demarcated red plaques with scales. The common pathologic changes include hyperkeratosis, parakeratosis, Munro's microabscesses, thinning or absence of a granular layer, acanthosis with elongation of the epidermal rete ridges, clubbing of the dermal papillae, dilation of the capillaries, and primarily of lymphocytes infiltration. In localized pustular psoriasis, abacterial pustular eruptions appear in keratinization scale plaques on the palms and soles. Pustular psoriasis is characterized by the presence of Kogoj spongiform pustules. Erythrodermic psoriasis appears as inflammation and exfoliation of the skin over most of the body surface, and condition may be accompanied by fever and lymphadenopathy, histopathological features similar to those of psoriasis vulgaris, and it usually exhibits a higher number of prominent dilated capillaries and hyperkeratosis.

However, there are only very few studies in the literature on the expression Caveolin-1 in various types of psoriasis. In the present study, we found that the expression of Caveolin-1 was decreased markedly in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis, compared to the level in normal tissues. The expression of Caveolin-1 were higher in psoriasis vulgaris than in localized pustular psoriasis and erythrodermic psoriasis. However, there was no difference between the expression levels of Caveolin-1 in localized pustular psoriasis and erythrodermic psoriasis. It was reported that caveolin-1 may contribute to epidermal homeostasis through regulating a range of signal-transduction events, which can promote some of the reported cellular and biochemical abnormalities of psoriasis, such as, an increased number or turnover rate of basal keratinocytes committed to proliferation, an increased resistance to apoptosis,[23] loss of cell–cell contact inhibition,[24] or reduced intracellular Ca²⁺ mobilization, leading to abnormal keratinocyte differentiation.[25] For example, at least in vitro, Caveolin-1 has been shown to sensitize a cell to programmed cell death via inhibition of the activity of the antiapoptotic phosphatidylinositol 3-kinase.[17] Caveolae have also been implicated in several facets of intracellular Ca²⁺ regulation.[26] The epidermal hyperplasia in psoriasis is paralleled by increased lipid raft formation. Caveolin-1 delivery to the apical plasma membrane by lamellar body trafficking to apical plasma membrane “brakes” further lamellar body secretion, signals terminal differentiation, and regulates epidermal hyperproliferation.[27]

Our results demonstrated that there was a decrease in Caveolin-1 expression in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis, and it may suggested that it has a potential role in the overall pathogenesis. The Caveolin-1 protein is potentially a novel target for the therapeutic treatment of psoriasis. We will continue further research on the potential therapeutic role of caveolin downregulation.

What is new?

In this study, we found that the expression level of Caveolin-1 decreased markedly in psoriasis vulgaris, localized pustular psoriasis, and erythrodermic psoriasis, compared to the level in the normal tissue. The Caveolin-1 protein had a similar expression in erythrodermic psoriasis and localized pustular psoriasis. The expression level of Caveolin-1 was higher in psoriasis vulgaris than in localized pustular psoriasis and erythrodermic psoriasis. This report also considers the potential role of Caveolin-1 in the overall pathogenesis.