Differential expression of transforming growth factor-alpha (TGF-alpha) and EGF receptor in transitional area of psoriatic epidermis

Thioredoxin-interacting protein regulates keratinocyte differentiation: Implication of its role in psoriasis

Thioredoxin-interacting protein (TXNIP), also known as Vitamin-D upregulated protein-1 (VDUP-1), interacts with thioredoxin to regulate redox responses and participates in diverse disorders including metabolic, cardiovascular, inflammatory and malignant diseases. Psoriasis is characterized by chronic skin inflammation and an aberrant pattern of keratinocyte differentiation. Clinically, psoriasis is associated with various cardiometabolic comorbidities but studies on TXNIP's biological role in skin disorders are limited. In this study, we investigated TXNIP expression in psoriasis and its regulation in normal human epidermal keratinocytes (NHEKs), and then explored how TXNIP regulated skin keratinocyte differentiation to determine its role in psoriasis pathogenesis. Our immunohistochemical study demonstrated extensive TXNIP expression in the upper and lower epidermis of psoriasis compared to predominant TXNIP expression in the basal layer of normal skin. 1, 25-dihydroxyvitamin D₃  suppressed but TGF-α and EGF enhanced TXNIP expression in NHEKs. An inducer of keratinocyte differentiation, phorbol 12-myristate 13-acetate (PMA), also diminished TXNIP expression, which was reversed by PKC-δ knockdown. TXNIP knockdown reduced PMA-induced involucrin and transglutaminse-1 expression, and increased p63 expression in NHEKs but did not significantly affect cell proliferation. H₂ O₂ -induced ROS production and EGFR phosphorylation decreased in NHEKs with TXNIP knockdown. Furthermore, PMA-induced PKC-δ phosphorylation, TGF-α, and EGF-triggered EGFR phosphorylation were attenuated by TXNIP knockdown. Our results unraveled the regulation and function of TXNIP expression in skin keratinocytes and the cross-regulation between TXNIP and EGFR signaling. These findings imply a role of TXNIP in psoriasis and provide insight into the possible impact of TXNIP regulators on the skin or psoriasis.

Decoy receptor 3 is involved in epidermal keratinocyte commitment to terminal differentiation via EGFR and PKC activation

Decoy receptor 3 (DcR3) is a soluble receptor for Fas ligand, LIGHT and TL1A, but it also exerts effector functions. Previously, we found that DcR3 is upregulated in the serum and lesional skin of patients with psoriasis and is upregulated by EGFR activation in proliferating primary human epidermal keratinocytes. However, the functional role of intracellular DcR3 in keratinocyte differentiation is still incompletely defined. Herein, primary cultured human epidermal keratinocytes were differentiated by phorbol 12-myristate 13-acetate (PMA) treatment, calcium treatment and cell confluence, which are three standard in vitro differentiation models. We found that the constitutive expression of the DcR3 gene and protein was progressively suppressed during terminal differentiation of keratinocytes. These changes were correlated with downregulation of EGFR activation during keratinocyte differentiation. EGFR inhibition by gefitinib further decreased confluence-induced suppression of DcR3 mRNA expression, and, vice versa, knocking down DcR3 expression attenuated EGFR and EGFR ligand expression as well as EGFR activation. Under conditions without a change in cell growth, DcR3 silencing reduced the expression of involucrin and transglutaminase 1 but enhanced the induction of the terminal differentiation markers keratin 10 and loricrin. Of note, DcR3 interacted with PKCα and PKCδ and enhanced PKC activity. In keratinocytes with PKCα and PKCδ silencing, differentiation markers were differentially affected. In conclusion, DcR3 expression in keratinocytes is regulated by EGFR and forms a positive feedback loop to orchestrate constitutive EGFR and PKC activity. During differentiation, DcR3 is downregulated and involved in modulating the pattern of terminal differentiation.

A protein linked to cancer and various inflammatory diseases may also be an important driver for the skin condition in psoriasis. The outer surface of the skin is formed by cells called keratinocytes, which transition from a highly proliferative state to a fully mature state where they no longer divide. This developmental process is disrupted in psoriasis. Researchers led by Wan-Wan Lin at National Taiwan University, Taipei, have now identified a prominent role for a protein called decoy receptor 3 (DcR3), which is a biomarker for a variety of disorders and is also abnormally expressed in keratinocytes in psoriatic lesions. Lin and colleagues demonstrated that DcR3 interacts with multiple cellular signaling pathways that coordinate cell differentiation. These findings reveal how aberrant DcR3 activity might lead to the abnormal keratinocyte developmental behavior observed in psoriasis.

EGFR-driven up-regulation of decoy receptor 3 in keratinocytes contributes to the pathogenesis of psoriasis

Decoy receptor 3 (DcR3) is a soluble receptor of Fas ligand (FasL), LIGHT (TNFSF14) and TNF-like molecule 1A (TL1A) and plays pleiotropic roles in many inflammatory and autoimmune disorders and malignant diseases. In cutaneous biology, DcR3 is expressed in primary human epidermal keratinocytes and is upregulated in skin lesions in psoriasis, which is characterized by chronic inflammation and angiogenesis. However, the regulatory mechanisms of DcR3 over-expression in skin lesions of psoriasis are unknown. Here, we demonstrate that DcR3 can be detected in both dermal blood vessels and epidermal layers of psoriatic skin lesions. Analysis of serum samples showed that DcR3 was elevated, but FasL was downregulated in psoriatic patients compared with normal individuals. Additional cell studies revealed a central role of epidermal growth factor receptor (EGFR) in controlling the basal expression of DcR3 in keratinocytes. Activation of EGFR by epidermal growth factor (EGF) and transforming growth factor (TGF)-α strikingly upregulated DcR3 production. TNF-αenhanced DcR3 expression in both keratinocytes and endothelial cells compared with various inflammatory cytokines involved in psoriasis. Additionally, TNF-α-enhanced DcR3 expression in keratinocytes was inhibited when EGFR was knocked down or EGFR inhibitor was used. The NF-κB pathway was critically involved in the molecular mechanisms underlying the action of EGFR and inflammatory cytokines. Collectively, the novel regulatory mechanisms of DcR3 expression in psoriasis, particularly in keratinocytes and endothelial cells, provides new insight into the pathogenesis of psoriasis and may also contribute to the understanding of other diseases that involve DcR3 overexpression.

Tyrosine kinases in inflammatory dermatologic disease

Tyrosine kinases (TKs) are enzymes that catalyze the phosphorylation of tyrosine residues on protein substrates. They are key components of signaling pathways that drive an array of cellular responses including proliferation, differentiation, migration, and survival. Specific TKs have recently been identified as critical to the pathogenesis of several autoimmune and inflammatory diseases. Small-molecule inhibitors of TKs are emerging as a novel class of therapy that may provide benefit in certain patient subsets. In this review, we highlight TK signaling implicated in inflammatory dermatologic diseases, evaluate strategies aimed at inhibiting these aberrant signaling pathways, and discuss prospects for future drug development.

Immunohistochemical localization of transforming growth factor-alpha and epithelial growth factor receptor in human fetal developing skin, psoriasis and restrictive dermopathy

Keratinocytes release a number of cytokines interacting with other intra- and subepidermal cells during the initiation and the perpetuation of skin inflammatory reactions. Cultured human keratinocytes overexpressing the transforming growth factor alpha (TGF-alpha) assumed a spindled morphology and displayed increased locomotion. Moreover, the receptor for TGF-alpha, the epithelial growth factor receptor (EGFR), is important for autocrine growth, promotion of cell survival, and regulation of cell migration. The expression of TGF-alpha and EGFR has not been widely studied in human developing skin and their roles in geno-dermatosis are not known. In this study, we investigated the expression of TGF-alpha and EGFR by immunohistochemistry in human developing skin at different gestational ages (14 th week, 20 th week, and 34 th week), in six patients with psoriasis, and, for the first time, in an infant affected with restrictive dermopathy, a very rare lethal genodermatosis, characterized by abnormal skin growth and differentiation with thin, tightly adherent skin. TGF-alpha and EGFR were expressed in the basal layer at the 14 th week and in all epidermal layers at the 20 th and 34 th week of gestation. In psoriasis, TGF-alpha was overexpressed in all layers of epidermis, while EGFR was expressed in the basal and first suprabasal layers. In restrictive dermopathy, we observed no expression of both TGF-alpha and EGFR at the level of the skin. The other organs showed comparable patterns to those of an age-matched infant. In conclusion, TGF-alpha and EGFR interact strictly to promote skin development during the intrauterine life. An interactive autocrine growth cycle between TGF-alpha and EGFR is present in psoriasis. A skin-localized alteration of the expression of TGF-alpha and EGFR may be at the basis of restrictive dermopathy. The delay of growth and differentiation of the skin in restrictive dermopathy may be related to the absent expression of TGF-alpha, which is probably due to a down regulation of EGFR by an abnormal autocrine mechanism.

Hsp72 antigen expression in the proliferative compartment of involved psoriatic epidermis

Oxidative damage to growth regulatory proteins has been implicated in the aetiology of psoriasis. However, the transient synthesis of heat shock proteins has been shown to protect cells against the adverse effects of oxidative and other forms of physiological stress. This study has used an hsp72 monoclonal antibody to measure inducible 72 kDa heat shock protein expression in heat stressed normal human skin and established plaque psoriasis. Hsp72 was detected in the basal and suprabasal layer cells of heat-stressed normal skin, and in 12 involved psoriasis lesions. Hsp72 expression was not detected in unstressed normal skin or in 12 cases of uninvolved psoriasis. Immunoprecipitation and Western blotting of cell lysates from heat stressed normal skin and involved psoriasis lesions confirmed the presence of a 72 kDa polypeptide with hsp72 immunoreactivity. The MIB-1 monoclonal antibody was used to determine the proliferative fraction of normal and involved psoriastic epidermis. The Ki67 antigen was localised to the nuclei of basal and suprabasal layer cells of normal and involved psoriatic epidermis. Involved psoriatic epidermis contained a higher number of proliferating keratinocytes when compared with normal skin. The study has also demonstrated a strong correlation between hsp72 expression and keratinocyte proliferation in involved psoriatic epidermis (r=0.864, p<0.001). We believe that the 72 kDa inducible heat shock protein performs a protective function in the proliferative compartment of normal and involved psoriatic skin.

The epidermal phenotype during initiation of the psoriatic lesion in the symptomless margin of relapsing psoriasis

BACKGROUND

The mature psoriatic lesion does not necessarily demonstrate changes relevant to early phases of the lesion.

OBJECTIVE

In a model for relapsing psoriasis we examined the epidermal phenotype by means of a panel of immunohistochemical parameters: keratins 14 and 16, epidermal growth factor receptor (EGFR), Ki-67 antigen, and Tdt-mediated Unscheduled Nick End Labeling to detect apoptosis.

METHODS

In 9 patients, we cleared psoriatic plaques by topical treatment with clobetasol-17-propionate under hydrocolloid occlusion. Relapse (defined as a clinical sum score > or = 6) was awaited. Biopsy specimens of the psoriatic lesion, the cleared skin, the relapsed plaque, and its clinically normal margin were assessed.

RESULTS

Psoriasis recurred after 19+/-6 weeks (mean +/- SEM). During treatment all parameters improved considerably; however, the number of apoptotic cells was not affected. Ki-67 values decreased well below the normal range. At initial relapse, the symptomless skin adjacent to the relapsing lesion (margin) showed a marked expression of keratin 16 and EGFR. Ki-67 expression was increasing in the margin but was below values of the mature lesion. The localization of cycling cells in the first suprabasal layers was a remarkable feature. Keratin 14 expression was increased in the recurrent lesion itself, but not in the symptomless margin.

CONCLUSION

Keratin 16 and EGFR expression are early phenomena in the evolution of the lesion, and they anticipate epidermal proliferation. The expression of keratin 14 follows overt epidermal hyperproliferation. The present observation in incipient psoriasis lends support to the hypothesis that the basal cell compartment does not have a primary involvement in the initiation of epidermal abnormalities in psoriasis, but that a coordinated sequence of events involving proliferation and differentiation markers in the first suprabasal layers of the epidermis could be the key to the pathogenesis of this puzzling disease.

Expression of insulin-like growth factor binding protein-3 (IGFBP-3) in the psoriatic lesion

Epidermal hyper-proliferation is a key feature of psoriasis, and a role for IGF-I in this process has previously been proposed. Herein we investigated the expression of IGF binding proteins in the psoriatic lesion and compared it with normal skin. With in situ hybridization, we found that IGFBP-3 mRNA was expressed in the basal layer of the epidermis in normal skin. IGFBP-3 was also detected immunohistochemically, exclusively in the basal layer. In the psoriatic lesion, IGFBP-3 mRNA was similarly limited to the basal layer despite the characteristic expansion of the basaloid keratinocyte compartment and was detected only in the suprapapillary epidermis, where IGFBP-3 mRNA was more abundant than in normal or uninvolved epidermis, and IGFBP-3 protein could be readily detected with specific antibody. As with IGFBP-3 mRNA, which represents the likely site of IGFBP-3 synthesis, IGFBP-3 was strictly limited to the basal keratinocytes of the suprapapillary epidermis. By using an antibody to the cell cycle antigen Ki67, we also showed that the suprapapillary epidermis, where IGFBP-3 expression was maximal, contained few keratinocytes undergoing mitosis, whereas the tips of the rete pegs, where IGFBP-3 expression was conspicuously absent, contained many keratinocytes undergoing mitosis. We suggest that IGFBP-3 is a growth inhibitor in basal keratinocytes and that absence of IGFBP-3 in the tips of rete pegs may contribute to epidermal hyper-proliferation in the psoriatic lesion.

Tape stripping induces marked epidermal proliferation and altered TGF-alpha expression in non-lesional psoriatic skin

Psoriasis is a chronic inflammatory disorder characterized by epidermal hyperproliferation. Although recent evidence suggests that T cell activation is a primary trigger for psoriasis lesions, there may be alterations in the keratinocyte growth regulatory pathways which induce epidermal hyperproliferation in psoriatic patients. To test this hypothesis, we investigated the proliferative activity of epidermal keratinocytes 48 h after tape stripping, one of the standard mechanical ways to stimulate the epidermis, in 20 psoriasis patients and in 18 controls. Epidermal cell kinetics were assessed with DNA flow cytometry, the mitotic index, bromodeoxyuridine incorporation, Ki-67 antigen expression and DNA polymerase alpha expression. The expression of TGF-alpha and EGF receptors, critical mediators of keratinocyte proliferation, were also investigated immunohistochemically. The results of multiparameter assays showed that the baseline proliferative activity in uninvolved skin was the same in psoriasis patients and normal controls. After tape stripping, although both psoriasis patients and the normal controls showed significant increases in epidermal cell proliferation, the values of all the parameters investigated were significantly greater in the psoriasis patients than in the normal controls. EGF receptors were overexpressed in basal and suprabasal keratinocytes after tape stripping in both the psoriasis patients and the normal controls. In contrast, overexpression of TGF-alpha was only observed in the patients with psoriasis, which may explain their increased proliferative response to trauma.

Increased epidermal growth factor receptor in fsn/fsn mice

Epidermal growth factor receptors (EGF-Rs) are elevated in active human psoriatic lesions, but decrease in resolving lesions. Similar biologic responses in EGF-R levels have been demonstrated within human psoriatic skin grafted onto mice. We tested the hypothesis that flaky-skin mice (fsn/fsn), one proposed genetic animal model of psoriasis, would display EGF-R levels comparable to human psoriatic epidermis and show similar biologic responses. EGF-R levels were characterized in unperturbed sites in fsn/fsn skin and +/? skin by enzyme-linked immunosorbent assay, 125I-EGF binding, and immunostaining. Altered EGF-R levels were noted after mild trauma (tape stripping) or under resolving conditions (30 doses of 50 mJ/CM2 ultraviolet B, 2.5 mg/kg oral cyclosporin A, or daily 30 microg/ml topical EGF). Increased EGF-R immunostaining was observed in involved flaky epidermal sites before treatment. To determine whether a hyperproliferative (Koebner) reaction could be induced, we tape stripped fsn/fsn tail and non-flaky dorsal sites. EGF-R levels in dorsal epidermis increased by days 3-4 after injury by enzyme-linked immunoabsorbent assay methods. When fsn/fsn mice received one of three different treatments for 6 weeks, the skin returned to a normal phenotype both grossly and microscopically. Immunoreactive EGF-R in treated, but not untreated, sites decreased to either normal or nondetectable levels. These data indicate that fsn/fsn mice exhibit an EGF-R profile identical to that of lesional and nonlesional human psoriatic epidermis. Modulations of the flaky phenotype in response to injury and three different treatments suggest that fsn/fsn is a useful in vivo model for examining new treatment modalities for psoriasiform skin diseases.