Normal response to tumor necrosis factor-alpha and transforming growth factor-beta by keratinocytes in psoriasis

Cytokines in psoriasis: From pathogenesis to targeted therapy

Psoriasis is a multifactorial disease that affects 0.84% of the global population and it can be associated with disabling comorbidities. As patients present with thick scaly lesions, psoriasis was long believed to be a disorder of keratinocytes. Psoriasis is now understood to be the outcome of the interaction between immunological and environmental factors in individuals with genetic predisposition. While it was initially thought to be solely mediated by cytokines of type-1 immunity, namely interferon-γ, interleukin-2, and interleukin-12 because it responds very well to cyclosporine, a reversible IL-2 inhibitor; the discovery of Th-17 cells advanced the understanding of the disease and helped the development of biological therapy. This article aims to provide a comprehensive review of the role of cytokines in psoriasis, highlighting areas of controversy and identifying the connection between cytokine imbalance and disease manifestations. It also presents the approved targeted treatments for psoriasis and those currently under investigation.

CD109 release from the cell surface in human keratinocytes regulates TGF-β receptor expression, TGF-β signalling and STAT3 activation: relevance to psoriasis

Transforming growth factor (TGF)-β is an important cytokine that negatively regulates keratinocyte proliferation. Deregulation of TGF-β signalling has been reported in psoriasis, where despite increased expression of TGF-β, psoriatic keratinocytes continue to hyperproliferate. Recently, we have identified CD109, a glycosyl phosphatidylinositol (GPI)-anchored protein, as a novel co-receptor and negative regulator of TGF-β signalling. In the current work, we demonstrate that release of CD109 from the cell surface or the addition of CD109 protein results in downregulation of TGF-β signalling and TGF-β receptor expression in human keratinocytes. Moreover, these effects are associated with an increase in phospho-STAT3 levels, enhanced total STAT3 and Bcl-2 expression and an increase in cell growth and survival, suggesting that released/soluble CD109 is able to induce molecular changes that are known to occur in psoriasis. Analysis of CD109 expression in psoriasis patients reveals that CD109 protein expression is markedly decreased in psoriatic epidermis as compared to adjacent uninvolved skin. In contrast, CD109 mRNA expression is unchanged in psoriatic plaques in comparison with normal skin. This raises a possibility that CD109 protein release is enhanced in psoriatic keratinocytes. Furthermore, psoriatic epidermis displays decreased expression of TGF-β receptors, consistent with the results obtained in vitro in keratinocytes with CD109 release or addition of CD109 recombinant protein. Together our findings suggest that aberrant CD109 release from the cell surface in human keratinocytes may induce molecular changes that are usually observed in psoriasis and may explain TGF-β receptor downregulation and decrease in TGF-β signalling in psoriasis.

Loss of expression of TGF-βs and their receptors in chronic skin lesions induced by sulfur mustard as compared with chronic contact dermatitis patients

BACKGROUND

Sulfur mustard (SM) is a blister-forming agent that has been used as a chemical weapon. Sulfur mustard can cause damage in various organs, especially the skin, respiratory system, and eyes. Generally, the multiple complications of mustard gas result from its alkalizing potency; it reacts with cellular components like DNA, RNA, proteins, and lipid membranes.TGF-β is a multi-functional cytokine with multiple biological effects ranging from cell differentiation and growth inhibition to extracellular matrix stimulation, immunosuppression, and immunomodulation. TGF-β has 3 isoforms (TGF-β 1, 2, 3) and its signaling is mediated by its receptors: R1, R2 and intracellular Smads molecules.TGF-β has been shown to have anti-inflammatory effects. TGF-βs and their receptors also have an important role in modulation of skin inflammation, proliferation of epidermal cells, and wound healing, and they have been implicated in different types of skin inflammatory disorders.

METHODS

Seventeen exposed SM individuals (48.47 ± 9.3 years), 17 chronic dermatitis patients (46.52 ± 14.6 years), and 5 normal controls (44.00 ± 14.6 years) were enrolled in this study.Evaluation of TGF-βs and their receptors expressions was performed by semiquantitative RT-PCR. Only TGF1 was analyzed immunohistochemically.

RESULTS

Our results showed significant decreases in the expression percentages of TGF-β 1, 2 and R1, R2 in chemical victims in comparison with chronic dermatitis and normal subjects and significant decreases in the intensity of R1 and R2 expressions in chemical victims in comparison with chronic dermatitis and normal controls. (P value < 0.05)

CONCLUSIONS

TGF-βs and their receptors appear to have a noticeable role in chronic inflammatory skin lesions caused by sulfur mustard.

Immunopathogenesis of psoriasis

Psoriasis is a chronic skin disease that affects about 1.5% of the Caucasian population and is characterized by typical macroscopic and microscopic skin alterations. Psoriatic lesions are sharply demarcated, red and slightly raised lesions with silver-whitish scales. The microscopic alterations of psoriatic plaques include an infiltration of immune cells in the dermis and epidermis, a dilatation and an increase in the number of blood vessels in the upper dermis, and a massively thickened epidermis with atypical keratinocyte differentiation. It is considered a fact that the immune system plays an important role in the pathogenesis of psoriasis. Since the early 1990s, it has been assumed that T1 cells play the dominant role in the initiation and maintenance of psoriasis. However, the profound success of anti-tumor necrosis factor-alpha therapy, when compared with T-cell depletion therapies, should provoke us to critically re-evaluate the current hypothesis for psoriasis pathogenesis. Recently made discoveries regarding other T-cell populations such as Th17 and regulatory T cells, dendritic cells, macrophages, the keratinocyte signal transduction and novel cytokines including interleukin (IL)-22, IL-23 and IL-20, let us postulate that the pathogenesis of psoriasis consists of distinct subsequent stages, in each of them different cell types playing a dominant role. Our model helps to explain the varied effectiveness of the currently tested immune modulating therapies and may enable the prediction of the success of future therapies.

The mast cell products histamine and serotonin stimulate and TNF-alpha inhibits the proliferation of murine epidermal keratinocytes in situ

To better characterize the proposed growth modulatory functions of mast cells and their products in the regulation of epidermal homeostasis, we have assessed keratinocyte proliferation by incorporation of [3H]thymidine in murine skin organ cultures after incubation with different concentrations of histamine, serotonin or TNF-alpha. Both histamine and serotonin significantly stimulate the proliferation of keratinocytes as compared to controls (P < 0.001), reaching maxima within a range from micro- to nanomolar concentrations. Even at subnanomolar concentration, TNF-alpha significantly inhibits the incorporation of labelled thymidine by epidermal keratinocytes in murine skin organ culture (P < 0.001). These observations support the concept of mast cell products as modulators of keratinocyte proliferation, and suggest a role for mast cells in the regulation of epidermal tissue turnover under physiological conditions.

A comparison of the stimulatory effects of cytokines on normal and psoriatic keratinocytes in vitro

Keratinocytes from normal and psoriatic skin were tested for their in vitro proliferative response to a range of concentrations of rIL-6, rTGF alpha, rIL-8 and rGM-CSF using a serum-free culture system. With one exception, all normal cultures (11/12) were stimulated by 1000 ng/ml IL-6 (P < 0.001). Six out of ten psoriatic keratinocyte cultures were also stimulated at this concentration, but this just failed to reach significance (P = 0.05). As a group, the response by psoriatic keratinocytes to IL-6 was significantly less than that of normal keratinocytes (P = 0.02). TGF alpha at 1 ng/ml induced proliferation in approximately 60% of both normal (8/12, P < 0.05) and psoriatic (6/10, P < 0.01) keratinocyte cultures; there was no significant difference between the responses of the two groups to this cytokine. In addition, small numbers of both normal and psoriatic cultures responded to TGF alpha over a concentration range of 0.1 to 100 ng/ml. Approximately half of the normal and psoriatic cultures were stimulated by 10-1000 ng/ml IL-8. However, the effect was not significant for the group at any of the concentrations tested. GM-CSF had minimal to no effect on most of the normal and psoriatic cultures tested. This study showed that psoriatic keratinocytes are equally responsive to the stimulatory effects of TGF alpha and IL-8, but are less susceptible to IL-6 compared to keratinocytes from normal skin. These findings are consistent with a role for these cytokines in the maintenance of a hyperproliferative epidermis in psoriasis.