Valentina Mariani

Blockade of the EGF Receptor Induces a Deranged Chemokine Expression in Keratinocytes Leading to Enhanced Skin Inflammation

During inflammatory skin disorders such as psoriasis, atopic dermatitis, and allergic contact dermatitis, epidermal keratinocytes overexpress large amounts of soluble epidermal growth factor receptor ligands in response to tumor necrosis factor alpha and interferon gamma. These cytokines also promote de novo synthesis of numerous chemokines, including CCL2/MCP-1, CCL5/RANTES, CXCL10/IP-10, and CXCL8/IL-8, in turn responsible for the recruitment of different leukocyte populations. This study demonstrates that stimulation of EGFR down-regulates CCL2, CCL5, and CXCL10, while it increases CXCL8 expression in keratinocytes. Conversely, EGFR signaling blockade produces opposite effects, with increased CCL2, CCL5, and CXCL10, and reduced CXCL8 expression. In a mouse model of contact hypersensitivity, a single topical administration of a selective EGFR kinase blocker before antigen challenge results in a markedly enhanced immune response with increased chemokine expression and heavier inflammatory cell infiltrate. Targeting EGFR on epithelial cells may thus have profound impact on inflammatory and immune responses.

ERK1/2 Regulates Epidermal Chemokine Expression and Skin Inflammation

Resident cell populations of the skin contribute to the inflammatory response by producing an array of chemokines, which attract leukocytes from the circulation. TNF-α is a major inducer of proinflammatory mediators in keratinocytes. We have recently observed that epidermal growth factor receptor (EGFR) signaling affects TNF-α-driven chemokine expression in epidermal keratinocytes, and its functional impairment increases the levels of crucial chemoattractants such as CCL2/MCP-1, CCL5/RANTES, and CXCL10/IFN-γ-inducible protein-10. In this study, we report evidence that EGFR-dependent ERK1/2 activity is implicated in this mechanism. Abrogation of ERK1/2 activity with specific inhibitors increased chemokine expression in keratinocytes by enhancing mRNA stabilization. In mouse models, inflammatory response to irritants and T cell-mediated contact hypersensitivity were both aggravated when elicited in a skin area previously treated with an EGFR or a MAPK kinase 1/2 inhibitor. In contrast, impairment of p38αβ MAPK phosphorylation markedly attenuated these responses. Our data indicate that EGFR-dependent ERK1/2 activity in keratinocytes takes part to a homeostatic mechanism regulating inflammatory responses, and emphasize the distinct role of MAPKs as potential targets for manipulating inflammation in the skin.

EGFR regulates the expression of keratinocyte-derived granulocyte/macrophage colony-stimulating factor in vitro and in vivo.

Recent advances in the knowledge of the EGFR pathway have revealed its contribution to distinct immune/inflammatory functions of the epidermis. The purpose of our study was to evaluate the role of EGFR in the regulation of keratinocyte GM-CSF expression. In cultured human keratinocytes, proinflammatory cytokines synergized with TGF-alpha to induce GM-CSF expression. Accordingly, high epidermal levels of EGFR activation are associated with enhanced expression of GM-CSF in lesional skin of patients with psoriasis or allergic contact dermatitis. In cultured keratinocytes, pharmacological inhibition of EGFR activity reduced GM-CSF promoter transactivation, whereas genetic inhibition of AP-1 reduced expression of GM-CSF. Furthermore, EGFR activation enhanced TNF-alpha-induced c-Jun phosphorylation and DNA binding, whereas c-Jun silencing reduced GM-CSF expression. Using two different mouse models, we showed that the lack of a functional EGFR pathway was associated with reduced cytokine-induced phosphorylation of ERK1/2, JNK1/2, c-Jun and reduced keratinocyte-derived GM-CSF expression both in vitro and in vivo. Finally, the analysis of GM-CSF expression in the skin of cancer patients treated with anti EGFR drugs showed an association between ERK activity, c-Jun phosphorylation, and epidermal GM-CSF expression. These data demonstrate that the EGFR pathway is critical for the upregulation of keratinocyte GM-CSF expression under conditions of cytokine stimulation.

Pollen-Derived E1-Phytoprostanes Signal via PPAR-γ and NF-κB-Dependent Mechanisms

In a humid milieu such as mucosal surfaces, pollen grains do not only release allergens but also proinflammatory and immunomodulatory lipids, termed pollen-associated lipid mediators. Among these, the E1-phytoprostanes (PPE1) were identified to modulate dendritic cell (DC) function: PPE1 inhibit the DC’s capacity to produce IL-12 and enhance DC mediated TH2 polarization of naive T cells. The mechanism(s) by which PPE1 act on DC remained elusive. We thus analyzed candidate signaling elements and their role in PPE1-mediated regulation of DC function. Aqueous birch pollen extracts induced a marked cAMP response in DC that could be blocked partially by EP2 and EP4 antagonists. In contrast, PPE1 hardly induced cAMP and the inhibitory effect on IL-12 production was mostly independent of EP2 and EP4. Instead, PPE1 inhibited the LPS-induced production of IL-12 p70 by a mechanism involving the nuclear receptor PPAR-γ. Finally, PPE1 efficiently blocked NF-κB signaling in DCs by inhibiting IκB-α degradation, translocation of p65 to the nucleus, and binding to its target DNA elements. We conclude that pollen-derived PPE1 modulate DC function via PPAR-γ dependent pathways that lead to inhibition of NFκB activation and result in reduced DC IL-12 production and consecutive TH2 polarization.

Plant polyphenols effectively protect HaCaT cells from ultraviolet C-triggered necrosis and suppress inflammatory chemokine expression.

Oxidative stress is a common response of epidermal cells to a variety of noxious stimuli such as ultraviolet (UV) radiation from solar light and proinflammatory cytokines from skin‐infiltrating leukocytes. Here, we report that two types of plant‐derived antioxidants, the phenylpropanoid glycoside verbascoside as well as the flavonoids rutin and quercetin possess protective effects against UVC‐induced cell damage and proinflammatory activation. The molecules under investigation were effective against the loss of cell integrity associated with necrosis in doses consistent with their antioxidant activity, whereas they did not significantly oppose UVC‐induced proliferation arrest and apoptosis. By contrast, only verbascoside effectively inhibited cytokine‐induced release of proinflammatory mediators in a dose‐dependent fashion. Verbascoside and its homologue teupolioside dramatically impaired NF‐κB and AP‐1 DNA binding activity. These results suggest that plant polyphenols with antioxidant properties have distinct mechanisms in the suppression of oxidative stress induced in keratinocytes by different stimuli. Verbascoside and teupolioside are hence of potential interest in the protection of the skin from both environmental and inflammatory insults.

Keratinocytes in skin inflammation

Substantial evidence during the past years has indicated that keratinocytes play an active role in the generation and expression of protective immune responses and immunopathological reactions in the skin. In resting keratinocytes, immune mediators are barely detectable. Upon stimulation by environmental, physical or chemical stimuli, a significant increase in the release of pro-inflammatory mediators can be observed both in vitro and in vivo. The outcome of many skin reactions, however, critically depends on the cross-talk between infiltrating T cells and keratinocytes. Indeed, T-cell-derived lymphokines have been identified as the most effective triggers of keratinocyte expression of soluble and membrane molecules, which in turn are, themselves, responsible for the recruitment and local activation of T cells and other leukocytes, leading to the eventual amplification of the inflammatory reaction.

α‐Fetoprotein as a modulator of the pro‐inflammatory response of human keratinocytes

Background and purpose:  The immunomodulatory effects of α‐fetoprotein (AFP) on lymphocytes and macrophages have been described in vitro and in vivo. Recombinant forms of human AFP have been proposed as potential therapeutic entities for the treatment of autoimmune diseases. We examined the effects of embryonic and recombinant human AFP on the spontaneous, UVA‐ and cytokine‐induced pro‐inflammatory responses of human keratinocytes.

Glutathione peroxidase activity in the blood cells of psoriatic patients correlates with their responsiveness to Efalizumab

Abstract Abstract Biological treatment of psoriasis, a chronic inflammatory immune-mediated pathology of huge social impact, has become a recent revolutionizing breakthrough in the management of the disease. Apart from anti-TNF-alpha biologics, recombinant proteins-inhibitors of the T lymphocytes-antigen presenting cells interaction, Efalizumab among them, have been successfully used in the therapy of psoriasis. Serious concern regarding safety and efficacy of biologics remains because they induce numerous adverse effects and a significant number of patients are non-responders. Up-to-now, there are no biochemical or/and immunological markers of the clinical efficacy of these drugs. This study searches for immunological and redox markers of the clinical response in the group of psoriatic patients treated with Efalizumab. Clinical response to Efalizumab was assessed by Psoriasis Area and Severity Index and correlated with suppression of T-cell functions, plasma cytokines, membrane-associated polyunsaturated fatty acids (PUFAs), antioxidant enzymes and markers of oxidative stress. A 12-week Efalizumab therapy did not affect abnormal plasma levels of pro-inflammatory cytokines and lower-than-normal content of PUFAs esterified in phospholipids of red cell membranes. It did, however, suppress T-cell-mediated functions and decrease nitrites/nitrates and malonyl dialdehyde levels independently on the clinical outcome. On contrast, activities of glutathione peroxidase (GPx) and glutathione S-transferase in granulocytes were remarkably increased and catalase decreased exclusively in non-responders vs complete or partial responders. High baseline GPx in erythrocytes decreased in responders. It is concluded that clinical response to Efalizumab correlates with GPx activity in the blood cells, suggesting that high hydroperoxide levels are involved in psoriasis persistence.