The Basophil-specific Protease mMCP-8 Provokes an Inflammatory Response in the Skin with Microvascular Hyperpermeability and Leukocyte Infiltration.

Basophils have often been erroneously considered to be minor relatives or blood-circulating precursors of tissue-resident mast cells because of some phenotypic similarity between them, including basophilic secretory granules in the cytoplasm. However, recent studies revealed that the repertoire of serine proteases stored in secretory granules is distinct in them. Particularly, mouse mast cell protease 8 (mMCP-8) is specifically expressed by basophils but not mast cells despite its name. Therefore, mMCP-8 is commonly used as a basophil-specific marker, but its functional property remains uncertain. Here we prepared recombinant mMCP-8 and examined its activity in vitro and in vivo Purified recombinant mMCP-8 showed heat-sensitive proteolytic activity when α-tubulin was used as a substrate. One intradermal shot of mMCP-8, not heat-inactivated, induced cutaneous swelling with increased microvascular permeability in a cyclooxygenase-dependent manner. Moreover, repeated intradermal injection of mMCP-8 promoted skin infiltration of leukocytes, predominantly neutrophils and, to a lesser extent, monocytes and eosinophils, in conjunction with up-regulation of chemokine expression in the skin lesion. These results suggest that mMCP-8 is an important effector molecule in basophil-elicited inflammation, providing novel insights into how basophils exert a crucial and non-redundant role, distinct from that played by mast cells, in immune responses.

An Essential Role for SHARPIN in the Regulation of Caspase 1 Activity in Sepsis.

Sepsis is burdened by high mortality due to uncontrolled inflammatory response to pathogens. Increased caspase 1 activation causing maturation of IL1ß/18 remains a therapeutic challenge in sepsis. SHARPIN (shank-associated regulator of G-protein signaling homology domain-interacting protein), a component of the LUBAC (linear ubiquitin chain-assembly complex), regulates inflammation, with unknown effects on caspase 1 activation. Mice lacking Casp1, Casp11, or both in a Sharpin-deficient background were generated, exposed to lipopolysaccharide-induced endotoxemia, and injected with caspase 1 inhibitor. We monitored survival, Il1ß/18, and caspase 1/11 levels in plasma and organs and deciphered mechanisms of SHARPIN-dependent caspase 1 inhibition. A correlation between LUBAC and active caspase 1 was found in blood mononuclear cells from septic patients. SHARPIN bound caspase 1 and disrupted p20/p10 dimer formation, the last step of caspase 1 processing, thereby inhibiting enzyme activation and maturation of IL1ß/18 in a LUBAC-independent manner. In septic patients, LUBAC-independent decline in SHARPIN correlated with enhancement of active caspase 1 in circulating mononuclear cells. Septic Sharpin-deficient mice displayed enrichment in mature Il1ß/18 and active caspase 1, and shortened survival. Inhibition of caspase 1 reduced levels of Il1ß/18 and splenic cell death, and prolonged survival in septic Sharpin-deficient mice. Our findings identify SHARPIN as a potent in vivo caspase 1 inhibitor and propose the caspase 1-SHARPIN interaction as a target in sepsis.

Therapeutic evaluation of HIV transduction basic domain-conjugated superoxide dismutase solution on suppressive effects of the formation of peroxynitrite and expression of COX-2 in murine skin.

BACKGROUND: Homeostasis of reactive oxygen species (ROS) in the skin is regulated by antioxidant defenses. The inflammatory states of skin diseases which range from acute rashes to chronic conditions are related to the level of ROS. The involvement of superoxide dismutase (SOD) in restoring the antioxidant capacity can then neutralize the inflammatory response. RESULTS: We found that denatured Tat-SOD formulated in an aqueous medium could be delivered into mouse skin and the penetration signals of Tat-SOD were detected in the epidermis and dermis. According to immunohistochemical staining, Tat-SOD successfully suppressed inflammation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), the expression of sodium nitroferricyanide (SNP)-induced cyclooxygenase-2 (COX-2), and the production of nitrotyrosine proteins. In nerve growth factor (NGF) induced differentiated PC12 pheochromocytoma cells, we demonstrated that the denatured Tat-SOD regained its antioxidant activity and effectively protected PC12 cells from DNA fragmentation induced by paraquat. Using a luciferase reporter assay, the data was shown Tat-SOD protected PC12 cells from ROS damage, through suppression of COX-2 or nuclear factor-κB (NF-κB) activity occurred at the transcriptional level. CONCLUSION: We showed that Tat-SOD inhibited SNP-induced COX-2 expression similarly to celecoxib and prevented the formation of peroxynitrite as 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. The results suggest that denatured Tat-SOD solution may perform potential protein therapy for patients suffering from disorders related to ROS.

The role of sterol-C4-methyl oxidase in epidermal biology.

Deficiency of sterol C4 methyl oxidase, encoded by the SC4MOL gene, has recently been described in four patients from three different families. All of the patients presented with microcephaly, congenital cataracts, and growth delay in infancy. The first patient has suffered since the age of six years from severe, diffuse, psoriasiform dermatitis, sparing only her palms. She is now 20 years old. The second patient is a 5 year old girl who has just started to develop dry skin and hair changes. The third and fourth patients are a pair of affected siblings with a severe skin condition since infancy. Quantitative sterol analysis of plasma and skin scales from all four patients showed marked elevation of 4α-methyl- and 4, 4'-dimethylsterols, consistent with a deficiency in the first step of sterol C4 demethylation in cholesterol biosynthesis. Mutations in the SC4MOL have been identified in all of the patients. SC4MOL deficiency is the first autosomal recessive disorder identified in the sterol demethylation complex. Cellular studies with patient-derived fibroblasts have shown a higher mitotic rate than control cells in cholesterol-depleted medium, with increased de novo cholesterol biosynthesis and accumulation of methylsterols. Immunologic analyses of granulocytes and B cells from patients and obligate carriers in the patients' families indicated dysregulation of immune-related receptors. Inhibition of sterol C4 methyl oxidase in human transformed lymphoblasts induced activation of the cell cycle. Additional studies also demonstrated diminished EGFR signaling and disrupted vesicular trafficking in cells from the affected patients. These findings suggest that methylsterols play an important role in epidermal biology by their influence on cell proliferation, intracellular signaling, vesicular trafficking and immune response. SC4MOL is situated within the psoriasis susceptibility locus PSORS9, and may be a genetic risk factor for common skin conditions. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Inhibitor κB kinase 2 is a myosin light chain kinase in vascular smooth muscle.

RATIONALE: Myosin light chain (MLC) phosphorylation determines vascular contractile status. In addition to the classic Ca²âº-dependent MLC kinase (MLCK), another unidentified kinase(s) also contributes to MLC phosphorylation in living cells. Inhibitor κB kinase 2 (IKK2)-deficient mouse embryonic fibroblasts demonstrate abnormal morphology and migration, suggesting that IKK2 may be involved in MLC phosphorylation. OBJECTIVE: Therefore, we tested whether IKK2 is an MLCK in living cells and the role of IKK2 in mediating vasoconstriction and blood pressure regulation. METHODS AND RESULTS: In the present study, we showed that recombinant IKK2-phosphorylated MLC and intact myosin in vitro, and the kinetic parameters were comparable with those of the classic MLCK. Overexpression of IKK2 increased cellular MLC phosphorylation level, and pharmacological inhibition of IKK2 markedly decreased vascular smooth muscle cell MLC phosphorylation, suggesting that IKK2 is an MLCK in living cells. IKK2 inhibitors dose- and time-dependently attenuated vasoconstriction elicited by diverse agonists, suggesting the physiological importance of IKK2 as an MLCK. Vascular smooth muscle cell-specific IKK2-deficient mice had decreased aortic contractile responses, and reduced hypertensive responses to several vasoconstrictors, compared with wild-type mice, confirming the physiological importance of IKK2 as an MLCK. CONCLUSIONS: Our data provide a novel mechanism whereby IKK2 regulates MLC phosphorylation as an MLCK and, thus, vascular function and blood pressure.

CD4, IL-17, and COX-2 Are Associated With Subclinical Inflammation in Malar Melasma.

The pathogenesis of melasma, a common, photo-induced hyperpigmentary disorder, is not clearly understood. Significant factors linked to melasma are ultraviolet radiation exposure and genetic predisposition. Histological analysis has demonstrated that melasma is caused by a network of cellular interactions among melanocytes, keratinocytes, mast cells, fibroblasts, and dermal vasculature exhibits, features similar to chronic sun damage. Dermal inflammation caused by ultraviolet radiation might play an important role in the hyperpigmentation and reactivation of melasma lesions through the production of melanogenic cytokines and growth factors. Because the role of inflammation in this disorder is unknown, we used histochemistry, immunohistochemistry, and quantitative real-time polymerase chain reaction to evaluate melasma lesions from healthy female patients (n = 20) with malar melasma. Lesional skin without specific solar exposure or photoprotection measures within the previous 4 weeks was compared with nonlesional skin. The increased lymphocytic infiltrate in lesional skin was mainly composed of CD4 T cells, mast cells, and macrophages. Levels of the cytokine interleukin (IL)-17 and the proinflammatory mediator cyclooxygenase (COX)-2 were significantly elevated in affected skin compared with healthy skin. In addition, the Melasma Activity and Severity Index score, fraction of solar elastosis, and epidermal melanin were positively associated with COX-2 expression. There was no statistically significant difference in IL-1α, IL-1ß, R-IL1, IL-6, IL-8, vascular endothelial growth factor, and tumor necrosis factor alpha expression levels. Together, these data indicated that melasma under unchallenged conditions is characterized by chronic inflammatory cells and mediators, which may explain its recurrent nature.

Deoxynivalenol induced mouse skin cell proliferation and inflammation via MAPK pathway.

Several toxicological manifestations of deoxynivalenol (DON), a mycotoxin, are well documented; however, dermal toxicity is not yet explored. The effect of topical application of DON to mice was studied using markers of skin proliferation, inflammation and tumor promotion. Single topical application of DON (84-672nmol/mouse) significantly enhanced dermal hyperplasia and skin edema. DON (336 and 672nmol) caused significant enhancement in [(3)H]-thymidine uptake in DNA along with increased myeloperoxidase and ornithine decarboxylase activities, suggesting tissue inflammation and cell proliferation. Furthermore, DON (168nmol) caused enhanced expression of RAS, and phosphorylation of PI3K/Akt, ERK, JNK and p38 MAPKs. DON exposure also showed activation of transcription factors, c-fos, c-jun and NF-κB along with phosphorylation of IkBα. Enhanced phosphorylation of NF-κB by DON caused over expression of target proteins, COX-2, cyclin D1 and iNOS in skin. Though a single topical application of DMBA followed by twice weekly application of DON (84 and 168nmol) showed no tumorigenesis after 24weeks, however, histopathological studies suggested hyperplasia of the epidermis and hypertrophy of hair follicles. Interestingly, intestine was also found to be affected as enlarged Peyer's patches were observed, suggesting inflammatory effects which were supported by elevation of inflammatory cytokines after 24weeks of topical application of DON. These results suggest that DON induced cell proliferation in mouse skin is through the activation of MAPK signaling pathway involving transcription factors NFκB and AP-1, further leading to transcriptional activation of downstream target proteins c-fos, c-jun, cyclin D1, iNOS and COX-2 which might be responsible for its inflammatory potential.

Feline eosinophilic dermatoses: a retrospective immunohistochemical and ultrastructural study of extracellular matrix remodelling.

BACKGROUND: Feline eosinophilic dermatoses (FEDs) are common diseases of cats with an unknown pathogenesis. They are histologically characterized by an eosinophilic infiltration and often by the presence of flame figures (FFs) and/or areas of loss of tissue architecture, here termed necrotic foci (NF). It has been postulated that an alteration in the degradation of the extracellular matrix could be responsible for these histological features. Matrix metalloproteinases (MMPs) are a group of proteases that are fundamental in extracellular matrix remodelling. HYPOTHESIS/OBJECTIVES: The aim of the study was to investigate retrospectively the expression of a subgroup of MMPs, in particular MMP-2 and MMP-9 gelatinases, in FEDs. The expression of one of their inhibitors, TIMP-2, was also investigated in order to establish the role of these molecules in the pathogenesis of FEDs. The ultrastructural characteristics of extracellular matrix in FFs and NF were subsequently assessed. METHODS: Fifty-one formalin-fixed, paraffin-embedded specimens from cutaneous and mucosal biopsies diagnosed as FEDs were investigated immunohistochemically. Two selected samples were processed for electron microscopy. RESULTS: This study revealed an increased expression of MMP-2 in NF and a decreased expression of this gelatinase in FFs. An imbalance between MMP-2 and TIMP-2 was evident using immunohistochemistry. No significative results were observed for MMP-9 expression. Electron microscopy confirmed the lack of normal collagen fibres in NF, whereas in FFs only occasional, amorphous material was observed among normal collagen fibres. CONCLUSIONS AND CLINICAL IMPORTANCE: Our study suggests that an imbalance in the expression of matrix metalloproteinases could be responsible for different morphological findings in FEDs. Further studies are needed to assess the role of matrix metalloproteinases in the pathogenesis of FEDs.

PXS-4681A, a potent and selective mechanism-based inhibitor of SSAO/VAP-1 with anti-inflammatory effects in vivo.

Semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1), is a member of the copper-dependent amine oxidase family that is associated with various forms of inflammation and fibrosis. To investigate the therapeutic potential of SSAO/VAP-1 inhibition, potent and selective inhibitors with drug-like properties are required. PXS-4681A [(Z)-4-(2-(aminomethyl)-3-fluoroallyloxy)benzenesulfonamide hydrochloride] is a mechanism-based inhibitor of enzyme function with a pharmacokinetic and pharmacodynamic profile that ensures complete, long-lasting inhibition of the enzyme after a single low dose in vivo. PXS-4681A irreversibly inhibits the enzyme with an apparent Ki of 37 nM and a kinact of 0.26 min(-1) with no observed turnover in vitro. It is highly selective for SSAO/VAP-1 when profiled against related amine oxidases, ion channels, and seven-transmembrane domain receptors, and is superior to previously reported inhibitors. In mouse models of lung inflammation and localized inflammation, dosing of this molecule at 2 mg/kg attenuates neutrophil migration, tumor necrosis factor-α, and interleukin-6 levels. These results demonstrate the drug-like properties of PXS-4681A and its potential use in the treatment of inflammation.

Netherton syndrome: skin inflammation and allergy by loss of protease inhibition.

Netherton syndrome (NS) is a rare autosomal recessive skin disease with severe skin inflammation and scaling, a specific hair shaft defect and constant allergic manifestations. NS is caused by loss-of-function mutations in SPINK5 (serine protease inhibitor of kazal type 5) encoding LEKTI-1 (lympho-epithelial kazal type related inhibitor type 5) expressed in stratified epithelia. In vitro and in vivo studies in murine models and in NS patients have cast light on the pathogenesis of the disease and shown that LEKTI deficiency results in unopposed kallikrein-related peptidase 5 (KLK5) and KLK7 activities and to the overactivity of a new epidermal protease, elastase 2 (ELA2). Two main cascades initiated by KLK5 activity have emerged. One results in desmoglein 1 degradation and desmosome cleavage leading to stratum corneum detachment. KLK5 also activates KLK7 and ELA2, which contribute to a defective skin barrier. This facilitates allergen and microbe penetration and generates danger signals leading to caspase 1 activation and the production of active interleukin-1ß. In parallel, KLK5 activates a specific cascade of allergy and inflammation by activating protease-activated receptor-2 (PAR-2) receptors. PAR-2 activation triggers the production of the major pro-Th2 cytokine TSLP (thymic stromal lymphopoietin) and several inflammatory cytokines, including tumour necrosis factor-α. Levels of thymus and activation-regulated chemokine (TARC) and macrophage-derived chemokine (MDC) also contribute to allergy in a PAR-2-independent manner. Patient investigations have confirmed these abnormalities and revealed a wide spectrum of disease expression, sometimes associated with residual LEKTI expression. These results have demonstrated that the tight regulation of epidermal protease activity is essential for skin homeostasis and identified new targets for therapeutic intervention. They also provide a link with atopic dermatitis through deregulated protease activity, as recently supported by functional studies of the E420K LEKTI variant.

[Effects of zhuhong ointment on MMPs activities and production by HSF].

HuaFu Shengji is the primary traditional Chinese medicine (TCM) therapy for treating chronic skin ulcer. The high activities of the protein enzyme in the wound fluids is one of the main cause of healing delay. In order to investigate the effect of TCM Zhuhong ointment for promoting wound healing. This research focused on its influence on matrix metalloproteinase (MMP) activities in wound fluids with TCM Yang syndromes, directly on the activated MMP-1,2 activities in vitro and on MMP-1,-2,-9 production by HSF. 8 wound fluid samples were collected, which were diagnosed Yang Syndromes in TCM. Wound fluid activities of MMP-2 and MMP-9 were measured by gelatin zymogram assay. MMP-1 and MMP-2 activities in vitro were measured by substrate cleavage. CCK-8 was used to observe the toxicity of Zhuhong ointment on HSF. MMP-1,-2,-9 production by HSF were detected by confocal microscope. Zhuhong ointment from 1 to 25 g x L(-1) obviously inhibited MMP-2 activity in wound fluid. When Zhuhong ointment was over 5 g x L(-1), it showed significantly inhibitory effect on wound fluid MMP-9 activity. In vitro study, when the mercury concentration was 320 mg x L(-1), Zhuhong ointment solution directly inhibited both MMP-1 activity and MMP-2. But mercury concentration from 0.51-2.56 mg x L(-1), it could activate MMP-1 activity, and from 0.51-64 mg x L(-1), activate MMP-2 activity instead. The mercury concentration when Zhuhong ointment saturated in DMEM was 39.6 mg x L(-1). When the mercury concentration was over 1.23 mg x L(-1), Zhuhong ointment showed toxicity to HSF. At 1.23, 0.62, 0.31 mg x L(-1) of mercury concentration, it increased MMP-1 expression by HSF, and at 1.23, 0.62 mg x L(-1), decreased MMP-2 expression. However, at 1.23, 0.62, 0.31 mg x L(-1), it decreased MMP-9 expression. At higher concentration, Zhuhong ointment can inhibit MMP-2, MMP-9 activities in wound fluid with dose-dependent way and show a direct inhibitory effect on activated MMP-1 and MMP-2 in vitro. But at a lower concentration, it showed two-way adjustment, with increased MMP-1, MMP-2 activities and its expression by HSF and decreased MMP-9 activity.

T-LAK cell-originated protein kinase (TOPK) phosphorylation of MKP1 protein prevents solar ultraviolet light-induced inflammation through inhibition of the p38 protein signaling pathway.

Solar UV radiation is a major environmental factor that causes DNA damage, inflammation, and even skin cancer. T-LAK cell-originated protein kinase (TOPK) is expressed widely in both normal and cancer cells and functions to inhibit apoptosis and promote carcinogenesis. However, its function in inflammation is not known. The p38 MAPK signaling pathway plays an important role in solar UV light-induced inflammation. In this study, we found that TOPK negatively regulated the activity of p38α by phosphorylating the p38α-specific phosphatase MKP1 and enhancing the stability of MKP1. Notably, the absence of TOPK in mice resulted in a striking increase in skin inflammation. Therefore, we conclude that TOPK has a protective function in solar UV light-induced inflammation.

Overexpression of phospholipase Cε in keratinocytes upregulates cytokine expression and causes dermatitis with acanthosis and T-cell infiltration.

Phospholipase Cε (PLCε) is an effector of Ras and Rap small GTPases. We showed previously using PLCε-deficient mice that PLCε plays a critical role in activation of cytokine production in non-immune skin cells in a variety of inflammatory reactions. For further investigation of its role in inflammation, we created transgenic mice overexpressing PLCε in epidermal keratinocytes. The resulting transgenic mice spontaneously developed skin inflammation as characterized by formation of adherent silvery scales, excessive growth of keratinocytes, and aberrant infiltration of immune cells such as T cells and DC. Development of the skin symptoms correlated well with increased expression of factors implicated in human inflammatory skin diseases, such as IL-23, in keratinocytes, and with the accumulation of CD4(+) T cells producing IL-22, a potent inducer of keratinocyte proliferation. Intradermal injection of a blocking antibody against IL-23 as well as treatment with the immunosuppressant FK506 reversed these skin phenotypes, which was accompanied by suppression of the IL-22-producing T-cell infiltration. These results reveal a crucial role of PLCε in the development of skin inflammation and suggest a mechanism in which PLCε induces the production of cytokines including IL-23 from keratinocytes, leading to the activation of IL-22-producing T cells.

Inhibiting glycogen synthase kinase-3 decreases 12-O-tetradecanoylphorbol-13-acetate-induced interferon-γ-mediated skin inflammation.

Glycogen synthase kinase-3 (GSK-3) facilitates interferon (IFN)-γ signaling. Because IFN-γ is involved in inflammatory skin diseases, such as psoriasis, the aim of this study was to investigate the pathogenic role of GSK-3 in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced IFN-γ-mediated ear skin inflammation. TPA (3 µg per ear) induced acute skin inflammation in the ears of C57BL/6 mice, including edema, infiltration of granulocytes but not T cells, and IFN-γ receptor 1-mediated deregulation of intercellular adhesion molecule 1 (CD54). TPA/IFN-γ induced GSK-3 activation, which in turn activated signal transducer and activator of transcription 1. Inhibiting GSK-3 pharmacologically, by administering 6-bromoindirubin-3'-oxime (1.5 µg per ear), and genetically, with lentiviral-based short-hairpin RNA, reduced TPA-induced acute skin inflammation but not T-cell infiltration. It is noteworthy that inhibiting GSK-3 decreased TPA-induced IFN-γ production and the nuclear translocation of T-box transcription factor Tbx21, a transcription factor of IFN-γ, in CD3-positive T cells. In chronic TPA-induced skin inflammation, inhibiting GSK-3 attenuated epidermis hyperproliferation and dermis angiogenesis. These results demonstrate the dual role of GSK-3 in TPA-induced skin inflammation that is not only to facilitate IFN-γ signaling but also to regulate IFN-γ production. Inhibiting GSK-3 may be a potential treatment strategy for preventing such effects.

Increased matriptase zymogen activation in inflammatory skin disorders.

Matriptase, a type 2 transmembrane serine protease, and its inhibitor hepatocyte growth factor activator inhibitor (HAI)-1 are required for normal epidermal barrier function, and matriptase activity is tightly regulated during this process. We therefore hypothesized that this protease system might be deregulated in skin disease. To test this, we examined the level and activation state of matriptase in examples of 23 human skin disorders. We first examined matriptase and HAI-1 protein distribution in normal epidermis. Matriptase was detected at high levels at cell-cell junctions in the basal layer and spinous layers but was present at minimal levels in the granular layer. HAI-1 was distributed in a similar pattern, except that high-level expression was retained in the granular layer. This pattern of expression was retained in most skin disorders. We next examined the distribution of activated matriptase. Although activated matriptase is not detected in normal epidermis, a dramatic increase is seen in keratinocytes at the site of inflammation in 16 different skin diseases. To gain further evidence that activation is associated with inflammatory stimuli, we challenged HaCaT cells with acidic pH or H(2)O(2) and observed matriptase activation. These findings suggest that inflammation-associated reactive oxygen species and tissue acidity may enhance matriptase activation in some skin diseases.

Inhibition of the IL-2-inducible tyrosine kinase (Itk) activity: a new concept for the therapy of inflammatory skin diseases.

T-cell-mediated processes play an essential role in the pathogenesis of several inflammatory skin diseases such as atopic dermatitis, allergic contact dermatitis and psoriasis. The aim of this study was to investigate the role of the IL-2-inducible tyrosine kinase (Itk), an enzyme acting downstream of the T-cell receptor (TCR), in T-cell-dependent skin inflammation using three approaches. Itk knockout mice display significantly reduced inflammatory symptoms in mouse models of acute and subacute contact hypersensitivity (CHS) reactions. Systemic administration of a novel small molecule Itk inhibitor, Compound 44, created by chemical optimization of an initial high-throughput screening hit, inhibited Itk's activity with an IC50 in the nanomolar range. Compound 44 substantially reduced proinflammatory immune responses in vitro and in vivo after systemic administration in two acute CHS models. In addition, our data reveal that human Itk, comparable to its murine homologue, is expressed mainly in T cells and is increased in lesional skin from patients with atopic dermatitis and allergic contact dermatitis. Finally, silencing of Itk by RNA interference in primary human T cells efficiently blocks TCR-induced lymphokine secretion. In conclusion, Itk represents an interesting new target for the therapy of T-cell-mediated inflammatory skin diseases.

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.

Role of p38 mitogen-activated protein kinase isoforms in murine skin inflammation induced by 12-O-tetradecanoylphorbol 13-acetate.

p38 mitogen-activated protein kinase plays a pivotal role in skin inflammation. The purpose of this study was to investigate the role of the various p38 isoforms. p38ß/δ-knockout-C57BL/6 mice were generated, studied in a 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced skin inflammation model and compared with wild-type mice. The inflammatory response was determined by ear thickness, myeloperoxidase activity and histology. mRNA and protein expression of interleukin (IL)-1ß and IL-6 was determined by quantitative real-time reverse transcription PCR and enzyme-linked immunoassay. In both groups application of TPA resulted in a significant increase in inflammation, and pretreatment with the p38α/ß inhibitor, SB202190 resulted in a significant inhibition. A significantly slower onset but prolonged duration of the response was seen in p38ß/δ knockout mice. This was paralleled by a significant, but transient, lower IL-1ß and IL-6 protein expression in p38ß/δ knockout mice. Although the p38α isoform is important, our data also demonstrate an important role of the p38ß and/or δ isoforms in the regulation of TPA-induced skin inflammation.

A conserved serine residue is required for the phosphatidate phosphatase activity but not the transcriptional coactivator functions of lipin-1 and lipin-2.

Mammalian lipins (lipin-1, lipin-2, and lipin-3) are Mg2+-dependent phosphatidate phosphatase (PAP) enzymes, which catalyze a key reaction in glycerolipid biosynthesis. Lipin-1 also functions as a transcriptional coactivator in conjunction with members of the peroxisome proliferator-activated receptor family. An S734L mutation in LPIN2 causes Majeed syndrome, a human inflammatory disorder characterized by recurrent osteomyelitis, fever, dyserythropoietic anemia, and cutaneous inflammation. Here we demonstrate that mutation of the equivalent serine in mouse lipin-1 and lipin-2 to leucine or aspartate abolishes PAP activity but does not impair lipin association with microsomal membranes, the major site of glycerolipid synthesis. We also determined that lipin-2 has transcriptional coactivator activity for peroxisome proliferator-activated receptor-response elements similar to lipin-1 and that this activity is not affected by mutating the conserved serine. Therefore, our results indicate that the symptoms of the Majeed syndrome result from a loss of lipin-2 PAP activity. To characterize sites of lipin-2 action, we detected lipin-2 expression by in situ hybridization on whole mouse sections and by quantitative PCR of tissues relevant to Majeed syndrome. Lipin-2 was most prominently expressed in liver, where levels were much higher than lipin-1, and also in kidney, lung, gastrointestinal tract, and specific regions of the brain. Lipin-2 was also expressed in circulating red blood cells and sites of lymphopoiesis (bone marrow, thymus, and spleen). These results raise the possibility that the loss of lipin-2 PAP activity in erythrocytes and lymphocytes may contribute to the anemia and inflammation phenotypes observed in Majeed syndrome patients.

A proinflammatory activity of interleukin 8 in human skin: expression of the inducible nitric oxide synthase in psoriatic lesions and cultured keratinocytes.

Psoriasis is a common chronic skin disease mediated by cellular immune mechanisms and characterized by an intense neutrophil cell infiltrate and proliferative activation of epidermal keratinocytes. We have previously described the expression of the inducible nitric oxide synthase (iNOS) in epidermal keratinocytes of psoriatic skin lesions. In this study, the role of iNOS in psoriatic inflammation was explored ex vivo in psoriatic skin biopsies and in vitro in primary cultures of human keratinocytes. Messenger RNA for the iNOS enzyme (iNOS mRNA) was detected by reverse transcriptase polymerase chain reaction in skin biopsies from patients with psoriasis, but not in skin specimens from patients with atopic eczema or from healthy volunteers. As demonstrated by in situ hybridization and immunohistochemistry, expression of iNOS mRNA and its gene product was localized to the epidermal keratinocytes of psoriatic skin lesions. In situ hybridization further revealed a complete colocalization of mRNA expression for iNOS with interleukin (IL) 8 receptor-specific mRNA either in the basal germinative cell layer or at focal sites of ongoing neutrophil inflammation in suprabasal cell layers. Because psoriatic keratinocytes have previously been shown to express mRNA transcripts for IL-8, it seemed reasonable to hypothesize that iNOS expression could be induced in an autocrine loop by IL-8. This hypothesis was substantiated by our in vitro experiments showing that a combination of IL-8 and interferon gamma induces the expression of iNOS-specific mRNA and of the functional enzyme in cultured human keratinocytes. These results suggest an important role for iNOS in concert with IL-8 and its receptor early during the formation of psoriatic lesions.