Keratinocytes In Psoriatic Lesions Research Articles

Cytosolic DNA Triggers Inflammasome Activation in Keratinocytes in Psoriatic Lesions

The proinflammatory cytokine interleukin-1β (IL-1β) plays a central role in the pathogenesis and the course of inflammatory skin diseases, including psoriasis. Posttranscriptional activation of IL-1β is mediated by inflammasomes; however, the mechanisms triggering IL-1β processing remain unknown. Recently, cytosolic DNA has been identified as a danger signal that activates inflammasomes containing the DNA sensor AIM2. In this study, we detected abundant cytosolic DNA and increased AIM2 expression in keratinocytes in psoriatic lesions but not in healthy skin. In cultured keratinocytes, interferon-γ induced AIM2, and cytosolic DNA triggered the release of IL-1β via the AIM2 inflammasome. Moreover, the antimicrobial cathelicidin peptide LL-37, which can interact with DNA in psoriatic skin, neutralized cytosolic DNA in keratinocytes and blocked AIM2 inflammasome activation. Together, these data suggest that cytosolic DNA is an important disease-associated molecular pattern that can trigger AIM2 inflammasome and IL-1β activation in psoriasis. Furthermore, cathelicidin LL-37 interfered with DNA-sensing inflammasomes, which thereby suggests an anti-inflammatory function for this peptide. Thus, our data reveal a link between the AIM2 inflammasome, cathelicidin LL-37, and autoinflammation in psoriasis, providing new potential targets for the treatment of this chronic skin disease.

Stat3 as a Therapeutic Target for the Treatment of Psoriasis: A Clinical Feasibility Study with STA-21, a Stat3 Inhibitor

Epidermal keratinocytes in psoriatic lesions are characterized by activated Stat3, and increased levels of cytokines and growth factors that promote Stat3 activation have been found within psoriatic lesions. K5.Stat3C transgenic mice, in which keratinocytes express a constitutively active Stat3, develop psoriasis-like skin lesions. In this study, we examined whether STA-21, a small Stat3 inhibitor, could be useful in ameliorating the skin lesions not only in the model mouse but also in human psoriasis. Treatment with STA-21 markedly inhibited the cytokine-dependent nuclear translocation of Stat3 in normal human keratinocytes in vitro. Keratinocyte proliferation was inhibited by STA-21 in a dose-dependent manner through downregulation of c-Myc and cyclin D1, whereas involucrin, transglutaminase 1, and keratin 10 levels were upregulated. Topical application of STA-21 abolished the generation of skin lesions in K5.Stat3C mice. Finally, we treated psoriasis patients with STA-21-containing ointment in a nonrandomized study. Psoriatic lesions in six of the eight patients showed improvement after topical STA-21 treatment for 2 weeks. Therefore, we conclude that targeting Stat3 may lead to a therapy for psoriasis.

Molecular pathophysiology of psoriasis and molecular targets of antipsoriatic therapy

Psoriasis is a chronic inflammatory skin disease characterised by elevated red scaly plaques on specific body sites. Histologically, the plaques are defined by epidermal hyperplasia, epidermal and dermal infiltration by leukocytes, and changes in the dermal microvasculature. Differentiation and activation are disturbed in lesional psoriatic keratinocytes, and the pool of proliferating keratinocytes is increased, which is accompanied by enhanced production of proinflammatory cytokines, adhesion molecules and antimicrobial peptides. These changes in psoriatic keratinocytes are caused by altered expression of genes associated with epidermal differentiation, and by activation of signalling pathways involving signal transducer and activator of transcription 3 (STAT3), type I interferon (IFN) and mitogen-activated protein kinase (MAPK). The number of T cells, and myeloid and plasmacytoid dendritic cells (DCs) is markedly increased in psoriatic lesions. Myeloid DCs produce interleukin (IL)-23, tumour necrosis factor (TNF)-alpha and inducible nitric oxide synthase (iNOS), which are crucial cytokines in the pathogenesis of psoriasis. IL-23 stimulates the secretion of IL-22 by T helper 17 cells, and IL-22 induces epidermal hyperplasia. The crosstalk between keratinocytes and leukocytes via their proinflammatory cytokines creates the vicious circle of chronic skin inflammation seen in psoriasis. This suggests that optimal treatment of psoriasis needs to target pathogenic pathways in both leukocytes and keratinocytes.

Increased HIF‐1 alpha immunostaining in psoriasis compared to psoriasiform dermatitides

Expression of hypoxia inducible factor 1 (HIF-1) alpha can be linked to inflammation through reciprocal interactions with several cytokines. This finding is in accordance with the previously noted HIF-1 alpha overexpression in psoriatic lesional keratinocytes. In this study we have employed a carefully selected panel of antibodies and quantitative morphometric analysis to compare HIF-1 alpha immunoreactivity in psoriatic biopsy samples vs. that in samples obtained from psoriasiform dermatitides. We found statistically significant HIF-1 alpha overexpression in psoriasis. Furthermore, we observed a previously unreported preferential localization of immunoreactive keratinocytes in the immediate vicinity of inflamed and elongated papillae. This pattern of immunoreactivity may partially account for the observed increase of HIF-1 alpha immunostaining in psoriasis. Overall, our findings imply that possible novel therapeutic intervention(s) on the HIF-1 alpha pathway may offer another approach in controlling the inflammatory activity of psoriatic lesions.

Increased expression of CD208 (DC‐LAMP) in epidermal keratinocytes of psoriatic lesions

Psoriasis is a chronic inflammatory skin disease characterized by epidermal hyperproliferation and infiltration of inflammatory leukocytes. The aim of this study was to clarify the role of innate immunity involving dendritic cells (DC) and keratinocytes in psoriasis. We immunohistochemically examined the expression of DC markers such as CD1a, CD83, CD207 (Langerin), CD208 (DC-LAMP) and CD209 (DC-SIGN) in psoriatic skin and gamma-interferon (IFN-gamma)/12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated keratinocytes in vitro. CD208 was strongly expressed in basal and suprabasal layer keratinocytes in addition to DC in the perivascular lesions of the psoriatic dermis. Furthermore, the enhanced expression of CD208 in the perinuclear lesions of IFN-gamma-/TPA-stimulated keratinocytes was observed in vitro. Because a defect of the granular layer in psoriatic lesions has been recognized, increased expression of lysosome-related CD208 in the basal and suprabasal keratinocytes of psoriatic lesions might represent aberrant epidermal differentiation. Additionally, these CD208-positive keratinocytes possessing putative antigen-processing activity might play a key role as antigen-presenting cells in psoriatic skin.

Overexpression of vascular endothelial growth factor (VEGF) receptors on keratinocytes in psoriasis: regulated by calcium independent of VEGF

Psoriasis is a common chronic inflammatory disease of the skin characterized by epidermal hyperplasia and angiogenesis. Recently, vascular endothelial growth factor receptors (VEGFRs, including VEGFR-1, VEGFR-2 and VEGFR-3) were found to be expressed in normal human epidermis and associated with proliferation and migration of keratinocytes. The purpose of this study is to investigate the expression of VEGFRs on psoriatic keratinocytes and the roles of calcium and VEGF in regulating VEGFR expression. Skin samples from 17 patients with chronic plaque psoriasis and 11 normal controls were included. The expression of VEGFRs in psoriatic keratinocytes at mRNA and protein levels was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. Localization of the VEGFRs in skin lesions was determined by immuno-fluorescent method. Since keratinocyte proliferation and differentiation rely on calcium concentrations, and VEGF is overexpressed in psoriatic epidermis, we further investigated the roles of calcium and VEGF in regulating the expression of VEGFRs. Overexpression of VEGFR-1, VEGFR-2 and VEGFR-3 in psoriatic epidermis was demonstrated both at mRNA and protein levels in vitro. VEGFRs were strongly labeled in non-lesional, perilesional and lesional psoriatic keratinocytes in all viable epidermal stratums in vivo. Furthermore, both exogenous VEGF165 and calcium enhanced the expression of VEGFRs. Calcium also enhanced the expression of VEGF in non-lesional psoriatic keratinocytes, while targeted blockade of VEGF activity by bevacizum-ab could not inhibit calcium-induced up-regulation of protein levels of VEGFRs. We conclude from these results that VEGFRs are overexpressed in lesional psoriatic epidermal keratinocytes. Both calcium and VEGF regulate VEGFRs expression in psoriatic epidermis. More importantly, calcium is a potential regulator for VEGFR independent of VEGF.

Adrenocorticotropin Hormone Stimulates Interleukin-18 Expression in Human HaCaT Keratinocytes

The hypothalamic-pituitary-adrenal (HPA) axis is activated by stress. This involves the production of corticotropin releasing hormone (CRH) with the subsequent release of proopiomelanocortin (POMC) peptides, of which adrenocorticotropin hormone (ACTH) is most important. Although the skin has the capacity to produce CRH and POMC peptides, the immunomodulatory roles of ACTH in skin are yet unknown. IL-18 has been known to affect cells involved in the inflammatory response. In this study, we aimed to identify the regulatory effect of ACTH on IL-18 expression of skin keratinocytes. Exposure of HaCaT cells to ACTH stimulated formation of IL-18 mRNA transcript and its protein products in a dose-dependent manner. Furthermore, we suggest that ACTH-induced IL-18 production is via the caspase-1 activation pathway, as IL-18 production induced by ACTH could be suppressed by caspase-1 inhibitor, and ACTH could increase caspase-1 activity. The effect of ACTH on IL-18 production was blocked by specific inhibitors of p38 kinase (SB203580) or extracellular signal-regulated kinase (ERK) (PD98059). In addition, ACTH-induced rapid phosphorylation of p38 kinase and ERK, and ACTH signaling occurred via melanocortin receptor 1 (MC1R) and receptor 2 (MC2R). These results suggest that ACTH stimulates IL-18 expression in human keratinocytes, which provides an insight into the interaction between ACTH and inflammatory mediators.

Vascular endothelial growth factor 121 is the predominant isoform in psoriatic scales

Vascular endothelial growth factor (VEGF) is a powerful agent that causes hyperpermeability of blood vessels as well as endothelial cell proliferation. Recent investigations have revealed that production of VEGF increases in epidermis of psoriatic lesions, and the overproduced VEGF plays an important role in the pathogenesis of psoriasis. In this study, we used immunohistochemical staining as well as extraction of stratum corneum with physiological saline to further analyse VEGF produced in psoriatic lesions. Biological activity of VEGF in the psoriatic scales was assayed by cultured human umbilical vein endothelial cells in vitro. The immunohistochemical examination confirmed an increased production of VEGF in the keratinocytes of psoriatic lesions. In addition, we found that the content of VEGF contained in the psoriatic scales was approximately 50 times greater than that in normal stratum corneum. We also found that VEGF 121 isoform, which has an exclusive ability to cause hyperpermeability of blood vessels, was predominantly detected in psoriatic scales, suggesting a major role of VEGF 121 isoform on the altered structure of microvessels in psoriatic lesions.

Stat3 links activated keratinocytes and immunocytes required for development of psoriasis in a novel transgenic mouse model

Here we report that epidermal keratinocytes in psoriatic lesions are characterized by activated Stat3. Transgenic mice with keratinocytes expressing a constitutively active Stat3 (K5.Stat3C mice) develop a skin phenotype either spontaneously, or in response to wounding, that closely resembles psoriasis. Keratinocytes from K5.Stat3C mice show upregulation of several molecules linked to the pathogenesis of psoriasis. In addition, the development of psoriatic lesions in K5.Stat3C mice requires cooperation between Stat3 activation in keratinocytes and activated T cells. Finally, abrogation of Stat3 function by a decoy oligonucleotide inhibits the onset and reverses established psoriatic lesions in K5.Stat3C mice. Thus, targeting Stat3 may be potentially therapeutic in the treatment of psoriasis.

Normalized proliferation of normal and psoriatic keratinocytes by suppression of sAPPalpha-release.

The soluble form of the beta-amyloid precursor protein (sAPPalpha) is known to function in the autocrine regulation of epidermal growth and repair. Here we show that its proteolytic release by alpha-secretase in normal human keratinocytes is susceptible to hydroxamic-acid-based zinc metalloproteinase inhibitors and suppressed by these inhibitors by 80%-90%. As various other growth factors participate in regulating epidermal growth we investigated whether the inhibitor-induced sAPPalpha-deficiency would affect keratinocyte proliferation. At optimal inhibitor concentrations the suppression of sAPPalpha-release was followed by a decline in proliferation by 50%-60%, indicating that sAPPalpha is a major growth factor that cannot be compensated for by other growth factors. This finding was the basis for the treatment of human lesional psoriatic keratinocytes with these inhibitors, which resulted in the normalization of their increased proliferation rates. The reversibility of these effects and the lack of toxicity underline the value of these inhibitors and suggest their therapeutic application in psoriatic skin diseases.

Climatotherapy at the Dead Sea is a remittive therapy for psoriasis: combined effects on epidermal and immunologic activation

Background The beneficial effect of climatotherapy at the Dead Sea (CDS) for psoriasis has been established clinically but there is a striking lack of studies assessing its in vivo effect at the molecular and cellular levels. Objective We sought to study the response of activated immunologic cells and keratinocytes in psoriatic lesions to CDS. Methods A total of 27 patients with chronic, stable, plaque-type psoriasis treated with CDS for 28 consecutive days were evaluated with the Psoriasis Area and Severity Index score and quantitative histologic measures. Results After 4 weeks of treatment, the overall Psoriasis Area and Severity Index score decreased by 81.5%. Complete clearance was achieved in 48% of the patients, and moderate to marked improvement in 41%. The average duration of remission was 3.3 months. Histologically, there was an overall reduction in malpighian layer thickness by 63.4%, and keratinocyte hyperplasia, assessed by Ki-67 cell cycle antigen expression, decreased by 78%; residual cell proliferation was confined mainly to the basal layer. These changes were accompanied by normalization of keratin 16 expression in 90% of the patients. T lymphocytes were almost totally eliminated from the epidermis (depletion of >90% of CD3 + and CD25 + cells), with only a low number remaining in the dermis (depletion of 69.4% of CD3 + cells and 77.4% of CD25 + cells). This reduction in activated T cells was accompanied by a marked reduction in HLA-DR expression by epidermal keratinocytes. Conclusions CDS is a highly effective and remittive treatment for moderate to severe plaque-type psoriasis, leading to a reversal of both pathologic epidermal and immunologic activation.

The inhibitory effect of VitD3 on proliferation of keratinocyte cell line HACAT is mediated by down-regulation of CXCR2 expression.

Psoriasis is a disease characterized by inflammation and increased population of hyperproliferative keratinocytes. It is well known that chemokines and chemokine receptors, such as interleukin-8 and its receptors (CXCR1 and CXCR2), play important roles in the pathogenesis of psoriasis. So far, examination of CXCR2 expression in psoriatic lesional keratinocytes by FACS calibur has not been reported and whether VitD3 inhibits psoriatic lesional keratinocyte proliferation through down-regulation of CXCR2 expression has not been elucidated. In the present study, CXCR2 expression in psoriatic lesional keratinocytes and HACAT treated with VitD3 was detected by flow cytometry. The proliferative capacity of HACAT treated with VitD3 was assayed by MTT assay. The results showed that CXCR2 expression in psoriatic lesional keratinocytes was higher than that in normal human keratinocytes. At the correct concentration VitD3 could inhibit human keratinocyte proliferation and down-regulate CXCR2 expression in HACAT. The data demonstrate that the inhibitory effect of VitD3 on keratinocyte proliferation might be mediated by down-regulation of CXCR2 expression.

17Beta-estradiol inhibits MCP-1 production in human keratinocytes.

A chemokine, monocyte chemoattractant protein 1 (MCP-1), attracts macrophages. The production of MCP-1 is enhanced in keratinocytes of psoriatic lesions, which may contribute to macrophage infiltration into the lesions. It is known that estrogen regulates the course of psoriasis. We examined in vitro effects of 17beta-estradiol (E2) on MCP-1 production by human keratinocytes. E2 inhibited constitutive and 12-O-tetradecanoylphorbol-13-acetate-induced MCP-1 secretion, mRNA expression, and promoter activity in keratinocytes, and these effects of E2 were counteracted by estrogen receptor antagonist ICI 182 780. GC-rich Sp1 element and activator protein 1 (AP-1) element on MCP-1 promoter were required for constitutive and 12-O-tetradecanoylphorbol-13-acetate-induced transcription, respectively, and involved in transrepression by E2. E2 inhibited constitutive Sp1 and 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 transcriptional activities whereas it did not inhibit DNA binding of Sp1 or AP-1 c-Fos/c-Jun. E2 inhibited Sp1 and AP-1 transcriptional activities and MCP-1 promoter activity in estrogen receptor beta (ERbeta) transfected SKBR3 cells. Deletion of the A/B region or mutation of activation function 2 in ERbeta abrogated E2-dependent transcriptional inhibition by ERbeta whereas mutation of DNA-binding domain retained the inhibitory effects. Transfection of ERbeta enhanced the inhibitory effects of E2 on Sp1 and AP-1 transcriptional activities and MCP-1 promoter activities in nontransfected keratinocytes. Coimmunoprecipitation studies showed an E2-dependent association of ERbeta with Sp1 or AP-1 in ERbeta-transfected keratinocytes. These results suggest that E2-bound ERbeta may inhibit MCP-1 gene expression by inhibiting Sp1 and AP-1 transcriptional activities in keratinocytes. A/B region and intact activation function 2 of ERbeta may be responsible for the effects of E2.

17β-Estradiol Inhibits MCP-1 Production in Human Keratinocytes

A chemokine, monocyte chemoattractant protein 1 (MCP-1), attracts macrophages. The production of MCP-1 is enhanced in keratinocytes of psoriatic lesions, which may contribute to macrophage infiltration into the lesions. It is known that estrogen regulates the course of psoriasis. We examined in vitro effects of 17β-estradiol (E2) on MCP-1 production by human keratinocytes. E2 inhibited constitutive and 12-O-tetradecanoylphorbol-13-acetate-induced MCP-1 secretion, mRNA expression, and promoter activity in keratinocytes, and these effects of E2 were counteracted by estrogen receptor antagonist ICI 182 780. GC-rich Spl element and activator protein 1 (AP-1) element on MCP-1 promoter were required for constitutive and 12-O-tetradecanoylphorbol-13-acetate-induced transcription, respectively, and involved in transrepression by E2. E2 inhibited constitutive Spl and 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 transcriptional activities whereas it did not inhibit DNA binding of Sp1 or AP-1 c-Fos/c-Jun. E2 inhibited Sp1 and AP-1 transcriptional activities and MCP-1 promoter activity in estrogen receptor P (ERβ) transfected SKBR3 cells. Deletion of the A/B region or mutation of activation function 2 in ERβ abrogated E2-dependent transcriptional inhibition by ERβ whereas mutation of DNA-binding domain retained the inhibitory effects. Transfection of ERβ enhanced the inhibitory effects of E2 on Sp1 and AP-1 transcriptional activities and MCP-1 promoter activities in nontransfected keratinocytes. Coimmunoprecipitation studies showed an E2-dependent association of ERβ with Sp1 or AP-1 in ERβ-transfected keratinocytes. These results suggest that E2-bound ERβ may inhibit MCP-1 gene expression by inhibiting Sp1 and AP-1 transcriptional activities in keratinocytes. A/B region and intact activation function 2 of ERβ may be responsible for the effects of E2.

Upregulation of interleukin-18 expression in mouse primary keratinocytes induced to differentiate by calcium.

Interleukin-18 (IL-18) is an immunomodulatory cytokine that stimulates interferon-gamma production by T helper cells. Recently, basal keratinocytes have been shown to constitutively express IL-18, and IL-18 expression increases in the suprabasal keratinocytes in psoriatic lesions. In the study reported here we showed that in mouse epidermis, IL-18 immunoreactivity was markedly increased in the granular and cornified layers. To further investigate whether differentiated keratinocytes synthesize more IL-18, we examined the expression of mouse IL-18 in primary mouse keratinocytes induced to differentiate by calcium, an in vitro cell culture system mimicking keratinocyte differentiation in the epidermis. We demonstrated that IL-18 mRNA and protein in cultured keratinocytes were increased by calcium treatment in a time- and dose-dependent manner. The upregulation of IL-18 was associated with an increase in keratinocyte differentiation markers, and was dependent on the synthesis of new RNAs and proteins. However, the IL-18 protein in the cytoplasm was predominantly in the precursor form, and no increase in IL-18 activity was detected in the culture medium treated with calcium. Furthermore, blocking the calcium-induced keratinocyte differentiation with protein kinase C inhibitor inhibited the upregulation of IL-18 expression. These findings suggest that IL-18 is synthesized in keratinocytes mainly in the inactive precursor form, and its expression is upregulated as basal keratinocytes differentiate in the epidermis.

Psoriatic Lesional Keratinocytes Promote the Maturation of Human Monocyte-Derived Langerhans Cells

Background: Langerhans cells (LCs) are important antigen-presenting cells in the epidermis and may play a key role in the pathogenesis of psoriasis. It has been proven that LCs isolated from psoriatic lesions are abnormal. However, the mechanism of the abnormality has not been reported so far. Objective: In the present study, we investigated the effect of psoriatic lesional keratinocytes on the maturation of LCs. Methods: Monocytes isolated from healthy peripheral blood could differentiate into LCs in the presence of granulocyte-macrophage colony-stimulating factor, interleukin (IL) 4 and transforming growth factor β1 for 5 days. Then, human monocyte-derived LCs were cultured with supernatants from psoriatic lesional keratinocytes for another 2 days. Their phenotypes and phagocytic capacity were analyzed by flow cytometry. IL-12 secreted by LCs was determined by ELISA. Results: Supernatants from psoriatic lesional keratinocytes could up-regulate the expression of HLA-DR and CD86 on LCs more significantly than supernatants from healthy keratinocytes, but less powerfully than lipopolysaccharide. The levels of IL-12 secreted by LCs also increased. In contrast, the expression of CD1a on LCs and their phagocytic capacity were reduced. Conclusion: Human monocyte-derived LCs cultured with supernatants from psoriatic lesional keratinocytes displayed the characteristics of maturation. This suggests that psoriatic lesional keratinocytes might secrete some factors that could promote the maturation of LCs, which may play important roles in immune reactions related to psoriasis.

Keratinocyte CDw60 Expression is Modulated by Both a Th-1 Type Cytokine IFN-γ and Th-2 Cytokines IL-4 and IL-13: Relevance to Psoriasis

Psoriasis is a chronic skin disease with an immunocytic infiltrate, including activated T lymphocytes, producing multiple cytokines that can influence the phenotype of epidermal keratinocytes. In these studies we examined the effect of the cytokines interferon-gamma and interleukin-13 or interleukin-4 on keratinocytes, alone and in combination, on surface levels of HLA-DR, intercellular adhesion molecule 1, and CDw60, as well as the transcription factors STAT1, STAT6, and BCL-6. As CDw60 is an acetylated form of the GD3 ganglioside and may function as a T cell costimulatory molecule, the modulation of CDw60 expression by keratinocytes in psoriatic lesions was highlighted to gain insight into potentially important T cell-keratinocyte interactions. Interferon-gamma was observed to block the interleukin-4- or interleukin-13-mediated induction of CDw60 on cultured keratinocytes, but not induction of the transcription factor STAT6. Interleukin-13 and interleukin-4 were unable to block interferon-gamma-mediated induction of STAT1 or BCL-6, however, or the upregulation of intercellular adhesion molecule 1 and HLA-DR. In psoriatic plaques, CDw60 was not consistently detected on keratinocytes in acute lesions, but was detected predominantly on basal layer keratinocytes in chronic lesions. In addition we found that BCL-6 levels were increased in psoriatic lesions; in acute lesions BCL-6 was primarily localized in the basal layer keratinocytes, whereas in chronic plaques nuclear BCL-6 was predominantly expressed by keratinocytes in the suprabasal cell layers. These studies highlight the complex modulation of the keratinocyte phenotype by immunocyte-derived cytokines, in which induction of CDw60 involving interleukin-4, or interleukin-13 was antagonized by interferon-gamma. We suggest in psoriatic plaques that the presence or absence of CDw60 expression by keratinocytes may reflect the dynamic interplay between Th-1-type cytokines such as interferon-gamma and Th-2-type cytokines such as interleukin-4 and interleukin-13. The ability of interferon-gamma to induce the transcription repressor BCL-6 may also contribute to the overall immunologic events in skin, including suppression of the intermediates in the synthetic pathway leading to expression of the T cell costimulatory ganglioside CDw60.

A candidate gene for psoriasis near HLA-C, HCR (Pg8), is highly polymorphic with a disease-associated susceptibility allele

A susceptibility gene for psoriasis, a chronic skin disorder, resides in chromosome 6p near the HLA-C locus. Sequencing of the region has allowed the identification of a new gene, HCR. We found that HCR is highly polymorphic with at least 12 coding variants. An association study of the new HCR polymorphisms and the previously suggested susceptibility alleles HLA-Cw*0602 and corneodesmosin allele 5 (CD*5) with psoriasis revealed a specific HCR variant associated with psoriasis susceptibility. However, the HLA-Cw*0602 allele was rarer in controls and associated with a stronger relative risk. Association analysis did not support CD*5 as a psoriasis susceptibility allele in our sample of patients (n = 100) and population-matched controls (n = 93) from an isolated population. We found HCR to be overexpressed in keratinocytes of psoriatic lesions compared with paired samples of healthy skin. Our results suggest a potential role for HCR in the pathogenesis of psoriasis.

The effects of substance P and vasoactive intestinal peptide on interleukin-6 synthesis in cultured human keratinocytes

Interleukin-6 (IL-6) is a cytokine implicated as a key mediator of immune and inflammatory responses in psoriasis. Recent studies have shown that neuropeptides, substance P (SP) and vasoactive intestinal peptide (VIP), can modulate a production of IL-6 from cells, such as monocytes and astrocytes, participating in an immune reaction. The aim of this study was to assess the role of the neuropeptides on cytokine production of keratinocytes in physiologic or pathologic conditions. Cultured human keratinocytes derived from normal foreskin and psoriatic lesions were treated with various concentrations of SP or VIP, in the presence or absence of fetal bovine serum. The secretion of IL-6 by the treated keratinocytes was analyzed by enzyme-linked immunosorbent assay. Although neither SP nor VIP, by itself, was able to induce IL-6 synthesis in cultured human keratinocytes, we have found that SP, not VIP, significantly reduced 5% fetal bovine serum-induced IL-6 production in time- and dose-dependent fashion. This down-regulatory effect of SP was reversed by spantide, a SP antagonist. Lesional psoriatic keratinocytes showed a similar, but weaker, response when compared with normal keratinocytes. These data suggested that SP might modulate IL-6 synthesis of keratinocytes in either physiologic or pathologic conditions such as psoriasis.

Upregulation of Connexin 26 Between Keratinocytes of Psoriatic Lesions

To assess whether the expression of connexins (Cx) by keratinocytes is altered under conditions of abnormal epidermal differentiation, we have compared Cx26, Cx32, Cx37, Cx40, and Cx43 in the epidermis of 11 psoriatic patients who had not been treated for at least 1 mo and of seven healthy individuals. In all samples of fully mature psoriatic plaques, we have observed a massive expression of Cx26, as judged at both the transcript level (northern blot) and the protein level (immunofluorescence). This protein became consistently detected between keratinocytes of the basal and granular layers at the periphery of psoriatic plaques and in all layers of fully developed psoriatic epidermis, except in regions of parakeratosis. None or a minimal amount of Cx26 was observed in both control and nonlesional regions of psoriatic epidermis. Psoriatic plaques also contained Cx43, the prominent gap junction protein in the interfollicular epidermis of normal human skin. The levels of this protein appeared to be slightly higher in psoriatic than in control skin, as judged at both the transcript level (northern blot) and the protein level (immunofluorescence). Three other connexins (Cx32, Cx37, and Cx40), which are not observed in control interfollicular epidermis, were not induced in either nonlesional or lesional regions of psoriatic skin. The data indicate that selective changes in the normal expression of connexins by keratinocytes are associated with the changes in the proliferation and differentiation program that these cells undergo in psoriasis.