Cornified Cell Envelope Research Articles

Down-regulation of peptidylarginine deiminase type 1 in reconstructed human epidermis disturbs nucleophagy in the granular layer and affects barrier function

Deimination is a post-translational modification catalyzed by a family of enzymes named peptidylarginine deiminases (PADs). PADs transform arginine residues of protein substrates into citrulline. Deimination has been associated with numerous physiological and pathological processes. In human skin, three PADs are expressed (PAD1-3). While PAD3 is important for hair shape formation, the role of PAD1 is less clear. To decipher the main role(s) of PAD1 in epidermal differentiation, its expression was down-regulated using lentivirus-mediated shRNA interference in primary keratinocytes and in three-dimensional reconstructed human epidermis (RHE). Compared to normal RHEs, down-regulation of PAD1 caused a drastic reduction in deiminated proteins. Whereas proliferation of keratinocytes was not affected, their differentiation was disturbed at molecular, cellular and functional levels. The number of corneocyte layers was significantly reduced, expression of filaggrin and cornified cell envelope components, such as loricrin and transglutaminases, was down-regulated, epidermal permeability increased and trans-epidermal-electric resistance diminished drastically. Keratohyalin granule density decreased and nucleophagy in the granular layer was disturbed. These results demonstrate that PAD1 is the main regulator of protein deimination in RHE. Its deficiency alters epidermal homeostasis, affecting the differentiation of keratinocytes, especially the cornification process, a special kind of programmed cell death.

Role of syntaxin3 an apical polarity protein in poorly polarized keratinocytes: regulation of asymmetric barrier formations in the skin epidermis.

The skin epidermis exhibits an asymmetric structure composed of multilayered keratinocytes and those in the outer layers form two-way physical barriers, cornified cell envelope (CCE), and tight junctions (TJs). While undifferentiated keratinocytes in the basal layer continuously deliver daughter cells outward, which undergo successive differentiation with losing their polarized characteristics, they retain the expression of several polarity proteins. In the present study, we revealed that the t-SNARE protein syntaxin3, a critical element for the formation of the apical compartment in simple epithelial cells, is required to confer the ability to organize the physical barriers on "poorly polarized" keratinocytes in epidermal outer layers. HaCaT keratinocytes with genetic ablation of syntaxin3 readily succumbed to hydrogen peroxide-induced cell death. Additionally, they lost the ability to organize TJ and CCE structures, accompanied by notable downregulation of transglutaminase1 and caspase14 (a cornification regulator) expression. These syntaxin3-knockout cells appeared to restore oxidative stress tolerance and functional TJ formation ability, in response to the inducible re-expression of exogenous syntaxin3. While plausible mechanisms underlying these phenomena remain unclear, syntaxin3, an apical polarity protein in the simple epithelia, has emerged as a potentially crucial element for barrier formation in poorly polarized keratinocytes in polarized epidermal tissue.

Homozygous Nonsense Mutation in SDR9C7 in a Chinese Patient With Autosomal Recessive Congenital Ichthyosis

Introduction: Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of cornification disorders. To date, 14 genes have been found to be related to ARCI. We herein describe a patient with ARCI who carried a homozygous nonsense mutation in the SDR9C7 gene and presented with generalized erythroderma, scales, recurrent blisters, and onychomycosis. Case presentation: A 23-year-old woman developed generalized erythroderma and scales over her trunk and limbs shortly after birth, followed by recurrent blisters and nail deformities. A diagnosis of ARCI was made based on her clinical manifestations, family history, and genetic analysis, which revealed a homozygous mutation in SDR9C7 (c.187C>T, p.Q63X). Discussion: Most genes responsible for ARCI are associated with epidermal lipid metabolism, which contributes to the cutaneous barrier. SDR9C7, which encodes short-chain dehydrogenase/reductase family 9C member 7, has also been recently found to play vital roles in this process by regulating ceramide binding to the epidermal cornified cell envelope. For patients clinically suspected to have ARCI, recurrent onychomycosis is a strong indication that they carry a SDR9C7 gene mutation. Conclusion: Remarkable phenotypic and genotypic heterogeneity exists among patients with ARCI. Genetic analysis is an effective tool in diagnosing this and other hereditary diseases. Our patient developed recurrent onychomycosis, a typical presentation of ARCI caused by SDR9C7 mutation, and the unusual blisters further expand the clinical phenotypic spectrum of ARCI.

Small Proline-Rich Protein 3 Regulates IL-33/ILC2 Axis to Promote Allergic Airway Inflammation.

Small proline-rich proteins (SPRRs), components of cornified cell envelope precursors, have recently been found to participate in airway diseases. However, their role in allergic airway inflammatory conditions remains unknown. Here, we explored the expression of SPRR3 in house dust mite (HDM)-sensitized/challenged mice and attempted to elucidate the regulatory role of SPRR3 in allergic airway inflammation. SPRR3 was identified via bioinformatics analysis of Gene Expression Omnibus (GEO) databases and further confirmed to be upregulated in the lungs of asthmatic mice. Knockdown of SPRR3 via the intratracheal route significantly inhibited eosinophils in bronchoalveolar lavage fluid (BALF) and suppressed the expressions of type 2 cytokines (IL-4, IL-5, and IL-13) in BALF and lung tissues. Further, SPRR3 knockdown reduced the expression of IL-33 and further attenuated the activation of the PI3K/AKT/NF-κB signaling pathway in the recruitment of group 2 innate lymphoid cells (ILC2s) to inhibit allergic airway inflammation. In vitro, SPRR3 siRNA could alleviate HDM-induced inflammatory responses in BEAS-2B cells. This study reveals the regulatory role of SPRR3 in allergic airway inflammation, identifying this protein as a potential novel therapeutic target for asthma.

Evaluation of serum long non-coding RNA (Gas5) level and keratinocyte transglutaminase 1 (TGM1) activity as novel biomarkers in psoriasis patients

BackgroundPsoriasis is considered an autoimmune disease, ecological and genetic factors together function a vital role in the cause, long non-coding RNA (lncRNAs) perform a regulatory key for the expression of an inflammatory gene by cooperating with the transcription factors. Keratinocyte transglutaminase enzymes are calcium-dependent serve enzymes that stimulate the progress of the cornified cell envelope, which characterize the epidermal keratinocytes that have subjected the ending of segregation. This study aimed to investigate the expression level of long non-coding RNA (GAS5) and keratinocyte transglutaminase 1 (TGM1) activity in psoriatic patients and its possible role in psoriasis pathogenesis. Subjects and methodsThis survey implicated thirty patients with chronic plaque psoriasis, 30 sex, and age-matched healthy controls. GAS5 was measured using quantitative PCR (qPCR). Keratinocyte transglutaminase 1 (TGM1) activity was detected by using the ELISA technique. ResultsThe serum level of long non-coding RNA (GAS5) values were significantly lower between patients with psoriasis in comparison to normal control and the serum levels of keratinocyte transglutaminase 1 (TGM1) values were significantly high between patients with psoriasis in comparison to normal control.

Loricrin and NRF2 Coordinate Cornification

Cornification involves cytoskeletal cross-linkages in corneocytes (the brick) and the secretion of lipids/adhesion structures to the interstitial space (the mortar). Because the assembly of lipid envelopes precedes corneocyte maturation, loricrin is supposed to be dispensable for the protection against desiccation. Although the phenotypes of Lor knockout (LKO) mice are obscure, the antioxidative response on the KEAP1/NRF2 signaling pathway compensates for the structural defect in utero. In this study, we asked how the compensatory response is evoked after the defects are repaired. To this end, the postnatal phenotypes of LKO mice were analyzed with particular attention to the permeability barrier function primarily maintained by the mortar. Ultrastructural analysis revealed substantially thinner cornified cell envelopes and increased numbers of lamellar granules in LKO mice. Superficial epidermal damages triggered the adaptive repairing responses that evoke the NRF2-dependent upregulation of genes associated with lamellar granule secretion in LKO mice. We also found that corneodesmosomes are less degraded in LKO mice. The observation suggests that loricrin and NRF2 are important effectors of cornification, in which proteins need to be secreted, cross-linked, and degraded in a coordinated manner.

Small Proline-Rich Protein 2A and 2D Are Regulated by the RBM38-p73 Axis and Associated with p73-Dependent Suppression of Chronic Inflammation.

Simple SummarySmall proline-rich protein 2A and 2D (SPRR2A and SPRR2D) are structure proteins of cornified cell envelopes and function as a protective barrier against diverse external insults. However, the role of SPRR2A/2D in chronic inflammation remains unclear. Here, we showed that SPRR2A/2D expression is controlled by a regulatory loop formed by RNA-binding protein RBM38 and tumor suppressor p73. We also found that RBM38-mediated expression of SPRR2A/2D was p73-dependent and that induction of SPRR2A/2D during keratinocyte differentiation was dependent on both p73 and Rbm38. Furthermore, We found that Rbm38−/−;Trp73+/− mice exhibited weak expression of SPRR2A/2D in multiple tissues and were susceptible to systemic chronic inflammation. Together, our data reveal that SPRR2A/2D are novel targets of the RBM38-p73 loop and contribute to p73-dependent suppression of chronic inflammation.Small proline-rich protein 2A and 2D (SPRR2A and SPRR2D) provide barrier function in terminally differentiated stratified squamous epithelia through the epidermal differentiation complex. However, little is known how SPRR2A/2D expression is controlled and their role in chronic inflammation. Here, we showed that that SPRR2A/2D expression is controlled by a regulatory loop formed by RNA-binding protein RBM38 and tumor suppressor p73. Specifically, we found that SPRR2A/2D expression was induced by ectopic expression of RBM38 or p73 but suppressed by knockout of Rbm38 or p73. We also found that RBM38-mediated expression of SPRR2A/2D was p73-dependent and that induction of SPRR2A/2D during keratinocyte differentiation was dependent on both p73 and Rbm38. Additionally, we found that SPRR2A/2D expression was closely associated with p73 expression in normal and cancerous tissues. To determine the biological function of the RBM38-p73 loop potentially via SPRR2A/2D, we generated a cohort of wild-type, Rbm38−/−, Trp73+/−, and Rbm38−/−;Trp73+/− mice. We found that Rbm38−/−;Trp73+/− mice had a much shorter lifespan than that for Rbm38−/−—and to a lesser extent for Trp73+/− mice—but were less prone to spontaneous tumors than Trp73+/− or Rbm38−/− mice. We also found that Rbm38−/−;Trp73+/− mice exhibited weak expression of SPRR2A/2D in multiple tissues and were susceptible to systemic chronic inflammation, suggesting that decreased SPRR2A/2D expression is likely responsible for chronic inflammation in Rbm38−/−;Trp73+/− mice, leading to a shortened lifespan. Together, our data reveal that SPRR2A/2D are novel targets of the RBM38-p73 loop and contribute to p73-dependent suppression of chronic inflammation.

Advances in our understanding of canine atopic dermatitis.

Canine atopic dermatitis (cAD) is a genetically inherited clinical syndrome that encompasses a diversity of mechanisms and can have a variety of triggers. Development of clinical disease is the result of genetic factors and environmental conditions, which shape the resulting immunological response. Clinical disease becomes evident once a threshold of inflammatory response is achieved. Skin barrier impairment plays a role in promoting cutaneous dysbiosis and increased allergen penetration. Keratinocytes shape the response of dendritic cells and subsequent lymphocytic response. Thymic stromal lymphopoietin is one of the links between the damaged skin barrier and the modulation of a T-helper (Th)2 response. It is still unclear whether mutations in skin barrier genes exist in atopic dogs, as they do in humans, or whether the observed alterations are purely secondary to inflammation. A dysregulated immune response with increased Th2, Th17 and CD4+ CD25+ regulatory T cells has been reported. A variety of cytokines [interleukin(IL)-31, IL-34, Macrophage migration inhibitory factor] are proposed as potential biomarkers and treatment targets because they are increased in the serum of atopic dogs when compared to controls, although a correlation between serum levels of these factors and severity of disease is not always present. The main issue with many published studies is that atopic dogs are always only compared to normal controls. Thus, it is unclear whether the changes that we find are truly a signature of cAD or merely a manifestation of nonspecific broad inflammatory responses. Studies considering comparison with other inflammatory diseases different from cAD are urgently needed to correctly identify what is specific to this complicated syndrome.

Contribution of transglutaminases and their substrate proteins to the formation of cornified cell envelope in oral mucosal epithelium.

Cornified envelope formation is crucial for the final differentiation of keratinized epithelium. However, the mechanisms of cornified envelope formation in the oral epithelium remain unclear. The aim of this study was to clarify the differences in the distribution and expression of cornified envelope related proteins and genes between keratinized and non-keratinized oral epithelia. We immunohistochemically investigated the distribution patterns of transglutaminase 1 (TG1), transglutaminase 3 (TG3), and their substrate proteins involucrin (IVL), loricrin (LOR), and small proline rich proteins (SPRs), in 19 keratinized and 14 non-keratinized oral epithelium samples. TG1 and TG3 mRNA levels were investigated in both types of epithelium by real time reverse transcription polymerase chain reaction (RT-PCR) using paraffin-embedded specimens. Data were analyzed to identify factors involved in cornified envelope formation. We demonstrate that 11 localization patterns show statistically significant differences between keratinized and non-keratinized oral epithelia. These factors clearly drove the separation of the two groups during cluster analysis. TG1 mRNA levels in keratinized oral epithelium were significantly higher than those in non-keratinized oral epithelium. In conclusion, the characteristic distribution of transglutaminases and their substrates and the mRNA levels of TG1 can regulate cornified envelope formation in keratinized oral epithelium, together with the contribution of TG3 first reported in this paper.

Loricrin: Past, Present, and Future.

The terminal differentiation of the epidermis is a complex physiological process. During the past few decades, medical genetics has shown that defects in the stratum corneum (SC) permeability barrier cause a myriad of pathological conditions, ranging from common dry skin to lethal ichthyoses. Contrarily, molecular phylogenetics has revealed that amniotes have acquired a specialized form of cytoprotection cornification that provides mechanical resilience to the SC. This superior biochemical property, along with desiccation tolerance, is attributable to the proper formation of the macromolecular protein-lipid complex termed cornified cell envelopes (CE). Cornification largely depends on the peculiar biochemical and biophysical properties of loricrin, which is a major CE component. Despite its quantitative significance, loricrin knockout (LKO) mice have revealed it to be dispensable for the SC permeability barrier. Nevertheless, LKO mice have brought us valuable lessons. It is also becoming evident that absent loricrin affects skin homeostasis more profoundly in many more aspects than previously expected. Through an extensive review of aggregate evidence, we discuss herein the functional significance of the thiol-rich protein loricrin from a biochemical, genetic, pathological, metabolic, or immunological aspect with some theoretical and speculative perspectives.

Molecular Genetic Study of a Large Inbred Pakistani Family Affected with Autosomal Recessive Congenital Ichthyosis Through Whole Exome Sequencing.

Background: Autosomal recessive congenital ichthyoses (ARCI) are a group of rare nonsyndromic genodermatoses characterized by generalized scaly appearance of the epidermis with markedly impaired cutaneous barriers owing to defects in keratinization related genes. In this study, we ascertained a consanguineous Pakistani family affected with ARCI. Aims: To investigate genetic defect underlying disease phenotype in the affected family. Methods: All available members of the family (affected and unaffected) were sampled. Whole exome sequencing (WES) was performed on DNA of the proband and the data were analyzed for probable pathogenic variants. Segregation of the identified variant was validated by Sanger sequencing. Results: Analysis of the WES data identified a novel nonsense mutation, c.762C>G, in the PNPLA1 (patatin-like phospholipase domain containing 1) gene. The protein product of of this gene is involved in lipid organization during cornified cell envelope formation. The variant is predicted to result in the generation of a premature truncation site at amino acid position 254 (p.Tyr254*). This would result in the loss of a large C-terminal portion of the protein suggesting it to be rendered nonfunctional. In silico protein structure modeling confirmed a detrimental effect of the variation on protein structure. Conclusions: The study supports the evidence for the prevalence of PNPLA1 mutations in distant ethnic groups. Despite the significant number of reported ARCI cases with PNPLA1 variants, a straightforward genotype-phenotype correlation cannot be established.

Skin Moisturizing Effect through the Stimulation of the Cornified Cell Envelope Formation by Bis-Glyceryl Ascorbate

Skin Moisturizing Effect through the Stimulation of the Cornified Cell Envelope Formation by Bis-Glyceryl Ascorbate

Cornulin Is Induced in Psoriasis Lesions and Promotes Keratinocyte Proliferation via Phosphoinositide 3-Kinase/Akt Pathways

Psoriasis is a chronic inflammatory skin disease characterized by abnormal proliferation of epidermal keratinocytes and infiltration of inflammatory cells. CRNN is a major component of the cornified cell envelope and implicated in several epithelial malignancies. Here, we show that CRNN expression was increased in the lesioned epidermis from the patients with psoriasis vulgaris and skin lesions from the imiquimod (IMQ)-treated mice. Expression of CRNN in cultured keratinocytes (HEKa and HaCaT) was also induced by M5, a mixture of five pro-inflammatory cytokines (i.e., IL-17A, IL-22, IL-1α, oncostatin M, and TNF-α). Lentiviral expression of CRNN increased cell proliferation by inducing cyclin D1. Conversely, knockdown of CRNN by small interfering RNA suppressed G1/S transition and attenuated the M5-induced proliferation. In addition, CRNN overexpression increased the phosphorylation and activation of phosphoinositide 3-kinase and Akt. Inactivation of the phosphoinositide 3-kinase and Akt pathways using small interfering RNA or selective inhibitors (LY294002 and MK2206) reduced the proliferative effects of CRNN. Furthermore, topical use of anti-psoriatic calcipotriol effectively decreased expression of CRNN, inhibited the Akt activation and improved the IMQ-stimulated psoriasis-like pathologies. Taken together, these results suggest that induced expression of CRNN may contribute to the pathogenesis of psoriasis.

Ectopic transglutaminase 1 and 3 expression accelerating keratinization in oral lichen planus

ObjectiveOral lichen planus (OLP) characterized by interface mucositis frequently shows hyper-keratinization. To clarify mechanisms of excess keratinization, we investigated key molecules for cornified cell envelope (CE).MethodsInvolucrin (IVL), loricrin (LOR), transglutaminase 1 (TGase 1) and transglutaminase 3 (TGase 3) were immunohistochemically examined in 20 specimens of OLP; five specimens of buccal mucosa served as controls. Subsequently, the data were statistically analyzed.ResultsIVL in OLP was localized in the cell membrane, in contrast to its localization in the cytoplasm in controls. No positive reaction indicative of LOR was noted in any specimens. Although the TGase 1 localization in controls was restricted to the upper three-quarters of the membrane, the localization in OLP was in both membrane and in the cytoplasm of full thickness mucosal layers. The TGase 3 localization pattern was dramatically altered from cytoplasmic to membranous in OLP.ConclusionOur data suggest that aberrant TGase 1 and TGase 3 localization and distribution are closely related to hyper-keratinization in OLP. This is the first report of ectopic transglutaminase localization in OLP.

Molecular basis of the skin barrier structures revealed by electron microscopy.

The barrier function of skin is indispensable for terrestrial animals. This function is mainly carried out by the epidermis, more specifically by its granular and cornified layers. The major structural components associated with this function are the intercellular lipid layer, desmosomes, corneodesmosomes, tight junctions, cornified cell envelope and keratin filaments. In this review, we discuss the current knowledge of their ultrastructure, their molecular basis and their relevance to skin disease.

Proteome analysis reveals that de novo regenerated mucosa over fibula flap-reconstructed mandibles resembles mature keratinized oral mucosa

AimThe aim of this study was to determine whether intra-oral de novo regenerated mucosa (D) that grew over free fibula flap reconstructed-mandibles resembled the donor tissue i.e. external skin (S) of the lateral leg, or the recipient site tissue, i.e. keratinized oral mucosa (K). Materials and methodsDifferential proteome analysis was performed with ten tissue samples from each of the three groups: de novo regenerated mucosa (D), external skin (S), and keratinized oral mucosa (K). Expression differences of cornulin and involucrin were validated by Western blot analysis and their spatial distributions in the respective tissues were ascertained by immunohistochemistry. ResultsFrom all three investigated tissue types a total of 1188 proteins were identified, 930 of which were reproducibly and robustly quantified by proteome analysis. The best differentiating proteins were assembled in an oral mucosa proteome signature that encompasses 56 differentially expressed proteins. Principal component analysis of both, the 930 quantifiable proteins and the 56 oral mucosa signature proteins revealed that the de novo regenerated mucosa resembles keratinized oral mucosa much closer than extra-oral skin. Differentially expressed cornification-related proteins comprise proteins from all subclasses of the cornified cell envelope. Prominently expressed in intra-oral mucosa tissues were (i) cornifin-A, cornifin-B, SPRR3, and involucrin from the cornified-cell-envelope precursor group, (ii) S100A9, S100A8 and S100A2 from the S100 group, and (iii) cornulin which belongs to the fused-gene-protein group. ConclusionAccording to its proteome signature de novo regenerated mucosa over the free fibula flap not only presents a passive structural surface layer but has adopted active tissue function.

Optimization of Cytokine Milieu to Reproduce Atopic Dermatitis-related Gene Expression in HaCaT Keratinocyte Cell Line.

Although atopic dermatitis (AD) is characterized by cytokine production predominantly mediated by T helper (Th) 2 cells, AD pathogenesis also involves innate immune and Th1 cells. To optimize the cytokine milieu required for accurate reproduction of AD-related gene expression profile in vitro, we evaluated the expression pattern of CCL22, CCL17, IL5, IL13, IL33, IL25, TSLP, FLG, and LOR in human lesional AD skin and cytokine-stimulated HaCaT cells. An increase in Th2 mediators (IL5, IL13, CCL22, CCL17, IL25, IL33, and TSLP) and a decrease in genes related to cornified cell envelope (filaggrin and loricrin) were observed in human AD lesions. Innate (tumor necrosis factor-α) and/or Th1/Th2 adaptive cytokines (interferon-γ/IL-4) were required for inducing these inflammatory changes in HaCaT cells, implying that a complex network of innate, Th1, and Th2 cytokines drives AD-like changes. Therefore, stimulation with various combinations of cytokines, beyond Th2 polarization, is necessary when HaCaT cell line is used to study genetic changes implicated in AD pathogenesis.

Dietary Fish Oil Supplementation Enhances Expression of Genes Involved in Cornified Cell Envelope Formation in Rat Skin

Dietary Fish Oil Supplementation Enhances Expression of Genes Involved in Cornified Cell Envelope Formation in Rat Skin

Water-Soluble Organic Germanium Promotes Both Cornified Cell Envelope Formation and Ceramide Synthesis in Cultured Keratinocytes

We investigated whether 3-(trihydroxygermyl) propionic acid increases the formation of cornified cell envelopes and the level of ceramide in cultured epidermal keratinocytes and in a three-dimensional human epidermis model. The activity and mRNA expression of transglutaminase were increased when 3-(trihydroxygermyl) propionic acid was added to the cell cultures. The formation of cornified cell envelopes in cultured human epidermal keratinocytes was increased in the presence of 3-(trihydroxygermyl) propionic acid. Ceramide levels were increased in the presence of 3-(trihydroxygermyl) propionic acid. The activity of serine palmitoyltransferase and mRNA levels of serine palmitoyltransferase 2 were also increased when 3-(trihydroxygermyl) propionic acid was added to the cultures. The extent to which ceramide levels were increased in the presence of 3-(trihydroxygermyl) propionic acid appeared dependent on serine palmitoyltransferase 2 upregulation. These results suggest that 3-(trihydroxygermyl) propionic acid can promote cornified cell envelope formation by inducing transglutaminase expression and ceramide synthesis via the induction of serine palmitoyltransferase activity, thereby improving the barrier function and moisture of dry, rough skin.

095 Loss of loricrin exacerbates psoriasis-like skin inflammation through altered dendritic cell homeostasis

Psoriasis is a chronic inflammatory skin disease associated with multiple predisposing factors, and one of susceptible loci known as PSORS4 is on human chromosome 1, in which epidermal differentiation complex (EDC) is located. An EDC gene loricrin (Lor) accounts for a major protein mass of cornified cell envelope (CE), the vital structure for epidermal integrity. In contrast to competent epidermal permeability barrier, Lor knockout (LKO) mice had reduced epidermal mechanical stability of the epidermis resulting from impaired cross-linking of filaggrin and keratin 1/10 in their CEs. Since mechanical stress/trauma can contribute to psoriasis induction and exacerbation, we evaluated the impact of the loss LOR in a psoriasis-like disease model. Reflecting mechanical weakness, application of mechanical stress onto the ear skin resulted in enhanced and sustained keratin 6 (K6) protein expression in LKO epidermis as determined by immunohistochemistry (IHC). LKO mice had significantly increased expression levels of cytokines that initiate psoriatic inflammatory response, including Tnf, Il1b and Ifn1a on quantitative reverse transcription PCR (RT-qPCR). Topical application of imiquimod (Aldara) cream on LKO mice resulted in a severe inflammatory phenotype; ear skin had augmented swelling, and back skin had enhanced erythema and hyperkeratosis accompanied by increased transcriptional expression levels of K6a. Since Ifn-a produced by plasmacytoid dendritic cell (pDC) is known to play a pivotal role in this model, pDC marker expression was analyzed in a steady state. Unchallenged LKO mice had significantly enhanced expression of Bst2 in the ear skin as determined by RT-qPCR and IHC. Taken together, these results indicate that reduced mechanical stability in the epidermis can exacerbate psoriasis-like skin inflammation through the alteration of DC homeostasis.