Fibroblasts in immune-mediated inflammatory diseases: The soil of inflammation.

As one of the most abundant stromal cells, fibroblasts are primarily responsible for the production and remodeling of the extracellular matrix. Traditionally, fibroblasts have been viewed as quiescent cells. However, recent advances in multi-omics technologies have demonstrated that fibroblasts exhibit remarkable functional diversity at the single-cell level. Additionally, fibroblasts are heterogeneous in their origins, tissue locations, and transitions with stromal cells. The dynamic nature of fibroblasts is further underscored by the fact that disease stages can impact their heterogeneity and behavior, particularly in immune-mediated inflammatory diseases such as psoriasis, inflammatory bowel diseases, and rheumatoid arthritis, etc. Fibroblasts can actively contribute to the disease initiation, progression, and relapse by responding to local microenvironmental signals, secreting downstream inflammatory factors, and interacting with immune cells during the pathological process. Here we focus on the development, plasticity, and heterogeneity of fibroblasts in inflammation, emphasizing the need for a developmental and dynamic perspective on fibroblasts.

Assessment of relationships between bullous pemphigoid and neurological diseases: A bidirectional two-sample Mendelian randomization study.

Bullous pemphigoid (BP) is the most prevalent autoimmune vesiculobullous skin illness that tends to affect the elderly. Growing evidence has hinted a correlation between BP and neurological diseases. However, existing observational studies contained inconsistent results, and the causality and direction of their relationship remain poorly understood. To assess the causal relationship between BP and neurological disorders, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and stroke. A bidirectional two-sample Mendelian randomization (MR) adopted independent top genetic variants as instruments from the largest accessible genome-wide association studies (GWASs), with BP (n = 218 348), PD (n = 482 730), AD (n = 63 926), stroke (n = 446 696), and MS (n = 115 803). Inverse variance weighted (IVW), MR-Egger, weighted mode methods, weighted median, and simple mode were performed to explore the causal association. Multiple sensitivity analyses, MR-Pleiotropy Residual Sum and Outlier (PRESSO) was used to evaluate horizontal pleiotropy and remove outliers. With close-to-zero effect estimates, no causal impact of BP on the risk of the four neurological diseases was discovered. However, we found that MS was positively correlated with higher odds of BP (OR = 1.220, 95% CI: 1.058-1.408, p = 0.006), while no causal associations were observed between PD (OR = 0.821, 95% CI: 0.616-1.093, p = 0.176), AD (OR = 1.066, 95% CI: 0.873-1.358, p = 0.603), stroke (OR = 0.911, 95% CI: 0.485-1.713, p = 0.773) and odds of BP. In summary, no causal impact of BP on the risk of PD, AD, MS and stroke was detected in our MR analysis. However, reverse MR analysis identified that only MS was positively correlated with higher odds of BP, but not PD, AD and stroke.

Cross-disease characterization of fibroblast heterogeneities and their pathogenic roles in skin inflammation.

Fibroblasts are critical pro-inflammatory regulators in chronic inflammatory and fibrotic skin diseases. However, fibroblast heterogeneity and the absence of a unified cross-disease taxonomy have hindered our understanding of the shared/distinct pathways in non-communicable skin inflammation. By integrating 10× single-cell data from 75 skin samples, we constructed a single-cell atlas across inflammatory and fibrotic skin diseases and identified 9 distinct subsets of skin fibroblasts. We found a shared subset of CCL19+ fibroblasts across these diseases, potentially attracting and educating immune cells. Moreover, COL6A5+ fibroblasts were a distinct subset implicated in the initiation and relapse of psoriasis, which tended to differentiate into CXCL1+ fibroblasts, inducing neutrophil chemotaxis and infiltration; while CXCL1+ fibroblasts exhibited a more heterogeneous response to certain inflammatory conditions. Differentiation trajectory and regulatory factors of these fibroblast subsets were also revealed. Therefore, our study presents a comprehensive atlas of skin fibroblasts and highlights pathogenic fibroblast subsets in skin disorders.

Enhanced phenotype of calcipotriol-induced atopic dermatitis in filaggrin-deficient mice.

Impaired function of filaggrin (FLG) is a major predisposing factor for atopic dermatitis (AD). Several studies on FLG-deficient (Flg-/- ) mice have indicated an essential role for FLG in the skin barrier and the development of AD, but none of the studies have described the characteristics on Flg-/- mice with calcipotriol (CPT)-induced atopic dermatitis, which restricts the comprehensive understanding of functions of FLG. The present study sought to generate Flg-/- mice and applied CPT to produce AD-like dermatitis for in vivo analysis of the FLG functions. CPT was applied on the skin of Flg-/- mice to establish the AD-like dermatitis mouse model. The lesion inflammation was evaluated by gross ear thickness, histopathology, immunofluorescence, and cytokine production. Also, mucopolysaccharide polysulfate (MPS) and ceramide were used to observe the therapeutic function in this model. The results showed that the inflammation of CPT-induced dermatitis in Flg-/- mice was more severer than that of wild-type (WT) mice, as evident by the increased level of gross appearance, ear thickness, inflammatory cell infiltration (mast cells and CD3+ T cells), and inflammatory cytokine expression (interleukin (IL)-4, IL-6, IL-13, and thymic stromal lymphopoietin (TSLP)). The emollients MPS and ceramide partially restored the epidermal function and alleviated the skin inflammation in Flg-/- mice with CPT-induced AD-like dermatitis. The current study demonstrated that skin barrier protein FLG is critical in the pathogenesis of AD. Also, the AD mouse model induced by CPT in Flg-/- mice could be utilized to search for drug targets in AD.

Neutrophil extracellular traps contribute to immune dysregulation in bullous pemphigoid via inducing B-cell differentiation and antibody production.

Bullous pemphigoid (BP), an autoimmune skin disease, is characterized by autoantibodies against hemidesmosomal proteins in the skin and mucous membranes. Neutrophils infiltrate BP skin lesions, however, their role in immune dysregulation remains unclear. We investigated whether BP involves aberrant neutrophil extracellular traps (NETs) formation in skin lesions and circulation; and examined the triggers and deleterious immuno-inflammatory consequences. In the present study, we found that circulating NET-related biomarker levels increased in serum and blister fluid of BP patients and significantly correlated with disease severity. Additionally, circulating neutrophils from BP patients displayed enhanced spontaneous NETs formation than healthy controls. In vitro, BP180-NC16A immune complexes-induced NETosis in neutrophils from BP patients, which was abrogated by Fcγ receptor and/or NADPH pathway blockade. Furthermore, the elevated levels of NETs from BP patients boosted autoantibody production by inducing B-cell differentiation into plasma cells, mediated by MAPK P38 cascade activation. Together, our findings provide strong evidence that NETs are involved in a pathogenic loop, causing excessive differentiation of B cells and promotion of autoantibody production. Hence, targeting aberrant neutrophil responses will provide novel potential targets for the treatment of BP.

Negative regulation of dendritic cell activation in psoriasis mediated via CD100-plexin-B2.

Psoriasis is a chronic inflammatory skin disease in which dendritic cells (DCs) play a pivotal role by inducing Th1/Th17 immune responses; however, the regulation of DC activation in psoriasis remains largely unknown. Previously we found that the level of soluble CD100 was increased in sera of psoriasis patients, and CD100 promoted the activation of inflammasome in keratinocytes. In the present study, CD100 knockout mice were utilized for generation of imiquimod (IMQ)-induced psoriatic dermatitis, with the result that skin inflammation in the early, but not late, phase of the psoriatic dermatitis was significantly exacerbated compared to that in wild-type controls. This was attributed mainly to the deficiency of CD100 in hematopoietic cells. Bone marrow-derived DCs, but not T cells or keratinocytes, from CD100 knockout mice produced significantly increased levels of IL-1ß, IL-36, and IL-23 upon stimulation with IMQ in a plexin-B2-dependent manner. Moreover, the surface level of plexin-B2 on DCs of psoriasis patients was lower than that of healthy individuals, and CD100 attenuated IMQ-induced production of IL-1ß and IL-36 from monocyte-derived DCs of psoriasis patients. Our results uncovered a negative regulatory mechanism for DCs activation in psoriasis, which was mediated via CD100-plexin-B2 in a cell type- and receptor-specific manner. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Phytopathogenic Fungus Pallidocercospora crystallina-Caused Localized Subcutaneous Phaeohyphomycosis in a Patient with a Homozygous Missense CARD9 Mutation.

PURPOSE: In the past decade, an increasing number of otherwise healthy individuals suffered from invasive fungal infections due to inherited CARD9 mutations. Herein, we present a patient with a homozygous CARD9 mutation who was suffering from localized subcutaneous phaeohyphomycosis caused by the phytopathogenic fungus Pallidocercospora crystallina which has not been reported to cause infections in humans. METHODS: The medical history of our patient was collected. P. crystallina was isolated from the biopsied tissue. To characterize this novel pathogen, the morphology was analyzed, whole-genome sequencing was performed, and the in vivo immune response was explored in mice. Whole-exome sequencing was carried out with samples from the patient's family. Finally, the expression and function of mutated CARD9 were investigated. RESULTS: A dark red plaque was on the patient's left cheek for 16 years and was diagnosed as phaeohyphomycosis due to a P. crystallina infection. Whole-genome sequencing suggested that that this strain had a lower pathogenicity. The in vivo immune response in immunocompetent or immunocompromised mice indicated that P. crystallina could be eradicated within a few weeks. Whole-exome sequencing revealed ahomozygous missense mutation in CARD9 (c.1118G>C p.R373P). The mRNA and protein expression levels were similar among cells carrying homozygous (C/C), heterozygous (G/C), and wild-type (G/G) CARD9 alleles. Compared to PBMCs or neutrophils with heterozygous or wild-type CARD9 alleles, however, PBMCs or neutrophils with homozygous CARD9 alleles showed impaired anti-P. crystallina effects. CONCLUSION: Localized subcutaneous phaeohyphomycosis caused by P. crystallina was reported in a patient with a homozygous CARD9 mutation. Physicians should be aware of the possibility of a CARD9 mutation in seemingly healthy patients with unexplainable phaeohyphomycosis.

Stevens-Johnson syndrome/toxic epidermal necrolysis mouse model generated by using PBMCs and the skin of patients.

BACKGROUND: Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening cutaneous reactions caused by drugs or infections and exhibiting widespread epidermal necrosis. Currently, there is no animal model that reproduces SJS/TEN symptoms. OBJECTIVE: We sought to develop a novel mouse model of SJS/TEN by using PBMCs and skin from patients who had recovered from SJS/TEN. METHODS: For our mouse model, patients' PBMCs were injected intravenously into immunocompromised NOD/Shi-scid, IL-2Rγ(null) (NOG) mice, followed by oral administration of a causative drug. Subsequently, to replace human skin, unaffected skin specimens obtained from patients who had recovered from SJS/TEN were grafted onto NOG mice, after which patient-derived PBMCs and the causative drug were applied. RESULTS: Mice injected with PBMCs from patients with SJS/TEN and given the causative drug showed marked conjunctival congestion and numerous cell death of conjunctival epithelium, whereas there were no symptoms in mice injected with PBMCs from patients with ordinary drug skin reactions. CD8(+) T lymphocyte-depleted PBMCs from patients with SJS/TEN did not elicit these symptoms. In addition, skin-grafted mice showed darkening of the skin-grafted areas. Cleaved caspase-3 staining showed that dead keratinocytes were more numerous in the skin-grafted mice than in the healthy control animals. CONCLUSION: We have established a novel human-oriented SJS/TEN mouse model and proved the importance of CD8(+) T lymphocytes in SJS/TEN pathogenesis. The mouse model promises to promote diagnostic and therapeutic approaches.

CREB1-driven CXCR4hi neutrophils promote skin inflammation in mouse models and human patients.

Neutrophils have a pathogenic function in inflammation via releasing pro-inflammatory mediators or neutrophil extracellular traps (NETs). However, their heterogeneity and pro-inflammatory mechanisms remain unclear. Here, we demonstrate that CXCR4hi neutrophils accumulate in the blood and inflamed skin in human psoriasis, and correlate with disease severity. Compared to CXCR4lo neutrophils, CXCR4hi neutrophils have enhanced NETs formation, phagocytic function, neutrophil degranulation, and overexpression of pro-inflammatory cytokines and chemokines in vitro. This is accompanied by a metabolic shift in CXCR4hi neutrophils toward glycolysis and lactate release, thereby promoting vascular permeability and remodeling. CXCR4 expression in neutrophils is dependent on CREB1, a transcription factor activated by TNF and CXCL12, and regulated by de novo synthesis. In vivo, CXCR4hi neutrophil infiltration amplifies skin inflammation, whereas blockade of CXCR4hi neutrophils through CXCR4 or CXCL12 inhibition leads to suppression of immune responses. In this work, our study identifies CREB1 as a critical regulator of CXCR4hi neutrophil development and characterizes the contribution of CXCR4hi neutrophils to vascular remodeling and inflammatory responses in skin.

CXCL12/CXCR4 Axis Drives the Chemotaxis and Differentiation of B Cells in Bullous Pemphigoid.

Bullous pemphigoid (BP) is an autoimmune bullous skin disease characterized by autoantibodies against the hemidesmosomal proteins in the skin and mucous membranes. The efficiency of B-cell‒targeting biologics in BP indicates the important role of B cells in its pathogenesis. However, abnormal B-cell migration and differentiation in BP require further elucidation. We showed that the number of antibody-secreting cells increased in the circulation and skin lesions of patients with BP and was correlated with disease severity. Bulk RNA sequencing of the peripheral B cells identified 171 upregulated and 408 downregulated genes in patients with BP compared with those in healthy controls, among which CXCR4 was significantly upregulated. Notably, CXCR4+ B cells were enriched in BP skin lesions and exhibited antibody-secreting cell characteristics. Correspondingly, an elevated level of CXCL12, the CXCR4 ligand, was detected in the blister fluid and serum of patients with BP, mediating the chemotaxis and accumulation of CXCR4+ B cells to BP skin lesions. Moreover, CXCL12 activated the transcription factor c-Myc, thus promoting B-cell differentiation into antibody-secreting cells and facilitating autoantibody production, which was blocked by CXCR4 inhibitor in vitro. Collectively, our study reveals that the CXCL12/CXCR4 axis plays a pathogenic role in modulating B-cell trafficking and differentiation, thus targeting CXCR4 represents a potential strategy for treating BP and other autoimmune diseases.

Noncollagenous 16A domain of type XVII collagen-reactive CD4+ T cells play a pivotal role in the development of active disease in experimental bullous pemphigoid model.

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is caused by autoantibodies against type XVII collagen (COL17). We recently demonstrated that CD4+ T cells were crucial for the production of anti-COL17 IgG and for the development of the BP phenotype by using a novel active BP mouse model by adoptively transferring immunized splenocytes into immunodeficient COL17-humanized mice. Noncollagenous 16A (NC16A) domain of COL17 is considered to contain the main pathogenic epitopes of BP, however, the pathogenicity of COL17 NC16A-reactive CD4+ T cells has never been elucidated. To address this issue, we modulated the immune responses against COL17 in active BP model by using anti-CD40 ligand (CD40L) monoclonal antibody MR1, an inhibitor of the CD40-CD40L interaction, in various ways. First, we show the essential role of CD4+ T cells in the model by showing that CD4+ T cells isolated from wild-type mice immunized with human COL17 enabled naïve B cells to produce anti-COL17 NC16A IgG in vivo. Second, we show that the activation of anti-COL17 NC16A IgG-producing B cells via CD40-CD40L interaction was completed within 5 days after the adoptive transfer of immunized splenocytes. Notably, a single administration of MR1 at day 0 was enough to inhibit the production of anti-COL17 NC16A IgG and to diminish skin lesions despite the presence of restored anti-COL17 IgG at the later stage. In contrast, the delayed administration of MR1 failed to inhibit the production of anti-COL17 NC16A IgG and the development of the BP phenotype. These results strongly suggest that COL17 NC16A-reactive CD4+ T cells play a pivotal role in the production of pathogenic autoantibodies and in the development of active disease in experimental BP model.

A novel active mouse model for bullous pemphigoid targeting humanized pathogenic antigen.

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is caused by autoantibodies against type XVII collagen (COL17). To establish an active stable BP animal model that demonstrates the persistent inflammatory skin lesions initiated by the anti-human COL17 Abs, we used COL17-humanized (COL17(m-/-,h+)) mice that we recently produced. First, we generated immunodeficient Rag-2(-/-)/COL17-humanized mice by crossing Rag-2(-/-) mice with COL17-humanized mice. Then, splenocytes from wild-type mice that had been immunized by grafting of human COL17-transgenic mouse skin were transferred into Rag-2(-/-)/COL17-humanized mice. The recipient mice continuously produced anti-human COL17 IgG Abs in vivo and developed blisters and erosions corresponding to clinical, histological, and immunopathological features of BP, although eosinophil infiltration, one of the characteristic histological findings observed in BP patients, was not detected in the recipients. Although the depletion of CD8(+) T cells from the immunized splenocytes was found to produce no effects in the recipients, the depletion of CD4(+) T cells as well as CD45R(+) B cells was found to inhibit the production of anti-human COL17 IgG Abs in the recipients, resulting in no apparent clinical phenotype. Furthermore, we demonstrated that cyclosporin A significantly suppressed the production of anti-human COL17 IgG Abs and prevented the development of the BP phenotype in the treated recipients. Although this model in an immunodeficient mouse does not exactly reproduce the induction mechanism of BP in human patients, this unique experimental system targeting humanized pathogenic Ag allows us to investigate ongoing autoimmune responses to human molecules in experimental animal models.

Human IgG1 monoclonal antibody against human collagen 17 noncollagenous 16A domain induces blisters via complement activation in experimental bullous pemphigoid model.

Bullous pemphigoid (BP) is an autoimmune blistering disease caused by IgG autoantibodies targeting the noncollagenous 16A (NC16A) domain of human collagen 17 (hCOL17), which triggers blister formation via complement activation. Previous in vitro analysis demonstrated that IgG1 autoantibodies showed much stronger pathogenic activity than IgG4 autoantibodies; however, the exact pathogenic role of IgG1 autoantibodies has not been fully demonstrated in vivo. We constructed a recombinant IgG1 mAb against hCOL17 NC16A from BP patients. In COL17-humanized mice, this mAb effectively reproduced a BP phenotype that included subepidermal blisters, deposition of IgG1, C1q and C3, neutrophil infiltration, and mast cell degranulation. Subsequently, alanine substitutions at various C1q binding sites were separately introduced to the Fc region of the IgG1 mAb. Among these mutated mAbs, the one that was mutated at the P331 residue completely failed to activate the complement in vitro and drastically lost pathogenic activity in COL17-humanized mice. These findings indicate that P331 is a key residue required for complement activation and that IgG1-dependent complement activation is essential for blister formation in BP. This study is, to our knowledge, the first direct evidence that IgG1 Abs to hCOL17 NC16A can induce blister formation in vivo, and it raises the possibility that IgG1 mAbs with Fc modification may be used to block pathogenic epitopes in autoimmune diseases.

A population of dermal Langerin+ dendritic cells promote the inflammation in mouse model of atopic dermatitis.

Cutaneous dendritic cells (DCs) have been implicated in the pathogenesis of atopic dermatitis (AD). However, the specific role of different subsets of DCs has not been well defined. This study aimed to investigate the contributions of Langerhans cells (LCs), resident dermal Langerin+ DCs (r-Langerin+ dDCs), and newly infiltrated inflammatory dermal Langerin+ DCs (i-Langerin+ dDCs) in an AD mouse model induced by the topical application of MC903. The result showed that depletion of i-Langerin+ dDCs in DTR mice after multiple diphtheria toxin (DT) injection significantly reduced thymic stromal lymphopoietin (TSLP) production in lesions and skin inflammation alleviation. However, depletion of LCs or r-Langerin+ dDCs didn't resulted in significant changes in skin inflammation of DTA or single DT injection-treated DTR mice compared with the wild-type (WT) mice. DT-treated DTR-WT chimeric mice with the depletion of bone marrow (BM)-derived i-Langerin+ dDCs resulted in markedly decreased skin inflammation than controls, while PBS-treated chimeric mice (DTR-WT) with only the depletion of r-Langerin+ dDCs showed inflammation comparable to that in WT mice. Furthermore, TSLP contributed to the upregulation of Langerin expression in BM-derived DCs and promoted the maturation of Langerin+ DCs. In summary, the present study demonstrated that the newly infiltrated inflammatory dermal Langerin+ DCs were essential for AD development and local TSLP production, and TSLP further promoted the production of BM-derived i-Langerin+ dDCs, which might maintain AD inflammation.

LCN2 Mediates Skin Inflammation in Psoriasis through the SREBP2‒NLRC4 Axis.

Lipocalins are a family of secreted adipokines that regulate cell lipid metabolism and immune responses. Although we have previously revealed that LCN2 modulates neutrophil activation in psoriasis, the other roles of LCN2 in psoriatic local inflammation have remained elusive. In this study, we found that 24p3R, the well-known specific receptor of LCN2, was highly expressed in the lesional epidermis of patients with psoriasis. Silencing 24p3R (also known as slc22a17) alleviated hyperkeratosis, inflammatory cell infiltration, and overexpression of inflammatory mediators in an imiquimod-induced psoriasis-like mouse model. In vitro, LCN2 enhanced the expression of proinflammatory factors in primary keratinocytes, such as IL-1ß, IL-23, CXCL1, and CXCL10, which was paralleled by enforced cholesterol biosynthetic signaling. Importantly, taking in vivo and in vitro approaches, we discovered the SREBP2, a vital transcriptional factor in cholesterol synthesis pathway, as the critical mediator of LCN2-induced keratinocyte activation, which bound to the promoter region of NLRC4. Suppressing SREBP2 in mice attenuated NLRC4 signaling and psoriasis-like dermatitis. Taken together, this study identifies the critical role of LCN2‒SREBP2‒NLRC4 axis in the pathogenesis of psoriasis and proposes 24p3R or SREBP2 as a potential therapeutic target for psoriasis.

Long-term follow-up of in situ extramammary Paget's disease in Asian skin types IV/V treated with photodynamic therapy.

Photodynamic therapy is a potentially advantageous treatment for non-melanoma skin cancers. We evaluated the clinical response, recurrence and adverse events of photodynamic therapy for in situ extramammary Paget's disease in 14 male and 3 female Chinese patients with 21 lesions. Topical 20% 5-aminolevulinic acid was applied for 6 h. Each lesion was irradiated with 633 nm red light three times, 1 week apart, at a total dose of 339 J/cm2, followed by three assessments at 6, 12 and 24 months. Overall complete response (CR) rates were 52.4%, 42.9%, and 33.3% at 6, 12 and 24 months, respectively. The CR rate was significantly higher in scrotal lesions (66.6%) than in non-scrotal lesions (8.3%). The overall recurrence rate was 50%. The highest CR rate was for the lesions < 4 cm in diameter (62.5%), followed by those 4-8 cm (33.3%) and > 8 cm (0%). Most adverse events were well tolerated. In conclusion, photodynamic therapy for extramammary Paget's disease is not recommended as the first option except for scrotal cases or lesions < 4 cm in diameter.

Author Correction: Up-regulation of Interferon-inducible protein 16 contributes to psoriasis by modulating chemokine production in keratinocytes.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Aryl Hydrocarbon Receptor in Cutaneous Vascular Endothelial Cells Restricts Psoriasis Development by Negatively Regulating Neutrophil Recruitment.

Vascular endothelial cells (VECs) that line the interiors of blood vessels participate in physiological and inflammatory processes. All skin cell types express the aryl hydrocarbon receptor (AhR), which is involved in the pathogenesis of psoriasis. However, the role of the cutaneous VEC AhR in the pathogenesis of psoriasis remains elusive. In the present study, we found that AhR protein expression and activation were downregulated in psoriatic VECs. Furthermore, cutaneous VEC-specific AhR-knockout (AhRcVECs-KO) mice were established. Using imiquimod and IL-23-induced psoriasis models, we found that skin inflammation was exacerbated with excessive neutrophil recruitment in AhRcVECs-KO mice. Furthermore, neutrophil neutralization alleviates exacerbated inflammation in imiquimod-treated AhRcVECs-KO mice. In addition, cutaneous VECs in AhRcVECs-KO mice exhibited increased dilation and activation compared with those in control mice. Finally, AhR-deficient microvascular endothelial cells stimulated by proinflammatory cytokines showed increased ICAM-1 expression in vivo and in vitro, which may have facilitated neutrophil recruitment. In summary, our study demonstrates that AhR in dermal VECs restricts psoriasis development by negatively regulating neutrophil recruitment, thereby providing insight into the pathogenesis of psoriasis.

Small interfering RNA targeting of keratin 17 reduces inflammation in imiquimod-induced psoriasis-like dermatitis.

BACKGROUND: Psoriasis is a common chronic inflammatory skin disease with 2% to 3% prevalence worldwide and a heavy social-psychological burden for patients and their families. As the exact pathogenesis of psoriasis is still unknown, the current treatment is far from satisfactory. Thus, there is an urgent need to find a more effective therapy for this disease. Keratin 17 (K17), a type I intermediate filament, is overexpressed in the psoriatic epidermis and plays a critical pathogenic role by stimulating T cells in psoriasis. Therefore, we hypothesized that inhibiting K17 may be a potential therapeutic approach for psoriasis. This study aimed to investigate the therapeutic effect of K17-specific small interfering RNA (siRNA) on mice with imiquimod (IMQ)-induced psoriasis-like dermatitis. METHODS: Eight-week-old female BALB/c mice were administered a 5% IMQ cream on both ears to produce psoriatic dermatitis. On day 3, K17 siRNA was mixed with an emulsion matrix and applied topically to the left ears of the mice after IMQ application every day for 7 days. The right ears of the mice were treated in parallel with negative control (NC) siRNA. Inflammation was evaluated by gross ear thickness, histopathology, the infiltration of inflammatory cells (CD3+ T cells and neutrophils) using immunofluorescence, and the expression of cytokine production using real-time quantitative polymerase chain reaction. The obtained data were statistically evaluated by unpaired t-tests and a one-way analysis of variance. RESULTS: The severity of IMQ-induced dermatitis on K17 siRNA-treated mice ears was significantly lower than that on NC siRNA-treated mice ears, as evidenced by the alleviated ear inflammation phenotype, including decreased ear thickness, infiltration of inflammatory cells (CD3+ T cells and neutrophils), and inflammatory cytokine/chemokine expression levels (interleukin 17 [IL-17], IL-22, IL-23, C-X-C motif chemokine ligand 1, and C-C motif chemokine ligand 20) (P < 0.05 vs. the Blank or NC siRNA groups). Compared to the NC siRNA treatment, the K17 siRNA treatment resulted in increased K1 and K10 expression, which are characteristic of keratinocyte differentiation (vs. NC siRNA, K17 siRNA1 group: K1, t = 4.782, P = 0.0050; K10, t = 3.365, P = 0.0120; K17 siRNA2 group: K1, t = 4.104, P = 0.0093; K10, t = 4.168, P = 0.0042; siRNA Mix group: K1, t = 3.065, P = 0.0221; K10, t = 10.83, P < 0.0001), and decreased K16 expression, which is characteristic of keratinocyte proliferation (vs. NC siRNA, K17 siRNA1 group: t = 4.156, P = 0.0043; K17 siRNA2 group: t = 2.834, P = 0.0253; siRNA Mix group: t = 2.734, P = 0.0250). CONCLUSIONS: Inhibition of K17 expression by its specific siRNA significantly alleviated inflammation in mice with IMQ-induced psoriasis-like dermatitis. Thus, gene therapy targeting K17 may be a potential treatment approach for psoriasis.

Plasma exosomal miR-375-3p regulates mitochondria-dependent keratinocyte apoptosis by targeting XIAP in severe drug-induced skin reactions.

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are severe drug-induced cutaneous reactions characterized by keratinocyte apoptosis. Exosomes are nanometer-sized membranous vesicles in body fluids. They contain functional proteins, mRNAs, and miRNAs, which induce immune dysfunction and influence disease progression. However, their roles and mechanisms in SJS/TEN remain unknown. Our results demonstrate that exosomes isolated from the plasma of patients with SJS/TEN were 30 to 200 nm in diameter and expressed CD9, CD63, CD81, and TSG101 exosome marker proteins. miR-375-3p was markedly up-regulated in 35 patients with SJS/TEN and correlated with clinical severity. Plasma exosomes were internalized by human primary keratinocytes and promoted keratinocyte apoptosis in vitro. Furthermore, miR-375-3p overexpression promoted intrinsic (mitochondria-dependent) apoptosis of human primary keratinocytes via down-regulation of the X-linked inhibitor of apoptosis protein (XIAP), a key apoptosis regulator in primary human keratinocytes. In sum, our study indicates that the circulating exosomal miR-375-3p enters keratinocytes, down-regulates XIAP, and induces keratinocyte apoptosis in patients with SJS/TEN.