Transgenic rescue of desmoglein 3 null mice with desmoglein 1 to develop a syngeneic mouse model for pemphigus vulgaris

Background

An active disease mouse model of pemphigus vulgaris (PV) was developed using the adoptive transfer of splenocytes from Dsg3^−/− mice with a mixed C57BL/6J (B6) and 129/Sv genetic background into B6-Rag2^−/− mice. Further immunological investigation is needed to resolve the genetic mismatch between host and recipient mice. The B6-Dsg3^−/− mice did not grow old enough to provide splenocytes, probably due to severe oral erosions, with resulting inhibition of food intake.

Objective

To rescue the B6-Dsg3^−/− mice and to produce syngeneic PV model mice.

Methods

Transgenic expression of mouse Dsg1 was attempted to compensate for the genetic loss of Dsg3 using the keratin 5 promoter. We evaluated the compensatory ability of Dsg1 in vivo by comparing Dsg1^wt/wt, Dsg1^tg/wt, and Dsg1^tg/tg mice. We generated a PV model via the adoptive transfer of B6-Dsg1^tg/tgDsg3^−/− splenocytes to B6-Rag2^−/− mice.

Results

Dsg1^tg/tg and Dsg1^tg/wt mice expressed ectopic Dsg1 on keratinocyte cell surfaces in the lower layers of the epidermis, oral epithelium, and telogen hair follicles. Ectopic Dsg1 blocked the pathogenic effects of AK23 anti-Dsg3 mAb, and improved the body weight loss, telogen hair loss, and survival rate dose-dependently. While the B6-Dsg1^wt/wtDsg3^−/− mice died by week 2, over 80% of the B6-Dsg1^tg/tgDsg3^−/− mice survived at week 6. Furthermore, the syngeneic PV model mice showed the characteristic phenotype, including stable anti-Dsg3 antibody production and suprabasilar acantholysis on histology.

Conclusion

Transgenic expression of Dsg1 rescued the severe B6-Dsg3^−/− phenotype and provided a syngeneic mouse model of PV, which may be a valuable tool for clarifying immunological mechanisms in autoimmunity and tolerance of Dsg3.     

An adult passive transfer mouse model to study desmoglein 3 signaling in pemphigus vulgaris

Evidence has accumulated that changes in intracellular signaling downstream of desmoglein 3 (Dsg3) may have a significant role in epithelial blistering in the autoimmune disease pemphigus vulgaris (PV). Currently, most studies on PV involve passive transfer of pathogenic antibodies into neonatal mice that have not finalized epidermal morphogenesis, and do not permit analysis of mature hair follicles (HFs) and stem cell niches. To investigate Dsg3 antibody-induced signaling in the adult epidermis at defined stages of the HF cycle, we developed a model with passive transfer of AK23 (a mouse monoclonal pathogenic anti-Dsg3 antibody) into adult 8-week-old C57Bl/6J mice. Validated using histopathological and molecular methods, we found that this model faithfully recapitulates major features described in PV patients and PV models. Two hours after AK23 transfer, we observed widening of intercellular spaces between desmosomes and EGFR activation, followed by increased Myc expression and epidermal hyperproliferation, desmosomal Dsg3 depletion, and predominant blistering in HFs and oral mucosa. These data confirm that the adult passive transfer mouse model is ideally suited for detailed studies of Dsg3 antibody-mediated signaling in adult skin, providing the basis for investigations on novel keratinocyte-specific therapeutic strategies.     

A novel mouse desmosomal cadherin family member,desmoglein 1 gamma

The mouse desmogleins are members of the desmosomal cadherin superfamily, and are critical structural components of the desmosome. The genes encoding mouse desmogleins are tightly clustered within 600 kb of chromosome 18, within a desmosomal cadherin gene family also containing the three desmocollin genes. In this study, we have characterized a novel mouse desmoglein gene, highly homologous to both mouse and human Dsg1, designated desmoglein 1 gamma (Dsg1c). Dsg1 gamma shares 83% amino acid identity to the previously described mouse Dsg1, now designated as Dsg1 alpha, and 32% and 40% identity to mouse Dsg2 and 3, respectively. The Dsg1 gamma gene maps within the desmosomal gene cluster, between Dsc1 and Dsg1 alpha. Comparison of its exon-intron structure revealed a high level of evolutionary conservation with related family members. In contrast to Dsg1 alpha and Dsg3 whose expression is largely restricted to the skin, Dsg1 gamma is also expressed in the brain, skeletal muscle, and liver, among other tissues, and is thus more similar to Dsg2 in its tissue distribution. Interestingly, an orthologous Dsg1 gamma was not found in the human genome, suggesting that the desmosomal cadherin gene cluster contracted during mammalian evolution.     

The humanized SCID mouse model to study HLA class II-linked autoimmunity to desmoglein 3 in pemphigus vulgaris

BACKGROUND: Pemphigus vulgaris (PV) is a severe autoimmmune skin disorder induced by antibodies against desmoglein (Dsg) 3 on epidermal keratinocytes. OBJECTIVES: To establish an active animal model of PV to analyse the T-cell-regulated production of pathogenic antibodies in vivo. METHODS: Immunodeficient SCID mice were injected with peripheral blood lymphocytes (PBL) from an HLA-DRB1*0402/DQ8+ patient with PV or a DRB1*0402/DQ8+ healthy donor, with or without subsequent injections of human Dsg3 or preincubation of PBL with Dsg3. RESULTS: Human immunoglobulins (2.7-18.5 mg mL-1) were detected in all the mice after 8 weeks. Only one of 30 PBL-treated mice developed IgM against Dsg3 and showed intercellular IgM deposits in skin, nostrils and tongue. In contrast, in a previous study, 41% of SCID mice injected with PBL from patients with PV developed anti-Dsg3 antibodies in vivo. CONCLUSIONS: Our inability to reproduce these findings may be due to the transfer of slightly lower numbers of PBL (20 x 10(6) vs. 25-30 x 10(6)).     

Evidence of an association between desmoglein 3 haplotypes and pemphigus vulgaris

BACKGROUND: Pemphigus vulgaris (PV, OMIM 169610) is a severe blistering disorder of the skin and mucous membranes, caused by the production of autoantibodies directed against the epithelial adhesive protein desmoglein 3. Although an association between PV and HLA class II alleles has been established, the genetic factors predisposing to the disease remain poorly understood, the rarity of PV hampering the recruitment of substantial patient cohorts. OBJECTIVES: To investigate DSG3 as a candidate PV susceptibility gene. METHODS: We examined five DSG3 single nucleotide polymorphisms (rs8085532, rs3911655, rs3848485, rs3794925 and rs1466379) in two case-control datasets respectively originating from the U.K. (62 PV patients, 154 controls) and northern India (28 patients, 98 controls). RESULTS: In the U.K. sample, we observed a significant association between PV and the DSG3*TCCTC haplotype (Fisher's exact test P = 0.002). A related haplotype (DSG3*TCCCC) was associated with PV in the Indian dataset (P = 0.002). We also found that all British and Indian patients bearing DSG3 risk haplotypes carried at least one copy of a PV-associated HLA allele. CONCLUSIONS: These results suggest that genetic variation of DSG3 may be an additive risk factor predisposing to PV and warrant further investigations of this gene.     

Interspecies conservation and differential expression of mouse desmoglein gene family

Epithelial cell adhesion is mediated by intercellular junctions, called desmosomes. Desmogleins (Dsg; Dsg1, Dsg2 and Dsg3) are calcium-dependent transmembrane adhesion components of the desmosomes. While Dsg1 and Dsg3 are mainly restricted to stratified squamous epithelia, Dsg2 is expressed in essentially all desmosome-containing epithelia. In the epidermis, Dsg2 and Dsg3 are expressed in the basal keratinocytes while Dsg1 is expressed throughout the upper differentiating cell layers. To date, in mouse, only Dsg3 has been characterized by molecular cloning. In this study, we have cloned and characterized the mouse Dsg1 and Dsg2 genes. The full-length mouse Dsg1 cDNA (5.5 kb) contains an open reading frame (ORF) of 3171 bp encoding a precursor protein of 1057 amino acids. The Dsg2 cDNA (6.3 kb) has an ORF of 3366 bp coding for a precursor protein of 1122 amino acids. Mouse Dsg2 protein shares 76% identity with human DSG2 but only 26% and 33% identity with mouse Dsg1 and Dsg3, respectively. Analysis of intron/exon organization of the desmoglein genes revealed significant conservation. However, the mRNA expression patterns of these desmogleins during mouse embryonic development and in various adult tissues are variable. While Dsg2 and Dsg3 are expressed in all developmental stages, Dsg1 expression is delayed until day 15 of mouse embryos. In adult mouse tissues, Dsg2 is widely expressed while the expression of Dsg1 and Dsg3 is restricted to select tissues. In summary, while desmogleins share high homology at both the gene and protein level, their expression is spatially and temporally regulated, potentially contributing to their significant role in cell-cell adhesion during development.     

Immunolocalization of desmoglein I ("band 3" polypeptide) on acantholytic cells in pemphigus vulgaris, Darier's disease, and Hailey-Hailey's disease.

Acantholysis is defined as loss of coherence between epithelial cells and is histologically shown in several bullous diseases. It was postulated that desmoglein I, one of the major transmembrane glycoproteins of the desmosome, may adhere to the attachment plaque inside the cell and contribute to desmoglea outside the cell. In this study we used a well characterized antibody against desmoglein I for immunofluorescence and immunoelectron microscopic techniques on 2 cases each of pemphigus vulgaris and Darier's disease and one case of Hailey-Hailey's disease. In the normal epidermis desmosomes were demonstrated in dotted or rim-like patterns along cell periphery on immunofluorescence study. In pemphigus vulgaris dotted or rim-like patterns were still identified in many acantholytic cells, particularly in early phase of acantholysis. In Darier's disease and Hailey-Hailey's disease, dotted or rim-like patterns were already lost in early acantholysis and immunoreactive desmoglein I proteins were observed diffusely in the cytoplasm. Immunoelectron microscopy confirmed these immunofluorescence observations. It was suggested that in pemphigus vulgaris desmoglein I is unlikely to be the primary site of acantholysis because dotted or rim-like patterns of immunoreactive desmoglein I are relatively preserved on lesional cells, whereas in genodermatoses such as Darier's disease and Hailey-Hailey's disease primary abnormalities of desmosomes may be involved in their acantholysis.     

Novel member of the mouse desmoglein gene family: Dsg1-beta

Desmosomes are major intercellular adhesion junctions that provide stable cell-cell contacts and mechanical strength to epithelial tissues by anchoring cytokeratin intermediate filaments of adjacent cells. Desmogleins (Dsg) are transmembrane core components of the desmosomes, and belong to the cadherin supergene family of calcium-dependent adhesion molecules. Currently, there are three known isoforms of Dsgs (Dsg1, Dsg2, and Dsg3), encoded by distinct genes that are differentially expressed to determine their tissue specificity and differentiation state of epithelial cells. In this study, we cloned a novel mouse desmoglein gene sharing high homology to both mouse and human Dsg1. We propose to designate the previously published mouse Dsg1 gene as Dsg1-alpha and the new gene as Dsg1-beta. Analysis of intron/exon organization of the Dsg1-alpha and Dsg1-beta genes revealed significant conservation. The full-length mouse Dsg1-beta cDNA contains an open reading frame of 3180 bp encoding a precursor protein of 1060 amino acids. Dsg1-beta protein shares 94% and 76% identity with mouse Dsg1-alpha and human DSG1, respectively. RT-PCR using a multitissue cDNA panel demonstrated that while Dsg1-alpha mRNA was expressed in 15- to 17-day-old embryos and adult spleen and testis, Dsg1-beta mRNA was detected in 17-day-old embryos only. To assess subcellular localization, a FLAG-tagged expression construct of Dsg1-beta was transiently expressed in epithelial HaCaT cells. Dsg1-beta-FLAG was found at the cell-cell border and was recognized by the anti-Dsg1/Dsg2 antibody DG3.10. In summary, we have cloned and characterized a novel member of the mouse desmoglein gene family, Dsg1-beta.     

IgG against extracellular subdomains of desmoglein 3 relates to clinical phenotype of pemphigus vulgaris

Abstract:  Pemphigus vulgaris (PV) is associated with autoantibodies against desmoglein (Dsg) 3 inducing epidermal loss of adhesion. The major pathogenic epitopes of Dsg3 are presumably dependent of their conformation. The aim of this study was to characterize the IgG reactivity of sera from a cohort of clinically well-characterized PV patients against presumably non-conformational subdomains of the Dsg3 ectodomain including recently described NH₂-terminal immunodominant epitopes. By ELISA, IgG reactivity against distinct subdomains of Dsg3 was related to disease activity and the clinical phenotype of PV patients. Our findings suggest that (i) autoantibody from PV sera react with non-conformational epitopes of Dsg3; (ii) IgG reactivity against the NH₂-terminus and the extracellular domains (EC) 2-4 of Dsg3 was associated with active PV, while IgG titres were not strictly correlated with disease activity and (iii) IgG reactivity against the EC1-4 was associated with mucosal dominant PV and was decreased in cutaneous dominant PV. The findings may help to define more refined serological disease markers of PV.     

Three cases of transition from pemphigus vulgaris to pemphigus foliaceus confirmed by desmoglein ELISA

We report 3 cases of pemphigus vulgaris (PV) confirmed by histology and direct and indirect immunofluorescence that showed transition to pemphigus foliaceus (PF) 2-4 years from the time of disease onset. Desmoglein (Dsg) ELISA testing of the sera from these 3 patients in the later stages of their disease showed the presence of anti-Dsg1 antibodies and the absence of anti-Dsg3 antibodies. These patients were on prednisolone and immunosuppressives at the time the sera were tested, and it is unclear if the transition from PV to PF is a permanent one or whether it is due to preferential suppression of Dsg3 antibodies below a certain threshold. Previously reported cases of transition from PV to PF and PF to PV are summarized.     

桥粒芯糖蛋白3刺激下寻常型天疱疮患者外周血T淋巴细胞增殖检测分析

目的 观察桥粒芯糖蛋白3（Dsg3）对寻常型天疱疮（PV）患者外周血T淋巴细胞增殖的影响。方法 PV患者12例,正常人22例,提取外周血单一核细胞（PBMC）,采用流式细胞仪技术分别检测Dsg3刺激下PBMC中T淋巴细胞亚群变化及T淋巴细胞增殖情况,分析PV患者与正常人之间存在的差异。结果 PV患者PBMC在Dsg3刺激下Th2型T淋巴细胞所占比例为12.17% ± 5.32%,Th1型T淋巴细胞所占比例为4.08% ± 1.50%;未经Dsg3刺激的阴性对照组分别为9.84% ± 5.41%和3.91% ± 1.38%。PV患者PBMC在Dsg3刺激和无Dsg3刺激时的Th2型T淋巴细胞所占比例均显著高于正常人（P < 0.05）;Dsg3刺激下PV患者T淋巴细胞发生增殖,CD4+ T淋巴细胞增殖率为4.65% ± 3.28%,显著高于正常人（P < 0.05）。结论 Dsg3可诱导PV患者CD4+ T淋巴细胞发生特异性增殖,且主要为Th2优势型。     

Cleavage of desmoglein 3 can explain its depletion from keratinocytes in pemphigus vulgaris

We have previously demonstrated that serum of patients with pemphigus vulgaris induces reduction of desmoglein 3 (Dsg3) half-life in keratinocytes (FEBS Lett 2006: 580: 3276). This phenomenon seems to occur as a consequence of the progressive depletion of Dsg3 from desmosomes. Here we reported that reduction of full-length Dsg3 may be due to its progressive cleavage, leading to the formation of two fragmentation products with apparent molecular masses of about 60 kDa (fragment 1) and 70 kDa (fragment 2), as revealed by Western blotting. Unexpectedly, analysis of fragmentation pattern suggested cleavage to occur intracellularly. Consistently, fragment 1 was shed and localized within the cytosol, as shown by living cell immunofluorescence microscopy. Total amounts of full-length plakoglobin and Dsg1 were apparently unchanged. Taken together, our findings provide evidence that proteolytic processing of Dsg3 can lead to depletion of Dsg3 from the cell.     

Delineation of diversified desmoglein distribution in stratified squamous epithelia: implications in diseases

Desmogleins play critical roles in cell adhesion and skin blistering diseases, as they are the target antigens of autoimmune antibodies and bacterial toxins. We recently cloned several novel members of the desmoglein gene family, bringing the number of desmogleins to four in the rat and human genomes and six in the mouse. Here, we have produced a monoclonal antibody to a cytoplasmic epitope of Dsg4, assessed its specificity and compared it to several existing Dsg1-3 antibodies. We also demonstrated cross-reactivity of commercially available and often used Dsg1 antibodies. Using these tools, we delineated the unique expression patterns of each desmoglein isoform in various human and mouse stratified squamous epithelia, including skin, hair, palm, and oral mucosa. Interestingly, in the epidermis, the expression of each desmoglein correlates with their gene arrangement in the cadherin locus. In human, Dsg4 was detected primarily in the granular and cornified cell layers of the epidermis, while present throughout all differentiated layers of the oral mucosa and palm, and in the matrix cells of anagen hair bulb. Similar pattern of expression for Dsg4 was observed in mouse, with the exception that it was expressed at significantly lower levels in the mouse epidermis. These results demonstrate the complexity of desmoglein gene expression and provide additional insights into the correlation between tissue expression patterns and disease phenotypes.     

The transition of pemphigus vulgaris into pemphigus foliaceus: a reflection of changing desmoglein 1 and 3 autoantibody levels in pemphigus vulgaris

The transition of pemphigus vulgaris (PV) into pemphigus foliaceus (PF) is rare and the immunological changes underlying this event are not well understood. We report a 44-year-old woman who presented with oral and cutaneous erosions typical of PV. Over a 9-year period, the clinical features evolved into those of PF. To examine whether quantitative changes in desmoglein (Dsg) antibodies were associated with this transition, Dsg1 and Dsg3 antibody levels were measured by enzyme-linked immunosorbent assay in 82 sequential serum samples collected over this period. At presentation, when the phenotype was PV with oral and cutaneous erosions, antibodies to both Dsg1 and Dsg3 were detected. The disappearance of oral involvement was associated with a decline in Dsg3 antibodies, which are now undetectable, while the development of more severe skin involvement was associated with rising Dsg1 antibody levels. These data strongly suggest that the change in clinical features is a reflection of qualitative and quantitative changes in antibody profile. It is not known whether the transition to PF is permanent or whether disease relapses in the future may be associated with the re-emergence of Dsg3 antibodies, oral ulceration and a PV phenotype.     

寻常型天疱疮抗原Dsg3基因的真核表达

目的 探讨寻常型天疱疮自身抗原Dsg3EC1-EC5在哺乳动物细胞的克隆、表达及纯化,并以重组的Dsg抗原检测寻常型天疱疮患者及正常人血清中的天疱疮抗体.方法 根据基因库中的Dsg3基因序列分析,采用RT-PCR法扩增自身抗原Dsg3EC1-EC5多肽片段的cDNA,定向插入真核表达质粒pcDNA3.1TM/myc-His(-)B中,稳定转染人宫颈癌细胞系表达重组融合蛋白,并经Ni+亲和层析柱纯化.采用蛋白质印迹法鉴定蛋白表达产物.以重组Dsg3EC1-EC5蛋白为抗原用ELISA检测40份寻常型天疱疮患者及40份正常人对照组血清.结果 成功构建真核表达重组体pcDNA3.1TM/myc-His(-)B-Dsg3.纯化的Dsg3EC1-EC5蛋白能够与寻常型天疱疮患者血清中的天疱疮抗体发生反应.ELISA方法检测寻常型天疱疮患者血清,结果显示,天疱疮抗体的阳性率为95%.结论 真核表达的Dsg3EC1-EC5蛋白与寻常型天疱疮患者血清中的抗体发生特异性反应.     

Inhibition of FAK prevents blister formation in the neonatal mouse model of pemphigus vulgaris

Pemphigus vulgaris (PV) is an autoimmune blistering skin disease characterized by suprabasal acantholysis and by autoantibodies against desmoglein 3 localized on desmosomes. In addition, caspases also seem to participate in this blistering disease. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase involved in cytoskeleton remodelling and formation and disassembly of cell adhesion structures. We have previously demonstrated that HER (human epidermal growth factor receptor related) isoforms, Src (Rous sarcoma) and mammalian target of rapamycin (mTOR), three molecules implicated in signalling processes, take part in suprabasal acantholysis and apoptosis induced by PV-IgG in a mouse model. Our aim was to investigate whether upregulation of FAK is implicated in the development of PV lesions. Herein, using a mouse model, PV-IgG administration showed an increased level of FAK phosphorylated on 397 and 925 tyrosine residues in the basal layer of epidermis. When mice were pretreated with a FAK inhibitor (FI), the acantholysis of the basal layer of epidermis was absent. More interestingly, we observed that phosphorylated FAK (Y397/925) decreased when HER isoforms, Src, mTOR and pan-caspases inhibitors were employed before PV-IgG administration. In addition, pretreatment with the FI before PV-IgG injection prevented the changes in both Bax and Bcl-2 expression and caspase-9 and caspase-3 activities induced by PV-IgG. Finally, FI reduced the expression of phosphorylated Src and mTOR in the basal cells of epidermis. In conclusion, our data reveal a novel role of phosphorylated FAK (Y397/925) in PV development involving HER isoforms, Src and mTOR kinases.     

抗Dsg—3 EC3—4的单链抗体片段在寻常型天疱疮鼠模型中的作用

目的 探讨抗桥粒芯糖蛋白3(Dsg-3)EC3-4的单链抗体片段(ScFv)在寻常型天疱疮(PV)鼠模型中的作用。方法 在不同时间点。将抗Dsg-3 EC3-4的ScFv通过皮下注射至BALB/c新生鼠,从临床表现、组织病理和免疫荧光三方面评价其对PV鼠模型构建的影响。结果 单独注射抗Dsg-3 EC3-4的ScFv不能在BALB/c新生鼠中诱导出PV的改变,任何时间点注射抗Dsg-3 EC3-4的ScFv都不能阻断PV患者血清对BALB/c新生鼠的致病作用。结论 单独注射抗Dsg-3 EC3-4的ScFv缺乏致病性,也不能阻断PV患者血清对BALB/c新生鼠的致病作用。