Membrane-Tethered Intracellular Domain of Amphiregulin Promotes Keratinocyte Proliferation

Epimorphic regeneration in the mammalian tympanic membrane

Adult mammals are generally believed to have limited ability to regenerate complex tissues and instead, repair wounds by forming scars. In humans and across mammalian species, the tympanic membrane (TM) rapidly repairs perforations without intervention. Using mouse models, we demonstrate that the TM repairs itself through a process that bears many hallmarks of epimorphic regeneration rather than typical wound healing. Following injury, the TM forms a wound epidermis characterized by EGFR ligand expression and signaling. After the expansion of the wound epidermis that emerges from known stem cell regions of the TM, a multi-lineage blastema-like cellular mass is recruited. After two weeks, the tissue architecture of the TM is largely restored, but with disorganized collagen. In the months that follow, the organized and patterned collagen framework of the TM is restored resulting in scar-free repair. Finally, we demonstrate that deletion of Egfr in the epidermis results in failure to expand the wound epidermis, recruit the blastema-like cells, and regenerate normal TM structure. This work establishes the TM as a model of mammalian complex tissue regeneration.

IL-17A promotes Psoriasis-associated Keratinocyte Proliferation via ACT1-depedent Activation of YAP-AREG Axis

Psoriasis is a recurrent inflammatory skin disorder characterized by epidermal hyperplasia which is primarily driven by interleukin (IL)-17A. The Hippo-YAP signaling pathway plays a vital role in cell survival and tissue growth, and its target gene, AREG, has been reported to promote the development of psoriasis. However, whether IL-17A promotes keratinocyte proliferation via regulating Hippo-YAP signaling has not been explored. Here, we show that the YAP-AREG pathway is activated in human psoriatic skin and is suppressed by IL-17A antagonist secukinumab and that IMQ and IL-17A administration activates the YAP-AREG axis in mice epidermis. In vitro studies using HaCaT and NHEK cells suggest that IL-17A enhances AREG expression and keratinocyte proliferation by activating Hippo-YAP signaling. Mechanistically, IL-17A stimulates the recruitment of MST1 to ACT1 in keratinocytes, which leads to reduced MST1-LATS1 interaction and YAP dephosphorylation. Together, our findings reveal a previously unknown mechanism in which IL-17A promotes keratinocyte proliferation in psoriasis, namely through activating YAP-AREG signaling.

A Defect of Amphiregulin Release Predicted Longer Survival Independently of YAP Expression in Patients with Pleural Mesothelioma in the IFCT-0701 MAPS Phase 3 Trial

The Hippo pathway effector YAP is dysregulated in malignant pleural mesothelioma (MPM). YAP's target genes include the secreted growth factor amphiregulin (AREG), which is overexpressed in a wide range of epithelial cancers and plays an elusive role in MPM. We assayed the expression of YAP and AREG in MPM pathology samples and that of AREG additionally in plasma samples of patients from the randomized phase 3 IFCT‐0701 Mesothelioma Avastin Cisplatin Pemetrexed Study (MAPS) using immunohistochemistry and ELISA assays, respectively. MPM patients frequently presented high levels of tumor AREG (64.3%), a high cytosolic AREG expression being predictive of a better prognosis with longer median overall and progression‐free survival. Surprisingly, tumor AREG cytosolic expression was not correlated with secreted plasma AREG. By investigating the AREG metabolism and function in MPM cell lines H2452, H2052, MSTO‐211H and H28, in comparison with the T47D ER+ breast cancer cell line used as a positive control, we confirm that AREG is important for cell invasion, growth without anchorage, proliferation and apoptosis in mesothelioma cells. Yet, most of these MPM cell lines failed to correctly execute AREG posttranslational processing by metalloprotease ADAM17/tumor necrosis factor‐alpha‐converting enzyme (TACE) and extracell secretion. The favorable prognostic value of high cytosolic AREG expression in MPM patients could therefore be sustained by default AREG posttranslational processing and release. Thus, the determination of mesothelioma cell AREG content could be further investigated as a prognostic marker for MPM patients and used as a stratification factor in future clinical trials.

Mechanisms for Alternaria alternata Function in the Skin During Induction of Peanut Allergy in Neonatal Mice With Skin Barrier Mutations

Neonatal mice with heterozygous mutations in genes encoding the skin barrier proteins filaggrin and mattrin (flaky tail mice [FT^+/-]) exhibit oral peanut-induced anaphylaxis after skin sensitization. As we have previously reported, sensitization in this model is achieved via skin co- exposure to the environmental allergen Alternaria alternata (Alt), peanut extract (PNE), and detergent. However, the function of Alt in initiation of peanut allergy in this model is little understood. The purpose of this study was to investigate candidate cytokines induced by Alt in the skin and determine the role of these cytokines in the development of food allergy, namely oncostatin M (Osm), amphiregulin (Areg), and IL-33. RT-qPCR analyses demonstrated that skin of FT^+/- neonates expressed Il33 and Osm following Alt or Alt/PNE but not PNE exposure. By contrast, expression of Areg was induced by either Alt, PNE, or Alt/PNE sensitization in FT^+/- neonates. In scRNAseq analyses, Osm, Areg, and Il33 were expressed by several cell types, including a keratinocyte cluster that was expanded in the skin of Alt/PNE-exposed FT^+/- pups as compared to Alt/PNE-exposed WT pups. Areg and OSM were required for oral PNE-induced anaphylaxis since anaphylaxis was inhibited by administration of neutralizing anti-Areg or anti-OSM antibodies prior to each skin sensitization with Alt/PNE. It was then determined if intradermal injection of recombinant IL33 (rIL33), rAreg, or rOSM in the skin could substitute for Alt during skin sensitization to PNE. PNE skin sensitization with intradermal rIL33 was sufficient for oral PNE-induced anaphylaxis, whereas skin sensitization with intradermal rAreg or rOSM during skin exposure to PNE was not sufficient for anaphylaxis to oral PNE challenge. Based on these studies a pathway for IL33, Areg and OSM in Alt/PNE sensitized FT^+/- skin was defined for IgE induction and anaphylaxis. Alt stimulated two pathways, an IL33 pathway and a pathway involving OSM and Areg. These two pathways acted in concert with PNE to induce food allergy in pups with skin barrier mutations.

Single-cell transcriptomics combined with interstitial fluid proteomics defines cell type-specific immune regulation in atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease, but its complex pathogenesis is only insufficiently understood, resulting in still limited treatment options.

OBJECTIVE

We sought to characterize AD on both transcriptomic and proteomic levels in humans.

METHODS

We used skin suction blistering, a painless and nonscarring procedure that can simultaneously sample skin cells and interstitial fluid. We then compared results with conventional biopsies.

RESULTS

Suction blistering captured epidermal and most immune cells equally well as biopsies, except for mast cells and nonmigratory CD163+ macrophages that were only present in biopsy isolates. Using single-cell RNA sequencing, we found comparable transcriptional profiles of key inflammatory pathways between blister and biopsy AD, but suction blistering was superior in cell-specific resolution for high-abundance transcripts (KRT1/KRT10, KRT16/KRT6A, S100A8/S100A9), which showed some background signals in biopsy isolates. Compared with healthy controls, we found characteristic upregulation of AD-typical cytokines such as IL13 and IL22 in Th2 and Th22 cells, respectively, but we also discovered these mediators in proliferating T cells and natural killer T cells, that also expressed the antimicrobial cytokine IL26. Overall, not T cells, but myeloid cells were most strongly enriched in AD, and we found dendritic cell (CLEC7A, amphiregulin/AREG, EREG) and macrophage products (CCL13) among the top upregulated proteins in AD blister fluid proteomic analyses.

CONCLUSION

These data show that by using cutting-edge technology, suction blistering offers several advantages over conventional biopsies, including better transcriptomic resolution of skin cells, combined with proteomic information from interstitial fluid, unraveling novel inflammatory players that shape the cellular and proteomic microenvironment of AD.

Blood and Salivary Amphiregulin Levels as Biomarkers for Asthma

Background: Amphiregulin (AREG) expression in asthmatic airways and sputum was shown to increase and correlate with asthma. However, no studies were carried out to evaluate the AREG level in blood and saliva of asthmatic patients. Objective: To measure circulating AREG mRNA and protein concentrations in blood, saliva, and bronchial biopsies samples from asthmatic patients. Methods: Plasma and Saliva AREG protein concentrations were measured using ELISA while PBMCs, and Saliva mRNA expression was measured by RT qPCR in non-severe, and severe asthmatic patients compared to healthy controls. Primary asthmatic bronchial epithelial cells and fibroblasts were assessed for AREG mRNA expression and released soluble AREG in their conditioned media. Tissue expression of AREG was evaluated using immunohistochemistry of bronchial biopsies from asthmatic patients and healthy controls. Publicly available transcriptomic databases were explored for the global transcriptomic profile of bronchial epithelium, and PBMCs were explored for AREG expression in asthmatic vs. healthy controls. Results: Asthmatic patients had higher AREG protein levels in blood and saliva compared to control subjects. Higher mRNA expression in saliva and primary bronchial epithelial cells plus higher AREG immunoreactivity in bronchial biopsies were also observed. Both blood and saliva AREG levels showed positive correlations with allergic rhinitis status, atopy status, eczema status, plasma periostin, neutrophilia, Montelukast sodium use, ACT score, FEV1, and FEV1/FVC. In silico analysis showed that severe asthmatic bronchial epithelium with high AREG gene expression is associated with higher neutrophils infiltration. Conclusion: AREG levels measured in a minimally invasive blood sample and a non-invasive saliva sample are higher in non-allergic severe asthma.

CLINICAL IMPLICATIONS

This is the first report to show the higher level of AREG levels in blood and saliva of non-allergic severe asthma.

Aberrant expression of the UPF1 RNA surveillance gene disturbs keratinocyte homeostasis by stabilizing AREG

The up-frameshift suppressor 1 homolog (UPF1) RNA surveillance gene is a core element in the nonsense-mediated RNA decay (NMD) pathway, which impacts a broad spectrum of biological processes in a cell-specific manner. In the present study, the contribution of the NMD pathway to psoriasis lesions and its moderating effects on the biological processes of keratinocytes was reported. Sanger sequencing for skin scales from two patients with psoriasis identified two mRNA mutations (c.2935_2936insA and c.2030-2081del) in the UPF1 gene. The somatic mutants produced truncated UPF1 proteins and perturbed the NMD pathway in cells, leading to the upregulation of NMD substrates. As the most abundant epidermal growth factor receptor ligand in keratinocytes, it was concluded that amphiregulin (AREG) mRNA is a natural NMD substrate, that is dependent on its 3′ untranslated region sequence. Perturbed NMD modulated keratinocyte homeostasis in an AREG-dependent but nonidentical manner, which highlighted the unique characteristics of NMD in keratinocytes. By targeting AREG mRNA post-transcriptionally, the UPF1-NMD pathway contributed to an imbalance between proliferation on the one hand, and apoptosis and abnormal differentiation, migration and inflammatory response on the other, in keratinocytes, which indicated a role of the NMD pathway in the full development of keratinocyte-related morbidity and skin diseases.

Transcriptional Programming of Normal and Inflamed Human Epidermis at Single-Cell Resolution

Perturbations in the transcriptional programs specifying epidermal differentiation cause diverse skin pathologies ranging from impaired barrier function to inflammatory skin disease. However, the global scope and organization of this complex cellular program remain undefined. Here we report single-cell RNA sequencing profiles of 92,889 human epidermal cells from 9 normal and 3 inflamed skin samples. Transcriptomics-derived keratinocyte subpopulations reflect classic epidermal strata but also sharply compartmentalize epithelial functions such as cell-cell communication, inflammation, and WNT pathway modulation. In keratinocytes, ~12% of assessed transcript expression varies in coordinate patterns, revealing undescribed gene expression programs governing epidermal homeostasis. We also identify molecular fingerprints of inflammatory skin states, including S100 activation in the interfollicular epidermis of normal scalp, enrichment of a CD1C⁺CD301A⁺ myeloid dendritic cell population in psoriatic epidermis, and IL1β^hiCCL3^hiCD14⁺ monocyte-derived macrophages enriched in foreskin. This compendium of RNA profiles provides a critical step toward elucidating epidermal diseases of development, differentiation, and inflammation.

Cheng et al. report single-cell RNA sequencing of normal and inflamed human epidermis, revealing a discrete set of specialized keratinocytes that exhibit a distinct composition at different anatomic sites. Myeloid dendritic cells and macrophages also vary sharply with epidermal anatomic site and inflammation, indicating dynamic programming of antigen-presenting cells.

Abnormal amphiregulin expression correlates with gastric cancer prognosis

Gastric cancer (GC) is a global health issue with a high mortality rate. Early diagnosis and tracking of GC is a challenge due to a lack of reliable tools. Amphiregulin (AREG) is a member of the epidermal growth factor (EGF) family that activates growth signaling upon binding of EGF receptors. Elevated AREG expression is associated with various pathological conditions, including cancer. Here, we investigated whether increased AREG expression is a disease indicator and/or prognostic biomarker for GC. We used tissue microarray and quantitative real-time polymerase chain reaction to assess AREG expression in clinical tissue specimens at various stages of GC and a conducted bioinformatics analysis to evaluate the value of AREG over-expression as a GC biomarker. We found that both mRNA and protein expression of AREG were increased in the tissues of GC patients when compared to tissues from non-cancer patients or normal tissues. High expression of AREG was also associated with GC clinicopathological characteristics and poor survival. Thus, over-expression of AREG could serve as a novel GC biomarker, and active surveillance of its expression could be a novel approach to GC diagnosis and monitoring.

EGF receptor ligands: recent advances

Seven ligands bind to and activate the mammalian epidermal growth factor (EGF) receptor (EGFR/ERBB1/HER1): EGF, transforming growth factor-alpha (TGFA), heparin-binding EGF-like growth factor (HBEGF), betacellulin (BTC), amphiregulin (AREG), epiregulin (EREG), and epigen (EPGN). Of these, EGF, TGFA, HBEGF, and BTC are thought to be high-affinity ligands, whereas AREG, EREG, and EPGN constitute low-affinity ligands. This focused review is meant to highlight recent studies related to actions of the individual EGFR ligands, the interesting biology that has been uncovered, and relevant advances related to ligand interactions with the EGFR.