Bettina Alexandra Buhren

Epidermal EGFR Controls Cutaneous Host Defense and Prevents Inflammation

Epidermal EGFR regulates skin inflammation and contributes to skin barrier function and host defense. Skin-Deep Search for the Effects of EGFR Inhibitors The goal of all medical interventions is to treat disease while minimizing the damage to healthy tissues in the body. This can be difficult to achieve for cancer drugs, however, especially when the effectiveness of a drug directly correlates with its side effects, as is the case for inhibitors of the epidermal growth factor receptor (EGFR). EGFR inhibitors are particularly known for causing a severe rash and skin damage, which sometimes forces patients to prematurely stop their treatments. Now, two papers by Mascia et al. and Lichtenberger et al. help clarify the mechanism of rash formation induced by EGFR inhibitors and uncover some of the skin components that contribute to this phenomenon. Both sets of authors used mouse models that lack EGFR only in the skin to replicate the pattern of injury seen in patients treated with EGFR inhibitors. They characterized the changes in chemokine expression in the skin of treated patients and study animals and examined the effects of EGFR inhibition on skin defenses and bacteria. They also investigated the effects of crossing mice that lack EGFR in the skin with mice deficient in different immune pathways and immune cell types to determine which ones are necessary for the rash phenotype. The findings of these two studies suggest that EGFR signaling is important for normal skin barrier function and antimicrobial defense, and that skin macrophages may contribute to the adverse effects of EGFR inhibitors. Additional work will be necessary to further expand our understanding of EGFR inhibitor toxicity and to continue the search for ways to prevent this disruptive side effect. The current studies provide mechanistic insights that should help guide further investigation in this area. The epidermal growth factor receptor (EGFR) plays an important role in tissue homeostasis and tumor progression. However, cancer patients treated with EGFR inhibitors (EGFRIs) frequently develop acneiform skin toxicities, which are a strong predictor of a patient’s treatment response. We show that the early inflammatory infiltrate of the skin rash induced by EGFRI is dominated by dendritic cells, macrophages, granulocytes, mast cells, and T cells. EGFRIs induce the expression of chemokines (CCL2, CCL5, CCL27, and CXCL14) in epidermal keratinocytes and impair the production of antimicrobial peptides and skin barrier proteins. Correspondingly, EGFRI-treated keratinocytes facilitate lymphocyte recruitment but show a considerably reduced cytotoxic activity against Staphylococcus aureus. Mice lacking epidermal EGFR (EGFRΔep) show a similar phenotype, which is accompanied by chemokine-driven skin inflammation, hair follicle degeneration, decreased host defense, and deficient skin barrier function, as well as early lethality. Skin toxicities were not ameliorated in a Rag2-, MyD88-, and CCL2-deficient background or in mice lacking epidermal Langerhans cells. The skin phenotype was also not rescued in a hairless (hr/hr) background, demonstrating that skin inflammation is not induced by hair follicle degeneration. Treatment with mast cell inhibitors reduced the immigration of T cells, suggesting that mast cells play a role in the EGFRI-mediated skin pathology. Our findings demonstrate that EGFR signaling in keratinocytes regulates key factors involved in skin inflammation, barrier function, and innate host defense, providing insights into the mechanisms underlying EGFRI-induced skin pathologies.

Rosacea: the Cytokine and Chemokine Network

Rosacea is one of the most common dermatoses of adults. Recent studies have improved our understanding of the pathophysiology of rosacea. Current concepts suggest that known clinical trigger factors of rosacea such as UV radiation, heat, cold, stress, spicy food, and microbes modulate Toll-like receptor signaling, induce reactive oxygen species, as well as enhance antimicrobial peptide and neuropeptide production. Downstream of these events cytokines and chemokines orchestrate an inflammatory response that leads to the recruitment and activation of distinct leukocyte subsets and induces the characteristic histopathological features of rosacea. Here we summarize the current knowledge of the cytokine and chemokine network in rosacea and propose pathways that may be of therapeutic interest.

Chemokines in tumor-associated angiogenesis.

Abstract Tumor growth is dependent on several key factors. Apart from immune escape and an efficient blockade of apoptotic signals, tumors require oxygen and nutrients to grow past a diameter of 2 μm. Therefore, it is of vital importance for the tumor to facilitate tumor-associated angiogenesis, e.g., the de novo formation of new blood vessels. In addition to established and key angiogenic factors, such as vascular endothelial growth factor, chemokines, a superfamily of cytokine-like proteins that bind to seven transmembrane-spanning G-protein-coupled receptors, have been associated with angiogenesis under homeostatic conditions. Chemokines were initially identified as key factors that control the directional migration of leukocytes, stem cells and cancer cells in vitro and which critically regulate their trafficking in vivo. Recently their role in establishing a favorable microenvironment for tumor-associated angiogenesis, a process that requires complex bidirectional interactions of the tumor and associated vessels, has been the focus of research. Chemokine-promoted angiogenesis not only facilitates tumor growth by supplying nutrients and oxygen but it is also a prerequisite to tumor metastasis. Hence, the pharmacologic control of tumor angiogenesis presents a promising strategy for novel anticancer therapeutics. Here, we discuss the current pathogenetic concepts of tumor-associated angiogenesis in the context of chemokines and their receptors and highlight promising therapeutic strategies.

Density of Demodex folliculorum in Patients Receiving Epidermal Growth Factor Receptor Inhibitors

Background: Rosacea-like papulopustular eruptions (rash) are considered the most frequent toxicities associated with the use of inhibitors of the epidermal growth factor receptor (EGFR). Recently, evidence has been accumulating of infectious complications in patients suffering from these adverse effects. Objective: We sought to analyze the density of Demodex folliculorum (DF) in cutaneous lesions of patients presenting with EGFR-inhibitor (EGFRI)-induced rashes. Methods: This is a retrospective study of 19 adult patients presenting with EGFRI rashes. Patients were reviewed for the density of DF (Demodex density, Dd; mites per square centimeter) by standardized skin surface biopsy. Results: In our patient collective the mean Dd of 4.7/cm2 significantly exceeded the mean Dd reported for the healthy adult population (Dd = 0.7/cm2). Limitations: The retrospective nature of the study. Conclusions: EGFRI patients have an increased susceptibility to DF colonization or infection, respectively. Our results support the recent concept that EGFRI may induce an impairment of antimicrobial defense mechanisms.

Glucose-dependent insulinotropic polypeptide (GIP) and its receptor (GIPR): Cellular localization, lesion-affected expression, and impaired regenerative axonal growth

Glucose‐dependent insulinotropic polypeptide (GIP) was initially described to be rapidly regulated by endocrine cells in response to nutrient ingestion, with stimulatory effects on insulin synthesis and release. Previously, we demonstrated a significant up‐regulation of GIP mRNA in the rat subiculum after fornix injury. To gain more insight into the lesion‐induced expression of GIP and its receptor (GIPR), expression profiles of the mRNAs were studied after rat sciatic nerve crush injury in 1) affected lumbar dorsal root ganglia (DRG), 2) spinal cord segments, and 3) proximal and distal nerve fragments by means of quantitative RT‐PCR. Our results clearly identified lesion‐induced as well as tissue type‐specific mRNA regulation of GIP and its receptor. Furthermore, comprehensive immunohistochemical stainings not only confirmed and exceeded the previous observation of neuronal GIP expression but also revealed corresponding GIPR expression, implying putative modulatory functions of GIP/GIPR signaling in adult neurons. In complement, we also observed expression of GIP and its receptor in myelinating Schwann cells and oligodendrocytes. Polarized localization of GIPR in the abaxonal Schwann cell membranes, plasma membrane‐associated GIPR expression of satellite cells, and ependymal GIPR expression strongly suggests complex cell type‐specific functions of GIP and GIPR in the adult nervous system that are presumably mediated by autocrine and paracrine interactions, respectively. Notably, in vivo analyses with GIPR‐deficient mice suggest a critical role of GIP/GIPR signal transduction in promoting spontaneous recovery after nerve crush, insofar as traumatic injury of GIPR‐deficient mouse sciatic nerve revealed impaired axonal regeneration compared with wild‐type mice.

The top skin-associated genes: a comparative analysis of human and mouse skin transcriptomes

Abstract The mouse represents a key model system for the study of the physiology and biochemistry of skin. Comparison of skin between mouse and human is critical for interpretation and application of data from mouse experiments to human disease. Here, we review the current knowledge on structure and immunology of mouse and human skin. Moreover, we present a systematic comparison of human and mouse skin transcriptomes. To this end, we have recently used a genome-wide database of human gene expression to identify genes highly expressed in skin, with no, or limited expression elsewhere – human skin-associated genes (hSAGs). Analysis of our set of hSAGs allowed us to generate a comprehensive molecular characterization of healthy human skin. Here, we used a similar database to generate a list of mouse skin-associated genes (mSAGs). A comparative analysis between the top human (n=666) and mouse (n=873) skin-associated genes (SAGs) revealed a total of only 30.2% identity between the two lists. The majority of shared genes encode proteins that participate in structural and barrier functions. Analysis of the top functional annotation terms revealed an overlap for morphogenesis, cell adhesion, structure, and signal transduction. The results of this analysis, discussed in the context of published data, illustrate the diversity between the molecular make up of skin of both species and grants a probable explanation, why results generated in murine in vivo models often fail to translate into the human.

The chemokine receptor CCR3 participates in tissue remodeling during atopic skin inflammation

BACKGROUND Recent studies provided insights into the recruitment and activation pathways of leukocytes in atopic dermatitis, however, the underlying mechanisms of tissue remodeling in atopic skin inflammation remain elusive. OBJECTIVE To identify chemokine-mediated communication pathways regulating tissue remodeling during atopic skin inflammation. METHODS Analysis of the chemokine receptor repertoire of human dermal fibroblasts using flow cytometry and immunofluorescence. Quantitative real-time polymerase chain reaction and immunohistochemical analyses of chemokine expression in atopic vs. non-atopic skin inflammation. Investigation of the function of chemokine receptor CCR3 on human dermal fibroblasts through determining intracellular Ca(2+) mobilization, cell proliferation, migration, and repair capacity. RESULTS Analyses on human dermal fibroblasts showed abundant expression of the chemokine receptor CCR3 in vitro and in vivo. Among its corresponding ligands (CCL5, CCL8, CCL11, CCL24 and CCL26) CCL26 demonstrated a significant and specific up-regulation in atopic when compared to psoriatic skin inflammation. In vivo, epidermal keratinocytes showed most abundant CCL26 protein expression in lesional atopic skin. In structural cells of the skin, TH2-cytokines such as IL-4 and IL-13 were dominant inducers of CCL26 expression. In dermal fibroblasts, CCL26 induced CCR3 signaling resulting in intracellular Ca(2+) mobilization, as well as enhanced fibroblast migration and repair capacity, but no proliferation. CONCLUSION Taken together, findings of the present study suggest that chemokine-driven communication pathways from the epidermis to the dermis may modulate tissue remodeling in atopic skin inflammation.

The α-chemokine CXCL14 is up-regulated in the sciatic nerve of a mouse model of Charcot–Marie–Tooth disease type 1A and alters myelin gene expression in cultured Schwann cells

At present the pathogenesis of CMT1A neuropathy, caused by the overexpression of PMP22, has not yet been entirely understood. The PMP22-overexpressing C61 mutant mouse is a suitable animal model, which mimics the human CMT1A disorder. We observed that myelin gene expression in the sciatic nerve of the C61 mouse was up-regulated at postnatal day 4 to 7 (P4-P7). When investigating the morphology of peripheral nerves in C61 and wildtype mice at early stages of postnatal development, hypermyelination could be detected in the femoral quadriceps and sciatic nerve of transgenic animals at postnatal day 7 (P7). In order to identify genes, other than Pmp22, that are modulated in sciatic nerve of P7 transgenic mice, we applied microarray technology. Amongst the regulated genes, the gene encoding the alpha-chemokine CXCL14 was most prominently up-regulated. We report that Cxcl14 was expressed exclusively by Schwann cells of the sciatic nerve, as well as by cultured Schwann cells triggered to differentiate. Furthermore, in cultured Schwann cells CXCL14 modulated the expression of myelin genes and altered cell proliferation. Our findings demonstrate that early overexpression of PMP22, in a mouse model of CMT1A, results in a strong up-regulation of CXCL14, which seems to play a novel regulatory role in Schwann cell differentiation.

METEORIN-LIKE is a cytokine associated with barrier tissues and alternatively activated macrophages.

Cytokines are involved in many functions of the immune system including initiating, amplifying and resolving immune responses. Through bioinformatics analyses of a comprehensive database of gene expression (BIGE: Body Index of Gene Expression) we observed that a small secreted protein encoded by a poorly characterized gene called meteorin-like (METRNL), is highly expressed in mucosal tissues, skin and activated macrophages. Further studies indicate that Metrnl is produced by Alternatively Activated Macrophages (AAM) and M-CSF cultured bone marrow macrophages (M2-like macrophages). In the skin, METRNL is expressed by resting fibroblasts and IFNγ-treated keratinocytes. A screen of human skin-associated diseases showed significant over-expression of METRNL in psoriasis, prurigo nodularis, actinic keratosis and atopic dermatitis. METRNL is also up-regulated in synovial membranes of human rheumatoid arthritis. Taken together, these results indicate that Metrnl represents a novel cytokine, which is likely involved in both innate and acquired immune responses.

The role of neoadjuvant and adjuvant treatment for adenocarcinoma of the upper gastrointestinal tract

Both locally advanced adenocarcinoma of the stomach and gastro-esophageal junction are associated with poor prognosis due to the lack of effective treatment. Recently multimodal treatment consisting of neoadjuvant chemotherapy in combination with radiotherapy is reported to improve survival when compared to surgery alone. Neoadjuvant therapy in these locally advanced tumors allows for early tumor responses and the extent of tumor regression that can be achieved is considered a significant prognostic factor. This, in turn, increases the resectability of these tumors. Also due to the high frequency of lymph node metastasis, patients with locally advanced adenocarcinoma should undergo a D2 lymphadenectomy. Postoperative chemoradiation and perioperative chemotherapy have been studied in gastric adenocarcinomas and showed a survival benefit. However, the surgical techniques used in these trials are no longer considered to be standard by todays surgical practice. In addition, there are no standard recommendations for adjuvant chemotherapy or chemoradiation after R0 resection and adequate lymph node dissection.