P4: Relevance of mast cells in maladaptation of the epidermal and endothelial barrier during chronic skin inflammation & Characterization of the specific functional relevance of perivascular mast cells in skin inflammation
Project Martin Voss: Relevance of mast cells in maladaptation of the epidermal and endothelial barrier during chronic skin inflammation
Contact allergy is an inflammatory skin disease of high socioeconomic relevance. We recently demonstrated an intimate interaction of dermal endothelial cells and mast-cells (MCs) in the skin. Importantly, MCs initiate the vascular response to haptens and neutrophil infiltration, and amplify the T cell-driven adaptive immunity. Surprisingly, we observed a massive MC hyperplasia several weeks after hapten-challenge, predisposing to chronified skin inflammation. Based on these observations we hypothesize that the perivascular MC hyperplasia provokes a disease-promoting micromilieu resulting in a permanent dysregulation of endothelial barriers. By combining longitudinal intravital imaging with cell biology approaches we aim to quantify parameters of vascular integrity, endothelial cell activation and luminal glycocalyx constitution. The interaction of the glycocalyx with the extracellular proteome will be analyzed (cooperation with ). To assess the effect of perpetuated inflammation on entire skin vascularity, we will analyze the vessel structure and 3D architecture. To directly assess the causality of MCs for epidermal and vascular alterations in perpetuated skin inflammation we will utilize novel mouse models of constitutive or inducible MC-depletion. To characterize the disease-promoting micromilieu at the pathophysiological endothelial barrier we need to identify the cellular actuators and regulators beyond MCs and therefore aim to analyze the impact of endothelial cell activation and luminal glycocalyx on macrophage differentiation (cooperation with ). The homeostasis of intercellular networks is tightly regulated by a number of tissue factors. We therefore aim to analyze alterations in the gene expression of transcription factors (cooperation with ), cytokines and chemokines, complement and coagulation factors (cooperation with and ), hypoxia induced factors (cooperation with ) and others, to identify key factors disrupting the endothelial barrier in the chronically inflamed skin as potential therapeutic targets.
Maladaptive cell accumulation and intercellular communication lead to chronic skin inflammation. Acute hapten-induced skin inflammation (arrow) leads to an accumulation of mast cells (MC, violet) beneath the epidermal (yellow) barrier. Repeated hapten encounter in hapten-primed skin causes an exaggerated inflammation and neutrophil (green) infiltration potentially due to persistent MC degranulation that may culminate in structural and functional maladaptation of the endothelium (red) and epidermis. We hypothesize that the epidermal stress response (1) is causative for the accumulation of MCs which subsequently provoke endothelial activation (2) and neutrophil infiltration (3) via degranulation, cytokine/chemokine release and PAR2 activation. The exaggerated neutrophil influx vice versa results in persistent MC activation (4), perpetuated epidermal stress (5), and hypoxia (6) that finally culminate in endothelial dysfunction.
Project Aaron Hoffmann: Characterization of the specific functional relevance of perivascular mast cells in skin inflammation
As the outermost layer of an organism, the skin is highly exposed to noxious environmental influences. By sensitizing with allergens or haptens able to penetrate this physiological barrier, an immunological response can be induced. In Europe, more than 20% of the population is affected by allergic skin diseases, such as atopic dermatitis or allergic contact dermatitis. These inflammatory skin disorders are a main cause for occupational disability and thereby a massive burden for the patients and the health care system. Recently, we could demonstrate that directional release of active mediators including tumor necrosis factor (TNF) by perivascular mast cells (MCs) into the blood stream initiates a vascular response and neutrophil infiltration. Moreover, this process affects immune cells systemically in distant organs, such as spleen and bone marrow. We hypothesize that repeated MC activation can lead to chronic disorders by a dysregulation of the vasculature or long-term systemic effects on myeloid immune cell populations. Given the longevity of tissue-resident MCs, their heterogeneity in both distinct tissues and within the skin, as well as their plasticity during inflammation is poorly understood. We therefore aim to characterize perivascular skin MCs and to investigate their specific functional relevance in skin inflammation, in particular in the activation and integrity of the endothelial barrier (cooperation with project 6). Further, we will study their organ-spanning acute and long-term effects (cooperation with Project 2, Project 8, Project 11, Project 12). Since MCs are known to interact with other cells along the blood vessels, such as dendritic cells or macrophages, our objective is further to study the perivascular immune cell niche. To address our topics, we will utilize novel mouse lines with specific knockouts of surface receptors that reduce the alignment and directional intravascular degranulation of perivascular MCs. We will use in vivo approaches such as intravital 2-photon fluorescence microscopy to analyze the intercellular network along the vascular system, and cross-validate our findings with in vitro cell communication assays (cooperation with Project 6). We aim to ascertain the mechanistic effects of MC degranulation on tissue homeostasis, gene expression of transcription factors, cytokines and chemokines and hypoxia induced factors (cooperation with Project 2, Project 6, Project 8 and Project 12). These studies will thereby assess the specific features and functional relevance of perivascular MCs in acute and chronic skin inflammation in order to identify novel therapeutic targets.
Photos: M. Schubert/University Hospital Magdeburg