Characterization of the oxytocin system in primary human dermal fibroblasts and keratinocytes

Characterization of the oxytocin system in primary human dermal

fibroblasts and keratinocytes

Dissertation

Zur Erlangung des akademischen Grades des Doktors der Naturwissenschaften (Dr. rer. nat.)

des Fachbereichs Biologie der Universität Konstanz

vorgelegt von

Verena Daniela Deing Juli 2013

Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-249928

Die vorliegende Arbeit wurde in der Zeit von Mai 2009 bis April 2013 an der Universität Konstanz unter der Leitung von Prof. Dr. Alexander Bürkle in Kooperation mit der Beiersdorf AG unter der Leitung von Dr. Gitta Neufang angefertigt.

Tag der mündlichen Prüfung: 11.09.2013

Referenten: Prof. Dr. Alexander Bürkle (Gutachter und Prüfer) PD Dr. Eva Peters (Gutachterin)

Prof. Dr. Christof Hauck (Prüfer) Prof. Dr. Daniel Legler (Prüfer)

Z USAMMENFASSUNG

Über das Oxytocin (OXT) System in der Haut war lange Zeit nichts bekannt. In einer Publikation von 2012 wurde erstmalig die Expression und Ausschüttung von OXT durch epidermale Keratinozyten gezeigt (1). In der vorliegenden Doktorarbeit sollte daher das OXT System der Haut charakterisiert werden und dessen Funktion, sowie Relevanz für die kutane Homöostase untersucht werden.

Die Ergebnisse zeigen, dass sowohl OXT als auch dessen Rezeptor von primären humanen dermalen Fibroblasten und Keratinozyten exprimiert werden. Außerdem konnte die Funktionalität des OXT Rezeptors (OXTR) festgestellt werden, da in beiden Zelltypen eine Stimulation mit OXT dosisabhängig intrazelluläre Calciumströme auslöste. Darüber hinaus deuten Analysen darauf hin, dass positive Rückkopplungsschleifen in der Selbstregulation des OXT Systems eine Rolle spielen. So konnte bei dermalen Fibroblasten die Expression des OXTR durch Stimulation mit OXT gesteigert werden. Zusätzlich führte eine verringerte OXTR Expression zu einer ebenfalls geringeren OXT Expression. Dass das OXT System auch in vivo moduliert werden kann, untermauerte eine 12 Probanden umfassende Studie.

Analysen von Saugblasenflüssigkeiten zeigten, dass taktile Stimulation eines Hautareals die lokale Ausschüttung von OXT bewirkt. Im Gegensatz dazu, wurde in der Literatur bislang lediglich die systemische Freisetzung von OXT nach taktiler Stimulation, wie beispielsweise bei der Laktation (2), beschrieben.

Untersuchungen zu OXT-vermittelten Funktionen in der Haut deuten auf eine Rolle in der Modulation von Proliferationsprozessen und Epidermisstruktur hin. So konnte eine dosisabhängige Hemmung der Proliferation bei OXT-behandelten dermalen Fibroblasten und Keratinozyten beobachtet werden. Daneben führte im 3-D Hautmodell eine kontinuierliche Behandlung mit OXT zu einer Reduktion der Epidermisdicke. Des Weiteren steigerte OXT die Expression des terminalen Differenzierungsmarkers Loricrin in der Epidermis des Hautmodells. Es bleibt daher zu klären, ob die Reduktion der Epidermisdicke in diesem Hautmodell auf eine OXT-vermittelte Hemmung der Proliferation oder auf eine vorzeitige Differenzierung der Keratinozyten zurückzuführen ist.

Weitere Untersuchungen weisen auf eine modulierende Funktion des OXT Systems bei neuroendokrinen, oxidativen und inflammatorischen Stressantworten der Haut hin.

Corticotropin-releasing hormone (CRH) und Corticosteron sind zentrale Mediatoren der systemischen sowie kutanen neuroendokrinen Stressantwort. Knockdown des OXTR in dermalen Fibroblasten führte zu einer erhöhten Expression von CRH und dessen Rezeptor.

Daneben wurde bei OXT-behandelten Keratinozyten eine verringerte Ausschüttung von Corticosteron gemessen. Aufgrund dieser Befunde wird die Hypothese abgeleitet, dass das OXT System als Antagonist der neuroendokrinen Hautstressachse auftritt. Des Weiteren

Zusammenfassung II resultierte der Knockdown des OXTR bei dermalen Fibroblasten und Keratinozyten in verstärktem oxidativen Stress. So wurden erhöhte Konzentrationen von reaktiven Sauerstoffspezies und verminderte Mengen des Antioxidants Glutathion gemessen. Es wird daher angenommen, dass das kutane OXT System zytoprotektiv wirkt. Diese Vermutung wird in Hinblick auf Entzündungsreaktionen dadurch bestärkt, dass bei OXTR-depletierten Keratinozyten eine drastisch erhöhte Ausschüttung der pro-inflammatorischen Zytokine IL6, CCL5 and CXCL10 detektiert wurde.

Eine Vielzahl von Hautkrankheiten ist mit einer abnormalen Zellproliferation und Hauttressantwort assoziiert. Die atopische Dermatitis gehört in diesem Zusammenhang zu den am häufigsten auftretenden Hautkrankheiten. Es wurde daher untersucht, ob das OXT System in atopischer Haut aberrant exprimiert wird. Tatsächlich konnte eine Herrunterregulation des OXT Systems sowohl in peri-läsionaler, als auch in läsionaler atopischer Haut gemessen werden.

Insgesamt deuten die Ergebnisse dieser Arbeit erstmalig darauf hin, dass das kutane OXT System zentrale Prozesse - wie Proliferation, inflammatorische- und oxidative Hautstressantworten - beeinflusst, welche im Krankheitsbild der atopischen Dermatitis fehlreguliert sind. Daraus wird geschlossen, dass das OXT System als wichtiger Modulator der Homöostase humaner Haut fungiert und relevant für gestresste Hautzustände, wie der atopischen Dermatitis, ist.

S UMMARY

The aim of this doctoral thesis was to characterize the oxytocin (OXT) system in human skin and to analyze its functional activity and relevance in cutaneous homeostasis. Apart from a recent study in 2012 showing OXT expression and release by epidermal keratinocytes (1), the OXT system in human skin has not been explored so far.

The results obtained in the present study show that both OXT and its receptor are expressed by primary human dermal fibroblasts and keratinocytes. OXT induced dose-dependent calcium fluxes in both cell types, demonstrating that the OXT receptor (OXTR) is functional.

In addition, analyses of dermal fibroblasts show that expression of the OXT system can be enhanced by its own components, suggesting its regulation in a positive feedback loop.

Previous studies have reported on increased OXT levels in plasma after massage-like stroking in rats (3), as well as hugs (4) and suckling (2) in humans. Here, in an in vivo study, tactile stimulation of the skin increased OXT concentrations in suction blister fluids. While former studies reported only on elevated systemic OXT release, this study demonstrates local cutaneous OXT release. In summary, these data show that the OXT system can be modulated in vitro and in vivo in human skin cells.

This work further reveals a functional role for the OXT system in the modulation of cutaneous proliferation and structure. OXT decreased proliferation of dermal fibroblasts and keratinocytes in a dose-dependent manner. Moreover, continuous OXT treatment reduced the epidermal layer thickness in a 3-D skin model. In the same model, OXT increased the expression of the terminal differentiation marker loricrin in the epidermis. Whether the reduction in epidermal layer thickness was due to OXT-mediated alteration of proliferation or of cell differentiation remains to be elucidated.

The OXT system appears also to be involved in neuroendocrine, oxidative and inflammatory stress responses of the skin. Corticotropin-releasing hormone (CRH) and corticosterone are central mediators of the systemic/cutaneous neuroendocrine stress response. OXTR knockdown in dermal fibroblasts resulted in an increased expression of CRH and its receptor. Additionally, OXT treatment of keratinocytes decreased the release of corticosterone. Therefore, it is hypothezised that the OXT system counteracts neuroendocrine stress in the skin. Furthermore, OXTR knockdown in dermal fibroblasts and keratinocytes led to elevated levels of reactive oxygen species and reduced levels of glutathione, pointing to a cytoprotective role of the cutaneous OXT system. This is also assumed to apply to inflammation, as OXTR-depleted keratinocytes exhibited an increased release of the pro-inflammatory cytokines IL6, CCL5 and CXCL10.

Numerous skin disorders are associated with abnormal proliferation and stress responses with atopic dermatitis as one of the most prominent representatives. Therefore, it was

Summary IV examined whether the OXT system might be aberrantly expressed in atopic compared to healthy skin. In fact, a downregulation of the OXT system in peri-lesional and lesional atopic skin was detected.

Taken together, the presented findings indicate that the OXT system modulates key processes which are dysregulated in atopic dermatitis, including proliferation, inflammation and oxidative stress responses. In conclusion, the data of this thesis suggest that the OXT system is a novel neuroendocrine mediator in human skin homoeostasis and relevant to stressed skin conditions like atopic dermatitis.

T ABLE OF CONTENT

ZUSAMMENFASSUNG ... I   SUMMARY ... III   TABLE OF CONTENT ... V   ABBREVIATIONS ... IX  

1   INTRODUCTION ... 12  

1.1   The oxytocin system ... 12  

1.2

Functions of the oxytocin system ... 14

1.2.1

Oxytocin modulates proliferation ... 16

1.2.2

Oxytocin modulates neuroendocrine, inflammatory and oxidative stress responses ... 18  

1.3   Structure and function of human skin ... 20  

1.3.1   The epidermis ... 21  

1.3.2   The dermis ... 22  

1.3.3   The hypodermis ... 23  

1.4

Atopic dermatitis ... 23

2   OBJECTIVE ... 26  

3   MATERIALS ... 27  

3.1   Antibodies and fluorescent dyes ... 27  

3.2   Chemicals and reagents ... 28  

3.3   Enzymes and synthetic peptides ... 30  

3.4   Kits ... 30  

3.5   Primers ... 31  

3.6   siRNAs ... 34  

3.7   Specific expendable materials ... 34  

3.8   Specific technical equipments ... 35  

3.9   Software ... 36  

3.10   Cell culture media, buffers and solutions ... 37  

4

METHODS ... 39

4.1

4.1.1   Clinical studies to gain healthy and atopic skin samples ... 39  

Table of content VI

4.1.2   Study of oxytocin release from tactile stimulated skin areas ... 40  

4.2   Cell culture ... 42  

4.2.1   Isolation and cultivation of primary human dermal fibroblasts and keratinocytes ... 42  

4.2.2   Organotypic 3-D skin cultures ... 42  

4.3

Cell biological methods ... 44

4.3.1

Quantification of corticosterone ... 44

4.3.2

Neutral red assay ... 44

4.3.3

Oxytocin receptor knockdown ... 44

4.3.4   Measurement of Ca

currents ... 45  

4.3.5   Proliferation assay ... 46  

4.3.6   UV irradiation ... 46  

4.3.7   Quantification of intracellular reactive oxygen species ... 46  

4.3.8   Quantification of intracellular glutathione ... 46  

4.4   Molecular biological methods ... 47  

4.4.1   Isolation of RNA ... 47  

4.4.2   Reverse transcription ... 47  

4.4.3   semi-quantitative Real Time PCR ... 47  

4.5   Protein analyses ... 48  

4.5.1   Immunofluorescence analyses ... 48  

4.5.2   Measurement of epidermal layer thickness ... 49  

4.5.3   Cell lysis and preparation of membrane fractions ... 49  

4.5.4   Quantification of protein concentrations ... 50  

4.5.5   SDS-Polyacrylamide gel electrophoresis ... 50  

4.5.6   Western Blot ... 50  

4.5.7   Detection of oxytocin protein levels ... 51  

4.5.8

Detection of cytokine protein levels ... 51

4.6

Statistics ... 51

5

RESULTS ... 52

5.1   Functional expression of the oxytocin system in primary human dermal

fibroblasts and keratinocytes ... 52  

5.1.1   Expression of oxytocin and the oxytocin receptor ... 52   5.1.2   Determination of non-toxic doses for the experimental use of oxytocin

and the oxytocin receptor antagonist L371,257 ... 56   5.1.3   siRNA-mediated knockdown of the oxytocin receptor ... 57   5.1.4   Functionality of the oxytocin receptor measured by intracellular calcium

fluxes ... 59

5.2

Modulation of the oxytocin system in human skin ... 62

5.2.1  

Modulation of oxytocin and oxytocin receptor expression in dermal

fibroblasts and keratinocytes in vitro ... 62

Modulation of oxytocin release in the skin in vivo ... 65   5.3   Comparison of the expression of the oxytocin system in healthy and atopic

skin cells ... 66   5.4   Cellular functions of the oxytocin system in primary human dermal

fibroblasts and keratinocytes ... 68   5.4.1   Effects of oxytocin receptor knockdown on the neuroendocrine stress

mediators CRH and corticosterone ... 68   5.4.2   Effects of oxytocin receptor knockdown on the pro-inflammatory

cytokines IL6, CCL5 and CXCL10 ... 70   5.4.3   Effects of oxytocin receptor knockdown on oxidative stress parameters

and stress-related enzymes ... 71   5.4.4   Influence of oxytocin on proliferation ... 74   5.4.5   Influence of oxytocin on epidermal structure in an organotypic 3-D skin

model ... 75   5.4.6   Influence of oxytocin on the expression of structural proteins in the

epidermis of a 3-D skin model ... 76   6   DISCUSSION ... 78  

6.1

Establishment and aspects of experimental settings ... 78

6.2

The oxytocin system is functionally expressed and can be modulated in

primary human skin cells ... 80

6.2.1   The oxytocin system is functionally expressed in dermal fibroblasts and

keratinocytes ... 80  

Table of content VIII

6.2.2   Expression of the oxytocin system is regulated in feedback loops in

dermal fibroblasts and keratinocytes ... 81  

6.2.3   Oxytocin is locally released from human skin upon tactile stimulation in

6.3   Oxytocin modulates stress responses and skin structure: Implications for atopic dermatitis ... 83

6.3.1

The oxytocin system is downregulated in atopic skin ... 83

6.3.2

Oxytocin receptor knockdown increases the release of the pro- inflammatory cytokines IL6, CCL5 and CXCL10 ... 84

6.3.3   The oxytocin system influences the neuroendocrine stress parameters CRH and corticosterone ... 85  

6.3.4   Oxytocin receptor knockdown increases oxidative stress ... 86  

6.3.5   Oxytocin inhibits proliferation ... 88  

6.3.6   Oxytocin reduces the epidermal layer thickness in an organotypic three- dimensional skin model ... 89  

7   CONCLUSION AND PERSPECTIVE ... 91  

8   REFERENCES ... 93  

LEBENSLAUF ... 107  

WISSENSCHAFTLICHE VERÖFFENTLICHUNGEN ... 108  

HILFSMITTEL ... 109  

EIDESSTATTLICHE ERKLÄRUNG ... 110  

DANKSAGUNG ... 111  

A BBREVIATIONS

ACTH Adrenocorticotropic hormone

AD Atopic dermatitis

ATP Adenosine triphosphate

BCA Bicinchoninic acid

BPE Bovine pituitary extract

BSA Bovine serum albumine

CCL5 C-C Motif Chemokine 5

CXCL10 C-X-C Motif Chemokine ligand 10

cDNA Complementary DNA

CRH Corticotropin releasing hormone

CRHR1 Corticotropin releasing hormone receptor 1

Ct Threshhold cycle, Schwellenwert

DAPI 4',6-diamidino-2-phenylindole

DMEM Dulbecco´s modified Eagle´s medium

DMSO Dimethylsulfoxide

DNA Deoxyribonucleic acid

EDTA Ethylenediaminetetraacetate

ELISA Enzyme-linked immunosorbent assay

ERK 1/2 Extracellular signal-regulated kinase 1/2

FACS Fluorescence activated cell sorting

FAM 6-Carboxy-Fluorescein

FCS Fetal calf serum

FRET Fluorescence resonance energy transfer

Abbreviations X

GSH Glutathione

H Hour

HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid

HPA Hypothalamic-pituitary-adrenal

IgG Immunoglobulin G

IL6 Interleukin 6

MAPK Mitogen-activated protein kinases

Min minute

mRNA Messenger RNA

NFκB Nuclear factor kappa B

OTC Organotypic culture

OXT Oxytocin

OXTR Oxytocin receptor

PAGE Polyacrylamide gel ectrophoresis

PBS Phosphate buffered saline

PCR Polymerase-chain-reaction

RNA Ribonucleic acid

ROS Reactive oxygen species

RTq-PCR quantitative real time polymerase-chain-reaction

SBF Suction blister fluid

SDS Sodiumdodecylsulfate

siRNA Small interfering RNA

SSR Solar simulated light

Th cells T helper cells

Tween 20 Polyoxyethylene (20) sorbitan monolaurate

WB Western blot

Introduction 12

1 I NTRODUCTION

1.1 The oxytocin system

The oxytocin system consists of the neuropeptide hormone oxytocin (OXT) and the oxytocin receptor (OXTR). In 1906, OXT was discovered by Sir Henry Dale when he found that extracts from the human posterior pituitary gland are able to contract the uterus of a pregnant cat. Due to its uterotonic action, he coined the name “oxytocin” deduced from the greek meaning “swift birth” (5). The effect on uterine contractions is of major pharmacological importance as OXT is the strongest uterotonic agent known and therefore, commonly used to augment labor (6). OXT is the first peptide hormone to be sequenced and synthesized by Vincent du Vigneaud in 1953 for which he received the Nobel Prize (7).

In the brain, OXT is transcribed as an inactive precursor molecule along with its carrier protein neurophysin I in the hypothalamus. Upon transport along the hypothalamic axon to terminals located in the posterior pituitary, the OXT-neurophysin I prepropeptide is subjected to cleavage and other modifications (8, 2). The human gene for OXT-neurophysin I is mapped to chromosome 20p13 (9) and consists of three exons (2) (Figure 1a). The first exon encodes a secretory signal peptide, oxytocin, a tripeptide processing signal, and the first nine residues of neurophysin I. The second exon encodes the central part of neurophysin I and the third exon encodes the COOH-terminal region of neurophysin I. OXT comprises nine amino acids which include a disulfide bond between cysteine residues 1 and 6 resulting in a peptide constituted of a six-amino acid cyclic part and a three-residue tail (Figure 1c). Its structure is very similar to the closely related peptide vasopressin, differing in its amino acids sequence at only two positions (2). The OXTR is a 389-amino acid polypeptide and is mapped to the gene locus 3p25–3p26.2 (10). The OXTR gene contains three introns and four exons (2) (Figure 1b). Exons one and two correspond to the 5’-noncoding region. Exons three and four encode the OXTR including the entire 3’-noncoding region. OXT acts through its receptor which contains seven transmembrane domains and belongs to the rhodopsin- type class I G-protein-coupled receptor superfamily (11) (Figure 1d, e).

OXT is mainly produced in the paraventricular and supraoptic nuclei of the hypothalamus and is released from hypothalamic nerve terminals of the posterior pituitary into the blood stream (8, 12). Apart from the brain, it is synthesized by several tissues such as uterus, ovary, testis, thymus, pancreas and myocardial tissue (13, 14, 2). In human skin, OXT is expressed in epidermal keratinocytes and its release can be triggered with an ATP-analogue by induction of calcium influx via P2X receptors (1).

The OXTR is differentially expressed in various tissues, correlating with the pattern of sex steroids (2). For instance, sites of expression are brain, uterus, placenta, testis, breast cancer cells, bone cells, myoblasts, cardiomyocytes and endothelial cells (6, 2).

Expression of OXT and the OXTR is dynamically modulated. That has been demonstrated in various studies: The OXT system is highly regulated during gestation, parturition and lactation, thus enabling circulating oxytocin to target a particular organ, depending on the precisely regulated tissue-specific expression of the OXTR (15, 16).

Figure 1. Oxytocin/oxtocin receptor genes and protein structures.

(a) Domains of the preprooxytocin gene. The precursor is enzymatically cleaved into the indicated fragments. The first exon encodes a secretory signal peptide, OXT, a tripeptide processing signal (GKR) and the first nine residues of neurophysin. The second exon encodes the central part of neurophysin and the third exon encodes the COOH-terminal region of neurophysin. Numbers indicate the amino acids encoded. (b) Organization of the human OXTR gene which consists of four exons (ex). Exons 3 and 4 encode the amino acid sequence for the OXTR. The start (ATG) and stop (TGA) codons of the receptor cDNA are indicated. The DNA sequences encoding for transmembrane regions I–VII are depicted by black areas. (c) Molecular protein structure of OXT. (d) Schematic protein structure of the OXTR. (e) Model of the OXTR (blue) and its interaction with its endogenous ligand OXT (red). The seven transmembrane domains are indicated by Roman numerals. Residues of the human OXTR are indicated by numbers. (Sources: 2, 17, 6)

Introduction 14 Concentrations of OXT in the neurohypophysis and plasma of both sexes are equivalent (2).

This fact already suggests that OXT has further physiological functions in both genders, beside its role in the female-restricted process of parturition. In addition, the systemic availability of OXT also indicates its relevance for the entire body.

1.2 Functions of the oxytocin system

Discoveries of OXT-mediated functions have greatly expanded the spectrum of OXT action beyond its classic role as an inducer of uterine contractions and lactation (2). OXT plays a key role in certain kinds of behavioural regulation, such as social recognition, attachment and anxiety (18, 19). Differential pharmacological profiles of the OXTR in the brain and peripheral tissues are associated with the existence of OXTR subtypes (20, 21). Furthermore, the OXTR displays promiscuous coupling to Gq-, Gs- and Gi-protein isoforms forming heterotrimeric complexes, depending on the localization of the receptor within the plasma membrane. The variety of OXTR subtypes, coupling with different G-protein isoforms, results in the activation of multiple signalling pathways. Consequently, this leads to the induction of diverse physiological functions of OXT in different cell types (22, 23) (Figure 2).

Figure 2. Oxytocin receptor signalling pathways.

OXTR activation leads to three different G-protein dependant mechanisms. The major mechanism is mediated by the G^q-PLC-IP³ pathway. When oxytocin binds to the OXTR, it activates Gαq/11 and then phospholipase C (PLC), which induces the cleavage of phosphatidylinositol-4,5-bisphosphate (PIP₂) to inositoltrisphosphate (IP3) and diacylglycerol (DAG). IP3induces Ca²⁺release from Ca²⁺stores. The activation of G_qalso causes membrane depolarization, e. g. in neurones,which facilitates Ca²⁺entry through voltage-gated Ca²⁺channels. Increased cytosolic Ca²⁺ stimulates the Calmodulindependent protein kinase (CaMK) after binding to the Ca²⁺binding protein Calmodulin (CaM). The Ca²⁺/CaM complex then activates CaMK and causes various cellular responses. DAG causes protein kinase C (PKC) activation mediating trophic effects. Additional pathways activated through the OXTR include extracellular-signal regulated kinases (ERK) pathways. Proliferative effects involve ERK-mediated activation of specific gene transcription. Increased transcription of Cyclooxygenase-2 (COX-2) mediates increased production and secretion of prostaglandins, contributing to contractile effects.

OXTR coupling to G_s- and G_i-proteins is linked with the adenylat-cyclase pathway. Anti-proliferative effects observed in certain cell types appear to be mediated via G_i proteins. (Source: 5, modified)

Introduction 16

1.2.1 Oxytocin modulates proliferation

OXT is able to promote, to inhibit or to have no effects on proliferation of various cell types (24, 25, 26). The proliferative effects are altered by cholesterol depletion of membranes or changes in OXTR–caveolae interaction (27), resulting in contrary observations (28, 29) (Figure 3).

Mitogenic effects of OXT are associated with OXTR localization inside caveolae and its coupling to Gαq/11-proteins (30). The first step of the G_q-triggered signalling cascade involves activation of phospholipase C-β (PLC-β) leading to hydrolyzation of phosphatidylinositol-4,5- bisphosphate, producing inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 leads to an increase in intracellular calcium concentrations. This reaction is paralleled by activation of protein kinase C (PKC) through DAG. Finally, PKC induces transient ERK1/2 phosphorylation and thereby promotes proliferation.

Suppression of proliferation is associated with OXTRs located outside caveolae and their coupling to Gi-proteins (30). Upon OXT stimulation, two signalling pathways from this coupling are initiated depending on the cell system. The first cascade results in sustained ERK phosphorylation via PLC-βγ activation and subsequent induction of the cyclin dependant kinase inhibitor p21. The second cascade leads to an increase in cAMP and activation of protein kinase A.

Figure 3. Oxytocin-mediated cell proliferation depends on the cellular localization of its receptor.

(a) Inside caveolae, OXTRs couple to Gq-proteins upon OXT stimulation. Subsequently, Gq-proteins initiate a signalling cascade via phospholipase C-ß (PLCß), phosphatidylinositol-4,5-bisphosphate (PIP2), diacylglycerol (DAG) and protein kinase C (PKC). Finally, PKC activation induces transient ERK1/2 phosphorylation promoting proliferation. (b) Outside caveolae, OXTRs couple to Gi-proteins upon OXT stimulation. Depending on the cell system, two signalling pathways from this coupling are initiated. The first results in sustained ERK phosphorylation via PLCß activation and subsequent induction of the cyclin dependant kinase inhibitor p21. The second pathway leads to an increase in cAMP and activation of protein kinase A (PKA). Triggering of both pathways suppresses proliferation.

(Source: 30, modified)

Introduction 18

1.2.2 Oxytocin modulates neuroendocrine, inflammatory and

oxidative stress responses

A growing body of evidence suggests that oxytocin functions to attenuate stress responsiveness at different levels (31). The OXT-mediated anti-stress effects include inhibition of the hypothalamic-pituitary-adrenal (HPA) axis, as well as alleviation of inflammatory and oxidative stress.

The central response to physical or psychological stressors involves signalling along the HPA axis. Stress exposure leads to the secretion of corticotropin-releasing hormone (CRH) from hypothalamic neurons, targeting the anterior pituitary to release adrenocorticotropin (ACTH). Systemically circulating ACTH, in turn, triggers the release of corticosteroids, e. g.

cortisol, from the adrenal glands. Finally, cortisol participates in an inhibitory feedback loop by blocking the secretion of CRH. Intracerebral OXT has been shown to dampen basal and stress-induced activity of the HPA axis (32, 33). Noteworthy, studies demonstrated that OXT- induced effects on HPA axis activity can be contrarious depending on the length of time of OXT adminstration (34). Acute administration of oxytocin to rats is followed by a short-lasting increased HPA axis activity. In contrast, the long-term effects caused by repeated oxytocin administration are always consistent with a lowered HPA axis activity. However, the inhibitory effect of OXT on the HPA axis is mediated by reducing cortisol/corticosterone levels in response to acute exposure to stressors (35, 33). Human skin is a part of the local, as well as the systemic neuroendocrine network (36). For instance, all key mediators of the HPA axis, including the neuropeptides CRH, proopiomelanocortin-derived ACTH and cortisol/corticosterone, are synthesized and released by skin cells (36-38). In view of possible cross-talks, ACTH and CRH receptors are also located on dermal fibroblasts and keratinocytes (37, 39-41).

Some of the factors that trigger and modulate HPA axis activity are cytokines (42). How closely the OXT system is integrated in neuroendocrine stress responses and immunological networks demonstrates the fact that OXTR expression is also regulated by cytokines.

Treatment with both IL1b and IL6 negatively regulates the transcription of the OXTR gene in cultured human immortalized myometrial cells (43). Furthermore, wound-healing, which involves a well-organized inflammatory phase, has been shown to be facilitated by OXT administration (44, 45). Moreover, in a rat model of dried-latex-induced paw oedema, OXT treatment showed anti-inflammatory and anti-nociceptive activity, thus pointing to a role of OXT in skin inflammation (46).

Inflammation is often accompanied by oxidative stress and vice versa (47). Increased levels of intracellular reactive oxygen species (ROS) can damage macromolecules, leading to lipid peroxidation, oxidation of amino acid side chains, formation of protein-protein cross-links, protein fragmentation, DNA damage and DNA strand breaks (48). Beside ROS generation by environmental stresses, free radicals are naturally generated in the organism. In mitochondria, ROS are produced as a byproduct of cell respiration (49) and play a role in cell signalling (50). In addition, ROS are generated during inflammation by immune cells, such as macrophages, to destroy pathogens. In turn, oxidative stress is able to drive inflammation by activation of transcription factors, such as NF-κB which regulates inflammatory mediator gene expression (51). Small amounts of ROS are usually scavenged by cellular defense systems including nonenzymatic and enzymatic antioxidants. The antioxidant glutathione (GSH) is a tripeptide consisting of glycine, cysteine and glutamate. GSH exists in a reduced (GSH) and an oxidized (GSSG) form. It represents the predominant low molecular weight thiol in mammalian cells, with its intracellular concentrations ranging from 0.2 to 10 mM (52).

85 to 90 % of GSH is freely distributed in the cytosol, but it is also found in mitochondria, peroxisomes, the nuclear matrix and the endoplasmic reticulum.

Beside inflammatory stress, OXT seems to attenuate also oxidative stress. OXT does not only decrease IL6 secretion, but also NADPH-dependent superoxide production in vascular cells and THP-1 macrophages in an in vitro model (53). In addition, subcutaneously administered OXT has been demonstrated to prevent sepsis-induced depletion of GSH contents in colonic and uterine tissues of rats (54). Oxidative stress occurs rapidly after the onset of ischemia. Subcutaneously injected OXT appears to improve renal ischemia- reperfusion induced lipid peroxidation in liver tissue of rats (55). In the same rat model, a reduction of nitrogen monoxide during ischemia which was supposed to be caused by endothelial dysfunction and diminished endothelial nitric oxide synthase activity, was measured. OXT treatment increased nitrogen monoxide levels in the hepatic tissue and thereby enhanced the cytoprotective effects of nitrogen monoxide, like inhibition of oxidative stress, cytokine release, apoptosis, adhesion and aggregation of neutrophil leukocytes. In mice, after induction of experimental stroke, exogenous OXT treatment increased antioxidant activity through elevation of brain GSH peroxidase levels (56). Additionally, OXT itself is an anti-oxidant in aqueous medium (57). OXT is able to scavenge free superoxide and reactive nitrogen species, exhibiting the capacity to directly suppress free radical-mediated damage of cell components (57). The antioxidant activity of OXT is supposed to derive from solvent- exposed tyrosine and tryptophan residues (57). In vitro, significant antioxidant effects can be observed at nanomolar concentrations of OXT. Notably, the potency of this hormone is comparable with classic low molecular weight anti-oxidants (57). Altogether, OXT appears to contribute to the organism’s defense system against oxidative stress.

Introduction 20

1.3 Structure and function of human skin

The skin is the largest organ of the body comprising a size of 1.5 to 1.8 m² and accounting for about 15 % of the total body weight in adult humans (58). It exerts multiple vital functions.

The skin forms the first line of defense against environmental stressors such as toxic xenobiotics, irritants, damaging radiation, and pathogenic microbes and prevents from excessive water loss (59, 60). Further key functions include the regulation of body temperature, the synthesis of vitamin D and the perception of heat, cold, touch and pain.

The skin’s structure is organized in three parts, called the epidermis, the dermis and the hypodermis (Figure 4). The epidermis forms the outermost layer of the skin and represents a stratified squamous epithelium. The dermis is located beneath the epidermis, separated by a permeability barrier, the basement membrane. The hypodermis lies below the dermis. The thickness of the skin varies from 1 to 4 mm depending on body region (58). Embryologically, the epidermis and its appendages are of ectodermal origin, whereas the dermis and hypodermis are of mesodermal origin.

Figure 4. Human skin with its appendages.

Schematic organization of human skin. (1) Epidermis , (2) dermis, (3) hypodermis, (4) hair follicle, (5) sebaceous gland, (6) sweat gland. (Source: Information brochure of Eucerin^®, Beiersdorf AG)

1.3.1 The epidermis

The epidermis forms the uppermost layer of the skin. Depending on body region, age and gender, its thickness varies between 0.05 mm (eyelids) to 1 mm (palms and soles) (58).

Keratinocytes represent the predominant cell type, constituting 90 % of all epidermal cells.

The remaining 10 % are composed of melanocytes, Langerhans cells and Merkel cells. The keratinocytes are arranged in several well-defined layers (58) (Figure 5). They constitute the stratum basale (single layer), the stratum spinosum (5 to 15 layers), the stratum granulosum (1 to 5 layers) and the stratum corneum (10 to 30 layers). The epidermis renews itself continuously in a cyclic time interval of 28 days. Within this period, keratinocytes undergo a specific morphological and biochemical terminal differentiation process, as they proceed from the stratum basale to the skin surface. In the basal layer, keratinocytes originate from mitotic divisions of transient amplifying cells and stem cells, which are also located in the bulb region of the hair follicle. Subsequently, the produced daughter keratinocytes migrate towards the stratum corneum, finally transforming to corneocytes, which are flattened and anucleated cells without cytoplasmic organelles. At the end of this process, the corneocytes slough off from the skin surface (58).

Figure 5. Epidermal structure.

The epidermis consists of four cell layers. Only the palms of the hands and the soles of the feet comprise a fifth layer, the thin and translucent stratum lucidum. (Source: Information brochure of Eucerin^®, Beiersdorf AG)

Introduction 22 The cytoskeleton of keratinocytes is primarily made of keratins. These are fibrous structural proteins forming an intermediate filament network. The keratins assembly to dimers, made of an acidic and a basic polypeptide. Depending on the differentiation status of the cells, the epidermal layers comprise specific keratin patterns. Proliferating, basal keratinocytes express keratin 5 and 14, whereas suprabasal cells express keratin 1 and 10 (58).

The cornified envelope is a structure that surrounds cells in the stratum corneum. It contributes to the skin's barrier function by preventing water evaporation and the penetration of noxious environmental agents. During epidermal differentiation, cytoskeleton proteins, such as involucrin, filaggrin and loricrin, become sequentially incorporated into the cornified envelope. In its formation, involucrin serves as a scaffold protein for the incorporation of other proteins (61), providing potent structural support to the cell to resist against invasion by microorganisms. Filaggrin plays an important role to secure skin hydration, as it is degraded to amino acids which act as moisturizing factors in the stratum corneum (62). The precursor profilaggrin is found in keratohyaline granules of the stratum granulosum. Profilaggrin is cleaved into filaggrin peptides, which rapidly aggregate keratin filaments, causing the collapse of granular cells to form flattened anucleus squames. Loricrin is highly insoluble and the major protein of the cornified envelope contributing over 70 % by mass (63). It occurs late during the terminal differentiation program of corneocytes. The cornified cell envelope is finally generated via cross-linking of the condensed cytoskeleton proteins by transglutaminases.

1.3.2 The dermis

The dermis is located between the epidermis and the hypodermis. It comprises two distinct layers: The pappilary dermis which is closest to the epidermis and the reticular dermis which overlies the hypodermis (64). The dermis cushions the body from stressors and strain. It also provides nourishment and waste removal for both dermal and epidermal cells. Fibroblasts are the principle cells of the dermis. Other cellular components are macrophages, mast cells, T and B lymphocytes, and cells of vascular and lymphatic vessels (64). It also contains mechanoreceptors, hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. The dermis is a connective tissue that is rich in collagen, comprising 75 % of the fat free dry weight. Fibroblasts are responsible for the production of collagen fibers, but also for further structural components of the extracellular matrix, such as elastic fibers and glycosaminoglycans.

1.3.3 The hypodermis

The hypodermis is loosely connected to the dermis. Adipoctes are the main cell type found in the hypodermis, forming the subcutaneous fatty tissue. This tissue plays an important role in the storage and provision of energy. Further functions of the hypodermis are its participation in thermoregulation, insulation and protection from mechanical injuries.

1.4 Atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that affects up to 20 % of children worldwide, but can also persist and be aquired in adulthood (65). Since 1980, the incidence of AD has increased up to three-fold in industrialized countries (66). More than 50 % of AD patients develop asthma and manifest other atopic disorders such as allergic rhinitis, allergic conjunctivitis and food allergies (67, 68). These additionally aquired hypersensitivities towards environmental stimuli define the socalled atopic march. AD significantly reduces the quality of life and its therapeutic treatment involves substantial economic burden (68).

The skin of patients suffering from AD is extremely dry and shows lichenification, erythema and eczema (Figure 6b). The eczema are highly pruritic and severe scratching results in weeping, bleeding and crusty skin lesions. Typically, the distribution of atopic lesions varies with age (Figure 6c). Although AD can potentially affect any part of the body, the skin on the surfaces of the joints belong to the most prominent affected regions.

AD is a multifactorial skin disease: genetic predisposition, bacterial and viral infections, immunological alterations, skin barrier disruption and psychological stress have all been discussed as causes and aggravation factors (67, 69).

Hypersecretion of Immunoglobulin E, exaggerated levels of eosinophils and an imbalance of T lymphocyte subgroups belong to the central immunological abnormalities in AD patients (70). AD comprises a biphasic inflammation with an initial, acute Th 2 phase and a chronic Th 1 phase (66). The initial, acute phase of the disease is predominantly characterized by secretion of Th 2 cell-derived cytokines, namely IL4 and IL13, which can be localized in lesional and non-lesional skin. In chronic AD skin lesions, an increase of IFN γ, IL-12, and GM-CSF could be detected, being typical for a Th 1 dominance.

Introduction 24

Figure 6. Atopic compared to healthy skin and the characteristic age-dependant pattern of atopic lesions.

(a) Arm with healthy skin (above) and cryosections of healthy skin stained with hematoxylin/esoin (below). Cell nuclei in cryosections are depicted in blue. (b) Arm with atopic skin lesions (above).

Cryosections of atopic skin stained with hematoxylin/eosin showing epidermal hyperplasia and infiltrates of immune cells in the dermis (below). (c) Distribution of atopic skin lesions modifying with age. In babies, atopic lesions affect typically the face, but patches are also located elsewhere. In childhood, atopic lesions settle into elbow and knee flexures as well as on wrists and ankles. In adolescence, atopic lesions can persist or change their pattern. The appearance of the rashes tend to shift: They become dryer in childhood and then scaly or thickened in adolescence while the itching is persistent. (Source: 71)

Up to 30 % of AD patients of European cohorts comprise mutations in the filaggrin gene (67), weakening the skin’s epidermal barrier. In addition, loricrin and involucrin, are reduced in lesional skin of AD patients (67), further pertubing the integrity of the cornified envelope. In turn, increased epidermal permeability leads to penetration of environmental allergens and pathogens into the skin and initiates immunological reactions and inflammation.

The skin of AD patients is very susceptible to cutaneous infections caused by vaccinia virus and herpes simplex virus (72). Furthermore, both perilesional and lesional skin of AD patients is severly colonized with Staphylococcus aureus (73). Beside defects in the skin barrier, decreased antimicrobial-protein synthesis is proposed as a possible cause for the increased susceptibility (74).

Occurrence of AD is often associated with psychological stress. In the setting of stress, sensory nerves release neuromediators that regulate inflammatory and immune responses, as well as barrier function. However, a blunted HPA axis activity, including diminished cortisol levels, with a concurrent overreactivity of the sympathetic adrenomedullary system in response to psycological stress has been demonstrated in AD (75). This might further promote the release of proinflammatory cytokines and may be one mechanism of psychological stress-related aggravation of AD.

Objective 26

2 O BJECTIVE

A recent study showed that OXT is produced by epidermal keratinocytes in human skin and released in response to calcium influx via P2X receptors (1). Nevertheless, OXTR expression and its role in cutaneous homoeostasis have not been explored so far.

OXT has been shown to be involved in proliferation and various types of stress responses, being potentially important for skin morphology and physiology. In fact, numerous skin disorders are associated with abberant proliferation and stress responses. Among these, AD and psoriasis are the most prominent.

The aim of this thesis was the characterization of the OXT system in human skin and the analysis of its functional activity and relevance in skin homeostasis.

In particular, primarily, the OXT system was investigated in dermal fibroblasts and keratinocytes. First, expression, functionality and modulation of the OXT system should be studied. Next, a potential role for the OXT system in neuroendocrine, inflammatory and oxidative stress responses should be evaluated. Additionally, it should be elucidated whether the OXT system has an impact on proliferation and skin structure. Finally, a comparison of the expression profile of the OXT system in healthy and atopic skin should provide hints to its in vivo relevance for pathogenic stressed skin conditions.

3 M ATERIALS

Unless otherwise stated, all chemicals, reagents, buffers and solutions were prepared with deionized water purified by Milli-Q Advantage A10 water system.

3.1 Antibodies and fluorescent dyes

Table 1. Antibodies against human peptides and proteins

1. Antibody Host Dilution Order number Source

Anti-actin (polyclonal)

Goat 1:1000 sc-1615 Santa Cruz, Dallas,

TX, USA Anti-cytokeratin 1

(polyclonal)

Rabbit 1:1000 Prb-149p-100 Covance, Princeton, NJ, USA

Anti-

cytokeratin 5/14 (monoclonal)

Mouse 1:500 MAB1984 Abnova, Taipei,

Taiwan

Anti-OXT (monoclonal)

Mouse 1:200 (single cells)

LS-C37953 LifeSpan

BioSciences, Seattle, WA, USA Anti-OXT

(monoclonal)

Mouse 1:500

(cryosections)

MAB5296 (clone 4G11)

Millipore, Billerica, MA, USA

Anti-OXTR (polyclonal)

Guinea pig

1:200 Customized

(SYC592)

Eurogentec, Seraing, Belgium 2. Antibody Host Dilution Order number Source

Anti-goat IgG IRDye 800CW

Donkey 1:15000 926-32214 Li-cor, Lincoln, NE, USA

Anti-guinea pig IgG Alexa Fluor 488

Goat 1:1000 A-11073 Life Technologies,

Carlsbad, CA, USA

Anti-guinea pig IgG IRDye 680CW

Donkey 1:10000 926-32421 Li-cor, Lincoln, NE, USA

Materials 28

Anti-mouse IgG Alexa Fluor 488

Goat 1:1000 A-11029 Life Technologies,

Carlsbad, CA, USA Anti-rabbit IgG

Alexa Fluor 594

Goat 1:1000 A-11001 Life Technologies,

Carlsbad, CA, USA

Table 2. Fluorescent dyes

Description Source

4',6-diamidino-2-phenylindole (DAPI), 5 mg/ml stock

Sigma-Aldrich, St. Louis, MO, USA

2′,7′-dichlorodihydrofluorescein diacetate Life Technologies, Carlsbad, CA, USA

Fluo-4 AM Life Technologies, Carlsbad, CA, USA

Fura Red Life Technologies, Carlsbad, CA, USA

ThiolTracker™ Violet Life Technologies, Carlsbad, CA, USA

3.2 Chemicals and reagents

Table 3. Chemicals and reagents

Description Source

Acetic acid, concentrated Merck, Darmstadt, Germany

Acetone Merck, Darmstadt, Germany

Ascorbic acid Sigma-Aldrich, St. Louis, MO, USA

Blocking Peptide, customized, I351-365- EP113440-KLH-MBS

Eurogentec, Seraing, Belgium

Bovine serum albumin (BSA), Fraction V Sigma-Aldrich, St. Louis, MO, USA Calcium chloride dihydrate Sigma-Aldrich, St. Louis, MO, USA

Collagen, Typ I Sigma-Aldrich, St. Louis, MO, USA

Complete Mini Protease Inhibitor Roche, Basel, Switzerland

Criterion Tris-HCl Gel, 4-15 % Bio-Rad, Hercules, CA, USA Dimethyl sulfoxide (DMSO) Sigma-Aldrich, St. Louis, MO, USA Dulbecco’s Modified Eagle Medium (DMEM),

low glucose

Life Technologies, Carlsbad, CA, USA

DMEM, 25 mM HEPES buffered Biochrom AG, Berlin, Germany

Dulbecco’s PBS w/o, 1x PAA, Linz, Austria

Ethanol, absolute Merck, Darmstadt, Germany

Fetal calf serum (FCS) PAA, Linz, Austria

Fluorescence mounting medium Dako, Glostrup, Denmark

Glutamax I, 100x Life Technologies, Carlsbad, CA, USA

Ham’s F12 Sigma-Aldrich, St. Louis, MO, USA

Hanks' Balanced Salt Solution, 10x Life Technologies, Carlsbad, CA, USA

Hydrocortisone Sigma-Aldrich, St. Louis, MO, USA

Ionomycin Merck, Darmstadt, Germany

Keratinocyte basal medium-2 (KBM-2) Lonza, Basel, Switzerland Keratinocyte growth medium-2 (KGM-2)

SingleQuot Kit Suppl. & Growth Factors

Lonza, Basel, Switzerland

L-371,257 Tocris, Bristol, UK

Laemmli buffer Bio-Rad, Hercules, CA, USA

Lipofectamine^® RNAiMAX Transfection Reagent

Life Technologies, Carlsbad, CA, USA

MagicMark™ XP Western Protein Standard Life Technologies, Carlsbad, CA, USA

Neutral red Life Technologies, Carlsbad, CA, USA

β-Mercaptoethanol Bio-Rad, Hercules, CA, USA

Mitomycin C Sigma-Aldrich, St. Louis, MO, USA

Materials 30

Novex^® Sharp Pre-stained Protein Standard Life Technologies, Carlsbad, CA, USA Opti-MEM^® I + GlutaMax^TM-I Life Technologies, Carlsbad, CA, USAå Paraformaldehyde (PFA) Sigma-Aldrich, St. Louis, MO, USA Penicillin/Streptomycin, 5000 U/ml Life Technologies, Carlsbad, CA, USA Pluronic Detergent F-127 Life Technologies, Carlsbad, CA, USA

Probenecid Life Technologies, Carlsbad, CA, USA

Propidium iodide Life Technologies, Carlsbad, CA, USA

Skimmed milk powder Merck, Darmstadt, Germany

Sodium dodecyl sulfate (SDS) Roth, Karlsruhe, Germany

Triton^TM X-100 Sigma-Aldrich, St. Louis, MO, USA

TWEEN^® 20 Sigma-Aldrich, St. Louis, MO, USA

3.3 Enzymes and synthetic peptides

Table 4. Enzymes and synthetic peptides

Description Source

Dispase II Roche, Penzberg, Germany

Oxytocin (OXT) Tocris, Bristol, UK

Trypsin-EDTA, 1x PAA, Linz, Austria

3.4 Kits

Table 5. Kits

Description Source

BC Assay Protein Quantification Kit (Uptima) Interchim, Montlucon, France

Bioplex Cell Lysis Kit Bio-Rad, Hercules, CA, USA

Bioplex Human Cytokine 27-plex Assay Bio-Rad, Hercules, CA, USA

Corticosterone ELISA Kit Enzo Life Sciences, Lörrach, Germany High Capacity cDNA Reverse Transcription Kit Applied Biosystems, Foster City, CA, USA

OXT ELISA Kit Enzo Life Sciences, Lörrach, Germany

ProteoExtract^® Subcellular Proteome Extraction K

(Calbiochem) MerckMillipore, Darmstadt, Germany

RNeasy Mini Kit Qiagen, Hilden, Germany

TaqMan^® Gene Expression Master Mix Applied Biosystems, Foster City, CA, USA

3.5 Primers

Table 6. TaqMan^® Gene Expression Assays, Applied Biosystems, Foster City, CA, USA

Target gene of primer Order number

CCL5 Hs00174575_m1

CRH Hs00384289_g1

CRHR1 Hs00366363_m1

CXCL10 Hs01124251_g1

Cytokeratin 5 Hs00361185_m1

Cytokeratin 10 Hs00166289_m1

Filaggrin Hs00856927_g1

IL6 Hs00985639_m1

Involucrin Hs00846307_s1

Loricrin Hs01894962_s1

OXT Hs00792417_g1

OXTR Hs00168573_m1

Materials 32

18S rRNA Hs99999901_s1

Table 7. TaqMan^® Low Density Array, Applied Biosystems, Foster City, CA, USA

Target gene of primer Order number

ABCC1 Hs00219905_m1

ACTB Hs03023943_g1

AHR Hs00169233_m1

AKR1C1;AKR1C2 Hs00413886_m1

BACH1 Hs00230917_m1

CANX Hs00233492_m1

CAT Hs00156308_m1

COX6B1 Hs00266375_m1

CYP1A1 Hs01054797_g1

CYP1B1 Hs00164383_m1

DPP3 Hs00245841_m1

DUOX2 Hs00204187_m1

FOS Hs99999140_m1

GADD45A Hs00169255_m1

GCLM Hs00978073_m1

GLO1 Hs00198702_m1

GPX1 Hs00829989_gH

GLRX Hs00829752_g1

GSR Hs00167317_m1

GSS Hs00609286_m1

GSTA1 Hs00275575_m1

GSTA3 Hs00374175_m1

GSTP1 Hs00943351_g1

HAGH Hs00193422_m1

HERPUD1 Hs01124269_m1

HMOX1 Hs01110250_m1

HPRT1 Hs99999909_m1

HRAS Hs00978051_g1

HSP90AA1 Hs00743767_sH

HSPA1A;HSPA1B Hs00271229_s1

HSPA4 Hs00382884_m1

HSPA5 Hs99999174_m1

HSPB2 Hs00155436_m1

JUN Hs01103582_s1

KEAP1 Hs00202227_m1

MAFG Hs00361648_g1

MDM2 Hs99999008_m1

NFE2L2 Hs00975960_m1

NFE2L3 Hs00852569_g1

NQO1 Hs00168547_m1

NRF1 Hs00602161_m1

OSGIN1 Hs00203539_m1

PRDX5 Hs00201536_m1

PRDX6 Hs00705355_s1

Materials 34

SOD1 Hs00166575_m1

SOD2 Hs01553554_m1

SQSTM1 Hs00177654_m1

SRXN1 Hs00607800_m1

STIP1 Hs00428979_m1

TXNRD1 Hs00917067_m1

TXNRD2 Hs00272352_m1

3.6 siRNAs

Table 8. siRNAs directed against human proteins and scrambled control siRNA

siRNA Order number Source

siOXTR I ID1859 Life Technologies, Carlsbad, CA, USA

siOXTR II ID1766 Life Technologies, Carlsbad, CA, USA

siOXTR III ID143368 Life Technologies, Carlsbad, CA, USA

scrambled siRNA 1027281 Qiagen, Hilden, Germany

3.7 Specific expendable materials

Table 9. Specific expendable materials

Description Source

Cell culture-inserts, 12-well, 3 µm membrane Falcon, Gräfelfing-Lochham, Germany

Cryomolds^® Leica, Wetzlar, Germany

Dissecting set Aesculap, Hammacher, Germany

Glass chamber slides Thermo Fischer Scientific, Waltham, MA, USA

Pap-Pen EMS, Munich, Germany

Super Frost object slides Menzel-Gläser, Braunschweig, Germany Tissue-Tek^® O.C.T.™ Compound Leica, Wetzlar, Germany

3.8 Specific technical equipments

Table 10. Specific technical equipments

Description Source

ABI 7900H Fast Real-Time PCR System Applied Biosystems, Foster City, CA, USA Axiovert S100 (microscope) Zeiss, Jena, Germany

Axiovert 200M (microscope) Zeiss, Jena, Germany

Bioplex 200 System Bio-Rad, Hercules, CA, USA

Criterion™ blotter Bio-Rad, Hercules, CA, USA

Criterion™ cell Bio-Rad, Hercules, CA, USA

Cryostat Leica CM3050S Leica, Wetzlar, Germany

FACSCanto^TM (flow cytometer) BD Bioscience, Franklin Lakes, NJ, USA IL1700 Research Radiometer International light, Newburyport, MA, USA SAFIRE photometer (microplate reader) Tecan, Männedorf, Switzerland

SP5 (confocal microscope) Leica, Bensheim, Germany Spectra Max 250 photometer (microplate

reader)

Molecular Devices, Sunnyvale, CA, USA

Nanodrop ND-1000 photometer PeqLab, Erlangen, Germany Odyssey Infrared Imaging System Li-cor, Lincoln, NE, USA

Oriel 1600W Newport Corporation, Stratford, CT, USA

Psorisan 900/5164 with H1 filter Dr. Hönle Medizintechnik, Kaufering, Germany

Materials 36

Thermocycler Biozym Scientific, Hessisch Oldendorf,

Germany

Ultrapure water system Milli-Q MerckMillipore, Darmstadt, Germany

3.9 Software

Table 11. Software

Description Source

Adobe Photoshop CS6 Adobe Systems Incorporation, San Jose, CA, USA

Axiovision 4.8 Zeiss, Göttingen, Germany

BD FACSDiva^TM BD Bioscience, Franklin Lakes, NJ, USA

Bioplex Manager 4.1.1 Bio-Rad, Hercules, CA, USA

FlowJo 7.6.3 Tree Star Inc., Ashland, OR, USA

GraphPad Prism 5 GraphPad, San Diego, CA, USA

ImageJ Wayne Rasband, National Institutes of

Health, Bethesda, MD, USA Leica Confocal Software 2.61 Leica, Bensheim, Germany

Microsoft Office 2011 Microsoft, Redmond, WA, USA

ND-1000 V3.3.0 PeqLab, Erlangen, Germany

RQ-Manager 1.2 Applied Biosystems, Foster City, CA, USA

SAFIRE XFluor4 4.51 Tecan, Männedorf, Switzerland

SDS 2.3 Analysis Software Applied Biosystems, Foster City, CA, USA Soft Max Pro Version 2.0.1 Molecular Devices, Sunnyvale, CA, USA

3.10 Cell culture media, buffers and solutions

Table 12. Cell culture media

Media for primary human dermal fibroblast cultures DMEM low Glucose (1 g/l)

Ingredients per 500 ml:

10 % (v/v) FCS 10 µg/ml Glutamax I 50 U/ml Penicillin G

50 µg/ml Streptomycin sulfate

Media for primary human keratinocyte cultures (0.1 mM Ca²⁺) KBM-2 (w/o Ca²⁺)

Ingredients per 500 ml (KGM-2 SingleQuot Kit):

Bovine Pituitary Extract (BPE)

Human Epidermal Growth Factor (hEGF) Insulin

Hydrocortisone Transferrin Adrenalin Gentamicin

Media for organotypic 3-D skin cultures (rFAD) DMEM : Ham’s F12 (3 : 1)

Ingredients per 500 ml:

10 % (v/v) FCS 50 U/ml Penicillin G

50 µg/ml Streptomycin sulfate

Materials 38

4.5 % Ascorbic acid 0.036 % Hydrocortisone

Table 13. Buffers

Running buffer for SDS-PAGE (10x)

250 mM Tris 1.9 M Glycin 0.1 % (v/v) SDS

Blotting buffer for Western Blot (20x)

248 mM Tris

2.5 M NaCl

TBS (10x)

200 mM Tris 1.4 M NaCl TBS-T

10 % (v/v) 10x TBS 0,05 % (v/v) Tween 20

Table 14. Solutions

Fixative solution

50 % ethanol

1 % glacial acetic acid  

4 M ETHODS

Unless otherwise stated, all experiments were conducted according to the manufactorer’s instructions of the reagents and kits that were used in this thesis.

4.1 In vivo studies

All in vivo studies were carried out according to the Declaration of Helsinki and approved by the ethics committees of the Medical Associations at Hamburg, Kiel and Freiburg, Germany.

All study participants gave written informed consent.

4.1.1 Clinical studies to gain healthy and atopic skin samples

Clinical studies were performed to obtain skin cells, suction blister fluids and suction blister roofs from the skin of healthy volunteers and atopic patients.

Punch biopsies were taken from areas located on the forearm of healthy volunteers and from peri-lesional/lesional areas of the forearm of atopic patients. Prior to punching, test arm areas were locally anesthetized. Punch biopsies exhibited a diameter of 6 mm. Afterwards, the biopsies were subjected to isolation of primary human dermal fibroblasts and keratinocytes.

Suction blisters were prepared as described by Kiistala (76). This technique allows the separation of viable epidermis from dermis, applying a negative pressure of 180 mbar for 30 min followed by 320 mbar for 2 to 2.5 h (Figure 7). Subsequently, suction blister fluids and roofs were isolated, immediately frozen in liquid nitrogen and stored at -80 °C. Suction blister fluids were subjected to quantification of OXT concentrations and suction blister roofs to gene expression analyses.

The AD patients, enrolled in these studies, displayed a local SCORAD of 5.8 ± 0.3 on test arm area. Furtermore, ages of healthy (n = 32) and AD (n = 24) participants were equivalent (healthy: 36.6 ± 2.1, atopic: 35.0 ± 1.7 years).

Methods 40

Figure 7. Preparation and isolation of suction blister fluids and roofs.

(a) On two defined areas on the arms of volunteers, suction blisters were raised as described by Kiistala (76) using partial vacuum, thereby mechanically separating the epidermis from the dermis. (b) Suction blisters developed between 2 to 3 h. Suction blister fluids (c) and roofs (d) were isolated. After collection, samples were immediately frozen in liquid nitrogen and stored at -80 °C until further use.

4.1.2 Study of oxytocin release from tactile stimulated skin areas

Suction blister fluids were taken from the inner upper arms of six healthy women and six healthy men at t₀ and t₁. At t₀, no treatment was performed. At t₁, participants caressed themselves with a soft brush every 30 min for 5 min during 3 h around the investigated area (tactile stimulation) leaving the other arm unstimulated (control). To avoid potential differences between body sides, half of the participants tactile stimulated their left arms, whereas the other half stimulated their right arms. Additionally, to ensure that healing of suction blister wounds was completed at each time point, the time interval between t0 and t1

was one month. In order to exclude environmental differences at the time points, the experimental settings of t0 and t1 were simultaneously performed: Half of the women and half of the men were subjected to t₀ whereas the other halfs were subjected to t₁. This was obverted one month later. All participants of this study aged between 20 and 40 years.

Suction blister fluids were collected, immediately frozen in liquid nitrogen and subjected to OXT-ELISA technique to determine OXT concentrations. The Data were analyzed by generating delta-values of OXT concentrations between both arms of each participant.

Afterwards, deltas of OXT concentrations between untreated (t0) and tactile stimulated (t1) participants were compared. A scheme of the study’s experimental setting and data analysis is displayed in Figure 8.

Figure 8. Setting of the experiment to study OXT release triggered by tactile stimuli.

The study included 12 volunteers. Suction blister fluids were taken from the arms of six women and six men at t₀ and t₁. At t₀, no treatment was performed. At t₁, participants stroke themselves with a soft brush every 30 min for 5 min during 3 h around the investigated area (tactile stimulation) leaving the other arm unstimulated (control). Half of the participants tactile stimulated their left arms or their right arms, respectively. The time period between t0 and t1 was one month. The experimental settings of t0

and t₁ were performed in parallel: Half of the women and half of the men were subjected to t₀ whereas the other halfs were subjected to t1. After a month, this setting was reversed. Suction blister fluids were collected and OXT concentrations were measured. The data were analyzed by generating delta- values of OXT concentrations between both arms of each participant. Deltas of OXT concentrations between untreated (t₀) and tactile stimulated (t₁) participants were compared.