University of Bradford Ethesis
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University of Bradford eThesis This thesis is hosted in Bradford Scholars – The University of Bradford Open Access repository. Visit the repository for full metadata or to contact the repository team © University of Bradford. This work is licenced for reuse under a Creative Commons Licence. THE ROLE OF BONE MORPHOGENETIC PROTEIN SIGNALLING IN THE CONTROL OF SKIN REPAIR AFTER WOUNDING Cellular and molecular mechanisms of cutaneous wound healing mediated by bone morphogenetic proteins and their antagonist Noggin Christopher John LEWIS Submitted for the degree of Doctor of Philosophy Medical Biosciences School of Life Sciences University of Bradford 2013 Abstract The role of bone morphogenetic protein signalling in the control of skin repair after wounding. Christopher John LEWIS Keywords: Wound healing, bone morphogenetic protein, BMP, skin, keratinocyte, Noggin, Smad Bone morphogenetic proteins (BMPs) and their receptors (BMPRs) coordinate tissue development and postnatal remodelling by regulating proliferation, differentiation and apoptosis. However, their role in wound healing remains unclear. To study this, transgenic mice overexpressing Smad1 (K14-caSmad1) or the BMP antagonist Noggin (K14-Noggin) were utilised, together with human and mouse ex vivo wound healing models and in vitro keratinocyte culture. In wild-type mice, transcripts for Bmpr-1A, Bmpr-II, Bmp ligands and Smad proteins were decreased following tissue injury, whilst Bmpr-1B expression was up-regulated. Furthermore, immunohistochemistry revealed a down-regulation of BMPR-1A in hair follicles adjacent to the wound in murine skin, whilst in murine and human wounds, BMPR-1B and phospho-Smad-1/5/8 expression was pronounced in the wound epithelial tongue. K14-caSmad1 mice displayed retarded wound healing, associated with reduced keratinocyte proliferation and increased apoptosis, whilst K14-Noggin mice exhibited accelerated wound healing. Furthermore, microarray analysis of K14- caSmad1 epidermis revealed decreased expression of distinct cytoskeletal and ii cell motility-associated genes including wound-associated keratins (Krt16, Krt17) and Myo5a versus controls. Human and mouse keratinocyte proliferation and migration were suppressed by BMP-4/7 both in vitro and ex vivo, whilst they were stimulated by Noggin. Additionally, K14-caSmad1 keratinocytes showed retarded migration compared to controls when studied in vitro. Furthermore, Bmpr-1B silencing accelerated migration and was associated with increased expression of Krt16, Krt17 and Myo5a versus controls. Thus, this study demonstrates that BMPs inhibit proliferation, migration and cytoskeletal re-organization in epidermal keratinocytes during wound healing, and raises a possibility that BMP antagonists may be used for the future management of chronic wounds. iii Acknowledgements I would like to pay special thanks to Professor Vladimir Botchkarev and Dr Natasha Botchkareva for their support and advice throughout this project, and to Professor David Sharpe for his unfailing enthusiasm and support, and for giving me the opportunity to work within the Bradford Plastic Surgery & Burn Research Unit. I would also like to thank Dr Andrei Mardaryev for his support and advice in all of my work, together with his patience. Finally, I would like to thank my wife Emma, for her support and love throughout this work. iv Dedicated to my family, whose sacrifices have made me who I am today Bradford City Football Club 11th May 1985 – You’ll Never Walk Alone v Contents Abstract ................................................................................................ ii Acknowledgements .............................................................................. iv Dedication ............................................................................................ v Contents .............................................................................................. vi List of tables ................................................................................. xi List of figures ................................................................................ xi Abbreviations ................................................................................ xv I. INTRODUCTION 1.1. The skin: a multifunctional organ ............................................ 2 1.2. Anatomy of the skin ................................................................ 3 1.2.1. Epidermis ......................................................................... 3 1.2.2. Dermis ............................................................................. 7 1.3. Molecular regulation of keratinocyte proliferation, differentiation and apoptosis in postnatal epidermis ..................................... 10 1.3.1. p63 transcription factor ..................................................... 10 1.3.2. Regulation of keratinocyte proliferation in the epidermis ... 12 1.3.3. Regulation of postnatal epidermal differentiation .............. 14 1.3.4. Regulation of keratinocyte apoptosis in the epidermis ...... 16 1.4. The hair follicle ....................................................................... 17 1.5. Hair follicle development and hair cycling ............................... 20 vi 1.6. The pathophysiology of wound healing ................................... 24 1.6.1. The haemostatic phase .................................................... 27 1.6.2. The inflammatory phase ................................................... 30 1.6.3. The proliferative phase ..................................................... 32 1.6.4. The remodelling phase ..................................................... 37 1.7. The molecular regulation of wound healing............................. 39 1.7.1. Transcriptional regulation of re-epithelialization ................ 39 1.7.2. Transcriptional regulation of acute inflammation ............... 41 1.7.3. Transcriptional regulation of skin remodelling ................... 42 1.8. Hair follicles and wound healing ............................................. 44 1.9. Bone morphogenetic proteins ................................................. 52 1.9.1. BMP structure and subgroups .......................................... 53 1.9.2. BMP receptors and signalling cascades ........................... 54 1.9.3. BMP antagonists .............................................................. 58 1.9.4. BMPs in skin development and postnatal remodelling ...... 60 1.9.5. The role of BMPs in hair follicle embryogenesis................ 62 1.9.6. The role of BMPs in hair cycle regulation .......................... 65 1.9.7. The role of BMPs in wound healing .................................. 66 RESEARCH AIMS ........................................................................ 72 II. MATERIALS AND METHODS 2.1. Animals and tissue collection ................................................. 75 2.2. Isolation and culture of primary mouse keratinocytes.............. 77 vii 2.3. Cell line culture ...................................................................... 78 2.4. Cell treatment with BMP-4/7 and Noggin ................................ 79 2.5. Cell transfection ..................................................................... 80 2.6. Cell proliferation assay ........................................................... 80 2.7. Flow cytometric cell cycle analysis ......................................... 81 2.8. Transwell migration assay ...................................................... 82 2.9. Mouse explant migration model .............................................. 83 2.10. Scratch migration assay ....................................................... 85 2.11. Human ex vivo wound healing model ................................... 86 2.12. Immunohistochemistry.......................................................... 88 2.13. Phalloidin staining ................................................................ 89 2.14. Alkaline phosphatase staining .............................................. 90 2.15. Quantitative wound histomorphometry .................................. 91 2.16. RNA isolation and cDNA synthesis ....................................... 92 2.17. Quantitative real-time PCR analysis ..................................... 93 2.18. Microarray analysis .............................................................. 95 III. RESULTS 3.1. BMP pathway components display a dynamic expression profile during wound healing .................................................. 98 3.2. Histomorphological analysis of wound healing in wild-type, K14-caSmad1 and K14-Noggin mouse models ....................... 103 3.3. Expression of injury-induced keratins and keratinocyte morphology in control and transgenic wounds ........................ 112 viii 3.4. Global microarray analysis reveals changes in the expression of cytoskeletal and cell migration-associated genes in the epidermis of K14-caSmad1 mice ............................................ 116 3.5. BMP signalling suppresses in vitro human and mouse keratinocyte proliferation ........................................................ 121 3.6. BMP signalling slows in vitro and ex vivo keratinocyte migration ................................................................................ 131 3.7. BMPRs differentially modulate keratinocyte migration in vitro . 137 3.8. BMPR-1B signalling regulates expression of migration-related genes ..................................................................................... 140 3.9. Human skin heals and exhibits