Articular cartilage damage and degeneration is a siginficant clinical problem which no technique has been able to adequately and reliably repair or regenerate. Recent research has investigated the use of cell-based therapies to treat focal cartilage lesions. In clinical practice proliferated autologous chondrocytes are used and clinical trials are investigating the use of mesenchymal stem cells. The aim of this thesis was to assess aspects of current cell-based therapy and to investigate the potential of perivascular stem cells for articular cartilage repair. The phenotype of expanded matrix-applied autologous chondrocytes utilised in current cell therapies was confirmed using immunocytochemistry and polymerase chain reaction (PCR) expression of hyaluronan and proteoglycan link protein 1 (HAPLN1), transcription factor sox-9 (SOX9) and aggrecan (ACAN). Quantitative real-time PCR demonstrated that they were down-regulated for expression of COL2A1, SOX9 and ACAN but up-regulated for COL1A1 compared to unproliferated chondrocytes. Confocal laser-scanning microscopy (CLSM) demonstrated a significant decrease in cell viability and density when the membranes were subjected to levels of trauma similar to those that could be experienced during surgery. Hyperosmolar solutions did not confer a chondroprotective effect. Pericytes and adventitial cells, collectively termed perivascular stem cells (PSCs), from the infra-patellar fat pad were identified using immunohistochemistry and isolated using enzymatic digestion and fluorescence-activated cell sorting (FACS). Cell identity was ascertained using PCR, FACS and mesenchymal differentiation (osteogenesis, adipogenesis and chondrogenesis). Quantitative real-time PCR analysis of micromass cultures indicated that PSCs displayed increased chondrogenic potential compared to mesenchymal stem cells. An ovine model of perivascular stem cells was developed and a pilot study using three sheep was undertaken to confirm the viability of the model. Autologous ovine PSCs were isolated and re-implanted into articular cartilage defects. Green fluorescent protein transfected cells were identified in the cartilage defect four weeks following re-implantation using CLSM. This thesis has examined aspects of matrix-applied autologous chondrocyte implantation for cell based cartilage repair and has identified a new source of prospectively identified and purified stem cells that have demonstrated increased chondrogenic potential compared to mesenchymal stem cells, which are commonly used in clinical research. The methods to identify and purify ovine perivascular stem cells were developed to investigate the use of autologous PSCs and to track the cells following implantation.

Osteoarthritis (OA) is a common disease with a strong genetic component. Despite this, previous attempts to identify genetic variants that predispose to OA have met with limited success. Recently, the results of a large genome wide association study in OA has identified a novel susceptibility locus on chromosome 3 tagged by two SNPs, rs11177 (p=1.25x10-10) which lies within the coding region of GNL3 and rs6976 (p=7.24x10-11) situated in the 3’UTR of GLT8D1. The GNL3 gene encodes the protein nucleostemin which is found within the nucleolus of stem cells and tumour cells. It functions to regulate cell cycle progression, embryogenesis, tumorigenesis, tissue regeneration and ribosome biogenesis but its role in the joint is unknown. In an attempt to identify the causal variant(s) at locus 3p21.1 I conducted a mutation screen of GNL3 which identified a common non-synonymous coding variant, rs2289247, which was in strong LD (r2=0.92) with rs11177, as well as several other variants. Localisation studies showed that GNL3 was expressed at the mRNA and protein level in several joint tissues. While levels of mRNA expression were found to be significantly higher in human articular chondrocytes from OA patients as compared with controls, levels of GNL3 protein were significantly lower in OA chondrocytes than controls. Further studies showed that cytokines which have been implicated in the pathogenesis of OA such as IL1β, IL13, TNFα and FGF2 had no effect on GNL3 mRNA in cartilage. Knockdown of GNL3 using siRNA in articular chondrocytes and the chondrosarcoma cell line, JJ012, did not alter the mRNA expression of chondrogenic markers; COL2A, ACAN, MMP3, MMP13, RUNX2 and SOX9. Cultures of mesenchymal stem cells and articular chondrocytes from patients of different rs11177 genotypes, showed no difference in chondrogenic potential. Furthermore, genotypes at rs11177 and rs2289247 did not influence the expression of p53, MDM2 or GNL3 in response to stressful stimuli, including cisplatin and hypoxia, when cloned into a melanoma cell line. Studies of zebrafish carrying a loss of function mutation in gnl3 revealed a significant reduction in cartilage volume and an alteration in cartilage structure, as evident by a reduced number of chondrocytes, disorganised stacking and an increase in cartilage extracellular matrix in the mutant fish. This research has shown that gnl3 plays a vital role in chondrogenesis in zebrafish and has shown evidence of dysregulation of GNL3 expression in OA human articular chondrocytes. The in vitro studies failed to identify any specific effects of the variants rs11177 and rs2289247 on GNL3 expression, chondrogenesis or p53 stress response although, it remains possible that the variants may have modest effects that were not detected by the assays used. The zebrafish studies illustrate that gnl3 plays a critical role in normal cartilage development however further studies on GNL3 in OA would be of interest.

Cheuk, Yau Chuk. / Thesis submitted in: Dec 2008. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 132-144). / Abstracts in English and Chinese. / ABSTRACT --- p.i / 論文摘要 --- p.iii / PUBLICATIONS --- p.v / ACKNOWLEDGEMENT --- p.vi / LIST OF ABBREBIVIATIONS --- p.vii / INDEX FOR FIGURES --- p.x / INDEX FOR TABLES --- p.xiv / TABLE OF CONTENTS --- p.xv / Chapter CHAPTER ONE - --- INTRODUCTION / Chapter 1.1 --- "Joint function, structure and biochemistry" / Chapter 1.1.1 --- Function of joint --- p.1 / Chapter 1.1.2 --- Types of cartilage --- p.1 / Chapter 1.1.3 --- Composition and structure of articular cartilage --- p.2 / Chapter 1.1.4 --- The subchondral bone --- p.3 / Chapter 1.1.5 --- Maturation of articular cartilage and subchondral bone --- p.3 / Chapter 1.2 --- Osteochondral defect / Chapter 1.2.1 --- Clinical problem --- p.6 / Chapter 1.2.2 --- Spontaneous repair --- p.7 / Chapter 1.2.3 --- Current treatment strategies --- p.7 / Chapter 1.2.4 --- Limitations of current treatment strategies --- p.8 / Chapter 1.2.5 --- Treatments under development --- p.11 / Chapter 1.2.6 --- Potential and limitations in cell therapies --- p.14 / Chapter 1.3 --- The 3-D scaffold-free cartilage / Chapter 1.3.1 --- Fabrication of scaffold-free cartilage --- p.16 / Chapter 1.3.2 --- Scaffold-free cartilage for chondral / osteochondral defect repair --- p.18 / Chapter 1.3.3 --- Scaffold-free bioengineered chondrocyte pellet from our group --- p.20 / Chapter 1.3.4 --- BCP as a possible treatment for OCD --- p.21 / Chapter 1.4 --- The objectives of the study --- p.22 / Chapter 1.5 --- The study plan / Chapter 1.5.1 --- Design of the study --- p.23 / Chapter 1.5.2 --- Choice of animal model --- p.23 / Chapter 1.5.3 --- Selection of evaluation time points --- p.24 / Chapter 1.5.4 --- Choice and modification of histological scoring system --- p.24 / Chapter CHAPTER TWO - --- METHODOLOGY / Chapter 2.1 --- Preparation of reagents and materials for tissue culture and histology --- p.26 / Chapter 2.2 --- Creation of osteochondral defect model --- p.28 / Chapter 2.3 --- Synthesis of scaffold-free cartilage using 3-D chondrocyte pellet culture / Chapter 2.3.1 --- Isolation of rabbit costal chondrocytes --- p.31 / Chapter 2.3.2 --- Three-dimensional chondrocyte pellet culture --- p.31 / Chapter 2.3.3 --- BrdU labeling for cell fate tracing --- p.32 / Chapter 2.4 --- Further characterization of the 3-D scaffold-free chondrocyte pellet / Chapter 2.4.1 --- Gross appearance --- p.35 / Chapter 2.4.2 --- Cell viability / Chapter 2.4.2.1 --- Alamar blue reduction assay --- p.35 / Chapter 2.4.3 --- Preparation of samples for histology --- p.36 / Chapter 2.4.4 --- General morphology and histomorphology / Chapter 2.4.4.1 --- H&E staining --- p.36 / Chapter 2.4.5 --- Cartilage properties / Chapter 2.4.5.1 --- Safranin O /Fast Green staining --- p.37 / Chapter 2.4.5.2 --- Immunohistochemistry of type II collagen --- p.37 / Chapter 2.4.5.3 --- Immunohistochemistry of type I collagen --- p.38 / Chapter 2.4.6 --- Angiogenic properties / Chapter 2.4.6.1 --- Immunohistochemistry of VEGF --- p.40 / Chapter 2.4.7 --- Osteogenic properties / Chapter 2.4.7.1 --- ALP staining --- p.40 / Chapter 2.5 --- Implantation of scaffold-free cartilage into osteochondral defect model / Chapter 2.5.1 --- Surgical procedures --- p.41 / Chapter 2.5.2 --- Experimental groups --- p.42 / Chapter 2.6 --- Assessment of osteochondral defect healing / Chapter 2.6.1 --- Macroscopic evaluation --- p.43 / Chapter 2.6.2 --- Preparation of samples for histology --- p.43 / Chapter 2.6.3 --- Histology for general morphology / Chapter 2.6.3.1 --- H&E staining --- p.45 / Chapter 2.6.4 --- Histological scoring / Chapter 2.6.4.1 --- Modification of the scoring system --- p.45 / Chapter 2.6.4.2 --- Procedures of scoring and validation --- p.45 / Chapter 2.6.5 --- Cell proliferation / Chapter 2.6.5.1 --- Immunohistochemistry of PCNA --- p.49 / Chapter 2.6.6 --- Cartilage regeneration / Chapter 2.6.6.1 --- Safranin O /Fast Green staining --- p.49 / Chapter 2.6.6.2 --- Immunohistochemistry of type II collagen --- p.49 / Chapter 2.6.6.3 --- Immunohistochemistry of type I collagen --- p.50 / Chapter 2.6.6.4 --- Polarized light microscopy --- p.50 / Chapter 2.6.7 --- Expression of angiogenic factor / Chapter 2.6.7.1 --- Immunohistochemistry of VEGF --- p.50 / Chapter 2.6.8 --- Bone regeneration / Chapter 2.6.8.1 --- μCT analysis --- p.50 / Chapter 2.6.9 --- Histomorphometric analysis of cartilage and bone regeneration --- p.53 / Chapter 2.6.10 --- BrdU detection for cell fate tracing --- p.55 / Chapter 2.6.11 --- Statistical analysis --- p.55 / Chapter CHAPTER THREE - --- RESULTS / Chapter 3.1 --- Further characterization of the 3-D chondrocyte pellet culture / Chapter 3.1.1 --- Gross examination --- p.57 / Chapter 3.1.2 --- Cell viability --- p.57 / Chapter 3.1.3 --- Cartilage properties --- p.61 / Chapter 3.1.4 --- Angiogenic properties --- p.63 / Chapter 3.1.5 --- Osteogenic properties --- p.64 / Chapter 3.2 --- Implantation of scaffold-free cartilage and assessment / Chapter 3.2.1 --- Gross examination --- p.65 / Chapter 3.2.2 --- General morphology --- p.67 / Chapter 3.2.3 --- Histological scores --- p.71 / Chapter 3.2.4 --- Cell proliferation --- p.75 / Chapter 3.2.5 --- Cartilage regeneration --- p.78 / Chapter 3.2.6 --- Expression of angiogenic factor --- p.90 / Chapter 3.2.7 --- Bone regeneration --- p.93 / Chapter 3.2.8 --- Histomorphometric analysis on cartilage and bone regeneration --- p.96 / Chapter 3.2.9 --- Cell fate tracing --- p.100 / Chapter CHAPTER FOUR - --- DISCUSSION / Chapter 4.1 --- Summary of key findings / Chapter 4.1.1 --- Further characterization of BCP and determination of implantation time --- p.102 / Chapter 4.1.2 --- Implantation of BCP in OCD --- p.102 / Chapter 4.2 --- Spontaneous healing in osteochondral defect / Chapter 4.2.1 --- Findings from the current study --- p.104 / Chapter 4.2.2 --- Comparison with other studies --- p.104 / Chapter 4.2.3 --- Factors affecting spontaneous healing --- p.105 / Chapter 4.3 --- Fabrication and further characterization of the 3-D chondrocyte pellet / Chapter 4.3.1 --- Comparison of different methods of producing scaffold-free cartilage construct --- p.106 / Chapter 4.3.2 --- Cartilage phenotype of the BCP --- p.107 / Chapter 4.3.3 --- Angiogenic and osteogenic potential of the BCP --- p.108 / Chapter 4.3.4 --- Role of mechanical stimulation on tissue-engineered cartilage --- p.109 / Chapter 4.4 --- Repair of osteochondral defect with allogeneic scaffold-free cartilage / Chapter 4.4.1 --- Advantages of the current scaffold-free chondrocyte pellet --- p.111 / Chapter 4.4.2 --- Remodeling of BCP after implantation --- p.111 / Chapter 4.4.3 --- Effect of BCP on cartilage repair --- p.112 / Chapter 4.4.4 --- Effect of BCP on bone regeneration / Chapter 4.4.4.1 --- Findings in the present study --- p.113 / Chapter 4.4.4.2 --- Possible reasons of slow bone repair --- p.114 / Chapter 4.4.4.3 --- Effect of BCP on bone region peripheral to defect --- p.115 / Chapter 4.4.5 --- Immunorejection-free properties of the BCP --- p.116 / Chapter 4.4.6 --- Comparison with other animal studies using scaffold-free cartilage --- p.117 / Chapter 4.4.7 --- Possibility of implanting a BCP cultured for shorter or longer period --- p.118 / Chapter 4.4.8 --- Scaffold-free cartilage construct and construct with scaffold for OCD repair --- p.119 / Chapter 4.4.9 --- Chondrocytes and stem cells for OCD repair --- p.120 / Chapter 4.5 --- Limitations of the study / Chapter 4.5.1 --- Animal model --- p.122 / Chapter 4.5.2 --- Histomorphometric analysis --- p.122 / Chapter 4.5.3 --- Lack of quantitative data analysis --- p.122 / Chapter 4.5.4 --- BrdU labeling of cells --- p.123 / Chapter 4.5.5 --- Lack of biomechanical test --- p.123 / Chapter 4.5.6 --- Small sample size --- p.123 / Chapter CHAPTER FIVE - --- CONCLUSION --- p.124 / Chapter CHAPTER SIX - --- FUTURE STUDIES / Chapter 6.1 --- Identification of factors affecting bone repair after OCD treatment --- p.125 / Chapter 6.2 --- Modifications of BCP treatment --- p.125 / Chapter 6.3 --- Alternative cell source --- p.126 / Chapter 6.4 --- Alternative cell tracking methods --- p.126 / Chapter 6.5 --- Inclusion of biomechanical test --- p.126 / APPENDICES / Appendix 1. Conference paper 1 --- p.129 / Appendix 2: Conference paper 2 --- p.130 / Appendix 3: Animal experimentation ethics approval --- p.131 / BIBLIOGRAPHY --- p.132

ShcA (Src Homology and Collagen A) est une protéine adaptatrice qui se lie à la partie cytoplasmique de LRP1 (Low Density Lipoprotein-related receptor 1), un récepteur transmembranaire qui protège contre l'athérosclérose. La calcification vasculaire est une complication majeure de cette maladie et ses mécanismes ressemblent au processus d’ostéochondrogenèse. Nous avons étudié le rôle de ShcA endothélial dans la formation des lésions d’athérosclérose ainsi que les rôles de ShcA et LRP1 dans la chondrogenèse. ShcA endothélial participe à la formation des lésions d’athérosclérose in-vivo. En inhibant la NOS endothéliale et activant l’expression de ICAM-1 via ZEB1, ShcA favorise l’adhésion des monocytes. La suppression de ShcA dans les chondrocytes a conduit au développement de souris présentant un phénotype de nanisme par une inhibition de la différenciation hypertrophique des chondrocytes. Ceci conduit également à une diminution du développement de l’arthrose liée au vieillissement. La suppression de LRP1 dans les chondrocytes conduit également à un phénotype de nanisme chez la souris, mais par des mécanismes différents. / ShcA (Src Homology and Collagen A) is an adaptor protein that binds to the cytoplasmic tail of the Low Density Lipoprotein-related receptor1 (LRP1), a trans-membrane receptor that protects against atherosclerosis. Vascular calcification is a major complication of this disease and its mechanisms highly resemble the process of osteochondrogenesis. We studied the role of endothelial ShcA in atherosclerotic lesion formation as well as the roles of ShcA and LRP1 in chondogenesis. Endothelial ShcA participates in the formation of atherosclerotic lesions in-vivo. By inhibiting endothelial NOS and activating the expression of ICAM-1 via ZEB1, ShcA enhances monocyte adhesion. The deletion of ShcA in chondrocytes led to the development of mice with a dwarfism phenotype by inhibiting chondrocyte hypertrophic differentiation. This also led to a decrease in the development of age-related osteoarthritis. The deletion of LRP1 in chondrocytes also led to a dwarfism phenotype in our mouse model, but trough different mechanisms.

While mechanical loading is essential for articular cartilage homeostasis, it also plays a central role in the etiology of osteoarthritis. The mechanotransduction events underlying these dual effects, however, remain unclear. Previously, we have shown that lethal amounts of reactive oxygen species (ROS) were liberated from mitochondrial complex 1 in response to a mechanical insult. The sensitivity of this response to an actin polymerase inhibitor, cytochalasin B, indicated a link between ROS release and cytoskeletal distortion caused by excessive compressive strain. It did not, however, rule out the possibility that ROS may also mediate the beneficial effects of normal stresses that induce lower tissue strains required for proper homeostasis. If this possibility is true, one would expect the amount of ROS released in loaded cartilage to be positively correlated with the level of strain, and ROS should only reach lethal levels under super-physiological deformations. To test this hypothesis, full cartilage tissue strains were measured in cartilage explants subjected to static normal stresses of 0, 0.1, 0.25, 0.5, and1.0 MPa. After compression, the percentage of ROS-producing cells was measured using the oxidation-sensitive fluorescent probe, dihydroethidium, and confocal microscopy. In support of our theory, the percentage of fluorescing cells increased linearly with increasing strains (0-75%, r2 = 0.8, p < 0.05). Additionally, hydrostatic stress, which causes minimal tissue strain, induced minimal ROS release. In terms of cell viability, cartilage explants compressed with strains >40% experienced substantial cell death, while explants with strains

Articular cartilage underwent serious joint injuries seldom repair spontaneously and might progress to post-traumatic osteoarthritis. This is majorly because articular cartilage’s unique properties that lack blood and nerve supply intrinsically. This peculiar structure, in addition, generates an unfavorable environment for certain phagocytes (macrophages, monocytes, neutrophils, etc) to infiltrate to cartilage to scavenge debris from cartilage matrix and cell caused from joint injuries. Therefore, physiological and functional regeneration of damaged cartilage is urgently needed and several clinical techniques have been developed, including microfracture, autograft transplantation, autologous chondrocytes implantation. We previously identified highly migratory cells emerged and repopulated in cartilage damaged surface after ~10 days of artificial cartilage injury. These cells were later named chondrogenic progenitor cells (CPCs) due to their enhanced potential of chondrogenic differentiation. However, this important finding contrasts the conventional theory that cartilage harbors only one cell type, chondrocytes. Here we hypothesize that CPCs are a distinct cell type in cartilage, and more importantly, one of CPCs’ crucial natures is to phagocytose debris more effectively than chondrocytes. To test these, we first harvested CPCs from cartilage surfaces, chondrocytes, synovial cells (synoviocytes and synovial fluid cells) for microarray assay to evaluate the closeness among these joint cells on whole gene expression level. Quantitative PCR were then conducted to verify gene expression of certain functional interests. Moreover, debris from cell and extracellular matrix were generated and incubated with CPCs and chondrocytes to compare their phagocytic capacity via multiple experimental assessments. In confocal microscopy examination, the emergence of CPCs could be clearly observed after cartilage injury. Aside from their distinguishable morphology compared to chondrocyte, CPCs possess several vital properties including highly migratory, chemotactic, clonogenic. Microarray data revealed that CPCs, from gene expression profile, are distinctively isolated from chondrocytes and are more akin to synovial cells. Additionally, the series of phagocytosis related experiments showed that CPCs are dramatically superior to chondrocytes in engulfing debris, along with enhanced lysosomal activities indicating the following debris degradation. Taken all these data together, CPCs, activated by cartilage injury, emerged and migrated to damaged sites. They are a distinct cell type residing in cartilage apart from chondrocytes. Their enhanced capacity to sustainably phagocytose and clear debris provides a novel insight for cartilage regeneration and prevention of osteoarthritis.

Articular cartilage is an avascular, aneural, and alymphatic tissue with a structure consisting of a superficial, a middle and a deep zone, overlie a calcified zone at the cartilage border between. Each zone has biological and mechanical properties. Self-repair of damaged cartilage seldom if ever occurs, and joint injuries that harm cartilage surfaces often result in osteoarthritis. This has prompted researchers to explore diverse approaches to cartilage regeneration. The superficial zone shows the highest cellularity and the lowest matrix density. Cartilage cells (chondrocytes) residing in the superficial zone had been thought to be a subpopulation of chondrocytes. However, our laboratory identified a second population of cells that were distinguishable from chondrocytes based on their clonogenicity, multipotency, migratory activity, higher proliferate rate and substantial morphological differences. These cells later proved to be chondrogenic progenitor cells (CPCs). Our continuing studies have shown that CPCs are less chondrogenic than normal chondrocytes and their function is to protect the cartilage surface rather than to regenerate cartilage matrix as previously supposed. In addition, we found evidence to suggest that CPCs act as pro-inflammatory cells in the context of cartilage injury. For these reasons, we undertook a more comprehensive comparison of the phenotypic differences between CPCs and normal chondrocytes and between CPCs and joint cells (tissue synoviocytes from the joint capsule and cells present in synovial fluid) which have been shown to be play roles in joint inflammation. Gene expression microarray analysis of >25,000 genes revealed that the overall pattern of gene expression in CPCs was distinct from normal chondrocytes, but closely related to synoviocytes and synovial fluid cells. Analysis of specific genes by quantitative PCR (qPCR) showed profound differences between CPCs and normal chondrocytes in terms of cartilage matrix gene expression (Collagen Type ІІ, Aggrecan, Link Protein and COMP) and pro-inflammatory gene expression (IL6, IL8, CCL2 and CXCL12). In contrast, the pattern of CPC gene expression closely resembled. Sulfated glycosaminoglycan assays revealed that cartilage matrix deposition by CPCs, as well as synoviocytes and synovial fluid cells, was significantly inferior to normal chondrocytes. However, chondrogenic and osteogenic differentiation assays, showed no significant differences among the four cell types. In addition to establishing that CPCs are distinct from chondrocytes, this work suggests significant revisions to our understanding of CPC function in cartilage. The weak chondrogenic ability and higher expression of inflammatory cytokines, suggests these cells don't play a regenerative role as previously thought. On the other, we found evidence that CPCs may form a protective layer on the top of the injured cartilage surfaces, preventing further cartilage injury. In vivo studies are needed to fully elucidate the significance of these roles in cartilage health and disease.

Lysophosphatidic acid (LPA) is the simplest of the glycerol lipids and regulates a number of cellular processes such as morphological changes, migration, proliferation, and inhibition of apoptosis. LPA exerts these effects through activation of the G-protein coupled receptors (GPCRs) LPA1-6 and the intracellular fatty acid receptor peroxisome proliferator-activated receptor-gamma (PPARγ). The overall goal of this thesis was to determine the mechanisms by which LPA enhances cell survival by inhibiting apoptosis. The project was divided into three studies: 1) to determine the mechanism of LPA-mediated inhibition of p53 in A549 lung carcinoma cells, 2) to investigate the regulation of growth plate chondrocytes by LPA, and 3) to determine the mechanisms of LPA-mediated effects in the growth plate. In the first study, evidence is provided that LPA reduces the cellular abundance of the tumor suppressor p53 in A549 lung carcinoma cells. The LPA effect depends upon increased proteasomal degradation of p53 and it results in a corresponding decrease in p53-mediated transcription. The result of LPA-mediated inhibition of p53 in A549 cells is enhanced resistance to chemotherapeutic-induced apoptosis. In the second study, the role of LPA in resting zone chondrocytes (RC cells) was investigated. RC cells are regulated by 24,25-dihydroxyvitamin D3 [24,25(OH)[subscript2]D [subscript 3]] via a phospholipase D-dependent pathway, suggesting downstream phospholipid metabolites are involved. In this study, we showed that 24R,25(OH)[subscript 2]D[subscript 3] stimulates rat costochondral RC cells to release LPA. Additionally, we demonstrated that RC cells respond to LPA with increased proliferation, maturation, and inhibition of apoptosis. In the final study, the mechanism of LPA and 24R,25(OH)[subscript 2]D[subscript 3]-mediated inhibition of chondrocyte apoptosis was further investigated. Our data show that 24R,25(OH)[subscript 2]D[subscript 3] inhibits apoptosis through Ca⁺⁺, PLD, and PLC signaling and through LPA/Gαi/PI[subscript 3]K/mdm2-mediated degradation of p53, resulting in decreased caspase-3 activity. Collectively, our data establish LPA, vitamin D, and p53 as an anti-apoptotic signaling axis.

Background: The clinical development of advanced therapy medicinal products (ATMPs), a new class of drugs, requires initial safety studies that deviate from standard non-clinical safety protocols. The study provides a strategy to address the safety aspects of biodistribution and tumorigenicity of ATMPs under good laboratory practice (GLP) conditions avoiding cell product manipulation. Moreover, the strategy was applied on a human ATMP for cartilage repair.

Summary Juliane Schneevoigt „Investigation of time- and pressure-dependent expression of different components of the extracellular matrix by chondrocytes in vitro” Institute of Anatomy, Histology and Embryology of the University of Leipzig Submitted in June 2015 98 pages, 34 figures, 41 tables, 153 references keywords: cartilage, chondrocytes, hydrostatic pressure, bioreactor, qPCR Introduction Hyaline cartilage maintains the basic function of transmitting articular pressure load within synovial joints and therefore provides the basis for the movements of an organism. Being a small coverage of the joint surface, it shows a composition designed to match this function specifically. A high amount of proteoglycans and its associated water determines the elastic formability of the hyaline cartilage which allows the absorbance of pressure and shear forces. These proteoglycans, mainly based on aggrecan as core-protein, are embedded into a meshwork of collagen fibres, primarily formed of collagen type II. This composition is not to be understood as a static construct; moreover it is exposed to biophysical forces that permanently require a dynamic adaptation. This adaptation of the extracellular matrix formed by proteoglycans and collagen type II is organised by a small number of embedded chondrocytes, the cells of the hyaline cartilage. As chondrocytes are post-mitotic cells and due to the lack of vascularisation within hyaline cartilage, there is hardly any chance for regeneration of defects in order to maintain the integrity of the tissue. The resulting replacement is formed as fibrocartilage, which has not the capability to withstand the biodynamical forces within the joint. As these defects in hyaline cartilage represent a gross of the diseases of the musculoskeletal system, there is a high medical interest in the development of innovative cell-based therapies, as autologous chondrocyte transplantation (ACT) is one. With this type of therapy in vitro cultivated chondrocytes are seeded into a cartilage defect with the aim of producing hyaline cartilage. Aims of the study In the last decades the need for a detailed understanding of the biodynamics of cartilage became obvious for further development of therapies. The aim of this study was therefore to establish a cell culture system to provide an insight into the biodynamics of chondrocytes. Aside from the examination of the differentiation of in vitro cultivated chondrocytes and their synthesis of extracellular matrix as a function of the cultivation time, another aim of this study was to determine whether the application of hydrostatic pressure might have beneficial influence on the expression of extracellular matrix components by chondrocytes in vitro, in accordance with the hyaline cartilage. Material and methods Human articular chondrocytes were cultivated in vitro without the application of hydrostatic pressure in the first place. The cells were observed phase contrast microscopically and the distribution of collagen type I and II was detected immuncytochemically. In further experiments optical confluent chondrocytes were transferred to a bioreactor system applying a hydrostatic pressure of 5 or 10 bar with variable time periods of the pressure applied. Subsequently, the expression of collagen type I, collagen type II and aggrecan was investigated and quantified using qPCR and Western Blot. Chondrocytes cultivated exclusively without the application of hydrostatic pressure served as controls. In this pilot-study the samples were analysed using arithmetic mean and standard deviation to evaluate the power statistically. In addition, similar test conditions with marginal differences were pooled and the necessary sample size to meet a power of 80 % with an alpha error of 0.05 was calculated using the maximum potential standard deviation. In cases where this statistic power was obtained, an analysis of significance (\"One Way Analysis of Variance”) was carried out meeting a significance level under 0.05. Results During the cultivation of chondrocytes in vitro without hydrostatic pressure the length of the cultivation time did neither show an effect on the phase contrast microscopical morphology nor on the immuncytochemically detected distribution of collagen typ I and II. The application of increased hydrostatic pressure for 24 hours results in a 0.2-0.8-fold decrease of the expression of collagen type I and II and a 1.7-2.2-fold increase of aggrecan expression compared to the unloaded controls. This effect was more distinct with 5 bar but was accompanied by instabilities in the cell culture. This is why further investigations concentrated on the use of 10 bar pressure with subsequently shortened time period of the applied pressure. With short times of loading (1.5 and 3 hours) a pressure load of 10 bar led to a 0.8 fold decrease of the expression of collagen type I and II and showed a 1.6-2.4 fold increase of aggrecan expression. These qPCR results were supported by the protein expression of collagen type I, II and aggrecan detected in Western Blot. Conclusions A cell culture system was established to examine the effect of hydrostatic pressure on the expression of chondrocytes on the one hand, which can further be modified for the assembly of cell transplants on the other hand. Subsequently the results of this study led to a definition of cell culture conditions, stimulating the extracellular matrix production of chondrocytes towards the composition of hyaline cartilage. This was the case using a seeding density of 104 cells/cm2 and a pre-cultivation time of 6 days of normal pressure, followed by the application of 10 bar hydrostatic pressure for 1.5-3 h. With the help of this pilot-study a cell culture system was established to gain more information on biodynamics of hyaline cartilage. Moreover it is possible that this information will provide a basis for further development of cell based therapies of cartilage defects, such as ACT. / Zusammenfassung Juliane Schneevoigt „Untersuchung der zeit- und druckabhängigen Expression verschiedener Komponenten der extrazellulären Matrix durch Chondrozyten in vitro“ Veterinär-Anatomisches Institut der Veterinärmedizinischen Fakultät der Universität Leipzig Eingereicht im Juni 2015 98 Seiten, 34 Abbildungen, 41 Tabellen, 153 Literaturangaben Schlüsselwörter: Knorpel, Chondrozyten, hydrostatischer Druck, Bioreaktor, qPCR Einleitung Der hyaline Knorpel gewährleistet die grundlegende Funktion der Druckübertragung innerhalb der synovialen Gelenke und stellt somit die Grundlage für die Bewegung des Organismus dar. Als schmaler Überzug der Gelenkflächen ist er in seinem Aufbau an diese Funktion spezifisch angepasst. Dabei bedingt der hohe Gehalt an Proteoglykanen und das an diese assoziierte Wasser die elastische Verformbarkeit des hyalinen Knorpels, die es ermöglicht, Druck- und Scherkräfte abzufedern. Die Proteoglykane, die hauptsächlich auf Aggrekan als Kernprotein basieren, sind in ein Maschenwerk kollagener Fasern eingelagert, welches im Wesentlichen durch Kollagen Typ II gebildet wird. Diese Zusammensetzung darf nicht als statisches Konstrukt verstanden werden. Vielmehr ist der hyaline Knorpel in vivo verschiedenen biophysikalischen Einflüssen ausgesetzt, die eine dynamische Anpassung erfordern. Solche Anpassungsvorgänge in Form einer Änderung der Zusammensetzung der aus kollagenen Fasern und Proteoglykanen bestehenden extrazellulären Matrix werden durch die wenigen eingelagerten Chondrozyten, die Zellen des hyalinen Knorpels, organisiert. Da die reifen Chondrozyten jedoch keine Zellteilungen aufweisen und dem hyalinen Knorpel eine Vaskularisierung fehlt, ist eine Defektregeneration kaum möglich, sodass eine Wiederherstellung der Integrität des Gewebes unterbleibt und stattdessen ein Ersatzknorpel, der Faserknorpel, gebildet wird, welcher den einwirkenden biodynamischen Belastungen jedoch nicht standhalten kann. Da die Defekte des hyalinen Knorpels einen Großteil der Erkrankungen des Bewegungsapparats darstellen und zudem die Arthrose als Langzeitfolge nach sich ziehen, besteht ein hohes medizinisches Interesse an der Entwicklung zellbasierter Therapieansätze, wie der Autologen Chondrozytentransplantation (ACT). Hierbei werden - bislang mit unterschiedlichen Erfolgen – in vitro kultivierte Chondrozyten mit dem Ziel, neuen hyalinen Knorpel zu bilden, in einen Knorpeldefekt eingebracht. Ziele der Untersuchungen In den letzten Jahrzehnten zeigte sich, dass die Entwicklung von Therapieansätzen zur Behandlung von Knorpeldefekten ein detaillierteres Verständnis des Knorpelgewebes und speziell dessen Biodynamik erfordert. Ziel dieser Arbeit war es daher, im Rahmen einer Pilotstudie, ein In-vitro-System zu etablieren, welches die Untersuchung der Biodynamik der Chondrozyten ermöglicht. Neben der Untersuchung der Morphologie der Chondrozyten und der durch sie synthetisierten extrazellulären Matrix in Abhängigkeit von der Kultivierungszeit der Zellen, wurde die Fragestellung bearbeitet, ob durch die Wirkung eines hydrostatischen Drucks günstige Effekte in Hinblick auf die Expression einer extrazellulären Matrix, wie sie im hyalinen Knorpel vorliegt, erzielt werden kann. Materialien und Methoden Eine Primärkultur humaner artikulärer Chondrozyten wurde zunächst unter Standardzellkulturbedingungen und atmosphärischem Druck kultiviert. Die Zellen wurden phasenkontrastmikroskopisch und hinsichtlich der Verteilung von Kollagen Typ I und II immunzytochemisch untersucht. In den weiteren Versuchen wurden optisch konfluente Chondrozyten in einen Bioreaktor überführt und weiter unter einem hydrostatischen Druck von 5 oder 10 bar kultiviert. Dabei wurde die Dauer der Druckeinwirkung auf die Chondrozyten variiert. Das Expressionsmuster der so kultivierten Chondrozyten wurde quantitativ in Hinblick auf Kollagen Typ I und II sowie Aggrekan mittels qPCR und Western Blot untersucht. Dabei dienten jeweils Chondrozyten, die ohne erhöhte Druckbedingungen kultiviert wurden, als Kontrollen. In dieser Pilotstudie wurden die Proben unter Berechnung der Mittelwerte und Standardabweichung hinsichtlich ihrer statistischen Power ausgewertet. Neben dieser Analyse der Einzelergebnisse wurden die Versuchsbedingungen, die kaum Unterschiede in den Ergebnissen aufwiesen, in Gruppen zusammengefasst und mit Hilfe der größtmöglichen vorhandenen Standardabweichung der Stichprobenumfang eines Versuchs errechnet, welcher die statistische Power der Ergebnisse bei einem Alpha-Fehler von 0,05 auf 80% erhöht. In den Fällen, in denen diese Power erreicht wurde, erfolgte eine Untersuchung der Unterschiede auf Signifikanz („One Way Analysis of Variance“) bei einem Signifikanzniveau < 0,05. Ergebnisse Während der In-vitro-Kultivierung der Chondrozyten unter atmosphärischem Druck zeigte die Länge der Kultivierungszeit weder einen Einfluss auf die phasenkontrastmikroskopisch untersuchte Morphologie der Zellen noch auf die immunzytochemisch detektierte Verteilung des Kollagen Typ I und II. Die Wirkung eines erhöhten hydrostatischen Drucks (5 bar, 10 bar) für 24 Stunden führte zu einer Abnahme der Expression von Kollagen Typ I und Typ II auf das 0,2-0,8-fache bei gleichzeitiger Zunahme der Expression des Aggrekan auf das 1,7-2,2-fache, verglichen mit der unbehandelten Kontrolle. Dieser Effekt war bei 5 bar ausgeprägter als bei 10 bar, führte jedoch gleichzeitig zu einer starken Instabilität des Zellkultursystems. Vor diesem Hintergrund wurde für den höheren Druck (10 bar) die Zeitdauer der Druckeinwirkung verkürzt. Hierbei konnten bei kurzzeitiger Druckeinwirkung von 10 bar (1,5 und 3 Stunden) bei Erhalt der Zellen ähnliche Effekte erzielt werden wie für die Bedingung 5 bar, 24 Stunden. Die Expression von Kollagen Typ I und Typ II sank auf das 0,8-fache, wohingegen ein Anstieg der Aggrekanexpression auf das 1,6-2,4-fache erreicht wurde. Diese Ergebnisse der qPCR konnten durch die im Western Blot für Kollagen Typ I, II und Aggrekan detektierte Proteinexpression gestützt werden. Schlussfolgerungen Im Rahmen dieser Arbeit wurde ein In-vitro-System etabliert, welches einerseits der Untersuchung des Einflusses von hydrostatischem Druck auf die Expression von Chondrozyten dienen und andererseits für die Herstellung von Zelltransplantaten weiter modifiziert werden kann. Die Ergebnisse der Untersuchungen führten zur Definition von Bedingungen für das In-vitro-System, unter denen die Expression der extrazellulären Matrix durch die Chondrozyten in Richtung der Zusammensetzung im hyalinen Knorpel stimuliert werden kann. Dies zeigte sich bei einer Aussaat der humanen Chondrozyten in einer Konzentration von 104 Zellen/cm2 und einer Vorkultivierungszeit von 6 Tagen unter Normaldruck, gefolgt von der Kultivierung unter hydrostatischem Druck von 10 bar für 1,5 bis 3 Stunden. Mit Hilfe dieser Pilotstudie wurde somit ein In-vitro-System etabliert, auf dessen Basis Untersuchungen durchgeführt werden können, die weiterführende Erkenntnisse zur Biodynamik des hyalinen Knorpels liefern und der zukünftigen Entwicklung zellbasierter Therapieansätze der Knorpeldefekte, wie der ACT, zu Gute kommen.