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Primary cilia are sensory organelles that facilitate early skeletal development, as well as maintenance and adaptation of bone later in life. These solitary, immotile organelles are known to be involved in cell differentiation, proliferation, and mechanotransduction, a process by which cells sense and covert external physical stimuli into intracellular biochemical signals. Bone is a metabolically active tissue that continuously recruits osteogenic precursors and relies on osteocytes, the sensory cells of bone, to coordinate skeletal maintenance. Overall bone quality is dependent on the integrity of the initial structure formed, as well as this organ’s ability to adapt to physical loads. Proper differentiation and controlled proliferation of osteogenic progenitors are critical to the initial formation of the skeleton, while osteocyte mechanotransduction is essential for adaptation of developed bone. These phenomena rely on primary cilia, but little is known about the origin of osteogenic precursors and the ciliary mechanisms that promote osteogenesis. In this thesis, we first characterize an osteochondroprogenitor (OCP) population that rapidly and extensively populates skeletal tissues during juvenile skeletal development (Chapter 2). We also demonstrate that the primary cilium is critical for these cells to differentiate and contribute to skeletogenesis. We then show this OCP population is required for adult bone adaptation and is mechanoresponsive (Chapter 3). Again, we demonstrate that primary cilia are necessary for these OCPs to sense physical stimuli and differentiate into active bone-forming cells. Finally, we identify a novel link between ciliary calcium and cAMP dynamics in the osteocyte primary cilium (Chapter 4). Specifically, we show that a calcium channel (TRPV4) and adenylyl cyclases, which produce cAMP, bind calcium to mediate calcium entry and cAMP production, respectively, and these phenomena are critical to fluid flow-induced osteogenesis. Collectively, our results demonstrate that an easily extracted progenitor population is pre-programmed towards an osteogenic fate and extensively contributes to bone generation through primary cilium-mediated mechanisms at multiple stages of life. Furthermore, we identified ciliary proteins that are potentially unique to the osteocyte and can be manipulated to encourage osteogenesis by tuning calcium/ cAMP dynamics. For these reasons, we propose that this OCP population and their primary cilia, as well as osteocyte ciliary proteins that coordinate calcium/ cAMP dynamics, are attractive therapeutic targets to encourage bone regeneration.

青少年特發性脊柱側凸(Adolescent idiopathic scoliosis , AIS)是一種複雜的脊柱三維畸形，常見於10-16 歲處於生長發育高峰期的青少年女性。儘管AIS 發生率較高並且臨床影響較大，但是到目前為止其病因未明。在眾多關於AIS 病因學的假設和理論研究中，普遍認為低骨密度是AIS 的一個重要影響因素。然而近年來對於AIS 患者低骨密度研究不足，其潛在的機制尚不明確。我們之前初步的組織學研究發現，AIS 患者的松質骨中成骨細胞功能下降，此研究為AIS中存在骨礦化異常提供了初步依據。 / 骨橋蛋白是骨組織中一種重要的非膠原細胞外基質蛋白，其在骨礦化過程中起著重要作用。近期的研究報導AIS 患者血漿中骨橋蛋白水準高於年齡匹配的正常對照。因此本研究假設AIS 患者血漿及骨組織中骨橋蛋白高於正常對照，并可能影響了骨基質的礦化，從而導致低骨密度。 / 本系列研究的第一部分旨在通過外周定量電腦斷層掃描（pQCT）明確AIS患者中皮質骨密度及松質骨密度是否均低於正常對照。pQCT 可以準確地三維評估皮質骨密度，松質骨密度及其他骨品質的相關參數。採用雙能X 線骨密度儀（DXA）測量受試者的非優勢側近端股骨面積骨密度（包括股骨頸，Ward’s 三角及大轉子）。而採用pQCT 測量受試者非優勢側橈骨遠端容積骨密度，包括皮質骨密度及松質骨密度。結果顯示AIS 患者面積骨密度，皮質骨密度及松質骨密度在不同年齡段和月經時間分組中均低於正常對照。並且AIS 與正常對照皮質骨密度的差異隨著年齡增長越來越大，而松質骨密度差異則隨著年齡增長越來越小。 / 第二部分通過顯微CT 及組織形態測定研究AIS 及正常骨組織的骨礦化及骨微結構。採用顯微CT 檢測骨組織的三維結構參數，包括材料骨密度及骨微結構。未脫鈣骨組織的切片通過Goldner’s 染色進行組織形態學測量。結果顯示AIS患者的骨體積分數，骨小梁數目，骨小梁厚度及結構模型指數與正常對照之間均無顯著差異，而材料骨密度顯著低於正常對照。組織形態學分析結果顯示AIS中低礦化骨顯著多於正常對照。 / 第三部分旨在研究AIS 及正常對照血漿中骨橋蛋白水準及其與骨密度的關係。採用酶聯吸附免疫法測量AIS 患者及年齡匹配的正常對照血漿中的骨橋蛋白水準。血漿骨橋蛋白水準與骨密度的關係採用多元回歸分析。研究結果顯示AIS 患者及正常對照血漿骨橋蛋白水平均與年齡及月經時間呈負相關。AIS 患者的血漿骨橋蛋白水準顯著高於正常對照，並且與松質骨密度呈顯著負相關。 / 本研究第四部分旨在探討骨組織中的骨橋蛋白表達與骨形態學及骨礦化指標在AIS 及正常對照中的關係。骨組織中骨橋蛋白的表達採用半定量免疫組織化學法評估。研究結果顯示在AIS 中血漿骨橋蛋白水準與骨組織中骨橋蛋白的表達呈正相關。且AIS 骨組織中骨橋蛋白的表達也顯著高於正常對照。進一步的研究發現骨組織中骨橋蛋白的表達與材料骨密度呈負相關，而與低礦化骨量呈正相關。 / 本研究明確了AIS 中骨礦化水準低於正常對照，進一步證明AIS 患者中的皮質骨及松質骨密度下降可能與骨礦化的調控異常有關。本研究發現的骨橋蛋白與低骨密度及低骨礦化水準的關係，可以推測AIS 患者中異常升高的骨橋蛋白水準可能在骨礦獲取的調解中起重要作用。本系列研究提供證據支援AIS 患者中骨橋蛋白的異常表達可能影響了骨基質的礦化，從而導致低骨密度。本研究為AIS 中低骨密度可能的機制提供了全新的見解，並可能進一步解釋AIS 的發病機理及其發生，發展。 / Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine occurring most commonly in girls between ages 10-16 during the pubertal growth spurt. Despite its high prevalence and clinical impact, etiology of AIS remains largely unknown. Among the number of proposed hypothesis and observations on the etiopathogenesis of AIS, low bone mineral density (BMD) is one of the most reported factor (Cheng et al. 1999; Hung et al. 2005; Cheung et al. 2006; Hui et al. 2011). However, the underlying mechanism of low BMD in AIS has not been sufficiently studied scientifically and its link to the etiopathogenesis is still not clear. From a previous pilot study, our group has reported the histological features of reduced osteoblastic activity in bone biopsy specimens obtained from AIS subjects intraoperatively, thus providing the early evidence of abnormal bone mineral acquisition and mineralization (Cheng et al. 2001). / Osteopontin (OPN) has been recognized as one the major non-collagen extracellular matrix proteins in bone and plays an important role in bone mineralization. Recent report suggested that AIS patients have higher OPN level than normal controls (Moreau et al. 2009). It was hypothesized that the low BMD in AIS is associated with abnormal bone matrix mineralization which may be related to abnormal expression of OPN in the plasma and at tissue level. / In this series of studies, the first part aimed to investigate the differential cortical and trabecular bone mineral density of AIS Vs normal controls. The non-dominant proximal femur areal BMD (aBMD) (femoral neck, Ward’s triangle and greater trochanter) of the subjects were measured with dual-energy x-ray absorptiometry (DXA). The volumetric bone mineral density (vBMD) in non-dominant distal radius was measured with peripheral quantitative computed tomography (pQCT) that allows accurate three dimensional assessment of the cortical and trabecular bone mineral density and other parameters of bone quality. AIS was found to have lower aBMDs, trabecular BMD (TBMD) and cortical BMD (CBMD) in different age groups and year since menarche (YSM) groups. Furthermore, the percentage difference of CBMD between AIS and controls was increased with age while a decreasing trend was observed in the TBMD. / The second part of the study investigated the bone mineralization and bone micro-architecture with micro-computed tomography (micro-CT) and histomorphometry study of bone biopsies obtained from AIS and normal controls. Three-dimensional structural parameters including material bone mineral density (mBMD) and bone architecture were evaluated by micro-CT. Bone histomorphometry was assessed by undecalcified sectioning with Goldner’s trichrome staining. mBMD of trabecular bone in AIS was found to be significantly lower than the normal control while no difference could be demonstrated in BV/TV, Tb.N, Tb.Th and SMI measurement between the two groups. It was also shown that the percentage of low-mineralized bone in AIS was significantly higher than that in normal controls. / The third part aimed to study the plasma OPN level and its association with the BMD in AIS Vs normal controls. Plasma OPN level in AIS and age-matched controls was measured by ELISA. With multivariate regression analysis, the plasma OPN level was found to be negatively correlated with Age and YSM in both AIS and normal controls. In addition, the plasma OPN level in AIS was significantly higher and correlated with the low trabecular BMD. / The fourth part of the study investigated the OPN expression in bone tissues level and its association with histomorphometric bone mineralization and bone micro-architectural parameters in AIS Vs normal controls. OPN expression in bone biopsy was semi-quantified by immunohistochemistry. It was found that the bone tissue OPN level was significantly higher in AIS and also positively correlated with plasma OPN level. In addition, in this pilot study, we found the trend that OPN expression in trabecular bone was negatively associated with mBMD, and positively with the percentage of low-mineralized bone. / The present study showed that AIS had lower bone mineralization than normal controls. The low cortical and trabecular BMD found in AIS is likely to be resulting from abnormal regulation of bone mineralization. The association of OPN with abnormal BMD and bone mineralization further suggested that abnormal OPN level might play an important role in affecting the bone mineral acquisition in AIS. All of these findings strongly supported the hypothesis that the low BMD in AIS is associated with abnormal bone matrix mineralization which could be related to abnormal expression of OPN. This study provided important additional insight into the possible mechanism of lower bone mineral density that might be linked to theetiopathogenesis, development and progression of the spinal deformity in AIS. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Sun, Guangquan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 143-160). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract and appendix A also in Chinese. / THE CHINESE UNIVERSITY OF HONG KONG --- p.I / ACKNOWLEDGEMENTS --- p.II / ABSTRACT --- p.IV / ABBREVIATION --- p.XI / TABLE OF CONTENTS --- p.XIII / LIST OF TABLES --- p.XVII / LIST OF FIGURES --- p.XIX / LIST OF PUBLICATIONS --- p.XXI / Chapter CHAPTER 1 --- STUDY BACKGROUND --- p.1 / Chapter 1.1 --- GENERAL OVERVIEW OF ADOLESCENT IDIOPATHIC SCOLIOSIS (AIS) --- p.2 / Chapter 1.1.1 --- NATURAL HISTORY --- p.4 / Chapter 1.1.2 --- CURRENT TREATMENTS --- p.6 / Chapter 1.1.2.1 --- Observation --- p.7 / Chapter 1.1.2.2 --- Bracing --- p.7 / Chapter 1.1.2.3 --- Surgical treatments --- p.9 / Chapter 1.1.3 --- CURRENT HYPOTHESIS ON THE ETIOLOGY OF AIS --- p.11 / Chapter 1.1.3.1 --- Genetic factors --- p.12 / Chapter 1.1.3.2 --- Neuromuscular impairment --- p.14 / Chapter 1.1.3.3 --- Abnormalities in skeletal development --- p.16 / Chapter 1.1.3.4 --- Low bone mineral density in AIS --- p.16 / Chapter 1.2 --- BONE MINERALIZATION --- p.18 / Chapter 1.2.1 --- Overview of bone mineralization --- p.18 / Chapter 1.2.2 --- Bone modeling --- p.18 / Chapter 1.2.3 --- Bone remodeling --- p.19 / Chapter 1.2.4 --- Factors affecting bone mineralization --- p.21 / Chapter 1.3 --- OSTEOPONTIN --- p.23 / Chapter 1.3.1 --- Structure of osteopontin --- p.23 / Chapter 1.3.2 --- Osteopontin - cellular and tissue distribution --- p.24 / Chapter 1.3.3 --- Osteopontin functions --- p.25 / Chapter 1.3.4 --- Osteopontin functions in bone --- p.25 / Chapter 1.3.5 --- Osteopontin and bone mineral density in human --- p.29 / Chapter CHAPTER 2 --- STUDY HYPOTHESIS AND PLAN --- p.31 / Chapter 2.1 --- INTRODUCTION --- p.32 / Chapter 2.2 --- HYPOTHESIS --- p.33 / Chapter 2.3 --- OBJECTIVES --- p.34 / Chapter 2.4 --- STUDY PLAN --- p.34 / Chapter CHAPTER 3 --- LOW BONE MINERAL DENSITY IN ADOLESCENT IDIOPATHIC SCOLIOSIS - AREAL VS VOLUMETRIC, CORTICAL VS TRABECULAR BONE MINERAL DENSITY --- p.36 / Chapter 3.1 --- INTRODUCTION --- p.37 / Chapter 3.2 --- SUBJECTS AND METHODS --- p.39 / Chapter 3.2.1 --- Subjects --- p.39 / Chapter 3.2.2 --- BMD Measurement --- p.40 / Chapter 3.2.3 --- Statistical Analysis --- p.41 / Chapter 3.3 --- RESULTS --- p.42 / Chapter 3.3.1 --- aBMD of AIS and normal controls by age groups --- p.42 / Chapter 3.3.2 --- TBMD and CBMD in AIS and normal controls by age groups --- p.42 / Chapter 3.3.3 --- aBMD in AIS and normal controls by year since menarche --- p.43 / Chapter 3.3.4 --- TBMD and CBMD in AIS and normal controls by year since menarche --- p.43 / Chapter 3.3.5 --- Correlation between CBMD & TBMD and chronological age or year since menarche --- p.44 / Chapter 3.3.6 --- Comparisons adjusted for chronological age or year since menarche --- p.44 / Chapter 3.4 --- DISCUSSION --- p.45 / Chapter 3.5 --- TABLES AND FIGURES --- p.50 / Chapter CHAPTER 4 --- ABNORMAL BONE MATRIX MINERALIZATION AND BONE MICROARCHITECTURE IN ADOLESCENT IDIOPATHIC SCOLIOSIS - A HISTOMORPHOMETRIC AND MICRO-CT STUDY --- p.60 / Chapter 4.1 --- INTRODUCTION --- p.61 / Chapter 4.2 --- SUBJECTS AND METHODS --- p.62 / Chapter 4.2.1 --- Subjects --- p.62 / Chapter 4.2.2 --- Micro-computed tomography --- p.63 / Chapter 4.2.3 --- Bone histomorphometry --- p.64 / Chapter 4.2.4 --- Statistical analysis --- p.68 / Chapter 4.3 --- RESULTS --- p.68 / Chapter 4.3.1 --- Results of micro-CT analysis --- p.68 / Chapter 4.3.2 --- Results of histomorphometric analysis --- p.69 / Chapter 4.3.3 --- Relationship of mBMD and percentage of low-mineralized bone --- p.69 / Chapter 4.4 --- DISCUSSION --- p.70 / Chapter 4.5 --- TABLES AND FIGURES --- p.74 / Chapter CHAPTER 5 --- PLASMA OSTEOPONTIN LEVEL AND ITS ASSOCIATION WITH BONE MINERAL DENSITY IN ADOLESCENT IDIOPATHIC SCOLIOSIS --- p.82 / Chapter 5.1 --- INTRODUCTION --- p.83 / Chapter 5.2 --- SUBJECTS AND METHODS --- p.84 / Chapter 5.2.1 --- Subjects --- p.84 / Chapter 5.2.2 --- Anthropometric assessment --- p.84 / Chapter 5.2.3 --- Plasma osteopontin measurement --- p.85 / Chapter 5.2.4 --- BMD Measurement --- p.86 / Chapter 5.2.5 --- Statistical Analysis --- p.86 / Chapter 5.3 --- RESULTS --- p.86 / Chapter 5.3.1 --- Comparison of anthropometric parameters between AIS and controls --- p.86 / Chapter 5.3.2 --- Correlation between OPN plasma level with age or YSM in AIS and controls --- p.87 / Chapter 5.3.3 --- Comparison of OPN plasma level between AIS and controls --- p.87 / Chapter 5.3.4 --- Correlation between OPN plasma level and curve severity in AIS --- p.87 / Chapter 5.3.5 --- Relationship between OPN plasma level and vBMD --- p.88 / Chapter 5.4 --- DISCUSSION --- p.88 / Chapter 5.5 --- TABLES AND FIGURES --- p.94 / Chapter CHAPTER 6 --- OSTEOPONTIN EXPRESSION IN BONE TISSUE AND ITS ASSOCIATION WITH BONE MATRIX MINERALIZATION IN ADOLESCENT IDIOPATHIC SCOLIOSIS - A PILOT STUDY --- p.102 / Chapter 6.1 --- INTRODUCTION --- p.103 / Chapter 6.2 --- SUBJECTS AND METHODS --- p.104 / Chapter 6.2.1 --- Subjects --- p.104 / Chapter 6.2.2 --- Micro-computed tomography --- p.104 / Chapter 6.2.3 --- Bone histomorphometry --- p.104 / Chapter 6.2.4 --- Semi-quantification of OPN expression in bone biopsy by immunohistochemistry --- p.105 / Chapter 6.2.5 --- Plasma osteopontin measurement --- p.107 / Chapter 6.2.6 --- Statistical Analysis --- p.108 / Chapter 6.3 --- RESULTS --- p.108 / Chapter 6.3.1 --- Comparison of anthropometric parameters between AIS and control subjects --- p.108 / Chapter 6.3.2 --- Comparison of OPN expression detected by immunohistochemistry in bone biopsy between AIS and control groups --- p.108 / Chapter 6.3.3 --- Comparison of histomorphometric and micro-CT results between AIS and control groups --- p.109 / Chapter 6.3.4 --- Relationship between plasma OPN level and OPN expression in bone biopsy --- p.109 / Chapter 6.3.5 --- Relationship between percentage of low-mineralized bone and OPN expression in bone biopsy --- p.109 / Chapter 6.3.6 --- Relationship between material bone mineral density and OPN expression in bone biopsy --- p.110 / Chapter 6.4 --- DISCUSSION --- p.110 / Chapter 6.5 --- TABLES AND FIGURES --- p.114 / Chapter CHAPTER 7 --- SUMMARY STUDY FLOWCHART, OVERALL DISCUSSION, CONCLUSIONS, LIMITATIONS AND FURTHER STUDIES --- p.119 / Chapter 7.1 --- SUMMARY OF THE STUDY FLOW CHART WITH KEY FINDINGS --- p.120 / Chapter 7.2 --- OVERALL DISCUSSION --- p.125 / Chapter 7.2.1 --- The novel findings on bone mineralization abnormality in AIS in this study --- p.125 / Chapter 7.2.2 --- OPN is a key modulator in AIS --- p.128 / Chapter 7.3 --- OVERALL CONCLUSIONS --- p.130 / Chapter 7.4 --- LIMITATION OF THIS STUDY AND FUTURE RESEARCH --- p.131 / Chapter APPENDIX A. --- CONSENT FORM OF AIS RESEARCH --- p.135 / Chapter APPENDIX B. --- CONSENT FORM OF BONE BIOPSY COLLECTION --- p.137 / Chapter APPENDIX C. --- MATERIALS AND REAGENTS INFORMATION AND PROTOCOL FOR SOLUTIONS PREPARATION --- p.138 / BIBLIOGRAPHY --- p.143

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional structural spine deformity with lateral curve and vertebral rotation occurring predominantly in adolescent girls during the peri-pubertal period. The prevalence of AIS is nearly 4% in Hong Kong and 2-3% worldwide. AIS without treatment or with improper treatment may deteriorate progressively and lead to significant cosmetic problems and functional disabilities. In severe cases, increased mortality rate can result from the associated early onset of cardiopulmonary failure. Up to now, the treatment of the AIS is basically passive through bracing and corrective spinal surgery. The current protocol of treatment is not totally satisfactory since the curve may continue to progress with brace treatment and corrective surgery is associated with major surgery and permanent fusion of parts of the spine. This is due to the fact that one is still uncertain about the etiology of AIS and therefore cannot directly treat the AIS. Among the different proposed etiology of AIS, the role of abnormal skeletal growth and development during peri-pubertal period has been one of the main focuses in addition to genetic predisposition in the development of AIS. / It has been well established that girls with idiopathic scoliosis have a tendency to be taller and more slender than their peers. Recently, it has been shown that the trabecular bone mineral density at the spine, hip, and peripheral bones of AIS girls was lower than their healthy peers. Studies from our center have also demonstrated growth discrepancy between anterior and posterior vertebral column using magnetic resonance imaging (MRI) technique. The vertebral bodies were shown to be slender in AIS patients than that in normal controls. The observation pointed to a disproportionate growth of the anterior and posterior spinal column resulting from imbalance in endochondral and membranous ossification. The present study hypothesizes that the abnormality of skeletal growth could be a systemic problem affected by both endochondral ossification and membranous ossification. The degree of abnormal growth could vary with different curve severities. The concurrent finding of abnormal skeletal growth and osteopenia could be related to certain underlying abnormal genetic factors affecting the etiopathogenesis of AIS. The hypothesis leads to the following objectives: (1) To study the anthropometric measurements and the related changes in AIS girls with different curve severity; (2) To document the presence of abnormal systemic growth through endochondral ossification; (3) To document the presence of abnormal membranous ossification through studies of the morphology and bone mineral density of the midshaft of the appendicular skeleton and the skull; (4) To study the association of occurrence of AIS and its related phenotypes with the genes associated with growth and osteopenia. (Abstract shortened by UMI.) / by Yeung Hiu-Yan. / "January 2006." / Adviser: Jack C. Y. Cheng. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6301. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 206-227). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.