abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Intervertebral disc (IVD) degeneration could lead to many serious complications including low back pain and disc herniation. However, the mechanism of disc degeneration is not fully understood, hindering the development of the therapeutics to cure this disease. The integrity of the nucleus pulposus (NP), which is derived from the notochord and situated in the core of the IVD, has long been implicated in the function and homeostasis of the IVD. Previous puncture-induced disc degeneration mouse model showed segregation of NP cell mass during the early stage of disc degeneration, indicating that an alteration in the cell adhesion molecule activities is involved in this process. By microarray analysis, our group have revealed specific expression of Cdh2 gene, encoding cadherin 2/N-cadherin, a subtype of cadherins in the NP cells, suggesting a regulatory role of cadherin 2 in the IVD. Cadherins are single transmembrane glycoproteins mediating calcium-dependent intercellular adhesions. Cadherin 2 is involved in chondrogenesis and skeletogenesis, suggesting that it is important in skeletal development and function. This study hypothesized that cadherin 2 is required in the normal IVD development and homeostasis. The purposes of this project is firstly to fully characterize changes in cadherin 2 expression in the normal and degenerative discs in rodent and human, and secondly to examine the effect of loss of function of cadherin 2 on IVD homeostasis by functional blocking of the protein in the rodent NP and conditional knock out of cadherin 2 from the murine NP. The rodent adult NP is similar to human fetal NP, where cadherin 2 is homogeneously expressed in the cell membranes of the notochordal (NC) cells, suggesting that cadherin 2 is a potential NC cell marker. The rodent degenerative NP is similar to human adult NP, where down-regulation of cadherin 2 is observed, the NC cells are replaced by small round cells, and the cell-cell contact is lost. Blocking cadherin 2 function in the rodent NP and conditional knock out of cadherin 2 in the notochord and consequently the NP will lead to transformation of NC cells into small cells, loss of cell-cell contact and a change in the extracellular matrix (ECM), suggesting that cadherin 2 is important in the maintenance of the phenotype and intercellular adhesion of the NC cells. In conclusion, this study indicates that cadherin 2 is mainly expressed in the NC cells of the NP and serves as a potential NC cell marker. It plays a regulatory role in the IVD homeostasis through the maintenance of the NC cell phenotype by intercellular adhesions. This study contributes to the knowledge about the role of cadherin 2 in the disc homeostasis and the early mechanism of disc degeneration, and this would help in developing a therapeutic method to intervene or even reverse the disease process of disc degeneration. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 278-292). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 269-295). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 208-243). Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 208-243). Also available online.

This research examined the role of the cartilaginous end-plate (CEP) in ageing and degeneration of the human intervertebral disc (IVD). The matrix component affected primarily during degeneration of the IVD is proteoglycan (PG) (Pearce et al., 1987). The CEP, a hyaline cartilage found between the nucleus pulposus (NP) and the anulus fibrosus (AF) and the vertebral body, has been proposed as the source of the PG of the AF and NP. This study was undertaken to: 1) assess the similarity of CEP PG to PG from articular cartilage and IVD, (2) compare the CEP PG from healthy young discs with those from older degenerate discs (3) distinguish the changes in CEP PG due to ageing from those due to degeneration. The combined effects of ageing and degeneration were studied using end-plates from three healthy young spines and three post-mature spines; those to degeneration alone by comparison of two healthy with one degenerate disc in each of three spines. Altogether 86 CEP from 10 lumbar spines were examined. The CEP PG were prepared from 4M guanidinium chloride tissue extracts by density gradient ultracentrifugation under associative conditions. PG were separated into high and low molecular weight (M) components by Sepharose CL-2B chromatography. The PG and the high M and low M fractions were analysed for hexose (hex) and hexuronate (hexA) as measures of keratan sulphate and chondroitin sulphate, respectively. Also, the two fractions were analysed by composite agarose-polyacrylamide gel electrophoresis. The CEP PG resembled the IVD PG more closely than those of articular cartilage PG: the fraction excluded from Sepharose CL-2B was low, the hex/hexA ratio was high, and five electrophoretically distinct subspecies were seen. With degeneration, several properties of the CEP PG altered irrespective of age: the extractable .total proteoglycan fell, the ratio hex/hexA rose and number of electrophoretically distinct PG subspecies declined. With age, the sizes of the high M and low M fractions fell and the electrophoretic mobilities of the subspecies changed. These results suggested that degeneration involves both a conversion of aggregating to non-aggregating PG and the preferential biosynthesis of a keratan sulphate-rich over a chondroitin sulphate-rich PG. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

published_or_final_version / abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.