published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Biochemistry / Master / Master of Philosophy

Endoplasmic Reticulum (ER) stress signal is a cellular response to various insults including abnormal protein folding load, activating the unfolded protein response. Under severe ER stress, apoptosis will occur in most cell types. Interestingly, this does not happen in a disease model for Metaphyseal chondrodysplasia type Schmid (MCDS), where ER stress was activated in the hypertrophic zone of the growth plate where mutant collagen X proteins that cannot be folded correctly is expressed. Instead of normal progression from proliferating chondrocytes (PCs) to hypertrophic chondrocytes (HCs) and conversion to bone, HCs in MCDS mice undergo re-differentiation to PCs as a survival strategy due to an activation of ER stress. Transcription factors are known to be important in regulating differentiation. p53 family members, as transcription factors, are known to play important roles in developmental processes including cellular reprogramming, thus, we hypothesize that the ectopic expression of key transcription factors, p53 and TAp63, which are activated by ER stress is involved in HC re-differentiation. p53 is normally expressed in late PCs, Pre-HCs, and upper HCs, while TAp63 is expressed in PCs and Pre-HCs suggesting they may have roles in chondrocyte differentiation. p53 activated under ER stress in HCs are nuclear localized in MCDS mice, but did not invoke the apoptotic programme. In this project, using quantitative analyse to study the expression level of p53 and p63 isoforms, it was confirmed that p53 and TAp63γ are in part transcriptionally activated upon ER stress. From functional study by inactivating p53 in MCDS mice, it was shown that p53 alone was not sufficient to mediate re-differentiation. Given that TAp63γ isoforms is also highly upregulated upon ER stress, and the negative regulator, ΔNp63, is downregulated, this combination of change in gene expression also need to be considered. Furthermore, known regulators of p53 and p63 activity such as ASPP1 and iASPP are also differentially expressed in HCs, and are altered upon activation of ER stress favouring cell survival. Thus, it would be important to evaluate the combination of TAp63 in the re-differentiation process from conditional inactivation of p63 or in combination with p53 to gain a clearer understanding of the contribution and relationship of these transcription factors in the survival strategy of stressed HCs. / published_or_final_version / Biochemistry / Master / Master of Philosophy

Perlecan is the major heparan sulfate proteoglycan (HSPG) in growth plate cartilage and is critical for growth plate chondrocyte proliferation and proper skeletal development. Its core protein and attached chondroitin sulfate (CS) and heparan sulfate (HS) chains mediate interactions with many diverse proteins. Fibroblast growth factor (FGF)-2 and FGF-18 are other regulators of chondrocyte proliferation in the growth plate. Additionally, FGF-18 controls the hypertrophy and cartilage vascularization necessary for endochondral ossification. The research presented in this dissertation aimed to identify known and novel perlecan-binding proteins that are endogenous to the growth plate and to characterize their interactions with perlecan. FGF-2 (known to bind HSPGs) bound to perlecan in both a cationic filtration (CAF) assay and an immunoprecipitation (IP) assay primarily via the HS chains on perlecan. When digested with chondroitinase ABC to remove its CS chains, perlecan augmented binding of FGF-2 to the FGFR-1 and FGFR-3 receptors and increased FGF-2 -stimulated proliferation in BaF3 cells expressing these FGF receptors. Thus, growth plate perlecan binds to FGF-2 by its HS chains but can only deliver FGF-2 to FGF receptors when its CS chains are removed. FGF-18 (known to bind to heparin and to heparan sulfate from some sources) bound to growth plate perlecan. This binding was unchanged by chondroitinase or heparitinase digestion of perlecan, indicating that perlecan GAGs are not involved in FGF-18 binding. FGF-18 bound equally to recombinant domains I-III of perlecan (Alt1) and to full-length perlecan purified from the growth plate. Additionally, FGF-18 bound equally to recombinant domain III of perlecan, to Alt1 and to Alt2 (a domain I-III variant with no heparan sulfate). Therefore, binding sites for FGF-18 are present in domain III of perlecan. Affinity chromatography isolated histone H3 as a perlecan-binding protein from the chondrocyte matrix. CAF assays confirmed the interaction as specific, dependent primarily on HS chains of perlecan, although CS chains and the perlecan core were also involved. Immunohistochemistry detected perlecan and histone H3 colocalized in growth plate cartilage. These results can help us better understand the growth factor-independent control that perlecan exerts on endochondral ossification and, therefore, long bone growth.

The mandibular condyles represent important growth sites within the facial skeleton. Condylar growth is not a pacemaker of mandibular development, but it provides regional adaptive growth that is of considerable clinical significance, as the condyle’s upward and backward growth movement regulates the anteriorly and inferiorly directed displacement of the mandible as a whole. Orthopedic problems of the temporomandibular joint (TMJ), such as displacement of the TMJ disk, are common in the adolescent population. Clinical studies of mandibular asymmetry and mandibular retrognathia in adults as well as in children and adolescents, have reported an association with coexisting non-reducing displacement of the TMJ disk without identifying the cause and effect. Through experimental studies causality has been established, and unilateral affliction during growth has been shown to retard ipsilateral mandibular development with facial asymmetry as the sequel. It was hypothesized that bilateral non-reducing TMJ disk displacement during growth would impair mandibular development bilaterally, resulting in mandibular retrognathia. TMJ disk displacement has repeatedly been demonstrated to induce histological reactions of the condylar cartilage. An additional assumption was therefore that a non-deranged TMJ disk function is crucial for the maintenance of the growing condyle’s biophysical environment, and that a connection ought to exist between the amount of condylar cartilage changes caused by TMJ disk displacement and the amount of subsequent adverse mandibular growth. It was also hypothesized that non-reducing displacement of the TMJ disk in growing individuals would result in qualitative and quantitative changes of the condylar subchondral bone. An improved experimental cephalometric method was developed in order to optimize the reliability of longitudinal radiographic evaluation of fast growing small animals. Bilateral non-reducing TMJ disk displacement was surgically created in ten growing New Zealand White rabbits, with ten additional rabbits serving as a sham operated control group. The amount and direction of craniofacial growth was followed over time in serial cephalograms, aided by tantalum implants in the jaws. The study period was chosen to correspond to childhood and adolescence in man. The assessed growth of each side of the mandible was correlated to the histological feature of ipsilateral condylar cartilage at the end of the growth period. The amount and composition of subchondral bone from three regions of interest in the condyle, and the expression of local growth factors in the adjacent condylar cartilage was evaluated. The results verified that bilateral non-reducing TMJ disk displacement retarded mandibular growth bilaterally; the extent corresponding to mandibular retrognathia in man. Displacement of the TMJ disk during the growth period induced condylar cartilage adaptive reactions that were associated with both an adverse amount and direction of mandibular growth, manifesting in a retrognathic mandibular growth pattern. Growth impairment fluctuated over time, with the most striking retardation occurring during periods of increased general growth, implying a local growth reduction explicitly counteracting general hormonal growth acceleration. A significant decrease of the total amount of subchondral bone, in spite of a general increase of new bone formation in the experimental condyles, pointed to a reparative compensation for an extensive resorption of subchondral bone due to displacement of the TMJ disk, but not to the extent that normal growth would be maintained. These results constitute an explanation for the adverse mandibular development following non-reducing TMJ disk displacement in growing individuals. This project has shown that non-reducing displacement of the TMJ disk during growth has significant consequences on facial development. The findings strongly advocate early and accurate diagnosis and treatment of TMJ disk displacement in the adolescent population, thereby presumably reducing the need for future orthodontic and surgical craniofacial corrective therapy. The results furthermore enhance the need for full appraisal of TMJ disk function in the adolescent population during orthodontic functional therapy, as the condylar cartilage and subchondral bone reactions to a concomitantly displaced non-reducing TMJ disk must be expected to interfere with the intended growth stimulating treatment. The findings of intact articular layers in spite of gross histological and morphological soft and hard tissue changes as a sequel to TMJ disk displacement in growing individuals, implicate a clinical risk of false positive radiographic diagnosis of degenerative changes of the TMJ in children and adolescents.

published_or_final_version / Surgery / Master / Master of Surgery

There exists a need for a biocompatible polymer system of appropriate degradation properties for use in the production of tissue-engineered cartilage replacement implants. The implant consists of a layer of cartilage grown using autogenous chondrocyte cells on a porous calcium phosphate base for anchoring in situ. This implant would serve to improve the current treatments for wear and age-related degradation of articular cartilage. Pilot dissolution studies of the biodegradable polymers Polyvinyl Alcohol (PVA), Polycaprolactone (PCL), and Polyethylene Glycol (PEG), provided strong evidence supporting the use of PVA and PEG, not PCL, in film preparation. Results indicate that the dissolution of PVA rapidly exceeds that required for this application while the dissolution of PCL is not fast enough. The results of a literature review indicate that PEG dissolves faster than PCL, but not PVA. Consequently, a co-polymer hydrogel film of PVA and PEG, to fully degrade in 10 hours, was prepared to serve as a support for the in vitro seeding of cartilage-producing chondrocyte cells onto the artificial bone scaffold base. In preparing the film, the concentration of the PVA and PEG stock solutions, the composition of PVA and PEG (by mass % ratio) in the film, and the thickness of the film were defined to be the design variables. The degradation properties of the film are hypothesized to be influenced by the design variables, such that the degradation rates can be engineered by manipulating these parameters. A full factorial DOE was applied to determine the significance of the design variables and their interaction on the degradation rate. To determine degradation rate, in vitro dissolution studies of the hydrogel film were conducted in Earle’s balanced salt solution at 37oC. Upon optimizing the degradation rate, it was theoretically determined that an optimized film of 50wt% PVA, 50wt% PEG, and thickness of 3mm dissolves by 88.19 % in 10 hours. Validation testing indicated that the optimized film was prematurely perforated at approximately 22 minutes of immersion in EBS at room temperature suggesting failure by bulk dissolution, which was later confirmed through investigation and identification of a heterogeneous, multi-phase microstructure under transmitting light microscope. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-05-01 14:28:06.935 / Octane Orthobiologics & Ontario Centres of Excellence (OCE)

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