Anatomy and Neuroscience - Theses
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ItemThe role of neurotrophic factors in osteoarthritis pain( 2023-10)Introduction: Osteoarthritis (OA) is a progressive disease of synovial joints and subchondral bone characterized by swelling, stiffness and pain. Brain-derived neurotrophic factor (BDNF) and artemin (ARTN) are neurotrophic factors that are important regulators of pain, and have recently been implicated in the pathogenesis of OA pain. This study aimed to explore roles for BDNF and ARTN in OA pain, by investigating whether the expression of BDNF and ARTN, and their receptors (TrkB and GFRa3), is altered in different tissues at different stages of OA, and whether blocking their signalling during late-stage OA can alleviate pain. Methods: The monoiodoacetate (MIA)-induced OA of the rat knee joint was used to explore roles for BDNF and ARTN signalling in OA pain. Pain behaviour was assessed using the dynamic weight-bearing apparatus to assay OA-induced changes in hindlimb weight bearing behaviour, at different stages of disease (early vs late). Histopathological alterations in the knee joint and surrounding bones were assayed using Haematoxylin and Eosin staining and scored using a modified OARSI scale. Changes in expression of BDNF/TrkB and ARTN/GFRa3 were explored using Western blot analysis of lysates from different tissues (joint, bone, and DRG), and at different timepoints of the disease (early vs late). The dynamic weight-bearing assay was used to determine if inhibiting BDNF signalling (with a peptide mimetic TrkB inhibitor) or ARTN signalling (with a sequestering antibody) could relieve pain at late-stage disease. Results: The results of this thesis highlight differential histopathological changes occurring in the early and late stages of OA, with joint involvement being prominent in early OA, and bone and cartilage involvement in late OA. BDNF expression was increased in the joint in early OA and in the bone in late OA. ARTN expression was also increased in the joint in both early and late OA and in the bone in late OA. Attempts to alleviate pain in MIA-injected animals by targeting the BDNF/TrkB and ARTN/GFRa3 signalling pathways did not yield pain relief outcomes with the therapeutic approach chosen in this study. Conclusion: Our findings suggest that altered pain behaviour in early MIA-induced OA is associated with changes in the joint not surrounding bones, while altered pain behaviour in late MIA-induced OA are attributable to the surrounding bones. Furthermore, BDNF and ARTN may contribute differentially to pain in early and late stages of MIA-induced OA through actions in joint versus bone. These findings support further investigations into the role of BDNF and ARTN signalling in OA pain and the development of novel targeted therapeutic approaches for managing OA pain.
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ItemInvestigating the role of neuronal TrkB in remyelination( 2023-02)Demyelinating diseases, such as multiple sclerosis (MS), involve damage to the fatty, proteinaceous myelin sheaths surrounding nerve fibres and subsequent development of neurological symptoms related to the damaged area. Repair of the damaged myelin can completely or partially reverse the neurological deficits, however, over time with repetitive demyelinating events and incomplete remyelination this ultimately results in the degeneration of neurons and development of permanent disabilities. Currently, there is a lack of therapies effective in promoting myelin repair. A complete understanding of the factors that promote remyelination is critical for developing therapeutic strategies for myelin repair to prevent permanent neurological disability. Many studies have focused on the potential of oligodendrocytes (the myelin-generating cells in the central nervous system) to enhance the generation of myelin. However, neurons certainly have an intimate relationship with oligodendrocytes and are well-positioned to influence the process of myelination. Previously, neuronal expression of the tyrosine kinase receptor TrkB has been shown to promote myelination in early development and during ageing. However, whether neuronally expressed TrkB receptors also influences the extent of oligodendroglial and myelin damage post a demyelinating injury, and the subsequent process of remyelination has not been elucidated. In this thesis, I generated an inducible, neuron-specific TrkB receptor knockout mouse line to investigate the role of neuronal TrkB receptors in the extent of both demyelination and remyelination following the induction of a demyelinating insult with cuprizone administration. I found that following deletion of TrkB, these mice exhibit a normally myelinated nervous system, but do however develop a motor phenotype consistent with a decrease in precise motor control. Following administration with cuprizone, I revealed that neuronal expression of TrkB is important for the differentiation of OPCs (oligodendrocyte progenitor cells) that are generated in response to the demyelinating insult. Finally, although reduced expression of neuronal TrkB did not influence the overall extent of remyelination, I found that axons with small diameter required expression of neuronal TrkB to be efficiently remyelinated. This work is the first to identify that neuronally expressed TrkB receptors have a role in OPC differentiation following demyelination. This thesis suggests there is therapeutic potential in targeting neuronal TrkB signalling to promote myelin repair, albeit this may only be specific to smaller diameter neurons.
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ItemThe role of neuronal TrkB in central nervous system myelination( 2019)Myelin, the specialised membrane surrounding many axons in the nervous system, is vital for the normal sensory and motor function as well as high order function such as learning and memory. Despite the importance of myelin in neural development and functions, little is known whether neuronally expressed molecules can promote the central nervous system (CNS) myelinating process. Through selectively deleting the expression of neurotrophin receptor TrkB in neurons in vivo (TrKB cKO), I have found that neuronal TrkB is essential for oligodendroglial cell production and lineage progression in multiple CNS regions including the lumbar spinal cord white matter tracts, cerebral cortex and corpus callosum and importantly de novo myelination, independent of axonal number and calibre in vivo. I have performed ultrastructural analysis of myelinated axons and found that TrkB cKO mice have significantly fewer myelinated axons compared to control mice during early postnatal development, indicative of delayed initiation of myelination. The analysis of myelin thickness via G ratio has revealed thinner myelin membranes in TrkB cKO mice compared to littermate control mice during development, persisting to late adulthood (n=3 mice/genotype/timepoint). This hypomyelinating phenotype has resulted in impaired myelin function, as evident by reduced optomoter responses in TrkB cKO mice compared to control mice. Moreover, I have found that TrkB cKO mice have significantly fewer oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes in both white and grey matter regions throughout postnatal development and into adulthood compared to littermate controls. A 24-hour EdU labelling experiment has demonstrated that neuronal TrkB expression is required for oligodendroglial production. Interestingly, the overall number of astrocytes and microglia has remained unchanged after neuronal TrkB deletion, suggesting a specific effect upon oligodendroglial lineage cells and myelination. In addition, assessment of neuronal morphology revealed no significant difference in overall dendritic branching including the number of primary and secondary processes. Taken together, results of this PhD study identify that TrkB is a novel neuronal signal that instructs oligodendroglial lineage development and de novo myelination within different neural circuits, indicating a new mechanism that underpins nervous system plasticity.