Browsing by Author "Yong, V. Wee"

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    Altering Inhibitory Extracellular Matrix Promotes Remyelination
    (2015-07-02) Keough, Michael; Yong, V. Wee
    Remyelination is the generation of new myelin sheaths after injury, and is accomplished by oligodendrocyte precursor cells (OPCs) that proliferate, migrate, and differentiate into myelin-forming oligodendrocytes. A number of lesion-associated factors have been identified that interfere with the remyelination response. Chondroitin sulfate proteoglycans (CSPGs) are a family of extracellular matrix molecules that provide structural rigidity to tissues and act as signalling molecules to neurons and glia in the developing nervous system. After injury, CSPGs become highly upregulated by astrocytes as part of the glial scar and restrict axonal regeneration. The role of injury-induced CSPG deposition on OPCs and remyelination is far less understood. In this thesis, I characterized a potent inhibitory phenotype of murine OPC adhesion and process outgrowth cultured on CSPGs in vitro. I explored the various mechanisms underlying this inhibitory response, including candidate receptors, downstream signalling molecules, and structural ligands on CSPGs through selective enzymatic degradation. I screened 245 orally available, Health Canada approved medicines for their ability to overcome OPC process outgrowth in the presence of CSPGs, and found a persistent inhibitory phenotype for all drugs tested. Lastly, I assessed the utility of a novel CSPG synthesis inhibitor, fluorosamine, and found that it reduced CSPG synthesis by astrocytes, resulting in a more permissive environment for OPC growth in vitro. Following experimental demyelination with lysolecithin in vivo, fluorosamine treatment reduced the deposition of CSPGs and enhanced OPC maturation and remyelination. Altering the inhibitory microenvironment after injury may be beneficial for promoting repair in a number of neurological diseases.
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    Characterization of early neuroinflammation after spinal cord injury
    (2006) Rice, Tiffany Katharine; Yong, V. Wee
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    Characterizing Susceptibility Weighted MRI in the Experimental Autoimmune Encephalomyelitis Mouse Model of Multiple Sclerosis
    (2014-10-07) Nathoo, Nabeela; Dunn, Jeff F.; Yong, V. Wee
    Susceptibility-based magnetic resonance imaging (MRI) methods have been used in multiple sclerosis (MS) patients for lesion detection, visualization of the venous vasculature and to show abnormal iron accumulation in the deep grey matter structures of the brain. The overarching goal of this thesis was to characterize one of the susceptibility-based MRI methods, susceptibility weighted imaging (SWI), in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. First, we investigated if SWI could detect lesions (or hypointensities) in the lumbar spinal cords and cerebella of EAE mice. We found that SWI hypointensities were present in a region-specific manner in the CNS of EAE mice, where most of these lesions were attributed to deoxyhemoglobin and a smaller number were due to parenchymal iron deposition. Next, we validated a method to identify deoxyhemoglobin-based SWI hypointensities in vivo which entailed combining SWI with hyperoxygenation. Following this, we sought to investigate when SWI hypointensities appear during the EAE disease course and how they change over the course of the disease. This was studied by carrying out serial SWI in vivo in naïve mice and mice immunized for EAE. Here, we found that SWI hypointensities are prominent before signs of motor dysfunction in EAE mice. SWI hypointensities were also observed to evolve over the disease course. Of note, the number of SWI hypointensities was always at a maximum before or at the same time as maximum motor dysfunction. Unlike EAE mice, the number of SWI hypointensities remained stable through all imaging time points in naïve mice, suggesting that SWI hypointensities are linked to EAE pathophysiology. Lastly we used SWI to assess treatment response to an anti-inflammatory treatment (dexamethasone) in EAE mice. This was carried out under the premise that SWI hypointensities may be linked to inflammation, so reducing inflammation could reduce the number of SWI hypointensities present. Our preliminary data suggest that SWI may be able to act as a surrogate marker of inflammation. Overall, findings from this thesis support the use of SWI in future studies in the EAE model to investigate the venous vasculature and parenchymal iron deposition.
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    Detecting Deoxyhemoglobin in Spinal Cord Vasculature of the Experimental Autoimmune Encephalomyelitis Mouse Model of Multiple Sclerosis Using Susceptibility MRI and Hyperoxygenation
    (PLOS ONE, 2015-05-18) Nathoo, Nabeela; Rogers, James A.; Yong, V. Wee; Dunn, Jeff F.
    Susceptibility-weighted imaging (SWI) detects hypointensities due to iron deposition and deoxyhemoglobin. Previously it was shown that SWI detects hypointensities in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS), most of which are due to intravascular deoxyhemoglobin, with a small proportion being due to iron deposition in the central nervous system parenchyma and demyelination. However, animals had to be sacrificed to differentiate these two types of lesions which is impractical for time course studies or for human application. Here, we proposed altering the inspired oxygen concentration during imaging to identify deoxyhemoglobin-based hypointensities in vivo. SWI was performed on lumbar spinal cords of naive control and EAE mice using 30% O2 then 100% O2. Some mice were imaged using 30% O2, 100% O2 and after perfusion. Most SWI-visible hypointensities seen with 30% O2 changed in appearance upon administration of 100% O2, and were not visible after perfusion. That hypointensities changed with hyperoxygenation indicates that they were caused by deoxyhemoglobin. We show that increasing the inspired oxygen concentration identifies deoxyhemoglobin-based hypointensities in vivo. This could be applied in future studies to investigate the contribution of vascular-based hypointensities with SWI in EAE and MS over time.
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    Development of tissue directionality-based measures of demyelination and remyelination for multiple sclerosis using structure tensor analysis
    (2014-10-10) Kamalpour-Ansari, Mohammad hadi; Zhang, Kunyan; Yong, V. Wee
    Changes in myelin integrity are key characteristics of many diseases including multiple sclerosis. The goal of this project was to evaluate the feasibility of structure tensor analysis, a potentially new measure of tissue directionality, to measure myelin health. Using histology and MR images obtained from a lysolecithin model of demyelination and remyelination, I quantified the coherency (anisotropy), energy (organization), and entropy (heterogeneity) of white matter in mouse spinal cords with different myelin integrity and found that demyelinated tissue had lower coherency and energy but higher entropy than tissues with intact myelin. I also tested the robustness of this technique to the change in image size in MRI and showed its practical feasibility. My findings suggest that tissues with better myelin integrity have greater alignment and anisotropy. Structure tensor analysis may have the potential to evaluate de- and re-myelination in patients with multiple sclerosis and similar disorders. Further validation is warranted.
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    Gray matter hypoxia in the brain of the experimental autoimmune encephalomyelitis model of multiple sclerosis
    (2016-01-14) Johnson, Thomas W.; Dunn, Jeff F.; Wu, Ying; Nathoo, Nabeela; Rogers, James A.; Yong, V. Wee
    Background: Multiple sclerosis has a significant inflammatory component. As inflammation can induce and be modulated by hypoxia, the presence of hypoxia could provide clues about immune response regulation in MS. Objective: quantify oxygenation in gray matter (GM) of mice with the experimental autoimmune encephalomyelitis (EAE) model to determine if hypoxia exists in a demyelination model associated with chronic inflammation. Methods: C57BL/6 mice were implanted with a fiber-optic sensor in the cerebellum (n=13) and cortex (n=21). We measured PO2 in awake, unrestrained animals from baseline up to 36 days post-induction for EAE. Results: There were more days with hypoxia compared with hyperoxia (cerebellum: 13/67 vs. 7/67 days; cortex: 15/112 vs. 2/112). Cerebellum showed the largest differences between days 13-17, corresponding to high behavioral deficits. This occurred later for cortex (day 23). Hypoxia in the cortex correlated with increased behavioral deficits and increased variation (based on z-score comparisons with baseline and age-matched controls) in the cerebellum correlated with clinical deficits. Conclusions: The presence of hypoxia and increased variation in GM oxygenation indicates that oxygen may change enough to modulate the immune response. The cause may relate to increased metabolic dysfunction, disruption of neurovascular coupling or increased oxidative metabolism in activated microglia.
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    Investigating the Effect of Inflammation Induced by Bacterial Lipopolysaccharide on Cerebral Blood Flow and Brain Oxygenation
    (2023-06) Shafqat, Qandeel; Dunn, Jeff F.; Camara-Lemarroy, Carlos; Yong, V. Wee
    Brain hypoxia is a pathological feature of various neurodegenerative diseases. Over 40% of people with multiple sclerosis (MS), an inflammatory disease of the central nervous system, experience brain hypoxia. It is proposed that hypoxia and inflammation are linked, where inflammation can cause hypoxia and hypoxia can then further contribute to inflammation, leading to a vicious cycle of damage. Given that hypoxia is present in MS, and in other neurological conditions, further research on putative mechanisms for its cause are needed. To better understand the hypoxia-inflammation cycle, we sought to determine whether systemic inflammation induces brain hypoxia and/or alterations in cerebral hemodynamics using non-invasive magnetic resonance imaging (MRI) techniques. We found that inflammation in a mouse model causes significant reductions in cerebral blood blow and an increase in brain R2* (an MRI marker of increased deoxyhemoglobin) in the cortex and hippocampus. We also discovered that LPS challenge causes significant changes in hippocampal oxygenation, with hypoxia occurring in all animals assessed, and hyperoxia occurring in 57% of the animals. Our findings suggest that inflammation may impair cerebrovascular regulation in the brain and contribute to brain hypoxia.
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    Investigating versican as a primary inhibitor of remyelination in models of multiple sclerosis
    (2022-01) Jelinek, Emily; Yong, V. Wee; Dufour, Antoine
    The demyelination that characterizes multiple sclerosis (MS) lesions can be repaired to a degree in some individuals, though in many patients, this repair is inadequate. Remyelination has the potential to restore function in the central nervous system (CNS). In order to promote remyelination in MS lesions, the inhibition of oligodendrocyte precursor cell (OPC) recruitment and differentiation must be overcome. Targeting the deposited extracellular matrix (ECM) factors in the lesion to create a more permissive environment for OPCs is a promising therapeutic strategy. Versican, and likely its V1 isoform, has been identified as a prominent inhibitory chondroitin sulfate proteoglycan (CSPG) that is upregulated in the MS lesion. In this thesis, I sought to determine the outcome of the interaction between newly available purified V1 and OPCs in culture. I observed a robust inhibitory effect of V1 as a substrate and as a soluble treatment on OPCs in vitro. Using the lysolecithin (LPC) murine model of demyelination and remyelination, where versican upregulation in CNS lesions appears to be in macrophages/microglia from previous studies, I conditionally deleted versican from CCR2+ monocytes to evaluate the outcome on OPC presence in the lesion. The conditional versican knockout was dependent on the administration of tamoxifen and resulted in reduced V1 in the lesion compared to controls. With less V1 in the lesion, there was an increase in oligodendrocyte lineage cells during the documented period of remyelination in the LPC lesion. These results are promising in proposing a target for future therapeutic strategies to improve remyelination in MS lesions.
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    Iron in multiple sclerosis: roles in neurodegeneration and repair
    (Nature Publishing Group, 2014-07-08) Stephenson, Erin; Nathoo, Nabeela; Mahjoub, Yasamin; Dunn, Jeffery F.; Yong, V. Wee
    MRI and histological studies have shown global alterations in iron levels in the brains of patients with multiple sclerosis (MS), including increases in the iron stored by macrophages and microglia. Excessive free iron can be toxic, and accumulation of iron in MS has generally been thought to be detrimental. However, iron maintains the integrity of oligodendrocytes and myelin, and facilitates their regeneration following injury. The extracellular matrix, a key regulator of remyelination, might also modulate iron levels. This Review highlights key histological and MRI studies that have investigated changes in iron distribution associated with MS. Potential sources of iron, as well as iron regulatory proteins and the detrimental roles of excessive iron within the CNS, are also discussed, with emphasis on the importance of iron within cells for oxidative metabolism, proliferation and differentiation of oligodendrocytes, and myelination. In light of the beneficial and detrimental properties of iron within the CNS, we present considerations for treatments that target iron in MS. Such treatments must balance trophic and toxic properties of iron, by providing sufficient iron levels for remyelination and repair while avoiding excesses that might overwhelm homeostatic mechanisms and contribute to damage.
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    Magnetic Resonance Imaging of Demyelination and Remyelination in the Lysolecithin Model of Multiple Sclerosis
    (2017-02) Dhaliwal, Raveena; Dunn, Jeff F.; Yong, V. Wee; Pike, Bruce; Ousman, Shalina
    We require magnetic resonance imaging methods sensitive to remyelination for evaluation of remyelinating therapies for multiple sclerosis (MS). The goal of this thesis was to characterize the sensitivity of quantitative magnetization transfer (qMT) and diffusion tensor imaging (DTI) to myelin and axonal loss and remyelination in the lysolecithin model. This model is being used to develop remyelinating therapies for MS. We found that the qMT parameters of bound pool fraction (f), T1 and several DTI parameters were able to detect demyelination in the lysolecithin model. The qMT parameters did not change with remyelination but several DTI parameters did recover slightly. f had the strongest correlation to the histological measure of myelin and T1 had the strongest correlation to the histological measure of axon content. Overall, the findings from this thesis support the inclusion of DTI and qMT as an outcome measure in future studies of potential MS therapeutics in the lysolecithin model.
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    Matrix metalloproteinases - clearning the way for myeline formation
    (2004) Larsen, Peter Hjorringgaard; Yong, V. Wee
    Myelin allows for the rapid conduction of electrical impulses along axons. The breakdown of myelin can have debilitating consequences reflected in diseases such as multiple sclerosis (MS), in which severe demyelination leads to numerous neurological impairments. Strategies to enhance the remyelinating capacity of the myelinating cells, the oligodendrocytes (OLs), are being investigated with the hope of bringing to a halt the demyelinating process. Myelin formation begins with the extension of OL processes to contact axons. Proteolytic activity has been suggested to play a role for OL process extension and this event was suggested to be mediated in part by matrix metalloproteinases (MMPs), and in particular MMP-9. In an attempt to extend these findings, it was hypothesized that MMP-9 activity might also be important in remyelination where the myelinating program is re­initiated after injury. An impaired ability to remyelinate was observed in mice deficient for MMP-9. However, the mechanisms of action did not directly involve process extension but rather a need for MMP-9 to remove proteoglycans that are inhibitory for OL maturation. To elucidate whether other MMP members could also have important functions in OL biology studies on OLs and OL progenitor cells were performed. Purified OL showed high expression of MMP-12 and subsequent experiments revealed that MMP-12 played a role in OL process extension and OL maturation in culture. Finally, it was hypothesized that a deficiency of both MMP-9 and -12 would affect the coordinated developmental myelination and OL biology in vivo. Indeed, these studies showed a transient delay in overall developmental myelination, which was correlated to an excess production of insulin growth factor binding protein-6 (IGFBP-6). This molecule can, by reducing the bioavailability of insulin-like growth factor, act as a negative factor for myelination. Altogether, these data suggest that MMPs are important in controlling the levels of IGFBPs in the environment and thereby regulate the levels of insulin-like growth factor and myelination. Overall, this thesis has uncovered a beneficial mechanism of MMP-9 actions following a demyelinating insult in mice. Furthermore, MMP-12 was implicated in OL biology both in process extension and maturation of these cells. Finally, these proteolytic molecules were found important in the normal timing of initial developmental myelination probably through regulating levels of IGFBPs.
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    Measurement of brain oxygenation and metabolism in a mouse model of multiple sclerosis
    (2017) Johnson, Thomas Wade; Dunn, Jeff; Yong, V. Wee; Goodyear, Brad
    Multiple sclerosis is a disease of the central nervous system, predominantly thought of as a white matter (WM) disease. However, evidence of the importance of grey matter (GM) involvement is beginning to accumulate. In this study, we set out to investigate whether altered oxygenation and metabolism was present in cortical and cerebellar brain GM using an auto-inflammatory mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Chronically implanted optical PO2 probes directly measured the tissue oxygen environment in GM in awake, unrestrained mice. Near-infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI) were used to detect hemoglobin oxygen saturation and blood flow in anaesthetized mice. This required the development of NIRS technologies to guide GM imaging. Numerical simulations were performed to determine NIRS sensitivity to brain tissue types in mice, rats and humans. NIRS on mice and rats is very sensitive to GM tissue in comparison to humans, and the region imaged can be determined through inter-fibre separation. Optical fibres were developed and their compatibility tested for use in a 9.4 T MRI system to enable simultaneous NIRS and MRI measurements on mice. The NIRS-MR system was validated by detecting changes in the cerebral metabolic rate for oxygen (CMRO2) when mice were subjected to hypothermia. Hypoxia, as measured by PO2 probes, was present in the cortex and cerebellum in approximately 50% of EAE mice, occurred much more frequently than hyperoxia, correlated with increased behavioural deficits and occurred before behavioural deficits appeared. NIRS-MR measurements found decreased cerebral blood flow, increased oxygen extraction fraction and constant CMRO2 at peak disease in EAE mice with high behavioural scores and inflammation-positive controls; no changes were found in naive controls. Some of these changes correlated with behavioural deficit. GM atrophy was observed in the cerebellar cortex, medulla and thalamus. Overall this study showed that NIRS-MR can detect changes in CMRO2 in mice, GM pathology exists in the EAE model and can be detected, and may be related to inflammation.
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