Biomedical Physiology and Kinesiology - Theses, Dissertations, and other Required Graduate Degree Essays

Receive updates for this collection

Thermodynamic characterization of hypertrophic cardiomyopathy associated troponin C mutations

Author: 
Date created: 
2019-07-15
Abstract: 

Hypertrophic Cardiomyopathy (HCM) is the leading cause of sudden cardiac death in young adults under the age of 35; a devastating disease that is not yet well understood. To date, greater than 1000 HCM-associated mutations have been found in genes that encode mostly sarcomeric proteins. Familial Hypertrophic Cardiomyopathy (FHC) is the heritable form of HCM. The overlying phenotype of FHC is thought to be derived from an increase in calcium (Ca2+) sensitivity of contraction and impaired relaxation of the myocardium. Dilated Cardiomyopathy (DCM) associated mutations are thought to have the opposite functional effect. This study focuses on cardiac troponin C (cTnC) a component of the cardiac troponin complex where binding of Ca2+ acts as the regulatory switch, leading to a series of conformational changes that culminate in muscle contraction. This project explores Ca2+ binding by focusing on the proximal-most unit of the contractile apparatus. The interaction of Ca2+ with the regulatory domain of cTnC is studied through isothermal titration calorimetry in conjunction with Molecular Dynamics simulations to understand structural and functional changes in the N-terminal region of cTnC. Initially, we established a workflow by exploring the functional consequences of sequence variations in coordinating Ca2+ binding and the genetic control of paralog expression in response to environmental temperature change in zebrafish. We then focused on a series of FHC-associated mutations (A8V, L29Q, A31S, and C84Y), as well as an engineered Ca2+ sensitizing mutation (L48Q), and a DCM-associated mutation (Q50R). The effects of temperature in modulating the Ca2+-cTnC interaction was also studied in these mutants. We further explored the role of cellularly abundant magnesium (Mg2+) which also interacts with cTnC and may modulate the Ca2+ coordinating capabilities of this contractile protein. Lastly, the role of Mg2+ binding to the mutants of interest, under normal cellular condition and in energy depleted states was explored to better understand the etiology of FHC and provide biomedical and physiological insight into potential treatments for this disease.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Glen Tibbits
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

When motor control hangs in the balance: Sensorimotor learning during balance-challenging conditions

Author: 
Date created: 
2021-03-10
Abstract: 

Maintaining balance while moving is fundamental for safe and successful motor performance. However, this aspect of daily movement is often overlooked in experimental paradigms that assess adaptation during constrained and/or isolated tasks. Consequently, we cannot easily extrapolate the results from these studies to naturalistic motor behaviours. The goal of this thesis is to determine how the necessity to maintain balance during unconstrained movement affects sensorimotor learning. For my first study, I assessed how challenging balance during adaptation affects generalization of learning. Four groups of participants adapted to a new visuomotor mapping induced by prism lenses while performing either a standing-based reaching or walking task, with or without a manipulation that challenged balance. To assess generalization, participants performed a single trial of each of the other group’s tasks without the prisms. I found that both the reaching and walking balance-challenged groups showed greater generalization to their equivalent, non-adapted task compared to the balance-unchallenged groups. I also found that challenging balance modulated generalization across the reaching and walking tasks. For my second study, I tested how challenging balance affected motor memory retention. To do this, the same four groups of participants returned to the lab and repeated their adaptation protocol one week later. I found that only the walking groups demonstrated faster relearning (or savings) during re-exposure to the prisms. Crucially, I found that challenging balance significantly enhanced savings during walking. In my third study, I determined how a stability consequence associated with movement errors affected sensorimotor learning. Two groups of participants adapted to a new visuomotor mapping while performing a precision walking task either with or without the possibility of experiencing a slip perturbation when making errors. I assessed generalization of learning across two visually guided walking tasks and motor memory consolidation. To assess consolidation, I introduced an opposite direction visuomotor mapping following adaptation and evaluated relearning one week later. I found that the experiencing a physical consequence when making errors enhanced generalization and motor memory consolidation. Overall, this thesis provides a novel perspective on how the necessity for balance control contributes to sensorimotor learning, which has intriguing implications for the development of rehabilitation interventions.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Daniel S. Marigold
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Examining the potential for information and communication technology to support patients with cardiovascular disease

Author: 
Date created: 
2020-12-01
Abstract: 

The overall goal of this work was to investigate the potential of information and communication technology (ICT) to support patients with cardiovascular disease (CVD). There were two specific aims: (1) to determine access to and willingness to use technology for health-related information in patients with CVD; and (2) to develop and pilot test a text-messaging intervention to support patients with acute coronary syndrome (ACS) following discharge from the hospital. The first aim was done with a cross-sectional survey (n=169). ICT ownership was common, as 98% of participants owned at least one ICT device. Computers were the most commonly owned device (88%), the device most commonly used for health information (74% of computer owners), and the device participants had the most interest in using for health information (72% of computer owners). Participants with lower incomes and education levels were less interested in receiving health information on at least one of their devices. The second aim was done with a mixed-methods, assessor-blinded, pilot randomized controlled trial (n=76). An advisory committee composed of patients, researchers, and clinicians developed 48 one-way text messages to send over 60 days to patients with ACS. There were no statistically significant differences between the intervention and usual care groups for self-management domains, medication adherence, health-related quality of life, self-efficacy, and healthcare resource use except for one self-efficacy domain. The study protocol was feasible, except recruitment took longer than anticipated. Ninety-three percent reported they were satisfied with the text messages. In the semi-structured interviews, many participants reported the program made them feel normal, perceived the program to be a source of social support, reinforced they were on the right track, and reminded them of their condition. However, some participants felt they did not need the messages, wished for a more tailored experience, or did not change their behaviours as a result. Learnings from the pilot study should be addressed prior to proceeding to a larger trial. Overall, these two studies indicate that ICT can be acceptable to patients with CVD. Further work needs to be done to determine how to best use ICT to support patients.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Scott Lear
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Inhibition of voltage-dependent sodium currents by cannabidiol

Date created: 
2020-09-29
Abstract: 

Voltage-gated sodium channels initiate action potentials in excitable tissues. Altering these channels’ function can lead to many pathophysiological conditions. The family of voltage-gated sodium channel genes encodes 10 proteins (including Nav2.1) distributed throughout the central and peripheral nervous systems, cardiac and skeletal muscles. The SCN4A gene encodes the Nav1.4 channel, which is primarily responsible for depolarization of the skeletal muscle fibers. Many mutations in SCN4A are found and associated with the myotonic syndromes and periodic paralyses. These conditions are both considered gain-of-function and can be severely life-limiting with respect to performing everyday tasks. From a broader standpoint, hyperexcitability presents as a significant problem in other tissues besides skeletal muscles. Gain-of-function in sodium channels has been linked to a wide-range of pathophysiological conditions such as inherited erythromelalgia, epilepsy, and arrhythmias. Treating these types of pathologies requires an in-depth understanding of their underlying mechanisms. One way to gain this understanding is to investigate physiological triggers. There is also a dire need for novel ways of reducing the hyperexcitability associated with mutant sodium channels. One promising compound is the non-psychotropic component of the Cannabis sativa plant, cannabidiol. This compound has recently been shown to modulate some of the neuronal sodium channels. Although cannabidiol has shown efficacy in clinical trials, the underlying mechanism of action remains unknown. Sodium channels could be among the molecular targets for cannabidiol.In my doctoral research: 1) I studied how a single missense mutation, P1158S, in Nav1.4 causes various degrees of gain-of-function (myotonia and periodic paralysis) by using pH changes to probe P1158S gating modifications; 2) I studied the inhibitory effects of cannabidiol on voltage-dependent sodium currents; 3) I investigated the mechanism through which cannabidiol imparts inhibition. Overall, these data reveal novel insights into sodium channel hyperexcitability and pharmacologically targeting of this hyperexcitability using cannabidiol.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Peter Ruben
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Using human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) to model inherited and acquired arrhythmias

Date created: 
2018-10-16
Abstract: 

The study of inherited human cardiovascular diseases has been hampered by limited access to cardiac tissue from patients harboring specific mutations, which are thought to be causal. The ability of the human induced pluripotent stem cells (hiPSCs) to differentiate to any cell type including cardiomyocytes, while carrying patients’ complex genetic backgrounds, has made them a promising and powerful tool for drug screening, assessing the cardiotoxicity of chemotherapeutic agents, and studying inherited cardiac diseases in vitro by recapitulating their cellular phenotypes. In Chapter 3, I used human pluripotent stem cell (hPSC)-derived ventricular and atrial cells to study the toxicity of ibrutinib, a novel Bruton’s tyrosine kinase (BTK) inhibitor, which has demonstrated benefit in B cell cancers, but is associated with atrial fibrillation. I showed that ibrutinib has a dramatic impact on the cardiac electrophysiology of hPSC-derived atrial cardiomyocytes, without affecting hPSC-derived ventricular cardiomyocytes. In Chapter 4, I investigated the arrhythmogenic role of a novel TNNI1 mutation (R37C TNNI1) in the death of “autopsy negative” sudden infant deaths (SIDs) victims. Specifically, I generated R37C+/- TNNI1 hiPSC-CMs using the genome-editing technology CRISPR/Cas9 and monitored voltage- and Ca2+ transients through optical mapping. Unlike the isogenic control cell line, irregular voltage- and Ca2+ transients and arrhythmic activities were observed in the presence higher rates of stimulation or β-adrenergic agonists in monolayer of R37C+/- TNNI1 hiPSC-CMs. Chapter 5 focused on the familial hypertrophic cardiomyopathy (FHC)-associated mutations found in patients, I79N TNNT2, which I generated using CRISPR/Cas9 in hiPSC-CMs. Compared to other FHC-associated mutations found in patients, I79N TNNT2 often results in significantly less ventricular hypertrophy and a higher incidence of sudden cardiac death. Unlike control hiPSC-CMs, the mutant hiPSC-CMs developed irregular and arrhythmogenic voltage- and Ca2+ transients at high stimulation rates and in the presence of β-adrenergic agonists. In sum, hiPSC-CMs have been successfully used to model a growing number of arrhythmogenic disorders, thereby enabling prediction of high-risk populations’ susceptibilities to drug-induced cardiotoxicity as a form of personalized medicine. Besides disease modeling and drug screening, hiPSC-CMs have emerged as a powerful platform for studying the cardiotoxicity of chemotherapeutic agents.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Glen Tibbits
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Principles of energy optimization underlying human walking gait adaptations

Author: 
Peer reviewed: 
No, item is not peer reviewed.
Date created: 
2020-09-10
Abstract: 

Learning to move in novel situations is a complex process. We need to continually learn the changing situations and determine the best way to move. Optimization is a widely accepted framework for this process. However, little is known about algorithms used by the nervous system to perform this optimization. Our lab recently found evidence that people can continuously optimize energy during walking. My goal in this thesis is to identify principles of optimization, particularly energy optimization in walking, that govern our choice of movement in novel situations. I used two novel walking tasks for this purpose. For the first task, I designed, built, and tested a mechatronic system that can quickly, accurately, and precisely apply forces to a user’s torso. It changes the relationship between a walking gait and its associated energetic cost—cost landscape—to shift the energy optimal walking gait. Participants shift their gait towards the new optimum in these landscapes. In my second project, I aimed to understand how the nervous system identifies when to initiate optimization. I used my system to create cost landscapes of three different cost gradients. I found that experiencing a steeper cost gradient through natural variability is not sufficient to cue the nervous system to initiate optimization. For my third and fourth projects, I used the task of split-belt walking. I collaborated with another research group to analyse the mechanics and energetics of walking with different step lengths on a split-belt treadmill. I found that people can harness energy from a split-belt treadmill by placing their leading leg further forward on the fast belt, and that there may be an energy optimal gait. In my fourth project, I used computer modelling to identify that there may exist an energy optimal gait due to the trade-off between the cost of swinging the leg and the cost of redirecting the body center of mass when transitioning from step to step. Together, these projects develop a new system and a new approach to understand energy optimization in walking. They uncover principles governing the initiation of this process and our ability to benefit from it.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Max Donelan
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Mechanisms that relate transverse loading of muscle to changes in contractile performance

Author: 
Date created: 
2020-07-09
Abstract: 

Research has shown that factors such as the contraction of surrounding muscle, resistance to radial expansion, and external transverse loading have an effect on the way that muscle performs. Such factors are often ignored when doing muscle experiments, yet they can have significant effects on the force and power that a muscle is able to produce. The aim of this thesis is to determine to what degree external loading affects muscle force and to study the changes in muscle architecture due to external loading. The purpose of this thesis was to determine whether external transverse loading causes force reduction in humans, how external transverse loading affects muscle architecture, and describe the mechanisms involved. We applied an external transverse load to the medial gastrocnemius of prone participants as a point loaded mass. Transverse loading reduced ankle torque with higher loads resulting in greater reductions. Passive transverse loading caused a decrease in the resting pennation angle and muscle thickness, with higher loads leading to greater decreases. During activation of the muscle the pennation angle, muscle thickness, and fascicle thickness increase transiently relative to the amount of transverse loading. Alterations to the design of the experiment were made by applying a multi-directional external transverse load and changing the position of the participants from prone to seated, where sitting changed the resting length of the muscle. Our altered experiments showed no change in ankle torque. Minor differences were shown for pennation angle and muscle thickness both at passive resting values and peak active values, but not for fascicle thickness and fascicle. Fascicle thickness decrease transiently, and fascicle length increased. We replicated the external transverse loading experiments using a three-dimensional finite element model of a fibre-reinforced, non-linearly-elastic transversely isotropic composite biomaterial. The model consists of active and passive force-length properties of muscle fibre as well as passive force-length properties of base material. Results show external transverse loading causes architecture changes and reductions in muscle force. Muscle force reduction is dependent on direction of loading, initial pennation, and initial muscle length.

Document type: 
Thesis
File(s): 
Supervisor(s): 
James M. Wakeling
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Design and validation of genetically encoded probes for the analysis of neuronal catecholamine and ATP co-transmission

Author: 
Date created: 
2019-07-31
Abstract: 

BACKGROUND: Sympathetic nerves co-release several neurotransmitters, including adenosine-5'-triphosphate (ATP) and norepinephrine (NE). Our studies are aimed at understanding how these nerves provide automatic regulation of blood vessel diameter and therefore blood pressure. Relatively little is known at the molecular level about how these nerves control the release of multiple neurotransmitters. Using immunofluorescence microscopy, we recently showed that clusters of vesicles containing ATP and NE are segregated within sympathetic nerve terminals. METHODS: To assess the mechanisms of ATP and NE release, we developed genetically encoded reporters of the vesicular monoamine transporter VMAT2 (SLC18A2) and the vesicular nucleotide transporter VNUT (SLC17A9) tagged with pH-sensitive fluorescent proteins to monitor the release of NE and ATP containing vesicles with molecular specificity and high spatial resolution. RESULTS: First, we characterized the dopaminergic Neuro-2a (N2a) cell line as a model to study catecholamine and ATP co-release. N2a cells express VMAT2 and VNUT, and we found that their expression is upregulated upon differentiation, induced by retinoic acid (RA) and serum deprivation. We optimized retinoic acid and serum concentrations to drive neurite outgrowth while minimizing cell death. Following differentiation, cells exhibited release of VMAT2-pHuji, evoked by field stimulation and the calcium Ionophore 4-Bromo-A23187. Second, we tested whether ATP and NE localize to separate vesicles in N2a cells. Nearest-neighbour colocalization analysis showed that VMAT2 and VNUT are located in common varicosities but in separate vesicles. VNUT and VMAT2 appear to traffic independently, and they appear to be localized into vesicles with pH <6.0 and >7.0, respectively. CONCLUSIONS: Our results corroborate reports that NE and ATP are stored in separate vesicles but segregated into separate pools within the varicosity. The N2a cell line is a promising model to further identify fundamental aspects of differential trafficking and release of VMAT2 and VNUT containing vesicles, while VMAT-pHuji and VNUT-pHluorin permit simultaneous detection of catecholaminergic and purinergic vesicle release.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Damon Poburko
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Sex differences in coordinated brain activity in clinical child populations

Date created: 
2020-07-08
Abstract: 

A disruption of normal brain development during early stages of life has been associated with higher male vulnerability expressed by male preponderance among affected individuals and/or more severe impairments in males for developmental disorders. Although this phenomenon is frequently acknowledged by the scientific community, its neurophysiological underpinnings remain largely unclear. In this thesis I investigate male vulnerability in very preterm children and individuals with Autism Spectrum Disorder (ASD). Both clinical child populations entail early developmental adversity leading to behavioural and cognitive alterations, believed to be elicited, in part, by disrupted communication between brain areas. Therefore, I examine resting state whole-brain connectivity and its developmental changes in these clinical populations using fMRI and MEG and test the hypothesis of sex-specific connectivity differences between males and females resulting in male disadvantage. In the first study I investigate sex differences in interhemispheric homotopic connectivity and its developmental trajectories in participants with ASD as well as in typically developing individuals. Our findings demonstrate differences in developmental trajectories rather than connectivity. Both females and males with ASD deviate from typical female trajectories while expressing similar developmental trajectories to typical males. In the second study I examine local connectivity and its age-related changes using a similar cohort of participants. Group and sex differences are observed in both local connectivity and its developmental trajectories. Females with ASD are characterised by more robust alterations. Lastly, in the third study I test the hypothesis that male vulnerability in very preterm children can be detected as more pronounced alterations in inter-regional connectivity in boys compared to girls. Our results confirm this hypothesis suggesting that connectivity alterations might contribute to male disadvantage reflected in long-term behavioural and cognitive outcome. Overall, this thesis highlights that disruptions in brain connectivity and/or its developmental trajectories differ between males and females with altered early development supporting the existence of female protective features preventing females from developing pathological outcome.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Sam Doesburg
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Altered structure-function relationships in children born preterm and in autism spectrum disorder

Date created: 
2020-07-06
Abstract: 

Sensation, perception, cognition and behavior depend on complex neural processes carried by the coordinated function of brain structures. This coordination is achieved through oscillatory activity and synchronization, and the main pathways can be captured with resting-state activity. Structural alterations might affect the functional coordination with other brain structures, and a structure-function approach can provide a better understanding of the underlying neural mechanism that characterizes human populations. This thesis will study altered structure-function relationships in Autism Spectrum Disorder and in children born preterm at school age. Functional activity is assessed with MEG or fMRI resting-state data and structural characteristics with MRI. Both populations present brain oscillatory and structural alterations related to the thalamic-cortical system. Recent evidence indicates that the development of brain networks connectivity is altered in ASD and in very preterm born children. Evidence remains scant, however, regarding the relationship between atypical brain network connectivity and altered structure-function relationships in these groups. In ASD, there is contradictory evidence on the nature of such alterations with some studies suggesting increased or decreased functional connectivity involving particular structural areas. In very preterm children, evidence regarding the overall nature of structure-function network alterations remains scarce. Both populations present structural alterations and atypical oscillatory activity, and this research will investigate how structure-function relationships in brain networks are altered in ASD and in very preterm children and their association with developmental difficulties. Specifically, in ASD it will be assessed the functional brain networks spatial maps variability and atypical structural developmental trajectories of cortical thickness, and in preterm, atypical oscillatory activity and synchrony, and altered thalamic structural measures.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Sam Doesburg
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.