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Student Podium Presentation (Session 2)

  • Isabel Bader Theatre (map)

5:00pm – 5:15pm

Yuhan Helena Liu, Berj Bardakjian

A Large-Scale Neuro-glial Network Model of Seizure Termination”

 Background: How seizures terminate remains elusive. This is clinically relevant as seizure termination is sometimes followed by the postictal generalized EEG suppression state (PGES), a period with suppressed activities and has been found to be associated with sudden unexpected death in epilepsy. Method: Large-scale neuroglial network modeling was combined with EEG data analysis to elucidate the processes involved in seizure termination. Results: Dominant frequency decay, increase in cross-frequency coupling strength, as well as shift in frequency of the phase signal were observed in EEG recordings with PGES as a seizure progresses. Those experimental observations were reproduced in the simulated local field potential (LFP) by changing synaptic strengths in the model network. Different effects on dominant frequency and cross-frequency coupling were observed by varying the strengths of four different types of synapses: connections between excitatory to excitatory, excitatory to inhibitory, inhibitory to excitatory and inhibitory to inhibitory neurons. Moreover, simulations showed that microglia could modulate synaptic strengths in response to neuronal activity to produce the aforementioned experimental observations. Conclusion: Changes in the functional connectivity of the neural network could underlie the dynamics in seizure termination and microglia could play a role in shaping the connectivity. Significance: Combining computer modeling and electrophysiological observations can formulate testable hypotheses for guiding future studies to elucidate mechanisms in seizure termination. 

5:15-5:30 PM

Raeesa Matadar, Rita Kandel, Paul Santerre

“The Metabolism of Inner Annulus Fibrosus Cells Regulates Phenotype”

 Introduction: Lower back pain is one of the largest causes of disability globally. It is associated with the degeneration of the intervertebral disc (IVD), a multi-tissue support structure that links the vertebral bodies. Changes in the extracellular matrix (ECM) reduce the disc’s ability to transfer loads resulting in progressive tissue degradation. As there is little capacity for self-repair, regenerating the IVD in vitro is now being explored. Previous work has shown that the addition of dexamethasone and sodium pyruvate contributes to the production and accumulation of appropriate ECM, and increases mitochondrial membrane potential in vitro. Thus, culture conditions appear to trigger metabolic changes that affect ECM accumulation, however, there have been few investigations into this link in annulus fibrosus (AF) cells. The purpose of this study was to investigate the role of the AMPK/PGC1α/PPAR/sox9 signalling axis in phenotype maintenance and appropriate ECM production without the use of a corticosteroid. 
Methods: AF cells were isolated enzymatically from bovine caudal tails and seeded onto multilamellar angle-ply nanofibrous PU scaffolds in spinning bioreactors to generate AF tissues in vitro. AF tissues were cultured for up to 3 weeks in DMEM containing either 1mM (low) or 25mM (high) glucose concentrations. Tissues were evaluated histologically, biochemically, immunohistochemically and for gene expression and protein levels. 
Results: IAF tissues grown in low-glucose accumulated collagen type II and aggrecan, as well as collagen type I whereas tissues grown in high glucose only accumulated collagen type I. Over time, gene expression showed an increase in PGC1α and mitochondrial transcription factor A, as well as SOX9, COL2A1 and ACAN which are components of the native IAF. We also observed an increase p-AMPK, p-ACC, PGC1α, and sox9 protein levels. ATP levels in tissue were not significantly lower in low-glucose, suggesting a non-canonical activation of AMPK. The next steps will be to inhibit AMPK to confirm its role in phenotype maintenance.
Conclusions: Here we demonstrated that low-glucose medium restored the IAF cell phenotype and activated the AMPK/PGC1α/PPAR/sox9 signalling axis when compared to high-glucose. These studies provide novel insights into the mechanisms regulating IAF phenotype which will facilitate the identification of an ideal medium formulation to enhance tissue formation appropriate for IVD regeneration and functionality. 

 5:30pm-5:45pm

Christopher McFaul, Christopher Yip, Rodrigo Fernandez-Gonzalez

“Understanding Cardiac Tube Formation in Developing Drosophila Embryos using Light Sheet Microscopy and Cardiac Drug Screening”

Heart development begins with the formation of a primitive tube, both in fruit flies and mammals. Tube formation is mediated by coordinated cell movements. In Drosophila, the heart is formed from 52 bi-lateral pairs of cardiac precursors that migrate dorsally and medially to join their counterparts. The cells must then undergo distinct morphological changes to control sites of adhesion and repulsion to their partner in order to form a lumen. While the genetic pathways that induce cardiac cell specification have been clearly defined, the cellular and molecular mechanisms that regulate collective cell migration during heart tube formation are not well understood. Leveraging the simplicity and pharmacological tractability of the fruit fly, Drosophila melanogaster, and the ability to perform live imaging of its embryos, we have developed a light-sheet microscopy platform and quantitative image analysis to characterize cell behaviours and molecular rearrangements during heart tube formation in living Drosophila embryos. Our system allows identification and tracking of cardiac precursors and the overlying epidermal cells. Automated image analysis allows quantitative comparison of the dynamics of tube formation across embryos. To identify the pathways that regulate collective cell movements during heart development, we are conducting a pharmacological screen for inhibitors of cardiac precursor migration. Screen hits will be followed up using our light sheet microscopy system. We are particularly interested in the role of the cytoskeleton as both actin and myosin are important for cell movements in heart development. The kinase Rho-kinase (Rok) phosphorylates and activates the myosin light chain, and thus inhibiting Rho-kinase results in impaired myosin contractility. Preliminary experiments suggest that Rok may be important for the coordinated movement of cardioblasts during Drosophila heart morphogenesis. Embryos injected with water (controls) developed normally but those injected with 10 mM Y-27632, a Rok inhibitor had disrupted coordination of cardioblasts, leading to defects in heart tube formation. Together, our novel tools will allow us to identify pathways critical for cardiac precursor migration, polarization, and cell-cell adhesion.

 5:45-6:00PM

Shumit Saha, Muammar Kabir, Nasim Montazeri, Hisham Alshaer, Azadeh Yadollahi

“Sleep Apnea Diagnosis using Tracheal Respiratory Sounds and Movement”

 Background: Sleep apnea is a chronic respiratory disorder due to intermittent partial (hypopnea) or complete (apnea) collapse of the pharyngeal airway during sleep. 26% of the Canadian adults are at high risk of sleep apnea. However, due to the complexity and limited access to polysomnography (PSG), 84% of Canadians who are at high risk of sleep apnea are not diagnosed. To address this problem, a robust and cost-effective home based technology to assess sleep apnea severity is required. Thus, we aimed to develop a new algorithm for sleep apnea diagnosis using respiratory sounds and respiratory related movement recorded over trachea. 
Methods: Adults referred to the sleep lab of Toronto Rehabilitations Institute for suspected sleep apnea were recruited for this study. Simultaneously with PSG, respiratory sounds and respiratory movement were recorded over the suprasternal notch using a wearable device developed by our group, which includes a microphone and an accelerometer. We developed an algorithm to differentiate breathing and snoring segments from the respiratory sounds. The accelerometer signal was low-pass filtered to extract respiratory related movements. Energy and duration of breathing and snoring segments as well as the magnitude of respiratory related movements were extracted. Extracted features were normalized between 0 and 1 and the weighted averages of the features were compared with an adaptive threshold to detect the events. We increased the threshold in the breathing segments around the time that subject was upright which shows high probability of wakefulness, and lowered the threshold for the supine position. The number of apneas and hypopneas per hour of recording time (apnea-hypopnea index, AHI) was estimated. Estimated AHI was compared to the AHI obtained from PSG (PSG-AHI) scored by technicians according to standard criteria. 
Results: Data from 59 subjects, age: 50.2±16.2 years, BMI: 29.6±5.4 kg/m2 were investigated. A high correlation was found between the estimated AHI and PSG-AHI (r = 0.84, p<0.01). Considering AHI cut-off of 15, sensitivity and specificity of diagnosing sleep apnea were 84.0% and 85.3%, respectively. 
Conclusion: Utilizing a microphone and an accelerometer embedded in a small wearable device, we could achieve very high accuracies in diagnosing sleep apnea. Introduction of small, cost-effective and easily accessible wearable devices will significantly increase the diagnostic rate of sleep apnea.