A Comparison Between Cervical and Thoracic Spinal Cord Injury: Critical Level-Dependent Differences in Pathobiology
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A Comparison Between Cervical and Thoracic Spinal Cord Injury: Critical Level-dependent Differences in Pathobiology by James Yuh-Luen Hong A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Institute of Medical Science University of Toronto © Copyright by James Hong 2020 A Comparison Between Cervical and Thoracic Spinal Cord Injury: Critical Level-dependent Differences in Pathobiology James Yuh-Luen Hong Doctor of Philosophy Institute of Medical Science University of Toronto 2020 Abstract Introduction: Despite advances in acute medical and surgical care, there are no effective regenerative or reparative strategies for traumatic spinal cord injury (SCI). Patients with SCI experience a lifetime of neurological impairment, respiratory and cardiovascular distress. While incomplete injuries to the cervical cord are amongst the most common, preclinical and clinical efforts—driven by ease-of-access-have mostly focused on the modeling and treatment of the thoracic injuries. While translational efforts remain difficult, no comparative study of level- dependent SCI pathogenesis exist. In this thesis, I have examined the local, systemic and peripheral responses to a clinically-relevant model of cervical and thoracic SCI with the overarching hypothesis that baseline differences between the levels of injury will result in distinct vascular pathologies following SCI and trigger contrasting profiles of downstream secondary injury locally and systemically. Methods: Female Wistars rats were subjected to either moderate-severe C6-7 or T6-7 SCI, RNA-sequencing, Western blot, ELISAs, Luminex arrays, immunohistochemistry and high-resolution ultrasound were used to characterize the local and peripheral changes in the spinal cord, spleen and plasma. Results: We found reduced baseline levels of collagen, fibronectin ii and astrocytic laminin in the cervical relative to the thoracic cord. This corresponded to rapid tissue clearance, increased neuroinflammation and gliosis after cSCI. Secondly, we found that there were profound reductions in the concentration of circulating cytokine and chemokines after cSCI. Finally, we found a dramatic surge in splenic norepinephrine, cortisol and cleaved caspase-3 and a corresponding reduction in leukocyte trafficking molecules to the spleen after thoracic, but not cervical, SCI. Discussion and Impact: Taken together, this work demonstrates that: 1) vascular disruption after cervical SCI should be a critical acute therapeutic target as it results in irreversible tissue and thereby functional loss following traumatic injury; 2) circulating reductions in cytokines and chemokines are likely due to a pooling at local injury sites; and 3) the level-dependent phenomenon of SCI-immunodeficiency syndrome (SCI-IDS) which has not been consistently shown in patients is reversed in our model of incomplete SCI, suggesting that incomplete injuries result only in local deafferentation and reconciles the reason why SCI-IDS has not been consistently shown in patients. iii Acknowledgments Dr. Michael Fehlings Thank you for the near decade of mentorship and for providing me with an environment to explore all my scientific curiosities. The breadth of research I was exposed to enabled me to reach new heights in academic productivity and has laid the foundations for many aspects of my scientific interest. It is my hope that someday I can follow in your footsteps and truly make a mark in the field. Drs. James Eubanks & Isabelle Aubert Thank you both for the conversations and critical evaluations of my work throughout our numerous committee meetings. At times when I was lost in the big data, these conversations helped me regain focus. I owe you both greatly for your time and hope that one day I can be considered a colleague in the field. Drs. Vince Tropepe and Phillip Marsden Thank you both for being a part of my journey, without you I would have never made the transition into my PhD. To Dr. Marsden especially, thank you for taking the time to read and assess both my transfer and my final defense—I am eternally grateful. Drs. Reaz Vawda and Mahmood Chamankhah Thank you both for being my primary mentors when I entered the laboratory. Without your initial guidance, I would have not been able to develop my skills at the numerous molecular techniques. My Parents Thank you for bringing me into this world, throughout the years I’ve often been ambiguous about what I wanted to do. It was through your support and love and I was able to find the things that I cherished and loved in life, and I hope to someday grow to become the man that you’ve brought me up to be. iv To My Friends You know who you are! Thank you for the fun times in the lab and on conferences, I enjoyed the numerous uncomfortable hikes in dress shoes and flip-flops, the sharing of dreams, the scientific arguments, the relationship advice, and the academic journey. I will cherish the connections I’ve made with all of you and hope to keep in touch. To Susan Thank you for being the love of my life. We met at the start of my academic journey, and without your love and support, I would be a very different person today. I look forward to spending the rest of our life together and hope that I can bring you a lifetime of happiness. v Statement of Contributions For the research described in this thesis, I maintain primary accountability for all results and interpretation of such results. I was principally responsible for the experimental design and execution of the project. However, I acknowledge that I received substantial assistance from lab members who are experts in their respective scientific areas, and I was responsible for training several research students who significantly contributed to the collection of the data displayed in this thesis. Therefore, I wish to formally recognize the scientific contributions of these individuals for their involvement in this research. Dr. Mahmood Chamankhah collected the thoracic samples for RNA-sequencing, conducted preliminary Western blots and qRT-PCR, trained me in the aforementioned molecular techniques. Involved in the interpretation and discussion of qPCR, Western blot and RNA- sequencing results. Drs. Jian Wang and Yang Liu executed the animal surgeries in C6-7 and T6-7. Drs. Dario Righelli and Claudia Angelini involved in the interpretation and discussion of RNA-sequencing results. Dr. Anna Badner collected the high-resolution ultrasound data and sectioned numerous samples for immunohistochemistry. Priscilla Chan sectioned numerous samples for immunohistochemistry. Dr. Chris Ahuja cultured primary astrocytes and pericytes for in vitro segment of the work. Alex Chang assisted in RNA-sequencing analysis using command line tools, ran ELISAs, and Western blots. vi Mohammad Zavvarian captures confocal images of cords, and stained cords for immunohistochemistry. Dr. Stefania Forner involved in post-operative behavioral assessments including BBB and grip strength. Behzad Azad provided substantial post-operative animal care for animals in all experiments throughout my entire thesis. vii Abbreviations ASIA American Spinal Injury Association ATP Adenosine Triphosphate BBB Blood Brain Barrier BBB scale Basso, Beattie, Bresnahan Locomotor Rating Scale BMS Basso Mouse Scale BSCB Blood-Spinal Cord Barrier + Ca2 Calcium Caspase Cysteine Protease, Which Cleaves at an Aspartate Residue CNS Central Nervous System CORT Corticosterone CSCI Cervical spinal cord injury CSF Cerebrospinal Fluid CSPG Chondroitin Sulfate Proteoglycan Da Dalton EB Evans Blue ECF Extracellular Fluid ECM Extracellular Matrix EGF Epidermal Growth Factor GCSF Granulocyte - colony stimulating factor GMCSF Granulocyte-macrophage colony-stimulating factor HRP Horseradish Peroxidase IHC Immunohistochemistry IL1 Interleukin 1 alpha IL1 Interleukin 1 beta viii IL10 Interleukin-10 IL12 Interleukin-12 IL17A Interleukin-17A IL18 Interleukin-18 IL2 Interleukin-2 IL4 Interleukin-4 IL5 Interleukin-5 IP10 Interferon gamma-induced protein 10 + K Potassium KDa Kilodalton LIX Lipopolysaccharide-induced CXC chemokine MCP1 Monocyte chemoattractant protein-1 MIP2 macrophage inflammatory protein 2 + Na Sodium NASCIS National Acute Spinal Cord Injury Study NE Norepinephrine NFκB Nuclear Factor Kappa Light Polypeptide Gene Enhancer in B-Cells NO Nitrous Oxide NPC Neural Precursor Cell NVU Neurovascular Unit OPC Oligodendrocyte Precursor Cell PAGE Poly Acrylamide Gel Electrophoresis PBS Phosphate Buffered Saline PDGF Platelet Derived Growth Factor qRT-PCR Quantitative Real-Time Polymerase Chain Reaction RANTES regulated on activation, normal T cell expressed and secreted Ras Small GTPase Involved in Cell Signaling ix ROS Reactive Oxygen Species SCI Spinal Cord Injury SCI-IDS Spinal cord injury-induced immunodeficiency syndrome SPN Spinal preganglionic neurons TBST Tris-buffered saline with 0.1% Tween-20 TJ Tight Junction TNFα Tumor Necrosis Factor Alpha ZO Zona Occludens x Table of Contents Contents Acknowledgments.......................................................................................................................... iv Statement of Contributions ............................................................................................................ vi Abbreviations ............................................................................................................................... viii Table of Contents ........................................................................................................................... xi