Pathophysiology and Proteogenomics of Post-infectious and Post-hemorrhagic Hydrocephalus in Infants
Date
2020-07-21
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Abstract
Post-infectious (PIH) and post-hemorrhagic (PHH) hydrocephalus occur as sequalae of neonatal sepsis or intraventricular hemorrhage (IVH) of prematurity, respectively. Together, PIH and PHH represent the most common form of infantile hydrocephalus, the most common indication for neurosurgery in children globally, and the leading cause of neurological morbidity and mortality worldwide. The lack of understanding of the pathophysiology of PIH and PHH, particularly with regards to the host central nervous system response to the antecedent infection and hemorrhage, perturbation of differentiating neural stems in the ventricular (VZ) and subventricular (SVZ) zones, and damage to periventricular white matter (PVWM) tracts carrying sensorimotor fibers, has hindered the identification of therapeutic targets to prevent these two debilitating conditions. To this end, we hypothesized that PIH and PHH share a common pathophysiological mechanism characterized by host immune response to infection or hemorrhage, activation of the metalloprotease ADAM10 and cleavage of the cell-junctional protein, N-cadherin, which results in impaired VZ/SVZ differentiation and PVWM damage. The studies presented in this dissertation collectively explore novel overarching lines of scientific inquiry - the concept that there are unique host immune responses to PIH and PHH, as well as ones that are common to both conditions that underlie their observed clinical similarities. To test the hypothesis, we leveraged the cerebrospinal fluid (CSF) of human PIH, PHH and matched non-infectious non-hemorrhagic hydrocephalic control infants. First, we defined the differentially expressed proteome and transcriptome of PIH using high throughput proteomics and RNA-seq, respectively. The integration of proteogenomic techniques defined critical gene networks and pathway level mechanisms of PIH pathophysiology. Second, our validated proteomics pipeline was used to identify the common and unique molecular pathways that underlie the pathophysiology of PIH and PHH. Third, our CSF findings were related to VZ/SVZ development and PVWM microstructural damage with diffusion MRI (dMRI) in PHH and control infants. Neurocytology of human postmortem brain tissues of PIH, PHH and controls was performed to correlate the dMRI findings. Fourth, we defined the mechanistic triggers underlying PIH and PHH pathogenesis utilizing a mouse in vitro cell culture model of periventricular VZ cells. Finally, we developed in vivo animal models of PIH (mice) and PHH (ferrets), to recapitulate our findings of VZ/SVZ disruption, neuroinflammation and PVWM injury in both PIH and PHH. Through our comprehensive experiments, we determined the following: 1) human CSF profiles of PIH and PHH reflect similar alterations in gene-activated pathways related to neuroinflammation and cell-cell junction structure; 2) neuroinflammation-associated cell junction (VZ/SVZ) disruption and PVWM injury is a pathophysiological mechanism that is common to both PIH and PHH; 3) dMRI can non-invasively assess the VZ/SVZ region as well as differentiate and quantify tract-specific patterns of PVWM injury. Therefore, it can distinguish direct effects on axons/myelin from changes in the extracellular milieu to reflect neuroinflammation, axonal fiber loss, and dysmyelination; 4) VZ/SVZ disruption in PIH and PHH is mediated by metalloprotease (e.g., ADAM10) cleavage of cell junctional proteins (e.g., N-cadherin); and 5) pharmacologic inhibition of ADAM10-mediated N-cadherin cleavage represents a viable therapeutic approach to prevent PIH and PHH. These novel insights into the pathophysiology of PIH and PHH may enable investigation of ADAM10 inhibitors and other therapeutic strategies to minimize the developmental disability in PIH and PHH patients. The biomarkers we identified can be further investigated as diagnostic measures for monitoring and providing therapy to infants who develop neonatal sepsis or IVH to prevent PHH/PIH. Finally, the in vitro and in vivo experimental models we generated are poised for future preclinical and translational studies into the pathogenesis of these previously inaccessible and debilitating conditions.
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Keywords
Proteomics, RNA-sequencing, Transcriptomics, Proteogenomics, Hydrocephalus, Post-infectious hydrocephalus, Post-hemorrhagic hydrocephalus, Ventricular zone, Subventricular zone, Periventricular white matter, Lateral ventricular perimeter, Frontal-occipital horn perimeter, Diffusion tensor imaging, Diffusion basis spectrum imaging, ADAM10, N-cadherin, Neuroinflammation, Ependyma
Citation
Isaacs, A. M. (2020). Pathophysiology and Proteogenomics of Post-infectious and Post-hemorrhagic Hydrocephalus in Infants (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.