Diffusion tensor imaging and resting state functional connectivity as advanced imaging biomarkers of outcome in infants with hypoxic-ischaemic encephalopathy treated with hypothermia

Therapeutic hypothermia confers significant benefit in term neonates with hypoxic-ischaemic encephalopathy (HIE). However, despite the treatment nearly half of the infants develop an unfavourable outcome. Intensive bench-based and early phase clinical research is focused on identifying treatments that augment hypothermic neuroprotection. Qualified biomarkers are required to test these promising therapies efficiently. This thesis aims to assess advanced magnetic resonance imaging (MRI) techniques, including diffusion tensor imaging (DTI) and resting state functional MRI (fMRI) as imaging biomarkers of outcome in infants with HIE who underwent hypothermic neuroprotection. FA values in the white matter (WM), obtained in the neonatal period and assessed by tract-based spatial statistics (TBSS), correlated with subsequent developmental quotient (DQ). However, TBSS is not suitable to study grey matter (GM), which is the primary site of injury following an acute hypoxic-ischaemic event. Therefore, a neonatal atlas-based automated tissue labelling approach was applied to segment central and cortical grey and whole brain WM. Mean diffusivity (MD) in GM structures, obtained in the neonatal period correlated with subsequent DQ. Although the central GM is the primary site of injury on conventional MRI following HIE; FA within WM tissue labels also correlated to neurodevelopmental performance scores. As DTI does not provide information on functional consequences of brain injury functional sequel of HIE was studied with resting state fMRI. Diminished functional connectivity was demonstrated in infants who suffered HIE, which associated with an unfavourable outcome. The results of this thesis suggest that MD in GM tissue labels and FA either determined within WM tissue labels or analysed with TBSS correlate to subsequent neurodevelopmental performance scores in infants who suffered HIE treated with hypothermia and may be applied as imaging biomarkers of outcome in this population. Although functional connectivity was diminished in infants with HIE, resting state fMRI needs further study to assess its utility as an imaging biomarker following a hypoxic-ischaemic brain injury.Open Acces

Towards the “Baby Connectome”: Mapping the Structural Connectivity of the Newborn Brain

Defining the structural and functional connectivity of the human brain (the human “connectome”) is a basic challenge in neuroscience. Recently, techniques for noninvasively characterizing structural connectivity networks in the adult brain have been developed using diffusion and high-resolution anatomic MRI. The purpose of this study was to establish a framework for assessing structural connectivity in the newborn brain at any stage of development and to show how network properties can be derived in a clinical cohort of six-month old infants sustaining perinatal hypoxic ischemic encephalopathy (HIE). Two different anatomically unconstrained parcellation schemes were proposed and the resulting network metrics were correlated with neurological outcome at 6 months. Elimination and correction of unreliable data, automated parcellation of the cortical surface, and assembling the large-scale baby connectome allowed an unbiased study of the network properties of the newborn brain using graph theoretic analysis. In the application to infants with HIE, a trend to declining brain network integration and segregation was observed with increasing neuromotor deficit scores

Study of the Term Neonatal Brain Injury with combined Diffuse Optical Tomography and Electroencephalography

This thesis describes the application of combined diffuse optical tomography (DOT) and electroencephalography (EEG) in the investigation of neonatal term brain injury. With hypoxic ischaemic encephalopathy (HIE) and perinatal stroke being the most frequent contributors to brain injury in the term neonatal population, the first part of the thesis focuses on the description and ongoing requirement for their further investigation. In continuation to that, the characteristics and unique properties of both DOT and EEG are described and explored. The combination of these two modalities was utilised in elucidating the relationship between neuronal activity and cerebral haemodynamics both in physiological processes as well as in disease, by the infant’s cot side. This work differs to previous studies using near-infrared technologies and EEG, as a denser whole head array was used, offering the potential of 3-dimensional image reconstruction of the cortical haemodynamic events in relation to electro-cortical activity. These methods were applied in the study of critically ill infants presenting with seizures in the first few days of life. The relevant results are presented in three separate chapters of the thesis. Distinct neurophysiological phenomena such as seizures and burst suppression were detected and studied in association to underlying HIE. On the grounds of a pre-existing pilot study of our research group, distinct prolonged de-oxygenated cortical areas were identified following electrical seizure activity. Further exploration of infants with seizures provided limited supporting evidence. The investigation of burst suppression in HIE led to the first ever identification of repeated, waveform, cortical haemodynamic events in response to bursts of electrical activity with some spatial correlation to regions of brain injury. Further analysis of the low frequencies within the diffuse optical signal in cases of perinatal stroke, showed a consistent interhemispheric difference between the healthy and stroke-affected brain regions. The limitations, prospects and conclusions are presented in the final chapter. The use of simultaneous DOT and EEG offers a unique neuro-monitoring and neuro-investigating tool in the neonatal intensive care environment, which is safe, portable, and cost-effective, Ongoing research is required for the exploration and development of the methodology and its potential diagnostic properties

Early brain activity : Translations between bedside and laboratory

Neural activity is both a driver of brain development and a readout of developmental processes. Changes in neuronal activity are therefore both the cause and consequence of neurodevelopmental compromises. Here, we review the assessment of neuronal activities in both preclinical models and clinical situations. We focus on issues that require urgent translational research, the challenges and bottlenecks preventing translation of biomedical research into new clinical diagnostics or treatments, and possibilities to overcome these barriers. The key questions are (i) what can be measured in clinical settings versus animal experiments, (ii) how do measurements relate to particular stages of development, and (iii) how can we balance practical and ethical realities with methodological compromises in measurements and treatments.Peer reviewe

The NESHIE and CP Genetics Resource (NCGR): A database of genes and variants reported in neonatal encephalopathy with suspected hypoxic ischemic encephalopathy (NESHIE) and consequential cerebral palsy (CP)

DATA AVAILABILTY : All data generated or analysed during this study are included in this published article, supplementary information files, and the NCGR database repository. Access to the NCGR database is available at http://ncgr.bi.up.ac.za/. Additional data will be made available on request.SUPPLEMENTARY DATA : SUPPLEMENTARY FIG. 1. User input for a complex query generated using NCGR's filter functionality to prioritise genes likely to predispose individuals to NESHIE. Abbreviations: CP: cerebral palsy; NESHIE: neonatal encephalopathy with suspected hypoxic ischemic encephalopathy; HPO: human phenotype ontology; NCGR: NESHIE and CP genetics resource.SUPPLEMENTARY FIG. 2. Protein-protein interaction network constructed using genes that were prioritised based on evidence of potential involvement in a genetic predisposition to neonatal encephalopathy with suspected hypoxic ischaemic encephalopathy (NESHIE). Protein products of the input set of genes are represented by blue nodes. Additional direct and secondary interactors of the input set are represented in grey.SUPPLEMENTARY DATA A. Methods used to perform gene ontology enrichment and protein-protein interaction network analyses.SUPPLEMENTARY DATA B. Gene Ontology enrichment resultsSUPPLEMENTARY TABLE 1. Variant Details table data.SUPPLEMENTARY TABLE 2. Ensembl Variant Effect Prediction table data.SUPPLEMENTARY TABLE 3. Gene Details table data.SUPPLEMENTARY TABLE 4. Gene Human Phenotype Ontology table data.SUPPLEMENTARY TABLE 5. MutationTaster Variant Effect Prediction table data.SUPPLEMENTARY TABLE 6. Study Details table data.SUPPLEMENTARY TABLE 7. Study Findings table data.Neonatal encephalopathy (NE) with suspected hypoxic ischaemic encephalopathy (HIE) (NESHIE) is a complex syndrome occurring in newborns, characterised by altered neurological function. It has been suggested that genetic variants may influence NESHIE susceptibility and outcomes. Unlike NESHIE, for which a limited number of genetic studies have been performed, many studies have identified genetic variants associated with cerebral palsy (CP), which can develop from severe NESHIE. Identifying variants in patients with CP, as a consequence of NESHIE, may provide a starting point for the identification of genetic variants associated with NESHIE outcomes. We have constructed NCGR (NESHIE and CP Genetics Resource), a database of genes and variants reported in patients with NESHIE and CP (where relevant to NESHIE), for the purpose of collating and comparing genetic findings between the two conditions. In this paper we describe the construction and functionality of NCGR. Furthermore, we demonstrate how NCGR can be used to prioritise genes and variants of potential clinical relevance that may underlie a genetic predisposition to NESHIE and contribute to an understanding of its pathogenesis.The Bill & Melinda Gates Foundation, Seattle, USA; the South African Medical Research Council, Cape Town, South Africa; and the University of Pretoria through the Institute for Cellular and Molecular Medicine.https://www.elsevier.com/locate/ygenohj2023BiochemistryGeneticsImmunologyMicrobiology and Plant Patholog

Animal models of intellectual disability: towards a translational approach

Intellectual disability is a prevalent form of cognitive impairment, affecting 2–3% of the general population. It is a daunting societal problem characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social and practical adaptive skills. Intellectual disability is a clinically important disorder for which the etiology and pathogenesis are still poorly understood. Moreover, although tremendous progress has been made, pharmacological intervention is still currently non-existent and therapeutic strategies remain limited. Studies in humans have a very limited capacity to explain basic mechanisms of this condition. In this sense, animal models have been invaluable in intellectual disability investigation. Certainly, a great deal of the knowledge that has improved our understanding of several pathologies has derived from appropriate animal models. Moreover, to improve human health, scientific discoveries must be translated into practical applications. Translational research specifically aims at taking basic scientific discoveries and best practices to benefit the lives of people in our communities. In this context, the challenge that basic science research needs to meet is to make use of a comparative approach to benefit the most from what each animal model can tell us. Intellectual disability results from many different genetic and environmental insults. Taken together, the present review will describe several animal models of potential intellectual disability risk factors

The Role of MicroRNAs in Neonates with Hypoxic - Ischaemic Encephalopathy.

PhD Theses MedicalWith increasing knowledge on the role of microRNAs in various diseases, we aimed to identify and study the role of a candidate microRNA in neonates with hypoxic ischaemic encephalopathy (HIE). Neonates with varying degrees of encephalopathy and healthy neonates were recruited to this study. After establishing a novel technique to study microRNAs from dried blood spots, we performed discovery microRNA next generation sequencing on 32 dried blood spots from 16 neonates which identified let-7b as a potential microRNA associated with the apoptotic Hippo pathway. Validation studies using RT-qPCR on 45 neonates showed that let-7b-5p expression was increased on day 1 in neonates with moderate to severe HIE with an unfavourable outcome when compared to mild HIE. Mechanistic studies for let-7b-5p and Yes Associated Protein (YAP) in the Hippo pathway were performed on two animal models of perinatal brain injury (hypoxic-ischaemic and intrauterine inflammation models) and glucose-deprived cell cultures using fluorescence in situ hybridisation and immunohistochemistry. There was significantly reduced let-7b-5p expression in the peripheral blood of the intrauterine inflammation model, and in the cortical neurones of both animal models. Additionally, Hippo pathway activation was evident with increased neuronal/nuclear YAP ratio in the cerebral cortex of both animal models with increased apoptotic neuronal cell death, when compared to the control pups. Similar results were noted for let-7b-5p and YAP expression in glucose-deprived cell cultures. In summary, our results show that in hypoxic ischaemic stress, increased neuronal to nuclear YAP ratio with decreased neuronal let-7b-5p is linked to neuronal apoptosis. Therefore, let-7b-5p could be a potential biomarker for the severity of HIE acting through the Hippo-YAP-Let-7b axis. Further validation of this novel association of let- 7b-5p and the Hippo pathway in larger cohorts and identification of downstream targets of let-7b-5p would help to improve our understanding of the role of let-7b-5p in neonatal HIE