Year: 2021
Type: dissertation
Abstract: Background:Newborn brain injury is the leading cause of childhood neurodisability, including cerebral palsy (CP).Cystic periventricular leukomalacia (cPVL) selectively affects preterm newborns.Hypoxic-ischemic encephalopathy (HIE) affects term newborns with childbirth complications disrupting blood/oxygen supply to the brain.Glutamate excitotoxicity and inflammation are key mechanisms of injury.The role of genetic and epigenetic factors in regulation of glutamate transport and inflammation is unclear.Hypotheses:1) Preterm survivors with risk variants at the glutamate transporter (EAAT2) and key proinflammatory cytokines (TNFα, IL1ß, IL6) have higher risk of impairment vs those with either variant or none 2) Hypoxia-ischaemia (HI) alters transcription of these genes in the term-equivalent rat brain 3) This is mediated by a DNA methylation change in the brain, which correlates with methylation in blood Methods:In the APIP cohort (n=308), genotypes were tested for association with CP at 2y; secondary outcomes included cPVL, and standardised motor and cognitive assessments at 2y (Griffiths Scales) and 5y (Movement ABC; British Ability Scales, BAS).In the rat study (n=42), the effects of HI on transcription of these genes were assessed in the cortex and hippocampus (qPCR), alongside DNA methylation of EAAT2 and TNFα in cortex and blood (bisulfite pyrosequencing) Results:Cytokine variants are associated with cPVL and CP (TNFα -308) and the BAS cognitive score (IL1ß -511).Evidence was weaker for white matter injury (IL6 -174), the non-verbal and verbal BAS subscales (IL1ß -511 and EAAT2 -200/-181 respectively).HI induced cytokine transcription in the rat brain, accompanied by astrogliosis and myelin injury.Evidence of suppression of glutamate transport in the cortex was very weak and not associated with DNA methylation changes. Conclusions:These exploratory studies support a role for neuroinflammation in neurological and neurodevelopmental impairment.Genetic and epigenetic biomarkers may facilitate early identification of high-risk newborns maximising chances of prevention and treatment. Lay Summary BackgroundEarly life stresses such as prematurity, infections and complicated childbirths can damage the delicate developing brain.Newborn brain injury is the leading cause of childhood disabilities affecting movement (e.g.cerebral palsy), perception (e.g.blindness, deafness) and cognition (e.g.learning, language and memory).A better understanding of how brain injuries occur is needed to develop strategies to protect the brain.Two mechanisms are emerging as central: brain inflammation and disruption of the neurotransmitter glutamate, which enables communication between neurons.Neonatologists often observe that some babies cope worse than others upon similar stresses, raising the question of whether genetic differences might be important.For example, genetic make-up could affect the strength of inflammatory responses or the extent of glutamate transport disruption.Another unanswered question regards the actual mechanisms through which early life stresses trigger changes in the brain's responses, e.g. after a severe interruption of blood and oxygen flow (hypoxia-ischaemia) seen in complicated childbirths.DNA methylation is an interesting candidate mechanism, acting like a signature or molecular memory left on the DNA by stressful events.This signature can turn the dial up or down on the brain's responses and potentially trigger stronger inflammation or greater disruption of glutamate transport.Since it is not possible to carry out such investigations in babies, animal models become valuable. Questions:1) Do genetic variants affecting inflammation and glutamate transport influence the risk of brain injury and disability in a cohort of newborns born very prematurely in Bristol? 2) Does hypoxia-ischaemia alter inflammation and glutamate transport in the rat brain?Is this mediated by DNA methylation changes?Can DNA methylation changes reflecting the early stages of brain injury be picked up in blood (which is accessible in newborns)? Results:1) Genetic variants affecting the strength of inflammation are associated with risk of severe brain injury at birth, cerebral palsy at 2y and poorer cognitive scores at 5y.Evidence was more uncertain for genetic variants affecting glutamate transport in relation to verbal skills at 5y. 2) Hypoxia-ischaemia caused inflammation in the rat brain, at the beginning of the injury process.DNA methylation related to inflammation could not be assessed because of COVID-19-related disruptions and remains a priority for future work.Evidence was more uncertain for disruption of glutamate transport, and DNA methylation was not affected in brain or blood. Conclusion:The study supports a key role for inflammation in newborn brain injuries and related disability, as well as a contribution of genetic factors to risk, and encourages further research in this direction.Having this type of information ahead of time might help the family and healthcare professionals produce a personalised plan of care, which makes the most of the available prevention strategies and treatments to protect the brain (e.g. more frequent monitoring during pregnancy, labour, and childbirth; plan childbirth in a specialised hospital to avoid last minute transfers).v I would like to thank Prof Karen Luyt, for being an inspirational mentor.She shared her vision with me from day one, supported me in becoming a part of the scientific community, and consistently fuelled my passion for research.She guided me by sharing expert knowledge, asking insightful questions, and offering plenty of positive encouragement.She challenged me when I needed it and encouraged me to develop my own path.I would like to thank Prof Anthony Isles, for sharing so much insight and knowledge with such kindness and approachability.I have truly appreciated being able to knock at his door during my time in Cardiff whenever I got stuck, and every time leaving with a clear mind and a better understanding.I am also thankful for his ability to bring me back to planet Earth whenever I went off on a tangent, both in the lab and in my writing.I would like to thank Dr Ela Chakkarapani, for his sharp questions, constructive comments, and high standards, which have regularly pushed me to do better.For giving me the invaluable opportunity to learn about many of the things behind working with animal models, both in the outlook and in the practice.For enabling a wonderful collaboration with Dr Hemmen Sabir and coming to Essen with me.Thanks to Dr Hemmen Sabir for agreeing to help with the animal work, for opening the doors of his lab and his house and sharing his expertise and resources, all with a brilliant sense of humour.Thanks to Dr David Harding for sharing the clinical data and cytokine genetic data
Author: Pregnolato, Silvia
Institution: University of Bristol
Language: English
Field: Medicine
Domain: Health Sciences
Open Access status: green
Funder: Medical Research Council
OpenAlex ID: W7139351831