CSF miRNAome reveals gliosis pathways in GM-IVH
One of the most common neurodevelopmental injuries in preterm born infants is the germinal matrix-intraventricular haemorrhage (GM-IVH). GM-IVH usually occurs in extremely preterm infants born with less than 28 weeks of gestation and is characterised by bleeding in the temporal structure of germinal matrix (GM). The GM is located around the lateral ventricles of the brain and is composed of neural progenitor cells (NPCs) and rich vasculature. Cerebral blood flow fluctuations and the fragile vasculature of GM are among the main suggested causes of this injury. Depending on the extend of the bleeding, blood may fill the brain ventricles and exceed to the cerebrospinal fluid (CSF). GM-IVH triggers local inflammatory response and collagen synthesis in the CSF, leading to CSF malabsorption. As such CSF is accumulated in the ventricles and usually leads to ventricular enlargement, called post-haemorrhagic ventricular dilation (PHVD)). Currently, clinicians typically manage the progressive ventricular dilation by drainage of the accumulated CSF.One approach to study the ongoing pathophysiology in the brain of infants with GM-IVH is by studying their CSF. CSF is mainly produced by choroid plexus, runs through the ventricles, and removes metabolic waste outside the brain while also carries important factors for the surrounding tissues. CSF shows distinct molecular signatures across the ventricles which indicate region-specific functions. Therefore, CSF interacts and influences the surrounding tissues in developing and adult healthy brain and in disease.The aim of this study was to explore the potential interactions between signalling molecules, such as microRNAs (miRs), in the CSF of preterm infants with the surrounding tissue in the pre-term developing brain. Growing evidence suggests that miRs, due to their key role in gene expression, have a significant utility as new therapeutics and biomarkers. However, miRs have not been studied in depth in the context of IVH.CSF samples were collected from 10 preterm infants born between 23-37 weeks of gestation (birth weight <1,000g) and treated for progressive PHVD at the regional tertiary Neonatal Intensive Care Unit at Southmead Hospital in Bristol, UK. GM-IVH was diagnosed as part of clinical assessment with serial trans-fontanel ultrasound and quantified according to the Levene and Starte (1981). External CSF drainage was initially undertaken via lumbar puncture before insertion of a ventricular access device (VAD). CSF used in this study was the excess fluid remaining after routine testing of samples taken for clinical indications following informed parental consent.Fifteen CSF samples from ten infants with IVH were analysed using the HTG Molecular Diagnostics miR whole transcriptome assay (https://www.htgmolecular.com/assays/mirna-wta). The CSF samples and Human Brain RNA control technical replicates were randomised prior to placement on the HTG EdgeSeq sample plate. The sequencing was performed on the Illumina MiSeq sequencer. HTG EdgeSeq Reveal software (https://www.htgmolecular.com/reveal) version 4 was used for analysis and visualisation of miR sequencing results. DESeq2 differential expression test, provided by HTG EdgeSeg Reveal software, was used for statistical analysis of differential expressed miRs across duration of CSF sampling after IVH.