Bioinformatic analysis of brain-specific miRNAs for identification of candidate traumatic brain injury blood biomarkers

BackgroundDetection of brain-specific miRNAs in the peripheral blood could serve as a surrogate marker of traumatic brain injury (TBI). Here, we systematically identified brain-enriched miRNAs, and tested their utility for use as TBI biomarkers in the acute phase of care.MethodsPublically-available microarray data generated from 31 postmortem human tissues was used to rank 1,364 miRNAs in terms of their degree of brain-specific expression. Levels of the top five ranked miRNAs were then prospectively measured in serum samples collected from 10 TBI patients at hospital admission, as well as from 10 controls.ResultsThe top five miRNAs identified in our analysis (miR-137, miR-219a-5p, miR-128-3p, miR-124-3p, and miR-138-5p) exhibited 31 to 74-fold higher expression in brain relative to other tissues. Furthermore, their levels were elevated in serum from TBI patients compared to controls, and were collectively able to discriminate between groups with 90% sensitivity and 80% specificity. Subsequent informatic pathway analysis revealed that their target transcripts were significantly enriched for components of signaling pathways which are active in peripheral organs such as the heart.ConclusionsThe five candidate miRNAs identified in this study have promise as blood biomarkers of TBI, and could also be molecular contributors to systemic physiologic changes commonly observed post-injury.A FINAL PEER REVIEWED VERSION OF THIS ARTICLE HAS BEEN PUBLISHED IN BRAIN INJURY AT THE FOLLOWING DOI: 10.1080/02699052.2020.1764102There are some notable differences between the analysis presented in this preprint and our final peer-reviewed article. There was a single tissue sample originating from spinal cord that we had classified as a non-brain tissue in our original analysis outlined in this preprint. Because the composition of spinal cord and brain are highly similar in terms of gene expression, classifying this sample as a non-brain tissue dramatically reduced the levels of brain enrichment observed in the analysis. Because brain and spinal cord are molecularly highly similar, but technically distinct anatomical structures, we simply decided to exclude this sample from our final analysis published in Brain Injury to avoid confounds. The top 5 miRNAs identified in our original analysis still fell within the top 7 of this final analysis. In addition, the final analysis identified two additional miRNAs which could be candidate biomarkers based on levels of brain enrichment.The final article published in Brain Injury also reports an additional confirmatory tissue specificity analysis performed in a second independent dataset, as well as additional analysis examining the brain specificity of several notable previously proposed miRNA TBI biomarkers, which is not described in this preprint.