Background:Detection 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. Methods:Publically-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. Results:The 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. Conclusions:The 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.

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The identification of precision blood biomarkers which can accurately indicate damage to brain tissue could yield molecular diagnostics with the potential to improve how we detect and treat neurological pathologies. However, a majority of candidate blood biomarkers for neurological damage that are studied today are proteins which were arbitrarily proposed several decades before the advent of high-throughput omic techniques, and it is unclear whether they represent the best possible targets relative to the remainder of the human proteome. Here, we leveraged mRNA expression data generated from nearly 12,000 human specimens to algorithmically evaluate over 17,000 protein-coding genes in terms of their potential to produce blood biomarkers for neurological damage based on their expression profiles both across the body and within the brain. The circulating levels of proteins associated with the top-ranked genes were then measured in blood sampled from a diverse cohort of patients diagnosed with a variety of acute and chronic neurological disorders, including ischemic stroke, hemorrhagic stroke, traumatic brain injury, Alzheimer’s disease, and multiple sclerosis, and evaluated for their diagnostic performance. Our analysis identifies several previously unexplored candidate blood biomarkers of neurological damage with possible clinical utility, many of which whose presence in blood is likely linked to specific cell-level pathologic processes. Furthermore, our findings also suggest that many frequently cited previously proposed blood biomarkers exhibit expression profiles which could limit their diagnostic efficacy.

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