Abnormal levels of expression of microRNAs in peripheral blood of patients with traumatic brain injury are induced by microglial activation and correlated with severity of injury.

BACKGROUND: Microglia play a crucial role in regulating the progression of traumatic brain injury (TBI). In specific, microglia can self-activate and secrete various substances that exacerbate or alleviate the neuroimmune response to TBI. In addition, microRNAs (miRNAs) are involved in the functional regulation of microglia. However, molecular markers that reflect the dynamics of TBI have not yet been found in peripheral tissues.

METHODS: Paired samples of peripheral blood were collected from patients with TBI before and after treatment. Next-generation sequencing and bioinformatics analysis were used to identify the main pathways and biological functions of TBI-related miRNAs in the samples. Moreover, lipopolysaccharide-treated human microglia were used to construct a cellular immune-activation model. This was combined with analysis of peripheral blood samples to screen for highly expressed miRNAs derived from activated microglia after TBI treatment. Quantitative reverse-transcriptase polymerase chain reaction was used to determine the expression levels of these miRNAs, allowing their relationship with the severity of TBI to be examined. Receiver operating characteristic (ROC) curves were constructed to analyse the clinical utility of these miRNAs for determining the extent of TBI.

RESULTS: Sequencing results showed that 37 miRNAs were differentially expressed in peripheral blood samples from patients with TBI before and after treatment, with 17 miRNAs being upregulated and 20 miRNAs being downregulated after treatment. The expression profiles of these miRNAs were verified in microglial inflammation models and in the abovementioned peripheral blood samples. The results showed that hsa-miR-122-5p and hsa-miR-193b-3p were highly expressed in the peripheral blood of patients with TBI after treatment and that the expression levels of these miRNAs were correlated with the patients' scores on the Glasgow Coma Scale. ROC curve analysis revealed that abnormally high levels of expression of hsa-miR-122-5p and hsa-miR-193b-3p in peripheral blood have some clinical utility for distinguishing different extents of TBI and thus could serve as biomarkers of TBI.

CONCLUSION: Abnormally high levels of expression of hsa-miR-122-5p and hsa-miR-193b-3p in the peripheral blood of patients with TBI were due to the activation of microglia and correlated with the severity of TBI. This discovery may help to increase understanding of the molecular pathology of TBI and guide the development of new strategies for TBI therapy based on microglial function.