Regulatory microRNAs-mediated cerebrovascular protection and traumatic braininjury

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Traumatic brain injury (TBI) is a major medical concern in service personnel and veterans as currently no therapy is available to alleviate post-trauma neurological deficits. The blood-brain barrier (BBB) provides a dynamic interface to separate the brain from the circulatory system, maintaining a stable brain microenvironment. As a major component of the BBB, brain microvascular endothelial cells (BMECs), together with intercellular tight junctions (TJs), play a dominant role in modulating BBB integrity and paracellular permeability1. Accumulating evidence has demonstrated that BBB breakdown after TBI promotes a devastating cascade of events such as transmigration of peripheral immune cells, cerebral inflammatory responses, edema, and hemorrhagic transformation, contributing to secondary injury in neurotrauma. Thus, it is necessary to identify mechanisms and develop effective therapeutic strategies that protect BBB integrity and prevent permanent brain damage after TBI. MicroRNAs (miRs) function as a major class of small non-coding RNAs that negatively modulate protein expression. In addition to their critical role in various biological processes, miRs have also been implicated in a variety of human neurological diseases. We and others have shown the involvement of miRs in the pathogenesis of TBI. However, the functional significance and molecular mechanisms of miR molecules in regulating cerebrovascular pathogenesis, in particular BBB disruption/dysfunction, and resultant long-term neurological outcomes are poorly understood in TBI. The miR-15a/16-1 cluster is the first identified miR group associated with human carcinogenesis. Dysregulated plasma miR-15a/16-1 levels have been found in TBI individuals, showing great potential as useful biomarkers in clinical diagnosis and prognosis. Interestingly, molecular inhibition of miR-15a/16-1 levels has been shown to protect against myocardial infarction (MI) and ischemic brain injury. Therefore, American and European pharmaceutical companies consider the miR-15a/16-1 cluster as one of the most important miR targets to develop miR-based drugs for the treatment of MI. In our recent preliminary studies, we have shown that expression of the miR-15a/16-1 cluster is selectively increased in the mouse cerebral vasculature after TBI. Of note, endothelial cell (EC)-selective miR- 15a/16-1 genetic deficiency leads to reduced BBB leakage, and less neuronal loss, white matter (WM) injury, and neurobehavioral impairments in mice after TBI. We also found that the miR-15a/16-1 cluster can bind to the 3’-UTRs of major BBB tight junctions, brain-enriched Claudins, and inhibit their translation, and genetic silencing or deletion of the miR-15a/16-1 cluster significantly increased endothelial or cerebral expression of claudins. These findings have provided the basis for our Central Hypothesis that genetic deletion of vascular miR-15a/16-1 attenuates BBB disruption and subsequent pathological cascades after TBI, thereby contributing to increased BBB stabilization, reduced neuronal/WM loss, and improved long- term neurological outcomes in TBI. Three aims will be performed in this proposal. Aim 1: Define the role of vascular miR-15a/16-1 in post-traumatic BBB dysfunction and TBI outcomes; Aim 2: Elucidate the mechanisms of miR-15a/16-1 regulation of post-traumatic BBB dysfunction; Aim 3: Explore systematic delivery of miR- 15a/16-1 antagomir (inhibitor) as a potential therapy in TBI through BBB stabilization. Elucidating the molecular mechanisms of miR-15a/16-1-mediated BBB dysfunction may lead us to discover novel and effective treatment against TBI.