Genetic Modulators of Traumatic Brain Injury in Animal Models and the Impact of Sex-Dependent Effects

Circulating extracellular vesicles from patients with traumatic brain injury induce cerebrovascular endothelial dysfunction

Endothelial dysfunction is a key proponent of pathophysiological process of traumatic brain injury (TBI). We previously demonstrated that extracellular vesicles (EVs) released from injured brains led to endothelial barrier disruption and vascular leakage. However, the molecular mechanisms of this EV-induced endothelial dysfunction (endotheliopathy) remain unclear. Here, we enriched plasma EVs from TBI patients (TEVs), and detected high mobility group box 1 (HMGB1) exposure to 50.33 ± 10.17% of TEVs and the number of HMGB1⁺TEVs correlated with injury severity. We then investigated for the first time the impact of TEVs on endothelial function using adoptive transfer models. We found that TEVs induced dysfunction of cultured human umbilical vein endothelial cells and mediated endothelial dysfunction in both normal and TBI mice, which were propagated through the HMGB1-activated receptor for advanced glycation end products (RAGE)/Cathepsin B signaling, and the resultant NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation and canonical caspase-1/gasdermin D (GSDMD)-dependent pyroptosis. Finally, von Willebrand factor (VWF) was detected on the surface of 77.01 ± 7.51% of HMGB1⁺TEVs. The TEV-mediated endotheliopathy was reversed by a polyclonal VWF antibody, indicating that VWF might serve a coupling factor that tethered TEVs to ECs, thus facilitating HMGB1-induced endotheliopathy. These results suggest that circulating EVs isolated from patients with TBI alone are sufficient to induce endothelial dysfunction and contribute to secondary brain injury that are dependent on immunologically active HMGB1 exposed on their surface. This finding provided new insight for the development of potential therapeutic targets and diagnostic biomarkers for TBI.

Increased level of exosomal miR-20b-5p derived from hypothermia-treated microglia promotes neurite outgrowth and synapse recovery after traumatic brain injury

Mild hypothermia has been proven to inhibit microglia activation after TBI. Exosomal microRNA derived from microglia played a critical role in promoting neurite outgrowth and synapse recovery. Here, we aimed to investigate the role of microRNAs in microglial exosomes after hypothermia treatment on neuronal regeneration after TBI. For in vitro study, stretch-injured neurons were co-cultured with microglial exosomes. For in vivo study, C57BL/6 mice were under controlled cortical impact and injected with microglial exosomes. The results showed that MG-LPS-EXO^HT increased the number of dendrite branches and total length of dendrites both in vitro and in vivo, elevated the expression levels of PSD-95 and GluR1 in stretch-injured neurons, and increased spine density in the pericontusion region. Moreover, MG-LPS-EXO^HT improved motor function and motor coordination. A high-throughput sequencing showed that miR-20b-5p was upregulated in MG-LPS-EXO^HT. Elevating miR-20b-5p promoted neurite outgrowth and synapse recovery of injured neurons both in vitro and in vivo. Following mechanistic study demonstrated that miR-20b-5p might promote neurite outgrowth and synapse recovery by directly targeting PTEN and activating PI3K-AKT pathway. In conclusion, mild hypothermia could modify the microRNA prolife of exosomes derived from LPS activated BV2 cells. Furthermore, high level of microglial exosomal miR-20b-5p induced by mild hypothermia could transfer into injured neurons and promote neurite outgrowth and synapse recovery after TBI via activating the PI3K-AKT pathway by suppressing PTEN expression.

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Despite extensive research efforts, the majority of trialed monotherapies to date have failed to demonstrate significant benefit. It has been suggested that this is due to the complex pathophysiology of TBI, which may possibly be addressed by a combination of therapeutic interventions. In this article, we have reviewed combinations of different pharmacologic treatments, combinations of non-pharmacologic interventions, and combined pharmacologic and non-pharmacologic interventions for TBI. Both preclinical and clinical studies have been included. While promising results have been found in animal models, clinical trials of combination therapies have not yet shown clear benefit. This may possibly be due to their application without consideration of the evolving pathophysiology of TBI. Improvements of this paradigm may come from novel interventions guided by multimodal neuromonitoring and multimodal imaging techniques, as well as the application of multi-targeted non-pharmacologic and endogenous therapies. There also needs to be a greater representation of female subjects in preclinical and clinical studies.