Exosomes derived from bone marrow mesenchymal stem cells inhibit neuroinflammation after traumatic brain injury.

Exosomes derived from bone marrow mesenchymal stem cells can inhibit neuroinflammation through regulating microglial phenotypes and promoting nerve injury repair. However, the underlying molecular mechanism remains unclear. In this study, we investigated the mechanism by which exosomes derived from bone marrow mesenchymal stem cells inhibit neuroinflammation. Our in vitro co-culture experiments showed that bone marrow mesenchymal stem cells and their exosomes promoted the polarization of activated BV2 microglia to their anti-inflammatory phenotype, inhibited the expression of proinflammatory cytokines, and increased the expression of anti-inflammatory cytokines. Our in vivo experiments showed that tail vein injection of exosomes reduced cell apoptosis in cortical tissue of mouse models of traumatic brain injury, inhibited neuroinflammation, and promoted the transformation of microglia to the anti-inflammatory phenotype. We screened some microRNAs related to neuroinflammation using microRNA sequencing and found that microRNA-181b seemed to be actively involved in the process. Finally, we regulated the expression of miR181b in the brain tissue of mouse models of traumatic brain injury using lentiviral transfection. We found that miR181b overexpression effectively reduced apoptosis and neuroinflamatory response after traumatic brain injury and promoted the transformation of microglia to the anti-inflammatory phenotype. The interleukin 10/STAT3 pathway was activated during this process. These findings suggest that the inhibitory effects of exosomes derived from bone marrow mesenchymal stem cells on neuroinflamation after traumatic brain injury may be realized by the action of miR181b on the interleukin 10/STAT3 pathway.

Traumatic Brain Injury Induces Gastrointestinal Dysfunction and Dysbiosis of Gut Microbiota Accompanied by Alterations of Bile Acid Profile.

Gastrointestinal dysfunction is a common peripheral organ complication after traumatic brain injury (TBI), yet the underlying mechanism remains unknown. TBI has been demonstrated to cause gut microbiota dysbiosis in animal models, although the impacts of gut microbiota dysbiosis on gastrointestinal dysfunction were not examined. Bile acids are key metabolites between gut microbiota and host interactions. Therefore, the aim of this study was to investigate the mechanistic links between them by detecting the alterations of gut microbiota and bile acid profile after TBI. For that, we established TBI in mice using a lateral fluid percussion injury model. Gut microbiota was examined by 16S rRNA sequencing, and bile acids were profiled by ultra-performance liquid chromatography-tandem mass spectrometry. Our results showed that TBI caused intestinal inflammation and gut barrier impairment. Alterations of gut microbiota and bile acid profile were observed. The diversity of gut microbiota experienced a time dependent change from 1 h to 7 days post-injury. Levels of bile acids in feces and plasma were decreased after TBI, and the decrease was more significant in secondary bile acids, which may contribute to intestinal inflammation. Specific bacterial taxa such as Staphylococcus and Lachnospiraceae that may contribute to the bile acid metabolic changes were identifed. In conclusion, our study suggested that TBI-induced gut microbiota dysbiosis may contribute to gastrointestinal dysfunction via altering bile acid profile. Gut microbiota may be a potential treatment target for TBI-induced gastrointestinal dysfunction.

A Retrospective Clinical Analysis of the Serum Bile Acid Alteration Caused by Traumatic Brain Injury.

Traumatic brain injury (TBI) can cause damage to peripheral organ systems, such as digestive organ system, and alterations of gut microbiota in addition to brain injury. Our previous study found that TBI induced gastrointestinal dysfunction accompanied by alterations of bile acid metabolism. Bile acid and its receptors have been reported to play important roles in various neurological diseases. To further examine the changes of bile acid metabolism in TBI patients, we performed a retrospective clinical analysis. In this study, 177 patients were included, and the results showed that TBI patients had more frequent antibiotic use compared with a control group. Regression analysis identified TBI as an independent factor for reduction of serum bile acid level (B = -1.762, p = 0.006), even with antibiotic use taken into a regression model. Sub-group regression analysis of TBI patients showed that antibiotic use was negatively associated with bile acid level, while creatinine and triglyceride were positively associated with bile acid level. In conclusion, these data indicated that TBI could greatly reduce serum bile acid. This study provided preliminary but novel clinical evidence of TBI interfering with bile acid metabolism, and further studies with large sample sizes are needed to validate these findings in the future.