Exosomes are important membranous vesicles in several physiological and pathological processes. It is postulated that the microRNAs contained in the exosomes play the major roles in these processes. Exosomal microRNAs from bone marrow mesenchymal stem cells (bMSCs) have emerged as promising therapeutic agents against inflammation. However, its specific mechanism has not been clarified. The present study was designed to elucidate the underlying mechanism of bone marrow mesenchymal stem cells derived exosomes on neuroinflammation in vitro and in vivo.Methods: In vitro co-culture experiments were done to demonstrate the effects of bMSCs and bMSCs-derived exosomes on the polarization state of BV2 microglia cells. In vivo experiments were subsequently done to validate the role of exosomes derived from bMSCs in neuro-inflammation after brain injury. MicroRNA sequencing was then done to reveal the potential expanded diversity between bMSCs and exosomes derived from bMSCs. The microRNAs were then screened and quantified by quantitative polymerase chain reaction (qPCR) to identify the most significant miRNAs. Moreover, lentiviral transfection was performed to establish animal models with overexpressed and downregulated microRNA expression levels. The animal models were subsequently used to determine the effects of specific microRNAs on neuroinflammation after TBI and their possible mechanisms of action. Results: Both bMSCs and exosomes derived from bMSCs promoted the polarization of activated BV2 microglia cells to the anti-inflammatory phenotype. They inhibited the expression of pro-inflammatory cytokines but promoted the expression of anti-inflammatory cytokines. Exosomes derived from bMSCs played a stronger role in regulating the expression of inflammatory factors. In vivo animal-based experiments further revealed that the exosomes reduced neuronal apoptosis in the cortical area. They also promoted inhibition of neuroinflammation and transformation of microglia to anti-inflammatory phenotype. In addition, MicroRNA sequencing and subsequent analysis revealed that microRNA-181b was actively involved in the process. Subsequent lentiviral transfection studies revealed that overexpression of miR181b effectively reduced neuronal apoptosis and neuroinflammatory response after traumatic brain injury. Overexpression of microRNA181b also promoted the transformation of microglia to the anti-inflammatory phenotype. These effects were achieved through activation of the IL-10/STAT3 pathway.Conclusion: Exosome derived from bMSCs promotes the polarization of microglia to anti-inflammatory phenotype and inhibit neuroinflammation both in vitro and in vivo. They also reduce neuronal apoptosis and protect damaged brain tissue. The microRNA-181b plays a vital role in this process by activating the IL-10/STAT3 pathway. Our study indicates that IL-10/STAT3 pathway may be involved in neuroinflammatory progression and that up-regulation of the microRNA-181b is a potentially new therapeutic approach for neuroinflammation.
