Mechanism Study Of The Astrocytes Activation By Brain Microvascular Endothelial Cells-derived Exosomes Upon Escherichia Coli Infection

Bacterial meningitis is one of the serious infectious disease in central nervous system(CNS).Extraintestinal pathogenic Escherichia coli(Ex PEC)is a common pathogen causing the diseases.Ex PEC induces high level bacteremia in vivo,adhere to and invade brain microvascular endothelial cells(BMECs)and penetrate the blood-brain barrier(BBB).In this process,bacteria activate glial cells and recruit peripheral immune cells migration into the CNS,eventually leading to neuroinflammation.However,it is not clear how Ex PEC activate astrocytes when penetrating BBB.Exosomes are tiny vesicles secreted by cells with a diameter of 30-140 nm.The vesicles are consisted with a bilayer membrane structure and many other bioactive substances such as protein,DNA and RNA,which could be changed by external stimulation.Exosomes has been found to be involved in various physiological and pathological processes,including myelin formation,repair of damaged tissues,transmission of toxic proteins,and induction of inflammatory response.To explore whether the exosomes derived from endothelial cells participate in the regulation of glial cells in bacterial meningitis,we isolated exosomes from BMECs infected with Ex PEC,and analyzed the exosomes contents by mass spectrometry.Then,we preliminarily discussed the molecular mechanism of astrocyte activation mediated by the protein content of exosomes.The main findings are as follows: 1.The exosomes were successfully isolated and identified from the brain microvascular endothelial cells.It was found that the exosomes in the infected group can be absorbed by astrocytes,and it can promote the activation of astrocytes to produce a variety of cytokines,chemokines and VEGFA;2.In this study,1294 kinds of exosomal proteins in the infected group and 1694 kinds of exosomal proteins in the control group were identified.Compared with exo-control,30 proteins were significantly up-regulated and 29 proteins were significantly down regulated.Bioinformatics analysis of proteomic results showed that GDF15 encapsulated in exosomes may be the main effector;3.GDF15 up-regulated in exo-infect can promote the activation of astrocytes to produce VEGFA.