In vivo evidence for the contribution of peripheral circulating inflammatory exosomes to neuroinflammation

Abstract

Abstract Background Neuroinflammation is implicated in the development and progression of many neurodegenerative diseases. Conditions that lead to a peripheral immune response are often associated with inflammation in the central nervous system (CNS), suggesting a communication between the peripheral immune system and the neuroimmune system. The underlying mechanism of this relationship remains largely unknown; however, experimental studies have demonstrated that exposure to infectious stimuli, such as lipopolysaccharide (LPS) or high-fat diet (HFD) feeding, result in profound peripheral- and neuro-inflammation. Methods Using the model of endotoxemia with LPS, we studied the role of serum-derived exosomes in mediating neuroinflammation. We purified circulating exosomes from the sera of LPS-challenged mice, which were then intravenously injected into normal adult mice. Results We found that the recipient mice that received serum-derived exosomes from LPS-challenged mice exhibited elevated microglial activation. Moreover, we observed astrogliosis, increased systemic pro-inflammatory cytokine production, and elevated CNS expression of pro-inflammatory cytokine mRNA and the inflammation-associated microRNA (miR-155) in these recipient mice. Gene expression analysis confirmed that many inflammatory microRNAs were significantly upregulated in the purified exosomes under LPS-challenged conditions. We observed accumulated signaling within the microglia of mice that received tail-vein injections of fluorescently labeled exosomes though the percentage of those microglial cells was found low. Finally, purified LPS-stimulated exosomes from blood when infused directly into the cerebral ventricles provoked significant microgliosis and, to a lesser extent, astrogliosis. Conclusions The experimental results suggest that circulating exosomes may act as a neuroinflammatory mediator in systemic inflammation.

Keywords

• Neuroinflammation
• Lipopolysacchride
• Microglia
• Exosomes