Accumulation of neuronal α-synuclein is a prominent feature in Parkinson’s disease. More recently, such abnormal protein aggregation has been reported to spread from cell to cell and exosomes are considered as important mediators. The focus of such research, however, has been primarily in neurons. Given the increasing recognition of the importance of non-cell autonomous-mediated neurotoxicity, it is critical to investigate the contribution of glia to α-synuclein aggregation and spread. Microglia are the primary phagocytes in the brain and have been well-documented as inducers of neuroinflammation. How and to what extent microglia and their exosomes impact α-synuclein pathology has not been well delineated. We report here that when treated with human α-synuclein preformed fibrils, exosomes containing α-synuclein released by microglia are fully capable of inducing protein aggregation in the recipient neurons. Additionally, when combined with microglial proinflammatory cytokines, these exosomes further increased protein aggregation in neurons. Inhibition of exosome synthesis in microglia reduced α-synuclein transmission. The in vivo significance of these exosomes was demonstrated by stereotaxic injection of exosomes isolated from α-synuclein preformed fibrils treated microglia into the mouse striatum. Phosphorylated α-synuclein was observed in multiple brain regions consistent with their neuronal connectivity. These animals also exhibited neurodegeneration in the nigrostriatal pathway in a time-dependent manner. Depleting microglia in vivo dramatically suppressed the transmission of α-synuclein after stereotaxic injection of preformed fibrils. Mechanistically, we report here that α-synuclein preformed fibrils impaired autophagy flux by upregulating PELI1, which in turn, resulted in degradation of LAMP2 in activated microglia. More importantly, by purifying microglia/macrophage derived exosomes in the CSF of Parkinson’s disease patients, we confirmed the presence of α-synuclein oligomer in CD11b+ exosomes, which were able to induce α-synuclein aggregation in neurons, further supporting the translational aspect of this study. Taken together, our study supports the view that microglial exosomes contribute to the progression of α-synuclein pathology and therefore, they may serve as a promising therapeutic target for Parkinson’s disease.

Astrocyte function is an important contributor to cellular viability during brain hypoxia and ischemia. Levels of the hypoxia‐inducible transcription factors (HIFs) HIF‐1 and HIF‐2 are increased in hypoxic conditions and impact the neuroprotective properties of astrocytes. For example, HIF‐2 induces levels of erythropoietin (EPO), a neuroprotectant, by astrocytes. In contrast, HIF‐1 activity in astrocytes diminishes the viability of neurons in co‐cultures during hypoxia. Thus, HIF‐1 and HIF‐2 may have opposing effects on astrocytes. In this study, we explore the balance of HIF‐1 and HIF‐2 signaling in astrocytes during chronic (1–7 d) hypoxia while altering the degree of hypoxia and glucose availability. In addition, we investigate the effects of these conditions on neuron apoptosis. During exposure to chronic moderate hypoxia (2% O2) and plentiful glucose (10 mM), HIF‐2 and EPO abundance increases from d 1 to 7. Similarly, pretreatment with moderate hypoxia markedly increases the abundance of HIF‐2 and EPO when astrocytes are subsequently exposed to severe hypoxia (0.5% O2; 24 h) in 10 mM glucose, which inhibits neuron apoptosis in coculture. Although HIF‐1 targets the expression increase during the 7 d in chronic moderate hypoxia (2% O2) and limited glucose (2 mM), further exposure to severe hypoxia (0.5% O2; 24 h) induces a decrease of most HIF‐1 targets in astrocytes. Notably, in astrocyte exposure to 2% O2 prior to 0.5% O2, the expression of iNOS, an HIF‐1–regulated protein, keeps increasing when glucose is limited, whereas EPO and VEGF abundance is suppressed, inducing increased apoptosis of neurons in coculture under limited glucose (2 mM). Thus, both hypoxic severity and glucose abundance regulate the balance of HIF‐1 and HIF‐2 activity in astrocytes, leading to diverse effects on neurons. These results could have important implications on the adaptive or pathologic role of astrocytes during chronic hypoxia and ischemia.—Guo, M., Ma, X., Feng, Y., Han, S., Dong, Q., Cui, M., Zhao, Y. In chronic hypoxia, glucose availability and hypoxic severity dictate the balance between HIF‐1 and HIF‐2 in astrocytes. FASEB J. 33, 11123–11136 (2019). http://www.fasebj.org

Trained immunity was recently discovered in innate immune cells and shown to facilitate the clearance of pathogens at the time of occurrence of the second insult. However, it exacerbates several aspects of neuropathologies, and proper therapy is needed to rectify this abnormal immune reaction. Mesenchymal-stem cells (MSCs) exhibit a distinct capability for brain repair but are associated with safety concerns. Extracellular vesicles derived from MSCs are a promising alternative therapy. In this study, we used lipopolysaccharides to activate trained immunity in the brain and examined the therapeutic potential of MSC-derived extracellular vesicles in mitigating the trained-immunity-induced exacerbated neuropathology. We found that MSC-derived extracellular vesicles showed comparable effects to those of MSCs in the mitigation of trained immunity in the brain. Moreover, the administration of MCS-derived extracellular vesicles mitigated the aggregated inflammatory responses in the acute stage of stroke and alleviated the trained-immunity-induced increased load of amyloid-β in APP/PS1 mice. We further investigated the molecular machinery of MSC-derived extracellular vesicles and found that IL-10 is important for the mediation of the therapeutic potential of MSC-derived extracellular vesicles toward the alleviation of trained immunity. Our study indicates that extracellular-vesicle-based regenerative strategies might be useful to mitigate trained immunity in the brain.