Vekrellis, K. | Search bioRxiv

bioRxiv2022

Microglia and astrocytes differentially endocytose exosomes facilitating alpha-Synuclein endolysosomal sorting

Exosomes have emerged as key players in cell-to-cell communication in both physiological and pathological processes in the Central Nervous System (CNS). Thus far, the intracellular pathways involved in uptake and trafficking of exosomes within different cell types of the brain (microglia and astrocytes) are poorly understood. In our study, the endocytic processes and subcellular sorting of exosomes were investigated in primary glial cells, particularly linked with the exosome-associated -synuclein (-syn) transmission. Mouse microglia and astrocytic primary cultures were incubated with DiI-stained mouse brain-derived exosomes. The internalization and trafficking pathways were analysed in cells treated with pharmacological reagents that block the major endocytic pathways. Brain-derived exosomes were internalized by both glial cell types; however, uptake was more efficient in microglia than in astrocytes. Colocalization of exosomes with early and late endocytic markers (Rab5, Lamp1) indicated that exosomes are sorted to endolysosomes for subsequent processing. Treatment with Cytochalasin D, that blocks actin-dependent phagocytosis and/or macropinocytosis, inhibited exosome entry into glial cells, whereas treatment with inhibitors that strip off cholesterol from the plasma membrane, induced uptake, however differentially altered endosomal sorting. Exosome-associated fibrillar -Syn was efficiently internalized and detected in Rab5- and Lamp1-positive compartments within microglia. Our study strongly suggests that exosomes enter glial cells through an actin network-dependent endocytic pathway and are sorted to endolysosomes for subsequent processing. Further, brain-derived exosomes are capable of mediating cell-to-glia transmission of pathological -Syn that is also targeted to the endosomal pathway, suggesting a possible beneficial role in microglia-mediated clearance of toxic protein aggregates, present in numerous neurodegenerative diseases.

neuroscience↗

bioRxiv2021

A double-hit in vivo model of GBA1 viral microRNA-mediated downregulation and human alpha-synuclein overexpression demonstrates nigrostriatal degeneration

Preclinical and clinical studies support a strong association between mutations in the GBA1 gene that encodes {beta}-glucocerebrosidase (GCase) (EC 3.2.1.45; glucosylceramidase beta) and Parkinsons disease (PD). Alpha-synuclein (AS), a key player in PD pathogenesis, and GBA1 mutations may independently and synergistically cause lysosomal dysfunction and thus, embody clinically well-validated targets of the neurodegenerative disease process in PD. However, double-hit in vivo models, recapitulating pathological features of PD that can be used to dissect the nature of the complex relationship between GCase and AS on the nigrostriatal axis, the region particularly vulnerable in PD, are direly needed. To address this, we implemented a bidirectional approach in mice to examine the effects of: 1) GCase overexpression (wildtype and mutant N370S) on endogenous AS levels and 2) downregulation of endogenous GCase combined with AS overexpression. Striatal delivery of viral-mediated GCase overexpression revealed minimal effects on cortical and nigrostriatal AS tissue levels and no significant effect on dopaminergic system integrity. On the other hand, microRNA (miR)-mediated GBA1 downregulation (miR GBA), combined with virus-mediated human AS overexpression (+AS), yields decreased GCase activity in the cortex, mimicking levels seen in GBA1 heterozygous carriers (30-40%), increased astrogliosis and microgliosis, decreased striatal dopamine levels (50% compared to controls) and loss of nigral dopaminergic neurons (~33%)-effects that were all reversible with miR rescue. Most importantly, the synergistic neurodegeneration of miR GBA+AS correlated with augmented AS accumulation and extracellular release in the striatum. Collectively, our results suggest that GCase downregulation alone is not sufficient to recapitulate key pathological features of PD in vivo, but its synergistic interplay with AS, via increased AS levels and release, drives nigrostriatal neurodegeneration. Furthermore, we demonstrate a novel double-hit model that can be used to identify putative mechanisms driving PD pathophysiology and can be subsequently used to test novel therapeutic approaches.

neuroscience↗