Extracellular Vesicles Derived from FGF2-Primed Astrocytes Against Mitochondrial and Synaptic Toxicities in Parkinson's Disease

Purpose: Mitochondrial dysfunction associated with neuronal degeneration and subsequent synaptic disconnection are essential for the development of Parkinson's disease (PD). Considering that astrocytes play key roles in synaptogenesis during development, we hypothesized that Fibroblast Growth Factor - 2 (FGF2), a key factor for astrocyte development, could reverse the toxic phenotype of reactive astrocytes, and the extracellular vesicles (EVs) derived from FGF2-primed astrocytes would enhance synaptogenesis in PD model. The present study was to test this hypothesis.

Methods: EVs isolated from FGF2-primed astrocytes (FGF2-EVs) were characterized by transmission electron microscopy and nanoparticle tracking analysis. FGF2-EVs were applied to both in vitro and in vivo models of PD. EVs derived from naïve astrocytes (CON-EV) were used as control. Mitochondrial alterations, neuronal survival, synaptogenesis, and mice behavior were subsequently evaluated by quantitative real-time polymerase chain reaction, Western-blotting, immunohistochemistry, and CatWalk gait analysis. To dissect the underlying mechanisms, proteomic analysis and small interfering RNA (siRNA) mediated gene silencing were adopted.

Results: FGF2 treatment restored the expression of neural progenitor markers and suppressed the levels of A1 astrocytic markers in MPP⁺ pretreated astrocytes. FGF2-EVs, in comparison with that of CON-EVs, effectively protected neurons from mitochondrial fragmentation and stimulated synaptogenesis, as evidenced by expression of Mitofusin 2 (Mfn2), postsynaptic density protein 95 (PSD-95) and synaptophysin (SYP). Proteomic analysis revealed high enrichment of neural cell adhesion molecule 1 (NCAM1) in FGF2-EVs. Knocking down NCAM1 severely influenced the expression of mitochondrial and synaptic proteins. Furthermore, delivery of FGF2-EVs significantly enhanced the survival of TH+ neurons, the levels of NCAM1 and synaptogenesis in the substantia nigra of PD mice, as well as the locomotion of PD mice.

Conclusion: EVs from FGF2-primed astrocytes are superior in protecting PD mice against mitochondrial and synaptic toxicities, possibly through NCAM1, which could be used as a therapeutic strategy for PD.

FGF2; Parkinson’s disease; astrocyte; extracellular vesicles; mitochondria; synaptogenesis.