Alpha synuclein pre-formed fibrils trigger astrocytic activation prior to intra-neuronal deposition in a seeding mouse model of Parkinson’s disease

• Aim: To monitor temporal evolution of glial and peripheral events occurring, prior to pSynS129 inclusion formation, after a single intra-cranial injection of pre-formed fibrils (PFFs) in the wild-type (wt) mice.Experimental plan: Here we perform intracerebral inoculations with mouse PFFs in wt mice (n=30) to study early pathological and inflammatory events from 1 to 30 days post-injections (dpi) at regular time intervals. The paraffin-fixed brain sections were stained against pSynS129 species with the in house developed  proximity ligation assay. Furthermore, studies using different glial and inflammatory markers revealed more information regarding the early cellular interactions involving formation and propagation pSynS129 species.Results: Already after 1 dpi, we observe strong pSynS129 immunoreactivity close the striatal injection site. Intriguingly, this type of staining disappeared with the concurrent formation of peri-nuclear pSynS129 inclusions in motor and piriform cortex, amygdala and periventricular hypothalamus after 14 dpi. Concomitantly, we observed astrocytic activation as early event happening prior to intracellular formation and propagation pSynS129 inclusions in the brain and peripheral organs.Significance: Our study elucidates the temporal relationship regarding inflammation and formation of pSynS129 inclusions. Our results indicate that a single PFF injection is enough to induce astrocytic activation and neuro-inflammatory response that occur prior to intra-neuronal accumulation of misfolded α-syn.

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