Synaptic phosphoproteome modifications and cortical circuit dysfunction are linked to the early-stage progression of alpha-synuclein aggregation
Cortical dysfunction is increasingly recognized as a major contributor to the non-motor symptoms associated with Parkinsons disease (PD) and other synucleinopathies. Although functional alterations in cortical circuits have been observed in preclinical PD models, the underlying molecular mechanisms are unclear. To bridge this knowledge gap, we investigated tissue-level changes in the cortex of rats and mice treated with alpha-synuclein (aSyn) seeds using a multi-omics approach. Our study revealed significant phosphoproteomic changes, but not global proteomic or lipid profiling changes, in the rat sensorimotor cortex 3 months after intra-striatal injection with aSyn preformed fibrils (PFFs). Gene ontology analysis of the phosphoproteomic data revealed that PFF administration impacted pathways related to synaptic transmission and cytoskeletal organization. Similar phosphoproteomic perturbations were observed in the sensorimotor cortex of mice injected intrastriatally or intracortically with aSyn PFFs. Functional analyses demonstrated increased neuronal firing rates and enhanced spike-spike coherence in the sensorimotor cortex of PFF-treated mice, suggesting that aSyn seeds induced cortical circuit dysfunction. Bioinformatics analysis of the altered phosphosites indicated the involvement of several kinases, including casein kinase-2 (CK2) and Protein Kinase A (PKA). Enrichment of kinase-activating pT/pY MAPK (ERK) phosphosites revealed apparent engagement of the ERK signaling cascade and led to the identification of pERK1/2-positive intraneuronal granulovacuolar body (GVB)-like structures specifically in aggregate-bearing neurons. Collectively, these findings highlight the importance of phosphorylation-mediated signaling pathways in the cortical response to aSyn pathology spread in PD and related synucleinopathies, setting the stage for developing new therapeutic strategies.