Accelerated senescence exacerbates α-synucleinopathy in senescence-accelerated prone 8 mice via persistent neuroinflammation

Parkinson's disease (PD) is characterized by the formation of α-synuclein (α-syn) aggregates, which lead to dopaminergic neuronal degeneration. The incidence of PD increases with age, and senescence is considered to be a major risk factor for PD. In this study, we evaluated the effect of senescence on PD pathology using α-synuclein preformed fibrils (PFF) injection model in senescence-accelerated mice. We injected PFF into the substantia nigra (SN) of senescence-accelerated prone 8 (SAMP8) mice and senescence-accelerated resistant 1 (SAMR1) mice. At 24 weeks after injection of saline or PFF, we found that SAMP8 mice injected with PFF exhibited robust Lewy pathology and exacerbated degeneration of dopaminergic neurons in the SN compared to PFF-injected SAMR1 mice. We further observed an increase in the number of Iba1-positive cells in the brains of PFF-injected SAMP8 mice. RNA sequencing revealed that several genes related to neuroinflammation were upregulated in the brains of PFF-injected SAMP8 mice compared to SAMR1 mice. Inflammatory chemokine CC-chemokine ligand 21 (CCL21) was upregulated in PFF-injected SAMP8 mice and expressed in the glial cells of these mice. Our research indicates that accelerated senescence leads to persistent neuroinflammation, which plays an important role in the exacerbation of α-synucleinopathy.