Alzheimers disease(AD)and Parkinsons disease(PD)are common neurodegenerative diseases.There is comorbidity of AD and PD in clinic,with their pathological features overlapping.The pathological protein assemblies formed by Aβ or α-synuclein may play a key role in this comorbidity,but up to now the mechanism remains to be elucidated.In this experiment,we synthesized preformed fibrils(pffs)composed of recombinant human α-synuclein,which were reported to enhance the conversion of endogenous α-synuclein into pathological LBs/LNs and stereotaxically injected into the dorsal striatum of 5XFAD transgenic mouse model.We observed that PD-like pathological changes including loss of tyrosine hydroxylase(TH)positive neurons in substantia nigra pars compacta(SNpc)and α-synuclein aggregation in neurons in 5XFAD transgenic mice treated with pffs were much more severe than in wild type mice with pffs injection.In conclusion,the aggregation and transmission of misfolded α-synuclein were accelerated by Aβ-related pathology in FAD transgenic brain.