Cytosolic Prion Protein Induces Apoptosis Via Mitochondrial Disruption Pathway In Human Neuronal SH-SY5Y Cells

Different neurodegenerative disorders like prion disease,Alzheimer's disease,and polyglutamine are caused by protein misfolding or aberrant conformers.Reverse-transfected cytosolic prion protein(PrP)and PrP expressed in the cytosol have been shown to be neurotoxic and induce rapid death in neurons.To investigate the possible mechanism of neurotoxicity due to accumulation of PrP in the cytosol,a PrP mutant lacking the signal and GPI peptides(CytoPrP)was introduced into the human neuroblastoma cell line SH-SY5Y. MTT and trypan blue assays indicated that the viability of SH-SY5Y cells expressing the CytoPrP was remarkably reduced after treatment of proteasome inhibitor MG-132.Obvious apoptosis phenomena were detected in the cells accumulated with CytoPrP,including loss of mitochondrial transmembrane potential(ψm),increase of caspase-3 activity,more annexin V and annexin V/PI-double positive-stained cells and reduced Bcl-2 level.Moreover,DNA fragmentation and TUNEL assays also revealed clear evidences of late apoptosis in the cells accumulated with CytoPrP.These data suggest that the accumulation of CytoPrP in cytoplasm may trigger cell apoptosis,in which mitoehondrial relative apoptosis pathway seems to play a critical role.