Transient expressions of doppel and its structural analog prionDelta32-121 in SH-SY5Y cells caused cytotoxicity possibly by triggering similar apoptosis pathway.

Doppel (Dpl) is a recently identified prion (PrP)-like protein due to the structural and biochemical similarities, however, its natural function and pathogenic role in neurodegenerative diseases remains unclear. To investigate the possible pathogenic pathway of Dpl and its structural analog for cell apoptosis, mammalian expressing recombinant plasmids containing human PRND gene encoding the full-length Dpl and a truncated human PRNP gene deleting the sequences encoding the peptide from aa 32 to 121 (PrPDelta32-121) were generated. MTT assays showed the cell viabilities of the human neuroblastoma cell line SH-SY5Y receiving Dpl and PrPDelta32-121 expressing plasmids were remarkably lower. Obvious apoptosis phenomena were observed to be associated with the cells transient expressing Dpl and PrPDelta32-121, including reduced mitochondrial transmembrane potential (psim), decreased pro-caspase-3 quantity, more numbers of annexin V- and annexin V/PI-double-stained cells and depressed Bcl-2 level. Moreover, we also found that the Dpl- and PrPDelta32-121-induced cytotoxicities and relevant apoptotic events in SH-SY5Y cells could be fully antagonized by co-expression of the human full-length PrP. These data highly indicate that cytotoxicity induced by the expression of Dpl and truncated PrP in neural derived cells are closely related with the apoptosis process, probably triggering the mitochondrial pathway. It also implies that the cell-benefit activity of the full-length PrP may result from its anti-apoptosis capacity.