Prion protein fragment PrP-(106-126) induces apoptosis via mitochondrial disruption in human neuronal SH-SY5Y cells

The synthetic peptide PrP-(106-126) has previously been shown to be neuroto xic. Here, for the first time, we report that it induces apoptosis in the h uman neuroblastoma cell line SH-SY5Y. The earliest detectable apoptotic eve nt in this system is the rapid depolarization of mitochondrial membranes, o ccurring immediately upon treatment of cells with PrP-(106-126). Subsequent to this, cytochrome c release and caspase activation were observed. Caspas e inhibitors demonstrated that while the peptide activates caspases they ar e not an absolute requirement for apoptosis. Parallel to caspase activation , PrP-(106-126) was also observed to trigger a rise in intracellular calciu m through release of mitochondrial calcium stores. This leads to the activa tion of calpains, another family of proteases. A calpain inhibitor demonstr ated that while calpains are activated by the peptide they also are not an absolute requirement for apoptosis. Interestingly a combination of caspase and calpain inhibitors significantly inhibited apoptosis. This illustrates alternative pathways leading to apoptosis via caspases and calpains and tha t blocking both pathways is required to inhibit apoptosis. These results im plicate the mitochondrion as a primary site of action of PrP-(106-126).