Involvement of mitochondria in endoplasmic reticulum stress-induced apoptotic cell death pathway triggered by the prion peptide PrP106-126

Prion disorders are progressive neurodegenerative diseases characterized by extensive neuronal loss and by the accumulation of the pathogenic form of prion protein, designated PrPSc. Recently, we have shown that PrP106-126 induces endoplasmic reticulum (ER) stress, leading to mitochondrial cytochrome c release, caspase 3 activation and apoptotic death. In order to further clarify the role of mitochondria in ER stress-mediated apoptotic pathway triggered by the PrP peptide, we investigated the effects of PrP106-126 on the Ntera2 human teratocarcinoma cell line that had been depleted of their mitochondrial DNA, termed NT2 rho 0 cells, characterized by the absence of functional mitochondria, as well as on the parental NT2 rho+ cells. In this study, we show that PrP106-126 induces ER stress in both cell lines, given that ER Ca2+ content is low, glucose-regulated protein 78 levels are increased and caspase 4 is activated. Furthermore, in parental NT2 rho+ cells, PrP106-126-activated caspase 9 and 3, induced poly (ADP-ribose) polymerase cleavage and increased the number of apoptotic cells. Dantrolene was shown to protect NT2 rho+ from PrP106-126-induced cell death, demonstrating the involvement of Ca2+ release through ER ryanodine receptors. However, in PrP106-126-treated NT2 rho 0 cells, apoptosis was not able to proceed. These results demonstrate that functional mitochondria are required for cell death as a result of ER stress triggered by the PrP peptide, and further elucidate the molecular mechanisms involved in the neuronal loss that occurs in prion disorders.