Prion disorders are progressive
neurodegenerative diseases characterized by extensive neuronal loss and by the accumulation of the pathogenic form of
prion protein, designated PrP(Sc). Recently, we have shown that PrP(106-126) 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 PrP(106-126) on the Ntera2 human
teratocarcinoma cell line that had been depleted of their
mitochondrial DNA, termed NT2 rho0 cells, characterized by the absence of functional mitochondria, as well as on the parental NT2 rho+ cells. In this study, we show that PrP(106-126) 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, PrP(106-126)-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 PrP(106-126)-induced cell death, demonstrating the involvement of Ca2+ release through ER
ryanodine receptors. However, in PrP(106-126)-treated NT2 rho0 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.