A new concept: Aβ1-42 generates a hyperfunctional proteolytic NCX3 fragment that delays caspase-12 activation and neuronal death

The silencing in PC-12 cells or the knocking-out in mice of the ncx3 gene, that encodes for the Na+/Ca2+ exchanger type 3, prevented the enhancement of both I(NCX) and Ca(2+) content in ER stores induced by beta -amyloid 1-42, suggesting that NCX3 was involved in the increase of ER Ca(2+) content stimulated by this peptide. By contrast, in the late phase (72 h), when the NCX3 proteolytic cleavage abruptly decreased, the occurrence of a parallel reduction in ER Ca(2+) content triggered ER stress, as revealed by caspase-12 activation. Concomitantly, the late increase in [Ca(2+)](i) coincided with neuronal death. Interestingly, NCX3 silencing caused an earlier activation of Aβ(1-42)-induced caspase-12. Indeed, in NCX3-silenced neurons, Aβ(1-42) exposure hastened caspase-dependent apoptosis, thus reinforcing neuronal cell death. These results suggest that Aβ(1-42), through Ca(2+)-dependent calpain activation, generates a hyperfunctional form of the Na+/Ca2+ exchanger NCX3 that, by increasing Ca(2+) content into ER, delays caspase-12 activation and thusER-stress and neuronal death.