Cytotoxic mechanisms by M239V presenilin 2, a little-analyzed Alzheimer's disease-causative mutant

Although neurotoxic functions are well characterized in familial Alzheimer's disease (FAD)-linked N141I mutant of presenilin (PS)2, little has been known about M239V-PS2, another established FAD-causative mutant. We found that expression of M239V-PS2 caused neuronal cytotoxicity. M239V-PS2 exerted three forms of cytotoxicity: one was sensitive to both an antioxidant glutathione-ethyl-ester (GEE) and a caspase inhibitor Ac-DEVD-CHO (DEVD); the second was sensitive to GEE but resistant to DEVD; and the third was resistant to both. The GEE/DEVD-sensitive cytotoxicity by M239V-PS2 was likely through NADPH oxidase and the GEE-sensitive/DEVD-resistant cytotoxicity through xanthine oxidase (XO). Both mechanisms by M239V-PS2 were suppressed by pertussis toxin (PTX) and were mediated by Gα_o, but not by Gα _i. Although Aβ1-43 itself induced no cytotoxicity, Aβ1-43 potentiated all three components of M239V-PS2 cytotoxicity. As these cytotoxic mechanisms by M239V-PS2 are fully shared with N141I-PS2, they are most likely implicated in the pathomechanism of FAD by PS2 mutations. Notably, cytotoxicity by M239V-PS2 could be inhibited by the combination of two clinically usable inhibitors of superoxide-generating enzymes, apocynin and oxypurinol.